Modification of polytetrafluoroethylene implants by depositing TiCaPCON films with and without stem cells

Shtansky, D. V.; Grigoryan, A. S.; Toporkova, A. K.; Arkhipov, A. V.; Sheveyko, A. N.; Kiryukhantsev-Korneev, Ph. V.

SURFACE & COATINGS TECHNOLOGY, 206, 6, 1188-1195

The present work is focused on the investigation of the structure and properties of TiCaPCON films deposited on the surface of polytetrafluoroethylene (PTFE) as potential bio-implant material. The films were deposited by DC magnetron sputtering of composite TiC(0.5)+Ca(3)(PO(4))(2) target produced by self-propagating high-temperature synthesis (SHS). The film structure was examined using X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. The films were also characterized in terms of their adhesion to the PTFE substrate, hardness, elastic modulus, elastic recovery, wettability, and friction coefficient both in physiological solution (normal saline) and Dulbecko modified Eagle medium with fetal calf serum. The biological properties of the films were evaluated by in vitro and in vivo experiments. In vitro studies showed that human fibroblasts well adhered and spread on the surface of the PTFE sample coated with TiCaPCON films. In vivo studies using rat hip and rabbit calvarial defect models demonstrated a high osseointegration potential of the TiCaPCON/PTFE implants. In vivo bone tissue regeneration using hybrid implants (adipose-derived stem cells/TiCaPCON film/PTFE porous membrane) were also reported. (C) 2011 Elsevier B.V. All rights reserved.

Parametric study of the gel-combustion synthesis of nanocrystalline ZrO2-based powders

Fabregas, I. O.; Lamas, D. G.

POWDER TECHNOLOGY, 214, 2, 218-228

In this paper, we report a study of the effect on the powder morphology of zirconia based solid solutions of several parameters of the synthesis by gel-combustion routes, such as fuel, metal/fuel ratio, composition of the nanopowder, pH of the precursor solution, etc. We evaluated the average crystallite size. BET specific surface area and the degree of agglomeration of the final ceramic nanopowders. The intermediate stages of the synthesis were characterized by Fourier Transform Infrared Spectroscopy, Small Angle X-ray Scattering, X-ray Powder Diffraction, X-ray Absorption Spectroscopy and Infrared Thermography. We found that the precursor gel remained compositionally homogeneous up to the self-combustion step and that in order to obtain a low average crystallite size (<10 nm) and a low degree of agglomeration, the combustion temperature must be tailored to be as high as possible. Finally, a novel gel-combustion route assisted with hydrogen peroxide is reported. (C) 2011 Elsevier B.V. All rights reserved.

Photocatalytic Activity of Combustion Synthesized ZrO2 and ZrO2-TiO2 Mixed Oxides

Polisetti, Sneha; Deshpande, Parag A.; Madras, Giridhar

INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 50, 23, 12915-12924

Tetragonal ZrO2, synthesized by solution combustion technique, was found to be photocatalytically active for the degradation of anionic dyes. The compound was characterized by FT-Raman spectroscopy, X-ray photoelectron spectroscopy, FT-infrared spectroscopy, UV-vis spectroscopy, BET surface area analysis, and zero point charge pH measurement. A high concentration of surface hydroxyl groups was observed over the catalyst, as confirmed by XPS and FUR. The photocatalytic degradation of orange G, amido black, remazol brilliant blue R, and alizarin cyanine green (ACG) was carried out with this material. The effect of pH, inorganic. salts, and H2O2 on the activity of the catalyst was also studied, and it was found that the catalyst maintained its activity at a wide range of pH and in the presence of inorganic salts. Having established that ZrO2 was photocatalytically active, mixed oxide catalysts of TiO2-ZrO2 were also tested for the photocatalytic degradation of ACG, and the 50% ZrO2-TiO2 mixed oxides showed activity that was comparable to the activity of TiO2.

Barium ferrite nanoparticles prepared by self-propagating low-temperature combustion method and its characterization

Swamy, P. M. Prithviraj; Basavaraja, S.; Havanoor, Vijayanand; Rao, N. V. Srinivas; Nijagunappa, R.; Venkataraman, A.

BULLETIN OF MATERIALS SCIENCE, 34, 7, 1319-1323

The barium ferrite particles were prepared using a self-propagating low-temperature combustion method using polyethylene glycol (PEG) as a fuel. The process was investigated with simultaneous thermogravimetric-differential thermal analysis (TG-DTA). The crystalline structure, morphology and the magnetic properties of the barium ferrite particles were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and SQUID susceptometer. The results show that the ignition temperature of PEG is lower compared with other combustion methods and gives nanocrystalline barium ferrite.

Synthesis and characterization of zinc ferrite nanoparticles obtained by self-propagating low-temperature combustion method

Swamy, P. M. Prithviraj; Basavaraja, S.; Lagashetty, Arunkumar; Rao, N. V. Srinivas; Nijagunappa, R.; Venkataraman, A.

BULLETIN OF MATERIALS SCIENCE, 34, 7, 1325-1330

The self-propagating low-temperature combustion method was used to produce nanocrystalline particles of zinc ferrite. The products were characterized for chemical and phase composition, morphology and magnetic properties. The results obtained showed the formation of single-phase zinc ferrite nanoparticles with an average particle size of about 40 nm. As-synthesized powder displayed good magnetic property. Due to the simplicity and low cost of this process, it could also become a valuable starting point for the generation of other mixed and complex ferrites.

Thermoluminescence of aluminum oxide co-doped with terbium and thulium obtained via combustion synthesis

Andrade, M. E. A.; Azevedo, W. M.; Barros, V. S. M.; Khoury, H. J.

RADIATION MEASUREMENTS, 46, 12, 1474-1476

In this work thermoluminescent properties of alpha-Al2O3 samples doped with Tb3+ and Tm3+, prepared by the combustion synthesis route, were studied. Samples were prepared by mixing stoichiometric amounts of aluminum nitrate, urea and dopants with different amounts of terbium and thulium nitrates varying from 0 to 0.15 mol%. The mixture was ignited in a muffle furnace at low temperature (500 degrees C). After the combustion, the samples were sintered at 1400 degrees C for 4 h in order to obtain the pure alpha-phase crystalline structure. The TL response of these samples for Co-60 gamma radiation was evaluated. It was observed a U glow peak around 220 degrees C and a linear response for doses in studied range of 0.1-1 Gy. It was observed that the 0.1 mol% concentrations of both dopants present the highest TL sensitivity. The sensitivity of the co-doped (0.10 mol%) samples is 5 times higher than the 0.1 mol% Tm-only doped Al2O3 and 40 times higher than the sample doped only with 0.1 mol% of Tb. These results strongly suggest that the Al2O3:Tm-Tb, prepared through the combustion method, is a potential material for U radiation dosimetry. (C) 2011 Elsevier Ltd. All rights reserved.

Combustion synthesis of Sr6AlP5O20:Dy3+ submicron phosphor for high dose TL dosimetry

Shinde, K. N.; Dhoble, S. J.; Brahme, Nameeta; Kumar, Animesh

RADIATION MEASUREMENTS, 46, 12, 1886-1889

Sr6AlP5O20:Dy3+ submicron phosphor was prepared by the combustion synthesis. The prepared phosphor was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), thermoluminescence (TL) and photoluminescence (PL) techniques and the results are reported in this paper. The TL glow curve of the submicron phosphor shows a prominent single peak at 194 degrees C. The TL peak intensity is thirty three times less as compare to CaSO4:Dy commercial TLD phosphor. The response curve of prepared phosphor with high dose gamma- ray exposure is linear upto 4.8 kGy as compared to well known CaSO4:Dy phosphor. When Dy activated Sr6AlP5O20 phosphor excited by 350 nm, the phosphors show an efficient blue and yellow band emission, which originates from the F-4(9/2) -> H-6(15/2) and F-4(9/2) -> H-6(13/2) transitions of Dy3+ ion. Thus this novel Sr6AlP5O20:Dy3+ submicron phosphor is good candidate for high dose TL dosimetry. (C) 2011 Elsevier Ltd. All rights reserved.

Ultrafast self-catalytic growth of silicon carbide nanowires

Huczko, Andrzej; Dabrowska, Agnieszka; Soszynski, Michal; Maryan, Natalia; Bystrzejewski, Michal; Baranowski, Piotr; Lange, Hubert; Gemming, Thomas; Bachmatiuk, Alicja; Ruemmeli, Mark

JOURNAL OF MATERIALS RESEARCH, 26, 24, 3065-3071

Silicon carbide nanowires (SiCNWs) (with diameters of tens of nanometer and aspect ratio well above 10(3)), consisting of beta-SiC one-dimensional single crystals wrapped in amorphous nitrogen-containing SiO2 sheaths, were efficiently synthesized in gram quantities by autogenous combustion synthesis using Si as a defluorination reagent of poly(tetrafluoroethylene). The combustion temperature was evaluated using the emission spectroscopy. Vapor-liquid-solid mechanism of a self-catalytic growth of the SiCNWs is proposed.

Simultaneous Synthesis and Densification of a Nanocrystalline (W,Ti)Si-2-SiC Composite from Mechanically Activated Powders by High Frequency Induction Heating

Shon, In-Jin; Song, Ha-Young; Ko, In-Yong

MATERIALS TRANSACTIONS, 52, 12, 2258-2261

(W,Ti)C and Si nanopowders were obtained using high-energy ball milling. A dense, nanostructured (W,Ti)Si-2-SiC composite was synthesized by a one-step, high-frequency induction heated combustion synthesis method within 2 min from mechanically activated powders of (W,Ti)C and 3Si. Simultaneous combustion synthesis and consolidation were accomplished under the combined effects of an induced current and mechanical pressure. The average grain size and mechanical properties of the composite were investigated. [doi:10.2320/matertrans.M2011204]

Phase Homogeneity in Y2O3-MgO Nanocomposites Synthesized by Thermal Decomposition of Nitrate Precursors with Ammonium Acetate Additions

Muoto, Chigozie K.; Jordan, Eric H.; Gell, Maurice; Aindow, Mark

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 12, 4207-4217

Nanocomposite powders with equal volume fractions of Y2O3 and MgO have been produced by the thermal decomposition of precursor mixtures of yttrium nitrate and magnesium nitrate. Solutions of the precursor salts were mixed with ammonium acetate fuel, dried to form a gel-like substance, and then calcined to give nanocrystalline ceramic powders. The amount of ammonium acetate added to the metal nitrate precursors was varied systematically, and the morphology and distribution of the component phases in consolidated compacts of the resultant ceramic powders were examined by a combination of focused ion beam sectioning, scanning, and transmission electron microscopy. The dispersion of the Y2O3 and MgO phases within the synthesized powders improved, and the sizes of the phase domains reduced, with increasing ammonium acetate content up to the quantity required for a stoichiometric redox reaction with the metal nitrates. The addition of excess ammonium acetate gave no further improvement in phase domain dispersion or reduction in phase domain sizes. These phenomena are related to the thermal characteristics for the decomposition of the precursors and their effect on phase separation during oxide crystallization.

Facile Synthesis and Characterization of Hexagonal Boron Nitride Nanoplates by Two-Step Route

Zhao, Zhengyan; Yang, Zhigang; Wen, Yan; Wang, Yuhua

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 12, 4496-4501

Large quantities of hexagonal boron nitride (h-BN) nanoplates with hexagonal morphologies have been successfully synthesized by a simple two-step route without using any template or catalyst, including combustion synthesis and then annealing processes. The phase content, morphology, and optical properties of the products have been characterized. It reveals that the obtained products are pure and of high crystallinity. The UVvis absorption spectrum indicates that the h-BN nanoplates have an optical band gap of 6.07 eV. Strong violetblue photoluminescence (PL) emission with a broad band ranging from 400 nm to 475 nm has been observed, indicating that the nanoplates as-grown by this simple route are promising for application in nanosize optical devices (LEDs, blue-light source, UV detector, etc.). The phonon lines features are obviously found in the PL spectra, the phonon frequency involved in these transitions is consistent with the BN E2g vibrational mode, which has been measured by the Raman spectroscopy.

Consolidation and mechanical properties of nanostructured (Mo,Ti)Si-2 from mechanically activated powder by high frequency induction heated sintering

Park, Na-Ra; Ko, In-Yong; Doh, Jung-Mann; Yoon, Jin-Kook; Shon, In-Jin

JOURNAL OF CERAMIC PROCESSING RESEARCH, 12, 6, 660-663

A dense nanostructured (Mo,Ti)Si-2 compound was sintered by the high frequency induction heating method within 2 minutes from mechanically activated powder of Mo, Ti and Si. A highly-dense (Mo,Ti)Si-2 compound was produced under simultaneous application of a 80 MPa pressure and the induced current. The mechanical properties and microstructure were investigated.

Evaluation of two different methods to synthesize cobalt-aluminate spinel

Salem, Shiva; Jazayeri, Seyyed Hamid; Bondioli, Federica; Allahverdi, Ali; Shirvani, Mansoor

JOURNAL OF CERAMIC PROCESSING RESEARCH, 12, 6, 677-681

The aim of this research is to study the efficiency of both microwave-hydrothermal and combustion methods to synthesize CoAl(2)O(4) spinel. To attain the objectives, precursor solutions of CoCl(2)center dot 2H(2)O and AlCl(3)center dot 6H(2)O were applied to prepare cobalt aluminate spinet by a microwave-hydrothermal method and the effects of pH (4, 8 and 12), residence time (1 and 2 h), and temperature of the digestion system (190 and 220 degrees C) on the properties of final powders were studied. Moreover, mixed solutions of Al(NO(3))(3)-9H(2)O, Co(NO(3))(2)-6H(2)O and glycine were used as a precursor in the combustion synthesis method and the effect of different molar ratios of fuel to nitrate (0.36, 0.56) and calcination temperatures (800, 1000 degrees C) were evaluated. The powders obtained were characterized by XRD, XPS, SEM, TEM, FT-IR and UV-Vis. The results show that CoAl(2)O(4) spinet is not formed by the microwave-hydrothermal method under the variable conditions studied, while the combustion synthesis method is capable of producing nano-particles of CoAl(2)O(4) spinel and according to the results of TEM and Scherrer's equation most of the particles have sizes less than 100 nm.

Synthesis and luminescence studies of novel rare earth activated lanthanum pentaborate

Nagpure, P. A.; Bajaj, N. S.; Sonekar, R. P.; Omanwar, S. K.

INDIAN JOURNAL OF PURE & APPLIED PHYSICS, 49, 12, 799-802

The lanthanum pentaborate (LaB(5)O(9))is a novel material which exhibits excellent luminescence when doped with rare earth ions. It was prepared by a novel technique which is a slight variation of solution combustion synthesis. The synthesis is based on the exothermic reaction between the fuel (urea) and oxidizer (ammonium nitrate). The structure of the prepared material was confirmed by powder XRD technique. The photoluminescence of rare earth ions (Ce(3+), Eu(3+)) and sensitized luminescence of Gd(3+)(Pr(3+)-Gd(3+) and Bi(3+)-Gd(3+)) in LaB(5)O(9) have been studied. LaB(5)O(9):Ce(3+) shows broad band UV emission at 317 nm and LaB(5)O(9):Eu(3+) shows orange red emission. LaB(5)O(9): Pr(3+)-Gd(3+) and LaB(5)O(9): Bi(3+)-Gd(3+) exhibit efficient luminescence of Gd(3+) in narrow UVB region at 310 nm. The material (La(0.5) Pr(0.4))B(5)O(9):Gd(0.1) exhibits intense narrow band UVB emission at 310 nm and could be a potential candidate for UVB phosphors used in phototherapy lamps.

Synthesis of nano-crystalline Zn-CoO pigment by the chemical combustion method: Effect of fuel to oxidizer ratio on structure, microstructure and color properties

Rasouli, Sousan; Arabi, Amir Masoud

INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 102, 12, 1477-1480

The aim of this study was to investigate the effect of fuel/oxidizer ratio on the combustion synthesis of nano-crystalline Zn-CoO green pigment. The fuel and oxidizer used in this study were glycine and nitrate respectively. Products were characterized by means of X-ray diffraction, Fourier transformation infra red spectroscopy, scanning electron microscopy and diffuse reflectance spectroscopy. X-ray diffraction patterns (XRD) showed that the formation of pure hexagonal ZnO phase was insensitive to fuel/oxidizer ratio variations. Well-crystalline single-phase ZnO was observed for low and stoichiometric fuel/oxidizer ratios. Average crystallite size determined from the Scherrer formula varied from 18 to 75 nm. The morphology of the obtained samples changed from hexagonal pyramidal to irregular porous sponge-like particles. The colorimetric results showed a broad reflectance band around 530 nm (green region) for all samples. The observation of green appearance of different samples synthesized using different fuel/oxidizer ratios was related to fade of Co(3)O(4) X-ray diffraction patterns and entrance of Co into ZnO structure.

Friction of composites based on titanium carbide produced by the process combustion method

Fadin, V. V.; Kolubaev, A. V.; Aleutdinova, M. I.

JOURNAL OF FRICTION AND WEAR, 32, 6, 462-466

The method of SHS force compaction is used to produce composites that include TiC + 50 vol % inert. Copper, iron, nichrome, and steel G13 served as the inert. It is noted that the lattice parameter, the TiC grain size, and the mass ratio Ti/C in TiC grains are practically independent of the inert composition. It is shown that some of the composites possess high mechanical properties. The friction of the composites that contain Ni-Cr is characterized by a friction coefficient of up to 0.5 and a high wear owing to their strong adhesion to the counterbody. The materials whose compositions are TiC + (Cu, Fe) and TiC + (Cu, G13) are effective under a pressure of about 100 MPa and can serve as a basis for developing tribological materials.

Eco-friendly combustion-based synthesis of metal aluminates MAl2O4 (M = Ni, Co)

Tirsoaga, Alina; Visinescu, Diana; Jurca, Bogdan; Ianculescu, Adelina; Carp, Oana

JOURNAL OF NANOPARTICLE RESEARCH, 13, 12, 6397-6408

Nanosized metal aluminates, MAl2O4 (M = Ni, Co), have been prepared following a nonpolluting, low temperature, and self-sustaining starch single-fuel combustion synthesis. The mixed fuel-coordinating actions of starch have given rise to an intermediary precursor which afforded monodisperse metal aluminate nanoparticles. The thermal analysis of the [M(II), Al(III)]-starch precursors indicates a similar thermochemical reactivity for the two compounds, displaying a sequence of well-defined decomposition stages associated with three endothermic effects and three/four (nickel/cobalt) exothermic ones. The XRD data confirm the formation of spinelic phase and a continuous growth of particle sizes with the increase of calcination temperatures. The mechanisms proposed for the formation of metal aluminates essentially consist in a combination of solid-state reactions of amorphous NiO/Co3O4 and Al2O3 simple oxides. The evaluation criterion of Ni(II) cations into the spinelic lattice is original and is based on the distinct occupancy degree of tetrahedral and octahedral sites in NiAl2O4 and gamma-Al2O3. TEM/HRTEM investigations performed on the cobalt(II) and nickel(II) aluminate oxide powders resulted after calcination at 800 and 900 A degrees C, respectively, for 1 h show the formation of irregular and isolated plate-like particles for Co(II)-based spinelic oxides (the average particle size is 16.6 nm) and submicron aggregates of small, bimodal, and almost uniform (as shape and size) of NiAl2O4 mixed oxide (the mean particle size is 33.6 nm). The NIR-UV-Vis spectra for the resulted MAl2O4 (M = Co, Ni) mixed oxides reveal a massive presence of tetrahedral divalent cations both for short- and long-time calcined samples. NiO impurities are detected using FTIR and electronic spectra for all NiAl2O4 samples.

Modification of the physical properties of semiconducting MgAl2O4 by doping with a binary mixture of Co and Zn ions

Iqbal, Muhammad Javed; Ismail, Bushra; Rentenberger, Christian; Ipser, Herbert

MATERIALS RESEARCH BULLETIN, 46, 12, 2271-2277

The effects of doping of MgAl2O4 by a binary mixture of Co and Zn ions on the absorbance, electrical resistivity, capacitance, thermal conductivity, heat capacity and thermal diffusivity are reported in this paper. The materials with the nominal composition Mg1-2x(Co,Zn)(x)Al2O4 (x = 0.0-0.5) are synthesized by solution combustion synthesis assisted by microwave irradiation. The substituted spinels are produced with a Scherrer crystallite size of 18-23 nm, as opposed to 45 nm for undoped samples, indicated by X-ray diffraction and confirmed by transmission electron microscopy. These materials also show better thermal stability in the temperature range of 298-1773 K. Three strong absorption bands at 536, 577 and 630 nm are observed for the doped samples which are attributed to the three spin allowed ((4)A(2) (F) -> T-4(1) (P)) electronic transitions of Co2+ at tetrahedral lattice sites while pure magnesium aluminate remains transparent in the whole spectral range. The semiconducting behavior of the materials is evident from the temperature dependence of the electrical resistivity. Resistivity and activation energy are higher for the substituted samples. Fitting of the resistivity data is achieved according to the hopping polaron model of solids. Both dielectric constant and loss increase on account of doping. The dielectric data are explained on the basis of space charge polarization. The thermal conductivity and diffusivity are lowered and the heat capacity is increased in the doped materials. Wiedemann-Franz's law is used to compute the electronic and lattice contributions towards the total thermal conductivity. (C) 2011 Elsevier Ltd. All rights reserved.

Luminescence response and CL degradation of combustion synthesized spherical SiO2:Ce nanophosphor

Nagpure, I. M.; Pitale, Shreyas S.; Tshabalala, K. G.; Kumar, Vinay; Ntwaeaborwa, O. M.; Terblans, J. J.; Swart, H. C.

MATERIALS RESEARCH BULLETIN, 46, 12, 2359-2366

This study was aimed to systematically investigate the luminescence response of SiO2:Ce3+ nanophosphors with different excitation sources. The powders were synthesized by using an urea assisted combustion method. SiO2:Ce-1m% samples were also annealed at 1000 degrees C for 1 h in a charcoal environment to reduce incidental Ce4+ to partial Ce3+ ions. High resolution transmission electron microscopy (HRTEM) images of the as synthesized and annealed powder samples confirmed that the particles were spherical and in the size range of 3-8 nm in diameter. X-ray diffraction (XRD) and electron dispersion spectroscopy (EDS) results showed that the SiO2 was crystalline and pure. Diffused reflectance, photoluminescence (PL) and cathodoluminescence (CL) results of the SiO2:Ce3+ samples were obtained and compared with each other. The CL degradation and the surface reactions on the surface of the SiO2:Ce3+ were studied with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). A clear improvement in the chemical stability of the SiO2:Ce3+ annealed at 1000 degrees C were obtained. (C) 2011 Elsevier Ltd. All rights reserved.

Continuous synthesis of controlled size carbon-encapsulated iron nanoparticles

Bystrzejewski, M.; Karoly, Z.; Szepvoelgyi, J.; Huczko, A.; Lange, H.

MATERIALS RESEARCH BULLETIN, 46, 12, 2408-2417

Carbon-encapsulated iron nanoparticles were continuously and selectively synthesised in a thermal plasma jet from ethanol (carbon source) and Fe powders with different grain sizes. The grain size of the Fe powder influenced the size distribution of the as-produced carbon encapsulates. The products obtained from large Fe particles (50-78 mu m) were comprised of small encapsulates with diameters between 5 and 10 nm. Larger carbon encapsulates with a broad diameter distribution (10-100 nm) were synthesised from the finest Fe particles (18 mu m). It was also found that Fe particle size was the most crucial parameter for determining the encapsulation yield. The encapsulation yield was also influenced by the carbon to iron ratio and the thermal conductivity of the plasma gas. (C) 2011 Elsevier Ltd. All rights reserved.

Sol-gel auto-combustion synthesis of totally immiscible NiAg alloy

Jiang, Yuwen; Yang, Shaoguang; Hua, Zhenghe; Gong, Jiangfeng; Zhao, Xiaoning

MATERIALS RESEARCH BULLETIN, 46, 12, 2531-2536

Immiscible crystalline NiAg alloy was successfully synthesized by the newly developed sot-gel auto-combustion method. The structure and composition were examined by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM). All evidence supports that homogeneous NiAg alloy with FCC structure was synthesized. The differential thermal analysis and thermogravimetry (DTA-TG) measurement shows that the alloy has a good thermal stability until 315 degrees C. Unusually some extinction planes are observed in the XRD pattern and HRTEM images. The random distribution of atoms and the large difference between Ni and Ag atom form factors should be regarded as the main reasons for the observation of the extinction planes. The quenching like nonequilibrium thermal process in the combustion is taken as the key factor in the synthesis of immiscible alloy. And the addition of ethylene glycol in the precursors is found to benefit the formation of NiAg alloy. (C) 2011 Elsevier Ltd. All rights reserved.

Selective oxidation of carbon monoxide in hydrogen-containing gas on CuO-CeO2/Al2O3 catalysts prepared by surface self-propagating thermal synthesis

Afonasenko, T. N.; Shlyapin, D. A.; Leont'eva, N. N.; Gulyaeva, T. I.; Buyal'skaya, K. S.; Trenikhin, M. V.; Tsyrul'nikov, P. G.

KINETICS AND CATALYSIS, 52, 6, 843-850

The CuO-CeO2/Al2O3 catalysts for the selective oxidation of CO in hydrogen-containing mixtures were prepared by surface self-propagating thermal synthesis (SSTS) with the use of cerium nitrate Ce(NO3)(3), the ammonia complex of copper acetate [Cu(NH3)(4)](CH3COO)(2), and citric acid C6H8O7 as a fuel additive. The effect of the C6H8O7/Ce(NO3)(3) molar ratio on the catalyst activity and selectivity for oxygen was studied. The catalyst samples were studied by X-ray diffraction (XRD) analysis, temperature-programmed reduction (TPR-H-2), IR spectroscopy of adsorbed CO, and transmission electron microscopy (TEM). It was found that an increase in the C6H8O7/Ce(NO3)(3) ratio resulted in an increase in the degree of dispersion of the resulting CeO2 phase. The greatest amount of dispersed CuO particles, which are responsible for catalytic activity in the oxidation of CO, was formed at C6H8O7/Ce(NO3)(3) = 1.

New isopropanol dehydration catalyst based on tungsten carbide prepared by modified self-propagating high-temperature synthesis

Zurnachyan, A. R.; Manukyan, Kh V.; Kharatyan, S. L.; Matyshak, V. A.; Mnatsakanyan, R. A.

KINETICS AND CATALYSIS, 52, 6, 851-854

The W(2)C/C catalytic system with a high specific surface area (55 m(2)/g) was synthesized for the first time using modified self-propagating high-temperature synthesis (SHS). The bulk and surface properties of the synthesized system were characterized using physicochemical methods and a model reaction of isopropanol conversion. It was found that the conversion of the alcohol with 100% selectivity occurs in the direction of dehydration with the formation of propylene and water. It was shown that active centers are the W(VI) surface ions of the carbide, whose activity is higher than the activity of tungsten as a constituent of the phase of WO(3).

Design formulations for non-welded and welded aluminium columns using Continuous Strength Method

Ashraf, Mahmud; Young, Ben

ENGINEERING STRUCTURES, 33, 12, 3197-3207

Aluminium members are used in structural applications due to their high strength-to-weight ratio, corrosion resistance, attractive appearance, recyclability, ease of production and availability. Thin aluminium sections are susceptible to buckling at a relatively low stress and welding makes it even worse; the design stress i.e. 0.2% proof stress is almost halved in the vicinity of the heat affected zones (HAZs). Currently available design codes have their guidelines both for welded and non-welded aluminium columns, but the predictions for welded aluminium columns are often quite inconsistent. The current research exploits a newly developed strain based design approach the 'Continuous Strength Method' (CSM) to predict the behaviour of aluminium members with SHS and RHS cross-sections subjected to compression. A new design curve is proposed herein to predict the cross-sectional resistance in compression; this concept is further extended to propose a new Perry type buckling curve to predict the flexural buckling resistance of aluminium columns. A simplified technique is proposed to include the effect of heat affected zone (HAZ) in CSM formulations. The CSM predictions for aluminium columns are compared against those obtained using available guidelines proposed by the European, American and Australian/New Zealand standards of aluminium structures. The CSM predictions for non-welded columns are in line with the code predictions, whilst the proposed simple technique for transversely welded columns seems to produce significantly improved predictions. (C) 2011 Elsevier Ltd. All rights reserved.

Solution Combustion Synthesis of Metal Nanopowders: Copper and Copper/Nickel Alloys

Kumar, A.; Wolf, E. E.; Mukasyan, A. S.

AICHE JOURNAL, 57, 12, 3473-3479

Based on a general methodology for the preparation of metal-nanopowders by solution combustion synthesis (SCS), the reaction pathways for SCS of pure copper and copper-nickel alloy nanopowders are investigated. It is confirmed that the necessary condition for SCS of metals in a metal-nitrate oxidizer-glycine system is the property of the oxidizer to decompose with formation of HNO3 species. In this case, for compositions with excess of glycine, a hydrogen reducing atmosphere develops in the reaction front, leading to the formation of reduced metals. The proposed reaction pathways are supported by X-ray diffraction analysis of the quenched samples and DTA-TGA studies of the Cu(NO3)(2)center dot 6H(2)O-glycine and Ni(NO3)(2)center dot 6H(2)O/Cu(NO3)(2)center dot 6H(2)O-glycine systems. The results show that the formation of Cu2O and CuO oxide phases takes place at early stages in the reaction front followed by their reduction to pure Cu phase in the postcombustion zones. However, in a Cu-Ni alloy, a fraction of intermetallic Cu-Ni phase appeared directly in the combustion front, whereas the rest of the oxygen-free alloy formed through reduction of oxide phases. (C) 2011 American Institute of Chemical Engineers AIChE J, 57: 3473-3479, 2011

Combustion synthesis of (Ti1-xNbx)(2)AlC solid solutions from elemental and Nb2O5/Al4C3-containing powder compacts

Yeh, C. L.; Chen, J. H.

CERAMICS INTERNATIONAL, 37, 8, 3089-3094

Preparation of the (Ti1-xNbx)(2)AlC solid solution (formed from the M(n+1)AX(n) or MAX carbides, where n = 1, 2, or 3, M is an early transition metal, A is an A-group element, and X is C) with x = 0.2-0.8 was investigated by self-propagating high-temperature synthesis (SHS). Nearly single-phase (Ti,Nb)(2)AlC was produced through direct combustion of constituent elements. Due to the decrease of reaction exothermicity, the combustion temperature and reaction front velocity decreased with increasing Nb content of (Ti1-x,Nb-x)(2)AlC formed from the elemental powder compacts. In addition, the samples composed of Ti, Al, Nb2O5, and Al4C3 were adopted for the in situ formation of Al2O3-added (Ti,Nb)(2)AlC. The SHS process of the Nb2O5/Al4C3-containing sample involved aluminothermic reduction of Nb2O5, which not only enhanced the reaction exothermicity but also facilitated the evolution of (Ti,Nb)(2)AlC. Based upon the XRD analysis, two intermediates, TiC and Nb2Al, were detected in the (Ti,Nb)(2)AlC/Al2O3 composite and their amounts were reduced by increasing the extent of thermite reduction involved in the SHS process. The laminated microstructure characteristic of the MAX carbide was observed for both monolithic and Al2O3-added (Ti,Nb)(2)AlC solid solutions synthesized in this study. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Solution combustion synthesis and physicochemical characterization of ZrO2-MoO3 nanocomposite oxides prepared using different fuels

Samantaray, Satish; Mishra, B. G.; Pradhan, D. K.; Hota, G.

CERAMICS INTERNATIONAL, 37, 8, 3101-3108

A series of MoO3-ZrO2 nanocomposite oxides with MoO3 content in the range of 2-20 mol% were prepared by solution combustion method. Three different fuels namely urea, glycine and hexamethylenetetramine (HMTA) were used for the preparation of MoO3-ZrO2 oxides. For the sake of comparison, the MoO3-ZrO2 composite oxides were also prepared by impregnation of zirconia with molybdenum salt precursor and subsequent heat treatment. The synthesized nanomaterials were characterized by XRD, SEM, TEM and UV vis spectroscopic technique. XRD study indicated selective stabilization of the tetragonal phase of zirconia in the presence of MoO3. The method of preparation was found to be crucial for the phase composition of zirconia in the composite oxide. The crystallite size and rms stain were calculated from the Fourier line shape analysis of the broadened X-ray diffraction profiles. With increase in the MoO3 content, the crystallite size of the tetragonal zirconia phase was found to be decreased. TEM study indicated the presence of small nanoparticles with size in the 5-10 nm range. UV-vis study of the composite oxide materials revealed well dispersion of the molybdenum oxide component in the form of monomer, dimers and nanoclusters in the zirconia matrix. The nature of fuel was found to be crucial in determining the morphology and shape of the particles. (C) 2011 Elsevier Ltd and Techna Group S.r.l All rights reserved.

Synthesis of CeAlO3/CeO2-Al2O3 for use as a solid oxide fuel cell functional anode material

Venancio, Selma A.; de Miranda, Paulo Emilio V.

CERAMICS INTERNATIONAL, 37, 8, 3139-3152

A composite electrocatalyst was developed to be fitted for the purpose of satisfying the features required for use as a solid oxide fuel cell functional anode material. The main functionality searched for was the ability to make the direct oxidation of carbon containing fuels in an SOFC without being severely coked. The present paper deals with the synthesis and characterization of such material. Therefore, ceramic electrocatalysts composed of CeAlO3, CeO2 and Al2O3 were synthesized by the amorphous citrate method and calcined at temperatures ranging from 300 degrees C to 900 degrees C. The synthesis procedures were designed to produce nanometric sized powders for which the calcination conditions were selected in order to fulfill requirements such as ease to be sintered; formation of selected phases upon calcinations at different temperatures; particle size control; surface area and morphology well suited for the production of ceramic suspensions to be processed into an SOFC functional anode. The main results have shown that increasing the calcination temperature under an oxidizing atmosphere induces the CeAlO3 phase with a tetragonal perovskite type structure to undergo a phase transformation to CeO2 (and Al2O3) with cubic fluorite type structure. However, the structure is able to be reversed and reduced back to the CeAlO3 phase if calcined under a hydrogen atmosphere. The increase in the calcination temperature increases the particle average size, reduces the surface area and increases the material density, considering the same phase and crystalline structure. It was shown that the synthesis and calcinations procedures hinder the crystallographic identification of the presence of alumina. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Synthesis and characterization of Cu-doped ceria nanopowders

Matovic, B. Z.; Bucevac, D. M.; Rosic, M.; Babic, B. M.; Dohcevic-Mitrovic, Z. D.; Radovic, M. B.; Popovic, Z. V.

CERAMICS INTERNATIONAL, 37, 8, 3161-3165

Nanopowdered solid solution Ce(1-x)Cu(x)O(2-gamma) samples (0 <= x <= 0.15) were synthesized by self-propagating room temperature synthesis (SPRT). Raman spectroscopy and XRD at room temperature were used to study the vibration properties of these materials as well as the Cu solubility in ceria lattice. The solubility limit of Cu(2+) in CeO(2) lattice was found to be lower than published in the literature. Results show that obtained powders with low dopant concentration are solid solutions with a fluorite-type crystal structure. However, with Cu content higher than 7.5 mass%, the phase separation was observed and two oxide phases, CeO(2) and CuO, coexist. All powders were nanometric in size with high specific surface area. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Oxidation behaviour of Al2O3-TiC-Co composites at 800-1000 degrees C in air

Shi, Ruixia; Li, Kang; Zhang, Aiyu; Cao, Yongqiang; Yang, Ping

CORROSION SCIENCE, 53, 12, 4058-4064

The oxidation behaviour of nanometre and micrometre sized Al2O3-TiC-Co composites is investigated at 800-1000 degrees C in air for 25 h. The oxidation resistance of nanometre sized samples is better than of micrometre sized. Phase compositions and microstructures were studied by XRD and SEM. The values of general rate constant k and oxidation exponent n are dependent on oxidation temperature and composites. The oxidation kinetics followed a rate that is slightly faster than the parabolic-rate law at 800-1000 degrees C. The activation energy of the nanometre sized is higher than of micrometre sized in the range of 800-1000 degrees C. (C) 2011 Elsevier Ltd. All rights reserved.

Structural studies of nanosized porous membrane catalytic systems highly active in dry reforming of biomass conversion products

Tsodikov, M. V.; Teplyakov, V. V.; Fedotov, A. S.; Uvarov, V. I.; Roizard, D.; Kiennemann, A.; Courson, C.; Moiseev, I. I.

RUSSIAN CHEMICAL BULLETIN, 60, 12, 2588-2596

The structures of porous ceramic membrane catalytic systems exhibiting high activity in dry reforming of biomass conversion products (methane, hydrocarbons C-2-C-4, and alcohols) to a hydrogen-containing gas were studied. The membrane catalytic systems represent porous inorganic membranes (supports) prepared by self-propagating high-temperature synthesis and modified by nanosized metallocompex components, which are uniformly distributed in the internal pore volume. Structural studies were carried out using scanning electron microscopy with energy dispersive analysis, transmission electron microscopy, temperature-programmed reduction with hydrogen, and X-ray diffraction analysis.

Flash synthesis of titanium(IV) oxide nanoparticles using exothermic reaction between solids without external energy

Okinaka, Noriyuki; Kitamura, Yasuaki; Akiyama, Tomohiro

SCRIPTA MATERIALIA, 65, 11, 970-973

This paper describes the innovative flash synthesis of oxide nanoparticles using only a strong exothermic reaction between solids without any external energy, and its implementation for synthesis of titanium(IV) oxide. Flash synthesis is regarded as a type of self-propagating high-temperature synthesis, in which the adiabatic flame temperature of the reaction is greater than the boiling point of the product. This method can be easily applied to produce other oxides, thus offering many benefits, such as energy-saving and short processing-time. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Combustion synthesis of Mg2Si

Godlewska, E.; Mars, K.; Mania, R.; Zimowski, S.

INTERMETALLICS, 19, 12, 1983-1988

Magnesium silicide and its derivatives are perceived as light-weight eco-friendly materials for multiple applications, because of the advantageous combination of physical, mechanical and chemical properties. The principal components, silicon and magnesium, are abundant in nature and thus easily accessible. Manufacturing of Mg2Si-based materials is, however, challenging and a lot of efforts have been made to better control their composition and microstructure. In this work, magnesium silicide dense sinters were successfully produced by self-propagating reaction and hot pressing. The reaction was studied by DTA/TG and high-temperature microscopy. Composition and microstructure of reactants and products were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Property assessment comprised density, hardness, elastic modulus, specific heat, thermal diffusivity, and electrical conductivity. (C) 2011 Elsevier Ltd. All rights reserved.

(Ni(0.75)Fe(0.25)-xMgO)/YSZ anode for direct methane solid-oxide fuel cells

Liu, Yan; Bai, Yaohui; Liu, Jiang

JOURNAL OF POWER SOURCES, 196, 23, 9965-9969

(Ni(0.75)Fe(0.25)-xMgO)/YSZ samples-with a varying weight percentage x (0, 5%. 10%) of MgO with respect to Ni(0.75)Fe(0.25)-were prepared and studied as anodes for intermediate temperature solid oxide fuel cells (SOFCs) operated on humidified methane (3% H(2)O). Among the cells with different anode compositions, it was found that the cell with the (Ni(0.75)Fe(0.25)-5%MgO)/YSZ anode showed the highest power density, giving 648 mW cm(-2) at 800 degrees C. The cells with MgO-doped anodes were able to operate stably for 20 h under a current density of 0.53 A cm(-2) at 700 degrees C without observed degradation, while the cells without MgO degraded rapidly. The mechanisms responsible for the superior performance and duration of the (Ni(0.75)Fe(0.25)-xMgO)/YSZ anode were analyzed. (C) 2011 Elsevier B.V. All rights reserved.

Solution combustion synthesis of layered LiNi0.5Mn0.5O2 and its characterization as cathode material for lithium-ion cells

Manikandan, P.; Ananth, M. V.; Kumar, T. Prem; Raju, M.; Periasamy, P.; Manimaran, K.

JOURNAL OF POWER SOURCES, 196, 23, 10148-10155

LiNi0.5Mn0.5O2, a promising cathode material for lithium-ion batteries, is synthesized by a novel solution-combustion procedure using acenaphthene as a fuel. The powder X-ray diffraction (XRD) pattern of the product shows a hexagonal cell with a = 2.8955 angstrom and c = 14.1484 angstrom. Electron microscopy investigations indicate that the particles are of sub-micrometer size. The product delivers an initial discharge capacity of 161 mAh g(-1) between 2.5 and 4.6V at a 0.1 C rate and could be subjected to more than 50 cycles. The electrochemical activity is corroborated with cyclic voltammetric (CV) and electrochemical impedance data. The preparative procedure presents advantages such as a low cation mixing, sub-micron particles and phase purity. (C) 2011 Elsevier B.V. All rights reserved.

Preparation of W-Ni graded alloy by combustion synthesis melt-casting under ultra-high gravity

Mai, Peilin; Fang, Weiling; Liu, Guanghua; Chen, Yixiang; He, Shuli; Li, Jiangtao

MATERIALS LETTERS, 65, 23-24, 3496-3498

This paper studied the high temperature self-propagating synthesis of W-Ni graded alloy under ultra-high gravity field. The evolution of composition and microstructure along ultra-high gravity direction was investigated. In this W-Ni alloy, ultra-high reaction temperature resulted in the production of stable ordered Ni(4)W phase, and ultra-high gravity field promoted the formation of W-Ni graded alloy. Composition and microstructure exhibited a graded variation along the ultra-high gravity direction, and three functional gradients formed on the cross section. The Ni-rich layer was mainly enhanced by the Ni(4)W phase, while the W-rich layer was primarily reinforced by the W particles. Between them, the transitional layer served as the buffer zone of thermal expansion to relax the thermal stress. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Microstructure and properties of in situ nanostructured ceramic matrix composite coating prepared by plasma spraying

Chen, Xueguang; Yang, Yong; Yan, Dianran; Dong, Yanchun; Wang, Lei; He, Jining; Zhang, Jianxin; Li, Xiangzhi

JOURNAL OF MATERIALS SCIENCE, 46, 23, 7369-7376

In situ nanostructured ceramic matrix composite coating toughened by metallic phase was fabricated by reactive plasma spraying micro-sized Al-Fe(2)O(3) composite powders. The microstructure of the composite coating was characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, respectively. The adhesive strength, microhardness, toughness, and wear resistance of the composite coating were explored. The results indicated that the composite coating exhibited dense microstructure with a lot of spherical alpha-Fe and gamma-Al(2)O(3) nano-sized grains embedded within the equiaxed and columnar FeAl(2)O(4) nano-grains matrix. The adhesive strength, toughness, and wear resistance of the composite coating were significantly enhanced despite its lower microhardness compared with the microsized Al(2)O(3) coating, which were attributed to the inclusion of ductile metallic phase Fe in the composite coating and the nanostructure of the composite coating.

NIR to visible upconversion in Er3+/Yb3+ co-doped CaYAl3O7 phosphor obtained by solution combustion process

Singh, Vijay; Rai, Vineet Kumar; Al-Shamery, Katharina; Nordmann, Joerg; Haase, Markus

JOURNAL OF LUMINESCENCE, 131, 12, 2679-2682

Using the combustion synthesis, CaYAl3O7:Er3+ phosphor powders co-doped with Yb3+ have been prepared at low temperatures (550 degrees C) in a few minutes. Formation of the compound was confirmed by X-ray powder diffraction. Near-infrared to visible upconversion fluorescence emission in the Er3+ doped CaYAl3O7 phosphor powder has been observed. The effect of co-doping with triply ionized ytterbium in the CaYAl3O7:Er3+ phosphor has been studied and the process involved is discussed. (C) 2011 Elsevier B.V. All rights reserved.

Effect of Mo addition on the microstructure and wear resistance of in situ TiC/Al composite

Wu, Qianlin; Yang, Caiding; Xue, Feng; Sun, Yangshan

MATERIALS & DESIGN, 32, 10, 4999-5003

In this work, Mo was investigated as an additive for in situ preparation of TiC/Al composite using a casting route assisted by self-propagating high-temperature synthesis (SHS). Experimental results show Mo improves the wettability between TiC phase and aluminium melt due to the formation of a Mo-rich shell around the formed TiC particles, which is a kind of good modificator. Compared with the composite without added Mo, 1.0 wt.% Mo addition developed finer matrix structure, significant refinement of TiC particles and more uniform distribution of TIC particles in the matrix. Meanwhile, both wear and tensile properties of TiC/Al composite were improved with 1.0 wt.% Mo addition and then deteriorated with the further increase of Mo content due to the formation of fragile phase Al(5)Mo. (C) 2011 Elsevier Ltd. All rights reserved.

Compression properties and work-hardening behavior of Ti2AlC/TiAl composites fabricated by combustion synthesis and hot press consolidation in the Ti-Al-Nb-C system

Shu, Shili; Qiu, Feng; Jin, Shenbao; Lu, Jianbang; Jiang, Qichuan

MATERIALS & DESIGN, 32, 10, 5061-5065

The Ti2AlC/TiAl composites are successfully fabricated utilizing the method of the combustion synthesis and hot press consolidation in the Ti-Al-Nb-C system and the effect of the (Nb-C) content on the compression properties and work-hardening behavior of the composites has been investigated. The compression properties and work-hardening capacity of the TiAl alloy improve remarkably with the addition of the (Nb-C) elements due to the formation of Ti2AlC particles and the solid solution of Nb in the TiAl matrix. The compression properties of the composites increase first then decrease with the increase in the (Nb-C) content and the TiAl-10 wt.% (Nb-C) sample possesses the best comprehensive compression properties and the highest work-hardening capacity. (C) 2011 Elsevier Ltd. All rights reserved.

Effect of milling variables on the synthesis of NiAl intermetallic compound by mechanical alloying

Kubaski, E. T.; Cintho, O. M.; Capocchi, J. D. T.

POWDER TECHNOLOGY, 214, 1, 77-82

NiAl intermetallic compound was synthesized by mechanical alloying of elemental mixtures of Ni and Al powders in a Spex mill. The compound formation took place according to a mechanically induced self-propagating reaction (MSR), and the influence of milling variables on its ignition time was determined using a factorial design. Results indicated ignition time as a function of initial particle size of Ni, process control agent, and ball-to-powder ratio. Also, an interaction between ball-to-powder ratio, process control agent, and a set of balls was found to control the average particle size of as-milled powders. (c) 2011 Elsevier B.V. All rights reserved.

Ultralight Metallic Microlattices

Schaedler, T. A.; Jacobsen, A. J.; Torrents, A.; Sorensen, A. E.; Lian, J.; Greer, J. R.; Valdevit, L.; Carter, W. B.

SCIENCE, 334, 6058, 962-965

Ultralight (<10 milligrams per cubic centimeter) cellular materials are desirable for thermal insulation; battery electrodes; catalyst supports; and acoustic, vibration, or shock energy damping. We present ultralight materials based on periodic hollow-tube microlattices. These materials are fabricated by starting with a template formed by self-propagating photopolymer waveguide prototyping, coating the template by electroless nickel plating, and subsequently etching away the template. The resulting metallic microlattices exhibit densities rho >= 0.9 milligram per cubic centimeter, complete recovery after compression exceeding 50% strain, and energy absorption similar to elastomers. Young's modulus E scales with density as E similar to rho(2), in contrast to the E similar to rho(3) scaling observed for ultralight aerogels and carbon nanotube foams with stochastic architecture. We attribute these properties to structural hierarchy at the nanometer, micrometer, and millimeter scales.

Ignition of an exothermal reaction by collision between Al and Ni crystals

Delogu, Francesco

JOURNAL OF APPLIED PHYSICS, 110, 10, 103505-

Classical molecular dynamics methods have been used to investigate the atomic-scale dynamics of collisions between two Al and Ni crystals with rough surfaces. The crystals were approached along the direction perpendicular to the surfaces and simultaneously displaced along the direction parallel to them at relative velocities in the range between 1 and 10 nm ns(-1). The mechanical stresses operating at collision determine a local deformation of Al and Ni lattices, accompanied by a significant temperature rise. As the Al melting point is reached, the Al crystal partially melts and Ni atoms start dissolving into the molten phase. The significant heat of mixing liberated further promotes the Al melting and the Ni dissolution processes. In the absence of neighboring Al-Ni interfaces, the heat dissipation processes and the limited rate of Ni dissolution gradually lead to the extinction of the reactive behavior. Conversely, the presence of Al-Ni interfaces in the vicinity of the Al-Ni one formed by collision permits the propagation of the high-temperature chemical reaction. It is shown that the ignition and propagation of the self-sustaining reaction is sensitive to the distance between Al-Ni interfaces and to their degree of chemical mixing. (C) 2011 American Institute of Physics. [doi:10.1063/1.3660523]

Low temperature combustion synthesis and performance of spherical 0.5Li(2)MnO(3)-LiNi0.5Mn0.5O2 cathode material for Li-ion batteries

Zhong, Zhuohong; Ye, Naiqing; Wang, Hai; Ma, Zhen

CHEMICAL ENGINEERING JOURNAL, 175, , 579-584

The cathode material 0.5Li(2)MnO(3)-LiNi0.5Mn0.5O2 had been synthesized via low temperature combustion process followed by an annealing treatment. The microstructure and morphology characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) showed that the synthesized product had high crystallinity, alpha-NaFeO2-like layered structure, and sphere-like morphology. Its 0.1 C discharge capacity rapidly increased with cycle number before 6th cycle and reached the highest value 217 mAh/g at 14th cycle. After 50 cycles its 0.1, 0.2 and 0.5 C discharge capacities still retained 191.6, 187.8 and 156.2 mAh/g, respectively, showing that the synthesized product had excellent electrochemical performance. (C) 2011 Elsevier B.V. All rights reserved.

Structure, chemical stability and mixed proton-electron conductivity in BaZr0.9-xPrxGd0.1O3-delta

Magraso, Anna; Frontera, Carlos; Gunnaes, Anette E.; Tarancon, Albert; Marrero-Lopez, David; Norby, Truls; Haugsrud, Reidar

JOURNAL OF POWER SOURCES, 196, 22, 9141-9147

BaZr0.9-xPrxGd0.1O3-delta (x=0.3 and 0.6) was prepared by combustion synthesis and characterised with respect to conductivity and stability in an attempt to combine the desirable properties of the end members. The polycrystalline materials exhibit a cubic or pseudo-cubic structure as determined by X-ray synchrotron radiation and transmission electron microscopy. The chemical stability of the compositions is strongly dependent on the praseodymium content, the materials with more Pr present lower stability. Electron holes dominate the conductivity under oxidising atmospheres in BaZr0.3Pr0.6Gd0.1O3-delta, while BaZr0.6Pr0.3Gd0.1O3-delta exhibits a mixed electron hole proton conducting behaviour. Substitution of Zr by Pr in acceptor-doped BaZrO3 decreases the sintering temperature and increases the grain growth rate. (C) 2011 Elsevier B.V. All rights reserved.

Sr2Fe1.5Mo0.5O6-delta as a regenerative anode for solid oxide fuel cells

Liu, Qiang; Bugaris, Daniel E.; Xiao, Guoliang; Chmara, Maxwell; Ma, Shuguo; zur Loye, Hans-Conrad; Amiridis, Michael D.; Chen, Fanglin

JOURNAL OF POWER SOURCES, 196, 22, 9148-9153

Sr2Fe1.5Mo0.5O6-delta (SFM) was prepared using a microwave-assisted combustion synthesis method. Rietveld refinement of powder X-ray diffraction data reveals that SFM crystallizes in the simple cubic perovskite structure with iron and molybdenum disordered on the B-site. No structure transition was observed by variable temperature powder X-ray diffraction measurements in the temperature range of 25-800 degrees C. XPS results show that the iron and molybdenum valences change with an increase in temperature, where the mixed oxidation states of both iron and molybdenum are believed to be responsible for the increase in the electrical conductivity with increasing temperature. SFM exhibits excellent redox stability and has been used as both anode and cathode for solid oxide fuel cells. Presence of sulfur species in the fuel or direct utilization of hydrocarbon fuel can result in loss of activity, however, as shown in this paper, the anode performance can be regenerated from sulfur poisoning or coking by treating the anode in an oxidizing atmosphere. Thus, SFM can be used as a regenerating anode for direct oxidation of sulfur-containing hydrocarbon fuels. (C) 2011 Elsevier B.V. All rights reserved.

Starch - A suitable fuel in new low-temperature combustion-based synthesis of zinc aluminate oxides

Visinescu, Diana; Jurca, Bogdan; Ianculescu, Adelina; Carp, Oana

POLYHEDRON, 30, 17, 2824-2831

Starch has been tested as single-fuel and in a two-fuel mixture, together with N-methylurea, in a new combustion-based synthesis of zinc aluminate oxides, using different fuel compositions and equivalence ratios Phi(e) (Phi(e) = fuel/oxidant). The combustion process has been analyzed by simultaneous thermal analysis. The corresponding oxides were characterized by X-ray diffraction analysis, UV-Vis spectroscopy, scanning electron microscopy and BET investigations. Crystal structures were refined by Rietveld method. The morphology, specific surface area and optical properties of the obtained zinc aluminate have proved to be strongly dependent on the fuel nature and composition. The lowest crystallite size (131 angstrom) is achieved for the oxide generated from the starch-based precursor, while the highest surface area (20.69 m(2)/g) has been obtained for a 3:1 N-methylurea/starch fuel composition. The non-zero value for microstrain has indicated spinelic defects in the starch-fuel corresponding oxide. UV-Vis spectroscopic analysis have confirmed the intrinsic properties of the resulted mixed metal oxide, but also shows the presence of a certain disorder degree for all the other samples. The superior values of the band gap (4.2-4.7 eV) for the obtained oxides relative to the bulk case (3.8 eV) are the result of the nanometric dimensions of the particles. (C) 2011 Elsevier Ltd. All rights reserved.

CO Methanation Over Ru-Al2O3 Catalysts: Effects of Chloride Doping on Reaction Activity and Selectivity

Djinovic, Petar; Galletti, Camilla; Specchia, Stefania; Specchia, Vito

TOPICS IN CATALYSIS, 54, 16-18, 1042-1053

The selective CO methanation (CO-SMET) process via Ru-Al2O3 catalysts was investigated as a tool for complete CO removal in fuel processors, when the H-2-rich gas so produced is employed for PEM-FCs applications to vehicles, boats, yachts and residential co-generators. CO-SMET seems, in fact, to be a good alternative to the most widely used CO preferential oxidation (CO-PROX) process. The performance of Ru-based catalysts on alumina carrier for efficient CO removal through CO-SMET was studied, exploring the role of two different Ru precursors (chloride and nitrate), and the doping effect of chloride and of Ru load (1%, 3% and 5%). First, two catalytic families (Ru-Al2O3_Cl and Ru-Al2O3_NO3) were prepared by incipient wetness impregnation of alumina powder synthesized via solution combustion synthesis, by varying the Ru load. Then, based on the best obtained results, a third catalytic family was prepared adding chloride to Ru-Al2O3_NO3 catalysts by impregnation. The CO removal performance was determined at catalyst powder level in a fixed bed micro reactor. Better performances were exhibited when Ru was deposited from chloride precursor, but the post-addition of chlorine to fresh Ru-Al2O3 catalysts prepared with nitrate precursor tremendously improved their selectivity toward CO methanation. In particular, with both 1% and 3% Ru-Al_NO3 catalyst chlorine doped, complete CO conversion was reached in a proper temperature range where the CO2 methanation was suitably kept at a low acceptable level.

Preparation of CeO2 based nanocomposites for fuel cell electrolyte via sol-gel method

Yang, H. Z.; Yu, H.; Ji, Y.; Yu, X. M.; Zhu, H.; Li, Z. M.

MATERIALS RESEARCH INNOVATIONS, 15, 6, 391-393

A Ce0.8Sm0.2O1.9 nanocomposite with potential for application as a fuel cell electrolyte was prepared via the sol-gel method. Nitrates and citric acid were respectively adopted as reactor and complexing agent to synthesise the composite. X-ray diffraction was used to investigate the influence of temperature and content of nitric acid on the purity and grain size of the CeO2 phase. It was found that nanocrystals with 20 nm grain size can be obtained following heating for 4 h at 800 degrees C and that addition of nitric acid improved the purity of the phase produced. A microscale model of the structural transformation from precursor gel to powder for the composite is proposed.

Fabrication of (Nd0.01LaxY0.99-x)(2)O-3 Nanoparticles and Transparent Ceramics by Combustion Synthesis

Luo, Jun-Ming; Deng, Li-Ping; Xu, Ji-Lin

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 11, 11, 9705-9708

Y2O3 acts as the matrix material when doped with different content of La2O3 for reducing sintering temperature and refining grains. The (Nd0.01LaxY0.99-x)(2)O-3 nanoparticles and transparent ceramics are fabricated by a combustion synthesis. The powder feature is characterized by TEM. The microstructure, mechanical properties and transmittance of the samples are examined by SEM, HV-1000 hardness tester and fluorescence analyzer respectively. The results show that the (Nd0.01LaxY0.99-x)(2)O-3 nanoparticles are homogeneous in size and nearly spherical with average diameter in the range of 40 similar to 60 nm. There are no other phases except the Y2O3 cubic phase in the (Nd0.01LaxY0.99-x)(2)O-3 nanoparticles. The grains of the samples significantly reduce with increasing La2O3 content. The hardness and fracture toughness increase rapidly first and then gradually tend to plateau with increasing La2O3 content. The transmittance of sample also increases gradually with increasing La2O3, the largest transmittance exceeds 77% when the La2O3 content is x = 0.12.

Preparation of CuO-CeO2 catalysts deposited on glass cloth by surface self-propagating thermal synthesis

Desyatykh, I. V.; Vedyagin, A. A.; Kotolevich, Yu. S.; Tsyrul'nikov, P. G.

COMBUSTION EXPLOSION AND SHOCK WAVES, 47, 6, 677-682

(CuO-CeO2)/glass cloth acting as CO oxidation catalyst was prepared by surface selfpropagating thermal synthesis. In the process of synthesis of (CuO-CeO2)/glass cloth samples, the content of active components (CuO-CeO2) and fuel additives and the conditions of thermal synthesis were varied. Impact of the nature of fuel additives and salts that are precursors of active components, and their ratio on the reaction of solid-phase combustion were studied. The resulting catalysts were studied with the use of scanning electron microscopy and in situ time-resolved synchrotron radiation powder x-ray diffraction.

Combustion of thermite systems in thin layers with an open surface

Ikornikov, D. M.; Sanin, V. N.; Yukhvid, V. I.

COMBUSTION EXPLOSION AND SHOCK WAVES, 47, 6, 697-702

SHS combustion of thermite compositions in the form of thin layers without formation of a continuous layer of cast products is studied. It is shown that combustion of thin layers of high-temperature compositions can be accompanied by almost complete dispersion of liquid-phase combustion products. The height of filling material and the caloric content of the mixture are effective parameters to control the size of the dispersed particles of cast synthesis products. It is established that the macrostructure of synthesis products is formed in the vicinity of the combustion wave through coalescence and capillary drift of metal droplets.

Fabrication and Magnetic Property of One-dimensional SrTiO3/SrFe12O19 Composite Nanofibers by Electrospinning

Liang, Qingrong; Shen, Xiangqian; Song, Fuzhan; Liu, Mingquan

JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 27, 11, 996-1000

The composite nanofibers of SrTiO3/SrFe12O19 with a molar ratio of 1:1 and diameter about 120 nm were prepared by electrospinning. Effects of calcination temperature on the formation, crystallite size, morphology and magnetic property were studied by infrared spectroscopy, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The binary phase of strontium ferrite and titanate was formed after being calcined at 900 degrees C for 2 h and the composite nanofibers were fabricated from nanograins of SrTiO3 about 24 nm and SrFe12O19 around 33 nm. The crystallite sizes for the nanofibers increase with increasing calcination temperature and the addition of SrTiO3 has an obvious suppression effect on SrFe12O19 grain growth. The specific saturation magnetization and remanence tend to increase with the crystallite size. With increasing calcination temperature from 900 to 1050 degrees C, the coercivity increases initially, achieving a maximum value of 520.2 kA.m(-1) at 950 degrees C, and then shows a reduction tendency.

DEVELOPMENT OF REFRACTORY MATERIALS PREPARED BY SHS TECHNOLOGY

Zharmenov, A. A.; Satbaev, B. N.; Kazhikenova, S. Sh.; Nurkenov, O. A.

REFRACTORIES AND INDUSTRIAL CERAMICS, 52, 4, 294-302

Scientific bases of self-propagating high-temperature synthesis of refractory materials, recipes, and methods for their creation from local raw material are developed. Thermochemical and kinetic parameters for solid-phase synthesis of systems based on chamotte, chromite, magnesium, and aluminum sulphate, and also phase composition, thermodynamic and physicomechanical properties of the products obtained are determined.

Obtaining composites Cu/TiO2 by combining mechanical activation and self-propagating high temperature synthesis

Grigor'eva, T. F.; Letsko, A. I.; Talako, T. L.; Tsybulya, S. V.; Vorsina, I. A.; Barinova, A. P.; Il'yushchenko, A. F.; Lyakhov, N. Z.

RUSSIAN JOURNAL OF APPLIED CHEMISTRY, 84, 11, 1851-1854

The possibility of obtaining nanostructured composites Cu/TiO2 by combining mechanical activation and self-propagating high temperature synthesis was investigated by X-ray diffraction and electron microscopy.

PHYSICAL AND TECHNOLOGICAL PRINCIPLES OF DESIGNING LAYER-GRADIENT MULTICOMPONENT SURFACES BY COMBINING THE METHODS OF ION-DIFFUSION SATURATION AND MAGNETRON- AND VACUUM-ARC DEPOSITION

Savostikov, V. M.; Potekaev, A. I.; Tabachenko, A. N.

RUSSIAN PHYSICS JOURNAL, 54, 7, 756-764

Using a technological system proposed by the authors, a combined process is developed for formation of stratified-gradient surface layers and multicomponent coatings. It is implemented under the conditions of a combined serial-parallel operation of a hot-cathode gas plasma generator and a duomagnetron with two targets and two electric-arc evaporators. The extended functional potential is ensured by using advanced multi-element and multi-phase cathode targets made of borides, carbides, silicides, and sulfides of metals produced by the SHS-process followed by their immediate compaction. The variations in composition, structure, and physicomechanical properties in the cross-section of the stratified-gradient surface layers and coating is provided by a predetermined alternating replacement of the sputtered cathode targets of the plasma sources, the plasma flow intensity ratios, and variation in the particle energy incident on the substrate, which is determined by the accelerating voltage on the substrate.

Mechanical activation and gasless explosion: Nanostructural aspects

Mukasyan, Alexander S.; Khina, Boris B.; Reeves, Robert V.; Son, Steven F.

CHEMICAL ENGINEERING JOURNAL, 174, 41335, 677-686

The underlying mechanism causing the enhanced reactivity of mechanically activated heterogeneous reactive materials, such as those treated through high-energy ball milling (HEBM), is studied. The combined contributions from previously suggested mechanisms, like energy storage in the media and non-equilibrium defects, are estimated from well-known theories and found to be insignificant for investigated conditions and specifically when compared to the experimentally measured changes in apparent activation energy. Investigation of the structural transformations at the micro-, nano-, and atomic lattice scales is performed using high resolution electron microscopy. It is shown that HEBM not only increases the interfacial area between Ni and Al on micro-level, but also creates a region near the interface where nanometric Ni crystallites are embedded into art Al matrix. In this region, the materials are intimately mixed on the nano-scale level without an oxide layer or intermediate phases, which typically act as diffusional barriers for the chemical reactions. This results to significant increase of the media reactivity leading to the "solid flame" phenomenon when solely solid-state reactions are responsible for the thermal explosion in such gasless energetic systems. (C) 2011 Elsevier B.V. All rights reserved.

Advancing lean combustion of hydrogen-air mixtures by laser-induced spark ignition

Boeker, Dietmar; Brueggemann, Dieter

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 22, 14759-14767

We investigate how ignition through laser-induced plasma can improve the application of lean combustion, in particular in environmental conditions relevant to hydrogen internal combustion engines (ICE). Major design goals when developing combustion engines are increasing thermal efficiency and decreasing combustion emissions. High compression ratios, lean combustion and precise ignition timings are contributing factors in ICE optimization. In our studies, several gains from laser spark ignition are investigated. The high energy content of laser-induced ignition kernels are shown to speed up the development of the early flame kernels. These extended ignition kernels transfer into self propagating flames even in lean mixtures. Leaner mixtures are ignited in our experiments using laser spark ignition in comparison to conventional electrical spark plugs. Precise ignition timing is realized. Multi-point ignitions are synchronized on the timescale of microseconds to enhance the progress of combustion. We modified the locus of ignition in a mixture flow to decrease the temporal extent of flame contact with the wall. Therefore, burning duration and heat loss can be reduced. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Synthesis and characterization of nanocrystalline ScSZ electrolyte for SOFCs

Lakshmi, V. Vijaya; Bauri, Ranjit; Gandhi, Ashutosh S.; Paul, S.

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 22, 14936-14942

Sc(2)O(3) stabilized zirconia (ScSZ) was processed by combustion synthesis. X-ray diffraction was carried for analyzing the phase and crystallinity of the processed powder. The results indicate the effectiveness of the combustion synthesis process to produce nanocrystalline ScSZ from the precursor salts without any intermediate calcination step. Comparison with the X-ray diffraction pattern of a commercial 8YSZ sample showed that the process is also effective in producing the desired cubic fluorite phase. The powder was compacted and sintered to produce a dense electrolyte pellet. The sintering temperature was found to be considerably lower compared to conventional microcrystalline zirconia ceramics. The electrical conductivity of the ScSZ electrolyte was found to be higher compared to 8YSZ processed under same conditions. The Arrhenius plot of conductivity yielded two activation energies corresponding to low and high temperature regions. The activation energy of the 10ScSz electrolyte was found to be considerably lower than the 8YSZ sample. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Efficient Bi3+ -> Nd3+ energy transfer in Gd2O3:Bi3+,Nd3+

Liu, Guan-Xi; Zhang, Rui; Xiao, Quan-Lan; Zou, Shao-Yu; Peng, Wen-Fang; Cao, Li-Wei; Meng, Jian-Xin

OPTICAL MATERIALS, 34, 1, 313-316

Bi3+,Nd3+ co-doped Gd2O3 were prepared by solid state reaction and the optical properties were investigated. The results show that the near-infrared emission of Nd3+ ions is significantly enhanced by the introducing of Bi3+ in co-doped samples. An efficient energy transfer from Bi3+ to Nd3+ corresponds to the near-infrared emission enhancement. The energy transfer efficiency reaches 64.1% for the sample with the strongest near-infrared emission, which has the optimized doping concentrations of 0.5% for Bi3+ and 2% for Nd3+. The interesting optical properties make Bi3+,Nd3+ co-doped Gd2O3 promising as the luminescent down-conversion layers in front of c-Si solar cells to enhance the performance of the solar cells. (C) 2011 Elsevier B.V. All rights reserved.

New concepts in molecular and energy transport within carbon nanotubes: Thermopower waves and stochastically resonant ion channels

Shimizu, Steven; Choi, Wonjoon; Abrahamson, Joel T.; Strano, Michael S.

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 248, 11, 2445-2448

Our laboratory has been interested in how carbon nanotubes can be utilized to illustrate new concepts in molecular and energy transfer. In the first example, we predict and demonstrate the concept of thermopower waves for energy generation. Coupling an exothermic chemical reaction with a thermally conductive CNT creates a self-propagating reactive wave driven along its length. We realize such waves in multi-walled nanotubes (MWNT) and show that they produce concomitant electrical pulses of high specific power >7 kW/kg. Such waves of high power density may find uses as unique energy sources. In the second system, we fabricate and study single-walled nanotube (SWNT) ion channels for the first time and show that the longest, highest aspect ratio, and smallest diameter synthetic nanopore examined to date, a 500 mu m SWNT, demonstrates oscillations in electro-osmotic current at specific ranges of electric field, that are the signatures of coherence resonance, yielding self-generated rhythmic and frequency-locked transport. The observed oscillations in the current occur due to a coupling between stochastic pore blocking and a diffusion limitation that develops at the pore mouth during proton transport. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Ultra-fast efficient synthesis of one-dimensional nanostructures

Dabrowska, Agnieszka; Huczko, Andrzej; Soszynski, Michal; Bendjemil, Badis; Micciulla, Federico; Sacco, Immacolata; Coderoni, Laura; Bellucci, Stefano

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 248, 11, 2704-2707

Self-propagating high-temperature synthesis (SHS) can be regarded as an efficient method to obtain new nanomaterials. Different starting mixtures of magnesium powder with various carbonates (Li2CO3, Na2CO3, CaCO3, FeCO3, (NH4)(2)CO3) were tried and the auto-thermal reactions were carried out under both reactive (air) and neutral atmosphere (argon) with an initial pressure of 1 or 10 atm to yield novel nanomaterials. Both SiC nanofibres and novel branched SiC nanostructures were also obtained from Si/polytetrafluoroethylene (PTFE) mixtures and their synthesis and purification have been optimized. The application of those one-dimensional (1-D) SiC nanostructures as a composite filler is presented. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Spontaneous formation and characterization of silicon carbide nanowires produced via thermolysis

Soszynski, Michal; Dabrowska, Agnieszka; Huczko, Andrzej

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 248, 11, 2708-2711

We report on experiments to optimize the process of preparation of silicon carbide nanowires (SiCNWs) by a combustion synthesis (thermolysis). The morphology of starting reactants and combustion atmosphere were varied and we observed the effect of those variables on product yield and characteristics. The produced SiCNWs were characterized using SEM, TEM, XRD, and wet chemistry analysis.[GRAPHICA]High-pressure reactor used for combustion synthesis, combustion reaction, and TEM of produced SiCNW(C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Lithium as a Modifier for Morphology and Defect Structure of Porous Magnesium Oxide Materials Prepared by Gel Combustion Synthesis

Zavyalova, Ulyana; Weinberg, Gisela; Frandsen, Wiebke; Girgsdies, Frank; Risse, Thomas; Dinse, Klaus Peter; Schloegl, Robert; Horn, Raimund

CHEMCATCHEM, 3, 11, 1779-1788

Defect rich MgO nanocrystals arranged in a hierarchic three-dimensional pore network were synthesized by using gel combustion synthesis (GCS). By adding Li to the combustion precursor, Li-induced changes in the morphology and defect structure of MgO could be studied systematically. At low Li loadings (up to 1 wt?parts per thousand), the three-dimensional pore network was resistant to temperatures up to 800?degrees C, even though the primary MgO nanoparticles had changed their morphology from on average 8 nm size {100} terminated nanocubes to up to 250 nm large complex polyhedral, exposing more and more {111} facets. At higher Li loadings, the primary MgO particles grow even further, to up to 500 nm, causing the three-dimensional pore network to collapse. After describing the GCS method, detailed structural characterizations of all of the materials synthesized were conducted by means of XRD, BET and pore size analysis, and electron microscopy. IR and thermogravimetric mass spectroscopy (TG-MS) in combination with XRD were used to investigate the formation and decomposition of carbonate species during synthesis and calcination. Diffuse reflectance UV/Vis (DR-UV/Vis) spectroscopy was used to characterize surface defects, such as low coordinated O2- ions at edges, corners, and kinks of the MgO surface. Bulk defects were studied by using electron paramagnetic resonance (EPR) spectroscopy. Morphology and defect concentration of the Li/MgO materials were found to be strongly dependent on the fuel-to-oxidizer ratio used in the combustion synthesis, the Li concentration, and the calcination atmosphere.

Low-Frequency Dependence of Conductivity and Dielectric Properties of Polyaniline/ZnFe2O4 Nanocomposites

Prasanna, G. D.; Jayanna, H. S.; Lamani, Ashok R.; Dinesha, M. L.; Naveen, C. S.; Shankaramurthy, G. J.

CHINESE PHYSICS LETTERS, 28, 11, 117701-

Conducting polyaniline/ZnFe2O4 nanocomposites are synthesized by using a simple and inexpensive one-step in-situ polymerization method in the presence of ZnFe2O4 nanoparticles. The structural, morphological and electrical properties of the samples are characterized by x-ray diffraction, Fourier transform infrared spectra and scanning electron microscopy. These results reveal the formation of polyaniline/ZnFe2O4 nanocomposites. The morphology of these samples is studied by scanning electron microscopy. Further, the ac conductivity (sigma(ac)) of these composites is investigated in the frequency range of 1 kHz-10 MHz. The presence of polarons and bipolarons are responsible for the frequency dependence of ac conductivity in these nanocomposites. The ac conductivity is found to be constant up to 1 MHz and thereafter it increases steeply. The ac conductivity of 0.695 S.cm(-1) at room temperature is observed as the maxima for the polyaniline with 40wt% of the ZnFe2O4 nanocomposite.

Influence of Al/CuO reactive multilayer films additives on exploding foil initiator

Zhou, Xiang; Shen, Ruiqi; Ye, Yinghua; Zhu, Peng; Hu, Yan; Wu, Lizhi

JOURNAL OF APPLIED PHYSICS, 110, 9, 94505-

An investigation on the influence of Al/CuO reactive multilayer films (RMFs) additives on exploding foil initiator was performed in this paper. Cu film and Cu/Al/CuO RMFs were produced by using standard microsystem technology and RF magnetron sputtering technology, respectively. Scanning electron microscopy characterization revealed the distinct layer structure of the as-deposited Al/CuO RMFs. Differential scanning calorimetry was employed to ascertain the amount of heat released in the thermite reaction between Al films and CuO films, which was found to be 2024 J/g. Electrical explosion tests showed that 600V was the most matching voltage for our set of apparatus. The explosion process of two types of films was observed by high speed camera and revealed that compared with Cu film, an extra distinct combustion phenomenon was detected with large numbers of product particles fiercely ejected to a distance of about six millimeters for Cu/Al/CuO RMFs. By using the atomic emission spectroscopy double line technique, the reaction temperature was determined to be about 6000-7000K and 8000-9000K for Cu film and Cu/Al/CuO RMFs, respectively. The piezoelectricity of polyvinylidene fluoride film was employed to measure the average velocity of the slapper accelerated by the explosion of the films. The average velocities of the slappers were calculated to be 381 m/s and 326 m/s for Cu film and Cu/Al/CuO RMFs, respectively, and some probable reasons were discussed with a few suggestions put forward for further work. (C) 2011 American Institute of Physics. [doi:10.1063/1.3658617]

Preparation of Nano Alumina Powder via Combustion Synthesis: Porous Structure Optimization via Taguchi L-16 Design

Norouzbeigi, Reza; Edrissi, Mohammad

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 11, 4052-4058

Nano alumina powders have been synthesized by combustion method using eight new fuels. The effectiveness of key process factors on the production of nanoparticles was investigated and optimized using Taguchi L-16 array design. The products were characterized by XRD, BET, TGA, EDX, FESEM, and TEM analyses. Results demonstrated that the nano-structured aluminum oxide powders had crystal sizes between 7.2 and 13 nm and specific surface areas between 21.0 and 70.0 m(2)/g. The synthesis of gamma-alumina was modified to achieve higher specific surface area (122.6 m(2)/g). A nano-network of powders which was woven by alumina nano-fibers was successfully fabricated by the modification route. The length and diameter of fibers were about 160 and 10 nm, respectively.

Physical and electrical properties of combustion synthesized NASICON type Na3Cr2(PO4)(3) crystallites: Effect of glycine molar ratios

Vijayan, Lakshmi; Cheruku, Rajesh; Govindaraj, G.; Rajagopan, S.

MATERIALS CHEMISTRY AND PHYSICS, 130, 3, 862-869

Thermally stable Na3Cr2(PO4)(3) nano-crystallites are synthesized through novel solution combustion technique using glycine fuel in three molar ratios. Effects of fuel molar ratio on structural and electrical properties are investigated. Reaction parameters like fuel molar ratio, flame temperature and number of moles of gases evolved, play a major role in deciding physical and electrical properties. Out of the synthesized samples, one which contains fuel in 1:1 molar ratio shows highest grain conductivity of 2.35 x 10(-6) S cm(-1). Improved conductivity is elucidated by least size and highest density of the crystallites, which in turn is decided by the flame temperature. Ac electrical properties are investigated using complex impedance spectroscopy. Activation energies for dc conduction and relaxation are determined and the results are reported. (C) 2011 Elsevier B.V. All rights reserved.

Luminescence in Dy3+ and Eu3+ Activated K3Al2(PO4)(3)

Shinde, K. N.; Dhoble, S. J.

JOURNAL OF FLUORESCENCE, 21, 6, 2053-2056

The Dy3+ and Eu3+ activated K3Al2 (PO4)(3) phosphors were prepared by a combustion synthesis. From a powder X-ray diffraction (XRD) analysis the formation of K3Al2 (PO4)(3) was confirmed. In the photoluminescence emission spectra, the K3Al2(PO4)(3):Dy3+ phosphor emits two distinctive colors: blue and yellow whereas K3Al2(PO4)(3):Eu3+ emits red color. Thus the combination of colors gives BYR (blue-yellow-red) emissions can produce white light. These phosphors exhibit a strong absorption between 340 and 400 nm which suggest that present phosphor is a promising candidate for producing white light-emitting diodes (LED).

Influence of the preparation method on the performance of Rh catalysts on CeO2 for WGS reaction

Galletti, C.; Djinovic, P.; Specchia, S.; Batista, J.; Levec, J.; Pintar, A.; Specchia, V.

CATALYSIS TODAY, 176, 1, 336-339

The present paper deals with the study concerning the CO removal from reforming H-2-rich gas stream through WGS reaction over Rh-based catalysts supported on CeO2 carriers. CeO2 was prepared by two different methods: solution combustion synthesis (SCS) and hard template (HT); incipient wetness impregnation method was used to deposit the active metal on the carriers. The screening at powder level in a fixed bed micro-reactor highlighted that feeding 5% CO and 20% H2O (N-2 balance) with the HT-prepared catalyst, CO conversion started at slightly lower temperature, but CH4 outlet concentrations were higher than those of the SCS-prepared one. With a simulated reformate mixture (5% CO + 20% H2O + 11% CO2 + 40% H-2, N-2 balance), the equilibrium WGS curve was exceeded for both catalysts (for the HT-prepared catalyst, CO conversion started at lower temperature and reached 100%), due to the parasite methanation reactions of both CO and CO2, favoured by the presence of a large hydrogen concentration in the reactor. A very high CH4 outlet concentration (max 18.6%) was measured for the HT-prepared catalyst. Then, tests at different weight space velocities WSV were carried out: with the SCS-prepared catalyst the best performance was obtained by lowering WSV. (C) 2010 Elsevier B. V. All rights reserved.

Low temperature DPF regeneration by delafossite catalysts

Bensaid, S.; Russo, N.

CATALYSIS TODAY, 176, 1, 417-423

Several Li-Cr delafossite catalysts (LiCrO(2), LiCr(0.9)O(2), LiCr(0.8)O(2), LiCr(0.7)O(2), Li(0.9)CrO(2), Li(0.8)CrO(2) and Li(0.7)CrO(2)) were prepared via a highly exothermic and self-sustaining reaction, the so-called "solution combustion synthesis (SCS)" method, and characterized by means of XRD, BET, FESEM-EDS, H(2)-temperature programmed reduction (TPR) and XPS analyses, as catalysts for the combustion of soot, a major pollutant emitted by diesel engines. These catalysts already showed appreciable activity at 350 degrees C towards the catalytic combustion of soot even under loose contact conditions. The best prepared catalyst (LiCr(0.9)O(2)) could ignite soot combustion well below 350 degrees C, which is inside the range of temperatures reached at the exhaust line of a diesel engine. The correlation between the activity order and the capability to provide surface adsorbed oxygen (O(-)) by the prepared delafossite catalysts, enabled by a shift of the chromium from a high valence to a low valence state, is pointed out as a peculiar feature of these catalysts. An in situ SCS method was tailored to the preparation of a LiCr(0.9)O(2)-catalyzed trap based on a SiC wall-flow monolith. Engine bench tests on these catalytic traps (trap loading and regeneration by induced temperature increase) showed that the presence of the catalyst enabled both a more complete regeneration and a one-third fold reduction of the regeneration time compared to the case of a bare, non-catalytic trap. The catalyzed trap was finally characterized in terms of soot emissions during both the loading and the regeneration phase. (C) 2010 Elsevier B.V. All rights reserved.

Synthesis, Characterization of Nanocrystalline LaMnO3+delta and Its Application for the Removal of Chemical Oxygen Demand from Industrial Effluents

Nagaraja, R.; Nagappa, B.; Girija, C. R.; Nagabhushana, B. M.; Donappa, N.; Sastry, K. Manjunatha

ASIAN JOURNAL OF CHEMISTRY, 23, 11, 5031-5034

Nanocrystalline LaMnO3+delta has been synthesized by low temperature initiated, self propagating solution combustion process. It is an inexpensive synthesis and readily yields nanocrystalline product. It was characterized by powder XRD, FT-IR and SEM. The surface area of product is ca. 24 m(2)/g. The SEM micrographs show that the product is voluminous, fluffy and porous. It is found that 60 mg of LaMnO3+delta powder could remove 85 % of chemical oxygen demand from 100 mL of industrial effluent at pH 10.

Solution Combustion Synthesis, Characterization and Photocatalytic Activity of Nanosized ZnO Catalyst for Textile Industrial Dye Effluents Degradation

Nagaraja, R.; Girija, C. R.; Nagabhushana, B. M.; Donappa, N.; Sastry, K. Manjunatha

ASIAN JOURNAL OF CHEMISTRY, 23, 11, 5040-5044

We report here the synthesis of ZnO nanoparticles by solution-combustion method employing a mixture of zinc nitrate and sugar (O/F = 1) as reactants. Powder X-ray diffraction, scanning electron microscopy and ultraviolet-visible absorption spectra were employed to characterize the product. The studies showed that the ZnO nanoparticles could be used to catalytically degrade organic dyes present in waste water of textile dye effluent under UV light irradiation. More than 95 % decolourization of textile dye effluent occurs with ZnO as catalyst with in 8 min at basic medium under solar light. It was also found that chemical oxygen demand takes place at a faster rate under solar light as compared to that under UV light. The results further suggest that, ZnO nanoparticles are better catalyst than the calcined ZnO under solar and UV light irradiation.

Combustion synthesis of YAG:Ce and related phosphors

Gupta, K. V. K.; Muley, A.; Yadav, P.; Joshi, C. P.; Moharil, S. V.

APPLIED PHYSICS B-LASERS AND OPTICS, 105, 2, 479-484

YAG:Ce is an important phosphor having applications in various fields ranging from solid state lighting to scintillation detectors. YAG phosphors doped with activators are mainly synthesized by solid state reaction techniques that require high sintering temperatures (above 1500A degrees C) to eliminate YAM and YAP phases. Though several soft chemical routes have been explored for synthesis of YAG, most of these methods are complex and phase pure materials are not obtained in one step, but prolonged annealing at temperatures around 1000A degrees C or above become necessary. One step combustion synthesis of YAG:Ce3+ and related phosphors carried out at 500A degrees C furnace temperature is reported here. Activation with Ce3+ could be achieved during the synthesis without taking recourse to any post-combustion thermal treatment. LEDs prepared from the combustion synthesized YAG:Ce3+, exhibited properties comparable to those produced from the commercial phosphor.

Formation of the complete range of Ti5Si3-xGex solid solutions via mechanically induced self-sustained reactions

Cordoba, Jose M.; Chicardi, Ernesto; Aviles, Miguel A.; Gotor, Francisco J.

INTERMETALLICS, 19, 11, 1688-1692

The complete range of Ti5Si3-Ti5Ge3 solid solutions was synthesised from elemental mixtures of Ti, Si, and Ge under an inert atmosphere via mechanically induced self-sustaining reactions (MSR). The stoichiometry of Ti5Si3-xGex solid solutions was controlled by adjusting the Si/Ge ratio of the initial mixture. The chemical composition and lattice parameters of the materials confirmed that Ti5Si3-Ti5Ge3 solid solutions with good chemical homogeneity could be produced via MSR. (C) 2011 Elsevier Ltd. All rights reserved.

Engineering of porosity, microstructure and electrical properties of Ni-BaCe0.9Y0.1O2.95 cermet fuel cell electrodes by gelled starch porogen processing

Taillades, Gilles; Batocchi, Pierre; Essoumhi, Abdel; Taillades, Melanie; Jones, Deborah J.; Roziere, Jacques

MICROPOROUS AND MESOPOROUS MATERIALS, 145, 41334, 26-31

The synthesis of electrode materials with controlled microstructural characteristics and high conductivity over 1000 S cm(-1) is a key factor in improving the performance of fuel cells. In this work, we propose an alternative route to the partial sintering of a powder mixture to control the porosity of a ceramic-metal composite currently used as an anode material in Protonic Ceramic Fuel Cells working at 400-600 degrees C. This new method is based on the use of nanopowdered cermet materials and starch in gelling form for the elaboration of Ni-BaCe0.9Y0.1O3 (Ni-BCY) cermets. The microstructure and the electrical properties have been investigated with respect to the initial starch content. A porous microstructure consisting of hornogenously distributed Ni and BCY phases is observed. It is shown that the degree of open porosity and the electrical conductivity of the cermets are sensitive to the starch content. Anodes elaborated from initial compositions comprising 10 and 20 wt.% of starch offer sufficient mechanical strength and an open porosity >30 vol.%. The measured conductivities vary with the composition, from 1000 to 3000 S cm(-1) at 600 degrees C. The use of starch in gelled form as porogen allows the engineering of the porosity and the control of pore shape and distribution. (C) 2011 Elsevier Inc. All rights reserved.

Ionoluminescence studies of combustion synthesized Dy3+ doped nano crystalline forsterite

Lakshminarasappa, B. N.; Prashantha, S. C.; Singh, Fouran

CURRENT APPLIED PHYSICS, 11, 6, 1274-1277

Ionoluminescence (IL) of nano crystalline Mg2SiO4:Dy3+ pellet samples bombarded with 100 MeV Si+8 ions with fluences in the range (1.124e22.480) x 10(12) ions cm(-2) have been studied. Two prominent IL bands with peaks at similar to 480 nm and similar to 580 nm and a weak band with peak at similar to 670 nm are recorded. The characteristic peaks are attributed to luminescence center activated by Dy3+ ions due to the transitions F-4(9/2)-> H-6(15/2), H-6(13/2) and H-6(11/2). It is found that IL intensity initially decreases rapidly and then continuous to decrease slowly with further increase in ion fluence. The reduction in the Ionoluminescence intensity with increase of ion fluence might be attributed to degradation of Si-O (2v(3)) bonds present on the surface of the sample and/or due to lattice disorder produced by dense electronic excitation under heavy ion irradiation. (C) 2011 Elsevier B.V. All rights reserved.

The microstructural evolution of Ti2SnC from Sn-Ti-C system by Self-propagating high-temperature synthesis (SHS)

Li, Yuxin; Bai, Peikang

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 6, 751-754

A mechanism of Ti2SnC from Sn-Ti-C powder mixture was investigated by the observation of the microstructural evolution in a quenched sample prepared using a combustion front self-extinguished method. Microstructural evolution in the quenched sample was observed using the scanning electron microscopy (SEM) equipped with energy-dispersive spectrum (EDS), and the phase constituents of the different zones of the sample were inspected by X-ray diffraction (XRD). The result shows that, In the Ti-Sn-C system, Ti6Sn5 and TiC compounds were firstly formed, between Ti, Sn and C. and then Ti6Sn5 compounds reacted with TiC to form Ti2SnC, at last Ti2SnC began to decompose partly. (C) 2011 Elsevier Ltd. All rights reserved.

Microwave-induced substitutional-combustion reaction of Fe3O4/Al ceramic matrix porous composite

Lee, C. C.; Yoshikawa, N.; Taniguchi, S.

JOURNAL OF MATERIALS SCIENCE, 46, 21, 7004-7011

Microwave processing and substitutional-combustion reaction have been utilized to fabricate ceramic matrix porous composite from the thermite reaction of Fe3O4/Al system. Stoichiometric and mixtures with lower and over aluminum were tested. As this system was highly exothermic, the melting of reaction products and destruction the porous structure may occur. In order to avoid that, reaction coupled with a smaller driving force by controlling the microwave (MW) ignition condition at low temperature exotherm, where substitutional reaction occurs has been investigated. The phase and microstructure evolution during the reaction is analyzed by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Thermogram of the DTA analysis, irrespective of their mole ratio, recorded two exothermic peaks, one at similar to 1310 degrees C and another one at similar to 1370 degrees C. Fe and alpha-Al2O3 were the main products for the combusted mixture. Hercynite appeared as the major phase in the stoichiometric and slightly lower Al content mixtures due to incompleteness of reaction. In contrary, over aluminized mixture revealed the presence of Al3.2Fe. When heated at 1360 degrees C, an additional FeO phase was observed. Mixtures with extremely low Al content showed the presence of unreacted Fe3O4 and some free Al due to the decrease of combustion velocity associated with a decrease in the sample exothermicities. Sample heated in electric furnace was dense. When heating by microwave, controlling the reaction progress at low temperature exotherm allowed the achievement of porous structure composite consisting of micron size iron particles well distributed and embedded in the hercynite and/or Al2O3 matrix.

Combustion synthesis and characterization of Cu-Sm co-doped CeO2 electrolytes

Dong, Yingchao; Hampshire, Stuart; Zhou, Jian-er; Dong, Xinfa; Lin, Bin; Meng, Guangyao

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 31, 13, 2365-2376

Nano-sized CSO (Ce0.80Sm0.20O2-delta) and CSCO (Ce0.79Sm0.20Cu0.01O2-delta) were synthesized by the PVA-assisted combustion method, and then characterized by the structure of PVA-cation complexes and nano-powders, as well as mechanical and electrical performance after sintering. The results indicate that the PVA-cation complexes (PVA-(Ce3+,Sm3+) and PVA-(Ce3+,Sm3+,Cu2+)) were formed by coordinating metal cations to hydroxyl groups, as well as the COO-1 group derived from the oxidation of PVA with NO3-1. Low temperatures (around 200 degrees C) caused intense combustion reactions, resulting in the direct crystallization of cubic fluorite nano-CSO (10-20 nm) and nano-CSCO (10-15 nm) crystals with homogeneous element distribution. This slight compositional modification of CSO by co-doping with 1 mol% CuO resulted in a significantly lowered densification temperature, as well as enhanced mechanical and electrical property. The strength improvement can be ascribed to the dense and fine-grained microstructure without normal grain coarsening, resulting in a transgranular-dominant fracture mode during strength testing. (C) 2011 Elsevier Ltd. All rights reserved.

Synthesis and Sm2+/Sm3+ doping effects on photoluminescence properties of Sr4Al14O25

Sakirzanovas, Simas; Katelnikovas, Arturas; Dutczak, Danuta; Kareiva, Aivaras; Juestel, Thomas

JOURNAL OF LUMINESCENCE, 131, 11, 2255-2262

Complete and partial samarium reduction was achieved under strong reducing atmosphere by solid-state and combustion synthesis of Sr3.96Sm0.04Al14O25. Dependence of different fluxing agents on the formation of various strontium aluminates was examined. The samples were investigated by X-ray powder diffraction, temperature dependent luminescence decay and photoluminescence measurements. Excitation with UV radiation resulted in sharp and well resolved emission lines of samarium ions. Distinct temperature behavior for Sm2+ and Sm3+ were detected in the range of 100-500 K. Estimated emission thermal quenching values (TQ(1/2)) for divalent samarium were approximately 270 K while for trivalent state around 660K. Measured luminescence decay values of Sm2+ are substantially lower than for Sm3+, approximate to 1.7 and approximate to 2.7 ms, respectively. The spectral feature of Sm2+ emission spectrum indicates that dopant occupies low symmetry site in Sr4Al14O25 compound. (C) 2011 Elsevier B.V. All rights reserved.

A novel UV-emitting phosphor: Li6CaB3O8.5:Pb2+

Pekgozlu, Ilhan; Erdogmus, Ertugrul; Demirel, Bilal; Gok, M. Sabri; Karabulut, Hakan; Basak, Ali Sadi

JOURNAL OF LUMINESCENCE, 131, 11, 2290-2293

Pure Li6CaB3O8.5 and Li6Ca1-xPbxB3O8.5 (0.005 <= x <= 0.04) materials were prepared by a solution combustion synthesis method. The phase of synthesized materials was determined using the powder XRD and FTIR. The synthesized materials were investigated using spectrofluorometer at room temperature. The emission and excitation bands of the synthesized phosphors were observed at 307 and 268 nm, respectively. The dependence of the emission intensity on the Pb2+ concentration for the Li6Ca1-xPbxB3O8.5 (0.005 <= x <= 0.04) was studied and observed that the optimum concentration of Pb2+ in phosphor is 0.01 mol. The Stokes shift of the synthesized phosphor was calculated to be 4740 cm(-1). (C) 2011 Elsevier B.V. All rights reserved.

Thermal loading induced near-infrared broadband upconversion emission of Sm3+-doped beta-NaYbF4 nano-phosphors

Wang, Xiangfu; Yan, Xiaohong; Kan, Caixia

JOURNAL OF LUMINESCENCE, 131, 11, 2325-2329

A non-closed hydrothermal synthetic processing is improved to synthesize Sm3+ doped beta-NaYbF4 nano-phosphors at 98 degrees C without any high-temperature and high-pressure treatments as a final step. Novel green, red, and near-infrared broadband (799-873 nm) upconversion emissions of Sm3+-doped beta-NaYbF4 nano-phosphors under 980 nm excitation are observed. These UC emissions can be assigned to the Sm3+ transitions of (4)G(j), F-4(3/2) and F-6(11/2)-> H-6(j). The half-width of 873 nm emission band is broadened nearly two-fold through the annealing treatment for nano-phosphors. The upconversion process in Yb3+-Sm3+ system is discussed based on energy transfer mechanisms. (C) 2011 Elsevier B.V. All rights reserved.

Infrared-to-visible upconversion luminescence of Er3+ doped barium-natrium-yttrium-fluoride phosphor

Lu, Liping; Zhang, Xiyan; Bai, Zhaohui; Wang, Xiaochun

JOURNAL OF LUMINESCENCE, 131, 11, 2372-2376

Infrared-to-visible upconversion luminescence has been investigated in Er3+-doped barium-natrium-yttrium-fluoride phosphor (BaxNayYzF2x+y+3z+3m:Er-m) with different cation concentrations. Intense upconversion emissions around 530, 550, and 660 nm corresponding to the H-2(11/2), S-4(3/2), and F-4(9/2) transitions, respectively to the I-4(15/2) ground state were observed when excited by CW laser radiation at 1550 nm. We adopted the low-temperature combustion synthesis (LCS) method to decrease the phosphor particle size to 40-70 nm in order to couple to the photosensitive surface of CCD. The effect of the amount of carbamide on the particle size and the upconversion luminescence intensity was analyzed. The upconversion luminescence mechanism was studied by the log-log plot of intensity-power. (C) 2011 Elsevier B.V. All rights reserved.

FE modelling and fire resistance design of concrete filled double skin tubular columns

Lu, Hui; Zhao, Xiao-Ling; Han, Lin-Hai

JOURNAL OF CONSTRUCTIONAL STEEL RESEARCH, 67, 11, 1733-1748

Concrete filled double skin tubular columns (CFDST) have excellent structural behaviour. They have been used as transmission towers and have potential to be used as building columns and bridge piers. Performance of the CFDST columns under ambient temperature has been well studied, whereas fire resistance of such columns is still a major concern. A summary of a series of fire tests on CFDST columns conducted by the authors is briefly presented in the paper. A finite element numerical model is developed to analyse the fire behaviour of CFDST columns, namely thermal and structural responses under fire exposure. The model is verified by the test results and then used to perform parametric analyses. Parameters which have significant effect on the fire behaviour of CFDST columns are identified. Based on the parametric studies, suggestions on the fire resistance design of such columns are made. Practical design tables are derived for the fire resistance design of some typical CFDST columns. (C) 2011 Elsevier Ltd. All rights reserved.

On changing the size of the atmosphere of a vortex pair embedded in a periodic external shear flow

Ryzhov, E. A.

PHYSICS LETTERS A, 375, 44, 3884-3889

The dynamics of fluid particles in the vicinity of a self-propagating vortex pair, embedded in a nonstationary shear flow, is studied. When the shear flow is steady, the vicinity of the pair, which is called as a vortex atmosphere, consists of closed stream-lines, which coincide with fluid particles' trajectories. When the shear flow is nonstationary, the trajectories' behaviour changes drastically, then chaotic advection occurs. It is shown in the Letter that the vortex pair propagation velocity varies with the parameters (amplitude, and frequency) of the nonstationary shear flow. It is demonstrated, that changing of the mean velocity leads to changing of the size of the atmosphere. (C) 2011 Elsevier B.V. All rights reserved.

Preparation and visible light photocatalytic activity of Zn1-xFexO nanocrystalline

Xiao, Qi; Yao, Chi

MATERIALS CHEMISTRY AND PHYSICS, 130, 41306, 5-9

Zn1-xFexO nanocrystallines are prepared by precipitation method, and characterized by X-ray powder diffraction (XRD), Transmission electron microscopy (TEM), and UV-vis diffuses reflectance spectroscopy. Zn1-xFexO nanocrystallines show high photocatalytic activities for xanthate degradation at pH 7 under visible light irradiation. Zn0.96Fe0.04O nanocrystallines exhibit the highest photocatalytic efficiency, which is attributed to the balance between visible light absorption and valence band edge potential. (C) 2011 Elsevier B.V. All rights reserved.

Thermoluminescence studies of solution combustion synthesized Y2O3:Nd3+ nanophosphor

Jayaramaiah, J. R.; Lakshminarasappa, B. N.; Nagabhushana, B. M.

MATERIALS CHEMISTRY AND PHYSICS, 130, 41306, 175-178

Thermoluminescence (TL) of neodymium doped yttrium oxide (Y2O3:Nd3+) nanocrystalline phosphors, synthesized by solution combustion route, using disodium ethylene diamine tetra acetic acid (EDTA-Na-2) as fuel, was studied at low temperature (<350 degrees C). Powder X-ray diffraction (PXRD) pattern of Y2O3:Nd3+ revealed the cubic crystalline phase and the average crystallites sizes were found to be in the range of 18-24 nm. The morphology of the samples was studied by scanning electron microscopy (SEM) and was foamy and fluffy in nature. Fourier transformed infrared spectroscopy (FTIR) revealed prominent absorption with peaks at 3400, 1435, 875 and 565 cm(-1). Optical absorption studies showed that the energy gap of the synthesized sample was found to be 5 eV. Thermoluminescence of gamma-irradiated Y2O3:Nd3+ showed two well resolved TL glows with peaks at 587 and 628 K and they were analyzed by glow curve shape method and the activation energies were found to be 1.83 eV and 2.2 eV respectively. (C) 2011 Elsevier B.V. All rights reserved.

Combustion of reactive solutions impregnated into a cellulose carrier: Modeling of two combustion fronts

Lennon, E. M.; Tanzy, M. C.; Volpert, V. A.; Mukasyan, A. S.; Bayliss, A.

CHEMICAL ENGINEERING JOURNAL, 174, 1, 333-340

We develop and solve a novel model for the combustion of reactive solutions impregnated into a cellulose carrier. This procedure has been shown to be effective in the synthesis of metallic oxides with a nanoscale microstructure, which are suitable for catalyst applications. The model involves three reactions, (i) combustion of the carrier matrix, (ii) an endothermic reaction related to the decomposition or gasification of the synthesis reaction precursors and (iii) the exothermic oxide synthesis reaction. This model is shown to provide qualitative agreement with experimental observations. A parametric study of the model demonstrates that increasing the heat released via the leading cellulose burning reaction (i) is most favorable in terms of increasing the reaction yield and providing conditions for smaller size of the synthesized material. (C) 2011 Elsevier B.V. All rights reserved.

Efficient synthesis route to quasi-aligned and high-aspect-ratio aluminum nitride micro- and nanostructures

Lee, Tae-Hyuk; Nersisyan, Hayk H.; Jeong, Ha-Guk; Lee, Kap-Ho; Noh, Jae-Soo; Lee, Jong-Hyeon

CHEMICAL ENGINEERING JOURNAL, 174, 1, 461-466

Quasi-aligned, high-aspect-ratio AlN micro- and nanostructures were synthesized under high nitrogen pressure by the exothermic reaction of an Al + 0.015 mol (C(2)F(4))(n) mixture. Structurally uniform AlN micro- and nanofibers with hexagonal and cylindrical morphologies were obtained when the system temperature was maintained within the range of 1600-1700 degrees C. The fibers had aspect ratios as high as 2000, diameters in the range of similar to 0.05-20 mu m, and were similar to 100-1000 mu m in length. High-resolution transmission electron microscopic and selected area diffraction analyses indicated that the as-synthesized AlN micro- and nanostructures are perfectly single crystalline with preferential growth along the [0 0 1] direction. Branching was also observed in some of the micro-fibers, giving rise to randomized, two-dimensional comb textures. Based on the results obtained in the present study, a mechanism for the formation of AlN micro- and nanostructures under combustion conditions was proposed. (C) 2011 Elsevier B.V. All rights reserved.

Combustion synthesis, characterization and Raman studies of ZnO nanopowders

Reddy, A. Jagannatha; Kokila, M. K.; Nagabhushana, H.; Rao, J. L.; Shivakumara, C.; Nagabhushana, B. M.; Chakradhar, R. P. S.

SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 81, 1, 53-58

Spherical shaped ZnO nanopowders (14-50 nm) were synthesized by a low temperature solution combustion method in a short time <5 min. Rietveld analysis show that ZnO has hexagonal wurtzite structure with lattice constants a = 3.2511(1) angstrom, c = 5.2076(2) angstrom, unit cell volume (V) = 47.66(5) (angstrom)(3) and belongs to space group P63mc. SEM micrographs reveal that the particles are spherical in shape and the powders contained several voids and pores. TEM results also confirm spherical shape, with average particle size of 14-50 nm. The values are consistent with the grain sizes measured from Scherrer's method and Williamson-Hall (W-H) plots. A broad UV-vis absorption spectrum was observed at similar to 375 nm which is a characteristic band for the wurtzite hexagonal pure ZnO. The optical energy band gap of 3.24 eV was observed for nanopowder which is slightly lower than that of the bulk ZnO (3.37 eV). The observed Raman peaks at 438 and 588 cm(-1) were attributed to the E(2) (high) and E(1) (LO) modes respectively. The broad band at 564 cm(-1) is due to disorder-activated Raman scattering for the A(1) mode. These bands are associated with the first-order Raman active modes of the ZnO phase. The weak bands observed in the range 750-1000 cm(-1) are due to small defects. (C) 2011 Elsevier B.V. All rights reserved.

Synthesis, structure, and scintillation of Ce-doped gadolinium oxyorthosilicate nanoparticles prepared by solution combustion synthesis

Jacobsohn, L. G.; Tornga, S. C.; Blair, M. W.; Bennett, B. L.; Muenchausen, R. E.; Wang, R.; Crozier, P. A.; Cooke, D. W.

JOURNAL OF APPLIED PHYSICS, 110, 8, 83515-

The synthesis of Ce-doped Gd oxyorthosilicate nanoparticles using the solution combustion synthesis (SCS) method was investigated as a function of the amount of SiO(2) in the precursor mixture. The SCS product consists of mixtures of Ce-doped Gd(2)SiO(5), Gd(4.67)(SiO(4))(3)O, and Gd(2)O(3), whose relative concentrations depend on the amount of SiO(2) in the precursor mixture; the synthesis of GSO:Ce was obtained with a reduction by 30% of the SiO(2) content. Accordingly, this is the brightest material produced, with a photoluminescence signal that is comparable to that obtained from the bulk sample. Thermoluminescence (TL) results showed a considerably lower concentration of trapping defects in the nanoparticles than in the bulk sample. A previous study [E. G. Yukihara, L. G. Jacobsohn, M. W. Blair, B. L. Bennett, S. C. Tornga, and R. E. Muenchausen, J. Lumin. 130, 2309-2316 (2010)] reporting a comparison between photoluminescence and scintillation measurements, coupled to the TL characterization, suggests that surfaces play a major role in decreasing the scintillation efficiency of the nanoparticles. These results show that it is possible to prepare relatively bright scintillator powders using the SCS method. (C) 2011 American Institute of Physics. [doi:10.1063/1.3647304]

Near-infrared quantum cutting in Ce3+, Er3+, and Yb3+ doped yttrium silicate powders prepared by combustion synthesis

Rakov, Nikifor; Maciel, Glauco S.

JOURNAL OF APPLIED PHYSICS, 110, 8, 83519-

Yttrium silicate (YS) powders doped with Ce3+, Er3+, and Yb3+ were prepared by combustion synthesis. The material was investigated for use as energy downconverters to reduce thermalization losses in crystalline Si solar cells. The powders were excited by UV light (355 nm), and near-infrared emission around 1 mu m was observed corresponding to a quantum cutting (QC) effect. The QC process occurs via cooperative energy transfer from Ce3+ (sensitizer) to Yb3+ (activator) in Ce3+:Yb3+ co-doped YS powders. QC was also observed in Er3+:Yb3+ co-doped YS powder via sequential energy transfer. The idea of synergy by use of Ce3+:Er3+:Yb3+ triply doped system to enhance the QC efficiency was investigated. We observed that the QC performance of Ce3+:Er3+:Yb3+ triply doped YS powder is not superior to that of Ce3+:Yb3+ co-doped YS powder due to near-infrared luminescence quenching induced by energy back-transfer from Yb3+ to Er3+. (C) 2011 American Institute of Physics. [doi:10.1063/1.3653968]

Hybrid supercapacitor with nano-TiP2O7 as intercalation electrode

Aravindan, V.; Reddy, M. V.; Madhavi, S.; Mhaisalkar, S. G.; Rao, G. V. Subba; Chowdari, B. V. R.

JOURNAL OF POWER SOURCES, 196, 20, 8850-8854

Nano-size (<= 100 nm)TiP2O7 is prepared by the urea assisted combustion synthesis, at 450 and 900 degrees C. The compound is characterized by powder X-ray diffraction, Rietveld refinement, high resolution transmission electron microscopy and surface area methods. Lithium cycling properties by way of galvanostatic cycling and cyclic voltammetry (CV) showed a reversible and stable capacity of 60 (+/- 3) mAh g(-1) (0.5 mole of Li) up to 100 cycles, when cycled at 15 mA g(-1) between 2-3.4 V vs. Li. Non-aqueous hybrid supercapacitor, TiP2O7 (as anode) and activated carbon (AC) (as cathode) has been studied by galvanostatic cycling and CV in the range, 0-3 Vat 31 mA g(-1) and exhibited a specific discharge capacitance of 29 (+/- 1)Fg(-1) stable in the range, 100-500 cycles. The Ragone plot shows a deliverable maximum of 13 Wh kg(-1) and 371 W kg(-1) energy and power density, respectively. (C) 2011 Elsevier B.V. All rights reserved.

Comparative study of microwave and conventional methods for the preparation and optical properties of novel MgO-micro and nano-structures

Selvam, N. Clament Sagaya; Kumar, R. Thinesh; Kennedy, L. John; Vijaya, J. Judith

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 41, 9809-9815

Magnesium oxide (MgO) was synthesised by a simple microwave-assisted combustion route without using any template, catalyst or surfactant. For the purpose of comparison, it was also prepared using conventional method. The as-synthesized MgO was characterized by powder X-ray diffraction (XRD), Fourier Transform infrared spectra (FT-IR), high resolution scanning electron microscopy (HR-SEM), transmission electron microscopy (TEM), Energy Dispersive X-ray analysis (EDX), diffuse reflectance spectroscopy (DRS) and Photoluminescence (PL) spectroscopy. The XRD results confirmed the formation of cubic phase MgO. FT-IR was used to investigate the adsorption of water and CO(2) on MgO surface and confirm the formation of Mg-O phase. The formation of MgO micro cubes structures was confirmed by HR-SEM. The formation of MgO nanosheets was confirmed by HR-SEM and TEM and their possible formation mechanisms were also proposed. The optical absorption and photoluminescence emissions were determined by DRS and PL spectra respectively. An attempt has been made to compare the lattice parameter and the PL intensity. (C) 2011 Elsevier B.V. All rights reserved.

Effect of fuel-to-nitrate ratio on the powder characteristics of nanosized CeO2 synthesized by mixed fuel combustion method

Palneedi, Haribabu; Mangam, Venu; Das, Siddhartha; Das, Karabi

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 41, 9912-9918

Synthesis of nanocrystalline ceria powders is carried out through the mixed fuel combustion approach by using different combinations of glycine and citric acid. The powders obtained with different fuel-to-nitrate (F/N) ratios are characterized by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), BET surface area analysis, and Raman spectroscopy. TGA and FTIR spectroscopy studies have revealed the presence of carbonaceous species and residual volatiles in the combustion synthesized ceria powders. It is observed that the variation of fuel-to-nitrate ratio has a profound influence on the carbonaceous residues from combustion, crystallite size (11-44 nm), surface area (9-39 m(2)/g) and morphology of the resultant powders. The Raman spectroscopy results on the variation of particle size with F/N ratio are consistent with the conclusions made from X-ray line broadening and BET surface area analysis. (C) 2011 Elsevier B.V. All rights reserved.

Visible-Light-Driven Photocatalyst AgNbO3: Citrate Complex Process Preparation and Photocatalytic Property

Bi Jin-Hong; Chen Bing-Qin; Che Jian-Gang; Liu Ming-Hua

CHINESE JOURNAL OF INORGANIC CHEMISTRY, 27, 10, 1952-1958

AgNbO3 particles with a perovskite-type structure were successfully synthesized via a citrate complex method from NH4H2 [NbO(C2O4)(3)center dot 3H(2)O] and AgNO3. The obtained samples were characterized by XRD, DRS, SEM, TEM and XPS. The photocatalytic activity was tested by the decomposition of organic dye methylene blue under visible light irradiation. The results showed that the sample prepared at 800 degrees C exhibited the best photocatalytic activity. And the decomposition of methylene blue is via a demethylation process. Compared to the sample prepared by the solid-state reaction, the sample prepared by citrate complex method displayed a higher photocatalytic activity.

Mechanism of Molten-Salt-Controlled Thermite Reactions

Manukyan, Khachatur V.; Kirakosyan, Khachatur G.; Grigoryan, Yeva G.; Niazyan, Ofik M.; Yeghishyan, Armenuhi V.; Kirakosyan, Artavazd G.; Kharatyan, Suren L.

INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 50, 19, 10982-10988

The present work was undertaken to study the chemistry and phase formation mechanism in the salt-controlled MoO(3) + Mg + NaCl thermite reaction. It was found that the structure and phase formation mechanism in the studied system primarily depend on the salt content in the initial mixtures. In salt-poor mixtures, nucleation of product particles takes place in the molten magnesium, whereas under salt-rich conditions, products are mainly formed in molten sodium chloride. Analyses of combustion temperature profiles and product microstructures and thermal analysis of reacting mixtures suggested that the molybdenum oxide reacts with the salt at early stages of the process. The formed intermediate molybdenum oxychloride and sodium molybdate then react with magnesium, yielding Mo, MgO, and NaCl phases. The low value of the activation energy (50 kJ/mol) of the combustion process also suggests that gaseous (liquid) intermediates play an important role in the phase formation mechanism.

Influence of the thermal treatment on the physicochemical properties and photocatalytic degradation of 4-chlorophenol in aqueous solutions with tungstophosphoric acid-modified mesoporous titania

Blanco, Mirta; Pizzio, Luis

APPLIED CATALYSIS A-GENERAL, 405, 41306, 69-78

Materials based on titania directly modified with tungstophosphoric acid were prepared using titanium isopropoxide as titania precursor and urea as a low-cost pore-forming agent. The obtained mesoporous solids presented an average pore diameter higher than 3.1 nm. The specific surface area decreased when the TPA amount and the calcination temperature increased. All the modified solids only showed the anatase structure of titania by X-ray diffraction, while for the unmodified sample this structure was transformed into the rutile phase from 600 degrees C on. The crystallite size increased with the calcination temperature, though the TPA-modified samples presented lower values when the TPA amount was increased. The P-31 nuclear magnetic resonance studies showed that the Keggin structure of the tungstophosphate anion was partially transformed when it was thermally treated up to 600 degrees C, though structure disruption took place at higher temperature. The band gap values estimated from the UV-vis-diffuse reflectance spectra did not show important variation, though they slightly decreased with the TPA content. The 4-chlorophenol degradation was studied in liquid phase, with an air flow continuously bubbled. The degradation behavior of the catalysts as a function of time depended on the TPA amount and the thermal treatment temperature, the samples containing 30% TPA calcined at 500-600 degrees C and 20% TPA calcined at 600 degrees C being more effective. The apparent reaction constant, estimated assuming a pseudo-first-order kinetics, followed the same trend. The catalysts can be reused at least three times without an important decrease in the degradation and mineralization degrees. (C) 2011 Elsevier B.V. All rights reserved.

Aqueous combustion synthesis and characterization of ZnO powders

Ianos, Robert; Lazau, Ioan; Pacurariu, Cornelia; Sfirloaga, Paula

MATERIALS CHEMISTRY AND PHYSICS, 129, 3, 881-886

New organic fuels (beta-alanine, valine, zinc acetate and acrylamide) have been successfully tested for the preparation of nanocrystalline ZnO powders via aqueous combustion synthesis. In all cases, ZnO resulted directly from the combustion process and no subsequent annealing was required. Properties of the as-prepared ZnO powders were investigated and it was found that morphology, specific surface area, crystallite size and cumulative volume of pores are determined by the used fuel. A correlation has been found between the total volume of generated gases, adiabatic temperature, the amount of ZnO and the characteristics of the resulting powders. Largest surface area (42.0 m(2) g(-1)) and smallest ZnO crystallite size (21 nm) were obtained for acrylamide. (C) 2011 Elsevier B.V. All rights reserved.

Synthesis, Structural Characterization and Thermal Stability of Nanocrystalline Rare-Earth Chromates (RECrO4) and Rare-Earth Chromites (RECrO3)

Thakur, J.; Shukla, R.; Raje, N.; Ghonge, D.; Bagla, H.; Tyagi, A. K.

NANOSCIENCE AND NANOTECHNOLOGY LETTERS, 3, 5, 648-654

In this study, a series of nanocrystalline single-phasic RECrO4(La-Lu, except Ce and Pm) compounds have been synthesized by glycine-nitrate combustion method in fuel-deficient ratio. The compounds were characterized by techniques such as XRD (X-ray diffraction) and TEM (Transmission Electron Microscopy). RECrO3 series of compounds were obtained after decomposition of the respective RECrO4 compounds. XRD studies of the respective products, confirms the formation of mono-phasic rare-earth chromates (RECrO4) and chromites (RECrO3). Thermal behavior of all the rare-earth chromates (RECrO4) was studied using simultaneous TG-DTA. Decreasing trend was observed in decomposition temperature from LaCrO4 to LuCrO4. Stability of RECrO4 compounds have been correlated with structural, thermodynamics and heat transport aspects of the respective compounds.

Combustion synthesis and photoluminescence study of silicate biomaterials

Bhatkar, V. B.; Bhatkar, N. V.

BULLETIN OF MATERIALS SCIENCE, 34, 6, 1281-1284

Silicate based bioceramics are promising candidates as biomaterials for tissue engineering. The combustion synthesis method provides control on the morphology and particle size of the synthesized material. This paper discusses the combustion synthesis of akermanite (Ca(2)MgSi(2)O(7) and Sr(2)MgSi(2)O(7)), which has been shown to have good in vitro and in vivo bioactivities by earlier studies. Both Ca(2)MgSi(2)O(7) and Sr(2)MgSi(2)O(7) have akermanite structure. Ca(2)MgSi(2)O(7) and Sr(2)MgSi(2)O(7) were prepared using urea and ammonium nitrate. The combustion synthesis using urea and ammonium nitrate was found to be cost effective and efficient method of synthesis. The photoluminescence study of Ca(2)MgSi(2)O(7) : Eu(2+) and Sr(2)MgSi(2)O(7) : Eu(2+) shows host specific intense emission of Eu(2+).

Comparison of Multilayer Dielectric Thin Films for Future Metal-Insulator-Metal Capacitors: Al2O3/HfO2/Al2O3 versus SiO2/HfO2/SiO2

Park, Sang-Uk; Kwon, Hyuk-Min; Han, In-Shik; Jung, Yi-Jung; Kwak, Ho-Young; Choi, Woon-Il; Ha, Man-Lyun; Lee, Ju-Il; Kang, Chang-Yong; Lee, Byoung-Hun; Jammy, Raj; Lee, Hi-Deok

JAPANESE JOURNAL OF APPLIED PHYSICS, 50, 10, 10PB06-

In this paper, two kinds of multilayered metal-insulator-metal (MIM) capacitors using Al2O3/HfO2/Al2O3 (AHA) and SiO2/HfO2/SiO2 (SHS) were fabricated and characterized for radio frequency (RF) and analog mixed signal (AMS) applications. The experimental results indicate that the AHA MIM capacitor (8.0 fF/mu m(2)) is able to provide a higher capacitance density than the SHS MIM capacitor (5.1 fF/mu m(2)), while maintaining a low leakage current of about 50 nA/cm(2) at 1 V. The quadratic voltage coefficient of capacitance, alpha gradually decreases as a function of stress time under constant voltage stress (CVS). The parameter variation of SHS MIM capacitors is smaller than that of AHA MIM capacitors. The effects of CVS on voltage linearity and time-dependent dielectric breakdown (TDDB) characteristics were also investigated. (C) 2011 The Japan Society of Applied Physics

Luminescent properties of a new red-emitting phosphor based on LaInO3 for LED

Tang, An; Zhang, Dingfei; Yang, Liu; Wang, Xiaohong

OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 10, 1031-1034

Red-emitting phosphor LaInO3:Eu3+ for LED was synthesized by solid-state reaction at 1250 degrees C. X-ray diffraction, particle size analyzer and spectrometer were used to characterize the phosphor. The prepared LaInO3:Eu3+ phosphor has an orthorhombic crystal structure with pure phase and the average diameter of LaInO3:Eu3+, Bi3+ particles is about 2.15 mu m. The phosphor LaInO3: Eu3+ can be efficiently excited by near ultraviolet and blue light to emit intense red light at 612 nm due to the Eu3+ transition of D-5(0)-> F-7(2). The emission intensity is the strongest when the Eu3+ content reaches 0.20 mole fraction. The optimal Bi3+ concentration in the LaInO3:0.20Eu(3+) is 0.03 mole fraction. The luminescence intensity of the LaInO3:0.20Eu(3+), 0.03Bi(3+) is higher than that of without Bi3+ phosphor. The results indicate that LaInO3:Eu3+, Bi3+ phosphor is a prospective potoluminescent material for white LED.

Enhancement of phosphorescence of BaAl12O19:Eu phosphor due to Dy, Nd co-activators

Yerpude, A. N.; Dhoble, S. J.

OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 10, 1118-1122

This paper reports the preparation of BaAl12O19:Eu2+ and BaAl12O19:Eu2+, (RE = Dy3+, Nd3+) phosphors synthesized by a combustion method. The samples were characterized by X-ray powder diffraction, photoluminescence (PL) and phosphorescence decay curve. The PL spectra was recorded when the powders were excited by UV light at room temperature showed broad blue emission, this emission can be ascribed to 4f(6)5d(1) to 4f(7) transition of the Eu2+ ions. More ever, small shift in wavelength was observed between the doped and co-doped phosphors. The phosphorescence characteristic was studied using the decay curves. The effect of Dy3+ and Nd3+ doping on enhancing the photoluminescence intensity and phosphorescence decay curve of BaAl12O19:Eu2+ is discussed.

Factors controlling thermoluminescence from self-propagating high-temperature synthesis in powder bodies

Leitsin, V. N.; Kolmakova, T. V.; Dmitrieva, M. A.

RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY B, 5, 5, 816-820

Computer simulations are used to study the physicochemical processes that determine the light emission from the lateral surface of the sample during self-propagating high-temperature synthesis (SHS) in the Ni-Al powder system. It is shown that endothermic phase transitions in the components of the powder mixture control the character of change of the chemiluminescence intensity. The behavior of the emission from of the subareas of the lateral surface carries information about the parameters of state of the medium and physical mechanisms underlying SHS.

Synthesis and microwave absorption properties of SiC-carbon fibers composite in S and C band

Zhao, Ju-Min; An, Wen-Xiu; Li, Deng-Ao; Yang, Xiaoli

SYNTHETIC METALS, 161, 19-20, 2144-2148

SiC powders were synthesized from the Si/C system in a nitrogen atmosphere by combustion synthesis. The carbon fiber/SIC composite with different mixture ratios have been prepared by as-prepared material. The structure, morphology and properties of the composites are characterized with IR, XRD, scanning electron microscope (SEM), Network Analyzer. The complex permittivity (epsilon(r)' - j epsilon(r)'') and reflection loss (dB) of the composites have been measured at different microwave frequencies in S-band and C-band (30-6000 MHz) employing vector network analyzer model PNA 3629D vector. The effect of the mol ratio of carbon fiber/SiC on the microwave loss properties of the composites is investigated. A possible microwave absorbing mechanism of carbon fiber/SiC composite has been proposed. The carbon fiber/SiC composite can find applications in suppression of electromagnetic interference (EMI), and reduction of radar signature. (C) 2011 Elsevier B.V. All rights reserved.

Rapid consolidation of binderless nanocrystalline silicon carbide by pulsed current activated sintering

Park, Na-Ra; Ko, In-Yong; Shon, In-Jin; Hong, Kyung-Tae; Doh, Jung-Mann; Oh, Se-Hoon; Yoon, Jin-Kook

JOURNAL OF CERAMIC PROCESSING RESEARCH, 12, 5, 534-537

Hard nanostructured SiC material was produced within 3 minutes from mechanically activated powder by the simultaneous application of a pressure of 500 MPa and a 2,800 A pulsed current. The pulsed current activated sintering was performed on SiC of various grain sizes. With a finer initial SiC powder size, the resulting density was higher and the SiC possessed improved mechanical properties. The fracture toughness, hardness, and grain size of the sintered SIC were investigated.

Preparation of CeB6 nano-powders by self-propagating high-temperature synthesis (SHS)

Dou Zhihe; Zhang Ting'an; Liu Yan; Guo Yongnan; He Jicheng

JOURNAL OF RARE EARTHS, 29, 10, 986-990

CeB6 powders were prepared by high-temperature self-propagating synthesis (SHS) in which CeO2, B2O3 and Mg were taken as reactants. The adiabatic temperature and dynamics of SHS reactions were investigated. The SHS reaction products and leached products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that the adiabatic temperature of Mg-B2O3-CeO2 reaction system was rather higher than 1800 K to make the reaction propagate by itself, and the apparent activation energy (E-a) and reaction order (n) of exothermic peak on Mg-B2O3-CeO2 differential scanning calorimetry (DSC) curve were 23.03 kJ/mol and 1.31, respectively. The apparent activation energy was lower, so the reaction occurred easily. The SHS products consisted of MgO, CeB6 and little Mg3B2O6. The leached products consisted of single CeB6 phase and its purity was higher than 99.0%, and the average particle sizes of CeB6 were smaller than 150 nm.

Effect of Processing Parameters on Synthesis of AlN Matrix Composites with the Help of Reaction between BN and Aluminum

Kobashi, Makoto; Saiki, Kenzo; Kanetake, Naoyuki

JOURNAL OF THE JAPAN INSTITUTE OF METALS, 75, 10, 525-531

The reactive infiltration of molten aluminum into a powder preform was investigated as a processing route for aluminum nitride (AlN) matrix composites. As the powder preform, titanium and boron nitride (BN) powders were blended and compacted, the infiltration occurred spontaneously at temperatures ranging from 1073 K to 1673 K. The conversion ratio of BN to TiB2 and AlN turned out to be insufficient (<0.8) at temperatures below 1273 K. The conversion ratio increased by increasing the processing temperatures, and it exceeded 0.95 at 1673 K. The conversion ratio at 1473 K was almost saturated with a 3.6 ks holding and the effect of extending the holding time was not confirmed. Decreasing the BN powder size was effective to promote the reaction between aluminum, titanium and BN. The effectiveness was particularly prominent at 1473 K in comparison with the specimen fabricated at 1673 K. The titanium powder size did not show a significant effect on the formation of AlN and TiB2. The volume fraction of AlN increased by changing the atmospheric gas from argon to nitrogen.

Reaction Synthesis of Annealed Ni-50at%Al Powder Compact

Chou, Yong-Jae; Lee, Han-Young

KOREAN JOURNAL OF METALS AND MATERIALS, 49, 10, 790-796

To reduce the heat released during intermetallic reaction, Ni-50at%Al powder compact has been previously annealed at several conditions before the reaction. The effects of the pre-annealing conditions on the reaction synthesis process have been investigated. Experimental results show that the heat released during the reaction synthesis decreased proportionally with increase of the pre-annealing temperature and duration time. The reaction duration period was significantly increased when the intermetallics were formed in the powder compact during the pre-annealing. This was attributed to the fact that the reaction occurred by solid-state diffusion between the un-reacted elemental atoms and that the NiAl(3) phase formed predominantly during pre-annealing.

Fast fabrication of glass ceramics by high gravity combustion synthesis

Liu, G. H.; Li, J. T.; He, B.

ADVANCES IN APPLIED CERAMICS, 110, 7, 394-399

Three systems of glass ceramics with different chemical compositions were prepared by high gravity combustion synthesis. Most samples were dense with a low porosity, which can be attributed to accelerated separation and removal of gas bubbles from ceramic melts in a high gravity field. The hardness of the as prepared glass ceramics varied in the range of 8.2-12.8 GPa and could be improved by a fine eutectic structure. Compared with conventional techniques, high gravity combustion synthesis can offer a fast and efficient way to prepare glass ceramic materials.

Combustible Mixtures of Lunar Regolith with Metals: Thermodynamic Analysis and Combustion Experiments

White, Christopher; Alvarez, Francisco; Shafirovich, Evgeny

JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER, 25, 4, 620-625

Construction materials could be produced in situ on the surface of the moon or Mars by combustion of regolith mixed with metals such as aluminum and magnesium. In the present paper, the adiabatic flame temperature and combustion products were calculated for the mixtures of JSC-1A lunar regolith simulant with aluminum and magnesium, as well as with a titanium/boron pair. It was shown that at the additive concentrations of 20-30 wt %, the reaction between titanium and boron provides a lower adiabatic flame temperature of the mixture as compared with the thermite-type reaction between regolith and aluminum or magnesium. Also, magnesium exhibits higher temperatures as compared with aluminum. The maximum temperatures for aluminum and magnesium are reached at 23 and 26 wt %, respectively. Combustion of magnesium/JSC-1A mixture pellets was studied experimentally in an argon environment. To facilitate ignition and achieve stable combustion, the original JSC-1A powder was ground in a ball mill. It was shown that, with increasing the milling time of JSC-1A, the combustion front velocity of Mg/JSC-1A mixture increases. A decrease in argon pressure from 90 to 10 kPa does not influence the front velocity.

Numerical Models Validation of Cracked Square Hollow Section (SHS) Y- and K-Joints

Lie, Seng-Tjhen; Yang, Zheng-Mao

JOURNAL OF STRUCTURAL ENGINEERING-ASCE, 137, 10, 1132-1140

To validate the accuracy of finite-element models of cracked square hollow section (SHS) Y- and K-joints, two full-scale precracked specimens were tested under static incremental loads up to failure. The load-displacement curves were plotted during the tests, and a set of linear variable displacement transducers (LVDTs) were used to record the crack mouth opening displacements (CMOD) at the deepest points, whereas the crack extension was captured using the standard Alternating Current Potential Drop (ACPD) technique. The experimental results are compared with the corresponding numerical results obtained using the nonlinear finite-element method. Both sets of results show good agreement with maximum percentage differences of 7.15 and 7.96% for the plastic collapse loads and crack mouth opening displacements, respectively. Hence, the numerical model adopted previously for the cracked SHS T-joints is robust and can also be used to estimate the plastic collapse load P(c) and crack driving force J(ep) of any uniplanar tubular cracked Y- and K-joints. DOI: 10.1061/(ASCE)ST.1943-541X.0000349. (C) 2011 American Society of Civil Engineers.

Eruption Combustion Synthesis of NiO/Ni Nanocomposites with Enhanced Properties for Dye-Absorption and Lithium Storage

Wen, Wei; Wu, Jin-Ming

ACS APPLIED MATERIALS & INTERFACES, 3, 10, 4112-4119

Large-scale energy-efficient productions of oxide nanoparticles are of great importance in energy and environmental applications. In nature, volcano eruptions create large amounts cif volcano ashes within a short duration. Inspired by such phenomena, we report herein our first attempt to achieve an artificial volcano for mass productions of various oxide nanoparticles with enhanced properties for energy and environmental applications. The introduction of NaF into the solution combustion synthesis (S.:CS), which is a generally adopted synthetic route for mass productions of various oxide nanoparticles, results in better particle dispersity and a drastic increase in specific surface area compared to the conventional SCS. In a fixed dosage of NaF, a new eruption combustion pattern emerges, which may be contributed to the more gas evolution, lower apparent density, and weaker interparticle force. The novel eruption combustion pattern observed in SCS provides a versatile alternative for SOS to control combustion behavior, microstructure, and property of the products. NiO/Ni nanocomposite yielded by the new approach shows an ideal dye-absorption ability as well as lithium storage capacity. The new SCS pattern reported in this paper is versatile, emerging in various systems of Ni-Co-O, Co-O, La-O, Ni-Co-O, Zn-Co-O, and La-Ni-O.

Stress and Phase Purity Analyses of Diamond Films Deposited through Laser-Assisted Combustion Synthesis

Guillemet, T.; Xie, Z. Q.; Zhou, Y. S.; Park, J. B.; Veillere, A.; Xiong, W.; Heintz, J. M.; Silvain, J. F.; Chandra, N.; Lu, Y. F.

ACS APPLIED MATERIALS & INTERFACES, 3, 10, 4120-4125

Diamond films were deposited on silicon and tungsten carbide substrates in open air through laser-assisted combustion synthesis. Laser-induced resonant excitation of ethylene molecules was achieved in the combustion process to promote diamond growth rate. In addition to microstructure study by scanning electron microscopy, Raman spectroscopy was used to analyze the phase purity and residual stress of the diamond films. High-purity diamond films were obtained through laser-assisted combustion synthesis. The levels of residual stress were in agreement with corresponding thermal expansion coefficients of diamond, silicon, and tungsten carbide. Diamond-film purity increases while residual stress decreases with an increasing film thickness. Diamond films deposited on silicon substrates exhibit higher purity and lower residual stress than those deposited on tungsten carbide substrates.

Solution combustion synthesis and visible light-induced photocatalytic activity of mixed amorphous and crystalline MgAl2O4 nanopowders

Li, Fa-tang; Zhao, Ye; Liu, Ying; Hao, Ying-juan; Liu, Rui-hong; Zhao, Di-shun

CHEMICAL ENGINEERING JOURNAL, 173, 3, 750-759

Mixed amorphous and crystalline MgAl2O4 nanopowders with visible light-induced photocatalytic activity were prepared via a simple solution combustion method using glycine and urea as fuel mixtures. The obtained samples were characterized by X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray, transmission electron microscopy, Brunauer-Emmett-Teller (BET) surface area, thermogravimetry. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and UV-Vis diffuse reflection spectrum. The results showed that the combustion was almost complete, the crystallinity and crystallite size of MgAl2O4 increased with the increase of fuels, and there was N atoms doped in the catalysts. The MgAl2O4 containing amorphism had photo-absorption ability in visible light region. The photocatalytic results for degradation of methylene blue (MB) indicated that the combustion-synthesized samples had photocatalytic activity, whereas the annealed well crystalline MgAl2O4 nanopowders had none. The MgAl2O4 sample containing about 45.6% crystalline and 55.4% amorphous materials showed the highest photocatalytic activity, with a 99.5% MB removal in 100 min under visible light irradiation. The fluorescence spectra verified that the greater the formation rate of center dot OH radicals, the higher the photocatalytic activity achieved. (C) 2011 Elsevier B.V. All rights reserved.

Modeling and analyzing the hydriding kinetics of Mg-LaNi5 composites by Chou model

Pan, Yan-Biao; Wu, Yu-Feng; Li, Qian

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 20, 12892-12901

Chou model was used to analyze the influences of LaNi5 content, preparation method, temperature and initial hydrogen pressure on the hydriding kinetics of Mg-LaNi5 composites. Higher LaNi5 content could improve hydriding kinetics of Mg but not change hydrogen diffusion as the rate-controlling step, which was validated by characteristic reaction time tc. The rate-controlling step was hydrogen diffusion in the hydriding reaction of Mg-30 wt.% LaNi5 prepared by microwave sintering (MS) and hydriding combustion synthesis (HCS), and surface penetration was the rate-controlling step of sample prepared by mechanical milling (MM). Rising temperature and initial hydrogen pressure could accelerate the absorption rate. The rate-controlling step of Mg-30 wt.% LaNi5 remained hydrogen diffusion at temperatures ranging from 302 to 573 K, while that of Mg-50 wt.% LaNi5 changed from surface penetration to hydrogen diffusion with increasing initial hydrogen pressure ranging from 0.2 to 1.5 MPa. Apparent activation energies of absorption for Mg-30 wt.% LaNi5 prepared by MS and MM were respectively 25.2 and 28.0 kJ/mol H-2 calculated by Chou model. Kinetic curves fitted and predicted by Chou model using temperature and hydrogen pressure were well exhibited. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Economical Route to Produce High Seebeck Coefficient Calcium Cobaltate for Bulk Thermoelectric Applications

Selig, Jiri; Lin, Sidney; Lin, Hua-Tay; Johnson, D. Ray; Wang, Hsin

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 10, 3245-3248

Phase pure calcium cobaltate (Ca(1.24)Co(1.62)O(3.86)) was prepared by Self-propagating High-temperature Synthesis (SHS) followed by a short post heat treatment. Prepared powders were characterized by XRD for phase purity, and SEM for particle size, and distribution. Temperature histories at the center and on the surface of reaction pellet during the SHS process were monitored and recorded. Particle size of synthesized powders was reduced using a planetary mill to increase its specific surface area. Electrical conductivity, thermal conductivity, and Seebeck coefficient of the prepared power were measured and figure of merit was reported.

The behavior of nanothermite reaction based on Bi2O3/Al

Wang, L.; Luss, D.; Martirosyan, K. S.

JOURNAL OF APPLIED PHYSICS, 110, 7, 74311-

We studied the impact of aluminum particle size and the thickness of surrounding alumina layer on the dynamic pressure discharge of nanothermite reactions in the Bi2O3/Al system. A pressure discharge from 9 to 13MPa was generated using as-synthesized Bi2O3 nano-particles produced by combustion synthesis and Al nanoparticles with size from 3 mu m to 100 nm. The maximum reaction temperature was measured to be similar to 2700 degrees C. The estimated activation energy of the reaction was 45 kJ/mol. A very large (several orders of magnitude) difference existed between the rate of the pressure pulse release by nanothermite reactions and by thermite reactions with large aluminum particles. The maximum observed pressurization rate was 3200 GPa/s. The time needed to reach the peak pressure was 0.01 ms and 100 ms for aluminum particles with diameter of 100 nm and 70 microns, respectively. The discharge pressure was a monotonic decreasing function of the thickness of the surrounding alumina layer. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3650262]

Effects of processing and powder size on microstructure and reactivity in arrested reactive milled Al plus Ni

Herbold, E. B.; Jordan, J. L.; Thadhani, N. N.

ACTA MATERIALIA, 59, 17, 6717-6728

Ball-milling Al-metal powders can result in self-sustaining high-temperature synthesis in intermetallic-forming systems. Here, Al and Ni powders with similar composition are used to investigate how microstructural differences affect the measured time to reaction (TTR) between powders of different sizes processed under milling conditions specified by statistically designed experiments. Linear statistical models predicting the TTR and the change in temperature (Delta T) are built from these experimental results. The time required to observe a self-sustained high-temperature synthesis of NiAl with different combinations of the powders and ball-milling conditions vary by almost an order of magnitude. Comparisons of powders milled to times corresponding to percentages of their averaged TTR show similar reaction initiation temperatures despite the difference in total milling time. Several distinct arrested reactions within the powder grains exhibit rapid solidification or incomplete diffusion of Ni into Al, forming porous Ni-rich layered structures. The partially reacted grains suggest that the composite laminate particles are not forming intermetallic on the grain scale, but on the localized scale between layers. Published by Elsevier Ltd. on behalf of Acta Materialia Inc.

Fluid Dynamics of Flow Through Microscale Lattice Structures Formed from Self-Propagating Photopolymer Waveguides

Fink, Kathryn D.; Kolodziejska, Joanna A.; Jacobsen, Alan J.; Roper, Christopher S.

AICHE JOURNAL, 57, 10, 2636-2646

The fluid dynamics of flow through microscale lattice structures is characterized for different unit cell sizes, flow angles, and flow rates. The structures consist of an octahedral-type periodic unit cell, which is formed from an interconnected pattern of self-propagating photopolymer wave guides. The periodic unit cell of each sample has a node-to-node spacing between 800 and 2400 pm and a truss member diameter between 148 and 277 pm. Water is directed through the microscale lattice structures, and the resulting pressure drop is investigated for two different flow angles and superficial flow rates between 0.5 and 4.8 L/min. Finite element analysis is used to determine pressure drop in the laminar flow regime. The results are used to develop a correlation describing friction factor as a function of flow direction, geometric characteristics, and Reynolds number. This work enables control of the fluid dynamics in microarchitected multifunctional truss materials through design and superficial flow angle. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 2636-2646, 2011

Fabrication of tungsten powder with sodium tungstate as raw material by SHS method

Jiang Guojian; Xu Jiayue; Zhuang Hanrui; Li Wenlan

MATERIALS LETTERS, 65, 19-20, 2969-2971

Tungsten powders were fabricated by Self-propagating High-temperature Synthesis (SHS) method with sodium tungstate (Na(2)WO(4)) and magnesium (Mg) as raw reactants. The effect of the molar ratios of Mg/Na(2)WO(4) on the compositions of combustion products was investigated. The results show that, it is advantageous for more Mg in the raw reactants than the stoichiometric quantity to decrease the impurities in the combustion products and increase the completeness of the synthesis reaction of tungsten. At last, tungsten powders can be obtained after the acid enrichment and distilled water washing. (C) 2011 Elsevier B.V. All rights reserved.

Thermal analysis of high-temperature fast reactions in energetic materials

Shteinberg, Alexander

JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 106, 1, 39-46

To get round two main difficulties of the kinetic study of fast reactions of high-temperature decomposition of energetic materials (EM) (spatial nonisothermality and self-inflammation) two new methods for sample preparation called ''mechanical dilution'' and ''thermal dilution'' were applied. In the first part of the presentation, some experimental and theoretical data on kinetics of fast high-temperature decomposition of some typical homogeneous and heterogeneous energetic materials (including pyroxylin, ammonia copper chromate, ammonium perchlorate, solid rocket propellants, and others) are given. In a number of cases, kinetic constants of fast reactions dominating at high temperatures were shown to significantly differ from those of low-temperature reactions. The second part of the presentation deals with a new method of thermal analysis-electrothermal analysis (ETA). By using a multi-channel high-speed optical pyrometer, variation of the temperature field in an electrically heated sample of conductive energetic material (or its mixture with metal powder) during its heating followed by thermal explosion is registered. Due to application of this method in the ETA-100 (allowing one to measure kinetic data at the temperature up to 3800 K with a time step as short as 0.1 ms, i.e., for full conversion times as short as 10(-3) s) some important patterns of mechanisms of gasless combustion and explosion in SHS-mixtures (Si + C, Ni + Al, and Ti + C) were identified. More details regarding these and some additional important aspects can be found in [1, 2].

Design rules for web crippling of CFRP strengthened aluminium rectangular hollow sections

Wu, C.; Zhao, X. L.; Duan, W. H.

THIN-WALLED STRUCTURES, 49, 10, 1195-1207

Web crippling failure (web buckling and web yielding) is critical for thin-walled members when subjected to concentrated load. Carbon fibre reinforced polymer (CFRP) is attracting increasing research interest as a strengthening material for metallic structural members. Improved web crippling capacity of aluminium rectangular hollow sections has been achieved with CFRP being attached to the exterior and/or interior of the webs from a series of tests conducted by the authors. This paper focuses on developing design rules for predicting the nominal crippling strength of CFRP strengthened sharp-corner aluminium tubular sections: rectangular hollow section (RHS) and square hollow section (SHS), under end bearing load. The existing design rules for bare sections without CFRP strengthening are firstly reviewed and assessed, including design rules for both cold-formed steel structural members (Australian/New Zealand standard (AS 4100-1998) and North American Specification) and aluminium structures (Australian/New Zealand standard (AS 1664-1997) and American aluminium design manual). They are modified to take account of the improved capacity due to CFRP strengthening. The proposed design rules are calibrated against test results. (C) 2011 Elsevier Ltd. All rights reserved.

Modification of Fe and Al elemental powders' sintering with addition of magnesium and magnesium hydride

Chojnacki, Michal; Jozwiak, Stanislaw; Karczewski, Krzysztof; Bojar, Zbigniew

INTERMETALLICS, 19, 10, 1555-1562

An attempt to modify sintering of iron and aluminium elemental powders with use of small additions of Mg and MgH(2) was presented in this paper. The kinetics of such modified sintering was investigated using DSC technique, XRD analysis and SEM observations. Significant changes in the mechanism of exothermal formation reaction of Fe-Al intermetallic phases in compositions doped with magnesium and its hydride was observed. Initiation temperature of Self-propagating High-temperature Synthesis (SHS) reaction was pronouncedly shifted to lower value as compared with undoped composition. Influence of additions on the SHS reaction kinetics parameters was also calculated with use of the JMA model and changes of the Avrami exponent value of specific phase formation was noticed. Positive effect of MgH(2) addition on partial homogeneity of final product was also studied. (C) 2011 Elsevier Ltd. All rights reserved.

Modification and optimization of nano-crystalline Al2O3 combustion synthesis using Taguchi L-16 array

Norouzbeigi, Reza; Edrissi, Mohammad

MATERIALS RESEARCH BULLETIN, 46, 10, 1615-1624

Nanocrystalline Al2O3 powders have been synthesized by combustion method using 8 new fuels. The effectiveness of important factors on the production of nanopowders was investigated and optimized using Taguchi L-16 array design. The products were characterized by XRD, BET, TGA, EDX, FESEM, and TEM analyses. Results demonstrated that the alumina nanoparticles had crystallite sizes between 8.31 nm and 13.54 nm. The optimized sample had the specific surface area of 72 m(2)/g and crystallite size of 7.25 nm. The synthesis of gamma-alumina was modified in order to achieve higher specific surface area (122.63 m(2)/g). A nano-network of alumina powders woven by alumina nano-fibers has been fabricated successfully by modified combustion synthesis. The length and diameter of fibers were about 160 nm and 10 nm respectively. (C) 2011 Elsevier Ltd. All rights reserved.

Microstructural evolution of reinforcements in the remelting in situ TiC/Al-12Si composites treated by ultrasonic vibration

Liu, Z. W.; Rakita, M.; Han, Q.; Li, J. G.

MATERIALS RESEARCH BULLETIN, 46, 10, 1674-1678

Clusters of reinforced particles and long rod-like Al(3)Ti particles are usually present in the matrix of in situ TiC/Al alloy composites fabricated via SHS reaction of the Al-Ti-C system in the molten aluminum alloys. In order to improve the properties of the composites, the above issues should be solved effectively. In our research, high-intensity ultrasonic vibration was introduced into the remelting TiC/Al-12Si composites containing clusters of TiC particles and long rod-like Al(3)Ti phase to optimize the microstructure of the composites. The results of SEM showed that long rod-like Al(3)Ti particles were turned into small blocky ones and large clusters were broken up into small ones. In the meantime, individual TiC particles could be peeled off from the clusters and distributed uniformly in the matrix. An in situ TiC/Al-12Si composite with a homogeneous microstructure was attained successfully. The evolution of the morphology of Al(3)Ti phase and the clusters in the ultrasonic field was also discussed. (C) 2011 Elsevier Ltd. All rights reserved.

Preparation and characterization of nanocrystalline and mesoporous strontium titanate thin films at room temperature

Mohammadi, M. R.; Fray, D. J.

JOURNAL OF COATINGS TECHNOLOGY AND RESEARCH, 8, 5, 585-593

The low temperature perovskite-type strontium titanate (SrTiO(3)) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol-gel route. The prepared sol had a narrow particle size distribution with hydrodynamic diameter of about 17 nm. X-ray diffraction (XRD) revealed that the synthesized powders had a perovskite-SrTiO(3) structure with preferable orientation growth along the (1 0 0) direction. TEM images showed that the average crystallite size of the powders annealed in the range 300-800A degrees C was around 8 nm. FE-SEM analysis and AFM images revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 25 nm at 600A degrees C. Based on Brunauer-Emmett-Taylor (BET) analysis, the synthesized powders showed mesoporous structure with BET surface area in the range 92-75 m(2)/g at 400-600A degrees C. One of the smallest crystallite sizes and one of the highest surface areas reported in the literature were obtained, which can be used in many applications, such as photocatalysts.

Preparation and luminescent properties of BaCa2Si3O9:Eu2+

Yao, Shanshan; Xue, Lihong; Yan, Youwei

OPTICS AND LASER TECHNOLOGY, 43, 7, 1282-1285

A blue emitting phosphor of the triclinic BaCa2Si3O9:Eu2+ was prepared by the combustion-assisted synthesis method and an efficient blue emission ranging from the ultraviolet to visible was observed. The luminescence and crystallinity were investigated using luminescence spectrometry and X-ray diffractometry (XRD), respectively. The emission spectrum shows a single intensive band centered at 445 nm, which corresponds to the 4g(6)5d(1) -> 4f(7) transition of Eu2+. The excitation spectrum is a broad extending from 260 to 450 nm, which matches the emission of ultraviolet light-emitting diodes (UV-LEDs). The critical quenching concentration of Eu2+ in BaCa2Si3O9:Eu2+ phosphor is about 0.05 mol. The corresponding concentration quenching mechanism is verified to be a dipole-dipole interaction. The CIE of the optimized sample Ba0.95Ca2Si3O9:Eu-0.05(2+) was (x, y)=(0.164, 0.111). The result indicates that BaCa2Si3O9:Eu2+ can be potentially useful as a UV radiation-converting phosphor for white light-emitting diodes (LEDs). (C) 2011 Elsevier Ltd. All rights reserved.

Formation of metal matrix composite reinforced with Nano sized Al2O3 + Ni-Al intermetallics during coating of Al substrate via combustion synthesis

Motlagh, E. Bahrami; Nasiri, H.; Khaki, J. Vahdati; Sabzevar, M. Haddad

SURFACE & COATINGS TECHNOLOGY, 205, 23-24, 5515-5520

A hard composite coating was synthesized upon an Aluminum1100 alloy substrate, using combustion synthesis reactions. A thin cylindrical compact of an exothermic pre-milled reactive powder mixture of "Ni + 14Al+ CuO + 2NiO" was utilized for this purpose. This compact was placed on the substrate and they were heated up to the ignition temperature of the reactants, under static pressure. The cross section of the coated substrate was investigated using X-ray diffraction experiments and a scanning electron microscope (SEM) which was equipped with energy dispersive spectrometer (EDS). The coating and the substrate Vickers microhardness profiles were obtained. Results revealed that the coating layer comprised multi-phases including Al2O3 Nano particles and different Al, Ni and Cu intermetallic compounds. A fusion layer from the bonding interface into Al1100 substrate was observed which was due to the released heat from the combustion synthesis reactions and caused the diffusion of Nickel into the substrate as well as a strong bonding so that no micro void or micro crack was observed at the interface even at high magnifications. The mean thickness and hardness of the obtained coating layer were 400 mu m and 80 VHN, respectively. (C) 2011 Elsevier B.V. All rights reserved.

Valence state of europium doping ions during pulsed-laser deposition

Pillonnet, A.; Pereira, A.; Marty, O.; Champeaux, C.

JOURNAL OF PHYSICS D-APPLIED PHYSICS, 44, 37, 375402-

The evolution of europium as a doping ion during the pulsed-laser deposition process of Eu : Al(2)O(3) films has been studied. A decrease in oxygen pressure in the deposition chamber generated the growth of gamma-Al(2)O(3) crystallites and a conversion of the 3+ to a 2+ valence state of europium ions. Excitation-selective emission of Eu(2+) and fluorescence line narrowing of Eu(3+) revealed that two kinds of europium site families were created in the alumina matrix. Time-of-flight emission spectroscopy shows that oxygen came preferentially from the target for the studied range of pressure.

Synthesis, Structure, Negative Thermal Expansion, and Photocatalytic Property of Mo Doped ZrV2O7

Sahoo, Pranga Parimita; Sumithra, S.; Madras, Giridhar; Row, T. N. Guru

INORGANIC CHEMISTRY, 50, 18, 8774-8781

A new series of compounds identified in the phase diagram of ZrO2-V2O8-MoO3 have been synthesized via the solution combustion method. Single crystals of one of the compounds in the series, ZrV1.50Mo0.50O7.25, were grown by the melt-cool technique from the starting materials with double the MoO3 quantity. The room temperature average crystal structure of the grown crystals was solved using the single crystal X-ray diffraction technique. The crystals belong to the cubic crystal system, space group Pa (3) over bar (No. 205) with a = 8.8969 (4) angstrom, V = 704.24 (6) angstrom(3), and Z = 4. The final R-1 value of 0.0213 was achieved for 288 independent reflections during the structure refinement. The Zr4+ occupies the special position (4a) whereas V5+ and Mo6+ occupy two unique (8c) Wyckoff positions. Two fully occupied O atoms, (24d) and (4b), one partially occupied 0 atom (8c) have been identified for this molybdovanadate, which is a unique feature for these crystals. The structure is related to both ZrV2O7 and cubic ZrMo2O8. The temperature dependent single crystal studies show negative thermal expansion above 370 K. The compounds have been characterized by powder X-ray diffraction, solid-state UV-vis diffuse reflectance spectra, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photocatalytic activity of these compounds has been investigated for the degradation of various dyes, and these compounds show specificity toward the degradation of non-azoic dyes.

Factors controlling pure-phase magnetic BiFeO3 powders synthesized by solution combustion synthesis

Yang, Jun; Li, Xiaoci; Zhou, Junyi; Tang, Yu; Zhang, Yuanming; Li, Yongwang

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 37, 9271-9277

Bismuth ferric oxide nanopowders were prepared through combustion method. Pure phase and well-crystallized BiFeO3 can be obtained by controlling the combustion process, fuel type and fuel-to-oxidant ratio. The evolutions of phase constitution and structural characteristics of the as-resulted nanopowders were investigated by X-ray diffraction, scanning electron microscope, and simultaneous thermogravimetric analysis. The results revealed that both the type and amount of fuel have to be carefully considered because they play an important role in total reaction characteristics. Among all tested fuels, L-alpha-alanine and glycine are the suitable fuels for BiFeO3 synthesis. For alpha-alanine, the optimal fuel-to-oxidant ratio is 0.22, which results in a suitable flame temperature for BiFeO3 formation. Still, too little fuel would result in only amorphous phase powders due to the low flame temperature and too much fuel would lead to transformation of the BiFeO3 phase to impurities because of the high flame temperature involved. The resulting BiFeO3 nanopowders exhibited strong H2O2-activiting ability and weak magnetism. When BiFeO3 nanopowders were used as a heterogeneous Fenton-like catalyst to degrade rhodamine B (RhB), the apparent rate constant for RhB degradation in the presence of H2O2 at pH 5.0 was evaluated to be 0.048 min(-1). (C) 2011 Elsevier B.V. All rights reserved.

Combustion synthesis and development of Ti-O-C aluminium composites

Naplocha, Krzysztof

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 36, 8853-8861

Aluminium matrix composite reinforced with Ti compounds was successfully fabricated by SHS combustion synthesis and squeeze casting course. Prepared samples from mixture containing Ti, C and Al(2)O(3) fibres were heated in microwave reactor to ignite synthesis and produce porous preform for subsequent infiltrating with liquid metal. Studies showed that synthesizing temperature has been remarkably increased by applying higher magnetron power and addition of graphite. Synthesis of specimens prepared from preliminary ball milled Ti and C powders proceeded at the highest propagation wave velocity. Microwave heating of metal Ti powder in the stream of CO(2) resulted in formation of corrugated precipitates composed of titanium oxide with carbon inclusions TiO(C) and Ti(2)O(3). The produced preforms were impregnated by squeeze casting with the aluminium alloy AlSi7Mg. Proper interface with slight reduction of Ti oxide between the reinforcement and the matrix was developed. Subsequently, the samples were annealed at 500 and 1000 degrees C. Annealing at the lower temperature induced creation of Ti(3)O(2)(C) and Al(2)O(3). This process was continued at 1000 degrees C, and additionally some Ti(Al(0,8)Si(0,2))(3) pellets appeared in the matrix. With prolonged annealing, oxygen was completely removed from Ti compound and oval grains of Ti(C) were created, enveloped with Al(2)O(3). In the matrix, larger and numerous Ti(3)AlSi(5) pellets were formed. Hardness examination showed that the best strengthening effect was achieved after annealing at 1000 degrees C. (C) 2011 Elsevier B. V. All rights reserved.

Fabrication of Ti3AlC2/Al2O3 Nanocomposite by a Novel Method

Zhu, J.; Ye, L.; Wang, F.

SCIENCE OF SINTERING, 43, 3, 289-294

A Ti(3)A(1)C(2)/Al2O3 nanocomposite was synthesized using Ti, Al, C and TiO2 as raw materials by a novel combination of high-energy milling and hot pressing. The reaction path of the 3Ti-8C-16Al-9TiO(2) mixture of powders was investigated, and the results show that the transitional phases TiC, Ti(x)A(y) and Al2O3 are formed in high-energy milling first, and then TixAly is transformed to the TiAl phase during the hot pressing. Finally, a reaction between TiC and TiAl occurs to produce Ti3AlC2 and the nanosized Ti3AlC2/Al2O3 composite is synthesized. The Ti3AlC2/Al2O3 composite possessed a good combination of mechanical properties with a hardness of 6.0 GPa, a flexural strength of 600 MPa, and a fracture toughness (K-IC) of 5.8 MPa.m(1/2). The strengthening and toughening mechanisms were also discussed.

Novel microwave assisted synthesis of highly doped phase pure Nd:YAG nanopowder

Kiranmala, L.; Rekha, M.; Neelam, M.

MATERIALS SCIENCE-POLAND, 29, 3, 184-188

For the first time, the studies on 2 to 10 at.% neodymium (Nd3+) ion doped Yttrium Aluminum Garnet (Nd:YAG) nanopowders obtained by microwave assisted citrate nitrate gel combustion synthesis is described in this work. This paper reports on high doping of Nd3+ ions with retaining the cubic garnet structure of YAG as evidenced from XRD, except the case of 8 at.% doped Nd:YAG. Phase pure YAG formation with 8 at.% Nd3+ doping was explored by using urea and alanine as alternative to citric acid complexing agents. Complete crystallization of YAG as a result of 2 hour thermal treatment at 900 A degrees C under oxygen supply was studied by using Fourier Transform Infra-Red Spectroscopy (FTIR) and X-Ray Diffraction (XRD) techniques. With an increase in the dopant concentration a red shift in the FTIR peaks was observed. Using the XRD data, the cell parameter of Nd3+ (2 to 6 and 10 at.%) YAG was found to increase with an increase in the dopant concentration. The average primary particle size calculated using Scherrer's equation was similar to 25 nm which was additionally supported by Transmission Electron Microscopy (TEM) results yielding particle sizes in the range of similar to 25 to 30 nm for all the cases.

Structures and Hydrogen Storage Properties of Magnesium-Based Composites Prepared by HCS plus MM

Liu Zhibing; Zhu Yunfeng; Li Liquan

RARE METAL MATERIALS AND ENGINEERING, 40, 9, 1653-1657

Mg(95)Ni(5-x)%TiFe(0.8)Mn(0.2)Zr(0.05) (x = 0, 10, 20, 30) (mass fraction) composites were prepared by hydriding combustion synthesis (HCS) and the products were mechanically milled (MM) to obtain Mg-based hydrogen-storage composites. By means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS) and pressure-composition-temperature (PCT) measurements, the phase structure, microstructure, particle composition and hydriding/dehydriding properties of the composites were studied. Results show that the Mg(95)Ni(5)-30%TiFe(0.8)Mn(0.2)Zr(0.05) composite has the best comprehensive hydriding/dehydridingn properties. It requires only 50 s to absorb its saturated hydrogen capacity of 4.11 wt% at 373 K and desorbs 1.91 wt% and 4.3 wt% hydrogen within 1800 s at 493 K and 523 K, respectively. Moreover, the dehydriding onset temperature of the composite is 420 K, which is 20 K lower than that of Mg(95)Ni(5). The improvement of hydriding/dehydriding properties are related greatly to the structures of the composites, and the addition of TiFe(0.8)Mn(0.2)Zr(0.05) can improve the dehydriding kinetics of the composites.

Self-purification effect in the synthesis of titanium carbonitride in a combustion regime

Tarasov, Aleksei G.; Seplyarskii, Boris S.; Barinov, Yurii N.; Semenova, Viktorina N.

MENDELEEV COMMUNICATIONS, 21, 5, 289-290

A self-purification effect was found in the combustion synthesis of carbonitrides from a powder mixture of titanium and carbon black under forced nitrogen filtration.

COMBUSTIBLE PRECURSOR BEHAVIOUR IN THE LANTHANUM CHROMITE FORMATION PROCESS

Zupan, Klementina; Marinsek, Marjan; Novosel, Barbara

MATERIALI IN TEHNOLOGIJE, 45, 5, 439-445

Combustion-derived lanthanum chromite (LC) powders were prepared with combustion synthesis from citrate-nitrate precursor gels. The transformation process of reactive citrate-nitrate gel to the cubic perovskite modification of (LC) was investigated. The influence of the fuel/oxidant molar ratio in the precursor gel on the combustion propagation and thermal characteristics of the combustion system was studied with simultaneous thermal analysis (TG, DTG and DTA), evolved gas analysis (MS) and gas chromatography (GC). The main (MS) responses detected were attributed to H(2), H(2)O and CO(2) generation. It was found that the citrate-nitrate reaction proceeds through several separate consecutive steps and the precursor thermal decomposition characteristics depended strongly on the citrate/nitrate ratio prior to the combustion. The first two steps of the thermal decomposition at approximately 150 degrees C and 250 degrees C are strongly related to the citrate-nitrate reaction, while at around 400 degrees C the combustion of citric acid residuals occurs. The last step of the thermal decomposition is caused by transformation of LaCrO(4) to LaCrO(3). Intermediate precursors and final powder ashes were also analyzed with X-ray diffraction.

Facile Microwave-Combustion Synthesis of Wurtzite CdS Nanoparticles

Amutha, R.; Muruganandham, M.; Lee, G. J.; Wu, J. J.

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 11, 9, 7940-7944

In this study we first report microwave-combustion synthesis of faceted CdS nanoparticles by using cadmium thiocyanate complex as a single source precursor. This is the first example of a metal-thiocyanate (M-SCN) complex being used as a source for metal sulfides (M-S) preparation in a microwave-combustion process. The synthesized CdS was characterized using X-ray diffraction (XRD), field mission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM). The by-product assisted combustion synthesis yields CdS nanoparticles with the mixtures of octahedral geometries, hexagonal, and triangle plate morphologies and the sizes were found to be 100 nm to 5 mu m. The XRD patterns imply the formation of well crystallized wurtzite CdS. The influence of cadmium and sulfur precursors and microwave irradiation time on the morphology of CdS nanoparticle was also investigated. The cadmium and sulfur precursors strongly influenced the CdS morphology and increasing the microwave irradiation time and intensity has no effect on the CdS morphology. In addition, a plausible mechanism of CdS nanoparticle formation has been proposed in this research.

Response of Foam- and Concrete-Filled Square Steel Tubes under Low-Velocity Impact Loading

Remennikov, Alex M.; Kong, Sih Ying; Uy, Brian

JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES, 25, 5, 373-381

This paper presents the results of experimental and numerical studies of the comparative behavior of square hollow section (SHS) tubes filled with rigid polyurethane foam (RPF) and concrete undergoing transverse impact loading. A series of instrumented drop hammer tests were performed on mild steel and stainless steel SHSs for both filled and unfilled constructions. The concrete-filled tubes had the highest impact resistance and energy absorption capacity, followed by the steel tubes filled with RPF, and then the hollow tubes. The results also show that RPFs can be used as an effective infill material in structural steel hollow columns when expedient enhancement of the energy absorption capacity is required, e. g., to increase blast and impact resistance of hollow structural elements. Nonlinear dynamic finite-element analyses were carried out to simulate drop hammer test conditions. The predicted impact forces, deformation histories, and failure modes were found to be in good agreement with the experimental results. DOI: 10.1061/(ASCE)CF.1943-5509.0000175. (C) 2011 American Society of Civil Engineers.

Combustion synthesis of Fe3Al/TiC composite powders

Mehrizi, M. Zarezadeh; Saidi, A.; Shamanian, M.

POWDER METALLURGY, 54, 4, 518-521

A mixture of (FeTi2+C) + 10 at-% Al based on stoichiometry of Fe3Al+TiC was used for a combustion front quenching test. The microstructural evolution during combustion synthesis was analysed by scanning electron microscopy and energy dispersive spectrometry. The phase constituents of the product were evaluated by X-ray diffraction. At first, Al powders were melted at 933 K and surrounded FeTi2 particles and carbon powders. When the temperature increased to 1358 K, FeTi2 melted, and Al and C dissolved in Fe and Ti. Then, solid-liquid and liquid-liquid reactions took place, and TiC and Fe3Al formed. At least at 1723 K, the iron aluminide phase surrounded large TiC particles. Because of formation of TiC0.95, a small amount of carbon remained in matrix and reacted with Fe3Al and formed Fe3AlC. Based on these results, the mechanism of the Fe3Al-TiC combustion synthesis could be described with a ternary solution precipitation mechanism.

Combustion synthesis of SiC nanosized powders at low nitrogen pressure

Yang, K.; Li, J. T.; Qi, L.; Zhang, H.; Zhang, D.; Yan, H.

POWDER METALLURGY, 54, 4, 529-532

Combustion synthesis of beta-silicon carbide (SiC) powders was accomplished at a nitrogen pressure lower than 2 MPa. The combination of mechanical activation and chemical stimulation was effective in enhancing the reactivity of Si powder reactants, which was responsible for the reduction in the minimum nitrogen pressure normally required for the combustion synthesis of SiC. Nanosized beta-SiC powders with spherical particles were synthesised at nitrogen pressure as low as 1 MPa. The combustion synthesised SiC powders have a narrow particle size distribution in the range of 50-100 nm and could be hot pressed to 99.1% theoretical density with 10 wt-% Y(2)O(3) and AlN as additives.

Formation of alloys in Ti-V system in hydride cycle and synthesis of their hydrides in self-propagating high-temperature synthesis regime

Aleksanyan, A. G.; Dolukhanyan, S. K.; Shekhtman, V. Sh; Huot, J.; Ter-Galstyan, O. P.; Mnatsakanyan, N. L.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, , S786-S789

In the present work, the possibility of formation of titanium and vanadium based alloys of BCC structure using hydride cycle was investigated. The mechanism of formation of alloys in Ti-V system from the powders of hydrides TiH2 and VH0.9 (or of V) by compaction followed by dehydrogenation was studied. Then, the interaction of the synthesized alloys with hydrogen in combustion regime (self-propagating high-temperature synthesis, SHS) resulting in hydrides of these alloys was investigated. DTA and DSC analyses of some alloys and their hydrides were performed and their thermal characteristics were measured. (C) 2010 Elsevier B.V. All rights reserved.

Chemical surface modification for the improvement of the hydrogenation kinetics and poisoning resistance of TiFe

Williams, M.; Lototsky, M. V.; Davids, M. W.; Linkov, V.; Yartys, V. A.; Solberg, J. K.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, , S770-S774

Hydrogen storage performance of the TiFe-based materials suffers from difficulties with hydrogenation and sensitivity towards impurities in hydrogen gas reducing hydrogen uptake rates and decreasing the cycle stability. In present work the surface modification of the sintered Ti1.1Fe0.9Ox and arc-melted TiFe was performed using autocatalytic deposition of the Pd-based catalytic layers in order to achieve improvement of the H storage characteristics. Pd deposition proved to be efficient in significant facilitation of the hydrogenation ability of the materials at moderate H-2 pressures and room temperature, even after their long exposure to air. Activation performance of the sintered Ti1.1Fe0.9Ox is superior than that for the arc-melted TiFe. This effect was associated with the presence of the oxygen-containing suboxide Ti4Fe2O1-x in the sintered sample acting as a hydrogen transfer catalyst. gamma-Aminopropyltriethoxysilane pre-functionalization and subsequent Pd-P autocatalytic deposition onto the sintered Ti1.1Fe0.9Ox intermetallic substrate resulted in a better hydrogenation kinetics compared to the samples prepared by the conventional Pd deposition. (C) 2010 Elsevier B.V. All rights reserved.

Fabrication of Transparent Y2Hf2O7 Ceramic from Combustion Synthesized Powders

Zou Xiao-Qing; Zhou Guo-Hong; Yi Hai-Lan; Yang Yan; Wang Shi-Wei

JOURNAL OF INORGANIC MATERIALS, 26, 9, 929-932

Y(NO3)(3), HfCl4 and EDTA as raw materials, Y2Hf2O7 nanopowder were successfully prepared by combustion synthesis method. The as-burnt powder were calcined at 1200 degrees C and then ball-milled for 15h. The powders were formed into green bodies with a size of phi 20mm x 2.5mm by cold isostatic pressing (CIP, 200MPa). Y2Hf2O7 transparent ceramics were obtained by sintering the green bodies at 1850 degrees C in vacuum for 6h. The resultant ceramics showed a transmittance of 50% in the visible spectral region. The sintering behavior of the prepared Y2Hf2O7 powders was investigated. When the sintering temperature was above 1850 degrees C, sintering temperature had little effect on the transmittance of the ceramic. Meanwhile the grain size became larger with sintering temperature increasing.

In situ fabrication of alpha-Al2O3 and Ni2Al3 reinforced aluminum matrix composites in an Al-Ni2O3 system

Zhu, Heguo; Ai, Yinglu; Li, Jianliang; Min, Jing; Chu, Da; Zhao, Jun; Chen, Jie

ADVANCED POWDER TECHNOLOGY, 22, 5, 629-633

alpha-Al2O3 ceramic particles and Ni2Al3 intermetallic compound reinforced aluminum matrix composites were successfully fabricated via exothermic dispersion (XD) reaction in an Al-Ni2O3 system. Thermodynamic analysis indicated that the reaction between Al and Ni2O3 could occur spontaneously due to its negative Gibbs free energy. The reaction characteristic was discussed by using X-ray diffraction (XRD) method and differential scanning calorimetry (DSC) analysis. The results showed that the reactions of the Al-Ni2O3 system consisted of two steps as following: (1) the Al firstly reacted with Ni2O3 to form the stable alpha-Al2O3 particles and active Ni atoms; (2) the active Ni atoms further reacted with Al to form Ni2Al3. The values of activation energy of the two step reactions were around 457.3 and 282.4 kJ/mol, respectively. The scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) revealed that the Ni2Al3 blocks were uniformly distributed throughout the matrix, while the alpha-Al2O3 particles were slightly segregated in the matrix. The strength of the composite is controlled by the strength of Ni2Al3 phase, and the tensile strength and the elongation rate of the composite with 30 vol.% reinforcement volume fraction are 210 MPa and 8%, respectively. (C) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

Solution combustion synthesis of Cu nanoparticles: a role of oxidant-to-fuel ratio

Jadhav, L. D.; Patil, S. P.; Chavan, A. U.; Jamale, A. P.; Puri, V. R.

MICRO & NANO LETTERS, 6, 9, 812-815

Solution combustion synthesis technique is one of the novel techniques used to prepare nanoparticles, nanocomposite and ceramic oxides. The authors prove in this study the usefulness of the technique in producing copper nanoparticles. In solution combustion, the stoichiometric ratio, according to propellant chemistry, needs the oxidiser-to-fuel ratio to be unity. The combustion of cupric nitrate and citric acid at stoichiometric ratio results in copper nanoparticles. The copper nanoparticles were characterised by different techniques, such as X-ray diffraction, thermal gravimetry/differential thermal analyser, Fourier transform infrared, FT-Raman and scanning electron microscopy. The Cu nanoparticles get oxidised to Cu(2)O slowly at 250 degrees C and to CuO at 530 degrees C. The combustion of the reactants with lean and rich oxidant-to-fuel ratio (O/F) ratios results in mixed phases except in the 1:0.71 ratio. The phases in lean O/F ratios were Cu, CuO, Cu(2)O, whereas only CuO was present in rich O/F ratios.

Combustion synthesis of ZnO and Ag-doped ZnO and their bactericidal and photocatalytic activities

Karunakaran, C.; Rajeswari, V.; Gomathisankar, P.

SUPERLATTICES AND MICROSTRUCTURES, 50, 3, 234-241

The combustion synthesized ZnO and 0.9 at.% Ag-doped ZnO have been characterized by powder X-ray diffraction and energy dispersive X-ray, UV-visible diffuse reflectance, photoluminescence and impedance spectroscopies. Doping sharpens the band gap absorption, displays surface plasmon resonance, suppresses the blue emission, enhances the near band gap emission and increases the charge transfer resistance and capacitance. Ag-doping by combustion method improves significantly the bactericidal activity but not the photocatalytic activity. (C) 2011 Elsevier Ltd. All rights reserved.

Highly Transmitting ZrO2-Doped Lu2O3 Ceramics from Combustion Synthesized Powders

Zou, Xiaoqing; Yi, Hailan; Zhou, Guohong; Chen, Shi; Yang, Yan; Wang, Shiwei

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 9, 2772-2774

Before shaping, Lu2O3 powders doped with different ZrO2 concentrations were synthesized by a simple combustion method and milled. The shaped green bodies were sintered at 1850 degrees C for 6 h in vacuum. The transmittance and microstructure of the resultant ceramics were characterized by spectrophotometer and SEM. The effects of ZrO2 concentration on the microstructure and optical property of transparent Lu2O3 ceramics were evaluated. When doped with 5 at.% ZrO2, the Lu2O3 ceramic showed the best optical transmission and the in-line transmittance reached 70% in the visible spectral region. The addition of ZrO2 was found effectively to prohibit grain growth and to remove residual pores.

Synthesis of High Purity Yb3+-Doped Lu2O3 Powder for High Power Solid-State Lasers

Kim, Woohong; Baker, Colin; Villalobos, Guillermo; Frantz, Jesse; Shaw, Brandon; Lutz, Austin; Sadowski, Bryan; Kung, Frederic; Hunt, Machael; Sanghera, Jasbinder; Aggarwal, Ishwar

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 9, 3001-3005

We have synthesized high-purity Yb3+-doped Lu2O3 powder by the coprecipitation method. We have demonstrated that the recrystallization of the metal nitrates greatly improve the chemical purity of the resulting oxides. From thermogravimetry and differential thermal analysis study, we have calculated the approximate formula of the oxinitrate precipitate precursor as Lu1.8Yb0.2(OH)(5.44)(NO3)(0.56).0.58H(2)O. Fine and soft agglomerate powders were obtained after calcinations. We have shown that the powder is mainly in the form of polycrystalline soft agglomerates composed with 15-20 nm size crystals. The resulting ceramic showed higher transparency (close to theoretical limit) compared with the ones fabricated with commercial powders.

Upconversion Luminescence in Er/Yb codoped Gd3Al5O12 Phosphors

Choi, Haeyoung; Kim, Jung Hwan; Park, Jin Young; Moon, Byung Kee; Jeong, Jung Hyun

JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 59, 3, 2329-2333

Gadolinium aluminum garnet (GAG) phosphors codoped with different concentrations of Yb3+ and 3.0 mol% Er3+ were synthesized by using a solvothermal reaction method. The XRD patterns confirmed that the GAG:Er3+/Yb3+ phosphors had a garnet structure with a single cubic phase. Strong green and red upconversion (UC) emissions of GAG:Er3+/Yb3+ powders were observed under excitation by a 975-nm laser diode. When 10-mol% Yb3+ and 3-mol% Er3+ doped GAG was used, the red UC emission was dramatically increased by a factor of 100. From the measurement of the lifetimes of the S-4(3/2) level and the pump power dependence of upconverion photoluminescence (UCPL), the energy back transfer (EBT) between Er3+ and Yb3+, the S-4(3/2) -> I-4(13/2)(Er3+):F-2(7/2) -> F-2(5/2)(Yb3+) process is believed to play a key role in the intense red UC emission.

Selective synthesis of boron nitride nanotubes by self-propagation high-temperature synthesis and annealing process

Wang, Jilin; Zhang, Laiping; Zhao, Guowei; Gu, Yunle; Zhang, Zhanhui; Zhang, Fang; Wang, Weimin

JOURNAL OF SOLID STATE CHEMISTRY, 184, 9, 2478-2484

Four types of BN nanotubes are selectively synthesized by annealing porous precursor in flowing NH(3) and NH(3)/H(2) atmosphere at temperature ranging from 1000 to 1200 degrees C in a vertical furnace. The as-synthesized BN nanotubes, including cylinder, wave-like, bamboo-like and bubble-chain, are characterized by XRD, FTIR, Raman, SEM, TEM and HRTEM. Three phenomenological growth models are proposed to interpret growth scenario and structure features of the four types of BN nanotubes. Selectivity of nanotubes formation is estimated as approximately 80-95%. The precursor containing B, Mg, Fe and O prepared by self-propagation high-temperature synthesis (SHS) method plays a key role in selective synthesis of the as-synthesized BN nanotubes. Chemical reactions are also discussed. (C) 2011 Elsevier Inc. All rights reserved.

Structural and magnetic properties of Cu1-xMnxO nanocrystal prepared by combustion synthesis

Xu, Mei; Yang, Lihong; Li, Youxia; Guo, Zhengang; Zhang, Yaping; Qiu, Hongmei; Pan, Liqing

PHYSICA B-CONDENSED MATTER, 406, 17, 3180-3186

Nanoscale Cu1-xMnxO powder is prepared by using the combustion synthesis technique with two different fuels. The structural properties of the powder are determined using Rietveld refinement of X-ray diffraction data, high-resolution transmission electron microscopy, and Fourier transform infrared spectroscopy, while its magnetic properties are analyzed by means of hysteresis loop and temperature dependence of magnetization. The results show that (1) the Cu1-xMnxO nanocrystal is of monoclinic CuO structure, with grain size of 10-30 nm varying with the type of fuel, the nitrate/fuel ratio (N/F), and the Mn concentration, the doping of Mn has a little influence on the lattice parameters; (2) when the Mn concentration is higher than 7%, a small amount of impurity phase of CuMn2O4 appears and annihilates the potential cation vacancies; (3) all of the samples with x >= 5% exhibit low-temperature ferromagnetism with the Curie temperature of similar to 90 K, which increases slightly by raising the Mn concentration; (4) the paramagnetic moment per Mn ion is around 2-4 bohr magneton above the Curie temperature, which decreases with increasing Mn concentration, implying that the nearest Mn ions are antiferromagnetically coupled and the ferromagnetic order could originate from the super-exchange of next nearest Mn ions along the [10 (1) over bar] direction. (C) 2011 Elsevier B.V. All rights reserved.

Synthesis of La1-xSrxMnO3 powders by polymerizable complex method: Evaluation of structural, morphological and electrical properties

da Conceicao, Leandro; Ribeiro, Nielson F. P.; Souza, Mariana M. V. M.

CERAMICS INTERNATIONAL, 37, 7, 2229-2236

Lanthanum strontium manganite (La1-xSrxMnO3, LSM) powders were synthesized by polymerizable complex method, based on complexation of metal ions (MI) with citric acid (CA) and polyesterification between CA and ethylene glycol (EG). Firstly, the effect of the molar ratio of CA:MI (=1-3) was investigated on the synthesis of La0.7Sr0.3MnO3 powders, which were characterized by thermal analysis (TGA/DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicated that the molar ratio CA:MI = 3 is adequate for a good crystallization of pure perovskite phase after calcination, with nanometric crystallite sizes and porous microstructure. For the La0.7Sr0.3MnO3 sample synthesized with CA:MI ratio of 3, it was investigated the effect of calcination temperature, showing that the perovskite structure is better crystallized at 900 degrees C, without secondary phase formation. Using this same CA:MI ratio and calcination temperature, powders with different Sr content (x = 0.2-0.4) were synthesized, with surface areas of 4-10 m(2) g(-1). These powders were sintered at 1100 degrees C to produce porous pellets. The porosity of the sintered pellets and the electrical conductivity, measured by two-probe technique, increased with increasing Sr content. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Synthesis and sintering behavior of La0.8Sr0.2CrO3 by a glycine nitrate process

Thomas, Elizabeth; Lee, Da Hae; Yoon, Mi Young; Ehrman, Sheryl. H.; Hwang, Hae Jin

CERAMICS INTERNATIONAL, 37, 7, 2269-2274

La0.8Sr0.2CrO3 powder was synthesized by a glycine nitrate process from an aqueous solution of lanthanum, strontium, and chromium nitrates, and glycine. The apparent density, size and morphology of the La0.8Sr0.2CrO3 powder depended on the glycine-to-nitrate ratio. However, the pH value of the precursor solution had no significant effect on these properties. It was found that a single-phase perovskite, La0.8Sr0.2CrO3, was synthesized when the dried ash was calcined at 1200 degrees C for 5 h. A secondary minor phase, SrCrO4, was observed in the powder calcined at temperatures lower than 1100 degrees C. The presence of the SrCrO4 phase has a significant effect on the sinterability and microstructural evolution of the La0.8Sr0.2CrO3. A relative density higher than 90% could be achieved when the 1000 degrees C-calcined La0.8Sr0.2CrO3 powder was sintered at 1450 degrees C. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Fabrication and characterization of a Ni-YSZ anode support using high-frequency induction heated sintering (HFIHS)

Yoo, Jong-Yeol; Shon, In-Jin; Choi, Byung-Hyun; Lee, Ki-Tae

CERAMICS INTERNATIONAL, 37, 7, 2569-2574

Ni-YSZ cermet anode supports solid oxide fuel cells (SOFCs) were fabricated by high-frequency induction heated sintering (HFIHS) under 60 MPa pressure with powders synthesized by the glycine nitrate process (GNP) as well as mechanically mixed commercial powders. The HFIHS method created a uniformly porous microstructure without abnormal grain growth compared to the conventional sintering method. Samples sintered by HFIHS show higher strength and electrical conductivity than conventionally sintered samples, even though they have similar porosity. (C) 2011 Elsevier Ltd and Techna Group Sr.l. All rights reserved.

Preparation of tungsten borides by combustion synthesis involving borothermic reduction of WO3

Yeh, C. L.; Wang, H. J.

CERAMICS INTERNATIONAL, 37, 7, 2597-2601

An experimental study on the preparation of two tungsten borides, WB and W2B5, was conducted by self-propagating high-temperature synthesis (SHS), during which borothermic reduction of WO3 and elemental interaction of W with boron proceeded concurrently. Powder mixtures with two series of molar proportions of WO3:B:W = 1:5.5:x (with x = 1.16-2.5) and 1:7.5:y (with y = 0.5-1.33) were adopted to fabricate WB and W2B5, respectively. The starting stoichiometry of the reactant compact substantially affected the combustion behavior and the phase composition of the final product. The increase of metallic tungsten and boron reduced the overall reaction exothermicity, leading to a decrease in both combustion temperature and reaction front velocity. The initial composition of the reactant compact was optimized for the synthesis of WB and W2B5. In addition to small amounts of W2B and W2B5, the powder compact of WO3 + 5.5B + 2 W produced WB dominantly. Optimum formation of W2B5 was observed in the sample of WO3 + 7.5B + 0.85W. Experimental evidence indicates that an excess amount of boron about 10-13% is favorable for the formation of WB and W2B5. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Characterization of the structure of TiB2/TiC nanocomposite powders fabricated by high-energy ball milling

Wang, Huihua; Wu, Wenyuan; Sun, Shucheng; Bian, Xue; Tu, Ganfeng

CERAMICS INTERNATIONAL, 37, 7, 2689-2693

TiB2/TiC nanocomposite powders were successfully prepared by high-energy ball milling of the powder mixtures of Ti and B4C. X-ray diffraction analysis showed that the TiC phase was not produced until the milling time was up to 24 h and only a minimal amount of TiB2 was generated, even after 48 h of milling. The critical grain size of Ti milled for the reaction between Ti and B4C was 31.2 nm. Transmission electron microscopy clearly indicated that the resulting powder mixture obtained after milling for 48 h and annealing at 800 degrees C for 30 min was composed of nanosized TIC and TiB2 particles. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Sb2Te3 and Bi2Te3 based thermopower wave sources

Walia, Sumeet; Weber, Rodney; Sriram, Sharath; Bhaskaran, Madhu; Latham, Kay; Zhuiykov, Serge; Kalantar-zadeh, Kourosh

ENERGY & ENVIRONMENTAL SCIENCE, 4, 9, 3558-3564

Exothermic chemical reactions from nitrocellulose are coupled onto Sb2Te3 (antimony telluride) and Bi2Te3 (bismuth telluride) layers to generate self-propagating oscillating thermopower waves. P-type Sb2Te3 and N-type Bi2Te3 are employed due to their large Seebeck coefficients, high electrical conductivities and their complementary semiconducting properties. Sources based on both materials exhibit high power to mass ratios: up to 0.6 kW kg(-1) for Sb2Te3 and 1.0 kW kg(-1) for Bi2Te3. Having both P- and N-type semiconductors in the system, the combination of the outputs can be used for generating sources with polarities alternating in time.

Phase Transformation Behavior of Porous TiNi Alloys Produced by Powder Metallurgy Using Magnesium as a Space Holder

Aydogmus, Tarik; Bor, Elif Tarhan; Bor, Sakir

METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 42A, 9, 2547-2555

Porous TiNi alloys with porosities in the range of 51 to 73 pct were prepared successfully applying a new powder metallurgy fabrication route in which magnesium was used as a space holder, resulting in either single austenite phase or a mixture of austenite and martensite phases dictated by the composition of the starting powders, but entirely free from secondary brittle intermetallics, oxides, nitrides, and carbonitrides. Since transformation temperatures are very sensitive to composition, deformation, and oxidation, for the first time, transformation temperatures of porous TiNi alloys were investigated using chemically homogeneous specimens in as-sintered and aged conditions eliminating secondary phase, contamination, and deformation effects. It was found that the porosity content of the foams has no influence on the phase transformation temperatures both in as-sintered and aged conditions, while deformation, oxidation, and aging treatment are severely influential.

Effect of KCl, NaCl and CaCl2 mixture on volume combustion synthesis of TiB2 nanoparticles

Nekahi, Atiye; Firoozi, Sadegh

MATERIALS RESEARCH BULLETIN, 46, 9, 1377-1383

Preparation of titanium diboride (TiB2) nanoparticles was carried out by volume combustion synthesis. TiO2. B2O3 and elemental Mg were mixed with 0-60% salt mixture of KCl, NaCl and CaCl2 with increment of 15% as a low melting temperature diluent. Compressed samples were synthesized in a tubular furnace at a constant heating rate under argon atmosphere. Thermal analysis of the process showed that the addition of the low melting temperature salts mixture led to a significant decrease in ignition and combustion temperatures. Synthesized samples were then leached by nitric and hydrochloric acids to remove impurities. The samples were examined by XRD, SEM and DLS analysis. The results showed the formation of fine deagglomerated particles with the addition of the salts mixture. The results revealed that 45% salts mixture had the smallest average particle size of about 90 nm. (C) 2011 Elsevier Ltd. All rights reserved.

Effect of C/Ti ratio on self-propagating high-temperature synthesis reaction of Sn-Ti-C system for fabricating Ti2SnC ternary compounds

Li, Yuxin; Bai, Peikang; Liu, Bin

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 35, L328-L330

Ti2SnC ternary compound was successfully synthesized utilizing laser ignited self-propagating high-temperature synthesis (SHS) of Sn-Ti-C system with the different C/Ti molar ratio. When C/Ti ratio is 0.7, Ti6Sn5 as the main phase appears, and a small amount of TiC is also found, most of the Ti6Sn5 phases synthesized exhibit the polygon-shaped coarse appearance with an obviously sintered morphology, and the distinct transgranular and intergranular microcracks can be observed. When C/Ti ratio increases over the range from 0.8 to 1.0, the relative content of Ti2SnC increase and the plate-like shape Ti2SnC appears. Furthermore, the sintered density increases firstly and then decreases with the increasing of C/Ti ratio. (C) 2011 Elsevier B.V. All rights reserved.

High work-hardening effect of the pure NiAl intermetallic compound fabricated by the combustion synthesis and hot pressing technique

Zhao, H. L.; Qiu, F.; Jin, S. B.; Jiang, Q. C.

MATERIALS LETTERS, 65, 17-18, 2604-2606

The pure NiAl intermetallic compound was fabricated by the combustion synthesis and hot pressing technique. Microstructure examination showed that the NiAl intermetallic compound contained fine grains. Analysis of the X-ray diffraction and the HRTEM studies showed that the phase in the intermetallics was the only NiAl phase. The NiAl showed prominent compression properties. The true ultimate compression strength and the fracture strain of the NiAl are 1002(-94)(+72) MPa and 21.6(-1.8)(+1.8)%, respectively. The work-hardening capacity (H(c)) is 1.40(-0.07)(+0.09) and the Vickers micro-hardness is 360(-19)(+15) HV. The finer grains, the high density dislocation and the seriously distorted lattices in the matrix, and the intense interactions between dislocations contribute to the prominent compression properties. (C) 2011 Elsevier B.V. All rights reserved.

NO Reduction Over Noble Metal Ionic Catalysts

Bera, Parthasarathi; Hegde, M. S.

CATALYSIS SURVEYS FROM ASIA, 15, 3, 181-199

In last 40 years, catalysis for NO (x) removal from exhaust gas has received much attention to achieve pollution free environment. CeO(2) has been found to play a major role in the area of exhaust catalysis due to its unique redox properties. In last several years, we have been exploring an entirely new approach of dispersing noble metal ions in CeO(2) and TiO(2) for redox catalysis. We have extensively studied Ce(1-x) M (x) O(2-delta) (M = Pd, Pt, Rh), Ce(1-x-y) A (x) M (y) O(2-delta) (A = Ti, Zr, Sn, Fe; M = Pd, Pt) and Ti(1-x) M (x) O(2-delta) (M = Pd, Pt, Rh, Ru) catalysts for exhaust catalysis especially NO reduction and CO oxidation, structure-property relation and mechanism of catalytic reactions. In these catalysts, lower valent noble metal ion substitution in CeO(2) and TiO(2) creates noble metal ionic sites and oxide ion vacancy. NO gets molecularly adsorbed on noble metal ion site and dissociatively adsorbed on oxide ion vacancy site. Dissociative chemisorption of NO on oxide ion vacancy leads to preferential conversion of NO to N(2) instead of N(2)O over these catalysts. It has been demonstrated that these new generation noble metal ionic catalysts (NMIC) are much more catalytically active than conventional nano crystalline noble metal catalysts especially for NO reduction.

Influence of the fuel structure on the flame synthesis of carbon nanomaterials

Hall, Brendan; Zhuo, Chuanwei; Levendis, Yiannis A.; Richter, Henning

CARBON, 49, 11, 3412-3423

Carbon nanomaterials (CNMs) were grown on nickel-coated stainless-steel mesh grids using a combustion synthesis method. Three fuel feedstocks of dissimilar chemical structures, ethylene, ethyl benzene and ethyl alcohol, were burned at fuel-rich equivalence ratios to generate disparate combustion products. The chemical compositions of these products were assessed to identify and contrast the species that contribute to the growth of CNMs. The generated CNMs were characterized using SEM and TEM. Each set of conditions produced a distinct distribution (bi-modal or mono-modal) of CNMs, including carbon nanotubes and carbon nanofibers, both of varying diameters and lengths. The effects of combustion-generated light aliphatic hydrocarbons and light aromatic hydrocarbons on CNM growth and structure were ascertained. It was found that ethylene and ethyl alcohol generated tubular CNMs under all tested conditions, whereas ethyl benzene generated only small amounts of CNMs and under much more limited conditions. It was also determined that concentrations of aliphatic species, notably methane and acetylene, at mole fractions as low as 500 ppm have a thickening effect on the resulting CNMs. Linear correlations were found between the concentrations of these species and the mean diameter of the CNMs. (C) 2011 Elsevier Ltd. All rights reserved.

Oxidation resistance of SHS Fe-Al-Si alloys at 800 degrees C in air

Novak, Pavel; Zelinkova, Michala; Serak, Jan; Michalcova, Alena; Novak, Michal; Vojtech, Dalibor

INTERMETALLICS, 19, 9, 1306-1312

Alloys formed by Fe-Al intermediary phases have lower density than common metallic high-temperature alloys and good high-temperature oxidation resistance. Previously it was proved that silicon additions to these alloys enable to produce them efficiently by reactive sintering and improves the wear resistance. In this work, the oxidation resistance of the novel Fe-Al-Si alloys containing 10-30 wt. % of aluminium and 5-30 wt. % of silicon produced by the reactive sintering technology was tested. Cyclic and isothermal oxidation tests were carried out at 800 degrees C in air. Tested alloys exhibit excellent oxidation resistance, which increases with silicon content up to 20 wt. %. The reasons are discussed in terms of the phase composition of the oxide layer and the changes in chemical composition under the oxide layer during oxidation. (C) 2011 Elsevier Ltd. All rights reserved.

Reaction path of the synthesis of alpha-Al2O3-TiC-TiB2 in an Al-TiO2-B4C system

Zou, Binglin; Shen, Ping; Cao, Xueqiang; Jiang, Qichuan

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 5, 591-595

Differential thermal analysis was undertaken to determine the reaction path of the synthesis of alpha-Al2O3-TiC-TiB2 in an Al-TiO2-B4C system under argon. The Al content plays a significant role in controlling the reaction path and product. When the Al content is no more than 26.7 wt.%,TiO2 first reacts with B4C to yield TiB2 with TiBO3 being the intermediate phase, and then increasing temperature leads to the subsequent reactions between Al and TiO2 or its sub-oxides to yield alpha-Al2O3 and Al3Ti, and the resultant Al3Ti then reacts with B4C to produce TiC and TiB2. When the Al content is high (e.g. >= 34 wt.%), the reaction between Al and TiO2 for the formation of alpha-Al2O3 and Al3Ti occurs initially, and then the Al3Ti reacts with B4C. With the increasing Al content, the onset of the exothermic reaction in the Al-TiO2-B4C system shifts to lower temperature and the degree of reaction conversion is enhanced. (C) 2011 Elsevier Ltd. All rights reserved.

Study of formation behavior of ZrC in the Fe-Zr-C system during combustion synthesis

Zhang, M. X.; Hu, Q. D.; Huang, B.; Li, J. Z.; Li, J. G.

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 5, 596-600

ZrC particles were prepared in situ by self-propagating high-temperature synthesis (SHS) reaction with the Fe-Zr-C elemental powder mixtures. The reaction behavior and formation route for synthesizing ZrC in the Fe-Zr-C system were investigated. With increasing Fe contents, the adiabatic temperatures, reaction temperatures and ZrC particles sizes were obviously decreased. Fe plays an important role in controlling the reaction behavior and morphology of products, Fe not only inhibits ZrC particle from growing, but also promotes the SHS reaction. The addition of Fe to Zr-C reactants promotes the ZrC-forming reaction. (C) 2011 Elsevier Ltd. All rights reserved.

Mechanochemical and volume combustion synthesis of ZrB2

Akgun, Baris; Camurlu, H. Erdem; Topkaya, Yavuz; Sevinc, Naci

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 5, 601-607

Formation of ZrB2 by volume combustion synthesis (VCS) and mechanochemical process (MCP) from ZrO2-Mg-B2O3 was studied. Production of ZrB2 by VCS in air occurred with the formation of side products, Zr2ON2 and Mg3B2O6 in addition to MgO and ZrB2. Zr2ON2 formation was prevented by conducting VCS experiments under argon. Wet ball milling was applied to the VCS products before leaching for easier removal of Mg3B2O6 phase. MgO and Mg3B2O6 were removed from wet ball-milled products by leaching in 5 M HCI for 2.5 h. In MCP, 30-hour ball milling was found to be sufficient for the formation of ZrB2 with no minor phase formation. Leaching of MCP products in 1 M HCI for 30 min was sufficient to remove MgO. Complete conversion of ZrO2 to ZrB2 did not take place in both production methods, even with excess amounts of Mg and B2O3. Therefore, formed ZrB2 contained residual ZrO2. (C) 2011 Elsevier Ltd. All rights reserved.

Combustion synthesis of aluminum carbonitride

Mu, Yunchao; Yu, Dongli; Wang, Mingzhi

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 5, 639-640

Aluminum carbonitride (Al(5)C(3)N and Al(6)C(3)N(2)) materials were prepared by combustion reaction. The result showed that the main phases of the product were Al(5)C(3)N, Al(6)C(3)N(2), and AlN. The lathed Al(5)C(3)N grains and the lamellar Al(6)C(3)N(2) grains had a same length of approximately 10 mu m. Additionally, some hexagonal AlN grains developed well. The combustion temperature reached 2256 K. (C) 2011 Elsevier Ltd. All rights reserved.

Eu3+ activated M6AlP5O20 (M=Sr/Ba/Mg) novel red phosphors

Shinde, K. N.; Dhoble, S. J.; Kumar, Animesh

JOURNAL OF LUMINESCENCE, 131, 9, 1939-1944

Eu3+ activated M6AlP5O20 (where M=Sr/Ba/Mg) phosphors prepared by combustion synthesis and the completion of the synthesis was confirm by XRD (X-ray diffraction) patterns. The surface morphology studied by scanning electron microscopy (SEM) and photoluminescence (PL) properties has been reported in this paper. The Eu3+ PL emission spectrum was observed in M6AlP5O20 phosphors (where M=Sr/Ba/Mg) at 592 (orange) and 618 nm (red) region, the spectrum due to D-5(0)-> F-7(1) and D-5(0)-> F-7(2) transitions at mercury free excitation, respectively. Its considerable emission intensity under 350 nm excitations makes it possible candidate materials as red component of tricolor luminescence materials and for near ultra violet light emitting diode (n-UVLED) phosphors. (C) 2011 Elsevier B.V. All rights reserved.

Microstructure and mechanical properties of in situ TiC and Nd2O3 particles reinforced Ti-4.5 wt.%Si alloy composites

Zhang, Xinjiang; Li, Yibin; Song, Guangping; Sun, Yue; Peng, Qingyu; Li, Yuxin; He, Xiaodong

MATERIALS & DESIGN, 32, 41525, 4327-4332

(TiC + Nd2O3)/Ti-4.5 wt.%Si composites were in situ synthesized by a non-consumable arc-melting technology. The phases in the composites were identified by X-ray diffraction. Microstructures of the composites were observed by optical microscope and scanning electron microscope. The composite contains four phases: TiC, Nd2O3, Ti5Si3 and Ti. The TiC and Nd2O3 particles with dendritic and near-equiaxed shapes are well distributed in Ti-4.5 wt.%Si alloy matrix, and the fine Nd2O3 particles exist in the network Ti + Ti5Si3 eutectic cells and Ti matrix of the composites. The hardness and compressive strength of the composites are markedly higher than that of Ti-4.5 wt.%Si alloy. When the TiC content is fixed as 10 wt.% in the composites, the hardness is enhanced as the Nd2O3 content increases from 8 wt.% to 13 wt.%, but the compressive strength peaks at the Nd2O3 content of 8 wt.%. (C) 2011 Elsevier Ltd. All rights reserved.

Thermoluminescence and photoluminescence of ZrO2 nanoparticles

Salah, Numan; Habib, Sami S.; Khan, Zishan H.; Djouider, Fathi

RADIATION PHYSICS AND CHEMISTRY, 80, 9, 923-928

This work describes the thermoluminescence (TL) and photoluminescence (PL) of zirconium oxide (ZrO2) nanoparticles synthesized using the propellant chemical combustion method. They were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The XRD result shows a nanocrystalline material with a major tetragonal phase along with a small portion of monoclinic phase, while SEM images display particles of spherical shapes of diameters in the 25-35 nm range. Samples from this powder were exposed to different doses of gamma-rays from a Cs-137 source in the range of 0.01 Gy-1 kGy. The induced TL glow curve has a single broad peak at around 600 K. TL response curve of this peak shows sublinearity for all the recorded doses, while its fading over two months is negligible. The intensity and structure of the TL glow curve did not change after several cycles of exposures and readout. PL excitation and emission spectra were also recorded and are investigated. When the material was excited by different wavelengths, several emission bands are observed in the range of 300-500 nm. The new nanocrystalline material shows excellent characterization such as good TL sensitivity, low fading and reusability making it a promising TL dosimeter. (C) 2011 Elsevier Ltd. All rights reserved.

Combustion synthesis of doped nanocrystalline ZnO powders for varistors applications

Hembram, K.; Sivaprahasam, D.; Rao, T. N.

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 31, 10, 1905-1913

Doped nanocrystalline ZnO powders in the size range between 15 and 250 nm were synthesized by chemical combustion method. The powders were characterized for their physical, structural and chemical properties by BET, X-ray diffraction, FESEM, TEM and XPS. These powders were consolidated into dense varistors discs by compaction, sintering and evaluated for their I-V characteristics. Post-calcinations of these powders were found to have great influence on the green density and sinterability. The formations of phases after sintering were confirmed by XRD analysis and EDX. The varistor properties have been studied for different calcination temperatures and compositions. Breakdown voltage as high as 9.5 kV/cm and coefficient of nonlinearity 134 were obtained. Leakage current density was found to be similar to 1.29 mu A/cm(2) for a specific composition and condition. These studies demonstrate the feasibility of one step synthesis of doped ZnO nanopowder and their consolidation into ZnO fine grain varistor exhibiting improved performance. (C) 2011 Elsevier Ltd. All rights reserved.

Self-propagating high-temperature synthesis of nano-TiCx particles with different shapes by using carbon nano-tube as C source

Jin, Shenbao; Shen, Ping; Zhou, Dongshuai; Jiang, Qichuan

NANOSCALE RESEARCH LETTERS, 6, , 515-

With using the carbon nano-tube (CNT) of high chemical activity, nano-TiCx particles with different growth shapes were synthesized through the self-propagating high temperature in the 80 wt.% metal (Cu, Al, and Fe)-Ti-CNT systems. The growth shapes of the TiCx particles are mainly octahedron in the Cu- and Al-Ti-CNT systems, while mainly cube-and sphere-like in the Fe-Ti-CNT system.

Combustion synthesis of tungsten powder from sodium tungstate

Jiang Guojian; Xu Jiayue; Zhuang Hanrui; Li Wenlan

MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 176, 14, 1037-1040

Tungsten powders were prepared by Self-propagating High-temperature Synthesis (SHS) method directly from hitherto unreported system: sodium tungstate (Na(2)WO(4)) and magnesium (Mg). The adiabatic temperatures of self-propagating combustion reactions with different amount of Mg in Na(2)WO(4) + Mg system were calculated. The influences of different starting conditions (molar ratios of Mg/Na(2)WO(4) and relative densities of samples) on the compositions and microstructure of reaction products were investigated. It shown that, the complete reduction of WO(3) required a 60% excess of magnesium over the stoichiometric molar ratio Mg/Na(2)WO(4) of 3. The amount of the impurities is minimal at appropriate relative density. At last, tungsten powders can be obtained after the acid enrichment and distilled water washing. (C) 2011 Elsevier B.V. All rights reserved.

Effect of a superhydrophobic coating on the combustion of aluminium and iron oxide nanothermites

Nixon, Eric; Pantoya, Michelle L.; Sivakumar, Ganapathy; Vijayasai, Ashwin; Dallas, Tim

SURFACE & COATINGS TECHNOLOGY, 205, 21-22, 5103-5108

There is an interest in broadening the range of applications of nanoenergetic composite materials to include their combustion and energy generation in submerged environments. Currently, their use is primarily limited to gas environments. Oceanic power generation, underwater ordnance, propulsion, metal cutting, and torch technologies are examples of applications that would significantly benefit from nanocomposite energetic materials. Recent research on superhydrophobic coatings has made it possible to coat nanoenergetic samples using a vapor-phase deposition process which significantly reduces the detrimental effects of water entering the composite that can occur during wet-chemistry based superhydrophobic processes. In this work, we discuss the process utilized to produce the superhydrophobic coating on nanoenergetic materials. We then analyze the bubble energy produced and compare this value to other energetic formulations. It was found that the ratio of the bubble energy to the total energy of combustion was an order of magnitude higher for the superhydrophobic coated materials compared to energetic composites containing a hydrophobic binder. (C) 2011 Elsevier B.V. All rights reserved.

Combustion synthesized materials as catalysts for liquid-phase oxidation

Jaeger, Benjamin; Stolle, Achim; Scholz, Peter; Mueller, Matthias; Ondruschka, Bernd

APPLIED CATALYSIS A-GENERAL, 403, 41306, 152-160

With combustion synthesis it is possible to achieve catalytic active binary oxides of chromium, iron, cobalt, nickel and copper within a few seconds. The catalytic activity of combustion synthesized oxides was compared with commercially available spinel oxides and materials obtained by thermal nitrate decomposition in the selective liquid-phase oxidation of benzyl alcohol to benzaldehyde with a stoichiometric amount of tert-butyl hydroperoxide as the oxidant. The combustion synthesized materials revealed both higher reactivity and higher stability compared to those oxides available from high temperature ceramic processes or thermal nitrate decomposition. Crystallite sizes, microstrains, and phase compositions have been analyzed by X-ray powder diffractometry as important parameters for the catalytic activity. By applying combustion synthesis, it is possible to obtain several different low density oxides with smaller crystallites and higher values for microstrains compared to other methods of preparation. Thus, providing an explanation for the improved catalytic performance of those materials. (C) 2011 Elsevier B.V. All rights reserved.

Effect of surface oxidation on thermal shock resistance of the ZrB2-SiC-ZrC ceramic

Wu, Zhanjun; Wang, Zhi; Shi, Guodong; Sheng, Jin

COMPOSITES SCIENCE AND TECHNOLOGY, 71, 12, 1501-1506

The isothermal oxidation of the ZrB2-SiC-ZrC ceramic was carried out in static air at a constant temperature of 1000 +/- 15 degrees C, 1200 +/- 15 degrees C and 1400 +/- 15 degrees C for 30 min, respectively. Compared with the original strength of 580 MPa, the strength for the specimen oxidized at 1000 degrees C, 1200 degrees C and 1400 degrees C for 30 min increased to 609 MPa, 656 MPa and 660 MPa, respectively, because the flaws in the surface of the specimen were sealed by the oxide layer. The thermal shock resistance of the specimens before and after the oxidation was measured by the water quenching. The measured Delta T-crit for the specimen oxidized at 1000 degrees C, 1200 degrees C and 1400 degrees C were 352 degrees C, 453 degrees C and 623 degrees C, respectively, which was obviously higher than 270 degrees C for the unoxidized specimen. The improvement in the thermal shock resistance was attributed to the formation the oxide layer on the surface of the specimen. The results here pointed to a promising method for improving strength and thermal shock resistance of ZrB2-based ceramics. (C) 2011 Elsevier Ltd. All rights reserved.

Self-propagating high-temperature synthesis of La(Sr)Ga(Mg, Fe)O3-delta with planetary ball-mill treatment for solid oxide fuel cell electrolytes

Nobuta, Akira; Hsieh, Feng-Fan; Shin, Tae Ho; Hosokai, Sou; Yamamoto, Satoshi; Okinaka, Noriyuki; Ishihara, Tatsumi; Akiyama, Tomohiro

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 33, 8387-8391

This study investigated the combined effects of self-propagating high-temperature synthesis (SHS), planetary ball-mill (PBM) treatment, and sintering temperature on La0.7Sr0.3Ga0.7Mg0.1Fe0.2O3-delta (LSGMF73712) as an electrolyte material for solid oxide fuel cells (SOFC). The SHS products (SHS-LSGMF73712) were compared with that prepared via solid-state reaction (SSR) in terms of sinterability and power generation performance. The SHS products were treated with PBM for 10, 30, 50, and 70 h. The SHS products contained the by-product LaSrGaO4; however, in the SHS products treated with PBM for longer than 50 h, the by-product disappeared after sintering at 1350 degrees C for 3 h in air. Among the samples, SHS products treated with PBM for 70 h displayed superior sintering (1350 degrees C), whereas the SSR product (SSR-LSGMF73712) was successfully sintered at 1450 degrees C for 3 h in air. Under the cell configuration of Ni-Fe/SHS-LSGMF73712-PBM70h (0.3 mm thick)/Sm0.5Sr0.5CoO3, the maximum power density was 0.673 W/cm(2) at 800 degrees C using humidified hydrogen gas (3 mol% H2O) as a fuel and air as an oxidizing agent at a flow rate of 100 mL/min, which was almost equivalent to that using SSR-LSGMF73712 (0.629 W/cm(2) at 800 degrees C) under the same conditions. (C) 2011 Elsevier B. V. All rights reserved.

Fourier-transform, integrated-optic spatial heterodyne spectrometer on a silica-based planar waveguide with 1 GHz resolution

Fontaine, Nicolas K.; Okamoto, Katsunari; Su, Tiehui; Yoo, S. J. B.

OPTICS LETTERS, 36, 16, 3124-3126

Spatial heterodyne spectrometers (SHS) can achieve high resolution with excellent optical throughput. We demonstrate a planar waveguide SHS incorporating 64 asymmetric Mach-Zehnder interferometers and show measurements that verify 1 GHz resolution across a 64 GHz measurement range. (C) 2011 Optical Society of America

Microwave synthesis of novel high voltage (4.6V) high capacity LiCuxCo1-xO2 +/-delta cathode material for lithium rechargeable cells

Nithya, C.; Thirunakaran, R.; Sivashanmugam, A.; Gopukumar, S.

JOURNAL OF POWER SOURCES, 196, 16, 6788-6793

Layered LiCuxCo1-xO2 +/-delta (0.0 <= x <= 0.3) has been synthesized using microwave method. This method possesses many advantages such as homogeneity of final product and shorter reaction time compared to other conventional methods. The structure and electrochemical properties of the synthesized materials are characterized through various methods such as XRD, SEM, FTIR, XPS and galvanostatic charge/discharge studies. The XRD patterns of LiCuxCo1-xO2 +/-delta confirm the formation of single-phase layered material. SEM images show that the particles are agglomerated and the average particle size decreases with increasing amount of copper. Electrochemical cycling studies are carried out between 2.7 and 4.6V using 1 M LiPF6 in 1:1 EC/DEC as electrolyte. The charge/discharge cycling studies of layered material with LiCu0.2Co0.8O19 exhibit an average discharge capacity of similar to 150 mAh g(-1) over the investigated 50 cycles. (C) 2010 Published by Elsevier B.V.

Synthesis and magnetic properties of ordered barium ferrite nanowire arrays in AAO template

Li, Yuqing; Huang, Ying; Yan, Li; Qi, Shuhua; Miao, Lu; Wang, Yan; Wang, Qiufen

APPLIED SURFACE SCIENCE, 257, 21, 8974-8980

BaFe(12)O(19) nanowire arrays having single magnetic domain size(<= 460 nm) in anodic aluminum oxide (AAO) templates were prepared by sol-gel and self-propagating high-temperature synthesis techniques. The diameter of the nanowire arrays is approximately 70 nm and the length is about 2-4 mu m. The specimens were characterized using X-ray diffraction, vibrating sample magnetometer, field emission scan electron microscope, atomic force microscopy and microwave vector network analyzer. The magnetic properties of BaFe(12)O(19) nanowire arrays embedded in AAO templates were measured by VSM with a field up to 1274 KA/m at room temperature. The results indicate that the nanowire arrays exhibit large saturation magnetization and high coercivity in the range of 6000 Oe and an obvious magnetic anisotropy with the easy magnetizing axis along the length of the nanowire arrays, probably due to the shape anisotropy and magneto-crystalline anisotropy. Finally the microwave absorption properties of the nanowires were discussed. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Effect of inorganic ions, H2O2 and pH on the photocatalytic inactivation of Escherichia coli with silver impregnated combustion synthesized TiO2 catalyst

Sontakke, Sharad; Modak, Jayant; Madras, Giridhar

APPLIED CATALYSIS B-ENVIRONMENTAL, 106, 41367, 453-459

The photocatalytic antibacterial activity of Ag impregnated combustion synthesized TiO2 (0.25 g/L) was studied against Escherichia coil in presence of UV irradiation. The effect of various parameters, such as anions, canons, hydrogen peroxide and pH, on the photocatalytic inactivation was investigated. The addition of inorganic ions showed a negative effect on inactivation. Among anions, the presence of chloride ions was observed to have a maximum negative effect and reduced the inactivation considerably. Among cations, the bacterial inactivation reduced significantly in the presence of Ca2+ ions. Hydrogen peroxide addition in combination with Ag/TiO2 photocatalysis, however, improved the inactivation. Photocatalysis with high concentration of H2O2 yielded complete bacterial inactivation within few minutes. The photocatalytic inactivation of E. coil was not affected by variation in pH. (C) 2011 Elsevier B.V. All rights reserved.

Reactive synthesis of Ti-Al intermetallics during microwave heating in an E-field maximum

Vaucher, S.; Stir, M.; Ishizaki, K.; Catala-Civera, J. -M.; Nicula, R.

THERMOCHIMICA ACTA, 522, 41306, 151-154

The time-resolved X-ray diffraction synchrotron radiation technique was used in combination with E-field microwave heating to study in situ the kinetics of intermetallic phase formation in the Ti-Al system. The reaction of Ti with Al is triggered by the melting and spreading of Al onto the surface of Ti particles. The tetragonal TiAl3 phase is the primary reaction product, formed by instantaneous nucleation at the interface between the unreacted Ti cores and the Al melt. The growth of TiAl3 layers is diffusion-controlled. These preliminary results demonstrate that microwave heating can be used to rapidly synthesise intermetallic phases from high-purity elemental powders. (C) 2010 Elsevier B.V. All rights reserved.

Pt-implanted intermetallides as the catalysts for CH4-CO2 reforming

Arkatova, Larisa A.; Pakhnutov, Oleg V.; Shmakov, Alexandr N.; Naiborodenko, Yury S.; Kasatsky, Nikolai G.

CATALYSIS TODAY, 171, 1, 156-167

A new type of catalytic system on the base of Ni3Al intermetallic compound was proposed for CO2 reforming of methane. Several catalysts were prepared by self-propagating high temperature synthesis and characterized by XRD (in situ and ex situ), DTA-TG, SEM + EDS, HRTEM + EDS and XPS. Ion implantation was used as a method of catalyst surface modification. Activity testing has been performed in the fixed bed reactor at the temperatures of 600-900 degrees C under atmospheric pressure and the reactant molar ratio of 1. The structure and morphology of different types of carbon deposits obtained on the surface of unmodified Ni3Al were investigated. The results indicated that the addition of a low amount (less than 0.1 wt%) of Pt to the Ni3Al intermetallide leads to a decrease in carbon deposition and Pt-implanted catalysts were stable for a long period of time. The evidence suggests that the differences in the stabilities may be due to the following reasons: (1) Pt prevents Ni phase sintering by avoiding particle coalescence, which is the main sintering process under severe CH4-CO2 reforming conditions, (2) Pt hinders deactivating carbon formation by limiting bulk nickel carbide and therefore carbon filament formation, which may lead to reactor plugging and/or particle fragmentation, and by suppressing encapsulating carbon formation which limits access of reactant to the active nickel phase. (C) 2011 Elsevier B. V. All rights reserved.

Heavy-Particle Radioactivity of Superheavy Nuclei

Poenaru, D. N.; Gherghescu, R. A.; Greiner, W.

PHYSICAL REVIEW LETTERS, 107, 6, 62503-

The concept of heavy-particle radioactivity (HPR) is changed to allow emitted particles with Z(e) > 28 from parents with Z>110 and daughter around (208)Pb. Calculations for superheavy (SH) nuclei with Z = 104-124 are showing a trend toward shorter half-lives and larger branching ratio relative to alpha decay for heavier SHs. It is possible to find regions in which HPR is stronger than alpha decay. The new mass table AME11 and the theoretical KTUY05 and FRDM95 masses are used to determine the released energy. For 124 we found isotopes with half-lives in the range of ns to ps.

Size- and Shape-Sensitive Reactivity Behavior of Al-n(n=2-5, 13, 30, and 100) Clusters Toward the N-2 Molecule: A First-Principles Investigation

Kulkarni, Bhakti S.; Krishnamurty, Sailaja; Pal, Sourav

JOURNAL OF PHYSICAL CHEMISTRY C, 115, 30, 14615-14623

Reactivity of aluminum clusters has been found to exhibit size-sensitive variations. N-2 reduction is a hard process, and its dissociation on the Al surface is one of the few chemical methods available under nonhazardous conditions. In this context, we attempt to understand the adsorption behavior of N-2 molecules as a function of varying size and shape of Al clusters using a Density Functional Theory (DFT) based method. During the complex formation, various N-2 adsorption modes are examined. The results clearly demonstrate that, while the interaction energy does not vary with respect to the cluster size, shape of the cluster is highly contributive toward the chemisorption (a prerequisite for the reactivity) of the N-2 molecule. The underlying electronic and structural factors influencing the adsorption of N-2 molecules on the Al clusters are analyzed with the help of the Electron Localization Function (ELF) and Frontier Molecular Orbitals. As an illustration, the activation barrier calculations on various Al-13 conformations are calculated, and results confirm the experimental propositions that high-energy structures (depending upon their geometrical and electronic orientation) are more favorable for N-2 reduction.

Fabrication of ZrC particles and its formation mechanism by self-propagating high-temperature synthesis from Fe-Zr-C elemental powders

Zhang, M. X.; Hu, Q. D.; Huang, B.; Li, J. G.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 31, 8120-8125

ZrC particles were prepared via self-propagating high-temperature synthesis (SHS) reaction from 0 to 30 wt.% Fe-Zr-C elemental powder mixtures. The ZrC particles of the SHS products greatly decreased from about 10 mu m with an irregular shape in free Fe addition to nano-meter order with a nearly spherical shape in 30 wt.% Fe addition. The reaction mechanism of ZrC during the SHS processing was explored through the microstructural observation and phase constituents analysis on the combustion-wave quenched sample in combination with differential thermal analysis (DTA). For the low Fe contents, the solid-state reaction between C and Zr powders should be responsible for the formation of ZrC. While for the high Fe contents, the formation mechanism of ZrC could be ascribed to the dissolution of C into the Fe-Zr melt and the precipitation of ZrC. The addition of Fe to Zr-C reactants not only inhibits the growth of ZrC particles but also promotes the occurrence of ZrC-forming reaction. (C) 2011 Elsevier B.V. All rights reserved.

Combustion synthesis and structural characterization of Li-Ti mixed nanoferrites

Sangshetti, R. M.; Hiremath, V. A.; Jali, V. M.

BULLETIN OF MATERIALS SCIENCE, 34, 5, 1027-1031

Polycrystalline samples of the mixed nanoferrites, Li0.5+0.5xTixFe2.5-1.5xO4 (0.02 <= x <= 0.1), were prepared by combustion method at lower temperatures compared to the conventional high temperature sintering for the first time at low temperatures, using PEG which acts as a new fuel and oxidant. XRD patterns reveal a single-phase cubic spinel structure. The as synthesized Li-Ti ferrites are in nanocrystalline phase. The crystallite size was found to be in the range 16-27 nm. SEM images reveal rod-like morphology in all the samples with a discontinuous grain growth. The B-H loops have been traced using VSM technique, for all the compositions, at room temperature and the hysteresis parameters are calculated. Saturation magnetization decreases with increase in Ti content due to the fact that the Ti4+ ion, which is a non-magnetic ion, replaces a magnetic Fe3+ ion. The hysteresis loops show clear saturation at an applied field of +/- 10 kOe and the loops are highly symmetric in nature. The cation distribution is known indirectly by using saturation magnetization values.

Hard Cr-Al-Si-B-(N) Coatings with Oxidation Resistance up to 1200 degrees C

Kiryukhantsev-Korneev, Ph. V.; Pierson, J. F.; Bauer, J. Ph.; Levashov, E. A.; Shtansky, D. V.

GLASS PHYSICS AND CHEMISTRY, 37, 4, 411-417

The results of studies of the structure and properties of Cr-Al-Si-B and Cr-Al-Si-B-N coatings prepared by magnetron sputtering of multicomponent CrAlSiB targets of the in an argon atmosphere and gas mixtures of argon and nitrogen are presented. The microstructure and the phase and chemical compositions of the coatings have been determined using X-ray diffraction (XRD), transmission and scanning electron microscopy, infrared spectroscopy (IR), and glow discharge optical emission spectroscopy. The hardness, elastic modulus, and elastic recovery of the coatings, as well as their resistance to high-temperature oxidation, have been determined. It has been found that the Cr-Al-Si-B-(N) coatings have an amorphous structure in which the B-N and Si-N bonds are revealed at high concentrations of nitrogen. Depending on the composition, the coatings exhibit a hardness in the range 18-30 GPa, an elastic modulus of 250-400 GPa, an elastic recovery of 39-44%, and an oxidation resistance up to 1100-1200 degrees C. A comparative analysis of data on the Cr-Al-Si-B-(N) and Cr-B-(N) systems has been performed.

Mixed doped lithium nickel vanadate as cathode material by sol-gel and polymer precursor method

Ismail, L.; Ramesh, S.; Winie, T.; Arof, A. K.

MATERIALS RESEARCH INNOVATIONS, 15, , 86-91

The mixed doped LiNi(1-x)Mn(x)VO(4) (0 <= x <= 1) has been synthesised by using sol-gel and polymer precursor methods. X-ray diffraction, thermogravimetric analysis/differential thermogravimetric analysis and scanning electron microscopy analyses have been carried out to study the structural and physical properties of the samples which can be used as the cathode material for lithium ion batteries. Citric acid was added during the sample preparation as the chelating agent. The prepared samples have been characterised thermally by thermogravimetric analysis/differential thermogravimetric analysis. The analysis shows few endothermic peaks at 80, 301, 371 and 573 degrees C and this is due to the weight loss during the thermal process which corresponds to the inorganic and organic decompositions of the precursor. Scanning electron microscopy images show that the grain size of the composite samples increases with increasing temperature for the sample fired from 500 to 800 degrees C, revealing a spherical shape of grain distribution at low temperature and a polyhedral shape at the highest sintering temperature. The size of the particle synthesised using both methods is also discussed in this work.

Extinguishing Threshold of SHS Reaction in Nanolayered Foils under Heat Sink Conditions

Zaporozhets, T. V.; Gusak, A. M.; Ustinov, A. I.

METALLOFIZIKA I NOVEISHIE TEKHNOLOGII, 33, 8, 1075-1081

Threshold behaviour of SHS reaction in layer structures is described depending on conditions of heat sink as well as on foil thickness and multilayer period.

Autocombustion Synthesis of Nanocrystalline Gadolinium Iron Garnet

Raj, S. Gokul; Nallamuthu, S.; Joseyphus, R. Justin

NANOSCIENCE AND NANOTECHNOLOGY LETTERS, 3, 4, 463-467

Nanocrystalline gadolinium iron garnet (Gd3Fe5O12) was successfully synthesized using auto combustion process. Simultaneous Thermogravimetric-Differential thermal analysis was carried out for the asprepared samples. The asprepared amorphous phase undergoes crystallization at 800 degrees C upon calcination, which is well below the phase formation temperature required by other synthesis methods. The powder X-ray diffraction pattern indicated an average grain size below 50 nm for all the annealed samples. The Curie temperature of nanocrystalline gadolinium iron garnet is similar to the bulk samples.

Preparation of porous zirconium microspheres by magnesiothermic reduction and their microstructural characteristics

Park, Kyung-Tae; Nersisyan, Hayk H.; Chun, Byong-Sun; Lee, Jong-Hyeon

JOURNAL OF MATERIALS RESEARCH, 26, 16, 2117-2122

Porous zirconium metal microspheres were synthesized successfully by a combustion technique using ZrO(2) + 2Mg starting mixture. In this process, a controlled amount of KClO(3) + 3Mg is mixed with ZrO(2) + 2Mg to enable a self-sustaining combustion process and to promote a reduction of the ZrO(2). The framework structure, morphology, and porosity of zirconium microspheres were determined using various techniques. Microscopic visualization suggested that the spherical structure has macroporous windows of diameter similar to 0.5-5.0 mu m and the space between the macropores has a wormhole-like mesoporous/microporous structure. The mesoporous structure had a pore diameter of similar to 1.19 nm. This procedure provides an easy method for the synthesis of porous microspherical assemblies of Zr composed of submicrometer size particles.

Multilayered Ti-Al intermetallic sheets fabricated by cold rolling and annealing of titanium and aluminum foils

Sun Yan-bo; Zhao Ye-qing; Zhang Di; Liu Cui-yun; Diao Hao-yan; Ma Chao-li

TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 21, 8, 1722-1727

Multilayered Ti-Al based intermetallic sheets were fabricated by sintering alternately layered titanium and aluminum foils. The microstructure and phase formation of the obtained sheets under different sintering conditions were evaluated by various techniques. The results reveal that when the sintering temperature is above the melting point of aluminum, the self-propagating high-temperature synthesis reaction occurs between Ti and Al, and forms various phases of Ti-based solid solutions including alpha-Ti Ti3Al, TiAl, TiAl2 and alpha-Ti including TiAl3, etc. When the sintering time increased, Ti-based solid solution, TiAl2 and TiAl3 disappeared gradually, and the sheet containing Ti3Al and TiAl phases in a multilayered structure formed finally. A lot of voids were also observed in the sintered structures, which were caused by the melting Al, Kirkendall effect and the difference of molar volumes between reactants and products. The voids were eliminated and a dense sample was obtained by the following hot press.

Open-celled porous NiAl intermetallics prepared by replication of carbamide space-holders

Wu Jie; Cui Hong-zhi; Cao Li-li; Gu Zheng-zheng

TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 21, 8, 1750-1754

Open-celled porous NiAl intermetallics with adjustable pore characteristics and mechanical properties were successfully prepared by using spherical carbamide as space-holders via combustion synthesis. Examinations of macroscopic and microscopic morphologies as well as the quasi-static compressive test for the resultant materials were carried out. Depending on the volume fraction and particle size of the carbamide, the porosity and pore size of the porous NiAl intermetallics can be controlled freely in a range of 57.57%-84.58% and 0.4-2.0 mm, respectively. Furthermore, quasi-static compressive tests indicate that the mechanical behavior of the present porous materials is in good agreement with the Gibson-Ashby model.

Preparation and characterization of LaB6 ultra fine powder by combustion synthesis

Dou Zhi-he; Zhang Ting-an; Zhang Zhi-qi; Zhang Han-bo; He Ji-cheng

TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 21, 8, 1790-1794

High-purity, homogeneous and ultra fine LaB6 powders were prepared by combustion synthesis. The effects of reactant ratio and molding pressure on the phase and morphology of the combustion products were studied. The combustion products and leached products were analyzed by XRD, SEM and EDS. The results indicate that the combustion product consists of LaB6, MgO and a little Mg3B2O6. The combustion product becomes denser and harder when the molding pressure increases. The purity of LaB6 is higher than 99.0%. The LaB6 particle size is in range of 1.92-3.00 mu m and the lattice constant of LaB6 is a=0.414 8 nm.

Fabrication and ultraviolet-shielding properties of silica-coated titania-doped ceria nanoparticles

Chen Weifan; Hong Jianming; Li Huiquan; Li Yongxiu

JOURNAL OF RARE EARTHS, 29, 8, 810-814

A series of well-dispersed titania-doped ceria nanoparticles Ce(1-x)TixO(2) were rapidly prepared by a novel salt-assisted solution combustion process using correspondent metal nitrates as oxidizers and ethyl glycol as fuel, and then coated with amorphous silica by seeded polymerization using tetraethyl orthoslicate (TEOS). The as-prepared samples were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and ultraviolet-visible light (UV-Vis) diffuse reflectance spectroscopy. The results indicated that compared with the as-prepared pure ceria nanoparticles, the red-shift phenomenon occurred for Ti-doped ceria nanoparticles with Ti incorporation. Meanwhile, the absorption intensity in the UV light region slightly decreased and transmission rate in visible light region was somewhat enhanced. In comparison with the silica-coated CeO(2) nanopowders, the silica-coated Ce(0.95)Ti(0.05)O(2) nanopowders displayed the same absorption intensity in the UV light region, broader UV absorption band and higher transmission rate in visible light region.

A MODEL CONSIDERING HYDROSTATIC STRESS OF POROUS NITI SHAPE MEMORY ALLOY

Zhu, Yuping; Dui, Guansuo

ACTA MECHANICA SOLIDA SINICA, 24, 4, 289-298

Based on the micromechanical method and thermodynamic theory, a constitutive model for the macroscopic mechanical behavior of porous NiTi shape memory alloy is presented. The hydrostatic stress is considered for porous NiTi according to the transformation function of dense NiTi. The present model takes account of the tensile-compressive asymmetry of NiTi, and can degenerate to model dense material. Numerical calculations, which only need material parameters of dense NiTi, are conducted to investigate the nonlinear and hysteretic strain of porous NiTi, and the predicted results are in good agreement with the corresponding experiments.

Synthesis of Air Stable Iron Nanopowders with Various Methods

Jeon, Kwang-Won; Cho, Sang-Geun; Moon, Ki-Woong; Kim, JinBae; Kim, Jongryoul

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 11, 8, 7261-7264

Magnetic properties and microstructures of iron-based nanopowders fabricated by several methods, such as sol-gel, thermal decomposition, and self-propagating combustion methods, were investigated. During a subsequent reduction annealing, added aluminum atoms formed coherent oxide shells with a hercynite structure around iron cores in all the nanopowders. In particular, the nanopowders synthesized by the self-propagating combustion method showed the highest saturation magnetization of 175.68 emu/g and oxidation stability to 200 degrees C in air.

Luminescence properties of (Sr0.95-x-yMgxYy)Si2O2-yN2+y:Eu-0.05(2+) for novel LED conversion phosphors

Jee, Soon Duk; Choi, Kang Sik; Kim, Ji Sik

METALS AND MATERIALS INTERNATIONAL, 17, 4, 655-660

By incorporating Mg and Y into SrSi2O2N2:Eu2+ phosphor, we intended to improve the relatively high thermal quenching and poor efficiency of emission in conventionalSrSi(2)O(2)N(2):Eu2+ phosphors. MSi2O2N2:Eu2+ (0.05) (M = Sr, Mg, Y) compounds were synthesized by ahigh-temperature solid-state reactionand were characterized using X-ray power diffraction as well as excitation and emission spectroscopy. As compared to the pure SrSi2O2N2:Eu2+ (0.05), the emission intensity of the new MSi2O2N2:Eu2+ (0.05) (M = Sr, Mg, Y) compound was increased by 65 %. Meanwhile, it was also possible to improve the ratio of thermal quenching up to 88 % by substituting the Sr with Mg and/or Y in the SrSi2O2N2:Eu2+ (0.05) crystal structure. This improvement was mainly due to the intrinsic electronic negativity and size effect of Y3+, which leads to the shrinkage of the O/N ratioand the relaxation of local strain around the Eu2+ ion in the (Sr0.95-x-yMgxYy)Si2O2-yN2+y:Eu2+ (0.05) structure. Consequently, the (Sr0.68Mg0.27)Si2O2N2:Eu2+ (0.05) phosphor is expected to be useful as a novel conversion phosphor with high thermal stability for white-light LEDs.

Optimal design of self-propagating high temperature one-dimensional nano-SnO2 synthesis

Liu, Nian; Zhang, Guodong

ACTA METALLURGICA SINICA-ENGLISH LETTERS, 24, 4, 321-325

The success in synthesizing high purity SnO2 nanobelts via self-propagating high temperature synthesis was achieved. According to the experimental results, a relationship between the residual heat of the reaction system at 2848 K and SnO2 nanobelts yield was identified. The most appropriate formula for this self-propagating high temperature synthesis method is turned out to be composed of Sn powder and thermite with weight ratio of 1:1.

Microwave-assisted gel combustion synthesis of ZnO-Co nano-pigments

Rasouli, Sousan; Valefi, Mahdiar; Moeen, Shirin Jebeli; Arabi, Amir Masoud

JOURNAL OF CERAMIC PROCESSING RESEARCH, 12, 4, 450-455

ZnO-Co ceramic pigments have been prepared by microwave-assisted gel combustion of zinc-nitrate-nitrate cobalt-citric acid precursors calcined at 700 to 1000 degrees C. The Combustion process has been investigated using thermal analysis and Fourier transformation infrared spectroscopy. X-ray diffraction, diffuse reflectance and scanning-transition electron microscopy was used to characterize the pigments. Results were compared with a solid state reaction. It was demonstrated that powders synthesis by combustion caused 200 degrees C reduction in the calcination temperature compared with the solid state reaction. The results demonstrated that the microwave-assisted combustion reaction was very simple and rapid to prepare 27-37.2 nm nanocrystalline pigments. Colorimetric results also indicated a broad reflectance band around 540 nm (green region) for all samples. It was deduced that the fuel-rich sample has more chromaticity and has a deeper green color.

SHS extrusion of materials based on the Ti-Al-C MAX phase

Bazhin, P. M.; Stolin, A. M.

DOKLADY CHEMISTRY, 439, , 237-239

The hsp 16 Gene of the Probiotic Lactobacillus acidophilus Is Differently Regulated by Salt, High Temperature and Acidic Stresses, as Revealed by Reverse Transcription Quantitative PCR (qRT-PCR) Analysis

Capozzi, Vittorio; Arena, Mattia Pia; Crisetti, Elisabetta; Spano, Giuseppe; Fiocco, Daniela

INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 12, 8, 5390-5405

Small heat shock proteins (sHsps) are ubiquitous conserved chaperone-like proteins involved in cellular proteins protection under stressful conditions. In this study, a reverse transcription quantitative PCR (RT-qPCR) procedure was developed and used to quantify the transcript level of a small heat shock gene (shs) in the probiotic bacterium Lactobacillus acidophilus NCFM, under stress conditions such as heat (45 degrees C and 53 degrees C), bile (0.3% w/v), hyperosmosis (1 M and 2.5 M NaCl), and low pH value (pH 4). The shs gene of L. acidophilus NCFM was induced by salt, high temperature and acidic stress, while repression was observed upon bile stress. Analysis of the 5' noncoding region of the hsp16 gene reveals the presence of an inverted repeat (IR) sequence (TTAGCACTC-N9-GAGTGCTAA) homologue to the controlling IR of chaperone expression (CIRCE) elements found in the upstream regulatory region of Gram-positive heat shock operons, suggesting that the hsp16 gene of L. acidophilus might be transcriptionally controlled by HrcA. In addition, the alignment of several small heat shock proteins identified so far in lactic acid bacteria, reveals that the Hsp16 of L. acidophilus exhibits a strong evolutionary relationship with members of the Lactobacillus acidophilus group.

Synthesis and Characterization of Nanostructured Niobium and Molybdenum Nitrides by a Two-Step Transition Metal Halide Approach

Choi, Daiwon; Kumta, Prashant N.

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 8, 2371-2378

Nanosized NbN(x) (1.64 > x > 1.33) and MoN(x) (1.32 > x > 0.77) crystallites were synthesized at a relatively low temperature (>= 600 degrees C) through ammonolysis and nitridation of the corresponding metal chlorides. The ammonolysis reaction in anhydrous chloroform at room temperature and the nitridation mechanism during subsequent heat treatment was investigated using Fourier transform infrared spectroscopy, X-ray diffraction (XRD), thermogravimetric (TG), and mass spectroscopy analysis. The effects of the synthesis parameters on the stoichiometry, structure, specific surface area, density, and electronic conductivity of the final nitrides were studied using TGA, XRD, N(2) adsorption, high-resolution transmission microscopy, helium pycnometry, and four-point probe technique. Preliminary electrochemical responses of the obtained nitrides were studied using cyclic voltammetry to explore their possible use as electrochemical capacitors.

Phase formation and ionic conductivity studies on ytterbia co-doped scandia stabilized zirconia (0.9ZrO(2)-0.09Sc(2)O(3)-0.01Yb(2)O(3)) electrolyte for SOFCs

Lakshmi, V. Vijaya; Bauri, Ranjit

SOLID STATE SCIENCES, 13, 8, 1520-1525

The effect of ytterbia co-doping in scandia stabilized zirconia (ScSZ) on phase formation and electrical conductivity Was studied. The ternary (ZrO2)(0.90) (Sc2O3)(0.09) (Yb2O3)(0.01) composition was prepared by solution combustion synthesis. The powder was characterized by X-ray diffraction, scanning and transmission electron microscopy. The processed powder of the co-doped sample was found to be nanocrystalline and it exhibited a single cubic phase. The powder was compacted in to disc and sintered to produce a dense electrolyte pellet. X-ray diffraction analysis showed that the cubic phase remains after sintering in the co-doped sample whereas peaks corresponding to the rhombohedral beta phase appear in the sintered binary (without co-doping) scandia stabilized zirconia (ScSZ) sample. The electrical conductivity was measured as a function of temperature by impedance spectroscopy. The electrical conductivity of the ytterbia co-doped sample was found to be higher than the ScSZ sample without co-doping. Consequently the activation energy of the co-doped sample was lower compared to the ScSZ sample. (C) 2011 Elsevier Masson SAS. All rights reserved.

Fabrication and Photoluminescence Properties of Hexagonal Micro-pyramids ZnO Powders by Combustion Synthesis

Chen Ai; Zhang Ying; Meng Fancheng; Wang Hairong; Li Zesong; Shen Yingping

JOURNAL OF WUHAN UNIVERSITY OF TECHNOLOGY-MATERIALS SCIENCE EDITION, 26, 4, 700-702

The ZnO powder with hexagonal-pyramids structure was prepared by the low-temperature combustion process. Ammonium acetate was used as the fuels, whereas zinc nitrate acted as the oxidant. The effect of different ration between fuel and oxidant on the morphology and photoluminescence (PL) characteristic was studied. The formation of hexagonal-pyramids structure was discussed. The optimum preparing parameter for fine morphology is that the ratio of zinc nitrate and ammonium acetate is 1:5, and ignition temperature is 500 degrees C. The PL measurement indicates all samples have the strong blue and yellow emission peak. The changes of surface energy of the polar surfaces result in the formation of micro-pyramids structure.

A fast-pyrolysis self-propagating high temperature synthesis route to single phase of boron carbide ultrafine powders

Zhang, Laiping; Gu, Yunle; Wang, Weiming; Wang, Jilin; Zhao, Guowei; Qian, Qiongli; Zhang, Zhanhui; Zhang, Fang

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, 119, 1392, 631-634

Single phase of boron carbide B(13)C(2) ultrafine powders was synthesized by a fast-pyrolysis-self-propagating high temperature synthesis method. The X-ray diffractometry is demonstrated a pure phase of rhombohedral structure. The field-emission scanning electron microscopy and transmission electron microscopy show that the size of particles ranged from 50 to 200 nm, with approximately 90 nm in average. The energy dispersive X-ray spectroscopy reveals that the sample has a uniform composition with the B/C atomic ratios ranging from 6.38 to 6.49. The Raman spectrum indicates the characteristic vibrations of C-B-C chain and B(12) icosahedron. Fast-pyrolysis-self-propagating high temperature synthesis and vapor solid growth mechanism ware proposed. (C) 2011 The Ceramic Society of Japan. All rights reserved.

Solution Combustion Synthesis of Metal Nanopowders: Nickel-Reaction Pathways

Kumar, A.; Wolf, E. E.; Mukasyan, A. S.

AICHE JOURNAL, 57, 8, 2207-2214

Nanopowders of pure nickel were directly synthesized for the first time by conventional solution combustion synthesis (SCS) method. In this article, a specific reaction pathway is suggested to describe the metallic phase formation during SCS. It is proposed that the exothermic reaction between NH(3) and HNO(3) species formed during the decomposition of glycine and nickel nitrate acts as the source of energy required to achieve the self-sustained reaction regime. A thermodynamic analysis of the combustion synthesis reaction indicates that increasing glycine concentration leads to establishing a hydrogen rich reducing environment in the combustion wave that in turn results in the formation of pure metals and metal alloys. TGA of reaction systems and XRD analysis of products in the quenched combustion wave show that the formation of oxide phases occurs in the reaction front, followed by gradual reduction of oxide to pure metallic phases in the postcombustion zone. A methodology for SCS of pure metals and metal alloys nanoparticles can be inferred from the results presented. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 2207-2214, 2011

Combustion Synthesized Vanadia Rods for Environmental Applications

Deshpande, Parag A.; Madras, Giridhar

AICHE JOURNAL, 57, 8, 2215-2228

Rod-shaped V(2)O(5) was synthesized using the solution combustion technique, and the morphology of the compound was confirmed by TEM. Rods of an average diameter of 500 nm and length 3-6 times the diameter were obtained after the calcination of freshly prepared V(2)O(5) at 550 degrees C for 24 h. Pd metal nanoparticles of 20 nm size were deposited onto the rods using the wet impregnation technique. The as-synthesized, calcined and Pd impregnated V(2)O(5) were characterized by a wide variety of techniques including energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. These compounds were tested for CO oxidation, adsorption, and photocatalytic degradation of dyes. The 1% Pd/V(2)O(5) showed a high activity for CO oxidation, the as-synthesized compound showed activity for the adsorption of cationic dyes, whereas the calcined V(2)O(5) sample showed high rates of photocatalytic degradation of dyes. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 2215-2228, 2011

Raman Spectroscopy Using a Spatial Heterodyne Spectrometer: Proof of Concept

Gomer, Nathaniel R.; Gordon, Christopher M.; Lucey, Paul; Sharma, Shiv K.; Carter, J. Chance; Angel, S. Michael

APPLIED SPECTROSCOPY, 65, 8, 849-857

The use of a spatial heterodyne interferometer-based spectrometer (SHS) for Raman spectroscopy is described. The motivation for this work is to develop a small, rugged, high-resolution ultraviolet (UV) Raman spectrometer that is compatible with pulsed laser sources and that is suitable for planetary space missions. UV Raman is a particular technical challenge for space applications because dispersive (grating) approaches require large spectrographs and very narrow slits to achieve the spectral resolution required to maximize the potential of Raman spectroscopy. The heterodyne approach of the SHS has only a weak coupling of resolution and throughput, so a high-resolution UV SHS can both be small and employ a wide slit to maximize throughput. The SHS measures all optical path differences in its interferogram simultaneously with a detector array, so the technique is compatible with gated detection using pulsed lasers, important to reject ambient background and mitigate fluorescence (already low in the UV) that might be encountered on a planetary surface where samples are uncontrolled. The SHS has no moving parts, and as the spectrum is heterodyned around the laser wavelength, it is particularly suitable for Raman measurements. In this preliminary report we demonstrate the ability to measure visible wavelength Raman spectra of liquid and solid materials using an SHS Raman spectrometer and a visible laser. Spectral resolution and bandpass are also discussed. Separation of anti-Stokes and Stokes Raman bands is demonstrated using two different approaches. Finally spectral bandpass doubling is demonstrated by forming an interference pattern in both directions on the ICCD detector followed by analysis using a two-dimensional Fourier transform.

The use of thermal analysis in the study of Ca3Al2O6 formation by the polymeric precursor method

Lazau, I.; Pacurariu, C.; Babuta, R.

JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 105, 2, 427-434

Single-phase Ca3Al2O6 was prepared via polymeric precursor method. The influence of the reactants nature in the Ca3Al2O6 synthesis was investigated. For this purpose, citric acid and soluble salts of calcium (nitrate, chloride, carbonate) and aluminium (nitrate, chloride, acetate) were used as starting materials, in the presence and, respectively, in the absence of ethylene glycol. Ca3Al2O6 resulted as single-phase after annealing at 1050 A degrees C for 1 h only starting from calcium nitrate or carbonate and aluminium nitrate or acetate as salts precursor for Ca2+ and Al3+ cations. The formation of Ca3Al2O6 is not conditioned by the ethylene glycol presence in these mixtures. Using calcium and aluminium chlorides, the phases present at 1050 A degrees C are Ca12Al14O33 and unreacted CaO.

Oxidation mechanism of diethyl ether: a complex process for a simple molecule

Di Tommaso, Stefania; Rotureau, Patricia; Crescenzi, Orlando; Adamo, Carlo

PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 32, 14636-14645

A large number of organic compounds, such as ethers, spontaneously form unstable peroxides through a self-propagating process of autoxidation (peroxidation). Although the hazards of organic peroxides are well known, the oxidation mechanisms of peroxidizable compounds like ethers reported in the literature are vague and often based on old experiments, carried out in very different conditions (e. g. atmospheric, combustion). With the aim to (partially) fill the lack of information, in this paper we present an extensive Density Functional Theory (DFT) study of autoxidation reaction of diethyl ether (DEE), a chemical that is largely used as solvent in laboratories, and which is considered to be responsible for various accidents. The aim of the work is to investigate the most probable reaction paths involved in the autoxidation process and to identify all potential hazardous intermediates, such as peroxides. Beyond the determination of a complex oxidation mechanism for such a simple molecule, our results suggest that the two main reaction channels open in solution are the direct decomposition (beta-scission) of DEE radical issued of the initiation step and the isomerization of the peroxy radical formed upon oxygen attack (DEEOO center dot). A simple kinetic evaluation of these two competing reaction channels hints that radical isomerization may play an unexpectedly important role in the global DEE oxidation process.Finally industrial hazards could be related to the hydroperoxide formation and accumulation during the chain propagation step. The resulting information may contribute to the understanding of the accidental risks associated with the use of diethyl ether.

Enhanced Erosion Protection of TWAS Coated Ti6Al4V Alloy Using Boride Bond Coat and Subsequent Laser Treatment

Mann, B. S.; Arya, Vivek; Pant, B. K.

JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 20, 6, 932-940

The material commonly used in low-pressure high-rating super critical/ultra super critical steam turbines as well as guide and moving blades of high speed aero compressors is Ti6Al4V alloy. These blades are severely affected owing to erosion which leads to drop in efficiency and increase in maintenance cost. This article deals with SHS 7170 coating on Ti6Al4V alloy using twin wire arc spraying (TWAS), enhancing its bonding by providing a thin bond coat and then treating with high-power diode laser (HPDL). Significant improvement in erosion resistance of this multilayer coating has been achieved because of the formation of fine-grained micro structure due to rapid heating and cooling rates associated with the laser surface treatment. After laser surface treatment, the fracture toughness of this multilayer has improved manifold. The water droplet and particulate erosion test results along with the damage mechanism are reported and discussed in this article.

Solution combustion synthesis of gamma(L)-Bi2MoO6 and photocatalytic activity under solar radiation

Saha, Dipankar; Madras, Giridhar; Row, T. N. Guru

MATERIALS RESEARCH BULLETIN, 46, 8, 1252-1256

The facile method of solution combustion was used to synthesize gamma(L)-Bi2MoO6. The material was crystallized in a purely crystalline orthorhombic phase with sizes varying from 300 to 500 nm. Because the band gap was 2.51 eV, the degradation of wide variety of cationic and anionic dyes was investigated under solar radiation. Despite the low surface area (< 1 m(2)/g) of the synthesized material, gamma(L)-Bi2MoO6 showed high photocatalytic activity under solar radiation due to its electronic and morphological properties. (C) 2011 Elsevier Ltd. All rights reserved.

Combusion synthesis, structural and photo-physical characteristics of Eu2+ and Dy3+ co-doped SrAl2O4 phosphor nanopowders

Shafia, Ehsan; Aghaei, Alireza; Bodaghi, Masoud; Tahriri, Mohammadreza

JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 22, 8, 1136-1142

In this research, we reported the synthesis of Eu2+ and Dy3+ co-doped SrAl2O4 phosphor nanopowders with high brightness and long afterglow by urea-nitrate solution combustion synthesis (SCS) at 600 A degrees C, followed by heating the resultant combustion ash at 1,200 A degrees C in a weak reductive atmosphere (5% H-2 + 95% N-2). The broad-band UV-excited luminescence of the SrAl2O4: Eu2+, Dy3+ nanopowders was observed at lambda (max) = 517 nm due to transitions from the 4f(6)5d(1) to the 4f(7) configuration of the emission center (Eu2+ ions). The excitation spectra consist of 240- and 254 nm broad peaks. Finally, it was found that the optimum ratio of urea is 2.5 times higher than theoretical quantities for the best emission condition of SrAl2O4: Eu2+, Dy3+ phosphor nanopowders.

Combustion synthesis of TiAl intermetallics and their simultaneous joining to carbon/carbon composites

Cao, J.; Wang, H. Q.; Qi, J. L.; Lin, X. C.; Feng, J. C.

SCRIPTA MATERIALIA, 65, 3, 261-264

The combustion synthesis of TiAl intermetallics and their joining to carbon/carbon composites was realized simultaneously. The successful joint configuration involved putting a carbon/carbon composite ball into the Ti-Al powder mixtures. The effect of the residual stresses at the interface on the joining of carbon/carbon composite to TiAl intermetallics was analyzed. Investigation of the reaction products of Ti-45 at.% Al mixtures showed that TiAl and Ti(3)Al phases were formed by combustion synthesis. The evolution of the interfacial microstructure was investigated. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Combustion synthesis and luminescence properties of NaY1-xEux(WO4)(2) phosphors

Qian, Xianhua; Pu, Xipeng; Zhang, Dafeng; Li, Lei; Li, Meijing; Wu, Shutong

JOURNAL OF LUMINESCENCE, 131, 8, 1692-1695

The red phosphors NaY1-xEux(WO4)(2) with different concentrations of Eu3+ were synthesized via the combustion synthesis method. As a comparison, NaEu(WO4)(2) was prepared by the solid-state reaction method. The phase composition and optical properties of as-synthesized samples were studied by X-ray powder diffraction and photoluminescence spectra. The results show that the red light emission intensity of the combustion synthesized samples under 394 nm excitation increases with increase in Eu3+ concentrations and calcination temperatures. Without Y ions doping, the emission spectra intensity of the NaEu(WO4)(2) phosphor prepared by the combustion method fired at 900 degrees C is higher than that prepared by the solid-state reaction at 1100 degrees C. NaEu(WO4)(2) phosphor synthesized by the combustion method at 1100 degrees C exhibits the strongest red emission under 394 nm excitation and appropriate GE chromaticity coordinates (x=0.64, y=0.33) close to the NTSC standard value. Thus, its excellent luminescence properties make it a promising phosphor for near UV InGaN chip-based red-emitting LED application. (C) 2011 Elsevier B.V. All rights reserved.

Effect of Cr alloying on friction and wear of sputter-deposited nanocrystalline (MoxCr1-x)(5)Si-3 films

Xu, Jiang; Xie, Zong-Han; Munroe, P.

INTERMETALLICS, 19, 8, 1146-1156

In the present work, five kinds of nanocrystalline (MoxCr1-x)(5))Si-3(x = 1, 0.78, 0.75, 0.64, 0.57) films with average grain size 8 nm have successfully been prepared on Ti6Al4V alloy by a double cathode glow discharge technique in order to improve its poor tribological properties. The influence of the Cr additions on the mechanical and tribological properties of nanocrystalline (MoxCr1-x)(5)Si-3 films have been studied. The microstructure of the films was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Nanoindentation was used to measure hardness (H) and elastic modulus (E) of the as-deposited films, and the adhesion strength between the as-deposited films and substrate was evaluated by scratch test. The dry sliding wear properties of the as-deposited films were investigated using against different counterbodies (ZrO2 ceramic balls and GCr15 rolling bearing steel) in ball-on-disk system at room temperature. The results indicated that alloying additions of Cr affected considerably the wear performance of nanocrystalline (MoxCr1-x)(5)Si-3 films. The friction coefficients and specific wear rates of nanocrystalline (MoxCr1-x)(5)Si-3 films were significantly reduced by the increasing Cr substitution, and its specific wear rates have been shown to be two orders of magnitude lower than for Ti6Al4V alloy. The dominant wear mechanism of the nanocrystalline (MoxCr1-x)(5)Si-3 films experiences a transition from delamination to tribo-oxidation wear, along with the increasing amount of Cr additions. (C) 2011 Elsevier Ltd. All rights reserved.

Comparison of titanium suicide and carbide reinforced in situ synthesized TiAl composites and their mechanical properties

Rao, K. P.; Vyas, A.

INTERMETALLICS, 19, 8, 1236-1242

This study explored a synthesizing route involving in situ development of reinforcements of titanium silicides in a series of TiAl-based matrices. The main features of this processing route are: (1) Incorporating a small quantity of mechanically alloyed Ti-Al-Si and Ti-Al-Si-C powders, referred to as precursors, into Ti-Al-X (X stands for Cr, Mn, Nb, or their combination) powder mixtures that act as matrices: and (2) Hot isostatic pressing (HIPing) of the cold compacted mixture at a temperature of 1100 degrees C for 4 h. A series of composites based on different Ti-Al-X matrix were synthesized. The structural evolution in these composites was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The mechanical properties and compression tests at room and elevated temperatures (600 degrees C and 800 degrees C) have been investigated. In addition, the influence of alloying elements in the matrix has been evaluated from their stress strain responses. (C) 2011 Elsevier Ltd. All rights reserved.

Cast Intermetallic Alloys by SHS Under High Gravity

Sanin, V.; Andreev, D.; Ikornikov, D.; Yukhvid, V.

ACTA PHYSICA POLONICA A, 120, 2, 331-335

Pilot-scale series of cast Ti-Al, Ti-Al-Nb, (Ni, Co, Mn)Al(x), Ni-Cr-Al-Si-C, and Co-V-Al-Si-C alloys were produced by thermit-type SHS under high gravity for their potential use as heat-resistant materials, master alloys, precursors for catalysts, etc.

Mechanochemical synthesis of Ti1-xZrxB2 and Ti1-xHfxB2 solid solutions

Aviles, M. A.; Cordoba, J. M.; Sayagues, M. J.; Gotor, F. J.

CERAMICS INTERNATIONAL, 37, 6, 1895-1904

Solid solutions of TiB2-ZrB2 and TiB2-HfB2 were obtained under an inert atmosphere by high-energy ball-milling mixtures of Ti/Zr/B and Ti/Hf/B, respectively. Milling promoted mechanically induced self-sustaining reactions (MSR), and the ignition time was dependent on the initial composition of the mixture. The stoichiometry of Ti1-xZrxB2 and Ti1-xHfxB2 solid solutions was controlled by adjusting the atomic ratio of the reactants. The solid solutions were characterised by X-ray diffraction, transmission electron microscopy, electron diffraction, and energy dispersive X-ray spectroscopy. The results revealed that TiB2-ZrB2 possessed a nanometric microstructure and good chemical homogeneity. However, in the TiB2-HfB2 system, an inhomogeneous solid solution was obtained when a Ti-rich mixture was employed. The solid solutions showed good thermal stability; thus, can be used as raw materials for the development of technological materials for structural applications. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Fabrication of ultrafine-grained alumina ceramics by two different fast sintering methods

Meng, Fancheng; Zhang, Fan; Huang, Weijiu; Yang, Youli; Guo, Minna; Jiang, Xiaojuan; Tian, Zhongqing

CERAMICS INTERNATIONAL, 37, 6, 1973-1977

The preparation of ultrafine-grained alumina ceramics by the fast sintering technique Self-propagating High-temperature Synthesis plus Quick Pressing (SHS-QP) method and spark plasma sintering (SPS) technique was reported. The effects of different heating rates (SHS-QP-1600 degrees C/min, SPS-200 degrees C/min) on the preparation of ultrafine structure were compared. The densification and grain growth as a function of sintering time and temperature were discussed. Within a short sintering time (<3 min), the full-dense alumina with ultrafine-grained structure was obtained by SHS-QP at 1550 degrees C under 100 MPa. By SPS, the sintering temperature was lower (1200 degrees C) than that of SHS-QP. The differences in densification parameters were explained by analyzing the thermodynamics of sintering process. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

EPR and photoluminescence studies of ZnO:Mn nanophosphors prepared by solution combustion route

Reddy, A. Jagannatha; Kokila, M. K.; Nagabhushana, H.; Rao, J. L.; Nagabhushana, B. M.; Shivakumara, C.; Chakradhar, R. P. S.

SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 79, 3, 476-480

Nanocrystalline ZnO:Mn (0.1 mol%) phosphors have been successfully prepared by self propagating, gas producing solution combustion method. The powder X-ray diffraction of as-formed ZnO:Mn sample shows, hexagonal wurtzite phase with particle size of similar to 40 nm. For Mn doped ZnO, the lattice parameters and volume of unit cell (a=3.23065 angstrom, c=5.27563 angstrom and V=47.684 (angstrom)(3)) are found to be greater than that of undoped ZnO (a=3.19993 angstrom, c=5.22546 angstrom and V=46.336 (angstrom)(3)). The SEM micrographs reveal that besides the spherical crystals, the powders also contained several voids and pores. The TEM photograph also shows the particles are approximately spherical in nature. The FTIR spectrum shows two peaks at similar to 3428 and 1598 cm(-1) which are attributed to O-H stretching and H-O-H bending vibration. The PL spectra of ZnO:Mn indicate a strong green emission peak at 526 nm and a weak red emission at 636 nm corresponding to (4)T(1) -> (6)A(1) transition of Mn(2+) ions. The EPR spectrum exhibits fine structure transition which will be split into six hyperfine components due to (55)Mn hyperfine coupling giving rise to all 30 allowed transitions. From EPR spectra the spin-Hamiltonian parameters have been evaluated and discussed. The magnitude of the hyperfine splitting (A) constant indicates that there exists a moderately covalent bonding between the Mn(2+) ions and the surrounding ligands. The number of spins participating in resonance (N), its paramagnetic susceptibility (chi) have been evaluated. (C) 2011 Elsevier B.V. All rights reserved.

Preparation, and magnetic and electromagnetic properties of La-doped strontium ferrite films

Li, Y. Q.; Huang, Y.; Qi, S. H.; Niu, F. F.; Niu, L.

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 323, 16, 2224-2232

SrLaxFe12-xO19 films (x=0-1.0) with large magneto-crystalline anisotropy were synthesized on SiO2 substrate by sol-gel and self-propagating high-temperature synthesis technique. The films were characterized by various experimental techniques including X-ray diffraction analysis, Field Emission Scanning Electron Microscope, Atomic Force Microscopy, Vibrating Sample Magnetometry and vector network analyzer. The results show that La ions completely enter into strontium ferrite lattice without changing the ferrite appearance; its grain size is approximately 40-80 nm, its length is 100 nm; the magnetoplumbite structure is proved through testing a concertina form of the crystal grain; the maximum coercivity is 5986 Oe at x=0.2; La-doped films possess a wider microwave absorption frequency range with better gross loss angle tangent (tan delta > 0.1), from 9 to 10.5 GHz at x=0.2, where the maximum value of tan delta reaches 0.2709. The La-doped films reach smaller nanometer size, better magnetic properties and microwave absorption properties with the doping of lanthanum. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Synthesis, characterization and thermal expansion measurements on uranium-cerium mixed oxides

Krishnan, R. Venkata; Panneerselvam, G.; Singh, Brij Mohan; Kothandaraman, B.; Jogeswararao, G.; Antony, M. P.; Nagarajan, K.

JOURNAL OF NUCLEAR MATERIALS, 414, 3, 393-398

Uranium-cerium mixed oxides (U(1-y)Ce(y))O(2) (y = 0.2, 0.4, 0.6, 0.8) were prepared by combustion synthesis using citric acid as the fuel. Sintering of the solid solutions was carried out at 1873 K under reduced atmosphere. From the room temperature XRD patterns of the sintered samples it was found that the solid solutions form single phase fluorite structure. The room temperature lattice parameters of (U(1-y)Ce(y))O(2) (y = 0.2, 0.4, 0.6, 0.8) are 0.5458, 0.5446, 0.5434 and 0.5422 nm respectively. Thermal expansion of (U(1-y)Ce(y))O(2) (y = 0.2, 0.4, 0.6, 0.8) in the temperature range 298-1973 K was measured by high temperature X-ray diffraction (HTXRD). The coefficients of thermal expansion increase with increase in CeO(2) content in the sample and the measured data in the temperature range 298-1973 K, for (U(1-y)Ce(y))O(2) (y = 0.2, 0.4, 0.6, 0.8) are 18.23, 19.91, 21.59, 23.29 x 10(-6) K(-1), respectively. (C) 2011 Elsevier B.V. All rights reserved.

In situ synthesis of TiC reinforced metal matrix composite (MMC) coating by self propagating high temperature synthesis (SHS)

Yuan, Xuanyi; Liu, Guanghua; Jin, Haibo; Chen, Kexin

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 30, L301-L303

This paper reports a simple and energy saving method to prepare ceramic particulate reinforced MMC coating via SHS. By this method, TiC reinforced Cu/Ni based MMC coating was produced on a steel substrate. No pores or micro cracks were found in the coating, and fine TiC particles were uniformly distributed in the metal matrix. A strong metallurgical bonding was achieved at the interface between the MMC coating and the steel substrate. (C) 2011 Elsevier B.V. All rights reserved.

Improving the dielectric properties of SiC powder through nitrogen doping

Li, Zhimin; Zhou, Wancheng; Luo, Fa; Huang, Yunxia; Li, Guifang; Su, Xiaolei

MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 176, 12, 942-944

Nitrogen-doped SiC powders were synthesized by combustion synthesis using alpha-Si(3)N(4) as solid nitrogen dopant. Results showed that beta-SiC phases were produced and the introduction of alpha-Si(3)N(4) resulted in the decrease of particle size of beta-SiC powder. The complex permittivities of the undoped and doped samples were determined in the frequency range of 8.2-12.4 GHz. The real part epsilon' and imaginary part epsilon '' of the complex permittivity of doped SiC powder were greatly increased compared to undoped one. The mechanism of nitrogen doping on increasing the complex permittivity of SiC has been discussed, indicating that N(C) defects contribute to higher permittivity. (C) 2011 Elsevier B.V. All rights reserved.

Optimization of the combustion synthesis towards efficient LaMnO3+y catalysts in methane oxidation

Najjar, Hend; Lamonier, Jean-Francois; Mentre, Olivier; Giraudon, Jean-Marc; Batis, Habib

APPLIED CATALYSIS B-ENVIRONMENTAL, 106, 41306, 149-159

The present work deals with the synthesis and the study of physico-chemical and catalytic properties of a series of lanthanum manganite perovskite-type oxide using the one-step combustion method. Glycine was used as complexing agent and fuel. Seven glycine-to-nitrate ratios from 0.32 to 0.8 were investigated. XRD patterns show a single phase perovskite type oxide when glycine-to-nitrate ratio is above 0.37. Glycine/nitrate ratio affects significantly the surface areas, which range in 18-37 m(2)/g. The use of fuel-rich precursor allows an enhancement of the specific surface area, the reducibility of manganese and the mobility of desorbed oxygen. The light-off temperature for 50% and 90% of methane conversion was found to be directly related to surface areas. The highest catalytic activity was obtained for glycine-to-nitrate ratio of 0.8, which exhibits the highest superficial concentration of manganese and the highest amount of active oxygen. This catalyst shows also a good thermal stability. (C) 2011 Elsevier B.V. All rights reserved.

Microstructures and mechanical properties of the in situ TiB-Ti metal-matrix composites synthesized by spark plasma sintering process

Shen, Xiangbo; Zhang, Zhaohui; Wei, Sai; Wang, Fuchi; Lee, Shukui

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 29, 7692-7696

In situ synthesized TiB reinforced titanium matrix composites have been synthesized by spark plasma sintering (SPS) process at 950-1250 degrees C, using mixtures of 15 wt% TiB(2) and 85 wt% Ti powders. The effects of the sintering temperature on densification behavior and mechanical properties of the TiB-Ti composites were investigated. The results indicated that with rising sintering temperatures, relative densities of the composites increase obviously, while the in situ TiB whiskers grow rapidly. As a result, bending strength of the TiB-Ti composites increases slowly at the combined actions of the factors referred above. Fracture toughness of the composites is improved remarkably due to the large volume fraction of Ti matrix, the crack deflection, pull-out and the micro-fracture of the needle-shaped TiB grains. The results also suggested that TiB-Ti composite sintered at 1250 degrees C by SPS process exhibits the highest relative density of 99.6% along with bending strength of 1161 MPa and fracture toughness of 13.5 MPa m(1/2). (C) 2011 Elsevier B. V. All rights reserved.

A comparative study of the tribological performances of laser clad TiB2-TiC-Al2O3 composite coatings on AISI 1020 and AISI 304 substrates

Masanta, Manoj; Shariff, S. M.; Choudhury, A. Roy

WEAR, 271, 41493, 1124-1133

In this work, an investigation has been carried out to study the effects of the choice of substrate material on the tribological performance of TiB2-TiC-Al2O3 composite coating developed by laser cladding. The coatings have been deposited employing different laser scan speeds on AISI 1020 mild steel and AISI 304 stainless steel substrates using pre-placed precursor powder mixture of TiO2 Al and B4C. The coatings are characterized by using XRD. FESEM, micro-hardness measurement and tribological tests. The dry sliding wear behavior of the coating is assessed by using ball-on-disc tribometer at various normal loads (9.8, 19.6. 29.4 and 39.2 N) in order to experimentally determine the effects of applied normal load on the composite coatings developed on the two different steel substrates. Average wear rates of the coatings developed on AISI 1020 steel are higher than those of the coatings developed on AISI 304 steel for similar applied load. Coefficient of friction does not have a significant dependence on the choice of substrate material. Difference in the values of thermal conductivity of the two steel substrate materials is considered to have a significant effect on the microstructure and tribological performance of the coatings. (C) 2011 Elsevier B.V. All rights reserved.

Combustion synthesis of Ni, Fe and Cu multi-component catalysts for hydrogen production from ethanol reforming

Kumar, A.; Mukasyan, A. S.; Wolf, E. E.

APPLIED CATALYSIS A-GENERAL, 401, 41306, 20-28

Solution combustion synthesis was used to prepare multi-component catalysts containing Ni, Fe, and Cu using a controlled volume combustion method. A series of catalysts containing the selected metals in different molar ratios were analyzed for their activity and hydrogen selectivity for ethanol decomposition and ethanol partial oxidative reforming reactions. The most active and selective catalyst was found to be Ni(1)Fe(0.5)Cu(1) yielding 80% conversion and similar to 42% hydrogen selectivity at the relatively low temperature of similar to 415 degrees C for the ethanol decomposition reaction. Decreasing the oxygen concentration in the feed increased the H(2) selectivity at lower temperature. In the absence of oxygen, i.e. during ethanol decomposition, hydrogen production starts at 120 degrees C and gives a selectivity of similar to 40% at about 380 degrees C. Studies with monometallic catalysts show that Ni at lower temperature was the most active and selective for hydrogen and methane, Cu was selective for acetaldehyde and Fe was selective for CO(2) and ethane. Hydrogen selectivity was found to be highest for Fe at high temperature. (C) 2011 Elsevier B.V. All rights reserved.

Preparation of porous Ni-YSZ cermet anodes for solid oxide fuel cells by high frequency induction heated sintering

Yoo, Jong-Yeol; Cho, Chun-Kang; Shon, In-Jin; Lee, Ki-Tae

MATERIALS LETTERS, 65, 13, 2066-2069

Ni-YSZ cermet anodes for solid oxide fuel cells were successfully prepared by high frequency induction heated sintering, producing a uniformly porous microstructure without abnormal grain growth found in the conventional sintering method. All sintering processes commenced below 1150 degrees C and finished within 2 min. The rupture strength and electrical conductivity of the sample sintered by high frequency induction heated sintering without addition of a pore former were over 180 MPa and about 2000 S cm(-1) at 800 degrees C, respectively. (C) 2011 Elsevier B.V. All rights reserved.

Understanding the sucrose-assisted combustion method: Effects of the atmosphere and fuel amount on the synthesis and electrochemical performances of LiNi0.5Mn1.5O4 spinel

Manuel Amarilla, Jose; Rojas, Rosa M.; Maria Rojo, Jose

JOURNAL OF POWER SOURCES, 196, 14, 5951-5959

The present paper comprises results of our studies about the influence of the atmosphere and fuel amount on the synthesis and electrochemical performance of LiNi0.5Mn1.5O4 spinet (LNMS). Reaction of mixtures of metal nitrates with and without sucrose (fuel) in Ar and in air flow has been studied by thermal analysis and coupled mass spectrometry (TG/DTA/MS). Products obtained after the thermal study have been identified and characterized by powder X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Gases evolved along the thermal treatment have been identified by coupled mass spectrometry (MS). From all these results the synthesis reactions have been put forward. When the reaction is conducted in air sub-micrometric LiNi0.5Mn1.5O4 spinet is obtained independently of the amount of sucrose. When the reaction is done in Ar the spinel is only obtained in absence of fuel. The electrochemical performances at 25 degrees C and 55 C of the synthesized LNMSs have been evaluated by galvanostatic cycling. The samples prepared in air furnish high capacity (approximate to 120 inAh g(-1)) and they work at high voltage (approximate to 4.7 V). Besides, they exhibit remarkable cycling properties, even at elevated temperature (55 degrees C), with capacity retentions higher than 90% after 50 cycles. (C) 2011 Elsevier B.V. All rights reserved.

Selective Catalytic Reduction of NOx with NH3 over Mn, Ce Substitution Ti0.9V0.1O2-delta Nanocomposites Catalysts Prepared by Self-Propagating High-Temperature Synthesis Method

Guan, Bin; Lin, He; Zhu, Lin; Huang, Zhen

JOURNAL OF PHYSICAL CHEMISTRY C, 115, 26, 12850-12863

This study focuses on promoting the low temperature performance of vanadium-based catalysts; for this, the SHS method was applied to synthesize a series of Ti0.9VxM0.1-xO2-delta catalysts. The performances of the catalysts (Ti0.9V0.1O2-delta, Ti0.9Mn0.05V0.05O2-delta, and Ti0.9Ce0.05V0.05O2-delta), were fully investigated with the temperature-programmed-reaction, which proved that these SHS catalysts with nanometer size had high activity over a broad temperature window of 150-400 degrees C. Compared with Ti0.9V0.1O2-delta, the substituted Catalysts, Ti0.9Mn0.05V0.05O2-delta and Ti0.9Ce0.05V0.05O2-delta, showed higher N-2 selectivity at high temperatures. The Ce substituted catalyst exhibited good resistance to H2O and SO2 poisoning at low temperatures. The structural and physical-chemical properties of catalysts were characterized comprehensively by BET, XRD, FTIR, TEM, EDX, XPS, and TPD. The XRD results indicated that the active components of V, Mn, and Ce were highly dispersed over the catalysts. The Mn substitution could enhance the Bronsted acid sites on the catalyst surface and accelerate the SCR reaction at low temperatures. The XPS shows that the Ce substitution led to high concentration of chemisorbed oxygen, which diminished the unselective oxidation of NH3 by O-2 to N2O, NO, or NO2 and resulted in superior N-2 selectivity. The active components of the catalysts, such as V, Mn, and Ce, mostly existed in the form of mixed-valence which was beneficial for the oxidation of NO to NO2. Furthermore, the SCR reaction mechanism over Ti0.9Ce0.05V0.05O2-delta catalyst was also examined using in situ DRIFTS. The results revealed that high active monodentate,e nitrate and bridging nitrate species as well as abundant ionic NH4+ (Bronsted acid sites) were the key intermediates in the SCR reaction since the ad-monodentate nitrate and bridging nitrate species disappeared quickly in the presence of NH3.

The influence of La doping on the catalytic behavior of Cu/ZrO2 for methanol synthesis from CO2 hydrogenation

Guo, Xiaoming; Mao, Dongsen; Lu, Guanzhong; Wang, Song; Wu, Guisheng

JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL, 345, 41306, 60-68

A series of Cu/ZrO2 catalysts with various La loadings for methanol synthesis from CO2 hydrogenation were prepared by a urea-nitrate combustion method. The catalysts were characterized with N-2 adsorption, XRD, reactive N2O adsorption, XPS, TPR, H-2-TPD and CO2-TPD techniques, and tested for methanol synthesis from CO2 hydrogenation. With increasing La loading, the Cu surface area increases first and then decreases, whereas the amount of basic site over catalysts increases continuously. The results of catalytic test reveal that a linear relationship exists between the conversion of CO2 and the Cu surface area. Moreover, it is found for the first time that the selectivity to methanol is related to the distribution of basic site on the catalyst surface. The presence of La favors the production of methanol, and the optimum catalytic activity is obtained when the amount of La doping is 5% of the total amount of Cu2+ and Zr4+. (C) 2011 Elsevier B.V. All rights reserved.

Combustion synthesis and characterization of Ba2NdSbO6 nanocrystals

Kavitha, V. T.; Jose, R.; Ramakrishna, S.; Wariar, P. R. S.; Koshy, J.

BULLETIN OF MATERIALS SCIENCE, 34, 4, 661-665

Nanocrystalline Ba2NdSbO6, a complex cubic perovskite metal oxide, powders were synthesized by a self-sustained combustion method employing citric acid. The product was characterized by X-ray diffraction, differential thermal analysis, thermogravimetric analysis, Fourier transform infrared spectroscopy, transmission electron microscopy and scanning electron microscopy. The as-prepared powders were single phase Ba2NdSbO6 and a mixture of polycrystalline spheroidal particles and single crystalline nanorods. The Ba2NdSbO6 sample sintered at 1500 degrees C for 4 h has high density (similar to 95% of theoretical density). Sintered nanocrystalline Ba2NdSbO6 had a dielectric constant of similar to 21; and dielectric loss = 8 x 10(-3) at 5 MHz.

Solution Combustion Synthesis and Photocatalytic Activity of alpha-Fe2O3 Nanopowder

Jahagirdar, A. A.; Ahmed, M. N. Zulfiqar; Donappa, N.; Nagabhushana, H.; Nagabhushana, B. M.

TRANSACTIONS OF THE INDIAN CERAMIC SOCIETY, 70, 3, 159-162

Nanocrystalline alpha-Fe2O3 was prepared using solution combustion method with glycine as fuel and ferric nitrate as oxidizer at about 300 degrees C. The alpha-Fe2O3 nanopowder was characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The PXRD pattern indicates that the alpha-Fe2O3 has hexagonal phase with a mean crystallite size of 30-40 nm as calculated from Scherrer's formula. The iron oxide nanopowder was used for the photocatalytic degradation of methyl orange (MO) dye in aqueous solution. The effects of catalyst dosage, H2O2 and irradiation time on the rate of photocatalytic degradation of MO dye were also investigated. The rate of photocatalytic degradation of MO dye was enhanced in the presence of H2O2 and UV light. The experimental results show that for concentration of 20 ppm, maximum decoloration of the dye solution was achieved in just 25 min for a catalyst dosage of 2.5 g per liter of the dye solution.

Effect of Adiabatic Flame Temperature on Nano Alumina Powders during Solution Combustion Process

Sherikar, Baburao N.; Umarji, A. M.

TRANSACTIONS OF THE INDIAN CERAMIC SOCIETY, 70, 3, 167-172

Nano ceramic alumina powders are synthesized by solution combustion synthesis using aluminium nitrate as oxidizer and urea as fuel with different fuel to oxidizer ratio. The variation of adiabatic flame temperatures are calculated theoretically for different fuel/oxidizer ratio according to thermodynamic concept and correlated with the observed flame (reaction) temperatures. A "multi channel thermocouple setup connected to computer interfaced Keithley multi meter 2700" is used to monitor the thermal events occurring during the process. The combustion products, characterized by XRD, show that the powders are composed of polycrystalline oxides with crystallite size of 32 to 52 nm. An interpretation based on maximum combustion temperature and the amount of gases produced during reaction for various fuel to oxide ratio has been proposed for the nature of combustion and its correlation with the characteristics of as-synthesized powder.

Synthesis, Characterization and Fluorescence Property of Doped SrAl2O4:Eu-x(2+), Dy-y(3+) Long Afterglow Phosphors

Bai Jian; Zhao Yongliang; Liu Yonggang; Sun Huaning

RARE METAL MATERIALS AND ENGINEERING, 40, , 60-63

Twelve kinds of doped SrAl2O4:Eu-x(2+), Dy-y(3+)(x:y=1:1, x:y=1:2) long afterglow phosphors were synthesized by self-propagating high-temperature synthesis method (SHS). The studies show that glow brightness of SrAl2O4:Eu2+, Dy-0.0125(3+) is the best. According to the proportion, cations Li+, Be2+ for synthesizing fluorescence material, Zn2+, Cd2+, Pb2+ for synthesizing fluorescence material and self-activated fluorescence material both are separately introduced in the SrAl2O4:Eu-0.0125(2+), Dy-0.0125(3+). In total, 22 doped SrAl2O4 long afterglow phosphors with 5 series were synthesized by the method. Afterglow brightness of SrAl2O4:Eu-0.0125(2+), Dy-0.0125(3+) can greatly increase because of Zn-0.0125(2+)-doped; furthermore, the rate of afterglow decay of SrAl2O4:Eu-0.0125(2+), Dy-0.0125(3+), Zn-0.0125(2+) is obviously slower than that of SrAl2O4:Eu-0.0125(2+), Dy-0.0125(3+), Result of XRD indicates that a little rare-earth ion-doped can not change crystalline structure of substance (SrAl2O4). Moreover, results of TEM and particle size distribution indicate that shapes of products are loose and porous solid that likes mushroom cloud, and the particle size is about 10 mu m.

Formation of Ultrafine Titanium Carbide Powder by Combustion Synthesis

Yin Chuanqiang; Zou Zhengguang; Li Xiaomin; Wu Yi; Wei Xiuqin; Zhou Lang

RARE METAL MATERIALS AND ENGINEERING, 40, , 80-83

Formation of ultrafine titanium carbide powder from FeTiO(3) (ilmenite)-Mg-C by combustion synthesis was reported. The laws of combustion and the effect of magnesium concentration on the characteristics of the product were discussed thermodynamically and investigated experimentally. It is found that the system is an intensively exothermic reaction and the start reaction temperature of the FeTiO(3)-Mg-C system is about 577.7 degrees C. When the molar ratio of ilmenite to magnesium is 1:4, ultrafine TiC powder after leaching is reasonably pure and shows a narrow particle size distribution. The average particle size of the final powder is 229.6 nm.

Preparation of a Single-Phase Solid Electrolyte La1-xSrxGa1-yMgyO3-(x plus y)/2 by Self-Propagating High-Temperature Synthesis

Krasil'nikov, V. N.; Shkerin, S. N.; Gyrdasova, O. I.; Korneva, A. A.; Nikonov, A. V.; Lipilin, A. S.

RUSSIAN JOURNAL OF INORGANIC CHEMISTRY, 56, 7, 999-1003

Highly dispersed single-phase powders described as La0.88Sr0.12Ga0.82Mg0.18O2.85 were prepared using a method based on the principles of self-propagating high-temperature synthesis (SHS). Lanthanum, strontium, gallium, and magnesium nitrates were used in the SHS as "oxidants", and ethylene glycol was used as the reducing agent. The initial reaction mixture was liquid. According to X-ray diffraction and scanning electron microscopy data, the sample becomes a single phase after annealing of the primary SHS product at 1200 degrees C, which is substantially lower than in other synthetic methods. Using so active powders (grain size of about 100-130 nm), it is possible to reduce the temperature of the final annealing of the ceramics to 1275 degrees C, which gives rise to single-phase finely dispersed ceramics having specific properties.

Rapid synthesis of Ti(C, N) powders by mechanical alloying and subsequent arc discharging

Yuan Quan; Zheng Yong; Yu Hai-zhou

TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 21, 7, 1545-1549

Ti(C,N) powders were synthesized by mechanical alloying (MA) from a mixture of pure titanium and graphite under a nitrogen atmosphere in a planetary mill. Effects of arc discharging on phase transformation and microstructure of MA powders milled for 1-7 h were explored. The results show that Ti(C, N) powders were prepared after mechanical milling for 1 h and subsequent arc discharge treatment, whereas the synthesis reaction did not occur in 7 h by mechanical milling alone. The ions produced during arc discharging interacted with powder particles and accelerated the diffusion of atoms and the nucleation on the surface of the as-milled powder, which results in fast synthesis of Ti(C, N) powders. The formation mechanisms of the two synthesis processes are self-propagating reactive synthesis.

Thermal Desorption of Hydrogen from Mg2Ni Hydrogen Storage Materials

Hur, Tae Hong; Han, Jeong Seb; Kim, Jin Ho; Kim, Byung Kwan

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 11, 7, 6499-6503

In order to investigate the influence of HCS on the hydrogen occupation site of Mg2Ni alloy, the thermal desorption technique has been applied to Mg2Ni hydride made by hydriding combustion synthesis (HCS). Mg2Ni was made under low temperature in a short time by the HCS compared to conventional melting process. At various initial hydride wt% from 0.91 to 3.52, the sample was heated to 623 K at a rate of 1.0 K/min. The starting temperature of the evolution of hydrogen goes higher as the initial hydride wt% increases. Only one peak is shown in the case of the small initial hydride wt%. But two peaks appeared with increasing initial hydride wt%. The activation energies obtained by the first and second peaks are 113.0 and 99.5 kJ/mol respectively. The two site occupation model by Darriet et al. was proved. The influence of HCS on the hydrogen occupation site of Mg2Ni alloy is nonexistent.

Effect of Foaming Agent and Endothermic Agent Addition on Foaming Behavior of NiTi Alloy Made by Combustion Synthesis

Arakawa, Yuya; Kobashi, Makoto; Kanetake, Naoyuki

JOURNAL OF THE JAPAN INSTITUTE OF METALS, 75, 7, 379-385

Closed cell nickel titanium (NiTi) alloy foams were made by combustion synthesis with the help of both foaming agent and endothermic agent powders. Nickel, titanium, the foaming agent (ZrH(2)) and the endothermic agent (TiB(2)) powders were mixed and pressed at room temperature into cylindrical compacts. By heating these powder compacts up to an ignition temperature of the combustion reaction, NiTi alloy specimens are made. In this method, pores in the specimens are made by the gas generation from the foaming agent during melting of NiTi alloy due to the high heat of combustion reaction. Cell wall rupture of these foams caused by the gas generation is successfully prevented by the endothermic agent addition which increases the viscosity of molten NiTi alloy. An optimum amount of endothermic agent addition turned out to be in between 30 and 35 vol%. This volume fraction range is close to the one that makes adiabatic temperature of the combustion reaction below melting point of NiTi alloy. Specimens made by the addition of 40 vol% endothermic agent did not foam sufficiently. Porosity of the NiTi alloy foams increased by increasing the additive amount of the foaming agent by 1 mass%. Cell wall rupture and large pore formation became remarkable by increasing the foaming agent addition.

Circulation system complex networks and teleconnections

Gong Zhi-Qiang; Wang Xiao-Juan; Zhi Rong; Feng Ai-Xia

CHINESE PHYSICS B, 20, 7, 79201-

In terms of the characteristic topology parameters of climate complex networks, the spatial connection structural complexity of the circulation system and the influence of four teleconnection patterns are quantitatively described. Results of node degrees for the Northern Hemisphere (NH) mid-high latitude (30 degrees N-90 degrees N) circulation system (NHS) networks with and without the Arctic Oscillations (AO), the North Atlantic Oscillations (NAO) and the Pacific-North American pattern (PNA) demonstrate that the teleconnections greatly shorten the mean shortest path length of the networks, thus being advantageous to the rapid transfer of local fluctuation information over the network and to the stability of the NHS. The impact of the AO on the NHS connection structure is most important and the impact of the NAO is the next important. The PNA is a relatively independent teleconnection, and its role in the NHS is mainly manifested in the connection between the NHS and the tropical circulation system (TRS). As to the Southern Hemisphere mid-high latitude (30 degrees S-90 degrees S) circulation system (SHS), the impact of the Antarctic Arctic Oscillations (AAO) on the structural stability of the system is most important. In addition, there might be a stable correlation dipole (AACD) in the SHS, which also has important influence on the structure of the SHS networks.

Effect of thermal properties on self-propagating fronts in reactive nanolaminates

Alawieh, Leen; Knio, Omar M.; Weihs, Timothy P.

JOURNAL OF APPLIED PHYSICS, 110, 1, 13509-

The effects of thermal diffusion on flame front dynamics in a (1: 1) Ni/Al multilayered system are computationally investigated. A systematic refinement of the thermal conductivity model is performed, namely by incorporating the effects of concentration, direction, and temperature dependence. The resulting thermal conductivity models are incoporated into the reduced reaction formalism developed by Salloum and Knio [Combust. Flame 157(6), 1154 (2010]). Computations using constant and variable conductivity models are contrasted with each other, for axial and normal front propagation. Notable differences between the predictions of the various conductivity models are observed, particularly concerning the thermal and reaction widths. Differences in the average front propagation velocity are, unexpectedly, less pronounced. Brief computational experiments are finally conducted for 3D front propagation using constant and variable thermal conductivity models. The 3D variable-conductivity computations reveal the occurrence of transient, spinlike reactions that appear to be consistent with recent experimental observations, whereas stable front behavior is observed when a constant-conductivity model is used. Thus, the present experiences suggest that thermo-diffusive instabilities are likely to play a role in the onset and manifestation of some of the experimentally-observed transient front propagation regimes. (C) 2011 American Institute of Physics. [doi:10.1063/1.3599847]

Reactive Molecular Dynamics Simulation of Fullerene Combustion Synthesis: ReaxFF vs DFTB Potentials

Qian, Hu-Jun; van Duin, Adri C. T.; Morokuma, Keiji; Irle, Stephan

JOURNAL OF CHEMICAL THEORY AND COMPUTATION, 7, 7, 2040-2048

The dynamic fullerene self-assembly process during benzene combustion was studied using classical Reactive Force Field (ReaxFF) nonequilibrium molecular dynamics (MD) simulations. In order to drive the combustion process, the hydrogen to carbon (H/C) ratio was gradually reduced during the course of the MD simulations. Target temperatures of 2500 and 3000 K were maintained by using a Berendsen thermostat. Simulation conditions and hydrogen removal strategies were chosen to match closely a previous quantum chemical MD (QM/MD) study based on the density-functional tight-binding (DFTB) potential (Saha et al. ACS Nano 2009, 3, 2241) to allow a comparison between the two different potentials. Twenty trajectories were computed at each target temperature, and hydrocarbon cluster size, C(x)H(y) composition, average carbon cluster curvature, carbon hybridization type, and ring count statistics were recorded as a function of time. Similarly as in the QM/MD simulations, only giant fullerene cages in the range from 155 to 212 carbon atoms self-assembled, and no C(60) cages were observed. The most notable difference concerned the time required for completing cage self-assembly: Depending on temperature, it takes between 50 and 150 ps in DFTB/MD simulations but never less than 100 ps and frequently several 100s ps in ReaxFF/MD simulations. In the present system, the computational cost of ReaxFF/MD is about 1 order of magnitude lower than that of the corresponding DFTB/MD. Overall, the ReaxFF/MD simulations method paints a qualitatively similar picture of fullerene formation in benzene combustion when compared to direct MD simulations based on the DFTB potential.

In situ synthesis of titanium diboride composites through volume combustion

Yilmaz, S. O.; Evin, E.; Guler, O.

MATERIALS SCIENCE AND TECHNOLOGY, 27, 7, 1123-1130

Hard in situ synthesis of TiB(2)-Fe(2)B metal matrix composite (MMC) has been synthesised by volume combustion synthesis (VCS) reactions of Fe-FeTi-FeB system. VCS samples were characterised by SEM, EDX, XRD and DTA. Results show that it is possible to synthesise in situ structured MMC samples (with TiB(2) and Fe(2)B phases) by VCS. Metallographic investigations show that Fe(2)B and TiB(2) are found dispersed throughout the metal matrix, and other borides are present in microlevel patches dispersed in a eutectic matrix. The Fe-TiB(2) composites sintered at temperature of 1200 degrees C consist of three different regions, i.e. alpha-Fe, TiB(2) and Fe(2)B regions. The increase in sintering temperature to 1400 degrees C leads to a hypereutectic microstructure of the Fe-B binary system having TiB(2) grains uniformly distributed throughout the matrix. A semiliquid phase sintering occurred by increasing eutectic phase transformation temperatures to 1400 degrees C, which increased the efficiency of VCS. On the other hand, increasing sintering time from 1 to 3 h decreased the volume fraction of alpha-Fe and increased the volume fraction TiB(2) phase.

Synthesis and Luminescent Properties of a Novel Red-Emitting Phosphor Ba2ZnSi2O7:Eu3+, B3+ for Ultraviolet Light-Emitting Diodes

Yao, Shanshan; Li, Yuanyuan; Xue, Lihong; Yan, Youwei

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, 8, 4, 701-708

A novel red-emitting phosphor Ba1.95ZnSi2O7:Eu-0.05(3+), B-x(3+) was prepared by combustion synthesis and an efficient red emission under near-ultraviolet (UV) was observed. The luminescence, crystallinity, and particle sizes were investigated using luminescence spectrometry, X-ray diffractometry, and scanning electron microscopy. The emission spectrum shows that the most intense peak is located at 614 nm, which corresponds to the D-5(0) -> F-7(2) transition of Eu3+. The phosphor has two main excitation peaks located at 394 and 465 nm, which match the emission of UV and blue light-emitting diodes, respectively. The optical absorption spectra of Ba1.95ZnSi2O7:Eu-0.05(3+), B-0.06(3+) exhibited a band-gap energy of 3.95 eV. The results showed that boric acid was effective in improving the luminescence intensity of Ba1.95ZnSi2O7:Eu-0.05(3+), and the optimum molar ratio of boric acid to zinc nitrate was about 0.06. The phosphor Ba1.95ZnSi2O7:Eu-0.05(3+), B-0.06(3+) synthesized by the combustion method showed 1.8 times improved emission intensity compared with that of the Ba1.95ZnSi2O7:Eu-0.05(3+) phosphor under lambda(ex) = 394 nm.

Combustion Synthesis and Luminescent Properties of Nano and Submicrometer-Size Gd2O3:Dy3+ Phosphors for White LEDs

Jayasimhadri, Mula; Ratnam, Bonam V.; Jang, Kiwan; Lee, Ho Sueb; Chen, Baojiu; Yi, Soung-Soo; Jeong, Jung-Hyun; Moorthy, L. Rama

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, 8, 4, 709-717

Monoclinic phase Dy3+:Gd2O3 nanophosphors were synthesized by a combustion method using glycine followed by sintering to obtain submicrometer-size phosphors. The X-ray diffraction patterns confirmed the monoclinic structure of Gd2O3:Dy3+ phosphors. The phosphors were characterized by a transmission electron microscope, Raman, Fourier transform infrared, and fluoresence spectroscopy. The sizes of the phosphor particles are in the range from nearly 35 to 93 nm. It was observed that the emission intensities are varied with the excitation wavelength and concentration. The mechanism responsible for concentration quenching was discussed. The enhancement of emission intensities was observed while increasing the sintering temperature of the phosphor. Moreover, the CIE chromaticity coordinates of Dy3+-doped Gd2O3 phosphors fall in the white light domain of the chromaticity diagram. The above characteristics indicate that these phosphors may be potential candidates for the application of near-ultraviolet-based white-light-emitting diodes.

Electrical and thermomechanical properties of materials based on nonstoichiometric titanium carbide prepared by self-propagating high-temperature synthesis

Shul'pekov, A. M.; Lyamina, G. V.

INORGANIC MATERIALS, 47, 7, 722-727

This paper examines the effect of the chemical and phase compositions of nonstoichiometric titanium carbide prepared by self-propagating high-temperature synthesis on the electrical and thermophysical properties of polymer compounds. Doping of titanium carbide with trace amounts of nitrogen raises the conductivity of the polymer compounds. The addition of epoxy to the polymer matrix markedly reduces the thermal expansion of the material. The proposed materials can be used at temperatures of up to 300-350A degrees C.

Effect of milling time and heat treatment on the composition of CuIn0.75Ga0.25Se2 nanoparticle precursors and films

Vidhya, B.; Velumani, S.; Asomoza, R.

JOURNAL OF NANOPARTICLE RESEARCH, 13, 7, 3033-3042

Preparation of pure phase CuIn0.75Ga0.25Se2 nanoparticle powder by ball milling technique has been confirmed for the milling time of more than 45 min at 1200 rpm. Formation of shear bands responsible for breakdown of grains and generation of nanostructure during mechanical alloying, dislocation and defects induced due to milling has been studied by High-Resolution Transmission Electron Microscopy (HRTEM) analysis. Deviation in final composition of the products from those of starting materials has been discussed based on low volatilization of Se. Effect of milling time on the phase formation, particle size, and composition has been discussed in detail. Decrease in grain size from 12.44 to 7.96 nm has been observed with the increase in milling time. Mechanically induced self-propagating reaction mechanism which occurred during milling process is also discussed. Nanoparticle precursor was mixed with organic binder material for rheology of mixture to be adjusted for screen printing, and the films are subjected to heat treatment at five different temperatures in nitrogen ambient for 25 min. Average grain size calculated by Scherrer's formula was almost the same irrespective of temperature. Reproducibility of precursor composition in the deposited films has been discussed in detail.

CO2 hydrogenation to methanol over Cu/ZnO/ZrO2 catalysts prepared via a route of solid-state reaction

Guo, Xiaoming; Mao, Dongsen; Lu, Guanzhong; Wang, Song; Wu, Guisheng

CATALYSIS COMMUNICATIONS, 12, 12, 1095-1098

Cu/ZnO/ZrO2 catalysts were prepared by a route of solid-state reaction and tested for the synthesis of methanol from CO2 hydrogenation. The effects of calcination temperature on the physicochemical properties of as-prepared catalysts were investigated by N-2 adsorption, XRD, TEM, N2O titration and H-2-TPR techniques. The results show that the dispersion of copper species decreases with the increase in calcination temperature. Meanwhile, the phase transformation of zirconia from tetragonal to monoclinic was observed. The highest activity was achieved over the catalyst calcined at 400 degrees C. This method is a promising alternative for the preparation of highly efficient Cu/ZnO/ZrO2 catalysts. (C) 2011 Elsevier B.V. All rights reserved.

Studies on Au catalysts for water gas shift reaction

Lenite, Brenno A.; Galletti, Camilla; Specchia, Stefania

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 13, 7750-7758

Gold-supported catalysts on alumina and ceria were prepared by means of deposition-precipitation method at different pH and molarity of the precursor solution. The screening at the powder level in a fixed bed micro-reactor of the catalytic activity of the 3% Au prepared catalysts, in terms of CO conversion for the WGS reaction, highlighted that the catalysts on alumina were not so active (maximum conversion of 30%), despite a satisfactory gold deposition on the support. On the contrary, ceria-based catalysts displayed better performances. By feeding only CO and H2O, with H(2)o/CO ratio equal to 4, catalysts prepared at different pH and M = 1 x 10(-3) approached satisfactorily the equilibrium WGS conditions, in particular when pH = 8.5 was used. However, catalytic activity tests carried out with a realistic reformate feed (containing also H-2 and CO2) showed fairly low CO conversions also at high temperature. Then, on this catalyst, tests at different weight space velocities WSV were carried out obtaining better performance by lowering WSV. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Development of nanostructured Mg2Ni alloys for hydrogen storage applications

Atias-Adrian, I. C.; Deorsola, F. A.; Ortigoza-Villalba, G. A.; DeBenedetti, B.; Baricco, M.

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 13, 7897-7901

The Mechanically Activated Self-propagating High temperature Synthesis (MASHS) has been employed to obtain nanostructured Mg2Ni alloys. MASHS process has been further improved by controlling the electrical parameter measurements during the combustion reaction under the thermal explosion mode. The samples were hydrogenated at 20 bar and 300 degrees C by means of a Pressflow Gas Controller while the dehydrogenation was conducted in a Differential Scanning Calorimetry (DSC) equipped with an H-2 detector of the purged gas. Nanostructured Mg2Ni demonstrated hydrogen storage capacity around 3.5 wt%. The desorption temperature was about 250 degrees C at 3 degrees C/min. The activation energy for dehydrogenation, calculated by the Kissinger method, was about 100 kJ/mol. Copyright 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Self-ignition combustion synthesis of LaNi(5) at different hydrogen pressures

Yasuda, Naoto; Tsuchiya, Tohru; Sasaki, Shino; Okinaka, Noriyuki; Akiyama, Tomohiro

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 14, 8604-8609

In this paper, we describe the self-ignition combustion synthesis (SICS) of LaNi(5) utilizing the hydrogenation heat of metallic calcium at different hydrogen pressures, and focus on the effect of hydrogen pressure on the ignition temperature and the initial activation of hydrogenation. In the experiments, La(2)O(3), Ni, and Ca were dry-mixed, and then heated at 0.1, 0.5, and 1.0 MPa of hydrogen pressure until ignition due to the hydrogenation of calcium. The products were recovered after natural cooling for 2 h. The results showed that the ignition temperature lowered with hydrogen pressure. The products changed from bulk to powder with hydrogen pressure. This was probably caused by volume expansion due to hydrogenation at higher pressure. The product obtained at 1.0 MPa showed the highest hydrogen storage capacity under an initial hydrogen pressure of 0.95 MPa. The results of this research can be applied as an innovative production route for LaNi(5) without the conventional melting of La and Ni. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Fabrication of Sr- and Co-doped lanthanum chromite interconnectors for SOFC

Setz, L. F. G.; Santacruz, I.; Colomer, M. T.; Mello-Castanho, S. R. H.; Moreno, R.

MATERIALS RESEARCH BULLETIN, 46, 7, 983-986

Many studies have been performed dealing with the processing conditions of electrodes and electrolytes in solid oxide fuel cells (SOFCs). However, the processing of the interconnector material has received less attention. Lanthanum chromite (LaCrO(3)) is probably the most studied material as SOFCs interconnector. This paper deals with the rheology and casting behaviour of lanthanum chromite based materials to produce interconnectors for SOFCs. A powder with the composition La(0.80)Sr(0.20)Cr(0.92)CO(0).(08)O(3) was obtained by combustion synthesis. Aqueous suspensions were prepared to solids loading ranging from 8 to 17.5 vol.%, using ammonium polyacrylate (PAA) as dispersant and tetramethylammonium hydroxide (TMAH) to assure a basic pH and providing stabilization. The influence of the additives concentrations and suspension ball milling time were studied. Suspensions prepared with 24 h ball milling, with 3 wt.% and 1 wt.% of PAA and TMAH, respectively, yielded the best conditions for successful slip casting. Sintering of the green discs was performed in air at 1600 degrees C for 4 h leading to relatively dense materials. (C) 2011 Elsevier Ltd. All rights reserved.

Nanostructured TiC-TiB2 composites obtained by adding carbon nanotubes into the self-propagating high-temperature synthesis process

Deorsola, F. A.; Adrian, I. C. Atias; Villalba, G. A. Ortigoza; DeBenedetti, B.

MATERIALS RESEARCH BULLETIN, 46, 7, 995-999

The synthesis of nanostructured TiC-TiB2 by self-propagating high-temperature synthesis (SHS) has been investigated by using carbon nanotubes as precursor materials in partial substitution of graphite according to the following reaction: 6Ti + B4C + (3-x)C + x CNT -> 4TiC + 2TiB(2).Different amounts of CNTs addition have been studied in order to achieve structural refinement of the SHS products. The CNT molar content was varied in order to define the optimal composition, which allows to obtain nanostructured TiC-TiB2 powders morphologically homogenous.The optimized composition has been chosen for the further densification step. The Pressure Assisted Fast Electric Sintering (PAFES) technique gave bulk composites with ultrafine grained microstructure. The mechanical characterization showed very high hardness and good fracture toughness values if compared to literature data. (C) 2011 Elsevier Ltd. All rights reserved.

Preparation of Y2O3-Al2O3-SiO2 glasses by combustion synthesis melt-casting under high gravity

He, Bin; Liu, Guanghua; Li, Jiangtao; Wu, Liang; Yang, Zengchao; Guo, Shibin; Chen, Yixiang

MATERIALS RESEARCH BULLETIN, 46, 7, 1035-1038

Y2O3-Al2O3-SiO2 glasses were prepared by combustion synthesis melt-casting under high gravity. The properties of the glasses strongly depended on the starting compositions and preparation conditions. With a higher SiO2 content in the starting compositions, the glass-forming ability of the melt was improved, but the density and hardness of the prepared glasses decreased. Crystallization occurred more frequently for larger samples and by using quartz crucibles instead of graphite ones. By increasing the high-gravity factors, both the density and hardness of the samples were improved. It is proposed that enhancing the high-gravity field facilitates the removal of bubbles from the melt. (C) 2011 Elsevier Ltd. All rights reserved.

Combustion synthesis of Fe-Al/TiC composite powders and effect of Al content on its characteristics

Mehrizi, M. Zarezadeh; Saidi, A.; Shamanian, M.; Eslami, H. R.

POWDER METALLURGY, 54, 3, 400-403

In this work, combustion synthesis of ferrotitanium-Al-C powder mixtures with different compositions was carried out to synthesise Fe-Al/TiC composites. Differential thermal analysis was performed on the precursor powder from ambient temperature to 1673 K at a heating rate of 30 K min(-1). Phase development and structural changes were investigated by X-ray diffraction technique and scanning electron microscopy. The results showed that no trace of TiAl(x) (x=1, 3) was formed in all samples, and the reaction of (Ti-Fe)-Al-C system took place in the following two steps: first, molten Al and Fe reacted exothermically to form Fe-Al intermetallic compound. Second, the produced heat melted the ferrotitanium with lower Fe content and resulted in a liquid containing Ti, Fe, Al and C. TiC formed in all samples, but depending on the Al content, different phases containing FeAl(2), FeAl, Fe(3)Al, Fe(3)AlC(x) and alpha-Fe formed as phases of matrix. The mixture with the lower Al content gave out a higher combustion temperature.

Criterion to control self-propagation high temperature synthesis for porous Ti-Al intermetallics

Jiang, Y.; He, Y. H.; Huang, B. Y.; Zou, J.; Huang, H.; Xu, N. P.; Liu, C. T.

POWDER METALLURGY, 54, 3, 404-407

The criterion to control self-propagation high temperature synthesis for the fabrication of porous Ti-Al intermetallics was established from the prereaction model and the thermal balance condition. The criterion equation reflecting the relation between the solid reaction layer thickness correlation parameter and the ignition temperature was deduced to be p(3)=C(1)/(T(ad)-T(0)) + C(2), according to which the near net shaping synthesis of porous Ti-Al intermetallics was realised, which was significantly important for the industrial productions and applications of this high performance novel porous material. The slight difference between theoretical predictions and experimental data was analysed according to the model analysis.

Properties and consolidation of nanocrystalline WSi2-SiC composite from mechanically activated powders by pulsed current activated combustion synthesis

Shon, In-Jin; Park, Jeong-Hwan; Ko, In-Yong; Doh, Jung-Mann; Yoon, Jin-Kook; Nam, Kee-Seok

CERAMICS INTERNATIONAL, 37, 5, 1549-1555

Dense nanostructured WSi2-SiC composite was synthesized by pulsed current activated combustion synthesis method within 2 mm in one step from mechanically activated powders of WC and 3Si. Simultaneous combustion synthesis and consolidation were accomplished under the combined effects of a pulsed current and mechanical pressure. Highly dense WSi2-SiC with relative density of up to 99.8% was produced under simultaneous application of a 80 MPa pressure and the pulsed current. The average grain size and mechanical properties of the composite were investigated. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

A comparative study on combustion synthesis of Ta-B compounds

Yeh, C. L.; Wang, H. J.

CERAMICS INTERNATIONAL, 37, 5, 1569-1573

A comparative study on the preparation of various tantalum borides (including Ta(2)B, Ta(3)B(2), TaB, Ta(5)B(6), Ta(3)B(4), and TaB(2)) in the Ta-B system was experimentally conducted by self-propagating high-temperature synthesis (SHS) from the elemental powder compacts of their corresponding stoichiometries. Both combustion temperature and reaction front velocity increased and then decreased with increasing boron content in the powder mixture. The fastest flame front with a reaction temperature of 1732 degrees C and a propagation rate of 11.2 mm/s was observed in the sample of Ta:B = 1:1. The combustion temperature (1205 degrees C) and flame-front velocity (3.82 mm/s) for the powder compact of Ta:B = 2:1 were the lowest. According to the XRD analysis, single-phase TaB and TaB(2) were produced from the samples of Ta:B = 1:1 and 1:2, respectively. However, multiphase products were synthesized from the samples of other stoichiometries. In the final products from Ta-rich samples of Ta:B = 2:1 and 3:2, two boride phases, Ta(2)B and TaB, along with a large amount of residual Ta were detected. The products yielded from boron-rich reactants of Ta:B = 5:6 and 3:4 were composed of TaB, Ta(3)B(4), and TaB(2). Based upon the temperature dependence of combustion wave velocity, the activation energies associated with the formation of TaB and TaB(2) by solid state combustion were determined to be 131.1 and 181.4 kJ/mol, respectively. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Fabrication of B4C from Na2B4O7 + Mg + C by SHS method

Jiang Guojian; Xu Jiayue; Zhuang Hanrui; Li Wenlan

CERAMICS INTERNATIONAL, 37, 5, 1689-1691

This paper deals with the formation of boron carbide (B4C) powders from Na2B4O7 + Mg + C system by self-propagating high-temperature synthesis (SHS) method. B4C without impurities could be obtained after the acid enrichment and distilled water washing. The reaction mechanism of SHS of B4C was proposed: the synthesis of B4C is a process involving the decomposition of Na2B4O7 into the intermediate phase B2O3, which reacts with Mg and carbon to form B4C. (C) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Kinetics of mechanically activated high temperature synthesis of Ni3Al in the thermal explosion mode

Filimonov, Valery Yu.; Korchagin, Michail A.; Smirnov, Evgeny V.; Sytnikov, Alexander A.; Yakovlev, Vladimir I.; Lyakhov, Nikolay Z.

INTERMETALLICS, 19, 7, 833-840

We present the features of macrokinetics of phase formation during the solid-state synthesis in the mechanically milled 3Ni + Al mixtures. It was found that with milling time, the activation energy decreases down to anomalously low values, which is related to structural changes in the powder mixtures. A method was proposed to process thermograms of the synthesis in the thermal explosion mode and was used to study the kinetic function structure and its parameters in the system. The numerical processing of the experimental data shows that the kinetic function most adequately corresponds to the law of homogeneous kinetics of phase formation with the reaction order close to unity. (C) 2010 Elsevier Ltd. All rights reserved.

Microstructure evolution and wear properties of bulk MoSi2 fabricated by field activated sintering

Hu, Qiaodan; Luo, Peng; Yan, Youwei; Li, Jianguo

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 4, 470-477

Field activated sintering (FAS) was employed to fabricate dense bulk MoSi2 from Mo and Si powders. During the FAS process, Si was melted first, and then Mo was dissolved leading to a precipitation of MoSi2. A eutectic reaction of MoSi2-Mo5Si3 resulted from a combined effect of Mo-Si exothermic reactions and field induced Joule heating. With hyper-stoichiometric amount of Si (Mo/Si = 1:2.06), the FAS MoSi2 is free of Mo5Si3 phase. Subsequently, an un-lubricated sliding wear test of MoSi2 against carbon steel was conducted. Both normal load and temperature have crucial points related to a transition from mild to severe wear. Sliding speed and relative density have a negative effect on wear rate. In addition, at room temperature the wear is with a protective layer composed of oxide and transferred substance, whereas poor oxidation resistance leads to spalling of the layer and brittle fracture at an elevated temperature up to 500 degrees C. (C) 2011 Elsevier Ltd. All rights reserved.

Mechanical Properties of Highly Porous NiTi Alloys

Bram, Martin; Koehl, Manuel; Buchkremer, Hans Peter; Stoever, Detlev

JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 20, 41398, 522-528

Highly porous NiTi alloys with pseudoelastic properties are attractive candidates for biomedical implants, energy absorbers, or damping elements. Recently, a new method was developed for net-shape manufacturing of such alloys combining metal injection molding with the application of suitable space-holder materials. A comprehensive study of mechanical properties was conducted on samples with a porosity of 51% and a pore size in the range of 300-500 mu m. At low deformations < 6%, fully pronounced pseudoelasticity was found. Even at higher strains, a shape recovery of maximum 6% took place, on which the onset of irreversible plastic deformation was superposed. Results of static compression tests were also used to calculate the energy-absorbing capacity. Fatigue of porous NiTi was investigated by cyclic loading up to 230,000 stress reversals. The failure mechanisms responsible for a reduction of shape recovery after an increased number of load cycles are discussed.

Synthesis of single phase beta-SiAlON ceramics by reaction-bonded sintering using Si and Al2O3 as raw materials

He, Enquan; Yue, Jianshe; Fan, Lei; Wang, Chao; Wang, Hongjie

SCRIPTA MATERIALIA, 65, 2, 155-158

Single-phase beta-SiAlON compacts with z = 1 have been synthesized by reaction-bonded sintering using Si and Al2O3 as raw materials. The nitrided samples consisted of fine equiaxed particles and continuous fibers. beta-SiAlON fibers with a diameter approximately 50 nm were obtained through the vapor solid mechanism. After post-sintering at 1650-1750 degrees C for 2 h, only beta-SiAlON phase with z = 1 was obtained. alpha-Si3N4 completely changed into beta-SiAlON through the solution-precipitation mechanism. beta-SiAlON shows different microstructures at different post-sintering temperature. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Analysis on thermite reactions of CuO nanowires and nanopowders coated with Al

Kim, Do Kyung; Bae, Jung Hyeon; Kang, Myung Koo; Kim, Hyun Jae

CURRENT APPLIED PHYSICS, 11, 4, 1067-1070

A thermite reaction between the CuO nanowires and the deposited nano-Al was studied. The heat energy obtained from the reaction was compared with that of CuO and Al nanopowders mixture. CuO nanowires were grown and patterned on glass substrate and nano-Al was deposited on top of it to produce nanoenergetic materials.The released heat energy of the reaction was approximately 1186 J/g, which was higher than that of mixed CuO and Al nanopowders. The higher heat formation mechanism could be explained by the intimate contact and reactivity between the CuO nanowires and the nano-Al. (C) 2011 Elsevier B.V. All rights reserved.

Combustion synthesis of Ti3Si1-xAlxC2 solid solutions from TiC-, SiC-, and Al4C3-containing powder compacts

Yeh, C. L.; Chen, J. H.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 26, 7277-7282

Preparation of the Ti(3)Si(1-x)AlxC(2) solid solution with x = 0.2-0.8 was investigated by self-propagating high-temperature synthesis (SHS) using TiC-, SiC-, and Al4C3-containing powder compacts. Due to the variation of reaction exothermicity with sample stoichiometry, the combustion temperature and reaction front velocity decreased with increasing Al content of Ti3Si1-xAlxC2 for the TiC- and Al4C3-added samples, but increased for the samples with SiC. In contrast to the formation of Ti-3(Si, Al)C-2 as the dominant phase for the TiC- and SiC-added samples, TiC was identified as the major constituent in the final products of samples adopting Al4C3. In addition, the evolution of Ti-3(Si, Al)C-2 was improved by increasing the Al content of the TiC-and SiC-added powder compacts, but deteriorated considerably upon the increase of Al4C3 in the Al4C3-containing sample. (C) 2011 Elsevier B. V. All rights reserved.

Evaluation of modulus of elasticity, nano-hardness and fracture toughness of TiB2-TiC-Al2O3 composite coating developed by SHS and laser cladding

Masanta, Manoj; Shariff, S. M.; Choudhury, A. Roy

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 528, 16-17, 5327-5335

Modulus of elasticity (E) and nano-hardness (H) of the composite TiB2-TiC-Al2O3 coating deposited on AISI 1020 steel by combined self-propagating high-temperature synthesis (SHS) and laser cladding process have been measured from load-displacement curves, resulting from nano-indentation testing. Fracture toughness (K-IC) of the coatings has been evaluated from the indentation method. A qualitative evaluation of interfacial strength between coating and substrate material was also performed by indentation method. Results indicated elastic modulus and fracture toughness of the composite coatings are in the range of 230-280 GPa and 5.46-6.12 MPa m(1/2) those are respectively lower and higher than those of the individual constituent ceramics. Nano-hardness of the coating microstructure obtained was in the range of 16-22 GPa and was found to vary depending on the laser-processing parameter adopted. Indentation taken with high load at the coating-substrate interface indicated a strong interfacial bond between coating and steel substrate. An attempt has been made to co-relate the wear rate of the coating with H/E ratio. (C) 2011 Elsevier B.V. All rights reserved.

Comparative investigation of Al- and Cr-doped TiSiCN coatings

Shtansky, D. V.; Kuptsov, K. A.; Kiryukhantsev-Korneev, Ph V.; Sheveiko, A. N.; Fernandez, A.; Petrzhik, M. I.

SURFACE & COATINGS TECHNOLOGY, 205, 19, 4640-4648

The aim of this work was a comparative investigation of the structure and properties of Al- and Cr-doped TiSiCN coatings deposited by magnetron sputtering of composite TiAlSiCN and TiCrSiCN targets produced by self-propagating high-temperature synthesis method. Based on X-ray diffraction, scanning and transmission electron microscopy. X-ray photoelectron spectroscopy, and Raman spectroscopy data, the Al- and Cr-doped TiSiCN coatings possessed nanocomposite structures (Ti,Al)(C,N)/a-(Si,C) and (Ti,Cr)(C,N)/a-SiC(x)N(y)/a-C with cubic crystallites embedded in an amorphous matrix. To evaluate the thermal stability and oxidation resistance, the coatings were annealed either in vacuum at 1000, 1100, 1200, and 1300 degrees C or in air at 1000 degrees C for 1 h. The results obtained show that the hardness of the Al-doped TiSiCN coatings increased from 41 to 46 GPa, reaching maximum at 1000 degrees C, and then slightly decreased to 38 GPa at 1300 degrees C. The Cr-doped TiSiCN coatings demonstrated high thermal stability up to 1100 degrees C with hardness above 34 GPa. Although both Al-and Cr-doped TiSiCN coatings possessed improved oxidation resistance up to 1000 degrees C, the TiAlSiCN coatings were more oxidation resistant than their TiCrSiCN counterparts. The TiCrSiCN coatings showed better tribological characteristics both at 25 and 700 degrees C and superior cutting performance compared with the TiAlSiCN coatings. (C) 2011 Elsevier B.V. All rights reserved.

Magnetic and Mossbauer behavior of the nanostructured MgFe2O4 spinel obtained at low temperature

Da Dalt, S.; Takimi, A. S.; Volkmer, T. M.; Sousa, V. C.; Bergmann, C. P.

POWDER TECHNOLOGY, 210, 2, 103-108

This study investigated the solution combustion synthesis technique to obtain the nanostructured magnesioferrite (MgFe2O4) spinel powder. The reaction was performed in an electric muffle furnace. Considering the characteristics of the as-synthesized powders, the 30% fuel-deficient formulation was selected for synthesis temperature evaluation. This formulation was synthesized at different furnace temperatures. Powder characterization was carried out by X-ray diffraction (XRD) to evaluate crystallographic analysis and crystallite size; Transmission Electron Microscopy (TEM) was done to assess the morphology and crystallite size; and Mossbauer spectroscopy and vibrational sample magnetometer (VSM) were performed to obtain magnetic measurements. Crystallite sizes estimated from the XRD technique increased with furnace temperature values, which were consistent with the results obtained by TEM. The characterized samples of MgFe2O4 had an average crystallite size of 42.8 nm using the DRX method, average saturation magnetization of 25.6 emu/g and coercive field not higher than 11 Oe. (C) 2011 Elsevier B.V. All rights reserved.

Effect of C particle size on the mechanism of self-propagation high-temperature synthesis in the Ni-Ti-C system

Yang, Y. F.; Wang, H. Y.; Wang, J. G.; Jiang, Q. C.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 25, 7060-7065

Effect of C particle size on the mechanism of self-propagation high-temperature synthesis (SHS) in the Ni-Ti-C system was investigated. Fine C particle resulted in a traditional mechanism of dissolution-precipitation while coarse C particle made the reaction be controlled by a mechanism of the diffusion of C through the TiC(x) layer. The whole process can be described: C atoms diffusing through the TiC(x) layer dissolved into the Ni-Ti liquid and TiC were formed once the liquid became supersaturated. Simultaneously, the heat generated from the TiC formation made the unstable TiC(x) layer break up. However, with the spread of Ti-Ni liquid, a new TiCx layer was formed again at the interface between spreading liquid and C particle. This process cannot stop until all the C particles are consumed completely. (C) 2011 Elsevier B.V. All rights reserved.

Combustion synthesis and characterization of highly crystalline single phase nickel ferrite nanoparticles

Prabhakaran, T.; Hemalatha, J.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 25, 7071-7077

Acombustion route of synthesizing highly crystalline single phase nickel ferrite (NiFe(2)O(4)) spinel nanoparticles using various amounts of DL-alanine as fuel has been reported in this paper. The role of the amount of fuel is found to be significant in the size control and phase purity of nano crystalline samples. The structural, thermal, morphological and magnetic studies have been carried out. XRD patterns reveal the formation of highly crystalline nano NiFe(2)O(4) with high degree of phase purity when fuel concentration is maintained at 1Mand 2M. FTIR spectra also prove the formation of pure nano NiFe(2)O(4). The temperature and fuel effects are found to have strong influence on size, structural, and magnetic properties of materials. The magnetic measurements show that the nano NiFe(2)O(4) samples exhibit soft ferromagnetism with the highest saturation magnetization Ms at room temperature as 42.53 emu/g. (C) 2011 Elsevier B.V. All rights reserved.

Oxidative reforming of diesel fuel over LaCoO3 perovskite derived catalysts: Influence of perovskite synthesis method on catalyst properties and performance

Villoria, J. A.; Alvarez-Galvan, M. C.; Al-Zahrani, S. M.; Palmisano, P.; Specchia, S.; Specchia, V.; Fierro, J. L. G.; Navarro, R. M.

APPLIED CATALYSIS B-ENVIRONMENTAL, 105, 41367, 276-288

Oxidative reforming of diesel fuel was studied over Co/La2O3 catalysts derived from LaCoO3 perovskite precursors synthesized by co-precipitation (COP), sal-gel (PEC) and combustion (SCS) methods. Physical-chemical characterization of perovskite precursors by N-2-adsorption isotherms, Hg-intrusion porosimetry. XRD, XPS, TPR and SEM showed that the method of preparation produced changes in the porosity and homogeneity both at bulk and surface levels of the LaCoO3 perovskite precursors. The perovskite prepared by the SCS method achieved a higher development of the porous network as well as higher homogeneity in bulk and surface compared to COP and PEC counterparts. By contrast, the PEC and COP methods produced perovskites with lower porosity and with the presence of some secondary phases such as Co3O4 and La(OH)(3). The modifications of the characteristics of LaCoO3 perovskites directly affected the structure and morphology of the catalytic materials derived from the thermal pre-treatment of perovskites before the activity tests. The differences in catalyst characteristics resulted from a different reduction and interaction between the gaseous reducing stream and the initial LaCoO3 perovskites which occurred during the thermal pre-treatment. The activity of the samples at the beginning of the reaction test followed the order: PEC > SCS > COP. The latter could be related to the different interaction of the catalysts with the reactants as well as with the larger presence of the La2CoO4 phase produced during the thermal pre-treatment. The evolution of the catalysts for long times on stream resulted in the activity order: SCS > PEC > COP. Characterization of used samples disclosed the key role of the Co-0 exposure on the catalyst surface as concerns the achieved catalytic activities and the extent of the La2O2CO3 phase on catalysts as regards the inhibition of coke deposition. (C) 2011 Elsevier B.V. All rights reserved.

Auto-combustion synthesis and properties of Ce0.85Gd0.15O1.925 for intermediate temperature solid oxide fuel cells electrolyte

Singh, Nitish Kumar; Singh, Prabhakar; Singh, Manish Kumar; Kumar, Devendra; Parkash, Om

SOLID STATE IONICS, 192, 1, 431-434

A typical composition of the system Ce1-xGdxO2-delta with x = 0.15 (CGO15) has been synthesized by auto-combustion method. DTA/TGA of the precursor compound indicated the completion of reaction at about 270 degrees C. Greater than 95% of the theoretical density has been achieved by sintering at 1300 degrees C for 10 h. Single phase formation in as-burnt stage has been confirmed by its powder X-ray diffraction (XRD) pattern. The structural morphology was studied employing bright field transmission electron micrograph (BFTEM) and high resolution transmission electron micrograph (HRTEM). BFTEM image indicates that particles are highly agglomerated and appear to be dispersed in amorphous matrix. Also BETEM image reveals that the average particle size is 26 +/- 5 nm. The presence of amorphous phase in as-prepared ash was also confirmed by HRTEM and selected area diffraction (SAD). The scanning electron micrograph (SEM) of the thermally etched system shows grains having an average size of 400 nm. Impedance measurements have been made in the frequency range 1 Hz to 1.3 MHz between 200 and 500 degrees C and the total conductivity was measured. An enhanced conductivity value is observed which may make this system suitable for application as a solid electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs). (C) 2010 Elsevier B.V. All rights reserved.

Synthesis, vacuum sintering and dielectric characterization of zirconia (t-ZrO2) nanopowder

Pazhani, R.; Kumar, H. Padma; Varghese, Angeo; Raj, A. Moses Ezhil; Solomon, Sam; Thomas, J. K.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 24, 6819-6823

Phase pure zirconium oxide powders have been synthesized using the single step auto-ignition combustion method, the particles were nanometer sized (20 nm) and the size distribution was very narrow (3.4 nm). Systematic structural characterization revealed the t-ZrO2 and indexed for its tetragonal structure (a = 3.5975 angstrom and c = 5.1649 angstrom). Calculated microstrain in most of the plane indicated the presence of compressive stress (65-288 MPa) along various planes of the particles. Observed space group (P4(2)/nmc) revealed the presence of cations in the 8e positions (0.75, 0.25, 0.75) and the anions in the 16 h positions (0.25, 0.25, 0.4534). The metal-oxide (Zr-O) band observed at the low wavenumber region further confirmed the phase purity of the as-prepared ZrO2 nanopowders. Peaks at the binding energy positions 2.042 and 0.525 keV in the energy dispersive X-ray spectrum revealed oxygen deficient zirconia. The particle size estimated by TEM was in good agreement with the results obtained through X-ray line broadening (20.81 nm) measurements. The nanopowders were sintered to above 98% of the theoretical density by using vacuum sintering technique at a relatively low temperature of 1300 degrees C. Stable tetragonal ZrO2 experimentally yield the permittivity value of about 28 at 10 MHz. (C) 2011 Elsevier B.V. All rights reserved.

Melt-casting of Y3Al5O12 (YAG) ceramics by combustion synthesis under high gravity with the addition of glass

Liu, Guanghua; Li, Jiangtao; Guo, Shibin; Ning, Xiaoshan; Chen, Yixiang

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 24, L213-L215

Bulk YAG-based ceramics have been prepared by melt-casting under high gravity with the addition of glass. The glass helps to reduce the porosity and grain size of the casted ceramics. In the casting process, the glass melt can feed the shrinkage cavities produced during fast solidification of YAG. With the addition of glass, the grain boundary migration of YAG is pinned and thus grain growth is limited. The effect of the glass strongly depends on its chemical composition and crystallization behavior, where a higher SiO2 content is necessary to avoid devitrification. (C) 2011 Elsevier B.V. All rights reserved.

Nuclear-grade zirconium prepared by combining combustion synthesis with molten-salt electrorefining technique

Li, Hui; Nersisyan, Hayk H.; Park, Kyung-Tae; Park, Sung-Bin; Kim, Jeong-Guk; Lee, Jeong-Min; Lee, Jong-Hyeon

JOURNAL OF NUCLEAR MATERIALS, 413, 2, 107-113

Zirconium has a low absorption cross-section for neutrons, which makes it an ideal material for use in nuclear reactor applications. However, hafnium typically contained in zirconium causes it to be far less useful for nuclear reactor materials because of its high neutron-absorbing properties. In the present study, a novel effective method has been developed for the production of hafnium-free zirconium. The process includes two main stages: magnesio-thermic reduction of ZrSiO(4) under a combustion mode, to produce zirconium suicide (ZrSi), and recovery of hafnium-free zirconium by molten-salt electrorefining. It was found that, depending on the electrorefining procedure, it is possible to produce zirconium powder with a low hafnium content: 70 ppm, determined by ICP-AES analysis. (C) 2011 Elsevier B.V. All rights reserved.

Fabrication of porous Al2O3-MgAl2O4 ceramics using combustion-synthesized powders containing in situ produced pore-forming agents

Bai, JiaHai; Wei, Chuncheng; Meng, Fantao; Liu, Juncheng; Wang, Ping; Du, Qingyang; Tang, Zhuxing

MATERIALS LETTERS, 65, 11, 1559-1561

Novel pore-forming agents as well as other starting materials were produced in situ via a solution combustion process and were used to fabricate porous Al2O3-MgAl2O4 ceramics. The relative fuel-to-oxidant ratios (phi(e)) of 1.06, 1.28, 1.49 and 1.70 were achieved by varying the amount of starch in the precursors. Effects of phi(e) on the weight percent of the pore-forming agents in the powders, open porosity and Vickers hardness of the as-prepared porous ceramics were investigated. Experimental results revealed that the weight percent of the pore-forming agents in the powders increased significantly, while porosity of the as-prepared ceramics first increased and then decreased as phi(e) rose from 1.06 to 1.70. Meanwhile, pore size distribution became far narrower and the Vickers hardness of the porous ceramics increased as phi(e) increased. (C) 2011 Elsevier B.V. All rights reserved.

Separation and Characterization of C-70(C14H10) and C-70(C5H6) from an Acetylene-Benzene-Oxygen Flame

Weng, Qun-Hong; He, Qiao; Sun, Di; Huang, Hui-Ying; Xie, Su-Yuan; Lu, Xin; Huang, Rong-Bin; Zheng, Lan-Sun

JOURNAL OF PHYSICAL CHEMISTRY C, 115, 22, 11016-11022

Although derivatives of fullerenes are prevalent in the fullerene-producing flame, the chemistry of these derivatives has rarely been discussed in the previous literature. In this paper, two D-Sh-C-70 derivatives, C-70(C14H10) and C-70(C5H6), were isolated from the soot of an acetylene benzene combustion. On the basis of detailed MS, NMR, IR, and UV/vis analyses in combination with DFT calculations, the cycloadduct structures of C-70(C14H10) and C-20(C5H6) were identified. Both the anthracene (C14H10) and the cyclopentadiene (C5H6) adducts, supposed as the intermediate species produced during the combustion process, were characterized to bond at a [6,6] ring junction at the end of the olivary C-70 cage. The present work exemplifies the capture of possible intermediates by the C-70 fullerene from the flame and thus provides insight into the mechanism responsible for the formation of fullerene-containing soot.

Combustion synthesis of CaSc2O4:Ce3+ nano-phosphors in a closed system

Peng, Wen-Fang; Zou, Shao-Yu; Liu, Guan-Xi; Xiao, Quan-Lan; Zhang, Rui; Xie, Li-Juan; Cao, Li-Wei; Meng, Jian-Xin; Liu, Ying-Liang

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 23, 6673-6676

The CaSc2O4:Ce3+ nano-phosphors were successfully prepared by a single-step combustion method at an ignition temperature as low as 200 degrees C in a closed autoclave using glycine as a fuel and PEG4000 as a dispersant. The samples were characterized by X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscope (TEM). The results revealed that CaSc2O4:Ce3+ nano-phosphors can be conveniently prepared at an ignition temperature as low as 200 degrees C, which was much lower than that in the ordinary combustion methods. The optimized ignition temperature was 220 degrees C. The CaSc2O4:Ce3+ nano-phosphors give a uniform particle size in the range of 15-20 nm. The low ignition temperature and the addition of PEG4000 dispersant play important roles in the formation of small sized nanoparticles. The as-prepared nano-phosphors were incompact aggregates, but highly dispersed nano-phosphors can be obtained after further ultrasonic treatment. The CaSc2O4:Ce3+ nano-phosphors give satisfactory luminescence characteristic benefiting from the closed circumstance, in which cerium atoms can be isolated from the oxidizing atmosphere and non-fluorescent Ce4+ ions can be ruled out. The present highly dispersed CaSc2O4:Ce3+ nano-phosphors with efficient fluorescence are promising in the field of biological labeling, and the present low temperature combustion method is facile and convenient and can be applied as a universal process for preparing non-aggregate oxide nano-phosphors, especially those being sensitive to air at high temperature. (C) 2011 Elsevier B.V. All rights reserved.

Oscillatory Thermopower Waves Based on Bi2Te3 Films

Walia, Sumeet; Weber, Rodney; Latham, Kay; Petersen, Phred; Abrahamson, Joel T.; Strano, Michael S.; Kalantar-zadeh, Kourosh

ADVANCED FUNCTIONAL MATERIALS, 21, 11, 2072-2079

Exothermic chemical reactions that are coupled to Bi2Te3 porous layers, which are deposited onto terracotta or alumina (Al2O3) substrates, are used to produce self-propagating thermal waves that are guided along the surface. Nitrocellulose is used as the highly reactive chemical. Bi2Te3 is employed because of its large Seebeck coefficient and high electrical conductivity. For the Al2O3 based structures, the thermal conduction of the substrate results in strong oscillations of the output signals. Such thermopower waves produce a power as large as 10 mW and voltages as high as 150 mV. The power per mass ratio of the developed system is quite remarkable, namely, on the order of 1 kW kg(-1). Depending on the thermal conductivity of the substrate used, the wave front average propagation velocity is either slow (ca. 0.009 m s(-1) for terracotta) or much faster (on the order of 0.4 m s(-1) for Al2O3). We have used a mathematical model based on two coupled heat transport equations, in conjunction with the chemical reaction equation, to predict the behavior of the system, which describes the average propagation velocity and the time between oscillation peaks.

Preparation, Structural, and Electrical Studies of Polyaniline/ZnFe2O4 Nanocomposites

Prasanna, Gunderi Dhananjaya; Jayanna, Halepoojar Siddalingappa; Prasad, Vishnu

JOURNAL OF APPLIED POLYMER SCIENCE, 120, 5, 2856-2862

Polyaniline/ZnFe2O4 nanocomposites were synthesized by a simple and inexpensive one-step in situ polymerization method in the presence of ZnFe2O4 nanoparticles. The structural, morphological, and electrical properties of the samples were characterized by wide angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). WAXD and SEM revealed the formation of polyaniline/ZnFe2O4 nanocomposites. Infrared spectroscopy indicated that there was some interaction between the ZnFe2O4 nanoparticles and polyaniline. The dc electrical conductivity measurements were carried in the temperature range of 80 to 300 K. With increase in the doping concentration of ZnFe2O4, the conductivity of the nanocomposites found to be decreasing from 5.15 to 0.92 Scm(-1) and the temperature dependent resistivity follows ln rho(T) similar to T-1/2 behavior. The nanocomposites (80 wt % of ZnFe2O4) show a more negative magnetoresistance compared with that of pure polyaniline (PANI). These results suggest that the interaction between the polymer matrix PANI and zinc nanoparticles take place in these nanocomposites. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 120: 2856-2862, 2011

Luminescence and energy transfer of Mn2+ and Tb3+ in Y3Al5O12 phosphors

Mu, Zhongfei; Hu, Yihua; Wu, Haoyi; Fu, Chujun; Kang, Fengwen

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 22, 6476-6480

Mn2+ is an excellent luminescent ion with variable color from green, yellow to red in different hosts and has been widely utilized in recent years. The luminescent intensity of Mn2+ in many hosts is so low that the correlative application is restricted. In the present paper, two methods, i.e. employing a charge compensator and introducing a sensitizer, were adopted to enhance the luminescence of Mn2+ in Y3Al5O12 (YAG). By employing Si4+ as a charge compensator, the doping content of Mn2+ (x) in Y3MnxAl5-2xSixO12 can be lifted up to 0.4. Mn2+ in YAG emits orange light in a broad band. The peak wavelength shifts from 586 to 593 nm with the increasing x. The luminescent intensity of Mn2+ reaches its maximum when x = 0.1. Co-doping Tb3+ into Mn2+ doped YAG, the sensitization effect of Tb3+ on Mn2+ was observed clearly. The resonance energy transfer from Tb3+ to Mn2+ occurs because there is a well overlapping between emission spectrum of Tb3+ and excitation spectrum of Mn2+. A reasonable explanation for the sensitization effect of Tb3+ on the luminescence of Mn2+ was brought forward. (C) 2011 Elsevier B.V. All rights reserved.

Large-Scale Solidified TiB2-(Ti,W)C Composite Ceramics Prepared by Combustion Synthesis under High Gravity

Huang Xuegang; Zhang Long; Zhao Zhongmin; Yin Chun; Pan Chuanzeng

RARE METAL MATERIALS AND ENGINEERING, 40, , 199-202

By introducing WO3 and CrO3 into the combustion system as the oxidants in thermit, large-scale solidified TiB2-(Ti,W)C composite ceramics were prepared by combustion synthesis under high gravity. XRD, FESEM and EDS results show that the ceramic matrix is mainly composed of TiB2 and TiC, and (Ti,Cr,W)C1-x and (Cr,W,Ti)(3)B-2 phases are distributed between the TiB2 platelets and TiC spherical grains. As W content increases, volume fraction of (Cr,W,Ti)(3)B-2 increases, and volume fraction of TiB2 and TiC decrease with their grain size increasing. Mechanical properties show that as W content increases, Vickers hardness, fracture toughness and flexural strength of the ceramics decrease simultaneously due to the decreases in relative density of the ceramics and volume fraction of TiB2 platelets and TiC spherical grains.

Al2O3-ZrO2 (Y2O3) Eutectic Ceramics Preparing by Self-Pressing Assisting Combustion Synthesis under High Gravity

Zhao Zhongmin; Zhang Long; Song Yigang; Wang Weiguo

RARE METAL MATERIALS AND ENGINEERING, 40, , 203-206

By self-pressing assisting combustion synthesis under high gravity to avoid bulk solidification of the ceramic melt in closed space, large bulk Al2O3-ZrO2(Y2O3) eutectic ceramics without the shrinkage cavities were achieved. XRD, SEM and EDS results show the eutectic ceramics are composed of alpha-Al2O3, t-ZrO2 and a few m-ZrO2 phases. As the self-pressing force increases, the transformable t-ZrO2 increases in the ceramics, and the ceramic matrix consisting of rod-shaped eutectic colonies is refined, followed by the increase of the volume fraction and the average aspect ratio of the colonies, whereas the irregular ZrO2 crystals around the colonies gradually develop fine t-ZrO2 spherical crystals, leading to the increases in flexural strength, Vickers hardness and fracture toughness of the ceramics. When the self-pressing force reaches 0.8 MPa under high gravity of 200 g (g is the acceleration of gravity, i.e. 9.8 m.s(-2)), the maximum values in mechanical properties of flexural strength (1050 +/- 105) MPa, Vickers hardness (17.8 +/- 1.5) GPa and fracture toughness (14.2 +/- 1.0) MPa.m(1/2) are achieved simultaneously.

Self-Propagating High-Temperature Synthesis (SHS) of Ti-Containing Ceramic Composites under Ultra-High Gravity

Liu Guanghua; Li Jiangtao; Chen Yixiang; Ning Xiaoshan

RARE METAL MATERIALS AND ENGINEERING, 40, , 262-264

Ti-containing ceramic composites were prepared by self-propagating high-temperature synthesis under ultra-high gravity. The effects of starting compositions and the ultra-high gravity field on the phase assemblage and microstructure of the products were discussed. The experimental results show that, the ultra-high gravity field has an evident influence on both the macro appearance and microstructure of the products. The products synthesized under ultra-high gravity have thicker layers and more homogenous microstructure with well-developed faceted grains and narrower grain size distribution. The phase assemblage of the products is mostly determined by the starting composition and little affected by the ultra-high gravity field.

Synthesis and Sintering Properties of La0.8Ca0.1Sr0.1CrO3 Powders

Luo Linghong; Liao Huamei; Wu Yefan; Cheng Liang; Shi Jijun; Hou Bingxue

RARE METAL MATERIALS AND ENGINEERING, 40, , 302-305

Low temperature combustion synthesis was used to prepare La0.8Ca0.1Sr0.1CrO3 nanopowders by different complex systems (citric-ethylene, glycine-citric and EDTA-citric-ethylene) and under different conditions of complex processes. The sintering property was investigated. The results show that high sintering activity La0.8Ca0.1Sr0.1CrO3 nano powder was synthesized with the EDTA alone chelated with Ca2+ ion or Sr2+ ion while the citric alone chelated with La3+ ion or Cr3+ ion in EDTA-citric-ethylene system, and then a mixture of complex solution process conditions. The theoretical density of ceramics doped with 0.6% CaF2 and sintered at 1250 degrees C reaches to 96.79%, improved by 3.15% compare with that of ceramics without CaF2.

Effect of Burning Rate on Solidification Microstructure of Thermite Welds

Yuan Xuanyi; Lu Huafei; Chen Kexin; Nin Xiaoshan

RARE METAL MATERIALS AND ENGINEERING, 40, , 440-442

A novel method of thermite welding was presented. A hand-operated portable welding can be conveniently realized by using thermite welding pencil without any outside energy sources and auxiliary equipments. Different thermite burning rates were obtained by varying addition of micro-silica fume and wollastonite as diluent respectively. The results show that massive shrinkage porosities and inclusions were formed in the fusion zone at high burning rate. With decreasing burning rate, those defects disappeared gradually. However, with further decreased burning rate, lots of porosities were obtained in the fusion zone. The investigation demonstrates that the change in microstructure of weld is most likely related to the solidification process of weld pool at different burning rates.

Study on Al2O3-SiO2-CaO Slags of Manual SHS Welding

Li Zhizun; Xin Wentong; Hu Renxi; Wu Yongsheng; Qu Lifeng

RARE METAL MATERIALS AND ENGINEERING, 40, , 627-630

SiO2 and CaO were added as slagging elements and the effect of their addition were studied. Results show that slagging addition accelerates the separation for slag from the weld pool. As the addition amount of SiO2 and CaO increases, the combustion velocity of the rod becomes lower and the density of the slag also changes, but without obvious changing rule. In view of the quality and the controlling of welding, the appropriate addition amount of SiO2 and CaO are 0.6-0.9 g and 0.3-0.6 g respectively. SEM results indicate that the microstructure of the manual SHS welding slag includes glass and crystalloid. XRD analysis show that the slag has 5 phases. A few of slagging inclusion appear in the fractured surface of welded joint, indicating some slag has not separated from the weld metal. The tensile strength of the joint reaches 350 MPa, meeting the requirement of mechanical properties for emergency welding.

Combustion synthesis of Eu2+ and Dy3+ activated Sr-3(VO4)(2) phosphor for LEDs

Singh, Roshani; Dhoble, S. J.

BULLETIN OF MATERIALS SCIENCE, 34, 3, 557-562

Combustion synthesis and photoluminescence (PL) characterization of Sr-3(VO4)(2):Eu,Dy phosphors are presented in this paper. PL emission of Sr-3(VO4)(2):Eu phosphor shows green broad emission band centring at 511 nm and a red sharp band at 614 nm by excitation wavelength of 342 nm. The PL emission spectrum of Sr-3(VO4)(2):Dy phosphor exhibits an intense blue emission peak at 479 nm, yellow broad band centring at 573 nm and red band at 644 nm by the excitation wavelength of 426 nm in near visible blue region. The excitation wavelength of Eu (342 nm) and Dy (426 am) activated Sr-3(VO4)(2) phosphor are well matched with the excitation of near UV excited solid state lighting and blue chip excitation of light emitting diodes, respectively. The effect of Eu2+ and Eu3+ ions concentration on the emission intensity of Sr-3(VO4)(2) was also investigated. The Sr-3(VO4)(2):Eu is a potential green and red emitting phosphor as well as Sr-3(VO4)(2):Dy is blue and yellow emitting phosphor for solid state lighting i.e. white LEDs. The XRD and SEM characteristics of Sr-3(VO4)(2) materials was also reported in this paper.

Estimation of Kinetic Parameters for Combustion Synthesis of FeAl Intermetallic Compound by Dipping Experiment of Fe Wire into Al Melt

Hibino, Atsushi

JOURNAL OF THE JAPAN INSTITUTE OF METALS, 75, 6, 332-340

The reaction rate for the formation of Fe-Al intermetallic compounds was examined by dipping experiment of Fe wire into Al melt in the temperature range between 973 K and 1373 K, to determine the kinetic parameters of combustion synthesis of FeAl. A piece of Fe wire and Al powder were put into an alumina crucible, and vacuum-sealed in a quartz tube. The tube was held in an electric furnace to promote the compound formation reaction. A microstructure observation and SEM-EDX analysis of the dipped Fe wire were performed. It was found that the compound formation reaction occurred at the interface between the molten Al and the Fe wire, and a cylindrical Fe(2)Al(5) layer was formed in the wire. The thickness of the formed layer depended on the holding time and the dipping temperature. The reaction process has been similar to the combustion synthesis of FeAl intermetallic compound. Therefore, the kinetic parameters could be determined by the dipping experiment. The experimental data have been analyzed using a cylindrical model which took into account the diffusion process of Al in the Fe(2)Al(5) compound layer and chemical reaction process on the interface between Fe(2)Al(5) and Fe. The diffusion coefficient, D(Al) and the reaction rate constant, k(c) were estimated. The curves were calculated by using the obtained kinetic parameters and were in satisfactory agreement with the experimental values.log(10) D(Al)/m(2).s(-1) = -1887/T - 8.369log(10) k(c)/mol.m(-2).s(-1) = 3177/T + 1.839

Facile synthesis of nanosized Li4Ti5O12 in supercritical water

Nugroho, Agung; Kim, Su Jin; Chung, Kyung Yoon; Cho, Byung-Won; Lee, Youn-Woo; Kim, Jaehoon

ELECTROCHEMISTRY COMMUNICATIONS, 13, 6, 650-653

The high rate capability of lithium titanate (Li4Ti5O12, LTO) is prepared using supercritical hydrothermal synthesis (SHS). The particle size, morphology, crystalline structure and electrochemical properties are analyzed and compared to the properties of LTO particles prepared using a typical solid-state method (SS). Nanosized LTO particles having a high crystallinity are produced in a very short reaction time (15 min) and with subsequent calcination at a low temperature (700 degrees C) or it can be produced in 6h without calcination. The size of SI IS particles is much smaller (20-200 nm, BET surface area of 10-38 m(2) g(-1)) than that of the SS particles (micron size, BET surface area of 5.4 m(2) g(-1)). The SHS LTO particles are highly phase-pure while the SS particles have impurity phases such as anatase TiO2, rutile TiO2 and Li2TiO3. The SHS LTO show higher initial discharge capacity (212 mAhg(-1)) and better cycling stability compared to those of the SS LTO particles (149 mAhg(-1)). Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Electrical properties of dense and nanocrystalline Sm3+-doped Ce1-xSmxO2-delta (0.05 a parts per thousand currency sign x a parts per thousand currency sign 0.3) electrolytes for IT-SOFCs

Park, K.; Hwang, H. K.

METALS AND MATERIALS INTERNATIONAL, 17, 3, 505-508

Sm3+-doped Ce1-xSmxO2-delta (0.05 a parts per thousand currency sign x a parts per thousand currency sign 0.3) nano-sized powders for solid electrolytes were synthesized by a solution combustion method, using aspartic acid as a combustion fuel. The calcined Ce1-xSmxO2-delta powders were a ceria-based single phase with a cubic fluorite structure. The nano-sized Ce(1-x)SmxO(2-delta) powders provided a high density, ultra-fine grain size, and high electrical conductivity even at a low sintering temperature of 1400 A degrees C. The grain size and relative density of the Ce1-xSmxO2-delta pellets ranged from 329 nm to 496 nm and from 91.9 % to 99.2 %, respectively. The grain size and density of the Ce1-xSmxO2-delta pellets decreased with an increase of Sm3+ content. The electrical conductivity of the Ce(1-x)SmxO(2-delta) increased with an increase of Sm3+ content up to x = 0.25 and then decreased with higher Sm3+ content. The maximal electrical conductivity (0.105 Scm(-1)) was obtained with Ce0.75Sm0.25O2-delta at 800 A degrees C.

Synthesis of dense ceramics of single-phase mayenite (Ca12Al14O32)O

Tolkacheva, A. S.; Shkerin, S. N.; Plaksin, S. V.; Vovkotrub, E. G.; Bulanin, K. M.; Kochedykov, V. A.; Ordinartsev, D. P.; Gyrdasova, O. I.; Molchanova, N. G.

RUSSIAN JOURNAL OF APPLIED CHEMISTRY, 84, 6, 907-911

The nanoporous material mayenite was synthesized by two methods: solid-phase and self-propagating high-temperature (combusting) (SHS) syntheses. The structure of the materials was determined by the X-ray diffraction analysis and IR and Raman spectroscopy.

Current-conducting coatings based on heat-resistant titanium compounds obtained by self-propagating high-temperature synthesis

Shul'pekov, A. M.; Lyamina, G. V.; Kal'yanova, T. V.; Lepakova, O. K.; Maksimov, Yu. M.

RUSSIAN JOURNAL OF NON-FERROUS METALS, 52, 3, 275-279

Titanium carbide, silicide, and carbosilicide are obtained by self-propagating high-temperature synthesis. The microstructure, phase composition, and properties of these compounds are given. Materials in the form of powders were used to form current-conducting polymer doughs. The influence of the type and content of the filling agent, the temperature of the thermal treatment, and the composition of the polymer binder on the electric resistance of polymer coatings is investigated. It is established that the binders that provide the lowest resistance of doughs are PMPP and PPG polymers, and the corresponding filling agent is titanium carbosilicide. The working temperature of doughs containing PMFP and PFG should not exceed 250A degrees C, that of SKTN should not exceed 150A degrees C, and the mixture of epoxy resin and PMFP and PFG should not exceed 300A degrees C.

Nanostructured Ti-Cr-B-N and Ti-Cr-Si-C-N coatings for hard-alloy cutting tools

Kiryukhantsev-Korneev, F. V.; Sheveiko, A. N.; Komarov, V. A.; Blanter, M. S.; Skryleva, E. A.; Shirmanov, N. A.; Levashov, E. A.; Shtansky, D. V.

RUSSIAN JOURNAL OF NON-FERROUS METALS, 52, 3, 311-318

Nanostructured Ti-Cr-B-N and Ti-Cr-Si-C-N coatings with various contents of chromium and nitrogen are obtained by the magnetron sputtering of multiphase composite targets. Their structure and phase composition are investigated by X-ray phase analysis, transmission and scanning electron microscopy, X-ray photoelectron spectroscopy, and optical emission glow-discharge spectroscopy. The Ti-Cr-B-N and Ti-Cr-Si-C-N coatings are based on the fcc phase with texture (100) and crystallite size < 25 nm. The Si3N4-based hexagonal phase was also revealed in the Ti-Cr-Si-C-N coatings. An investigation into the properties of coatings with the use of methods of nanoindentation, scratch testing, and by performing tribological tests showed that they have a hardness of up to 30 GPa, an adhesion strength no lower than 35 N, and their friction coefficient falls in the range of 0.35-0.57. Coatings also possess high thermal stability, resistance to oxidation, and corrosion stability in a 1N H2SO4 solution. The data obtained in tests of hard-alloy cutting tools indicate that the deposition of nanostructured Ti-Cr-B-N and Ti-Cr-Si-C-N coatings increases its resistance by a factor of 11-17.

Synthesis of Suitable SiO2 Nano Particles as the Core in Core-Shell Nanostructured Materials

Ghahari, Mehdi; Aghababazadeh, Roya; Ebadzadeh, Touradj; Mirhabibi, Alireza; Brydson, Rik; Fabbri, Paola; Najafi, Farhod

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 11, 6, 5311-5317

The effect of surfactant on the luminescent intensity of SiO2@Y2O3:Eu3+ particles with a core shell structure is described. Core-shell particles are used in phosphor materials and employing spherical particles with a narrow size distribution is vital for the enhancement of luminescent properties. Three kinds of different surfactants were used to synthesis SiO2 nano particles via a sol gel process. The results demonstrated that comb polycarboxylic acid surfactant had a significant influence on the morphology and particle size distribution. Somehow, particles with 100 nm size and narrow size distribution were produced. These particles had relatively uniform packing, unlike particles produced with other surfactants or without surfactant which had irregular assembly. The photoluminescence intensity of SiO2@Y2O3:Eu3+ particles that was synthesized by comb polycarboxylic acid surfactant was higher than those which were produced without surfactant.

A New Red-Emitting La1-xPrxSr2AlO5 Phosphor Powder Prepared by Combustion Synthesis

Rodriguez-Garcia, C. E.; Tejeda, E. M.; Castillon, F. F.; Hirata, G. A.

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 11, 6, 5587-5591

New red luminescent powders of La1-xPrxSr2AlO5 (x = 0.01 at.) were prepared by the combustion synthesis method. Microstructural properties were characterized by using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The La1-xPrxSr2AlO5 X-ray diffraction pattern revealed a tetragonal phase. Morphology of the grains showed nanobars with sizes of approximately 550 nm in length. Photoluminescence, cathodoluminescence and diffuse reflectance were analyzed in detail. Photoluminescence revealed two narrow emission peaks located at lambda(em1) = 497 nm (green) and lambda(em2) = 620 nm and a single maximum excitation peak of lambda(ex) = 287 nm. The cathodoluminescence spectrum confirmed the peaks detected by photoluminescence analysis. The absorbance spectrum showed broad absorption with a maximum around lambda = 280 nm, which agrees with the maximum excitation peak detected by photoluminescence.

Combustion synthesis of TiCxN1-x-TiB2 ceramic composites in a high-gravity field

Liu, Guanghua; Li, Jiangtao; Ning, Xiaoshan; Chen, Yixiang

MATERIALS RESEARCH BULLETIN, 46, 6, 958-961

TiCxN1-x-TiB2 ceramic composites were prepared by combustion synthesis in a high-gravity field in air. The high-gravity field caused no change in phase composition but resulted in reduced delamination and grain refinement in the microstructure of the products. In a high-gravity field of 100g, well-developed faceted grains with a narrow size distribution were obtained. It is proposed that the combustion reaction happened by a pulsating combustion mode and the pulsating period was prolonged by the high-gravity field. (C) 2011 Elsevier Ltd. All rights reserved.

Solution-combustion: the versatile route to synthesize silver nanoparticles

Sharma, Poonam; Lotey, Gurmeet Singh; Singh, Sukhpreet; Verma, N. K.

JOURNAL OF NANOPARTICLE RESEARCH, 13, 6, 2553-2561

The solution-combustion synthesis (SCS) method was used to prepare silver nanoparticles using glycine and citric acid as fuels. The different combination of fuel to oxidant ratio was used to prepare Ag nanoparticles and its effect on optical spectra, structure and the morphology explored. The purposed method is rapid, effective, cheap and convenient. Silver nanoparticles with different sizes and shapes were synthesized depending upon the different oxidant/fuel ratios. The nanoparticles were characterized using transmission electron microscopy, X-ray diffraction and ultraviolet-visible absorption spectroscopy. Histograms were drawn to compare the mean particle size of synthesized nanoparticles. It was found that citric acid was better fuel as compared to glycine as it results in the more spherical symmetrical nanoparticles, which are supported by various characteristic studies.

Statistical Experimental Design Approach for the Solvothermal Synthesis of Nanostructured Tantalum Carbide Powders

Kelly, James P.; Graeve, Olivia A.

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 6, 1706-1715

We report on the preparation of tantalum carbide nanopowders via a modified solvothermal synthesis route by using experimental design principles. The reaction proceeds by self-propagating behavior in a molten metal after thermal-ignition of tantalum chloride, carbon, and a metal reductant. A 4 x 4 x 3 experimental design matrix was performed, without replication, to observe the effects of carbon stoichiometry, reductant stoichiometry, and reductant type on process response variables concerning phase purity, compound stoichiometry, crystallite size, particle size, and surface characteristics. Statistical verifications of the observed effects were performed using a 2 x 2 x 2 experimental design matrix with replication. Eleven conditions resulted in phase-pure tantalum carbide, with an additional four nonoxide conditions with low secondary-phase content. The stoichiometry (x in TaC(x)) ranged from 0.92 to 0.96, the average crystallite size ranged from 24 to 68 nm, the specific surface area ranged from 25 to 66 m2/g, and the average particle size ranged from 93 to 123 nm, indicating a low level of agglomeration.

Amorphous, Monoclinic, and Tetragonal Porous Zirconia Through a Controlled Self-Sustained Combustion Route

Raghavendra, Venugopal B.; Naik, Swati; Antony, Meera; Ramalingam, Gopalakrishnan; Rajamathi, Michael; Raghavan, Srinivasan

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 6, 1747-1755

Porous, large surface area, metastable zirconias, are of importance to catalytic, electrochemical, biological, and thermal insulation applications. Combustion synthesis is a very commonly used method for producing such zirconias. However, its rapid nature makes control difficult. A simple modification has been made to traditional solution combustion synthesis to address this problem. It involves the addition of starch to yield a starting mixture with a "dough-like" consistency. Just 5 wt% starch is seen to significantly alter the combustion characteristics of the "dough." In particular, it helps to achieve better control over reaction zone temperature that is significantly lower than the one calculated by the adiabatic approximation typically used in self-propagating high-temperature synthesis. The effect of such control is demonstrated by the ability to tune dough composition to yield zirconias with different phase compositions from the relatively elusive "amorphous" to monoclinic (> 30 nm grain size) and tetragonal pure zirconia (< 30 nm grain size). The nature of this amorphous phase has been investigated using infrared spectroscopy. Starch content also helps tailor porosity in the final product. Zirconias with an average pore size of about 50 mu m and specific surface area as large as 110 m2/g have been obtained.

Morphological development and oxidation of elongated beta-SiA1ON material

Hou, Xin-mei; Yue, Chang-Sheng; Singh, Ankit Kumar; Zhang, Mei; Chou, Kuo-Chih

CORROSION SCIENCE, 53, 6, 2051-2057

Elongated beta-SiA1ON whiskers and ribbons have been synthesized at 1700 K under flowing nitrogen atmosphere. A series of experiments have been performed using thermogravimetry (TG) and thermal field emission scanning electron microscope (FE-SEM) to investigate its oxidation resistance. The results showed that the synthesized beta-SiA1ON material possessed good oxidation resistance and the shape can be well kept up to 1373 K. Chou's model has been used to investigate the oxidation kinetics, from which it was concluded that beta-SiA1ON in shape of ribbons has better oxidation resistance than that in shape of whisker from the view point of a new index of the characteristic oxidation time. (C) 2011 Elsevier Ltd. All rights reserved.

Low Temperature NH3 Selective Catalytic Reduction of NOx over Substituted MnCr2O4 Spinel-Oxide Catalysts

Zamudio, Miguel A.; Russo, Nunzio; Fino, Debora

INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 50, 11, 6668-6672

The present work describes the development of Mn1-xMxCr2O4 (M = Mg, Ca; x = 0-0.1) substituted spinel catalysts prepared via gel combustion synthesis for the low-temperature selective catalytic reduction (SCR) of NOx with NH3. The catalysts have been characterized by means of X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FESEM) and temperature programmed reduction (TPR) analyses, whereas their catalytic activity has been tested in a temperature programmed reaction (TPRe) apparatus over a temperature range of 100-200 degrees C (W/F= 0.072 g.s.cm(-3)) in the presence of oxygen. The catalytic activity of alkali earth-metal substituted Mn-Cr spinels is compared with that of the stoichiometric MnCr2O4 in order to assess the effect of the substitutions. All the spinet catalysts have shown both high NO conversion and high selectivity to N-2. Mn0.95Ca0.05Cr2O4 has shown the best performance, reaching an NO conversion of 96% and a selectivity to N-2 of 97% at 125 degrees C. All the catalysts were then deposited by means of a modified dip-coating procedure over cordierite honeycomb monoliths and tested in a lab-scale test rig. The monolith catalyzed with the Mn0.95Ca0.05Cr2O4 spinel showed the best performance, reaching an NO conversion of 87.4% at 200 degrees C, with a good selectivity to N-2 (94.8%). When the catalyzed monoliths were also tested in the presence of 10 vol % of water vapor, an activity decrease was observed. The correlation between the reducibility of the B site, determined from TPR experiments, and the spinels catalytic activity order is discussed.

Synthesis and characterization of Ni0.6Zn0.4Fe2O4 nano-particles obtained by auto catalytic thermal decomposition of carboxylato-hydrazinate complex

Gawas, U. B.; Verenkar, V. M. S.; Mojumdar, S. C.

JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 104, 3, 879-883

Ni0.6Zn0.4Fe2O4 nano-particles have been synthesized by self-propagating auto-combustion of nickel zinc ferrous fumarato-hydrazinate complex. The precursor complex has been characterized by chemical analysis, IR, AAS, thermal analysis and isothermal mass loss studies. The precursor on ignition undergoes self-propagating auto combustion to give Ni0.6Zn0.4Fe2O4. The X-ray diffraction studies confirmed the single phase formation of nano-size 'as synthesized' Ni0.6Zn0.4Fe2O4. TEM observation showed the average particle size to be 20 nm. Infrared and magnetization studies were also carried out on the 'as synthesized' Ni0.6Zn0.4Fe2O4. The lower value of saturation magnetization and higher Curie temperature of 'as synthesized' ferrite also hint at the nano size nature.

Effect of mechanical activation of reagents' mixture on the high-temperature synthesis of Al2O3-TiB2 composite powder

Mousavian, R. Taherzadeh; Sharafi, S.; Roshan, M. R.; Shariat, M. H.

JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 104, 3, 1063-1070

A powder mixture of Al/TiO2/H3BO3 = 10/3/6 in molar ratio was used in this study to form the Al2O3-TiB2 ceramic composite via thermite reactions (combustion synthesis). As no combustion synthesis occurred for an unmilled sample in a furnace, the mixture was milled in a planetary ball-mill for various milling times, and the as-milled samples were in situ synthesized in the furnace at a heating rate of 10 A degrees C/min. The differential scanning calorimetry (DSC) measurements were performed with the same heating rate on the unmilled and the as-milled samples to evaluate the influences of the milling on the mechanisms and efficiencies of reactions. Although no combustion synthesis occurred for the unmilled sample in the furnace, two exothermic peaks were detected in its DSC curve after the melting of the Al. For the as-milled samples, significant changes revealed in the DSC curves, suggest that the milling process before the combustion synthesis changed the mechanisms and efficiencies of reactions. In addition, the intensity and the temperature of the exothermic peaks in the DSC curves changed by increasing the milling time. According to the XRD analyses, by enhancing the milling time, the purity of the final products would increase, confirming that the efficiency of the reactions increased. Finally, the microstructures of the as-milled and as-synthesized samples were examined by a SEM, and it was shown that the morphology of the reactant powders was altered by increasing the milling time.

Thermal stability and reaction properties of passivated Al/CuO nano-thermite

Wang, Jeff; Hu, Anming; Persic, John; Wen, John Z.; Zhou, Y. Norman

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 72, 6, 620-625

Thermal stability and reaction properties of Al-CuO system, a mixture of 50-200 nm aluminum nanoparticles passivated by nitrocellulose and 12 nm copper (11) oxide, were investigated with microstructure characterization, differential thermal analysis (DTA), and thermogravimetric analysis (TGA). Transmission electron microscopy observation confirmed that the passivation coating successfully hinders the oxidization. TGA revealed that the passivation shell does not influence the ignition temperature of the thermite reaction. Reaction chemistry of the nano-thermite was elucidated by heating the composite both in inert ambient and vacuum. It was found that the thermite reaction composes of three continuing steps: At 570 degrees C, Al is oxidized into Al(2)O(3) by reacting with CuO, which forms Cu(2)O and produces a significant amount of heat. Subsequently two endothermic reactions occur. Starting at 800 degrees C, alumina reacts with Cu(2)O and forms CuAlO(2). Above this temperature CuAlO(2) will decompose and eventually produce alumina, Cu, and O(2) at 1000 degrees C. Since the nano-thermite reaction pathway differs greatly from bulk thermite reactions, these results are important to develop a nano-thermite platform that can be used for a novel low cost, low temperature, and copper based microjoining and advance IC packaging. (C) 2011 Elsevier Ltd. All rights reserved.

Combustion synthesis of Ce3+, Eu3+ and Dy3+ activated NaCaPO4 phosphors

Shinde, K. N.; Dhoble, S. J.; Kumar, Animesh

JOURNAL OF RARE EARTHS, 29, 6, 527-535

The preparation of NaCaPO4 doped with rare earth (RE) ions Ce3+, Eu3+ and Dy3+ by combustion method was described. Under UV excitation (251 nm) of NaCaPO4:Ce3+ showsd emission (367 nm) in UV range. When NaCaPO4:Dy3+ phosphor was excited at 349 nm, the emission spectrum showed intense bands at 482 nm (blue) and 576 nm (yellow). In Eu activated NaCaPO4 phosphor, the emission spectrum showed a dominant peak at 594 nm (orange) while others were at 614 and 621 nm (red) when excited at 393 nm. The prepared phosphor was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence (PL) measurement. Thus, the photoluminescence behavior of NaCaPO4:Ce3+ was strongly suggested for scintillator. Likewise, Eu3+ and Dy3+ activated NaCaPO4 phosphors were recommended for near-UV white light-emitting diodes (LEDs).

Synthesis and characterization of hybrid films of polyimide and silica hollow spheres

Lee, Sang Joon; Choi, Myeon-Cheon; Park, Sung Soo; Ha, Chang-Sik

MACROMOLECULAR RESEARCH, 19, 6, 599-607

Hybrid films were prepared with pyromellitic dianhydride (PMDA)/4,4'-oxydianiline (ODA) polyimide (PMDA-ODA PI) and amino-modified silica hollow spheres (a-SHS). Scanning electron microscopy confirmed the formation of silica hollow spheres without aggregation or deformation. Thermogravimetric analyses showed that the thermal stability of the hybrid films was superior to those of the neat PMDA-ODA PI films. The dielectric constant of the PMDA-ODA PI films was reduced from 3.33 to 2.24 for a hybrid film containing 5 wt% silica hollow spheres. On the other hand, when the content of silica hollow spheres was > 7 wt%, the dielectric constant increased due to the aggregation and collapse of silica hollow spheres. The tensile properties of the hybrid films degraded with increasing a-SHS content compared to those of the neat PMDA-ODA PI film, whereas they were still sufficient for applications as a low-k passivation coating material.

Determination of the local site occupancy of Eu3+ ions in ZnAl2O4 nanocrystalline powders

Silva, Da; Abreu, Alison; Davolos, M. R.; Rosaly, Marian

OPTICAL MATERIALS, 33, 8, 1226-1233

Once lanthanides-doped ZnAl2O4 have attracted attention for highly efficient phosphors and due to the complexity of this system, this work is focused in the understanding of the local site occupancy of the doped ions in the spinet structure by using Eu3+ as a spectroscopic probe. Europium(III)-doped ZnAl2O4 nanocrystalline powder samples were prepared by the Pechini method. Different heat treatment temperatures and doping levels were investigated. No impurities of residual Eu2O3 were observed for the samples with Eu3+ doping levels up to 10 at.%, indicating that the doping ions are diluted into the host. The luminescence spectroscopy from the Eu3+ ions revealed the Eu3+ ions might occupy at least two non-centro-symmetric sites and that the occupation ratio might be dependent on the heat treatment or doping level. It is observed that one site is related to a high covalent environment while at the other the ionic character prevails. This behavior is in agreement with the luminescence lifetime results. The decay curves were fitted according to double first-order decay model and it was confirmed the covalence difference between the two sites and also the population variation with the doping level. There are strong evidences that the europium ions substitute for the aluminum ones in the normal spinel structure. It cannot be disregarded that the dopant ions may be present on the surface of the particles. (C) 2011 Elsevier B.V. All rights reserved.

Aging of electrolyte La(0.88)Sr(0.12)Ga(0.82)Mg(0.18)O(3-delta) made using magnetic-pulse compaction

Nikonov, A. V.; Shkerin, S. N.; Lipilin, A. S.; Korneva, A. A.; Krasil'nikov, V. N.; Gyrdasova, O. I.

RUSSIAN JOURNAL OF ELECTROCHEMISTRY, 47, 6, 733-736

Ceramics of the La(0.88)Sr(0.12)Ga(0.82)Mg(0.18)O(3 - delta) solid electrolyte was obtained by magnetic-pulse compaction (MPC) of a powder synthesized using the self-propagating high-temperature synthesis technique with further sintering at 1380A degrees C. Conductivity and its change in time were studied. It was shown that conductivity of fresh samples coincides with conductivity of ceramics obtained using the classical solid-phase synthesis. It was established that conductivity of electrolyte decreased by 18% during isothermal exposure at 700A degrees C for 1 year.

Solvent effect in monoclinic to hexagonal phase transformation in LaPO4:RE (RE=Dy3+, Sm3+) nanoparticles: Photoluminescence study

Phaomei, Ganngam; Singh, W. Rameshwor; Ningthoujam, R. S.

JOURNAL OF LUMINESCENCE, 131, 6, 1164-1171

Nanosized phosphor materials, LaPO4:RE (RE=Dy3+, Sm3+) have been synthesized using water, dimethyl sulfoxide (DMSO), ethylene glycol (EG) and mixed solvents at a relatively low temperature of 150 degrees C. X-ray diffraction (XRD) study reveals that as-prepared nanoparticles prepared in DMSO and EG are well crystalline and correspond to monoclinic phase. In the mixed water-DMSO or water-EG solvents, XRD patterns are in good agreement with hexagonal phase, but transformed to monoclinic phase at higher temperature of 900 degrees C. TEM images show well-dispersed and rice-shaped nanoparticles of diameter 5-10 nm, length of 13-37 nm for Dy3+-doped LaPO4 and diameter of 25-35 nm, length of 73-82 nm for Sm3+-doped LaPO4. Dy3+-doped LaPO4 shows two prominent emission peaks at 480 and 572 nm corresponding to E-4(9/2)-> H-6(15/2) (magnetic dipole) and E-4(9/2)-> H-6(13/2) (electric dipole) transitions, respectively. Similarly, for Sm3+-doped LaPO4, three prominent emission peaks at 561,597 and 641 nm were observed corresponding to (4)G(5/2)-> H-6(5/2), (4)G(5/2)-> H-6(7/2) (magnetic dipole) and (4)G(5/2)-> H-6(9/2) (electric dipole) transitions, respectively. The luminescence intensity of the sample prepared in EG is more than that of DMSO or mixed solvents. Enhancement of luminescence is also observed after heat-treatment at 900 degrees C due to removal of quencher such as water, organic moiety and surface defects/dangling bonds. The samples are re-dispersible in polar solvent and can be incorporated in polymer film. (C) 2011 Elsevier B.V. All rights reserved.

Multi-band and broadband acoustic metamaterial with resonant structures

Ding, Chang-Lin; Zhao, Xiao-Peng

JOURNAL OF PHYSICS D-APPLIED PHYSICS, 44, 21, 215402-

We design an acoustic metamaterial (AM) with multi-band of negative modulus composed of different sized split hollow spheres (SHSs). From acoustic transmitted experiment, the AM exhibits simultaneously negative modulus at frequencies 914, 1298 and 1514 Hz. Based on the multi-band designed concept, broadband AM is fabricated by arraying gradually sized SHS. The transmission results indicate that this medium can achieve negative modulus at the frequency range from 900 to 1500 Hz. This kind of broadband AM is very convenient to couple with other structures to gain the double-negative AM.

Reactions leading to ignition in fully dense nanocomposite Al-oxide systems

Ermoline, Alexandre; Schoenitz, Mirko; Dreizin, Edward L.

COMBUSTION AND FLAME, 158, 6, 1076-1083

Aluminum-metal oxide energetic compositions with components mixed on the nano-scale are substantially more reactive than conventional thermites and are of interest as potential additives to propellants, explosives, and pyrotechnics. For such nanocomposite materials prepared by Arrested Reactive Milling (ARM), the exothermic reactions leading to ignition were detected to begin at relatively low temperatures. These materials are prepared by mechanical processing at room temperature, and the nature of the interface present between aluminum and the oxidizer (metal oxide, e.g., CuO, MoO3, Bi2O3, etc.) is unknown. Experiments using a Thermal Activity Monitor (TAM III) quantify the reaction rates between aluminum and CuO at temperatures between 303 and 373 K. Results of the present TAM III measurements and results of earlier measurements using differential scanning calorimetry for the same 2Al center dot 3CuO nanocomposite are interpreted considering two different reaction models. The rate-limiting step is described either as a conventional thermally activated diffusion, or using the Cabrera-Mott model developed originally for oxidation of fresh metal surfaces. It is shown that the thermally activated diffusion model is inadequate for description of the low-temperature reactions observed in nanocomposite thermites prepared by ARM. The Cabrera-Mott model provides a description qualitatively matching the experimental results; achieving the quantitative match is expected to be possible by adjusting the model parameters. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Enabling and controlling slow reaction velocities in low-density compacts of multilayer reactive particles

Fritz, Gregory M.; Joress, Howie; Weihs, Timothy P.

COMBUSTION AND FLAME, 158, 6, 1084-1088

Uniformly-shaped, micron-scale particles with nanoscale layers of Al and Ni and a volume fill of 20% +/- 1% were fabricated by depositing Al/Ni multilayer films onto mesh substrates with a square weave. The films break into individual particles at the weave intersections during removal and the resulting particles have lengths equal to three times their widths. Exothermic formation reactions in loose compacts of these particles were shown to self-propagate up to 200 times slower than reactions in continuous multilayer foils with similar chemistries, layer thicknesses and ignition thresholds. The difference is attributed to the time delay associated with heating each subsequent particle to the point of ignition as the reaction propagates. The results presented here demonstrate an ability to separately control the rate of mass diffusion and the rate of thermal diffusion in particle compacts and thereby produce slow and stable self-propagating formation reactions. Such reactions are desirable for both industrial and military applications such as chemical time delays. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Ionic conductivity, sintering and thermal expansion behaviors of mixed ion conductor BaZr0.1Ce0.7Y0.1Yb0.1O3-delta prepared by ethylene diamine tetraacetic acid assisted glycine nitrate process

Zhou, Xiaoliang; Liu, Limin; Zhen, Jiangman; Zhu, Shengcai; Li, Baowen; Sun, Kening; Wang, Peng

JOURNAL OF POWER SOURCES, 196, 11, 5000-5006

BaZr0.1Ce0.7Y0.1Yb0.1O3-delta as a candidate electrolyte material is prepared by ethylene diamine tetraacetic acid assisted glycine-nitrate process. After calcining at 900 degrees C, the single-phase perovskite is obtained due to the better distribution of starting materials and the more feasible reaction kinetic conditions than solid state reaction method. The relative densities reach 96.8 and 98.4% respectively after sintering the pressed pellets at 1280 and 1400 degrees C for 10 h. In humidified oxygen the ionic conductivities are 0.015, 0.045, 0.101 and 0.207 S cm(-1) at 500, 600, 700 and 800 degrees C, respectively. In air and humidified oxygen the activation energies for ionic conductivity are 66.1 and 68.9 kJ mol(-1). In humidified hydrogen, however, different activation energies occur in low and high temperature ranges. The thermal expansion curve inflections at 500-800 degrees C with respect to possible phase changes are found. Zirconia aggregation possibly results in the higher activation energy and peculiar thermal expansion behavior. The results indicate the ethylene diamine tetraacetic acid assisted glycine-nitrate process is a very promising preparation method for solid oxide fuel cell practical application. (C) 2011 Elsevier B.V. All rights reserved.

Investigations on green-emitting, Mn2+: BaAl12O19 phosphors obtained by solution combustion process

Singh, Vijay; Chakradhar, R. P. S.; Rao, J. L.; Kwak, Ho-Young

JOURNAL OF MATERIALS SCIENCE, 46, 11, 3928-3934

Manganese-doped BaAl12O19 green phosphor was prepared using a self-propagating (combustion) synthesis. Powder X-ray diffraction and scanning electron microscopy were used to characterize the as-prepared combustion product. A room temperature photoluminescence study shows an emission line at 513 nm corresponding to a transition from the upper T-4(1) -> (6)A(1) ground state of Mn2+ ions. The electron paramagnetic resonance (EPR) spectrum exhibits six line hyperfine structure at g = 1.981. From the EPR spectrum, the spin-Hamiltonian parameters have been evaluated. The g value indicates that the site symmetry around Mn2+ ions is distorted tetrahedral. The number of spins (N) participating in the resonance for g = 1.981 is measured as a function of temperature. The paramagnetic susceptibility (chi) is calculated from the EPR data at various temperatures. From the plot 1/chi versus T, the Curie constant (C) and Curie paramagnetic temperature (theta(p)) have been evaluated and discussed.

Studies on the emission behavior of polypropylene by gas chromatography/mass spectrometry with static headspace or thermodesorption

Reingrubera, E.; Reussner, J.; Sauer, C.; Standler, A.; Buchberger, W.

JOURNAL OF CHROMATOGRAPHY A, 1218, 21, 3326-3331

Emissions from polypropylene (PP) may cause undesired smell, be harmful, or lead to so-called fogging which prohibits its use for car interiors. Thus, qualitative as well as quantitative emission studies are necessary. Thermodesorption (TDS) and static headspace (sHS) with subsequent GC-MS analysis are two powerful tools for analyzing the emission behavior of polymers with a minimum of sample handling. In this work we investigated the emission behavior of PP with TDS and sHS coupled to GC-MS paying special attention to quantitative considerations and to the relevance of emitted substances for fogging phenomena. After extraction for 30 min and incubation for 2 h, TDS-GC-MS and sHS-GC-MS results were satisfyingly repeatable (with relative standard deviations up to 5%). TDS allowed to introduce substances up to higher boiling points into the GC-MS system, but required to control sample geometry, as emission depended rather on sample surface than on sample mass. In sHS, emission was governed by partitioning between the gas and the sample phase rather than by full evaporation of the analytes. Above a certain analyte-dependent amount, peak area became independent of the sample amount. However, if the sample amount was kept constant, peak areas of emitted substances showed a linear dependence upon concentration of volatiles. Therefore, accurate quantitation was still possible. Typically alkanes, alkenes and dialkenes dominate TDS-GC-MS and sHS-GC-MS chromatograms of PP. They only contributed to fogging if they had a chain length higher than C16. These substances were only detectable when TDS was used for sample introduction, but not with sHS. sHS-GC-MS is thus not useful for judging fogging behavior. (C) 2010 Elsevier B.V. All rights reserved.

Thermite reduction of Ta2O5/SiO2 powder mixtures for combustion synthesis of Ta-based silicides

Yeh, C. L.; Huang, Y. S.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 21, 6302-6306

Tantalum silicides (including TaSi2, Ta5Si3, Ta2Si, and Ta3Si) were prepared by solid state combustion of the Ta-Si reaction system involving thermite reduction of Ta2O5 and SiO2. The thermite-based combustion is self-sustaining and contributes to the in situ formation of tantalum silicides along with Al2O3. The combustion front temperature and propagation velocity increased with the extent of thermite reactions for the systems adopting the thermite mixture of Al-Ta2O5, while both of them decreased for those using Al, Ta2O5, and SiO2 as the thermite reagents. Among four silicide compounds, a better degree of phase evolution was observed for TaSi2 and Ta5Si3 when compared to that of Ta2Si and Ta3Si. The XRD analysis indicated the presence of a small amount of Ta5Si3 in the TaSi2-Al2O3 composite. On the formation of Ta5Si3 with Al2O3, the minor phase was Ta2Si for the Al-Ta2O5-containing system. In addition to Ta2Si, an intermediate phase TaSi2 was detected when the Al-Ta2O5-SiO2 mixture was used. However, combustion yielded comparable amounts of Ta2Si and Ta5Si3 in the synthesis of the Ta2Si-Al2O3 composite. Moreover, instead of forming Ta3Si the reaction produced Ta2Si as the dominant phase along with unreacted Ta. (C) 2011 Elsevier B.V. All rights reserved.

Phase Behavior of Sick House Syndrome(SHS) Chemicals

Lee, Seung Bum; Shin, Myung Keun; Hong, In Kwon

JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY, 17, 3, 554-559

The vapor/liquid phase equilibrium data of sick house syndrome (SHS) materials were measured experimentally. SHS materials are chemical species to which the human body is exposed, such as the volatile organic chemicals emitted from constructing finishes. In this study, acetone(1) + toluene(2) and benzene(1) + m-xylene(2), as two sets of mixed SHS, were selected in the experimental system. These SHS are used as solvents for various chemical processes and finishing materials for residential dwellings, as well as the components contained in interior construction materials. It is very important to identify their vapor phase concentration and diffusion characteristics under atmospheric pressure. The vapor phase equilibrium concentration of the mixed SHS was measured experimentally, the data were correlated with their phase behavior characteristics, and then their nonideal behaviors were predicted by means of calculating their activity coefficients. The NRTL model and Wilson equation were employed as the thermodynamic equilibrium prediction model, in which the parameters of the experimental system were optimized in the course of calculation. The vapor phase concentration for each pair of mixed SHS was proposed with the given temperature range. (C) 2011 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

A study of Ni3Si-based composite coating fabricated by self-propagating high temperature synthesis casting route

Niu, Muye; Bi, Qinling; Kong, Lingqian; Yang, Jun; Liu, Weimin

SURFACE & COATINGS TECHNOLOGY, 205, 17-18, 4249-4253

A Ni3Si-Cr7C3 composite coating was fabricated on AISI 1020 steel substrate by self-propagating high-temperature synthesis (SHS) casting route. Phase composition, microhardness and dry sliding wear behavior of the coating were studied. The results indicated that the coating was mainly consisted of Ni3Si and Cr7C3. The microhardness of coating is about 900 HV. The friction and wear tests showed that although the friction coefficient had no obvious change, the wear resistance of the AISI 1020 steel matrix was improved greatly. Also, the corrosion test result showed that the coating had an excellent corrosion resistance. (C) 2011 Elsevier B.V. All rights reserved.

Microwave absorption properties and complex permittivity of Fe/FeAl2O4 coatings deposited by reactive plasma spraying Al/Fe2O3 powders

Zhao, Dong; Luo, Fa; Zhou, Wancheng; Zhu, Dongmei

SURFACE & COATINGS TECHNOLOGY, 205, 17-18, 4254-4259

In this study, spray dried Al/Fe2O3 composite powders were deposited for application as microwave absorbers by reactive plasma spraying (RPS). The morphology of the composite powders and cross-section of coatings were examined by scanning electron microscope (SEM). The main products were identified as hercynite (FeAl2O4) and iron (Fe) by X-ray diffraction. The effects of Al/Fe2O3 ratio on the complex permittivity and microwave absorption properties of the coatings were investigated in the frequency range from 8.2 to 12.4 GHz. In addition, the mechanisms of polarization and microwave energy loss are discussed. The real part (epsilon') of the complex permittivity increases with increasing Al concentration, which is attributed to the more interfacial polarization and the imaginary part (epsilon '') also increases which is ascribed to the increasing electrical conductivity of the coatings. By calculating the microwave absorption as a single-layer absorber, we find that the reflection loss varies with the changes of thickness and the amount of reduced Fe in coatings, due to the deviation of impedance matching condition. (C) 2011 Elsevier B.V. All rights reserved.

Structural stability, electronic and optical properties of Ni-doped 3C-SiC by first principles calculation

Dou, Yankun; Jin, Hai-bo; Cao, Maosheng; Fang, Xiaoyong; Hou, Zhiling; Li, Dan; Agathopoulos, S.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 20, 6117-6122

Structural stability along with the electronic and the optical properties of intrinsic 3C-SiC and Ni-doped 3C-SiC were studied by the first principles calculation. For the Ni-doped 3C-SiC, substitution of Ni in Si sub-lattice is energetically more favorable than that in C sub-lattice. Some new impurity energy levels appear in the band gap of Ni-doped 3C-SiC, which can improve the conductivity of 3C-SiC. The imaginary part of the dielectric function of Ni-doped 3C-SiC has three remarkable peaks at 0.69 eV, 2.35 eV, and 4.16 eV. This reveals that doping with Ni can improve the photo-absorption efficiency of 3C-SiC. In the absorption spectrum of Ni-doped 3C-SiC, the absorption edge red-shifts towards the far-infrared region. Furthermore, three new absorbing peaks emerge in the near-infrared region, visible region, and middle-ultraviolet region. These features confer Ni-doped 3C-SiC qualifications of a promising optical material. (C) 2011 Elsevier B.V. All rights reserved.

Axle box acceleration: Measurement and simulation for detection of short track defects

Molodova, Marija; Li, Zili; Dollevoet, Rolf

WEAR, 271, 41306, 349-356

Short track defects cause large dynamic contact forces at the wheel-rail interface, leading to fast deterioration of the track. Early detection of such defects is very important for timely maintenance. The track technical state can be assessed with the aid of axle box acceleration measurements, which can indicate short track defects like squats, welds with poor finishing quality, insulated joints, corrugation, etc. As a first attempt to determine a quantitative relationship between the characteristics of the accelerations and the track defects, axle box acceleration at a squat and a thermite weld were simulated through finite-element modeling. The magnitude and frequency contents of axle box acceleration at squats agreed with measurements. The results for welds had some discrepancies, which were mainly attributed to the fact that the modeled geometry of the weld deviated from the real one. (C) 2010 Elsevier B.V. All rights reserved.

Modified single-phase hematite nanoparticles via a facile approach for large-scale synthesis

Esmaeili, Elahe; Salavati-Niasari, Masoud; Mohandes, Fatemeh; Davar, Fatemeh; Seyghalkar, Hamideh

CHEMICAL ENGINEERING JOURNAL, 170, 1, 278-285

Shape- and size-controlled single-phase alpha-Fe(2)O(3) (hematite) nanoparticles have been successfully synthesized via a simple and facile thermal treatment route using modified precursors. At first, various ferric-surfactant systems such as: ferric-sugars, ferric-hydrazine, ferric-oleic acid, and ferric-sugar-hydrazine were prepared via a wet-chemical precipitation method and then, these intermediate adducts as precursor were decomposed in at ordinary atmosphere to iron oxide. The morphology and particle size of products were investigated by SEM and TEM images and XRD patterns. These results revealed that the best quality alpha-Fe(2)O(3) nanoparticles are synthesized through thermal decomposition of ferric-glucose precursor with molar ratio of 1:8 heated at 500 degrees C in a step-wise manner. (C) 2011 Elsevier B.V. All rights reserved.

Chemically activated combustion synthesis of MoSi2/Al cermet foams

Hobosyan, M. A.; Khachatryan, H. L.; Davidoya, A.; Kharatyan, S. L.

CHEMICAL ENGINEERING JOURNAL, 170, 1, 286-291

In this work the feasibility of synthesizing MoSi2/Al cermet foam under the combustion mode was studied. A halogen containing organic polymer, namely, polytetrafluoroethylene (PTFE) was used as foaming agent. It was shown that the target product reached the maximum porosity, up to 70%, when amount of the foaming agent was 0.04 mol. SEM analyses have shown there are two types of pores (macro and micro) in the products with diameter 0.2-1 mm and 0.01-0.05 mm, respectively. It was established that the portion of macro- and micro-pores depends on the amount of foaming agents and the inert gas pressure. It was established that increase of the metal amount leads to the decrease of the porosity while the toughness increases. (C) 2011 Elsevier B.V. All rights reserved.

Judd-Ofelt analysis of luminescence emission from Zn2SiO4:Eu3+ nanoparticles obtained by a polymer-assisted sol-gel method

Dacanin, Lj.; Lukic, S. R.; Petrovic, D. M.; Nikolic, M.; Dramicanin, M. D.

PHYSICA B-CONDENSED MATTER, 406, 11, 2319-2322

In this research we prepared Zn2SiO4:Eu3+ phosphor nanopowders using a combination of sol-gel and combustion synthesis with the aim to examine the influence of synthesis conditions on the optical properties of the phosphor. As combustion fuels we used polyethylene glycol (PEG) with different average molecular weights, and the combustion was performed in two ways-in a microwave oven and a conventional furnace. Optical properties were examined by photoluminescence spectroscopy and spectra of all samples showed intense red emission, typical for f-f electronic transitions of the Eu3+ ions. Emission decays exhibited classical one exponential behavior at longer times and nonlinear nature at short times, with average lifetimes varied from 0.49 to 0.71 ms between samples. Judd-Ofelt theory was applied to experimental data for the quantitative determination of optical parameters such as Omega(2,4) Judd-Ofelt parameters, radiative and nonradiative transition rates and emission quantum efficiency. Calculated parameters vary moderately between samples prepared with different PEGs and combusted in different manner. (C) 2011 Elsevier B.V. All rights reserved.

Effect of process parameters on combined EDTA-citrate synthesis of Ba0.5Sr0.5Co0.8Fe0.2O3 (-) (delta) perovskite

Patra, H.; Rout, S. K.; Pratihar, S. K.; Bhattacharya, S.

POWDER TECHNOLOGY, 209, 41334, 98-104

Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) has been synthesized following combined EDTA-citrate method as a function of different process parameters viz. variation of molar ratio of EDTA:citric acid:metal ions in the precursor solution and pH of the precursor solution. Thermal decomposition behavior study of the precursor gel reveals that EDTA strongly influences the citrate/nitrate complex formation. The BSCF phase formation is preceded by formation and dissolution of several intermediate phases. The pure phase BSCF powder is obtained on calcining the combustion residue at 950 degrees C and above. A possible schematic reaction sequences leading to the formation of pure phase BSCF powder have been suggested from the study of XRD pattern as a function of calcination temperatures. The synthesized powders are found to be agglomerated. The agglomeration size changes with change in the process parameters. The densification behavior of the BSCF samples has been correlated with the powder characteristics. (C) 2011 Elsevier B.V. All rights reserved.

Photocatalytic performance of silver TiO2: Role of electronic energy levels

Devi, L. Gomathi; Reddy, K. Mohan

APPLIED SURFACE SCIENCE, 257, 15, 6821-6828

Nano-sized silver deposits on the surface of Degussa P25 TiO2 (Ag-DP25) particles act as sites of electron accumulation where the reduction of adsorbed species takes place. Electrons can be transferred from Degussa P25 TiO2 (DP25) to Ag particles because of the difference in the work functions of the two materials. The efficiency of the electron transfer depends on the size and the distribution of metal deposits. A significant photocatalytic oxidation enhancement by metal deposit will only be observed if the metal deposits play a more dominant role than just increasing the life time of charge carriers. The properties of metal deposits like, loaded amount, oxidation state of the deposit and its size will influence the performance. Further, a decrease in band-gap in DP25 and Ag-DP25 was observed due to the carbide ion substitution for the oxide ion in TiO2. Such unintentional carbon incorporation is expected mostly in combustion synthesized materials. Silver metal deposits and unintentional incorporation of the carbon shows the beneficial effect by specific mechanism in the photocatalytic degradation of Congo Red (CR). (C) 2011 Elsevier B. V. All rights reserved.

SYNTHESIS OF THE NANOCRYSTALLINE NICKEL FERRITE BY A NOVEL MECHANO SOL-GEL AUTO-COMBUSTION METHOD

Shahmirzaei, M.; Ebrahimi, S. A. Seyyed; Dehghan, R.

MODERN PHYSICS LETTERS B, 25, 11, 855-861

In this work, a novel method of mechano sol-gel auto-combustion has been developed for production of single phase nickel ferrite nano crystalline powder, consisting of a sol-gel auto-combustion synthesis followed by a high energy milling process before calcination. Sol-gel auto-combustion was carried out using a gel including citric acid as a reductant and metal nitrates as oxidants. This gel exhibited a self-propagating behavior after ignition in air. The effects of the intermediate high energy milling on the physical properties of the final product after calcination were investigated. The results showed that with a high energy milling of the sol-gel auto-combusted powders with a ball-to-powder mass ratio of 20 for 20h, the temperature of calcination for synthesis of the single phase ferrite reduced from 1000 degrees C to 700 degrees C and the size of the ferrite crystallites decreased from 72 nm to 15 nm.

In Situ Synthesis of Ti5Si3 Matrix Nanocomposites Reinforced with Nanoparticles by High-Energy Mechanical Alloying

Li, Chuang; Gu, Dongdong; Shen, Yifu; Meng, Guangbin; Li, Yufang

ADVANCED ENGINEERING MATERIALS, 13, 5, 418-425

In the present work, in situ TiN/Ti5Si3 nanocomposite powder was prepared by high-energy mechanical alloying of a Ti and Si3N4 powder mixture via the following route: 9Ti+Si3N4 - Ti5Si3+4TiN. Constitution phases and microstructural features of the milled powders at different milling times were studied by XRD, SEM, and TEM. The operative formation mechanisms behind the microstructural developments were disclosed. It showed that the original Si3N4 and Ti constituents demonstrated two different reaction mechanisms during milling, i.e., a progressive mechanism of Si3N4 (<= 20 h) and a speedy mechanism of Ti (<= 10 h). The morphologies of the milled composite powders experienced a successive change: pre-refining - coarsening - re-refining on increasing the applied milling time. The variation of the operative mechanisms was ascribed to the existence/exhaustion of the ductile Ti constituent in the milling system due to the nonoccurrence/initiation of the in situ reaction. The 20 h milled powder was the typical nanocomposites featured by the nanocrystalline Ti5Si3 matrix reinforced with in situ TiN nanoparticles. The grain sizes of the in situ formed Ti5Si3 and TiN phases were generally <= 15 nm, exhibiting coherent interfacial structure between reinforcement and matrix.

Synthesis and luminescence properties of composite CaAl2O4-2CaAl(4)O(7):Eu3+ phosphor applied to white LEDs

Dong, H. J.

OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 41430, 617-620

Composite CaAl2O4-2CaAl(4)O(7):Eu3+ phosphor is prepared by the SPCS technique. The study results of XRD and FT-IR spectrum show that crystal lattice structure of that engenders slight distortion to improve luminescence properties. Luminescence spectrum indicates that CaAl2O4-2CaAl(4)O(7):Eu3+ shows strong red-light at 618 nm corresponding to electric dipole transition D-5(0)-F-7(2) of Eu3+ ions, upon exciting with 382 nnn. SEM micrographs reveal that the products fired at 900 degrees C exhibit high quality crystallinity and the size of that is approximately 1-3 mu m. All above characteristics of the CaAl2O4-2CaAl(4)O(7):Eu3+ is beneficial to phosphors applying to white LEDs.

Self-Propagating High-Temperature Synthesis of Y2O3 Powders from Y(NO3)(3x)(CH3COO)(3(1-x))center dot nH(2)O

Balabanov, S. S.; Gavrishchuk, E. M.; Kut'in, A. M.; Permin, D. A.

INORGANIC MATERIALS, 47, 5, 484-488

We have studied the self-propagating high-temperature synthesis (SHS) of yttrium oxide from Y(NO3)(3x)(CH3COO)(3(1-x)) center dot nH(2)O (0.3 <= x <= 0.7) acetate nitrates, calculated their standard enthalpies of formation using the method of valence states of atoms in a chemical compound, and compared calculated and experimentally determined yttrium oxide SHS temperatures. Using thermogravimetry and differential scanning calorimetry data and thermodynamic analysis, we have determined the optimal range of yttrium acetate nitrate compositions for the SHS of Y2O3 powder.

Reduction of Ni release and improvement of the friction behaviour of NiTi orthodontic archwires by oxidation treatments

Espinar, E.; Llamas, J. M.; Michiardi, A.; Ginebra, M. P.; Gil, F. J.

JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 22, 5, 1119-1125

This work studies NiTi orthodontic archwires that have been treated using a new oxidation treatment for obtaining Ni-free surfaces. The titanium oxide on the surface significantly improves corrosion resistance and decreases nickel ion release, while barely affecting transformation temperatures. This oxidation treatment avoids the allergic reactions or toxicity in the surrounding tissues produced by the chemical degradation of the NiTi. In the other hand, the lack of low friction coefficient for the NiTi superelastic archwires makes difficult the optimal use of these materials in Orthodontic applications. In this study, the decrease of this friction coefficient has been achieved by means of oxidation treatment. Transformation temperatures, friction coefficient and ion release have been determined.

THEORETICAL ASPECTS OF THE CREATION OF HIGHLY EFFICIENT REFRACTORIES ON THE BASIS OF SHS TECHNOLOGY

Kazhikenova, S. Sh.; Nurkenov, O. A.; Satbaev, B. N.

REFRACTORIES AND INDUSTRIAL CERAMICS, 52, 1, 55-60

The theoretical principles behind the self-propagating high-temperature synthesis of refractory materials are established. The physico-chemical characteristics of these materials are studied and the technology for their production is optimized. The thermochemical and kinetic parameters of the solid-phase combustion of systems based on fireclay, chromite, magnesium sulfate, and aluminum are examined; the phase composition and thermodynamic and physico-mechanical characteristics of the combustion products are determined and formulations are developed for refractory concretes and gunites.

Mechanochemical assisted synthesis of B4C nanoparticles

Sharifi, E. Mohammad; Karimzadeh, F.; Enayati, M. H.

ADVANCED POWDER TECHNOLOGY, 22, 3, 354-358

The present work reports on the preparation of boron carbide nanoparticles by the reduction of boron oxide with magnesium in the presence of carbon using the mechanochemical processing. The phase transformation and microstructure of powders during ball milling were investigated by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that during ball milling the B2O3-Mg-C reacted with a self-propagating combustion mode producing MgO and B4C compounds. To separate B4C from the milled powder mixture, an appropriate leaching process was used. After leaching, the purified powder mixture was characterized using XRD and transmission electron microscope (TEM). XRD studies indicated that the prepared particles were single phase crystalline B4C. Moreover, TEM studies showed the size of B4C particles were ranging from 10 to 80 nm. (c) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

Synthesis of Mg1-xCoxAl2O4 blue pigments via combustion route

Ianos, Robert; Lazau, Radu; Barvinschi, Paul

ADVANCED POWDER TECHNOLOGY, 22, 3, 396-400

MgAl2O4 was successfully used as crystalline host network for the synthesis of cobalt-based blue ceramic pigments. Different compositions of Mg1-xCoxAl2O4 (x = 0.1-0.3) powders have been prepared by the combustion reaction of corresponding metal nitrates with mixtures of urea and beta-alanine. The resultant powders were characterized by means of XRD, TG-DTA, EDAX, SEM, BET surface area, diffuse reflectance spectrometry and CIEL*a*b* color measurement. For x = 0.2, thermal analysis investigations evidenced that combustion reaction occurs at 276 degrees C. XRD analysis certified the formation of the designed solid solution, no additional thermal treatment being required. EDAX elemental analysis confirmed the purity of the as-prepared compound. The resulted powders had large surface areas, which varied from 8.7 to 62.6 m(2)/g. The crystallite size of Mg1-xCoxAl2O4 powders was less than 15 nm. Experimental results evidenced that as the proportion of Co2+ increased, the crystallite size decreased and the specific surface area increased. The diffuse reflectance spectra of the Mg1-xCoxAl2O4 pigments confirmed the presence of tetrahedrally coordinated Co2+. CIEL*a*b* chromatic coordinates indicated that the bluest color was obtained for x = 0.2. (c) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

A Method to Adjust Dielectric Property of SiC Powder in the GHz Range

Su, Xiaolei; Xu, Jie; Li, Zhimin; Wang, Junbo; He, Xinhai; Fu, Chong; Zhou, Wancheng

JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 27, 5, 421-425

The SiC powders by Al or N doping have been synthesized by combustion synthesis, using Al powder and NH4Cl powder as the dopants and polytetrafluoroethylene as the chemical activator. Characterization by X-ray diffraction, Raman spectrometer, scanning electron microscopy and energy dispersive spectrometer demonstrates the formation of Al doped SiC, N doped SIC and the Al and N co-doped SiC solid solution powders, respectively. The electric permittivities of prepared powders have been determined in the frequency range of 8.2-12.4 GHz. It indicates that the electric permittivities of the prepared SiC powders have been improved by the pure Al or N doping and decrease by the Al and N co-doping. The paper presents a method to adjust dielectric property of SiC powders in the GHz range.

Fast X-ray microdiffraction techniques for studying irreversible transformations in materials

Kelly, Stephen T.; Trenkle, Jonathan C.; Koerner, Lucas J.; Barron, Sara C.; Walker, Noeel; Pouliquen, Philippe O.; Tate, Mark W.; Gruner, Sol M.; Dufresne, Eric M.; Weihs, Timothy P.; Hufnagel, Todd C.

JOURNAL OF SYNCHROTRON RADIATION, 18, , 464-474

A pair of techniques have been developed for performing time-resolved X-ray microdiffraction on irreversible phase transformations. In one technique capillary optics are used to focus a high-flux broad-spectrum X-ray beam to a 60 mu m spot size and a fast pixel array detector is used to achieve temporal resolution of 55 mu s. In the second technique the X-rays are focused with Kirkpatrick-Baez mirrors to achieve a spatial resolution better than 10 mu m and a fast shutter is used to provide temporal resolution better than 20 mu s while recording the diffraction pattern on a (relatively slow) X-ray CCD camera. Example data from experiments are presented where these techniques are used to study self-propagating high-temperature synthesis reactions in metal laminate foils.

Effect of preparation method on the anti-corrosive properties of nanocrystalline Zn-CoO ceramic pigments

Rasouli, S.; Danaee, I.

MATERIALS AND CORROSION-WERKSTOFFE UND KORROSION, 62, 5, 405-410

Zn-CoO green ceramic pigments were synthesized by two different methods; high energy ball milling and solution combustion, with two different fuels; citric acid and glycine. Products were characterized by X-ray diffraction and scanning transmission electron microscopy (TEM). The anti-corrosive properties of the obtained pigments were investigated by electrochemical impedance spectroscopy (EIS) techniques. Results have shown that either by solid state reaction or combustion by citric acid, a calcination step was needed to obtain the desired phase whereas by glycine fuel, pure ZnO phase was obtained directly. TEM showed particles with mean particle size of about 70, 150, and 180 nm for glycine, citric acid, and solid state reaction samples, respectively. The corrosion performance of the coating in 3% w/v NaCl solution was evaluated by EIS and polarization measurements. According to the measurements of EIS and electrochemical polarization, the coatings with glycine-based pigment showed the highest corrosion resistance among the prepared coatings.

Synthesis of Nano Crystalline MgAl2O4 Spinel Powder by Microwave Assisted Combustion

Torkian, Leila; Amini, Mostafa M.; Bahrami, Zohreh

JOURNAL OF INORGANIC MATERIALS, 26, 5, 550-554

Stoichiometric MgAl2O4 spinel nanoparticles were synthesized by microwave assisted combustion reaction from aluminium nitrate nanohydrate (Al(NO3)(3)center dot 9H(2)O) and Sol-Gel prepared magnesium hydroxide (Mg(OH)(2)) in the presence of urea ((NH2)(2)CO) as a fuel, in about 20 min of irradiation. X-ray diffraction (XRD) studies reveal that microwave assisted combustion synthesis route yields single-phase spinel nanoparticles with larger crystalline size (around 75 nm) than other conventional heating methods. Scanning electronic microscope (SEM) images show nanoparticles with spherical shape and homogenous morphology. The surface area measurements (S-BET) show crystals with 2.11 m(2)/g and 0.0033 mL/g pore volume.

Large-scale atomistic simulations of nanostructured materials based on divide-and-conquer density functional theory

Shimojo, F.; Ohmura, S.; Nakano, A.; Kalia, R. K.; Vashishta, P.

EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS, 196, 1, 53-63

A linear-scaling algorithm based on a divide-and-conquer (DC) scheme is designed to perform large-scale molecular-dynamics simulations, in which interatomic forces are computed quantum mechanically in the framework of the density functional theory (DFT). This scheme is applied to the thermite reaction at an Al/Fe(2)O(3) interface. It is found that mass diffusion and reaction rate at the interface are enhanced by a concerted metal-oxygen flip mechanism. Preliminary simulations are carried out for an aluminum particle in water based on the conventional DFT, as a target system for large-scale DC-DFT simulations. A pair of Lewis acid and base sites on the aluminum surface preferentially catalyzes hydrogen production in a low activation-barrier mechanism found in the simulations.

Synthesis of WO3 nanoparticles for superthermites by the template method from silica spheres

Gibot, Pierre; Comet, Marc; Vidal, Loic; Moitrier, Florence; Lacroix, Fabrice; Suma, Yves; Schnell, Fabien; Spitzer, Denis

SOLID STATE SCIENCES, 13, 5, 908-914

Nanosized WO3 tungsten trioxide was prepared by calcination of H3P4W12O40 center dot xH(2)O phosphotungstic acid, previously dissolved in a silica colloidal solution. The influence of the silica spheres/tungsten precursor weight ratio (x) was investigated. The pristine oxide powders were characterized by XRD, nitrogen adsorption, SEM and TEM techniques. A specific surface area and a pore volume of 64.2 m(2) g(-1) and 0.33 cm(3) g(-1), respectively, were obtained for the well-crystallized WO3 powder prepared with x = 2/3 and after the removal of the silica template. The WO3 particles exhibit a sphere-shaped morphology with a particle size of 13 and 320 nm as function of the x ratio.The performance and the sensitivity levels of the thermites prepared from aluminium nanoparticles mixed with (i) the smallest tungsten (VI) oxide material and (ii) the microscale WO3 were compared. The combustion of these energetic composites was investigated by time resolved cinematography (TRC). This unconventional experimental technique consists to ignite the dried compressed composites by using a CO2 laser beam, in order to determine their ignition delay time (IDT) and their combustion rate. The downsizing WO3 particles improves, without ambiguity, the energetic performances of the WO3/Al thermite. For instance, the ignition delay time was greatly shortened from 54 +/- 10 ms to 5.7 +/- 0.2 ms and the combustion velocity was increased by a factor 50 to reach a value of 4.1 +/- 0.3 m/s. In addition, the use of WO3 nanoparticles sensitizes the mixture to mechanical stimuli but decreases the sensitivity to electrostatic discharge. (C) 2011 Elsevier Masson SAS. All rights reserved.

OBTAINING HEATPROOF COATINGS ON FIRECLAY REFRACTORIES BY SHS

Khina, B. B.; Volochko, A. T.; Zhukova, A. A.

GLASS AND CERAMICS, 68, 41306, 65-68

The possibility of obtaining heatproof coatings on fireclay refractories by self-propagating high-temperature synthesis in the system MgO - SiO(2) - Al using as the binder liquid sodium glass with the additives sodium tripolyphosphate and titanium dioxide, the latter activating the SHS process, is investigate. The optimal composition is determined and the physical-mechanical properties and the macro- and microstructure of the coatings are investigated.

Effect of rapid solidification on hydrogen solubility in Mg-rich Mg-Ni alloys

Bendersky, L. A.; Chiu, C.; Skripnyuk, V. M.; Rabkin, E.

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 9, 5388-5399

The hydrogenation properties of Mg(100-x)Ni(x) alloys (x = 0.5, 1, 2, 5) produced by melt spinning and subsequent high-energy ball milling were studied. The alloys were crystalline and, in addition to Mg matrix, contained finely dispersed particles of Mg(2)Ni and metastable Mg(6)Ni intermetallic phases. The alloys exhibited excellent hydrogenation kinetics at 300 degrees C and reversibly absorbed about 6.5 mass fraction (%) of hydrogen. At the same temperature, the as prepared Mg(99.5)Ni(0.5) and Mg(95)Ni(5) powders dissolved about 0.6 mass fraction (%) of hydrogen at the pressures lower than the hydrogen pressure corresponding to the bulk Mg-MgH(2) two-phase equilibrium, exhibiting an extended apparent solubility of hydrogen in Mg-based matrix. The hydrogen solubility returned to its equilibrium value after prolonged hydrogenation testing at 300 degrees C. We discuss this unusually high solubility of hydrogen in Mg-based matrix in terms of ultrafine dispersion of nanometric MgH(2) precipitates of different size and morphology formed on vacancy clusters and dislocation loops quenched-in during rapid solidification. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Fabrication, characterization and magnetic behaviour of alumina-doped zinc ferrite nano-particles

Deraz, N. M.

JOURNAL OF ANALYTICAL AND APPLIED PYROLYSIS, 91, 1, 48-54

Zinc ferrite nano-powders with a nominal composition of ZnFe(2)O(4) were prepared by combustion synthesis using mixture of urea and ammonium nitrate as fuel. The influence of alumina-doping on the structural, morphological and magnetic properties of ZnFe(2)O(4) nano-particles was investigated by means of X-ray powder diffraction (XRD), infrared (IR) spectroscopy, scanning and transmission electron microscopy (SEM and TEM) and vibrating sample magnetometer (VSM). XRD and IR analyses confirm the cubic spinel phase of ZnFe(2)O(4) nano-particles. The Zn ferrite presented a uniform microstructure with grain size in nano-scale. Alumina-doping brought about a change in the morphology of the as prepared ferrite from sphere-like to regular hexagon. Al(2)O(3)-treatment led to a decrease in the coercivity (H(c)), magnetization (M(s)) and magnetic moment (n(B)) of the investigated system. The maximum decrease in the values of H(c), M(s) and n(B) due to the treatment with 1.5 wt% Al(2)O(3) attained 13.5, 17.4 and 13.5%, respectively. The observed results can be explained on the basis of particle size and the Fe(3+) concentration in the octahedral and tetrahedral sites involved in the cubic spinel structure. (C) 2011 Elsevier B.V. All rights reserved.

Characterization and evaluation of Fe2O3/Al2O3 oxygen carrier prepared by sol-gel combustion synthesis

Wang, Baowen; Yan, Rong; Lee, Dong Ho; Zheng, Ying; Zhao, Haibo; Zheng, Chuguang

JOURNAL OF ANALYTICAL AND APPLIED PYROLYSIS, 91, 1, 105-113

The sol-gel combustion synthesis (SGCS) for oxygen carrier (DC) to be used in chemical looping combustion (CLC) was first designed and experimented in this work, which is a new method of DC synthesis by combining sol-gel technique and solution combustion synthesis. Cheap hydrated metal nitrates and urea were adopted as precursors to prepare Fe2O3/Al2O3 DC at the molar ratio to unity (Fe1Al1), which was characterized through various means, including Fourier transforms infrared (FIR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffractor (XRD). and N-2 isothermal adsorption/desorption method. FTIR analysis on the chemical structure of the dried gel of Fe1Al1 indicated that urea was partly hydrolyzed and the hydrated basic carbonate was formed by the combination of groups such as (Fe(Al-1-y(y))(1-x)O1-3x, CO32- and -OH-. By analyzing the staged products during SGCS, calcination was found as a necessary step to produce Fe2O3/Al2O3 DC with separate phases of alpha-Fe2O3 and alpha-Al2O3. Through TGA-DTA, the decomposition of the dried gel was found to undergo five stages. The analysis of the evolved gases from the gel decomposition using FTIR partially confirmed the staged decomposition and assisted a better understanding of the mechanism of SGCS. XRD identification further substantiated the necessity of calcination to synthesize Fe2O3/Al2O3 DC with separate phases of alpha-Fe2O3 and alpha-Al2O3, though it was not necessary for the synthesis of single phase alpha-Fe2O3 and alpha-Al2O3. Structural characterization performed on N-2 adsorption analyzer displayed that the pore shape of Fe1Al1 particles was heterogeneous. Finally, H-2 temperature-programmed reduction (TPR) of Fe1Al1 products in TGA indicated that the reduction reaction of Fe1Al1 DC after calcination was a single step reaction from alpha-Fe2O3 to Fe, and calcination benefited to improve the transfer rate of the lattice oxygen from the OC to fuel H-2. Furthermore, four times of reduction and oxidization (redox) reaction by alternating with H-2 and air demonstrated the synthesized DC had good reactivity and sintering-resistance, much suitable to be used in the realistic CLC. Overall, the SGCS method was found superior to other existent methods to prepare Fe2O3/Al2O3 DC for CLC application. (C) 2011 Elsevier B.V. All rights reserved.

Production of Ni-Doped SiC Nanopowders and their Dielectric Properties

Li, Dan; Jin, Hai-Bo; Cao, Mao-Sheng; Chen, Tao; Dou, Yan-Kun; Wen, Bo; Agathopoulos, Simeon

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 5, 1523-1527

Nanopowders of nickel-doped beta-silicon carbide (beta-SiC) with improved dielectric properties (compared with pure beta-SiC) were successfully produced using the mechanically activated self-propagating high-temperature synthesis method in an argon (Ar) atmosphere. The molar substitution of nickel (Ni) for silicon (Si) was 1%, 3%, and 5%. Powders of poly(tetrafluoroethylene) and ammonium chloride (NH(4)Cl) were used to promote the combustion reaction. The experimental results indicated an active role of Ni in the mechanism of combustion synthesis of SiC powders, which was reflected in the increase in combustion temperature and the velocity of propagation of the combustion wave, the microstructure of the produced nanopowders with a grain size of 100 nm for 5% Ni, and an improvement in the dielectric properties, specifically the increase in real (epsilon') and imaginary parts (epsilon '') of the complex permittivity, in the frequency range of 8.2-12.4 GHz, compared with pure SiC. The X-ray analysis of the produced powders suggests that Ni is accommodated in the lattice of SiC, which shrinks with increasing amounts of Ni.

Real-Time Tracking of CO2 Injected into a Subsurface Coal Fire through High-Frequency Measurements of the (CO2)-C-13 Signature

Krevor, Samuel C. M.; Ide, Taku; Benson, Sally M.; Orr, Franklin M., Jr.

ENVIRONMENTAL SCIENCE & TECHNOLOGY, 45, 9, 4179-4186

CO2 was injected into a coal fire burning at a depth of 15 m in the subsurface in southwestern Colorado, USA. Measurements were made of the (CO2)-C-13 isotopic signature of gas exhaust from an observation well and two surface fissures. The goal of the test was to determine (1) whether CO2 with a distinct isotopic signature could be used as a tracer to identify flow pathways and travel times in a combustion setting where CO2 was present in significant quantities in the gases being emitted from the coalbed fire, and (2) to confirm the existence of a self-propagating system of air-intake and combustion gas exhaust that has been previously proposed. CO2 was injected in three separate periods. The (CO2)-C-13 isotopic signature was measured at high frequency (0.5 Hz) before, during, and after the injection periods for gas flowing from fissures over the fire and from gas entering an observation well drilled into the formation just above the fire but near the combustion zone. In two cases, a shift in the isotopic signature of outgassing CO2 provided clear evidence that injected CO2 had traveled from the injection well to the observation point, while in a third case, no response was seen and the fissure could not be assumed to have a flowpath connected with the injection well. High-frequency measurements of the (CO2)-C-13 signature of gas in observation wells is identified as a viable technique for tracking CO2 injected into subsurface formations in real-time. In addition, a chimney-like coupled air-intake and exhaust outlet system feeding the combustion of the coal seam was confirmed. This can be used to further develop strategies for extinguishing the fire.

Effects of PVA content on the synthesis of LaFeO3 via sol-gel route

Feng, Jiansheng; Liu, Ting; Xu, Yebin; Zhao, Jingyuan; He, Yanyan

CERAMICS INTERNATIONAL, 37, 4, 1203-1207

LaFeO3 were synthesized via a sol gel route based on polyvinyl alcohol (PVA). Differential scanning calorimetry (DSC), Thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM) techniques were used to characterize precursors and derived oxide powders. The effect of the ratios of positively charged valences to hydroxyl groups of PVA (Mn+/-OH) on the formation of LaFeO3 was investigated. XRD analysis showed that single-phase and well-crystallized LaFeO3 was obtained from the Mn+/-OH = 4:1 molar ratio precursor at 700 degrees C. For the precursor with Mn+/-OH = 2:1, nanocrystalline LaFeO3 with average particle size of 50 nm was formed directly in the charring procedure. With increase of PVA content to Mn+/-OH = 1:1, phase pure LaFeO3 was obtained at 500 degrees C. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Synthesis of high surface area Al2O3-CeO2 composite nanopowder via inverse co-precipitation method

Hassanzadeh-Tabrizi, S. A.; Taheri-Nassaj, E.

CERAMICS INTERNATIONAL, 37, 4, 1251-1257

In the present work, Al2O3-CeO2 composite nanopowder was synthesized by inverse co-precipitation method using metal chlorides, aluminum powder and NH4OH as precipitant agent. The thermal decomposition of the precipitate and subsequent formation of Al2O3-CeO2 were investigated by X-ray diffractometery, scanning electron microscopy, thermogravimetric and differential thermal analysis, Brunauer-Emmett-Teller surface area measurement and Fourier transform infrared spectroscopy. The results showed that the presence of ceria suppressed the formation of alpha-Al2O3. The BET-specific surface area was 173 m(2)/g for powders calcined at 800 degrees C. The particle size examined by using scanning electron microscopy was in the range 30-70 nm. The activation energy of Al2O3-15 wt.% CeO2 nanocrystallite growth during calcination was measured to be 32.4 kJ/mol whereas that of Al2O3 was about 23.8 kJ/mol. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

SGCS-made ultrafine CaO/Al2O3 sorbent for cyclic CO2 capture

Luo, Cong; Zheng, Ying; Ding, Ning; Wu, Qi Long; Zheng, Chu Guang

CHINESE CHEMICAL LETTERS, 22, 5, 615-618

Multi-cyclic CaO carbonation/calcination is an attractive method for CO2 capture during coal combustion. However, the capture capacity of CaO sharply decreases with increasing carbonation/calcination cycles. In order to improve the stability of CO, capture capacity of CaO during carbonation/calcination cycles, synthetic CaO/Al2O3 sorbents were synthesized by two methods: wet chemistry and sol gel-combustion-synthesis (SGCS) to make a further comparison. The results indicate that the SGCS-made CaO/Al2O3 = 80:20 wt% sorbent provides a competitive performance of a capture capacity of 0.43 g-CO2/g-sorbent after 20 cycles. (C) 2010 Ying Zheng. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Fabrication of grinding tool material by the SHS of Ni-Al/diamond/dilute

Zhang, F. L.; Yang, Z. F.; Zhou, Y. M.; Wang, C. Y.; Huang, H. P.

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 3, 344-350

A mixture of Ni-Cr-P. Cu and B powder was used as a dilute for modifying the microstructure of the reacted product and easing the fast propagating rate and the high temperature in the self-propagating high-temperature synthesis (SHS) of Ni-Al matrix grinding tool material. The SHS process of the Ni-Al/diamond/dilute was examined and the microstructure of the reacted product was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The grinding performance of the tool was tested in the grinding of a synthetic single crystal of sapphire. The results showed that the dilute substantially reduced the propagating rate and the combustion temperature of Ni-Al SHS. Besides the dominating intermetallics NiAl and NiAl(3), Ni(4)Al(3) was also identified in the reacted Ni-Al/diamond/dilute composite owing to the Ni rich environment. In the reacted composite there was a Cr-rich zone at the boundary of the diamond grit due to the formation of Cr(3)C(2) between Cr and the diamond. In the grinding a lower wear rate and a better retention ability of diamond grits could be achieved for the grinding tool material that contained finer diamond grits. (C) 2011 Elsevier Ltd. All rights reserved.

Study of formation behavior of TiC in the Fe-Ti-C system during combustion synthesis

Zhang, M. X.; Hu, Q. D.; Huang, B.; Li, J. Z.; Li, J. G.

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 3, 356-360

TiC particles were prepared in situ by self-propagating high-temperature synthesis (SHS) reaction in the Fe-Ti-C elemental powder mixture. The reaction behavior and formation route of synthesizing TiC in the Fe-Ti-C system were investigated. With Fe contents increasing, the adiabatic temperatures, reaction temperatures and TiC particles sizes obviously decreased. The addition of Fe promotes the reaction between Ti and C through a "bridging" effect. Fe plays an important role in controlling the reaction behavior and morphology of products, serving not only as a diluent to inhibit the TiC particles from growing, but also as an intermediate reactant to promote the reaction. (C) 2011 Elsevier Ltd. All rights reserved.

In situ fabrication of ZrC powder obtained by self-propagating high-temperature synthesis from Al-Zr-C elemental powders

Song, M. S.; Ran, M. W.; Kong, Y. Y.

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 3, 392-396

The in situ synthesis of ZrC powder utilizing self-propagating high-temperature synthesis (SHS) reaction that occurred in the compact consisting of Al, Zr and C powders was investigated. The result shows when Al contents were 0-40 wt.% SHS reaction proceeded favorably. The as-products display a uniform distribution of ZrC particles with the sizes ranging from 8 mu m at Al free to 50 nm at 40 wt.% Al. The temperature curve, coupled with the quenched treatment, indicates that the Al-Zr reaction to form ZrAl(3) initiated and then C reacted with ZrAl(3) to form the more stable ZrC phase. It also proves that the mechanism of reaction-precipitation should be responsible for the formation of ZrC in this system. Al has been playing an important role in determining the formation of ZrC, not only as a diluent to inhibit the ZrC grains from coarsening, but also as an intermediate reactant to participate in the total reaction. (C) 2011 Elsevier Ltd. All rights reserved.

Synthesis of novel Dy3+ activated phosphate phosphors for NUV excited LED

Shinde, K. N.; Dhoble, S. J.; Kumar, Animesh

JOURNAL OF LUMINESCENCE, 131, 5, 931-937

The new trivalent dysprosium activated X6AlP5O20 (where X=Sr, Ba, Ca and Mg) phosphors were prepared by the combustion method. The prepared phosphors are characterized by XRD, photoluminescence and SEM techniques. Excited by 350 nm near-ultraviolet (NUV) light, the phosphors show an efficient blue and yellow band emissions, which originates from the F-4(9/2)-> H-4(15/2) and F-4(9/2)-> H-6(13/2) transitions of Dy3+ ion, respectively. The excitation spectra of the phosphors are broadband extending from 340 to 400 nm, which are characteristics of NUV excited LED. The effect of the Dy3+ concentration on the luminescence properties of X6AlP5O20:Dy3+ (where X=Sr, Ba, Ca and Mg) phosphors is studied. Ca6AlP5O20 phosphors show strong PL emission intensity around 25 times more as compared to Ba6AlP5O20, Sr6AlP5O20 and Mg6AlP5O20 phosphors. The investigated prepared phosphors are suitable for a NUV excited LED. (C) 2010 Elsevier B.V. All rights reserved.

Luminescence properties of MgO produced by solution combustion synthesis and doped with lanthanides and Li

Orante-Barron, V. R.; Oliveira, L. C.; Kelly, J. B.; Milliken, E. D.; Denis, G.; Jacobsohn, L. G.; Puckette, J.; Yukihara, E. G.

JOURNAL OF LUMINESCENCE, 131, 5, 1058-1065

The objective of this study is to explore the possibility of synthesizing MgO with controlled luminescence and thermoluminescence (TL) properties using the Solution Combustion Synthesis (SCS) method by doping with different lanthanides (Ln) and co-doping with lithium (Li). The goal is to further establish the SCS technique as a new route for developing new TL and optically stimulated luminescence (OSL) dosimetric materials. Undoped and doped MgO samples were synthesized by SCS and characterized using radioluminescence (RL) and TL The data obtained showed that Li doping can increase considerably the intensity of the RL and TL from Ln-doped MgO produced by SCS. In MgO:Ln,Li the introduced lanthanides are responsible for the emission during both RL and TL processes, although other emission bands are also observed (e.g., similar to 700-750 nm). The incorporation of lanthanides also introduces trapping centers as indicated by different peaks in the TL curves. The results in this study show that the SCS technique can potentially produce materials with TL intensity comparable to commercial dosimetric materials, although further optimizations are still required. (C) 2011 Elsevier B.V. All rights reserved.

Low-temperature synthesis and characterization of the Mn-Zn ferrite

Szczygiel, Irena; Winiarska, Katarzyna

JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 104, 2, 577-583

Nanocrystalline ferrite with the composition: Mn0.6Zn0.4Fe2O4 was synthesized by two-stage route: the precipitation of Zn, Mn and Fe hydroxides from sulphates solution and the synthesis of a precursor by the sol-gel auto-combustion method. The ferrite powder obtained from the gel by ashing was sintered under air at a temperature of 720, 1150 and 1300 A degrees C. The composition and morphology of the as-obtained phases were examined by ICP-AES, TG/DTA, XRD, FTIR, SEM and low-temperature nitrogen adsorption (BET). It was found that the spinel phase forms after gel combustion. The nanometric ferrite powder obtained as a result of the combustion is soft-agglomerated. The zinc content in the ferrite during ashing and auto-combustion is lower by about 21 mol% than the assumed one and the final product turn out to be Mn0.68Zn0.32Fe2O4.

Exothermic reaction waves in ZrSiO4/Mg/diluent systems

Kim, S. H.; Ryu, H. R.; Nersisyan, H. H.; Lee, J. H.

COMBUSTION AND FLAME, 158, 5, 1008-1014

An experimental study of thermal behavior in exothermic wave propagation in ZrSiO4 + 4Mg + kSH systems (where SH is a sodium halide) was conducted using a thermocouple technique. Temperature-time profile investigations provide deeper insight into the combustion wave propagation mechanism and reveal the values of combustion parameters: ignition and combustion temperatures, wave propagation velocity, and the actual size of pre-flame and reaction zones. It was shown that the measured maximum temperature was reduced from 1900 degrees C for the undiluted sample to 1490 degrees C for samples containing 1.5 mol of sodium halide. As a consequence, pure-phase zirconium monosilicide (ZrSi) was obtained under theses temperature conditions. Scanning electron microscope (SEM) examination revealed that ZrSi particles were spherical in shape and uniform in size when NaCl was used as an inert diluent. The obtained ZrSi particles had mean diameters ranging from 0.4 to 2.5 mu m based on NaCl concentration. The chemical mechanism of ZrSi formation is discussed, and a simple model for nucleation and grain growth processes is proposed. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Nanoscale investigation of surfaces exposed to a thermite spray

Crane, Charles A.; Collins, Eric S.; Pantoya, Michelle L.; Weeks, Brandon L.

APPLIED THERMAL ENGINEERING, 31, 41461, 1286-1292

A thermite spray gun was recently developed as a means for discharging the reaction products and intermediates of the highly exothermic thermite reaction. The thermite spray gun was inspired by more widely used hydrocarbon spray guns with the modification that the reactants are in the solid phase. This device has been used in conjunction with a heat flux sensor to examine the energy transfer characteristics of the spray. The current study broadens the previous work of thermite sprays by examining the influence of reactant composition on heat flux characteristics as well as the penetration behavior of the ejected spray evaluated with atomic force microscopy (AFM). Specifically, the apparatus was loaded with a fuel lean (Phi = 0.61) and a fuel rich (Phi = 1.52) Al-Fe(2)O(3) thermite and both nanometric and micron-scale reactants were investigated. The gas generating, fuel rich nano-thermite exhibited slight ablation of the silicon substrate, exhibiting 7.5 times shorter exposure to the thermite spray, and an order of magnitude faster spray velocity as compared to the non-gas generating, fuel lean nano-thermite. The micron-thermite demonstrated comparatively more ablation of the silicon substrate such that it was determined particle size plays an important role in surface removal with micron-scale particles also producing higher heat fluxes and surface temperatures. (C) 2011 Elsevier Ltd. All rights reserved.

Plastic Collapse Loads of Cracked Square Hollow Section T-, Y-, and K-joints

Lie, S. T.; Yang, Z. M.

JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING-TRANSACTIONS OF THE ASME, 133, 2, 21601-

This paper concerns on the development of numerical models for cracked square hollow sections (SHSs) T-, Y-, and K-joints. Based on these numerical models, the plastic collapse loads P(c) are calculated using nonlinear finite element method and through twice-elastic compliance criterion. It is found that the numerical plastic collapse loads P(c) are slightly conservative compared with the ones calculated using formulae proposed by BS7910 [ British Standards, 2005, "Guide on Methods for Assessing the Acceptability of Flaws in Metallic Structures," BS 7910-Amendment 1] and are in close agreement with the experimental tests data. Therefore, the proposed numerical model is robust and it can be used to calculate the plastic collapse loads P(c) of the cracked (SHS) T-, Y-, and K-joints. [DOI: 10.1115/1.4001960]

Characterization of Mg1-xNixAl2O4 solid solutions prepared by combustion synthesis

Ianos, Robert; Barvinschi, Paul

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 31, 5, 739-743

Mg1-xNixAl2O4 (x=0, 0.25, 0.5, 0.75 and 1) solid solutions have been prepared by combustion synthesis. After annealing the combustion synthesized powders at 1000 degrees C for 3 h single-phase Mg1-xNixAl2O4 was obtained over the entire range of compositions. The lattice parameter of Mg1-xNixAl2O4 gradually increased from 8.049 angstrom (NiAl2O4) to 8.085 angstrom (MgAl2O4), which certified the formation of the spinel solid solutions. All samples prepared by combustion synthesis had blue color shades, denoting the inclusion of Ni2+ in the spinel structure in octahedral and tetrahedral configuration. The crystallite size of Mg1-xNixAl2O4 was in the range of 35-39 nm and the specific surface area varied between 5.8 and 7.0 m(2)/g. (C) 2010 Elsevier Ltd. All rights reserved.

One-step fabrication of Cu-Al2O3 nanocomposite via solution combustion synthesis route

Nasiri, H.; Khaki, J. Vahdati; Zebarjad, S. M.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 17, 5305-5308

Solution combustion synthesis (SCS) is a well-known method for production of different metal oxides and composite materials such as metal matrix composites. To the best of our knowledge, producing of metal matrix composite needs an extra reduction step after combustion synthesis. In the current research, the authors introduced a novel method to eliminate the reduction step and showed that Cu matrix composite could be produced just in one-step. For this purpose, Cu(NO3)(2)center dot 3H(2)O and Al (NO3)(3)center dot 9H(2)O were used as oxidizers and urea as fuel, and one-step combustion synthesis was performed in the presence of graphite. The structure and morphology of the products were studied by XRD, SEM and TEM techniques, respectively. XRD patterns proved that the presence of graphite could prevent formation of copper oxides. SEM and TEM micrographs showed that Cu matrix reinforced with nano-sized alumina could be achieved in one-step through SCS method. (C) 2011 Elsevier B.V. All rights reserved.

Structural and electrochemical hydrogen storage properties of Mg2Ni-based alloys

Zhu, Yunfeng; Yang, Chen; Zhu, Jinyu; Li, Liquan

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 17, 5309-5314

Four different methods, i.e. hydriding combustion synthesis + mechanical milling (HCS + MM), induction melting (followed by hydriding) + mechanical milling (IM(Hyd) + MM), combustion synthesis + mechanical milling (CS + MM) and induction melting + mechanical milling (IM + MM), were used to prepare Mg2Ni-based hydrogen storage alloys used as the negative electrode material in a nickel-metal hydride (Ni/MH) battery. The structural and electrochemical hydrogen storage properties of the Mg2Ni-based alloys have been investigated systematically. The XRD results indicate that the as-milled products show nanocrystalline or amorphous-like structures. Electrochemical measurements show that the as-milled hydrides exhibit higher discharge capacity and better electrochemical kinetic property than the as-milled alloys. Among the four different methods, the HCS + MM product possesses the highest discharge capacity (578 mAh g(-1)), the best high rate dischargeability (HRD) and the highest exchange current density (58.8 mA g(-1)). It is suggested that the novel method of HCS + MM is promising to prepare Mg-based hydrogen storage electrode alloy with high discharge capacity and activity. (C) 2011 Elsevier B.V. All rights reserved.

Structural, optical and EPR studies on ZnO:Cu nanopowders prepared via low temperature solution combustion synthesis

Reddy, A. Jagannatha; Kokila, M. K.; Nagabhushana, H.; Chakradhar, R. P. S.; Shivakumara, C.; Rao, J. L.; Nagabhushana, B. M.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 17, 5349-5355

Cu (0.1 mol%) doped ZnO nanopowders have been successfully synthesized by a wet chemical method at a relatively low temperature (300 degrees C). Powder X-ray diffraction (PXRD) analysis, scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier transformed infrared (FTIR) spectroscopy, UV-Visible spectroscopy, Photoluminescence (PL) and Electron Paramagnetic Resonance (EPR) measurements were used for characterization. PXRD results confirm that the nanopowders exhibit hexagonal wurtzite structure of ZnO without any secondary phase. The particle size of as-formed product has been calculated by Williamson-Hall (W-H) plots and Scherrer's formula is found to be in the range of similar to 40 nm. TEM image confirms the nano size crystalline nature of Cu doped ZnO. SEM micrographs of undoped and Cu doped ZnO show highly porous with large voids. UV-Vis spectrum showed a red shift in the absorption edge in Cu doped ZnO. PL spectra show prominent peaks corresponding to near band edge UV emission and defect related green emission in the visible region at room temperature and their possible mechanisms have been discussed. The EPR spectrum exhibits a broad resonance signal at g similar to 2.049, and two narrow resonances one at g similar to 1.990 and other at g similar to 1.950. The broad resonance signal at g similar to 2.049 is a characteristic of Cu(2+) ion whereas the signal at g similar to 1.990 and g similar to 1.950 can be attributed to ionized oxygen vacancies and shallow donors respectively. The spin concentration (N) and paramagnetic susceptibility (X) have been evaluated and discussed. (C) 2011 Elsevier B. V. All rights reserved.

Preparation of single phase molybdenum boride

Camurlu, Hasan Erdem

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 17, 5431-5436

The formation of MoB through volume combustion synthesis (VCS), and through mechanochemical synthesis (MCS) followed by annealing has been investigated. MoO(3), B(2)O(3) and Mg were used as reactants while MgO and NaCl were introduced as diluents. Products were leached in dilute HCl solution and were subjected to X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) examinations. Mo was the major phase component in the VCS products under all the experimental conditions. Mo(2)B, MoB, MoB(2) and Mo(2)B(5) were found as minor phases. Products of MCS contained a mixture of Mo(2)B, MoB, MoB(2) and Mo. After annealing the MCS product at 1400 degrees C for 3 h, single phase alpha-MoB was obtained. (C) 2011 Elsevier B. V. All rights reserved.

Hydrogen production by methane tri-reforming process over Ni-ceria catalysts: Effect of La-doping

Pino, Lidia; Vita, Antonio; Cipiti, Francesco; Lagana, Massimo; Recupero, Vincenzo

APPLIED CATALYSIS B-ENVIRONMENTAL, 104, 41306, 64-73

The objective of the present work is the study of CH(4) tri-reforming process (simultaneous carbon dioxide reforming, steam reforming and oxygen reforming) that can contribute to the CO(2) abatement producing synthesis gas with the desiderate H(2)/CO ratio.A series of Ni-CeO(2) catalysts with different La loadings is prepared by combustion synthesis and tested as catalysts in CH(4) Tri-reforming reaction at 800 degrees C under atmospheric pressure with a GHSV of 30,000 h(-1).It has been found that during tri-reforming reaction the activity of Ni-ceria catalysts can be enhanced by an appropriate amount of La doping (10 at.%), the CH(4) and CO(2) conversion increases from 93% and 83% to 96% and 86.5%, respectively. The activity enhancement appears to be related to synergic effect of nickel-lanthana-surface oxygen vacancies of ceria via interfacial active sites that contribute to increase the nickel dispersion and create a basic site distribution on the surface able to interact with CO(2). (C) 2011 Elsevier B.V. All rights reserved.

In-situ measurements of the onset of bulk exothermicity in shock initiation of reactive powder mixtures

Jette, Francois-Xavier; Higgins, Andrew J.; Goroshin, Samuel; Frost, David L.; Charron-Tousignant, Yannick; Radulescu, Matei I.; Lee, Julian J.

JOURNAL OF APPLIED PHYSICS, 109, 8, 84905-

The shock initiation process was directly observed in different powder mixtures that produce little or no gas upon reaction. The samples of reactive powder were contained in recovery capsules that permitted the samples to be analyzed after being shocked and that allowed the initiation of reaction to be monitored using three different methods. The microsecond time-scale processes were observed via a fast two-color pyrometer. Light intensity detected from the bottom of reactive samples was slightly greater compared to inert simulants in the first 10 mu s after shock arrival. However, this light was much less intense than that which would correspond to the bulk of the material reacting. Thus it seemed that only small, localized zones, or hot spots, had begun to react on a time scale of less than 30 mu s. Light emissions were then recorded over longer time scales, and intense light appeared at the bottom of samples a few milliseconds to a few hundreds of milliseconds after shock arrival at the bottom of the test samples. Thus it appeared that the bulk of the material reacted as the hot spots spread via convective/diffusive means. This bulk reaction was also observed using thermocouples for a large number of mixtures and incident shock pressures. The delay time for the onset of bulk reaction was found to be not strongly dependent upon shock pressure but seemed to correlate with the burning speed of the mixtures. The shock initiation process appeared to take place via the initiation and growth of hot spots, as in high explosives, except that burning speeds are much slower in reactive powders that produce little gas. VC 2011 American Institute of Physics. [doi: 10.1063/1.3553861]

Sol-gel autocombustion synthesis of Co-Ni alloy powder

Hua, Zhenghe; Cao, Zongwei; Deng, Yu; Jiang, Yuwen; Yang, Shaoguang

MATERIALS CHEMISTRY AND PHYSICS, 126, 3, 542-545

Sol-gel autocombustion is confirmed to be an efficient method in the synthesis of Co-Ni alloy powder. Addition of adequate amount of ethanol can make the reduction reaction thorough and increase the purity of the samples. X-ray diffraction measurement indicates that the obtained samples consist of a single phase with bcc structure. Transmission electron microscopy study shows the grain size is about 10 nm. The magnetic measurements show that the samples are a soft magnetic material with the coercive field smaller than 100 Oe and the saturation magnetization about 95% of the theoretical value. (C) 2011 Elsevier B.V. All rights reserved.

Effect of fuel type on microstructure and electrical property of combustion synthesized nanocrystalline scandia stabilized zirconia

Lakshmi, V. Vijaya; Bauri, Ranjit; Paul, Soumalya

MATERIALS CHEMISTRY AND PHYSICS, 126, 3, 741-746

Nanocrystalline 10 mol% scandia stabilized zirconia (10ScSZ) powders were prepared by combustion synthesis using three different types of fuels (urea, glycine and citric acid). The influence of nature of fuel on phase formation, particle size and morphological characteristics was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of fuel type on electrical conductivity was also evaluated. The 10ScSZ prepared by urea and glycine was fully crystalline whereas citric acid resulted in amorphous form. The powder turned crystalline on calcination at 800 degrees C. Urea resulted in highly agglomerated powder whereas porous and loose agglomerates were formed with glycine and citric acid as fuels. The powder processed with urea showed higher crystallite size compared to powders processed with glycine and citric acid. The ScSZ electrolyte pellet processed with glycine and citric acid exhibited better conductivity and lower activation energy compared to the electrolyte processed with urea. (C) 2010 Elsevier B.V. All rights reserved.

Neodymium zirconate (Nd2Zr2O7) transparent ceramics as a solid state laser material

Feng, Tao; Clarke, David R.; Jiang, Danyu; Xia, Jinfeng; Shi, Jianlin

APPLIED PHYSICS LETTERS, 98, 15, 151105-

Transparent neodymium zirconate (Nd2Zr2O7) ceramics have been fabricated from nanoparticles prepared by combustion synthesis. Emission at 1054.5 nm has been demonstrated using a laser diode pump at 800 nm. A transmittance of 60% at wavelengths longer than similar to 900 nm was achieved. A consequence of the very high concentration of Nd ions (1.32 x 10(28) ions/m(3)) is that the absorption bands are wider than those of Nd doped Y3Al5O12 (Nd:YAG) facilitating pumping over a broader range of wavelengths. The full width at half maximum of the emission peak is also larger than that of Nd: YAG, and the decay time is 460 mu s making Nd2Zr2O7 an excellent candidate for efficient high-power microchip lasers emitting at 1054 nm with diode pumping at similar to 800 or similar to 900 nm. (C) 2011 American Institute of Physics. [doi:10.1063/1.3579526]

Fe50Co50 nanoparticles via self-propagating high-temperature synthesis during milling

Azizi, A.; Yourdkhani, A.; Koohestani, H.; Sadrnezhaad, S. K.; Asmatulu, R.

POWDER TECHNOLOGY, 208, 3, 623-627

Self-propagating exothermic reactions during mechanical milling of FeCl3/CoCl2 mixture together with sodium seeds resulted in formation of Fe50Co50 nanoparticles. Highly exothermic reactions resulted in temperature raise and formation of Fe50Co50 phase within the first 5 min; however Fe50Co50 single-phase was obtained after 30 min of milling. The products were characterized by XRD, SEM, EDS, TEM and VSM. Obtained results showed that both milling time and NaCl salt matrix affected the size, morphology, microstructure and magnetic properties of the produced particles. (C) 2011 Elsevier B.V. All rights reserved.

Consolidation and mechanical properties of reactive nanocomposite powders

Stamatis, Demitrios; Zhu, Xiaoying; Schoenitz, Mirko; Dreizin, Edward L.; Redner, Paul

POWDER TECHNOLOGY, 208, 3, 637-642

Reactive nanocomposite powders with bulk compositions of 8Alqq center dot MoO(3), 12Al center dot MoO(3), and 8Al center dot 3CuO were prepared by arrested reactive milling (ARM) and consolidated into cylindrical and rectangular pellets using a uniaxial die. Pellets were pressed at room temperature without any binder. Reference pellets were prepared from conventional Al powder and from Al-metal oxide powder blends with bulk compositions identical to those of the nanocomposite powders. Materials could be consolidated to densities greater than 90% of the theoretical maximum density while maintaining their high reactivity. Tensile strength and flexural strength of the consolidated materials were measured using diametrical compression and three-point flexural strength tests, respectively. Higher strengths were observed for higher relative densities, and the strength of the composite materials was comparable to that of consolidated aluminum powders. Yield strength of the reactive nanocomposite powders was determined from compaction load vs. die displacement curves using the Heckel equation. It was greater for the nanocomposite powders as compared to the powder blends or pure aluminum. Organic, or low melting point metal binders were added to selected samples to improve strength. Respective pellets were pressed at temperatures above the melting point of the metal binder. The highest density (similar to 2.9 g/cm(3)) and tensile strength (similar to 17.5 MPa) was observed with indium as binder. All consolidated samples were found to be highly reactive, and the effect of partial reaction during consolidation remained below the limit quantifiable by differential scanning calorimetry. (C) 2011 Elsevier B.V. All rights reserved.

Single step synthesis of GdAlO3 powder

Sinha, Amit; Nair, S. R.; Sinha, P. K.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 14, 4774-4780

A novel method for preparation of nano-crystalline gadolinium aluminate (GdAlO3) powder, based on combustion synthesis, is reported. It was observed that aluminium nitrate and gadolinium nitrate exhibit different combustion characteristics with respect to urea, glycine and beta-alanine. While urea was proven to be a suitable fuel for direct formation of crystalline alpha-Al2O3 from its nitrate, glycine and beta-alanine are suitable fuels for gadolinium nitrate for preparation of its oxide after combustion reaction. Based on the observed chemical characteristics of gadolinium and aluminium nitrates with respect to above mentioned fuels for the combustion reaction, the fuel mixture composition could be predicted that could lead to phase pure perovskite GdAlO3 directly after the combustion reaction without any subsequent calcination step. The use of single fuel, on the other hand, leads to formation of amorphous precursor powders that call for subsequent calcination for the formation of crystalline GdAlO3. The powders produced directly after combustion reactions using fuel mixtures were found to be highly sinterable. The sintering of the powders at 1550 degrees C for 4 h resulted in GdAlO3 with sintered density of more than 95%. T.D. (C) 2011 Elsevier B.V. All rights reserved.

Synthesis and Characterization of SrAl2O4:Eu2+, Dy3+ Nanocrystalline Phosphorescent Pigments

Shafia, E.; Aghaei, A.; Davarpanah, A.; Bodaghi, M.; Tahriri, M.; Alavi, S. H.

TRANSACTIONS OF THE INDIAN CERAMIC SOCIETY, 70, 2, 71-77

In this research, the Eu2+ and Dy3+ co-doped strontium aluminate (SrAl2O4) nanocrystalline phosphorescent pigments with high brightness and long afterglow was successfully synthesized by urea-nitrate solution combustion method (SCS) at 600 degrees C, followed by heating the resultant combustion ash at 1200 degrees C in an atmosphere which was weak reducing (5%H-2 + 95%N-2). The pure SrAl2O4 monoclinic phase as host structure could be formed by combustion method in which the temperature is very much lower than solid-state method. A broad-band UV-excited luminescence of the SrAl2O4:Eu2+, Dy3+ phosphorescent pigments was observed at lambda(max) = 517 nm due to transitions from 4f(6)5d(1) to 4f(7) configuration of the emission center (Eu-2 ions). The excitation spectra showed two main peaks at 240 and 256 nm. Eventually, the average grain size of the combustion ash powder and SrAl2O4:Eu2+, Dy3+ phosphor particles were obtained as 40 and 62 nm, respectively via Scherrer's formula and these particles were in thin flake form.

Synthesis of Highly Sinterable Neodymium Ion doped Yttrium Oxide Nanopowders by Microwave Assisted Nitrate-Alanine Gel Combustion

Mann, Rekha; Laishram, Kiranmala; Malhan, Neelam

TRANSACTIONS OF THE INDIAN CERAMIC SOCIETY, 70, 2, 87-91

Microwave assisted gel combustion synthesis of neodymium doped yttria (Nd:Y(2)O(3)) nanopowders using L-alanine complexing agent is being reported. Gelation of metal nitrates with L-alanine followed by combustion in microwave and subsequent calcinations at 1000 degrees C for 3 h under oxygen supply gave phase pure nanopowders characterized by FTIR and XRD. Highly sinterable Nd:Y(2)O(3) nanopowders with size range 20-80 nm, close to spherical and uniform morphology were obtained as observed by TEM compared to particles in size range 40-160 nm, with polyhedral morphology, obtained by sol-gel route. Compaction of calcined powders by cold isostatic press at 400 MPa followed by sintering at 1700 degrees C for 7 h gave ceramic with 26% transmission which increased to 32% after 10 h without any sintering aid for microwave gel combustion compact, compared to 6.7% transmission for sol-gel route compacts. XRD of sintered samples showed retention of phase purity in all the cases. SEM of sintered samples showed good grain fusion for close to spherical particles of microwave assisted gel combustion route than polyhedral particles of sol-gel route. Since spherical particles undergo faster densification and sintering, microwave assisted route gave highly sinterable nanopowders compared to sol-gel route.

Synthesis of Pr0.70Sr0.30MnO3 +/-delta and Nd0.70Sr0.30MnO3 +/-delta Powders by Solution-Combustion Technique

Vargas, Reinaldo Azevedo; Bonturim, Everton; Chiba, Rubens; Andreoli, Marco; Miymaru Seo, Emilia Satoshi

MATERIALS RESEARCH-IBERO-AMERICAN JOURNAL OF MATERIALS, 14, 2, 161-165

Powders of Pr0.70Sr0.30MnO3 +/-delta (PSM) and Nd0.70Sr0.30MnO3 +/-delta (NSM) compositions are being investigated as alternative cathode materials for Intermediate Temperature Solid Oxide Fuel Cells. The compositions were synthesized by a solution-combustion method using metal nitrates and urea as fuel. Combustion synthesis is a highly suitable synthesis route for achieving fine and homogeneous powders at low temperatures. Single phase pseudo-perovskite was obtained by X-ray diffraction after heat treatment of PSM and NSM powders at 900 degrees C. The synthesized and milling powders had an average particle size between 0.27 to 0.07 mu m. Chemical analyses of the powders calcined was performed by X-ray fluorescence and morphological analysis by scanning electron microscopy. The results were compared with literature values, indicating characteristics adjusted for preparation of ceramic suspensions.

Properties and Rapid Consolidation of Nanocrystalline 8MoSi(2)-Si3N4 by High Frequency Induction Heated Sintering

Park, Na-Ra; Ko, In-Yong; Yoon, Jin-Kook; Doh, Jung-Mann; Shon, In-Jin

METALS AND MATERIALS INTERNATIONAL, 17, 2, 233-237

Nanopowders of MoSi2 and Si3N4 were synthesized from Mo2N and Si by high ball milling. Dense nanostructured 8MoSi(2)-Si3N4 composite was consolidated by high frequency induction heated sintering (HFIHS) method within two minutes from mechanically synthesized powders of MoSi2 and Si3N4. Highly dense 8MoSi(2)-Si3N4 composite with a relative density of up to 97 % was produced under simultaneous application of 80 MPa pressure and the induced current. The average grain size and mechanical properties (hardness and fracture toughness) of the composite were investigated.

Microstructure and Dynamo-Mechanical Behavior of NiTi Sintered-Porous Sheets from Pre-Alloyed Powders

Coda, A.; Gallitognotta, A.; Fumagalli, L.; Bertoldi, M.

METALLURGIA ITALIANA, , 4, 3-9

The common way to produce parts from NiTi shape memory alloys is preparing the alloy by arc or induction melting with several re-melts to reach a sufficient homogeneity. The use of graphite crucible can cause carbon contamination. After cold and/or warm working with annealing steps, final shaping is done by drawing, cutting, and drilling. But high work hardening and pseudoelasticity make NiTi alloys difficult to machine. High wear of cutting tools is observed. The material loss is also an expense factor. Powder Metallurgical (PM) methods are promising ways to overcome these problems. Many investigations have focused on combustion synthesis (CS) also called self-propagating high temperature synthesis (SHS) or powder metallurgy for production of bulk NiTi phase [1-3]. Considerable attentions have also been attracted on the porous NiTi SMA. The porous NiTi SMA was usually used for hard tissue implants because of its porous structure, good mechanical properties and biocompatibility [4]. SHS, pre-alloy powder metallurgy, and element powder metallurgy (EPM) [5] were the three popular methods to produce porous NiTi SMA. Aim of this paper is to present a study on the preparation by sintering of NiTi porous sheets from the characterized NiTi pre-alloyed powders. A better understanding about the microstructural and functional properties, the effects of composition and sintering parameters on shape memory and superelastic behavior were investigated by dynamo-mechanical analysis (DMA). The experimental campaign has been carried out on NiTi 55.5 and 56 wt.% pre-alloyed powders according to Table I. The powder has been constrained in a graphite mould and sintered under vacuum at 1200 degrees C and 1250 degrees C for different times. Carbon and Oxygen concentrations were detected by LECO analyzers, using the combustion infrared absorption method. The samples morphology has been investigated by using an Field Emission Scanning Electron Microscope (FESEM) equipped with an Oxford x-ray microprobe (EDS) for elemental micro-analysis. Transformation Temperatures Range (TTR) were investigated using Differential Scanning Calorimetry (DSC). The analysis was carried out in accordance to the standard practice, ASTM F2004-05. For Dynamo Mechanical Analysis (DMA) a static loading cell of 25N, an heating rate of 1 degrees C/min and a frequency of 10 Hz were fixed. Common 3-points bending test and hysteresis test under different bending load conditions were performed (Table 1). C and 0 content and DSC results for fresh and sintered powders are given in Table II. For fresh NiTi 56 powder a flat peak was detected under cooling. This peak is identified as martensite. A separate, clear R-phase peak was also revealed. Since the martensitic transformation temperature is directly correlated with the Ni content of the NiTi phase, Hie less pronounced peak is considered to be an indication of a non-uniform Ni distribution within the starting powder. DSC measurements on the same powders after sieving at different grain sizes confirmed this hypothesis. After sintering a general increase of the transformation temperatures was observed. Due to diffusion processes, for the austenitic transformation the wide shoulder present on the main peak decreases, confirming that a more homogeneous distribution of Ni in the NiTi phase occurs with increasing sintering temperature. The shift of the transformation peaks to higher temperatures in general is associated to the Ni reduction within the intermetallic due to the formation of Ni-rich precipitates at the grain boundaries region.However, Ti2Ni orcomplex oxide have been detected. These compounds have the tendency to reduce Ti content within the matrix and a decreasing of TTR might be observed. In fact, the measured increasing of Oxygen content can explain the shift of some DSC peaks to lower temperatures. The microstructures of the NiTi 56 powder sintered at 1250 degrees C for 2h and 411 are compared in Fig. 1. EDS analysis of the matrix gives a composition of near equiatomic NiTi. In addition to the NiTi phase, a secondary phase is present in the material with a Ni/Ti ratio of about 1:2. This larger dark grey phase can be attributed to Ti2Ni or Ti4Ni2Ox. These two phases show overlapping XRPD peaks which do not allow a clear distinction. By increasing the sintering time, a general reduction of the porosity was observed. From a mechanical point of view, the samples sintered at 1200 degrees C appear to be more fragile. To obtain a good mechanical stability, sintering temperature had to be elevated at 1250 degrees C, which is more than 0.95*Tmelt. The high sintering temperature indicates a low sinterability of the intermetallic NiTi phase itself. Figure 2 shows tan cycling values of specimen 3 under different loading conditions. Several peaks are evident during the phase transformation. The behavior of these peaks is, however, very complicated since it depends on experimental parameters such as frequency, cycling rate, as well as composition and thermo-mechanical history of the samples. On heating it seems that only one peak appears. At least two peaks are observed on cooling. This could be a further indication of a non-uniform Ni distribution within the starting powder. A general shift to higher temperatures is visible by increasing the testing load. The stress-strain curves and the hysteresis curves under constant bending load of 0.5, 1.0, and 1.5N on sintered sheets will also be presented. Aim of this paper was to present some interesting results obtained by using powder metallurgy technologies in order to realize NiTi shape memory or superelastic components. The preparation of Nitinol sintered-porous sheets from pre-alloyed powders was reported. Both microstructural and functional properties of the sintered samples were characterized. The summary of data suggests that the evolution of DSC charts of NiTi sintered Porous sheets may be very complex, depending on several factors, such as starting composition, impurity content, grain size distribution, homogeneity of the pre-alloyed powders. DMA results confirm the feasibility of NiTi sintered porous parts with sound shape memory properties. Further experiments have to be done in order to better understand the sintered sheets behavior under different working conditions.

Microwave ignited combustion synthesis of intermetallic compounds, modelling and experimental results

Colombini, E.; Rosa, R.; Veronesi, P.; Casagrande, A.

METALLURGIA ITALIANA, , 4, 29-34

The process of Combustion synthesis (CS) is based on the highly exothermic reaction by reactants, which, if properly ignited, spontaneously turn into products. The aim of this work is to study the CS of beta-NiAl formed starting from Ni and Al (1:1 at. %) powders activated by microwaves at 2.45 GHz. Numerical simulation is used to obtain data otherwise difficult to be measured experimentally and to develop a predictive model of microwave ignited and sustained CS of metal powder compacts. The simulation couples an electro-thermal model with a chemical model, required to study the exothermic reaction between powders. A simplify model was obtained and validated, neglecting volume changes, to study compositional and temperature change and reaction kinetics during the CS. It allowed to demonstrate how microwave application, during and after, synthesis could control the cooling rate of products and hence the microstructure of the newly formed intermetallics.

Blue-green BaAl2O4:Eu2+,Dy3+ phosphors synthesized via combustion synthesis method assisted by microwave irradiation

Sun Feilong; Zhao Junwu

JOURNAL OF RARE EARTHS, 29, 4, 326-329

Blue-green luminescent BaAl2O4:Eu2+,Dy3+ phosphor powders were synthesized via combustion synthesis method assisted by microwave irradiation in air. The phosphors were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectrophotometer. The XRD results revealed that when the concentration of urea was over 3 times higher than theoretical quantities, a BaAl2O4 single hexagonal phase was obtained. The SEM results revealed that the surface of the BaAl2O4:Eu2+,Dy3+ powder samples showed lots of voids and pores. The BaAl2O4:Eu2+,Dy3+ phosphors exhibited a broad emission band of main peak at 496 nm and a shoulder peak at 426 nm under excitation of 337 nm. The BaAl2O4:Eu2+,Dy3+ phosphors at the Eu2+ concentration of 1 mol.% showed the strongest luminescent intensity. Long afterglow phosphorescence was observed in the dark with naked eyes after the removal of the excitation source.

Combustion synthesis and upconversion luminescence of CaSc2O4:Yb3+,Er3+ nanopowders

Peng Wenfang; Zou Shaoyu; Liu Guanxi; Xiao Quanlan; Meng Jianxin; Zhang Rui

JOURNAL OF RARE EARTHS, 29, 4, 330-334

Novel up-conversion (UC) luminescent nano-powders, (CaScO4)-O-2:Yb3+:Er3+ were prepared with a combustion method at an ignition temperature as low as 200 degrees C. The CaSc2O4:Yb3+,Er3+ nano-powder had an orthorhombic CaFe2O4-type structure, and showed sphere-like morphology with an average diameter of about 30 nm. It gave strong green (525, 552 nm) and red (652-674 nm) up-conversion luminescence due to the H H-2(11/2)-> I-4(15/2), (4)S3/2 -> I-4(15/2) and F-4(9/2)-> I-4(15/2) transitions of Er3+ under a 980 nm semiconductor laser excitation at room temperature. The optimized doping concentrations for Yb3+ and Er3+ were 6.0 mol.% and 1.0 mol.%, respectively. Effects of ignition temperature and glycine-to-metal nitrate molar ratio on up-conversion emission intensity were also investigated. The log-log plots of luminescence intensity and pump power revealed that the 652-674 nm red emissions and 552 nm green emissions belonged to a two-photon process, while the 525 nm green emissions belonged to a three-photon process. The possible UC mechanisms were briefly discussed.

In-Situ Synthesis of (TiC)(p)Ni/TiAl/Ti Functional Gradient Materials via Field-Activated Process

Zhang Nan; Chen Shaoping; Liang Lianjie; Xue Pengfei; Meng Qingsen

RARE METAL MATERIALS AND ENGINEERING, 40, 4, 620-624

(TiC)(p)Ni/TiAl/Ti functional gradient materials (FGMs) were prepared by field-activated pressure-assisted synthesis ( FAPAS) and in-situ synthesis processes. The roles of the electric field in material synthesis and diffusion bonding of layers were investigated. The microstructure and phase composition of each layer as well as component distribution of elements across the interfaces of the layers were analyzed by means of OM, SEM, EDS and XRD. The results show that the imposition of the electric field and the combustion reaction of TiAl is the key for the successful synthesis of FGMs; the TiC particles formed by in-situ synthesis process are fine and distributed uniformly; moreover, concentration profiles of elements across the interfaces of the layers show significant inter-diffusion and good metallurgical bonding. The sample has an excellent thermal shock resistance ability and gradient distribution of micro-hardness across the titanium substrate to the surface layer.

Al2O3-ZrO2 nanocomposites produced by solution combustion synthesis followed by ultrasonic milling

Biamino, Sara; Ambrosio, Elisa Paola; Manfredi, Diego; Fino, Paolo; Badini, Claudio

JOURNAL OF CERAMIC PROCESSING RESEARCH, 12, 2, 207-211

Zirconia toughened alumina materials (ZTA) have been produced by solution combustion synthesis (SCS). SCS has proved to be a rather rapid and simple method to produce nano-structured ceramic oxides powders. Its main drawback is a limited sinterability of the powder due to aggregation of the nanometric grains into larger particles characterized by irregular shapes. It was found out that when coupling the preparation of ZTA nanocomposites by SCS with ultrasonic milling it is possible to improve the powder sinterability. The effect of ultrasonic irradiation on the powders was observed by BET and SEM analyses, and by its effect on the final density.

Combustion synthesis, characterization and catalytic application of MoO3-ZrO2 nanocomposite oxide towards one pot synthesis of octahydroquinazolinones

Samantaray, Satish; Mishra, B. G.

JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL, 339, 41306, 92-98

Pure ZrO2 and MoO3 (10 mol%)-ZrO2 nanocomposite oxides were prepared by solution combustion method using glycine as fuel. The synthesized materials were characterized by X-ray diffraction (XRD), Scanning Electron microscopy (SEM). Transmission electron microscopy (TEM) and UV-vis spectroscopic technique. XRD study revealed selective stabilization of the tetragonal phase of zirconia in presence of MoO3. The crystallite size was calculated from the Fourier line shape analysis of the broadened X-ray diffraction profiles as well as from TEM measurements. Oxide nanoparticles with size in the range of 5-40 nm was observed depending upon the fuel content in the combustion mixture. UV-vis study indicated well dispersion of the molybdenum oxide component in the zirconia matrix in the form of isolated and cluster molybdates. The MoO3-ZrO2 nanocomposite oxide was used as an efficient and environmentally benign catalyst for the synthesis of octahydroquinazolinones by multicomponent condensation reaction of dimedone, urea and arylaldehydes in aqueous media as well as under solvent free condition using microwave irradiation. A series of zirconia based heterogeneous catalyst with different acidity and surface area were screened for this reaction. The MoO3 (10 mol%)-ZrO2 catalyst was found to be highly active for the transformation with excellent yield and purity of the product in a short reaction time. (C) 2011 Elsevier B.V. All rights reserved.

Direct reduction of ammonium molybdate to elemental molybdenum by combustion reaction

Manukyan, Khachatur; Davtyan, Davit; Bossert, Joerg; Kharatyan, Suren

CHEMICAL ENGINEERING JOURNAL, 168, 2, 925-930

Self-sustaining reduction of ammonium molybdate tetrahydrate (AMT) by mixture of zinc and magnesium is investigated. It is shown that utilizing mixtures of metallic reducers is an attractive methodology to control the reduction conditions and product characteristics. Optimal intervals of key parameters, e.g. composition of reducing mixtures and pressure of inert gas are determined. Analysis of combustion temperature profiles, XRD, SEM/FESEM, DTA, microanalysis, and quenching techniques are applied to investigate the reduction mechanism. Based on the obtained fundamental knowledge, for the first time, highly crystalline molybdenum powder with particle sizes in the range 0.1-1 mu m is produced by direct reduction of AMT in a single-stage and energy saving process. Proposed combustion-based approach of Mo production has high potential to become an alternative to the conventional hydrogen reduction processes. (C) 2011 Elsevier B.V. All rights reserved.

Mechanisms of Combustion Synthesis and Magnetic Response of High-Surface-Area Hexaboride Compounds

Kanakala, Raghunath; Escudero, Roberto; Rojas-George, Gabriel; Ramisetty, Mohan; Graeve, Olivia A.

ACS APPLIED MATERIALS & INTERFACES, 3, 4, 1093-1100

We present an analysis of the combustion synthesis mechanisms for the preparation of hexaboride materials using three compounds as model systems: EuB(6), YbB(6), and YB(6). These three hexaborides were chosen because of the differences in ionic radii between Eu(3+), Yb(3+), and Y(3+), which is a factor in their stability. The powders were prepared using metal nitrates, carbohydrazide, and two different boron precursor powders. The resulting materials were analyzed by X-ray diffraction, which showed that combustion synthesis is effective for the synthesis of EuB(6), since the Eu(3+) ion has an ionic radius greater than similar to 1 angstrom. The synthesis of YbB(6) and YB(6) is not as effective because of the small size of the Yb(3+) and Y(3+) ions, making the hexaborides of these metals less stable and resulting in the synthesis of borates due to the presence of oxygen during the combustion process. Scanning electron microscopy and dynamic light scattering of the EuB(6) powders shows that the particle size of the hexaboride product is dependent on the particle size of the boron precursor. The magnetic susceptibility of our EuB(6) powders manifests irreversible behavior at low applied fields, which disappears at higher fields. This behavior can be attributed to the increase in size and number of magnetic polarons with increasing magnetic field.

Hydrogen production by reacting water with mechanically milled composite aluminum-metal oxide powders

Dupiano, Paul; Stamatis, Demitrios; Dreizin, Edward L.

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 8, 4781-4791

Several composite aluminum-metal oxide powders were prepared by mechanical milling and considered for hydrogen production in the Al-water split reaction. The powders included compositions capable of independent, highly exothermic thermite reaction between components: Al center dot MoO3, Al center dot Bi2O3, and Al-CuO, as well as chemically inert compositions Al center dot MgO and Al center dot Al2O3. Experiments used a water displacement method to quantify hydrogen production. In most experiments, the flask containing water and composite powder was maintained at 80 degrees C; additional limited experiments were performed at varied temperatures. Condensed reaction products were collected and examined using electron microscopy and X-ray diffraction. For all compositions, the aluminum water split reaction was nearly complete. Average reaction rates were comparable to those reported earlier for materials with similar particle sizes prepared by ball milling. Reaction rates were affected by the specific composition; the Al center dot Bi2O3 composite reacted substantially faster than other materials. It was observed that the Al water split reaction initiated at 80 degrees C could be completely stopped by cooling the reacting flask to room temperature; the reaction did not restart at room temperature but could be resumed at its previous rate by heating the flask back to 80 degrees C. For Al center dot MoO3 composite, an interruption in the hydrogen production was observed at a constant temperature; it was associated with the formation of MoO2.4(OH)(0.6), a hydrated MoO3 phase. Evidence of thermite reactions interfering with the Al-water split reaction and generating metallic Bi and Cu was obtained for experiments with Al center dot Bi2O3, and Al center dot CuO composites, respectively. A qualitative reaction mechanism is proposed assigning different rate controlling processes to different stages of the Al-water split reaction for the composites prepared by ball milling. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Synthesis and sintering of Gd-doped CeO2 electrolytes with and without 1 at.% CuO dopping for solid oxide fuel cell applications

Dong, Yingchao; Hampshire, Stuart; Zhou, Jian-er; Meng, Guangyao

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 8, 5054-5066

Nano-sized Ce0.8Gd0.2O2-delta and ce(0.79)Gd(0.2)Cu(0.01)O(2-delta) electrolyte powders were synthesized by the polyvinyl alcohol assisted combustion method, and then characterized by powder characteristics, sintering behaviors and electrical properties. The results demonstrate that the as-synthesized Ce0.8Gd0.2O2-delta and ce(0.79)Gd(0.2)Cu(0.01)O(2-delta) possessed similar powder characteristics, including cubic fluorite crystalline structure, porous foamy morphology and agglomerated secondary particles composed of gas cavities and primary nano crystals. Nevertheless, after ball-milling these two powders exhibited quite different sintering abilities. A significant reduction of about 400 degrees C in densification temperature of ce(0.79)Gd(0.2)Cu(0.01)O(2-delta) was obtained when compared with Ce0.8Gd0.2O2-delta. The ce(0.79)Gd(0.2)Cu(0.01)O(2-delta) pellets sintered at 1000 degrees C and the Ce0.8Gd0.2O2-delta sintered at 1400 degrees C exhibited relative densities of 96.33% and 95.7%, respectively. The sintering of ce(0.79)Gd(0.2)Cu(0.01)O(2-delta) was dominated by the liquid phase process, followed by the evaporation-condensation process, Moreover, ce(0.79)Gd(0.2)Cu(0.01)O(2-delta) shows much higher conductivity of 0.026 S cm(-1) than Ce0.8Gd0.2O2-delta (0.0065 S cm(-1)) at a testing temperature of 600 degrees C. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Synthesis of ferromagnetic nanoparticles with a core/shell structure by a self-propagating combustion method

Cho, S. G.; Jeon, K. W.; Moon, K. W.; Kim, J. B.; Kim, K. H.; Kim, J.

JOURNAL OF APPLIED PHYSICS, 109, 7, 07B533-

Ferromagnetic nanoparticles with a core/shell structure were fabricated by a self-propagating combustion method and subsequent hydrogen reduction process. Before the reduction process, synthesized particles were Fe oxide phases. Transmission electron micrographs confirmed that the nanoparticles were composed of alpha-Fe core and Fe-Al oxide shell after the reduction process. The saturation magnetization of the nanoparticles was measured about 180 emu/g and the permeability kept constant value of about 1.8 up to 10 GHz without any noticeable loss. These microstructural and magnetic analyses showed that the oxide phase changed into alpha-Fe and then Al atoms diffused out to the surface of the particles during the reduction process. (C) 2011 American Institute of Physics. [doi:10.1063/1.3563062]

Melt-casting of Si-Al-Y-O glasses and glass-ceramics by combustion synthesis under high gravity

Liu, Guanghua; Li, Jiangtao; He, Bin

JOURNAL OF NON-CRYSTALLINE SOLIDS, 357, 7, 1764-1767

Si-Al-Y-O glasses and glass-ceramics were prepared via melt-casting by combustion synthesis under high gravity. The phase assemblage and microstructure of the cast products strongly depended on the content of SiO(2) and the additive ZrO(2) or La(2)O(3) in the starting compositions. With increasing content of SiO(2), the glass-forming ability of the melt was enhanced. The additive ZrO(2) was not dissolved into the glass and inclined to crystallize, but La(2)O(3) was inclined to remain in the glass matrix instead of precipitation. With a short processing period and lower energy consumption, combustion synthesis under high gravity can offer a new approach to fast fabrication of glass and glass-ceramic materials. (C) 2011 Elsevier B.V. All rights reserved.

RAPID SYNTHESIS OF PURE AND Pr-DOPED TiCeO4 NANOPIGMENTS BY SOLUTION COMBUSTION METHOD

Sam, S. P. Chandini; Prasad, V. S.; Kumar, K. Sudarsana

NANO, 6, 2, 139-144

Combustion synthesis has emerged as a facile and economically viable technique for the preparation of advanced ceramics, catalysts and nanomaterials. This paper is the report of the investigations carried out on the synthesis of titania-rare-earth mixed oxide pigments: TiCe1-xPrxO4-delta by the solution combustion method and their characterization by X-ray powder diffraction, transmission electron microscopy, reflectance spectral data, thermal analysis and surface area measurements. The synthesized nanopigments exhibit yellow to brick red color with the increase of praseodymium content. The dominant reflectance of these pigments lies above a wavelength of 600 nm. These pigments are found to be promising candidates as ecological pigments because of their high reflectance, lightness and intense coloration.

Preparation of Ti-Fe based hydrogen storage alloy by SOM method

Ye, Xiao Su; Lu, Xiong Gang; Li, Chong He; Ding, Wei Zhong; Zou, Xing Li; Gao, Yong Hui; Zhong, Qing Dong

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 7, 4573-4579

Solid-oxide-oxygen-ion conducting membrane (SOM) process is a novel, high efficient, low cost, energy-saving, environmentally friendly electrochemical extraction method of metals or alloys. This work demonstrated the prototype development of preparation of hydrogen storage alloys by SOM process, and Ti-Fe based quaternary alloy was successfully prepared directly from the oxides in molten calcium chloride. The assembling process of electrode utilized in the recycled battery was extended to prepare the novel cathode, it proved that this design can effectively simplify the assembly process and dissolve the problem of incomplete electrolysis. It is shown that SOM electro-deoxidization process was faster and more efficient for the current, the as-prepared alloy showed a good stability in the charging/discharging cycles and the capacity reached 27.88 mAh g(-1) after ten activated cycles. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Microstructure and magnetic properties of electrospun one-dimensional Al3+-substituted SrFe12O19 nanofibers

Liu, Mingquan; Shen, Xiangqian; Song, Fuzhan; Xiang, Jun; Meng, Xianfeng

JOURNAL OF SOLID STATE CHEMISTRY, 184, 4, 871-876

SrAlxFe12-xO19 (x=0-3.0) nanofibers with diameters about 100 nm have been prepared by electrospinning and subsequent heat treatment. With Al3+ ion content ranging from 0 to 3.0, the lattice parameters decrease due to Fe3+ ions substituted by smaller Al3+ ions and the average grain size calculated by the Scherrer's equation reduces from 65 to 37 nm. The magnetization shows a continuous reduction with the Al content and its value measured at 77 K is higher than at room temperature, which can be explained by Bloch's law. For the coercivity, its value initially increases, reaching a maximum value of 617 (298 K) and 547 kA m(-1) (77 K) at x=2.0, and then reduces with the Al content further increase largely arising from the substituted Al3+ ion arrangement in different interstitial sites of the strontium ferrite unit cell. (C) 2011 Elsevier Inc. All rights reserved.

Characterization and photoluminescence properties of some MLn(2(1-x))O(4):2xEu(3+) or 2xTb(3+) systems (M=Ba or Sr, Ln=Gd or La)

Mari, B.; Singh, K. C.; Sahal, M.; Khatkar, S. P.; Taxak, V. B.; Kumar, Mukesh

JOURNAL OF LUMINESCENCE, 131, 4, 587-591

BaGd2O4, BaLa2O4 and SrLa2O4 powders doped with different concentrations of Eu3+ or Tb3+ are prepared by combustion synthesis method and the samples were further heated to 500, 700 and 900 degrees C to improve the crystallinity of the materials. The structure and morphology of materials have been examined by X-ray diffraction and scanning electron microscopy. It is remarkable that all the samples of BaGd2O4, BaLa2O4 and SrLa2O4 have similar morphology. The SEM images show homogeneous aggregates of varying shapes and sizes, which are composed of a large number of small elliptical shaped crystallites with an average diameter of about 0.5-3.0 mu m. Photoluminescence for all materials increases with increase of temperature and shows a maximum for the samples heated to 900 degrees C with 4 mole% doping of Eu3+ or Tb3+ ions. The luminescence is almost same for all powders when doped with same concentration of Eu3+. (C) 2010 Elsevier B.V. All rights reserved.

Effect of powder particle size on laser induced self-propagating high temperature synthesis reaction in Al-Ti-C system

Xue, Z.; Li, Y. X.

POWDER METALLURGY, 54, 2, 113-117

Effect of powder particle size on the combustion temperature, microstructure and densification of products in Al-Ti-C system had been investigated. The results showed that Ti and C particle size had a great effect on the combustion temperature, microstructure and densification of products. With the increasing Ti powder particle size, the combustion temperature of the system increased and the densification of the products decreased, the size of TiC particle increased in the self-propagating high temperature synthesis reaction products. With the increasing C powder particle size, the combustion temperature of the system decreased and the densification of the products increased, the size of TiC particle decreased.

Synthesis of Fe-Al-Si intermediary phases by reactive sintering

Novak, P.; Knotek, V.; Serak, J.; Michalcova, A.; Vojtech, D.

POWDER METALLURGY, 54, 2, 167-171

In this work, Fe-Al-Si alloys were prepared by reactive sintering. The contents of silicon and aluminium ranged between 0-30 wt-% and 10-40 wt-% respectively. Aluminium, silicon and AlSi30 master alloy powders prepared by mechanical machining and/or milling and commercial powder of high purity iron were used for sintering. Powders were blended and pressed at room temperature. Sintering was carried out at 950 degrees C for 60 min. Compact low porosity products without unreacted components were prepared, if a powder mixture contained 15-20 wt-% of silicon and 20-25 wt-% of aluminium. It was shown that these materials contain two phases (Al(2)FeSi and AlFeSi). Hardness of the alloys increased with growing silicon content, while the increase in aluminium content reduced the hardness.

Synthesis and characterization of In-doped ZnO nano-powders produced by combustion synthesis

Garcia, R.; Nunez-Gonzalez, R.; Berman-Mendoza, D.; Barboza-Flores, M.; Rangel, R.

REVISTA MEXICANA DE FISICA, 57, 2, 10-12

Indium-doped ZnO powder was performed by a solution combustion technique using metal nitrates as oxidizer agents and carbohydrazide as fuel. The powders synthesized by this method are spongy clusters consisting of platelet-shaped nanocrystals with a wurtzite structure and narrow particle size distribution. Photoluminescence studies reveal that the powders emit high intensity luminescence. Defect-related green-yellow luminescence was found to be dependent upon the level of indium doping.

Preparation of Gd2O2S:Yb,Ho Phosphor via Thermolysis of Sulfur-Contained (Gd,Yb,Ho)[S2CN(C4H8)](3) Phen Complexes

Zhong Hai-Yang; Luo Xi-Xian; Ma Lu-Bin; Zhang Ming; Xing Ming-Ming; Fu Yao

CHINESE PHYSICS LETTERS, 28, 4, 47805-

A novel handy single-source precursor method is adopted to prepare Gd2O2S:Yb,Ho up-conversion phosphors. Pure Gd2O2S:Yb0.06Ho0.02 phosphors are prepared via thermolysis of the air-stable ternary solid complexes RE[S2CN(C4H8)](3)phen (RE=Gd, Yb, Ho) in a nitrogen atmosphere with certain amount of oxygen at 600-1100 C. The as-prepared Gd2O2S:Yb0.06Ho0.02 exhibits a strong green up-conversion luminescence under 980 nm IR excitation. The intensity of the green emission component is 37.4 and 53.4 times more than that of the red and NIR emissions, respectively. It is indicated that the material is of excellent color purity. Under an IR excitation density of 34.75 mW/mm(2) with a laser beam diameter of 1 mm, the material exhibits an up-conversion luminescence brightness of 43.68 Cd/m(2).

Fabrication of Transparent Y2Zr2O7 Ceramics from Combustion-Synthesized Powders

Zou, Xiaoqing; Zhou, Guohong; Yi, Hailan; Zhang, Guangjun; Wang, Shiwei

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 4, 1002-1004

Y2Zr2O7 transparent ceramic was successfully fabricated from combustion-synthesized powders. The as-prepared Y2Zr2O7 powders were characterized by XRD, FE-SEM, TEM, and BET area. After high-energy ball milling, the porous structure of the powder was destroyed. The Y2Zr2O7 transparent ceramics were obtained by sintering the ball-milled powders at 1850 degrees C for 6 h in vacuum. Ball milling of the as-burnt powders was found to play a key role on the in-line transmittance of the resultant ceramic.

Luminescence Investigation of Eu-Activated Sr-5(PO4)(2)SiO4 Phosphor by Combustion Synthesis

Huang, Yanlin; Gan, Jiuhui; Seo, Hyo Jin

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 4, 1143-1148

Eu-activated Sr-5(PO4)(2)SiO4 with apatite structure was synthesized by the combustion synthesis. The phase formation and morphology were investigated by X-ray powder diffraction and scanning electron microscopy measurements, respectively. The phosphors were characterized by photoluminescence excitation and emission spectra, and decays. The band gap of Sr-5(PO4)(2)(SiO4) host is found to be about 7.3 eV from the VUV excitation spectra. The replacement of the (PO4)3- anionic network by the more covalent (SiO4)4- in apatite results in red-shift of the Eu2+ emission giving rise to the two broad emission bands with peaks at 495 and 560 nm corresponding to the 4f65d1 -> 4f7(8S(7/2)) transition of Eu2+. Together with the Eu2+ luminescence, the unusual emission line (572 nm) due to the 5D(0)-> 7F(0) transition of Eu3+ is observed in Sr-5(PO4)(2)SiO4 prepared by the combustion synthesis. The temperature-dependent luminescence and decay curves of the Eu2+ and Eu3+ ions are investigated from 10 to 300 K. The crystallographic sites and reduction mechanism for Eu2+ and Eu3+ in the Sr-5(PO4)(2)SiO4 lattice are discussed. The Eu3+ ions doped in Sr-5(PO4)(2)(SiO4) are suggested to occupy MII sites with the charge compensation related to the interstitial oxygen O-i: 2Sr2+-> 2Eu3++O '(i). The unusual emission line due to the 5D(0)-> 7F(0) transition of Eu3+ in Sr-5(PO4)(2)(SiO4) is attributable to the charge-compensating oxide ion and an abnormal crystal field strength experienced by the Eu3+ ions.

Enhanced cyclic stability of CO2 adsorption capacity of CaO-based sorbents using La2O3 or Ca12Al14O33 as additives

Luo, Cong; Zheng, Ying; Ding, Ning; Zheng, Chuguang

KOREAN JOURNAL OF CHEMICAL ENGINEERING, 28, 4, 1042-1046

To improve the stability of CaO adsorption capacity for CO2 capture during multiple carbonation/calcination cycles, modified CaO-based sorbents were synthesized by sol-gel-combustion-synthesis (SGCS) method and wet physical mixing method, respectively, to overcome the problem of loss-in-capacity of CaO-based sorbents. The cyclic CaO adsorption capacity of the sorbents as well as the effect of the addition of La2O3 or Ca12Al14O33 was investigated in a fixed-bed reactor. The transient phase change and microstructure were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FSEM), respectively. The experimental results indicate that La2O3 played an active role in the carbonation/calcination reactions. When the sorbents were made by wet physical mixing method, CaO/Ca12Al14O33 was much better than CaO/La2O3 in cyclic CO2 capture performance. When the sorbents were made by SGCS method, the synthetic CaO/La2O3 sorbent provided the best performance of a carbonation conversion of up to 93% and an adsorption capacity of up to 0.58 g-CO2/g-sorbent after 11 cycles.

Structural, morphological and optical investigations on BaMgAl10O17:Eu2+ elaborated by a microwave induced solution combustion synthesis

Pradal, Nathalie; Potdevin, Audrey; Chadeyron, Genevieve; Mahiou, Rachid

MATERIALS RESEARCH BULLETIN, 46, 4, 563-568

Blue-emitting Eu2+-doped barium magnesium aluminate (BaMgAl10O17:Eu2+) for advanced displays and lighting devices was prepared by a microwave induced solution combustion synthesis using urea as combustion fuel and nitrates as oxidizer. Purity control of as-synthesized blue phosphor particles was undertaken by modifying the fuel to oxidizer molar ratio. X-ray diffraction, scanning electron microscopy and photoluminescence were used to investigate powders crystallinity, particles size, morphology and luminescent properties, respectively. Fuel-rich urea reactions preferentially lead to pure phases compared to the powders synthesized with a stoichiometric fuel to oxidizer ratio. In both cases, we produce a nearly pure well-crystallized and nanostructured BaMgAl10O17:Eu2+. Photoluminescence measurements exhibit the characteristic blue emission of Eu2+ under UV light excitation however a weak red emission associated to Eu3+ is also detected. (C) 2011 Elsevier Ltd. All rights reserved.

Development of Ni-TiC and Ni- (Ti,W)C composite powders for high velocity oxy-fuel (HVOF) coating and characterisation of coatings

Karbasi, M.; Saidi, A.; Ghavidel, M. R. Zamanzad

MATERIALS SCIENCE AND TECHNOLOGY, 27, 4, 839-844

The main objective of this research work was to develop Ni-TiC and Ni-(Ti,W)C composite powders for high velocity oxy-fuel (HVOF) coating and characterisation of the coatings. For this purpose, two kind of composite powders were produced by the self-propagation high temperature synthesis (SHS) method (Ni-TiC and Ni-(Ti,W)C composites). Subsequently composite powders were used as feedstock for HVOF coating. Also, as reference sample, similar coating was prepared using Ni and TiC powders mixture. Samples were characterised by X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy and adhesion tests. According to results, Ni-TiC and Ni-(Ti,W)C composite powders were developed via the SHS method yield appropriate HVOF coatings with dense, homogeneous, rounded, fused carbide distribution as well as suitable adhesive strength and high crack resistance. With an initial powdermixture of Ni and TiC for HVOF coating, TiC oxidation and Ti2O3 formation occurred; the microstructure of the coating was heterogeneous and irregular morphology having sharp facets. This coating had a low density and low adhesive strength and low crack resistance.

Self-propagating high-temperature synthesis of nanostructured titanium aluminide alloys with varying porosity

Farley, Cory; Turnbull, Travis; Pantoya, Michelle L.; Hunt, Emily M.

ACTA MATERIALIA, 59, 6, 2447-2454

Metallic foams were synthesized by means of a self-propagating high-temperature reaction producing a highly porous solid metal alloy with customizable material properties. Nanoscale aluminum (nAl) and nanoscale titanium (nTi) particles were mixed with either nanoscale aluminum passivated with a gasifying agent such as perfluoroalkyl carboxylic acid (C(13)F(27)COOH) or polytetrafluoroethylene (Teflon) (C(2)F(4))(n) particles and pressed into pellets. These samples were then ignited with a laser producing a reaction product composed of an AlTi alloy that has a highly porous structure. Objectives of this study were to use combustion synthesis to create a functionally graded porous AlTi alloy and identify correlations between the product microstructure and parameters such as type and amount of gasifying agent present in the reactants. Photographic data allowed interpretation of the reaction propagation while characterization of the final product indicated porosity and morphology. Results from this study may have applications in biomaterial development by tailoring porosity throughout the matrix. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Microstructural Aspects during the Preparation of Y3Al5O12 by Combustion Synthesis and Temperature Field Simulation

Song, Yuepeng; Li, Jiangtao; Chen, Yixiang; Ji, Wenwen; Lee, Chong Soo; Kim, Hyoung Seop

MATERIALS TRANSACTIONS, 52, 4, 685-690

The combustion front quenching method (CFQM) combined with the temperature field simulated using the finite element method was used to investigate the microstructural aspects of the fabrication of transparent Y3Al5O12 via combustion synthesis. The simulated results indicate that there are three regions corresponding with the temperature distribution whose microstructural aspects were studied. The composite mixtures of the products cannot be separated depending only on their gravities. The filamentous profile of aluminum along with many aluminous intermediate products are detected by XRD, SEM and EDS analysis in the preheat region, which indicates that the heat-transfer can affect the mass-transfer process and the subsequent reaction process. The microstructural aspects show that the combustion reaction of the Al/NiO/Y2O3 powder mixture was initiated by the melting of Al particles. [doi:10.2320/matertrans.M2010295]

Correction for phase-shift deviation in a complex Fourier-transform integrated-optic spatial heterodyne spectrometer with an active phase-shift scheme

Takada, Kazumasa; Aoyagi, Hirotaka; Okamoto, Katsunari

OPTICS LETTERS, 36, 7, 1044-1046

We report that a spectrum can be retrieved with a planar waveguide spatial heterodyne spectrometer (SHS) incorporating an active phase-shift scheme, where the phase shifts are distributed around pi/2. This was confirmed experimentally with an SHS that had 32 interleaved Mach-Zehnder interferometers and whose free spectral range was 625 GHz. The phase shifts ranged from 0.71 to 2: 2 rad against the target of pi/2 rad. (C) 2011 Optical Society of America

Characteristics of exothermic reaction fronts in the gasless combustion system

Kang, Tae Sung; Park, Chang-Ho; Kim, Sang Hwan

CERAMICS INTERNATIONAL, 37, 3, 825-833

Gasless combustion model of the self-propagating high-temperature synthesis process was numerically studied in the non-adiabatic cylindrical sample. The model equations, which are very stiff in the dimension of length as well as time, were solved using finite difference method on adaptive meshes. Travelling waves with constant pattern were observed for adiabatic systems. For higher values of heat of reaction and activation energy, combustion fronts started to oscillate for adiabatic and non-adiabatic systems. Simple and complex oscillatory fronts were observed. Multi-peak and irregular oscillations were also detected to presumably result in the gasless chaotic combustion. In oscillatory fronts the temperature can overshoot the adiabatic reaction temperature to result in the complete conversion of solid reactant. In the two dimensional non-adiabatic cylindrical sample in the domain of longitudinal and angular directions, oscillatory piston waves were observed. In addition asymmetrical fingering as well as rotating waves were detected for an asymmetrical perturbation. For the adiabatic annulus cylindrical sample, the velocity of propagating fronts increased with time and the temperature overshooted the adiabatic reaction temperature if the sample were ignited from the inside. If the sample were ignited from the outside, the velocity of propagating fronts decreased with time and the temperature again overshooted the adiabatic reaction temperature. For smaller diameter of sample, the temperature increased very slowly with time for inside ignition. The temperature after ignition increased very fast overshooting the adiabatic reaction temperature for outside ignition. After several oscillations, the reaction rate decreased and the region with very slow reaction was established. (c) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Synthesis of nanocrystalline lithium niobate powders via a fast chemical route

Kuo, Chia-Liang; Chang, Yee-Shin; Chang, Yen-Hwei; Hwang, Weng-Sing

CERAMICS INTERNATIONAL, 37, 3, 951-955

Lithnium niobate (LiNbO(3)) can be obtained by mixing lithium nitrate (LiNO(3)), ammonium niobate oxalate hydrate (C(4)H(4)NNbO(9)) and glycine and then calcining at 600 degrees C for I h. The thermal analysis, structure, and morphology of the as-prepared LiNbO(3) were characterized by thermogravimetric and differential thermal analyses (TG/DTA), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The crystallization temperature of LiNbO(3) precursor is 580 degrees C based on the TG/DTA results. After being calcined at 600 degrees C, the structure of the LiNbO(3) synthesized using various ratios of glycine to metal nitrates (Psi-value) was formed with a particle size of about 29-38 nm, as found by XRD analysis. The crystal size has the lowest value at Psi = 2, and the highest level of crystallization is at Psi = 3. (c) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

EPR and photoluminescence properties of combustion-synthesized ZnAl2O4:Cr3+ phosphors

Singh, Vijay; Chakradhar, R. P. S.; Rao, J. L.; Kwak, Ho-Young

JOURNAL OF MATERIALS SCIENCE, 46, 7, 2331-2337

An efficient red emitting ZnAl2O4:Cr3+ powder phosphor material was prepared at furnace temperatures as low as 500 A degrees C by using the combustion method. The prepared powders were analyzed by X-ray diffraction and scanning electron microscopy techniques. The optical properties were studied using photoluminescence technique. The EPR spectra exhibit an intense resonance signal at g = 3.74 which is attributed to Cr3+-Cr3+ pairs, and the weak resonance signal of at g = 1.97 is attributed to Cr3+ single ion transition. The spin population (N) has been evaluated as a function of temperature. The excitation spectrum exhibits two broad bands in the visible region which are characteristic of Cr3+ ions in octahedral symmetry and the emission spectrum exhibits zero-phonon line frequencies along with vibronic frequencies. The crystal field parameter (Dq) and Racah parameters (B and C) have been evaluated and discussed.

Investigation of the mechanism of self-propagating high-temperature synthesis of TiNi

Che, Han-Qing; Ma, Yan; Fan, Qun-Cheng

JOURNAL OF MATERIALS SCIENCE, 46, 8, 2437-2444

An improved combustion front quenching method was used to investigate the mechanism of self-propagating high-temperature synthesis (SHS) of TiNi from Ti and Ni powders. The microstructural evolution in the quenched sample was observed with scanning electron microscope (SEM) and analyzed with energy dispersive X-ray spectrometry. Also, the combustion temperature of the reaction was measured, and the phase constituent of the synthesized product was inspected by X-ray diffraction. Based on those experimental results, a dissolution-precipitation-diffusion mechanism was proposed and compared with those mechanisms concluded by other authors, thus the mechanism for the SHS of TiNi was systematically discussed. In addition, the influence and necessity of pre-heating before the ignition was discussed.

Development of copper matrix composite reinforced with FeAl particles produced by combustion synthesis

Azem, S.; Nechiche, M.; Taibi, K.

POWDER TECHNOLOGY, 208, 2, 515-520

This work focuses on the synthesis of FeAl intermetallic compound by combustion synthesis (SHS process) and its inclusion as dispersoids in a copper matrix to develop a metal matrix composite (MMC) by sintering. In the first step, FeAl compound was produced by the sintering of Fe-50 at.%Al at 1100 degrees C. Then, after grinding and mixing with copper powder, it was sintered in solid phase and liquid phase to obtain a metal matrix composite. The Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy (SEM and EDS-X) analysis showed that copper diffuses in the microporosity of the FeAl particles and leaves porosity in the matrix. FeAl was milled by high energy to reduce the size of particles. It was then co-milled with copper to coat its particles in order to achieve higher density. The results showed that copper coats the FeAl particles which become finer and less porous. However, a low porosity persists in the matrix after sintering. (C) 2010 Elsevier B.V. All rights reserved.

Dense Mosi(2) produced by reactive flash sintering: Control of Mo/Si agglomerates prepared by high-energy ball milling

Cabouro, G.; Le Gallet, S.; Chevalier, S.; Gaffet, E.; Grin, Yu.; Bernard, F.

POWDER TECHNOLOGY, 208, 2, 526-531

The objective of this work is to determine the influence of the agglomeration state of the MA mixture on the microstructure and the chemical composition of SPS end-products. In order to produce MoSi2 with a microstructure and a density perfectly controlled via reactive sintering implying an SHS reaction, the characteristics of Mo/Si mechanically activated (MA) powder mixtures were investigated. Indeed, the MA powders have been characterized in terms of their surface specific area, size, phase composition and microstructure. The high-energy milling allows the formation of agglomerates (0.8 to 800 gm) composed of nanometric crystallites of molybdenum and silicon, as a consequence of a continuous fracture-welding process. This enhances the reactivity of powder mixtures due to an increase of interface number. The simultaneous synthesis-consolidation in one step could be performed using the spark plasma sintering (SPS) process. This study was performed on three agglomerate sizes: empty set < 125 mu m, <= 125 mu m < 250 mu m and >= 250 mu m. (C) 2010 Elsevier B.V. All rights reserved.

Different Effect of the Atmospheres on the Phase Formation and Performance of Li4Ti5O12 Prepared from Ball-Milling-Assisted Solid-Phase Reaction with Pristine and Carbon-Precoated TiO2 as Starting Materials

Yuan, Tao; Cai, Rui; Shao, Zongping

JOURNAL OF PHYSICAL CHEMISTRY C, 115, 11, 4943-4952

Pristine Li4Ti5O12 and Li4Ti5O12/C composite are prepared by high-energy ball-milling (HEBM)-assisted solid-state reaction with TiO2 anatase and Li2CO3 or carbon-precoated TiO2 anatase and Li2CO3 as reactants. The influence of calcination atmosphere on the phase formation and particulate morphology of those two products are systematically investigated by XRD, SEM, TEM, O-2-TPO, and TPR techniques. The optimal calcination atmospheres for the synthesis of Li4Ti5O12 and Li4Ti5O12/C are diluted hydrogen and nitrogen atmospheres, respectively. TPR in various atmospheres demonstrates the difference in optimal atmospheres is due to the suppressing effect of hydrogen for Li2CO3 decomposition, the reducing properties of carbon and hydrogen, and the blocking effect of carbon for the reaction between TiO2 and Li2O. Both the pristine and carbon-coated Li4Ti5O12 show good rate and cycling performance. A near theoretical capacity of 175 mA h g(-1) is achieved for both samples at 0.5 C rate. After a total cycling number of 40 at various rates between 0.5 and 40 C, the capacity retention for Li4Ti5O12 and Li4Ti5O12/C is 97.8 and 98.5%, respectively. The HEBM-assisted solid-state reaction in controlled atmosphere may be a practical way for the economic synthesis of both pristine and carbon-coated Li4Ti5O12 as high-performance electrodes of lithium-ion batteries.

Amorphous Carbon Coated High Grain Boundary Density Dual Phase Li4Ti5O12-TiO2: A Nanocomposite Anode Material for Li-Ion Batteries

Rahman, Md Mokhlesur; Wang, Jia-Zhao; Hassan, Mohd Faiz; Wexler, David; Liu, Hua Kun

ADVANCED ENERGY MATERIALS, 1, 2, 212-220

This work introduces an effective, inexpensive, and large-scale production approach to the synthesis of a carbon coated, high grain boundary density, dual phase Li4Ti5O12-TiO2 nanocomposite anode material for use in rechargeable lithium-ion batteries. The microstructure and morphology of the Li4Ti5O12-TiO2-C product were characterized systematically. The Li4Ti5O12-TiO2-C nanocomposite electrode yielded good electrochemical performance in terms of high capacity (166 mAh g(-1) at a current density of 0.5 C), good cycling stability, and excellent rate capability (110 mAh g(-1) at a current density of 10 C up to 100 cycles). The likely contributing factors to the excellent electrochemical performance of the Li4Ti5O12-TiO2-C nanocomposite could be related to the improved morphology, including the presence of high grain boundary density among the nanoparticles, carbon layering on each nanocrystal, and grain boundary interface areas embedded in a carbon matrix, where electronic transport properties were tuned by interfacial design and by varying the spacing of interfaces down to the nanoscale regime, in which the grain boundary interface embedded carbon matrix can store electrolyte and allows more channels for the Li+ ion insertion/extraction reaction. This research suggests that carbon-coated dual phase Li4Ti5O12-TiO2 nanocomposites could be suitable for use as a high rate performance anode material for lithium-ion batteries.

Convenient synthesis of Fe-filled boron nitride nanotubes by SHS method

Qian, Qiongli; Wang, Jilin; Gu, Yunle; Li, Jie; Zhao, Guowei; Zhang, Laiping; Pan, Xinye

MATERIALS LETTERS, 65, 5, 866-868

Fe-filled boron nitride (BN) nanotubes with high purity and good yield were conveniently synthesized by a novel ball-milling and self-propagation high-temperature synthesis (SHS) method at a low temperature (700 degrees C). The as-prepared product was characterized by XRD, FTIR, SEM, TEM and HRTEM. The results of XRD, FTIR and HRTEM reflect that the product is a hexagonal BN nanotube filled with Fe. The results of SEM and TEM reveal that the Fe-filled BN nanotubes have a diameter of 20-150 nm with the wall-thickness of about 20 nm and the length of more than 5 mu m. The possible growth mechanism was also discussed. (C) 2010 Elsevier B.V. All rights reserved.

Improved electrochemical performance and thermal compatibility of Fe- and Cu-doped SmBaCo2O5+delta-Ce0.9Gd0.1O1.95 composite cathode for intermediate-temperature solid oxide fuel cells

Lee, Seung Jun; Kim, Dong Seok; Muralidharan, P.; Jo, Seung Hwan; Kim, Do Kyung

JOURNAL OF POWER SOURCES, 196, 6, 3095-3098

Fe- and Cu-doped SmBaCo2O5+delta (FC-SBCO)-Ce0.9Gd0.1O1.95 (CGO) composites with various CGO contents (0-40 wt.%) are investigated as new cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on a Ce0.9Gd0.1O1.95 electrolyte. The effect of CGO incorporation on the thermal expansion coefficient (TEC), electrochemical properties and thermal stability of the FC-SBCO-CGO composites is investigated. A composite cathode of 30 wt.% CGO-70 wt.% FC-SBCO (CS30-70) coated on a Ce0.9Gd0.1O1.95 electrolyte shows the lowest area specific resistance (ASR), i.e., 0.049 Omega cm(2) at 700 degrees C. The TEC of the CS30-70 cathode is 14.1 x 10(-6) degrees C-1 up to 900 degrees C, which is a lower value than that of the FC-SBCO (16.6 x 10(-6) degrees C-1) counterpart. Long-term thermal stability and thermal cycle tests of the CS30-70 cathode are performed. Stable ARS values are observed during both type of test. An electrolyte-supported (300-mu m thick) single-cell configuration of CS30-70/CGO/Ni-CGO delivers a maximum power density of 535 mW cm(-2) at 700 degrees C. The unique composite composition of CS30-70 demonstrates improved electrochemical performance and good thermal stability for IT-SOFCs. (C) 2010 Elsevier B.V. All rights reserved.

Electrochemical effects of ALD surface modification on combustion synthesized LiNi1/3Mn1/3Co1/3O2 as a layered-cathode material

Riley, Leah A.; Van Ana, Sky; Cavanagh, Andrew S.; Yan, Yanfa; George, Steven M.; Liu, Ping; Dillon, Anne C.; Lee, Se-Hee

JOURNAL OF POWER SOURCES, 196, 6, 3317-3324

Combustion synthesized Li(Ni1/3Mn1/3Co1/3)O-2 particles are coated with thin, conformal layers of Al2O3 by atomic layer deposition (ALD). XRD, Raman, and FTIR are used to confirm that no change to the bulk, local structure occurs after coating. Electrochemical impedance spectroscopy (EIS) results indicate that the surface of the Li(Ni1/3Mn1/3Co1/3)O-2 are protected from dissolution and HF attack after only 4-layers, or similar to 8.8 angstrom of alumina. Electrochemical performance at an upper cutoff of 4.5 V is greatly enhanced after the growth of Al2O3 surface film. Capacity retention is increased from 65% to 91% after 100 cycles at a rate of C/2 with the addition of only two atomic layers. Due to the conformal coating, the effects on Li(Ni1/3Mn1/3Co1/3)O-2 overpotential and capacity are negligible below six ALD-layers. We propose that the use of ALD for coating on Li(Ni1/3Mn1/3Co1/3)O-2 particles makes the material a stronger replacement candidate for LiCoO2 as a positive electrode in lithium ion batteries. (c) 2010 Elsevier B.V. All rights reserved.

Effect of reactant Ti/B4C ratio on the stoichiometry and mechanical properties of h-BN-Ti(C,N) prepared by combustion synthesis

Li, Hongbo; Zheng, Yongting; Han, Jiecai; Zhou, Lijuan

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 528, 6, 2380-2384

h-BN-Ti(C,N) ceramic composites were prepared by combustion synthesis from B4C-Ti powder compacts ignited under high gaseous nitrogen pressure. The influences of Ti/B4C ratio in reactant on the combustion temperature and velocity, phase composition and N content in Ti(C,N) phase were analyzed through theoretical and experimental studies. Experimental results show that combustion temperature and velocity increased with the increase of Ti/B4C ratio in reactant. TiN is the preferential formation phase under high nitrogen pressure, which resulted in higher N content in Ti(C,N) phase. Mechanical properties of the composites increased with the increase of Ti/B4C ratio because of higher Ti(C,N) content in products. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.

Preparation and characterization of La1-xKxFeO3 (x=0-1) by self-propagating high-temperature synthesis for use as soot combustion catalyst

Taniguchi, Keita; Okinaka, Noriyuki; Akiyama, Tomohiro

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 10, 4084-4088

This paper proposes La1-xKxFeO3 prepared by self-propagating high-temperature synthesis (SHS) as an alternative to platinum catalysts for promoting diesel soot combustion. The catalytic property of eleven products SHSed with different substitution ratios of potassium (x = 0-1) was experimentally evaluated using a thermobalance. In the mass loss curves of the product, T-50 was defined as the temperature at which the weight of the reference soot decreases to half its initial weight. The BET specific surface area of SHSed La1-xKxFeO3 depended on x strongly. All the products showed good oxidation catalytic activity. Despite having the smallest surface area (0.11 m(2)/g) among the obtained products, La0.91K0.1FeO3 (x = 0.1) was found to be the best catalyst with the lowest T-50 (442 degrees C). T-50 of La1-xKxFeO3 decreased with increasing x for x > 0.2. The products with x = 0.6 and 0.8 were the second-best catalysts in terms of their T-50. Moreover, average apparent activation energy of La0.91K0.1FeO3 (x = 0.1) calculated by Friedman method using TG was as much as 61 kJ/mol lower than that of Pt/Al2O3 catalyst. In conclusion, potassium-substituted SHSed La1-xKxFeO3 can be used as an alternative to Pt/Al2O3 for soot combustion. (C) 2011 Published by Elsevier B.V.

Lanthanum ferrite ferromagnetic nanocrystallites by a polymeric precursor route

Popa, Monica; Moreno, Jose M. Calderon

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 10, 4108-4116

Reactive lanthanum orthoferrite nanoparticles were obtained by a polymeric precursor route. Nanoparticle growth and crystallization from amorphous precursor, as well as the formation of a grain boundary network in polycrystalline aggregates at different calcination temperatures were studied by conventional and high-resolution electron microscopy; electron and X-ray diffraction analysis; Raman; IR; and UV-vis spectroscopy. Microstructure measurements were compared to X-ray diffraction and chemical analysis results. Electron diffraction, combined with electron microscopy results were used to determine the content of amorphous phase. The coherent crystalline domain size and the particle size have been monitored by XRD and electron microscopy in order to determine the evolution of both crystal size and the onset temperature for crystallites formation. The results demonstrate that at 550 degrees C we obtain pure single-phase nanocrystalline LaFeO(3), sized similar to 40 nm, without the presence of amorphous phase. The magnetization curves in the 5-350 K range indicate weak ferromagnetism of the LaFeO(3) powders. (C) 2010 Elsevier B.V. All rights reserved.

Effects of alpha- and beta-Si3N4 as precursors on combustion synthesis of (alpha plus beta)-SiAlON composites

Yeh, C. L.; Wu, F. S.; Chen, Y. L.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 9, 3985-3990

Preparation of (alpha + beta)-SiAlON composites from the powder compacts of Si, Si3N4, SiO2, Al, and AlN was investigated by self-propagating high-temperature synthesis (SHS) in nitrogen of 2.17 MPa. Test samples adopted not only pure alpha- and beta-Si3N4, but also a mixture of (alpha + beta)-Si3N4. The combustion temperature and flame-front propagation velocity decreased with increasing ratio of Si/Si3N4, but they increased with proportion of alpha/beta-Si3N4. For the sample containing pure alpha-Si3N4, the synthesis reaction yielded only alpha-SiAlON with various morphologies including equiaxed crystals, elongated grains, and fine whiskers. As a mixture of (alpha + beta)-Si3N4 was employed, the resulting products were (alpha + beta)-SiAlON composites, within which the content of beta-SiAlON increased with increasing beta-Si3N4. For the sample adopting 100% beta-Si3N4, comparable amounts of alpha- and beta-SiAlON were produced. Additionally, the morphology of (alpha + beta)-SiAlON composites was dominated by elongated grains with a high aspect ratio. (C) 2011 Elsevier B. V. All rights reserved.

Catalytic Consequence of Oxygen of Lanthanum Ferrite Perovskite in Chemical Looping Reforming of Methane

Mihai, Oana; Chen, De; Holmen, Anders

INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 50, 5, 2613-2621

LaFeO(3) perovskites were prepared by solution combustion method using Dextro D-(-) Levo-(+) tartaric acid as a complexing agent. Characterization by different techniques such as X-ray diffraction, Brunauer-Emmett-Teller surface area, and scanning electron microscopy revealed relatively small crystals of perovskites. A relatively high capacity of reversible oxygen storage (3 mmol/gcat) of LaFeO(3) has been evidenced. High activity and high selectivity to synthesis gas make LaFeO(3) attractive as a catalyst and oxygen carrier for methane partial oxidation by the chemical looping process. The study of the reaction rate as function of oxygen site coverage reveals a kinetic relevant step in methane partial oxidation involving a pair of surface oxygen and oxygen vacancy. Removal of lattice oxygen,generated vacancy sites which increase the reaction rate at relatively high oxygen concentrations, while the availability of surface oxygen determines the reaction rate at relatively low surface oxygen concentrations. The surface. adsorbed oxygen is highly active to complete combustion while the lattice oxygen is very selective to synthesis gas.

Influence of the MgCo2O4 Preparation Method on N2O Catalytic Decomposition

Zamudio, Miguel A.; Bensaid, Samir; Fino, Debora; Russo, Nunzio

INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 50, 5, 2622-2627

MgCo2O4 spinel catalysts were prepared via the solution combustion synthesis (SCS) and coprecipitation (CP) methods. The produced powder catalysts were. characterized by XRD, BET, FESEM, TPD, and XPS. The performance of these catalysts toward the decomposition of N2O to N-2 and O-2 was evaluated in a temperature programmed reaction (TPRe) apparatus in the absence and in the presence of oxygen (W/F = 0.03 g.s/cm(3)). The catalyst prepared by the CP method has been found to provide the best activity; the half conversion temperature (T-50) of nitrous oxide was 380 and 415 degrees C in the absence and in the presence of oxygen, respectively. The MgCo2O4 spinet catalysts were directly deposited, by in situ SCS and CP, over ceramic honeycomb monoliths and tested :in a lab-scale test rig. Again in this case, a prevalent activity of the catalytic monolith prepared by CP has been observed. The higher activity of the catalyst prepared by CP could be correlated with its higher surface area and its higher capacity of enriching the surface with the more reactive suprafacial, weakly chemisorbed, oxygen species.

An Experimental Study on Creep Damage of In-Situ TIC-Based Composites

Li, Bin; Liu, Zong-de; Wang, Song

ADVANCED SCIENCE LETTERS, 4, 3, 1244-1248

TiC-based composite is a potential high-temperature structural material. So studying the high temperature performance of TIC-based composite is necessary. The creep experiments of TiC/Ni composite were carried out at 650 degrees C and 750 degrees C. The creep damage properties of these composites were discussed. An increase of the stress exponent and the creep threshold stress with decreasing temperature was found experimentally. Creep damage analyses are made under constant stress. The creep fracture mechanism was analyzed by creep microstructures.

Producing Cu/ZrO2 Composites by Combining Mechanical Activation and Self-Propagating High-Temperature Synthesis

Grigor'eva, T. F.; Letsko, A. I.; Talako, T. L.; Tsybulya, S. V.; Vorsina, I. A.; Barinova, A. P.; Il'yushchenko, A. F.; Lyakhov, N. Z.

COMBUSTION EXPLOSION AND SHOCK WAVES, 47, 2, 174-178

The possibility of producing Cu/ZrO2 composites by combining mechanical activation and self-propagating high-temperature synthesis (SHS) is studied using x-ray diffraction and electron microscopy. It is shown that Cu/ZrO2 composites are formed in SHS using CuO/Cu/Zr mechanocomposite as a precursor.

Reductive/expansion synthesis of zero valent submicron and nanometal particles

Zea, Hugo; Luhrs, Claudia C.; Phillips, Jonathan

JOURNAL OF MATERIALS RESEARCH, 26, 5, 672-681

Upon rapid heating to a high temperature (similar to 800 degrees C), mixtures of nitrate compounds and urea created nano and submicron metal particles. The process (reductive/expansion synthesis, RES) results in atomic scale mixing. The product formed from mixed-nitrate (Fe + Ni) salts and urea created true metallic alloy. Unlike other product-from-powder synthesis processes, this process produced only zero valent metal. Initial work suggests this method is a scalable and efficient means for making metallic nanoparticles. Although this is primarily a phenomenological report, a preliminary model is presented: Initially, nitrates decompose to oxide; thus in the absence of urea metal oxide particles form, as in the case of combustion synthesis. In the case of urea/nitrate mixtures, there is a "convolution" of decomposition processes. Urea decomposes to yield reducing gases, leading to the formation of metal rather than oxide. Rapid "expansion" of gas leads to "shattering," resulting in highly dispersed particles.

Synthesis of Ni ferrite powders by coprecipitation and hydrothermal methods

Popescu, S. A.; Vlazan, P.; Notingher, P. V.; Novaconi, S.; Grozescu, I.; Bucur, A.; Sfirloaga, P.

JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 41366, 260-262

The coprecipitation and hydrothermal methods were used to obtain Ni ferrite nanopowders with Ni(0.8)Fe(2.2)O(4) stoichiometry. Morphological and magnetic properties of the synthesized nickel ferrites nanopowders have been studied. The structural properties of the Ni(0.8)Fe(2.2)O(4) nanopowders were studied by X-ray diffraction (XRD). Surface morphology was examined by scanning electron microscopy (SEM). The results show that both the synthesis method and conditions used to obtain the Ni ferrites have significant influence on their structure and properties. The low frequency (50 Hz) magnetic behavior of the Ni ferrites also exhibits important differences evidenced by magnetic hysteresis curves.

Promising blue emitting Ca3.5Mg0.5Si3O8Cl4:Eu2+ nanophosphor for near UV-excited white-LEDs

Pawade, V. B.; Dhoble, N. S.; Dhoble, S. J.

OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 41367, 208-210

In this paper we reported Eu2+ luminescence in novel Ca3.5Mg0.5Si3O8Cl4 phosphors synthesized by combustion method at 550 degrees C furnace temperature. Phosphor was well characterized by XRD for confirmation of phase purity and PL properties of Ca3.5Mg0.5Si3O8Cl4:Eu2+ shows emission wavelength at 494 nm corresponds to 4f(6)5d(1)-> 4f(7) transition of Eu2+ ion by keeping excitation extending broad-band from 300-400 nm centred at 345 nm. Scanning electron microscopy has been used for exploring the morphological properties of the prepared phosphors. The PL characteristics show that prepared phosphor have potential application for near UV-excited white-LEDs.

Study on catalytic properties of Ni3Al made by self-propagating high-temperature synthesis

Kocemba, Ireneusz; Arkatova, Larisa; Rynkowski, Jacek M.

PRZEMYSL CHEMICZNY, 90, 3, 434-439

Ni3Al powder was prepd. by self-propagating high-temp. synthesis, studied for chem. structure and used as catalyst for air oxidn. of CO and for dry reforming of CH4 with CO2 after temp.-programmed oxidn. and redn. Formation of thin Ni layer on Ni3Al support was assumed as catalytically active component of the catalyst. Reaction mechanisms were proposed.

Preparation of ultrafine Co3O4 powders by continuous and controllable combustion synthesis

Wu Chong-hu

TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 21, 3, 679-684

The continuously dynamic-controlled combustion synthesis (CDCCS) was developed based on the continuous fluidization and combustion synthesis technologies. CoC2O4 center dot 2H(2)O powders were transformed to Co3O4 in a gas-solid fluid bed unit designed and build independently, where the reactant of CoC2O4 center dot 2H(2)O powders and the reactant of air were poured and introduced from the top and the bottom of the bed at a certain rates respectively. The reagents met in the bed and ignited at a given low temperature, resulting in formation of Co3O4. The results show a significant difference in combustion wave models. In the case of CDCCS, there was an immobile combustion wave, floating in the combustion zone located in the middle of the bed, instead of propagating of the combustion wave. The temperature of the combustion wave can be controlled by adjusting the flow rate of carrier gas. The resultant Co3O4 powders (diameter size <= 0.8 mu m) have a narrow particle size distribution and spherical or quasi-spherical shape. This novel technique has many advantages, such as continuation, efficiency, energy conservation and environmental friendly and has been used in mass production.

Dispersion of ultrafine SiC particles in molten Al-12Si alloy

Park, Jin-Ju; Lee, Sang-Hoon; Lee, Min-Ku; Rhee, Chang-Kyu

TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 21, , S33-S36

The bulk Al-12 Si eutectic composites were fabricated through a conventional liquid metal casting route, especially with the help of ultrafine ceramic powders made by self-propagating high-temperature synthesis (SHS) process. The SHS powders were fabricated by the chemical reaction between micro-sized SiC and Al particles at very high combustion temperatures, producing the coarse Al particles (several tens of microns) containing ultrafine SiC ceramic particles. Microstructural observation revealed that the addition of ultrafine SiC particles has a crumbling tendency of Si eutectic phase. It is suggested that the casting method combined with SHS process is promising for fabricating the Al-based MMC with ultrafine ceramic particles.

Reactive Atmospheric Plasma Spraying of AlN Coatings: Influence of Aluminum Feedstock Particle Size

Shahien, Mohammed; Yamada, Motohiro; Yasui, Toshiaki; Fukumoto, Masahiro

JOURNAL OF THERMAL SPRAY TECHNOLOGY, 20, 3, 580-589

Feedstock powder characteristics (size distribution, morphology, shape, specific mass, and injection rate) are considered to be one of the key factors in controlling plasma-sprayed coatings microstructure and properties. The influence of feedstock powder characteristics to control the reaction and coatings microstructure in reactive plasma spraying process (RPS) is still unclear. This study, investigated the influence of feedstock particle size in RPS of aluminum nitride (AlN) coatings, through plasma nitriding of aluminum (Al) feedstock powders. It was possible to fabricate AlN-based coatings through plasma nitriding of all kinds of Al powders in atmospheric plasma spray (APS) process. The nitriding ratio was improved with decreasing the particle size of feedstock powder, due to improving the nitriding reaction during flight. However, decreasing the particle size of feedstock powder suppressed the coatings thickness. Due to the loss of the powder during the injection, the excessive vaporization of fine Al particles and the completing nitriding reaction of some fine Al particles during flight. The feedstock particle size directly affects on the nitriding, melting, flowability, and the vaporization behaviors of Al powders during spraying. It concluded that using smaller particle size powders is useful for improving the nitriding ratio and not suitable for fabrication thick AlN coatings in reactive plasma spray process. To fabricate thick AlN coatings through RPS, enhancing the nitriding reaction of Al powders with large particle size during spraying is required.

INFLUENCE OF HEAT TREATMENT ON SHAPE MEMORY EFFECT IN POROUS TITANIUM NICKEL SYNTHESIZED BY THE SHS PROCESS

Khodorenko, V. N.; Guenther, V. E.; Soldatova, M. I.

RUSSIAN PHYSICS JOURNAL, 53, 10, 1024-1034

An analysis of the influence of heat treatment on the features of variation in parameters of multiple shape-memory effect for porous titanium nickel produced by the method of self propagating high-temperature synthesis (SHS) is presented. It is shown that heat treatment of porous titanium nickel substantially affects its structure and physicomechanical properties. Annealing at the temperatures within T = 400-600 degrees C favors an improvement of its physicomechanical characteristics and manifestation of the maximum shape memory effect. It is revealed that a further increase in the temperature, however, results in deterioration of its properties. An optimal temperature of heat treatment of articles made from pore-permeable titanium nickel is proposed - T = 400-450 degrees C for 1 hour in vacuum.

Application of Parallel Synthesis and High Throughput Characterization in Photocatalyst Discovery

Sun, Song; Ding, Jianjun; Bao, Jun; Luo, Zhenlin; Gao, Chen

COMBINATORIAL CHEMISTRY & HIGH THROUGHPUT SCREENING, 14, 3, 160-172

The last decade has seen significant progresses in the application of combinatorial approaches and high throughput screening in photocatalyst discovery. This paper aims at providing a comprehensive review on the parallel synthesis and high throughput characterization of photocatalysts, including the development of instrumentation, strategy of experiment, preparation of libraries, high throughput screening technique and data analysis. The review ends with a summary of the remaining challenges and prospects on combinatorial photocatalyst discovery.

Manufacturing of aluminum foam sandwich panels: comparison of a novel method with two different conventional methods

Nabavi, A.; Khaki, J. Vahdati

JOURNAL OF SANDWICH STRUCTURES & MATERIALS, 13, 2, 177-187

In this study, a novel method for manufacturing metal foam sandwich panels via self-propagating high temperature synthesis (SHS) has been introduced. In this method, a powder mixture of metallic aluminum and copper oxide was placed in core-sheet interface, and then sandwich panel was heated under static pressure. During heating, SHS reaction (3CuO + 2Al = + 3Cu, Delta H < 0) occurred in the interface. The generated heat from this exothermic reaction caused sheets to join the core by melting the interface and nearby. In order to evaluate the shear strength of the interface, the shear test was applied to the manufactured sandwich panels and its results were compared with sandwich panels, which were produced by diffusion and adhesive bonding processes. Furthermore, by the aid of energy dispersive spectrometer and X-ray diffraction analyses, the formation of copper in the core-sheet interface and its diffusion into the sheets and the core were investigated. The results showed that metal foam sandwich panels produced by using SHS method have higher joint strength than those produced by diffusion and adhesive bonding processes, and the maximum shear strength of the interface was achieved in shorter heating time. Significantly, this innovating method for manufacturing metal foam sandwich panels can be applied as a proper and alternative method.

Combustion Synthesis and Properties of Gd3Ga5O12:Eu3+ Luminescence Nanocrystals

Li Yan-Hong; Lu Hai-Yan; Zhang Yong-Ming; Liu Qian

CHINESE JOURNAL OF INORGANIC CHEMISTRY, 27, 3, 533-536

Gd3Ga5O12:Eu3+ nanocrystals were prepared by a combustion method using urea as fuel agent and glycol as dispersing agent.. The structure, morphology and luminescence properties of the precursors and the samples after heat treatment were characterized by XRD, SEM and luminescence spectroscopy. The results of XRD indicated that Gd3Ga5O12:Eu3+ nanocrystals with cubic phase could be obtained by annealing precursor at 700 degrees C for 2 h. The average crystallite size by using the Scherrer equation is 28 nm and 42 nm for samples annealed at 700 degrees C and 900 degrees C, respectively. The results of excitation spectra and emission spectra showed that the emission peaks were ascribed to D-5(0)-F-7(J) tranisition, and the magnetic dipole transition originated front D-5(0)-> F-7(1) of Eu3+ was the strongest, the broad excitation bands belonged to charge transfer band of Eu-O and the host absorption of Gd3Ga5O12. The intensities of emission and excitation increased with increase in annealing temperature.

Phase Relations in the TiO2-CsNO3 System between 550 and 1140 K

Kobyakov, V. P.; Barinova, T. V.; Sichinava, M. A.

INORGANIC MATERIALS, 47, 3, 290-295

We have studied reactions in the TiO2 CsNO3 system in the temperature range 550 1140 K in air using sample weight measurements, X-ray diffraction, electron microscopy, and electron probe microanalysis. The samples heat-treated at temperatures from 850 to 1140 K contained titanium cesium oxides.

Reaction synthesis and wear resistance of a TiCp/Ni3Al-Fe composite coating on steel

Wei, Minxian; Wang, Shuqi; Cui, Xianghong; Yang, Zirun; Zhao, Yutao

INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 102, 3, 298-303

A multiphasic composite coating on steel was fabricated by reaction synthesis in the melt. The ceramic particulate reinforced intermetallic matrix composite (TiCp/Ni3Al) and the mixture (TiCp/Ni3Al Fe) of the composite and steel were successively formed from the coating surface to the steel matrix. Metallurgical fusion of the reactive products with the steel melt occurred to form the multiphasic composite coating after solidification. The Ti-C-3Ni-Al system was employed to synthesize the composite coating. The reaction processes of the system were investigated using a differential scanning calorimeter and an X-ray diffractometer. The coating presented higher elevated-temperature wear resistance than H13 steel and markedly postponed the transition from mild wear to severe wear.

Effect of Solution Treatment on Thermal Conductivity of Porous NiTi Shape Memory Alloy

Kaya, Mehmet; Bugutekin, Abdulcelil; Orhan, Nuri

INTERNATIONAL JOURNAL OF THERMOPHYSICS, 32, 3, 665-673

In this study, a new solution treatment "solution treatment under loading" was applied to a porous Ni-50 at.%Ti shape memory alloy (SMA), which was fabricated by self-propagating high-temperature synthesis (SHS), to explore the microstructural improvement regarding single-phase NiTi. The effects of solution treatment under loading and without loading on the phase constituent and thermal conductivity were investigated and discussed. The phase constituent and thermal conductivity of the specimens considerably changed with solution treatment under loading, but they were not affected significantly with solution treatment without loading. Intermetallic phases such as B19'(NiTi), Ti2Ni, and Ni4Ti3 disappeared, the density of the B2(NiTi) phase increased with solution treatment under loading, and thus the thermal conductivity was increased. It was also seen that the thermal conductivity of porous NiTi was less than that of solid NiTi.

Preparation and Spectroscopy Analysis of Spinel CoCr2.xAlxO4 by Low-temperature Combustion Synthesis

Hu Dong-Sheng; Han Ai-Jun; Ye Ming-Quan; Chen Hou-He; Zhang Wei

JOURNAL OF INORGANIC MATERIALS, 26, 3, 285-289

As a member of complex metal oxides, spinel CoCr2O4 has wide application in ceramic pigment, catalysis and magnetic materials. In order to reduce the Cr content and modify the color performance, nanoscaled spinel solid solution CoCr2-xAlxO4(x=0, 0.05, 0.1, 0.2, 0.3 and 0.5) was synthesized by low-temperature combustion synthesis (LCS) method using citric acid (reductant) and metal nitrates (oxidants) as starting materials. XRD, TEM, FT-IR, UV-Vis spectrometer and color spectrometer were employed to characterize the structure, morphology, infrared, ultraviolet-visible curve and the color parameters of the as-prepared sample, respectively. Results show that single-phased and uniform CoCr2-xAlxO4 with about 15-30 nm in size can be prepared by LCS at 800 degrees C. Absorption bands at about 520 cm(-1) 630 cm(-1) and 410-450 cm(-1) in IR curve are corresponding to the vibration of octahedron group and the complex vibration of octahedron and tetrahedron group. Absorption bands at 570, 610 and 660 nm in the visible region of UV-Vis curve are assigned to the (4)A(2)(F)-> T-4(1)(P) of Co2+ and (4)A(2g)-> T-4(2g) of Cr3+. Color spectrometer characterization results indicate that the sample exhibits best color performance with x=0.2, showing a bright bluish green color.

Catalytic synthesis of bamboo-like multiwall BN nanotubes via SHS-annealing process

Zhang, L. P.; Gu, Y. L.; Wang, J. L.; Zhao, G. W.; Qian, Q. L.; Li, J.; Pan, X. Y.; Zhang, Z. H.

JOURNAL OF SOLID STATE CHEMISTRY, 184, 3, 633-636

Bamboo-like multiwall boron nitride (BN) nanotubes were synthesized via annealing porous precursor prepared by self-propagation high temperature synthesis (SHS) method. The as-synthesized BN nanotubes were characterized by the field emission scanning electron microscopy (FE-SEM), transmission electron microscope (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD), Raman and Fourier transform infrared (FTIR) spectroscopy. These nanotubes have uniform diameters of about 60 nm and an average length of about 10 mu m. Four growth models, including tip, base, based tip and base-tip growth models, are proposed based on the catalytic vapor-liquid-solid (VLS) growth mechanism for explaining the formation of the as-synthesized bamboo-like BN nanotubes. Chemical reactions and annealing mechanism are also discussed. (C) 2011 Elsevier Inc. All rights reserved.

Numerical modeling of field-activated combustion synthesis process of the B4C system

Zhang, Gang; Xiao, Guoqing; Fan, Quncheng

MATERIALS RESEARCH BULLETIN, 46, 3, 345-349

A field-activation combustion synthesis process of the 4B + C reactive system was numerically simulated to investigate the effect of external field and porosity on the combustion reaction by an implicit difference method and a Gauss-Seidel iteration procedure. The new features of the model include a consideration of the melting of each constituent of the reactants and product and the inclusion of considerations involving porosity and dilution. The results show that the self-sustaining reactions are not possible until field-activated temperature is more than 1100 K. which agree with the theoretic calculation. As the reactant porosity values are decreased from 60% to 20%, the combustion velocity first increases because of an increase in the thermal conductivity. The combustion velocity, after reaching a maximum, decreases with a further decrease in the porosity because of the high value of the thermal conductivity of the reactants. (C) 2010 Elsevier Ltd. All rights reserved.

Sol-Gel Combustion-Derived CoCuMnOx Spinels as Pigment for Spectrally Selective Paints

Geng, Qing-Fen; Zhao, Xin; Gao, Xiang-Hu; Liu, Gang

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 3, 827-832

In this work, sol-gel combustion synthesis of spinel CoCuMnOx was reported. X-ray diffraction (XRD) and Fourier transformation infrared spectroscopy (FTIR) techniques were used to study the reaction processes. The as-synthesized spinel CoCuMnOx was further characterized by XRD, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. The CoCuMnOx powders with a deep black hue were then used as solar energy-absorbing additive to make a novel kind of spectrally selective paint coatings. The solar absorptance (alpha(s)) and the thermal emittance (epsilon(T)) of the coatings were determined from the corresponding diffuse reflectance spectra in the 0.3-20 mu m range. The optimum selective sample exhibited values of alpha(s)=0.928 and epsilon(100)=0.198. Besides ideal optical properties, the coatings also show excellent long-term stability, which is confirmed by results of accelerated tests established by IEA-SHC Task X, indicating that they could be a good alternative to the materials present today in the market.

Diffeomorphic Image Registration of Diffusion MRI Using Spherical Harmonics

Geng, Xiujuan; Ross, Thomas J.; Gu, Hong; Shin, Wanyong; Zhan, Wang; Chao, Yi-Ping; Lin, Ching-Po; Schuff, Norbert; Yang, Yihong

IEEE TRANSACTIONS ON MEDICAL IMAGING, 30, 3, 747-758

Nonrigid registration of diffusion magnetic resonance imaging (MRI) is crucial for group analyses and building white matter and fiber tract atlases. Most current diffusion MRI registration techniques are limited to the alignment of diffusion tensor imaging (DTI) data. We propose a novel diffeomorphic registration method for high angular resolution diffusion images by mapping their orientation distribution functions (ODFs). ODFs can be reconstructed using q-ball imaging (QBI) techniques and represented by spherical harmonics (SHs) to resolve intra-voxel fiber crossings. The registration is based on optimizing a diffeomorphic demons cost function. Unlike scalar images, deforming ODF maps requires ODF reorientation to maintain its consistency with the local fiber orientations. Our method simultaneously reorients the ODFs by computing a Wigner rotation matrix at each voxel, and applies it to the SH coefficients during registration. Rotation of the coefficients avoids the estimation of principal directions, which has no analytical solution and is time consuming. The proposed method was validated on both simulated and real data sets with various metrics, which include the distance between the estimated and simulated transformation fields, the standard deviation of the general fractional anisotropy and the directional consistency of the deformed and reference images. The registration performance using SHs with different maximum orders were compared using these metrics. Results show that the diffeomorphic registration improved the affine alignment, and registration using SHs with higher order SHs further improved the registration accuracy by reducing the shape difference and improving the directional consistency of the registered and reference ODF maps.

Identification of material model of TiN using numerical simulation of nanoindentation test

Kopernik, M.; Milenin, A.; Major, R.; Lackner, J. M.

MATERIALS SCIENCE AND TECHNOLOGY, 27, 3, 604-616

The development of the model of the multistep nanoindentation test with Berkovich indenter, accounting for the residual stress distribution, is one of the aims of the present paper. The specimen is unloaded in the intervals between the deformation steps. Substrate, which is composed of a ferritic steel and biocompatible pulsed laser deposition TiN coating, is considered. The selection of the TiN was inspired by its perspective application as the coating for a constructional element of the heart prosthesis (blood chamber and aortic valves). Sensitivity analysis of the model predictions with respect to its parameters is presented in the present paper. The theory of elastic-plastic deformations is used in the finite element model, which simulates both loading and unloading phases, accounting for the real geometry of the indent. The main goal of the present paper was to inversely analyse the tests for coating/substrate system. Square root error between measured and predicted forces is the objective function in the analysis. Results of the inverse calculations, which are presented in the present paper, may be helpful in simulations of the behaviour of TiN deposited on substrate in various applications as bionanomaterials.

A proposed System of Hierarchical Scorecards to assess the implementation of maritime regulations

Karahalios, H.; Yang, Z. L.; Williams, V.; Wang, J.

SAFETY SCIENCE, 49, 3, 450-462

The successful implementation of a regulation in the modern complicated world is a major issue for states. A newly introduced regulation may cause conflicts of interest among various parties that are affected. A common conflict is that from one hand, the public demands the introduction of regulations that will increase safety, environmental and security standards while on the other hand industries are concerned about potential costs caused by new regulations. In this paper, the shipping industry, which is a typical example of an international industry, is chosen to carry out a cost and benefit analysis generated from the implementation of a newly introduced regulation. Consequently, a methodology is proposed capable of evaluating the implementation performance of a regulation in the shipping industry with respect to the costs and benefits that can be generated. For a simple and effective computation, a System of Hierarchical Scorecards (SHS) is developed to assist regulators in evaluating any proposed and/or existing regulations. (C) 2010 Elsevier Ltd. All rights reserved.

Structure and properties of nanocrystalline BaHfO3 synthesized by an auto-igniting single step combustion technique

Thomas, J. K.; Kumar, H. Padma; Prasad, V. S.; Solomon, Sam

CERAMICS INTERNATIONAL, 37, 2, 567-571

High quality nanoparticles of barium hafnate have been synthesized using an auto-ignition modified combustion technique. The nanoparticles thus obtained have been characterized by powder X-ray diffraction, thermo gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy and transmission electron microscopy. The XRD studies have shown that the as-prepared BaHfO3 powders are phase pure. The particle size of the as-prepared powder was in the range 20-50 nm. The nanopowder could be sintered to 95% of the theoretical density at 1650 degrees C for 2 h. The ultrafine cuboidal nature of nanopowders with small degree of agglomeration improved the sinterability at relatively lower temperature and time. The microstructure of the sintered surface was examined using scanning electron microscopy. The dielectric constant (epsilon(r)) of 30.8 and loss factor (tan delta) of 2.3 x 10(-3) were obtained at 1 MHz. (C) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Preparation of single-phase magnesium silicon nitride powder by a two-step process

Yang, J. H.; Qiu, J. F.; Li, J. T.

CERAMICS INTERNATIONAL, 37, 2, 673-677

Single-phase magnesium silicon nitride (MgSiN(2)) powder was prepared by a two-step process: combustion synthesis followed by acid washing. The effects of starting material compositions, diluent addition and N(2) pressure on the phase compositions of the final products were studied, and the acid washing process was also discussed. It is difficult to synthesize single-phase MgSiN(2) by one-stage combustion reaction through regulating the process parameters because of the evaporative loss of Mg. Combustion synthesis of MgSiN(2) by using an excess of magnesium in the starting materials and then acid washing off the impurity was an effective way to prepare the single-phase MgSiN(2) powder. (C) 2010 Published by Elsevier Ltd and Techna Group S.r.l.

High room-temperature plastic and work-hardening effect of the NiAl-matrix composites reinforced by particulates

Zhao, Hailong; Qiu, Feng; Jin, Shenbao; Jiang, Qichuan

INTERMETALLICS, 19, 3, 376-381

The microstructures, interfaces, compression properties and work-hardening effect of the NiAl-matrix composites reinforced by 5-20 wt.% ceramic particulates (Nb(2)C, NbC and NbB(2)) fabricated by combustion synthesis and hot pressing (CSHP) have been investigated. The ultimate compression strength and yield strength increase with the increasing content of the ceramic particulates, while the fracture strain and work-hardening capacity (H(c)) decrease. The NiAl-matrix composite with 5 wt.% ceramic particulates has a high true ultimate strength of 1497 MPa, a fracture strain of 18.3%, and work-hardening capacity H(c) = 1.29. The good interface bonding between ceramic particulate and matrix, the high density dislocation in the NiAl matrix, the seriously distorted lattices and the intense interactions between dislocations and other crystal defects contribute to its prominent mechanical properties. (C) 2010 Elsevier Ltd. All rights reserved.

Fabrication of in-situ Ti-Si-C fine grained composite by the self propagating high temperature synthesis (SHS) process

Mishra, S. K.; Khusboo; Sherbakov, V. A.

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 2, 209-213

An attempt has been made to synthesise a Ti-Si-C composite with fine TiC and Ti-Si phase dispersed composite, using titanium, silicon and carbon powders using SHS dynamic compaction. The Ti-Si-C bulk composite with a high hardness (22.50 GPa), with a homogeneous distribution of a softer Ti-Si phase having more than 99% density of theoretical value has been successfully synthesised by the SHS dynamic process. The composite was found to be consisting of titanium carbide and titanium suicide. SEM and EDX analysis showed uniform distribution of phases and an average grain size varying around 1-2 mu m. Nanoindentation studies revealed modulus of composite about 400 GPa with an elastic recovery of 30%. (C) 2010 Elsevier Ltd. All rights reserved.

Self-propagating high temperature synthesis of SiC-Cu and SiC-Al cermets: Role of chemical activation

Zurnachyan, A. R.; Kharatyan, S. L.; Khachatryan, H. L.; Kirakosyan, A. Gh.

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 2, 250-255

Ceramic-metal composites (cermets) are widely adopted in the modern technology. These materials with ceramic and metallic phases have properties of both the constituents. In the article the possibility of synthesizing SiC-Cu and SiC-Al cermets under the activated combustion mode was studied. The influence of various parameters such as the composition of initial mixture, amount of chemical activator and metallic phase, etc. on the combustion laws was investigated. It was shown that depending on the amount of metal phase the combustion can proceed in the two different regimes - low temperature (T(c)<1200 degrees C) and high temperature (T(c)>1600 degrees C). X-ray diffraction investigations testified that the combustion products, obtained in the optimal conditions, contain silicon carbide and corresponding metal phase (copper or aluminum). According to SEM analyses the obtained products have submicron granular particles and they are characterized by uniform structure. (C) 2010 Elsevier Ltd. All rights reserved.

Microwave-assisted combustion synthesis in a mechanically activated Al-TiO2-H3BO3 system

Mousavian, R. Taherzadeh; Sharafi, S.; Shariat, M. H.

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 2, 281-288

The Al2O3-TiB2 in-situ composite has been fabricated by different techniques. In this work, the mechanical activation process has been used to aid microwave-assisted combustion synthesis (MACS) to produce the Al2O3-TiB2 in-situ composite. For this purpose, the thermite mixture of Al, TiO2 and boric acid (H3BO3) powders was used as the raw materials, and was mechanically activated at different milling speeds. The results of X-ray phase analysis of the mechanically activated samples after combustion synthesis showed that the Al2O3-TiB2 in-situ composite has been successfully fabricated by thermal explosion mode of combustion synthesis in microwave, while no combustion synthesis occurred for the unmilled sample. Also, it was found that by increasing the milling speed from 250 to 400 rpm, the purity of the final products has been increased: while further milling speed up to 550 rpm reduced the purity of the final products. The effects of milling speed were also studied by means of differential scanning calorimetry (DSC) measurements. It was shown that by increasing the energy level of the reactants via milling speed, the ignition temperature and the intensity of exothermic peaks in the DSC curves have been changed. Finally, in order to have a good understanding about the in-situ formation of such ceramic composites, a reaction mechanism was proposed based on the experimental results. The synthesized composite exhibited high microhardness value of about 1950 Hv in dense parts. (C) 2010 Elsevier Ltd. All rights reserved.

Synthesis of Ti(CN) powders by combustion reaction from Ti powder and a novel carbon-nitrogen precursor

Mu, Yunchao; Wang, Mingzhi; Yu, Dongli

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 2, 326-328

Titanium carbonitride, Ti(C, N) has been prepared by combustion synthesis from Ti powder and a carbon-nitrogen precursor. The phase composition of the sample was investigated by X-ray diffraction. The scanning electron microscopy image indicates that the average size of the obtained Ti(C, N) particles was 3 mu m. (C) 2010 Elsevier Ltd. All rights reserved.

Vitreous carbon micro-lattice structures

Jacobsen, Alan J.; Mahoney, Sky; Carter, William B.; Nutt, Steven

CARBON, 49, 3, 1025-1032

A new approach is presented to fabricate open-cellular carbon materials with an ordered, lattice-type micro-scale architecture. The carbon micro-lattice materials were fabricated by pyrolyzing a polymer precursor template formed from an interconnected three-dimensional array of self-propagating photopolymer waveguides. Impregnating the polymer precursor template with acrylonitrile increased the carbon yield of the material from 19% to 46%. Structural analysis and density measurements of the solid carbon phase are consistent with vitreous carbon. Compression experiments yielded a compressive modulus (E) of 1.1 GPa and a failure strength (sigma(f)) of 10.2 MPa for a structure with relative density of 12.8%. (C) 2010 Elsevier Ltd. All rights reserved.

Design of cold-formed stainless steel tubular T- and X-joints

Feng, Ran; Young, Ben

JOURNAL OF CONSTRUCTIONAL STEEL RESEARCH, 67, 3, 421-436

This paper describes the numerical investigation of cold-formed stainless steel tubular T-joints, X-joints and X-joints with chord preload using finite element analysis. The stainless steel joints were fabricated from square hollow section (SHS) and rectangular hollow section (RHS) brace and chord members. The geometric and material nonlinearities of stainless steel tubular joints were carefully incorporated in the finite element models. The joint strengths, failure modes as well as load-deformation curves of stainless steel tubular joints were obtained from the numerical analysis. The nonlinear finite element models were calibrated against experimental results of cold-formed stainless steel SHS and RHS tubular T- and X-joints. Good agreement between the experimental and finite element analysis results was achieved. Therefore, an extensive parametric study of 172 T- and X-joints was then carried out using the verified finite element models to evaluate the effects of the strength and behaviour of cold-formed stainless steel tubular joints. The joint strengths obtained from the parametric study and tests were compared with the current design strengths calculated using the Australian/New Zealand Standard for stainless steel structures, CIDECT and Eurocode design rules for carbon steel tubular structures. Furthermore, design formulae of cold-formed stainless steel tubular T- and X-joints are proposed. A reliability analysis was performed to assess the reliability of the current and proposed design rules. It is shown that the design strengths calculated using the proposed equations are generally more accurate and reliable than those calculated using the current design rules. (C) 2010 Elsevier Ltd. All rights reserved.

Microwave Absorption Properties of Ni-Foped SiC Powders in the 2-18 GHz Frequency Range

Jin Hai-Bo; Li Dan; Cao Mao-Sheng; Dou Yan-Kun; Chen Tao; Wen Bo; Agathopoulos, Simeon

CHINESE PHYSICS LETTERS, 28, 3, 37701-

Ni-doped SiC powder with improved dielectric and microwave absorption properties was prepared by self-propagating high-temperature synthesis (SHS). The XRD analysis of the as-synthesized powders suggests that Ni is accommodated in the sites of Si in the lattice of SiC, which shrinks in the presence of Ni. The experimental results show an improvement in the dielectric properties of the Ni-doped SiC powder in the frequency range of 2-18 GHz. The bandwidth of the reflection loss below -10 dB is broadened from 3.04 (for pure SiC) to 4.56 GHz (for Ni-doped SiC), as well as the maximum reflection loss of produced powders from 13.34 to 22.57 dB, indicating that Ni-doped SiC could be used as an effective microwave absorption material.

SYNTHESIS, STRUCTURE, AND PROPERTIES OF TITANIUM CARBOSILICIDES FROM MATERIALS FROM THE FeSi-Ti-C SYSTEM

Lepakova, O. K.; Shul'pekov, A. M.; Golobokov, N. N.; Kitler, V. D.; Avramchik, A. N.; Afanas'ev, N. I.

GLASS AND CERAMICS, 67, 41619, 351-353

The possibility of obtaining titanium carbosilicides by self-propagating high-temperature synthesis from materials based on the FeSi - Ti - C system was demonstrated. The microstructure and phase composition of the synthesized materials Ti3SiC2 and Ti5Si3Cx (x < 1), were investigated.

GAS-DYNAMIC MODEL OF THE FORMATION OF OPEN AND CLOSED POROSITY IN SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS

Uvarov, V. I.; Borovinskaya, I. P.; Lukin, E. S.

GLASS AND CERAMICS, 67, 41619, 377-379

A gas-dynamic model of the formation of open and closed porosity of materials under the conditions of combustion in SHS systems, when a liquid phase (which can boil under certain conditions), impurity-gas pressure, vapor-phase pressure, and external pressure or vacuum exist, is examined. It is shown that there exists a critical pressure which characterizes the boundary of the transition of closed to open porosity. Experimental studies for the system Ti - C showed that the size of the open pores of a synthesized sample, measured according to the volume of the sample, correlates with the computed values obtained in a study of the gas-dynamic model of the formation of open porosity using the theory of cavitation.

Mechanochemical synthesis of Al2O3-TiB2 nanocomposite powder from Al-TiO2-H3BO3 mixture

Khaghani-Dehaghani, M. A.; Ebrahimi-Kahrizsangi, R.; Setoudeh, N.; Nasiri-Tabrizi, B.

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 2, 244-249

Alumina-titanium diboride nanocomposite (Al2O3-TiB2) was produced using mixtures of titanium dioxide, acid boric and pure aluminum as raw materials via mechanochemical process. The phase transformation and structural characterization during mechanochemical process were utilized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analyses (TG-DTA) techniques. A thermodynamic appraisal showed that the reaction between TiO2, B2O3 and Al is highly exothermic and should be self-sustaining. XRD analyses exhibited that the Al2O3-TiB2 nanocomposite was formed after 1.5 h milling time. The results indicate that increasing milling time up to 40 h had no significant effect other than refining the crystallite size. (C) 2010 Elsevier Ltd. All rights reserved.

Preparation and property-performance relationships in samarium-doped ceria nanopowders for solid oxide fuel cell electrolytes

Kosinski, Marcin R.; Baker, Richard T.

JOURNAL OF POWER SOURCES, 196, 5, 2498-2512

In a systematic study, Samarium doped ceria (SDC) nanopowders, Sm(x)Ce(1-x)O(2-x/2) (x = 0.1, 0.2 or 0.3), were prepared by a low temperature citrate complexation route. The synthesis and crystallisation of the SDC powders were followed by thermochemical techniques (TGA/DTA). X-ray diffraction, elemental analysis, specific surface area determination (BET) and electron microscopy (SEM and TEM). Mean crystallite sizes were found to be around 10 nm for all compositions calcined at 500 degrees C. Dense electrolyte bodies were prepared at 1300 degrees C, 1400 degrees C and 1450 degrees C using two sintering times, 4 h or 6 h. Densities of 91-97% of theoretical were obtained, with a marked improvement in density on going from 1300 degrees C to higher sintering temperatures. Grain size analysis was conducted using SEM. Grain size distributions were related to %Sm and sintering conditions. Impedance spectroscopy was used to determine the total, bulk and grain boundary conductivities, the related activation energies and enthalpies of defect association and ion migration. Sintering at 1400 degrees C/6 h or 1450 degrees C/4 h gave superior grain structure and conductivity, with oversintering occurring after more severe treatments. At 600 degrees C the highest total ionic conductivity was 1.81 x 10(-2) S cm(-1) for Sm(0.2)Ce(0.8)O(1.9). The relationships between chemical composition, sintering parameters, grain structure and electrochemical performance are discussed. (C) 2010 Elsevier B.V. All rights reserved.

Synthesis and photocatalytic properties of BiVO4 by a citric acid complexation process

Lu Wei; Yu Jianqiang; Zhang Yan; Yu Deshuang; Zhou Xiaochen

RARE METALS, 30, , 203-207

The visible-light responsive photocatalyst BiVO4 was synthesized through a complexation process. The photophysical and phtotcatalytic properties of the photocatalyst were characterized by XRD, SEM, BET surface area, and DRS techniques. By calcining at various temperatures, the crystalline structure of BiVO4 converted from tetragonal scheelite to monoclinic scheelite phases. The crystallization of BiVO4 occurred when the calcination treatment was carried out at 673 K. The visible-light photocatalytic activities were comparative studied by the decomposition of red FN-3G. The results show the highest efficiency is the sample calcined at 573 K. It also found that large surface area can improve the visible light absorption and phtotcatalytic activities.

Fabrication of TiAlNb alloy sheet by sintering pure metal foils

Zhao Yeqing; Zhang Di; Sun Yanbo; Wang Zengjie; Zheng Ruixiao; Ma Chaoli

RARE METALS, 30, , 331-334

Ti-Al-Nb ternary intermetallic alloy sheet was fabricated by sintering pure metal foils of Ti, Al and Nb(foil-foil method). The phase evolution during sintering process and the final microstructure were analyzed by various techniques, including Back-scattered Electron Image (BEI), X-ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS), etc. Results reveal that the structure evolution in the sintering processes is very complex and strongly depends on the sintering conditions, especially depends on whether or not the occurrence of the self-propagating high-temperature synthesis (SHS) during sintering. When sintered at relatively lower temperature, the alloy sheets are composed of multi phases of Nb2Al (sigma), Nb3Al (delta), Ti3Al (alpha(2)) and TiAl (gamma) in a lamellar form. Sintered at higher temperature and annealing for sufficient long time, the sheet is composed of uniform structures mainly containing Ti2AlNb (O phase) and solid solution (beta).

Synthesis of TiB2-TiC-Ni/TiAl/Ti functionally gradient materials by FAPAS process

Liang Lianjie; Meng Qingsen; Chen Shaoping; Liu Zefeng; Xue Pengfei; Chen Ruixue

RARE METALS, 30, , 467-471

Field-activated pressure-assisted synthesis (FAPAS) was used to prepare TiB2-TiC-Ni/TiAl/Ti functionally gradient materials. Interfacial microstructure and bonding strength of materials were mainly investigated. The microstructure, phase composition and distribution of elements of interface were analyzed by SEM, XRD and EDS. The shear strength and micro-hardness were also tested. The results show that the particles of TiB2-TiC composite ceramics prepared by FAPAS are fine and homogeneous disperse. Closely metallurgical bonding forms between layers by mutual diffusion of different elements across the interfaces. The maximum shear strength of joint reaches 85.878 MPa and the fracture occurs at the interface of cermet and TiAl. The micro-hardness of the sample changes gradually from titanium substrate to the cermet with a maximum hardness of 2760HV in the cermet.

Interfacial products in SiC fiber reinforced Ti-Al based intermetallic alloys

Zhang Di; Sun Yanbo; Zhao Yeqing; Wang Tingting; Chen Jing; Li Huanxi; Ma Chaoli

RARE METALS, 30, , 524-528

Continuous SiC fiber reinforced Ti-Al based intermetallic alloys were prepared by sintering pure Ti and Al foils as well as SiC fibers. Owing to a complex self-propagating combustion reaction and diffusion reactions occurring during sintering process, the emphasis of the present paper is on identifying the interfacial products between SiC fibers and matrix, which is crucial for the mechanical properties of the sintered materials. Microstructure observation reveals that the sintered alloys contain lamellar matrix and SiC fibers with various interfacial products. The lamellar matrix compose chicly of TiAl3, TiAl2, TiAl, Ti3Al and alpha-Ti phases, the SiC fibers locate in TiAl3/TiAl layer and/or Ti3Al/alpha-Ti layer. The Al content is very little in the interfacial reaction zone. The main interfacial products are considered to mainly be compounds of Ti5Si3Cx, Ti3AlC, and Al4C3Six, etc. The interfacial reaction layer in the Ti-rich phase (Ti3Al and alpha-Ti) is thicker than in the Al-rich phase layer (TiAl3, TiAl2 and TiAl).

Electron beam heating effects during environmental scanning electron microscopy imaging of water condensation on superhydrophobic surfaces

Rykaczewski, K.; Scott, J. H. J.; Fedorov, A. G.

APPLIED PHYSICS LETTERS, 98, 9, 93106-

Superhydrophobic surfaces (SHSs) show promise as promoters of dropwise condensation. Droplets with diameters below similar to 10 mu m account for the majority of the heat transferred during dropwise condensation but their growth dynamics on SHS have not been systematically studied. Due to the complex topography of the surface environmental scanning electron microscopy is the preferred method for observing the growth dynamics of droplets in this size regime. By studying electron beam heating effects on condensed water droplets we establish a magnification limit below which the heating effects are negligible and use this insight to study the mechanism of individual drop growth. (C) 2011 American Institute of Physics. [doi:10.1063/1.3560443]

Performance evaluation of laser surface alloyed hard nanostructured Al2O3-TiB2-TiN composite coatings with in-situ and ex-situ reinforcements

Chatterjee, Satyajit; Majumdar, J. Dutta; Singaiah, K.; Shariff, S. M.; Padmanabham, G.; Choudhury, A. Roy

SURFACE & COATINGS TECHNOLOGY, 205, 11, 3478-3484

Hard and wear resistant Al2O3-TiB2-TiN composite coatings have been developed on low carbon steel (AISI 1025) substrate by following two different routes involving laser surface treatment. In the first (termed 'in-situ' process), reinforcing phases TiB2 and TiN, as well as the matrix Al2O3 of the composite are synthesized in-situ by laser-triggered self-propagating high temperature synthesis (SHS) from a mixture of Al, TiO2 and h-BN and coated onto the substrate surface by laser surface alloying (LSA). In the second (termed 'ex-situ' process), the constituents Al2O3, TiB2 and TiN of the coating are provided directly as a pre-placed precursor powder mix and laser surface alloyed onto the substrate. Of these two laser assisted manufacturing procedures, it is of interest to determine the one that is more appropriate for the development of a hard, wear resistant coating. In the present work, investigation of the comparative merits and demerits of Al2O3-TiB2-TiN coatings produced by in-situ and ex-situ processes is attempted through analysis of microstructure and evaluation of mechanical and tribological properties. (C) 2010 Elsevier B.V. All rights reserved.

High volume fraction TiCx/Al composites with good comprehensive performance fabricated by combustion synthesis and hot press consolidation

Shu, Shili; Lu, Jianbang; Qiu, Feng; Xuan, Qianqian; Jiang, Qichuan

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 528, 41398, 1931-1936

In situ high volume fraction (50-70 vol.%) TiCx/Al composites were successfully fabricated by combustion synthesis and hot press consolidation in an Al-Ti-C system. Microstructure characterization of the TiCx/Al composites shows relatively uniform distribution of the TiCx particles with the particle size in the range of about 1-5 mu m. All of the yield strength (sigma(0.2)), hardness and abrasive wear resistance of the TiCx/Al composites increase with the increase in the TiCx content, and the sigma(UCS) firstly increases and then decreases. The sigma(0.2), sigma(UCS), fracture strain (epsilon(f)) and hardness of the 70 vol.% TiCx/Al composite are 576 MPa, 744 MPa, 3.09% and 253.5 +/- 6 Hv, respectively. The abrasive wear resistance of the 70 vol.% TiCx/Al composite is about 4 times higher than that of the cast hypereutectic Al-Si alloy when the applied load is no more than 25 N and the Al2O3 abrasive particle size is no more than 20 mu m. (C) 2010 Elsevier B.V. All rights reserved.

Properties and electronic structures of titanium aluminides-alumina composites from in-situ SHS process

Shen, Y. F.; Zou, Z. G.; Xiao, Z. G.; Liu, K.; Long, F.; Wu, Y.

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 528, 41398, 2100-2105

Titanium aluminides-alumina composite was synthesized by in-situ self-propagating high-temperature synthesis (SHS) method, followed by hot-pressing process. To understand the fundamental differences between the composite and Al(2)O(3) ceramic, a comparative study was carried out using first-principles plane-wave pseudopotential method based on density functional theory (OFT). XRD analysis of final products confirmed the formation of TiAl, Al(2)O(3) and a small amount of Ti(3)Al phases in the composites and the reaction mechanisms of the process were proposed. SEM observation revealed that a two-phase (gamma + alpha(2)) TiAl-Ti(3)Al lamellar structure was formed, and the composites exhibited a homogeneous microstructure. Moreover, density of states (DOS), band structure, charge density difference and Mulliken population analysis showed that metallic, covalent and ionic bonding were produced at the interfaces of the composite. O-Al interface bonds showed more covalent character with respect to pure Al(2)O(3). Therefore, interface combination of the composite was improved, making the composite tougher (a toughness as high as 7.9 MPa m(1/2)) than monophase Al(2)O(3) ceramic. (C) 2010 Elsevier B.V. All rights reserved.

Preparation of BaMgAl10O17:Eu2+ phosphor with small particle size by co-precipitation method

Dong, Yan; Wu, Zhisen; Han, Xuelin; Chen, Rong; Gu, Weijie

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 8, 3638-3643

A BaMgAl10O17:Eu2+ phosphor with fine particle size was synthesized by a chemical co-precipitation method. Co-precipitation of Ba2+, Al3+, Mg2+, and Eu2+ was achieved under precisely controlled precipitation conditions. The Al3+ ions were precipitated as ammonium aluminum carbonate hydroxide (AACH). Phase transition and particle growth processes of the precipitate mixture during calcining process were investigated, and the formation mechanism of the BaMgAl10O17 phase was discussed. The results show that the formation temperature of the BaMgAl10O17 phase in the co-precipitation mixture was significantly lower than that of a high temperature solid state reaction method. The BaMgAl10O17 phase was formed from the reaction between the BaAl2O4 phase and gamma-Al2O3 phase; no alpha-Al2O3 phase appeared during the entire process. Well-dispersed BaMgAl10O17:Eu2+ phosphor powder in the form of hexagonal flakes with small particle size (1-2 mu m) could be prepared by this method. (C) 2010 Elsevier B.V. All rights reserved.

Combustion synthesis of vanadium borides

Yeh, C. L.; Wang, H. J.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 7, 3257-3261

An experimental study on the preparation of various vanadium borides (including V(3)B(2), VB, V(5)B(6), V(3)B(4), V(2)B(3), and VB(2)) in the V-B system was conducted by self-propagating high-temperature synthesis (SHS) from the elemental powder compacts. Close flame-front velocities and comparable combustion temperatures were observed for the reactant compacts with V:B = 1:1, 5:6, and 3:4, and they were much higher than those for the samples of other compositions. The lowest combustion velocity and temperature were detected in the sample of V:B = 1:2. According to the XRD analysis, pure VB was produced not only from the sample of V:B = 1:1, but also from those of V:B = 5:6 and 3:4. For the powder compact with V:B = 1:2, VB(2) was dominantly formed along with trivial amounts of VB and V(3)B(4). A multiphase product composed of VB and V(3)B(4) at comparable quantities was yielded from the sample of V:B = 2:3. The only V-rich sample formulated at V:B = 3:2 generated monoboride VB and left the end product a large amount of unreacted vanadium. (C) 2010 Elsevier B.V. All rights reserved.

Nanoparticles of Al2O3:Cr as a sensitive thermoluminescent material for high exposures of gamma rays irradiations

Salah, Numan; Khan, Zishan H.; Habib, Sami S.

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 269, 4, 401-404

Aluminum Oxide (Al2O3) doped with proper activators is a highly sensitive phosphor commonly used for radiation dosimetry using thermoluminescence (TL) technique. Nanoparticles of this material activated with Chromium (Cr) have been synthesized using the propellant chemical combustion technique and studied for their TL response. They were characterized by X-ray diffraction and scanning electron microscope. The synthesized material has spherical nanoparticles with grain size around 25 nm. These nanoparticles were exposed to heavy doses from gamma-rays of Cs-137. The TL glow curves show a prominent peak at around 474 K. This peak is found to be sensitive for high exposures of gamma-rays and has linear response in the range of 100 Gy-20 kGy without showing saturation. This remarkable result suggests that Al2O3:Cr nanoparticles might be used for the dosimetry of food and seed irradiations. (C) 2010 Elsevier B.V. All rights reserved.

Synergism in Multicomponent Self-Propagating Molecular Assemblies

Motiei, Leila; Sassi, Mauro; Kaminker, Revital; Evmenenko, Guennadi; Dutta, Pulak; Iron, Mark A.; van der Boom, Milko E.

LANGMUIR, 27, 4, 1319-1325

Multicomponent self-propagating molecular assemblies (SPMAs) have been generated from an organic chromophore, a redox-active polypyridyl complex, and PdCl(2). The structure of the multicomponent SPMA is not a linear combination of two assemblies generated with a single molecular constituent. Surface-confined assemblies formed from only the organic chromophore and PdCl(2) are known to follow linear growth, whereas the combination of polypyridyl complexes and PdCl(2) results in exponential growth. The present study demonstrates that an iterative deposition of both molecular building blocks with PdCl(2) results in an exponentially growing assembly. The nature of the assembly mechanism is dictated by the polypyridyl complex and overrides the linear growth process of the organic component. Relatively smooth, multicomponent SPMAs have been obtained with a thickness of similar to 20 nm on silicon, glass, and indium tin oxide (ITO) coated glass. Detailed information of the structure and of the surface-assembly chemistry were obtained using transmission optical (UV/Vis) spectroscopy, ellipsometry, atomic force microscopy (AFM), synchrotron X-ray reflectivity (XRR), and electrochemistry.

Low temperature combustion synthesis of CoxMg1-xAl2O4 nano pigments using oxalyldihydrazide as a fuel

Ahmed, I. S.; Shama, S. A.; Dessouki, N. A.; Ali, A. A.

MATERIALS CHEMISTRY AND PHYSICS, 125, 3, 326-333

Oxalyldihydrazide as a fuel was used to prepare new nano size blue refractory ceramic pigments MgAl2O4: xCo(2+) (0.00 <= x <= 0.10) using low temperature combustion synthesis (LCS) method. The synthesized and calcined powders were characterized by Fourier transform infra red (FTIR) spectrometry, electronic spectra, thermogravimetry, differential thermogravimetry, differential thermal analysis. X-ray diffraction (XRD) analysis, and transmission electron microscopy (TEM). Also, the color measurements of nano pigments are studied by diffuse reflectance spectroscopy (DRS) using CIE-L*a*b* parameter method. The FTIR spectra show frequency bands in range the 422-700 cm(-1) correspond to metal oxygen bonds through vibrations for the spinel structure compound. The average particle size of prepared samples as determined from XRD and TEM was 30 nm at 1100 degrees C. Also, the results revealed the varying bulk density, particle size, shape and color with different calcination times and temperatures. (C) 2010 Elsevier B.V. All rights reserved.

Selective Laser Melting of in-situ TiC/Ti5Si3 composites with novel reinforcement architecture and elevated performance

Gu, Dongdong; Hagedorn, Yves-Christian; Meiners, Wilhelm; Wissenbach, Konrad; Poprawe, Reinhart

SURFACE & COATINGS TECHNOLOGY, 205, 10, 3285-3292

A novel Selective Laser Melting (SLM) process was applied to prepare bulk-form TiC/Ti5Si3 in-situ composites starting from Ti/SiC powder system. The influence of the applied laser energy density on densification, microstructure, and mechanical performance of SLM-processed composite parts was studied. It showed that the uniformly dispersed TiC reinforcing phase having a unique network distribution and a submicron-scale dendritic morphology was formed as a laser energy density of 0.4 kJ/m was properly settled. The 96.9% dense SLM-processed TiC/Ti5Si3 composites had a high microhardness of 980.3HV(0.2), showing more than a 3-fold increase upon that of the unreinforced Ti part. The dry sliding wear tests revealed that the TiC/Ti5Si3 composites possessed a considerably low friction coefficient of 0.2 and a reduced wear rate of 1.42 x 10(-4) mm(3)/Nm. The scanning electron microscope (SEM) characterization of the worn surface morphology indicated that the high wear resistance was due to the formation of adherent and strain-hardened tribolayer. The densification rate, microhardness, and wear performance generally decreased at a higher laser energy density of 0.8 kJ/m, due to the formation of thermal cracks and the significant coarsening of TIC dendritic reinforcing phase. (C) 2010 Elsevier B.V. All rights reserved.

Dielectric properties of Cu substituted Ni0.5-xZn0.3Mg0.2Fe2O4 ferrites

Bhandare, M. R.; Jamadar, H. V.; Pathan, A. T.; Chougule, B. K.; Shaikh, A. M.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 6, L113-L118

Dielectric properties of Cu substituted Ni-Zn-Mg ferrite samples having the general formula Ni0.5-xCuxZn0.3Mg0.2Fe2O4 (where x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) synthesized by Pramanik method are reported. The single phase formation of the ferrites was confirmed by XRD technique. The lattice parameter is found to increase with increase in Cu content. Average grain size, obtained from SEM micrographs, is found to increase with increase in Cu content. Dielectric parameters were measured as a function of frequency at room temperature as well as at higher temperatures. The variation in dielectric constant (epsilon') with temperature at four different fixed frequencies viz. 1 kHz, 10 kHz, 100 kHz, and 1 MHz was also studied. The room temperature dielectric constant (epsilon') and dielectric loss (tan delta) are found to decrease with increase in frequency. The ac conductivity (sigma(ac)) is found to increase with increase in the frequency. (C) 2010 Elsevier B.V. All rights reserved.

Blue shift of Tm3+ upconversion owing to Nd3+ in yttrium oxide powders pumped by pulsed red laser

Rakov, Nikifor; Maciel, Glauco S.

CHEMICAL PHYSICS LETTERS, 503, 41334, 124-128

Tm3+:Y2O3 powder prepared by combustion synthesis exhibits blue emission centered at lambda similar to 450 nm, corresponding to D-1(2) --> F-3(4) transition of Tm3+, when the sample is irradiated by a pulsed (5 ns, 10 Hz) red laser operating at lambda similar to 690 nm. The blue emission band shifts to lambda similar to 480 nm, corresponding to (1)G(4) --> H-3(6) transition of Tm3+, when Nd3+ is added to the sample. When the laser is tuned to lambda similar to 680 nm, the blue shift effect is not observed. The shifting effect is explained based on single shot laser excitation and energy transfer mechanisms involving Tm3+ and Nd3+ ions. (C) 2010 Elsevier B. V. All rights reserved.

A systematic study on the synthesis of Ca, Gd codoped cerium oxide by combustion method

Ainirad, A.; Motlagh, M. M. Kashani; Maghsoudipoor, A.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 5, 1505-1510

Co-doped of CeO(2) nanopowders are ideal electrolyte materials for intermediate temperature solid oxide fuel cells. In this work, Ce(1-(x+y))Gd(x)Ca(y)O(2)-((0.5x+y)) nanopowders are successfully synthesized by a glycine-nitrate combustion process. Then calcination was carried out at 450, 700, 850, 950 and we found that calcined powders were single phase by room temperature X-ray diffraction (XRD) and have an average crystallite size of 45 nm (based on Scherrer formula). Scanning electron microscopy (SEM) was employed to characterize the morphology of powder. Finally we studied the effect of fuel to nitrate ratio on the properties of resulting powders. (C) 2010 Elsevier B.V. All rights reserved.

Microstructure, mechanical properties and thermal shock behavior of h-BN-AlN ceramic composites prepared by combustion synthesis

Li, Hongbo; Zheng, Yongting; Han, Jiecai; Zhou, Lijuan

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 5, 1661-1664

h-BN-SiC-AlN-TiN ceramic composites with volume content of AlN-TiN ranging from 20% to 70% were prepared by combustion synthesis from powder compacts of B4C, Si, Al and TiN under 100 MPa nitrogen pressure. The volume fraction of AIN-TiN was found to have a significant influence on the microstructure, mechanical properties and thermal shock resistance of the composites. With the increasing volume content of AIN-TiN, the mechanical properties of the composites were improved remarkably, while thermal shock resistance decreased. Thermal shock tests showed that the critical thermal shock temperature (AT) was higher than 1200 degrees C for the composites with AIN-TiN contents of 30 vol%; while it was decreased to 850 and 670 degrees C for the composites with AIN-TiN contents of 50 and 70 vol%, respectively. (C) 2010 Elsevier B.V. All rights reserved.

Solution combustion synthesis and characterization of lead-free piezoelectric sodium niobate (NaNbO3) powders

Chaiyo, Nopsiri; Muanghlua, Rangson; Niemcharoen, Surasak; Boonchom, Banjong; Vittayakorn, Naratip

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 5, 2445-2449

Nano-crystalline sodium niobate (NaNbO3) powder was synthesized by the solution combustion synthesis of sodium nitrate (NaNO3) and Nb2O5 using glycine as the fuel. The chemical reaction, nucleation mechanisms and influence of the fuel-to-oxidizer ratio to phase formation were studied. The precursor and product powders were characterized, using thermo gravimetric analysis (TGA), differential thermal analysis (DTA), the X-ray diffraction technique (XRD), scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. As-prepared powder possesses an orthorhombic crystal structure with an X-ray diffraction pattern that could be matched with the perovskite, NaNbO3 JCPDS no. 82-0606. Perovskite NaNbO3 phase, with a mean crystalline size (calculated by X-ray line broadening) ranging from 44.51 +/- 11.99 nm (ratio of 0.7) to 26.11 +/- 13.69 nm (ratio of 2.0) was obtained. The SEM image shows polyhedral-shaped powder with a mean particle size of 137 +/- 52 nm and 226 +/- 46 nm for as-prepared and calcined powder, respectively. (C) 2010 Elsevier B.V. All rights reserved.

Structural and optical characterization of BaSnO3 nanopowder synthesized through a novel combustion technique

Deepa, A. S.; Vidya, S.; Manu, P. C.; Solomon, Sam; John, Annamma; Thomas, J. K.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 5, 1830-1835

Nanocrystalline Barium stannate (BaSnO3) was synthesized through auto-ignited combustion technique. The X-ray diffraction studies of BaSnO3 nanoparticles reveals that the nanopowder is single phase, crystalline, and has a cubic perovskite structure with a lattice constant a = 4.115 angstrom. The average particle size calculated from full width half maximum (FWHM) using Scherer formula is similar to 25 nm. The phase purity of the powder was further examined using Fourier transform infrared spectroscopy, Raman spectroscopy and transmission electron microscopic techniques. XRD pattern of BaSnO3 was refined for atomic coordinates, lattice parameters and occupancies using Rietveld analysis. Vibrational analysis of sample shows that there is a phase transition from distorted cubic to ideal cubic structure during heat treatment. The thermal stability of BaSnO3 nanopowder has been confirmed using thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). The particle size of the as-prepared powder from transmission electron microscopy was found to be in the range 20-30 nm. The absorption spectra and photoluminescence spectra of the sample were also studied. The band gap determined was 2.887 eV and found to be a semiconductor. (C) 2010 Elsevier B.V. All rights reserved.

Combustion synthesis of Co-doped zinc oxide nanoparticles using mixture of citric acid-glycine fuels

Rasouli, Sousan; Moeen, Shirin Jebeli

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 5, 1915-1919

In this study, cobalt-doped ZnO nanoparticles were synthesized by combustion method. Mixtures of citric acid and glycine were used as fuel. As-prepared powders were characterized by XRD. XPS, SEM-EDX, TEM and spectrophotometer. XRD patterns indicated that combustion reaction by different fuel mixture resulted in the formation of pure ZnO phase. However, citric acid combustion alone led to amorphous powder. Scherrer's equation demonstrated that the crystallite size increases with citric acid/glycine (C/G) ratio (38-61 nm). SEM and TEM images illustrated that the morphology of the powder depends on the C/G ratios and changes from rod-like to spongy hexagonal particles. Reflectance spectra showed that by higher C/G ratios, deeper green colors are obtained. (C) 2010 Elsevier B.V. All rights reserved.

Luminescence properties of novel Sm3+, Dy3+ doped LaMoBO6 phosphors

Zhang, Xinmin; Seo, Hyo Jin

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 5, 2007-2010

Luminescence properties of the Sm3+, Dy3+ doped LaMoBO6 phosphors are reported. LaMoBO6:Sm3+ exhibits orange emission corresponding to the (4)G(5/2) -> H-6(7/2) transition. LaMoBO6:Dy3+ exhibits two emission bands. The yellow band (570 nm) corresponds to the F-4(9/2) -> H-6(13/2) transition, and the blue one (482 nm) corresponds to the F-4(9/2) -> H-6(15/2) transition. The optimum concentration of Sm3+ and Dy3+, the critical distance of the concentration quenching, and the decay curves have also been investigated. The analysis of the decay curves indicates that cross-relaxation is primarily responsible for the concentration quenching. (C) 2010 Elsevier B.V. All rights reserved.

High temperature friction and wear behaviour of sputter-deposited nanocrystalline (MoxCr1-x)(5)Si-3 films by a double cathode glow discharge technique

Xu, Jiang; Liu, Linlin; Lu, Xiaolin

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 5, 2450-2460

In order to improve the wear resistance of titanium alloys, five kinds of sputter-deposited nanocrystalline (MoxCr1-x)(5)Si-3(x = 1, 0.78, 0.75, 0.64, 0.57) films with average grain size 8 nm were fabricated on a substrate of Ti6Al4V alloy by means of a double cathode glow discharge technique. The microstructure and composition of the as-deposited films were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). Nanoindentation was used to measure hardness (H) and elastic modulus (E) of the as-deposited films. High temperature friction and wear properties of the as-deposited films were investigated against ZrO2 ceramic balls by a ball-on-disk system at 600 degrees C. Compared with the Ti6Al4V alloy, the friction coefficient values of the nanocrystalline (MoxCr(1-x))(5)Si-3 films were reduced by 0.2-0.3, and specific wear rates decreased by two orders of magnitude and were around or lower than 10(-6) mm(3)/(N m) at the load ranging from 3.3 N to 4.8 N. The friction coefficient and specific wear rates of the as-deposited films relied on the Cr content in the nanocrystalline (MoxCr1-x)(5)Si-3 films, and the higher the Cr content, the lower friction coefficient and wear rates. (C) 2010 Elsevier B.V. All rights reserved.

Dependence of Eu3+ luminescence dynamics on the structure of the combustion synthesized Sr-5(PO4)(3)F host

Nagpure, I. M.; Dhoble, S. J.; Mohapatra, Manoj; Kumar, Vinay; Pitale, Shreyas S.; Ntwaeaborwa, O. M.; Godbole, S. V.; Swart, H. C.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 5, 2544-2551

Europium (Eu3+) activated strontium fluoropatite (Sr-5(PO4)(3)F) phosphor powders were prepared by a combustion method. The structure and luminescence properties of this potential red emitting phosphor are explored. In order to improve the luminescent properties the obtained powders were also annealed at 900 and 1200 degrees C. The X-ray diffraction (XRD) data indicated that the major crystalline phases from the as-prepared or annealed powder samples were identical to the hexagonal apatite structure of Sr-5(PO4)(3)F. The Eu3+ occupied two different sites (C-s (S1) and C-3 (S2)) of Sr in the Sr-5(PO4)(3)F host, giving rise to two emission sites, as inferred from the time resolved luminescence spectroscopy (TRES) data. The photoluminescence (PL) intensity of Eu3+ from the as prepared sample was found to be more intense than the annealed samples. In addition from the PL data it was evident that a reduction of the Eu3+ to Eu2+ occurred. (C) 2010 Elsevier B.V. All rights reserved.

In situ nanostructured ceramic matrix composite coating prepared by reactive plasma spraying micro-sized Al-Fe2O3 composite powders

Yang, Yong; Yan, Dianran; Dong, Yanchun; Wang, Lei; Chen, Xueguang; Zhang, Jianxin; He, Jining; Li, Xiangzhi

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 5, L90-L94

In situ nanostructured ceramic matrix composite coating was prepared by reactive plasma spraying micro-sized Al-Fe2O3 composite powders. The microstructure of the composite coating was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy, respectively. The results indicated that the composite coating exhibited dense and crack-free microstructure with a number of spherical alpha-Fe and gamma-Al2O3 nano-grains embedded within equiaxed and columnar FeAl2O4 nano-grains matrix. The composite coating showed markedly higher toughness and wear resistance than the conventional Al2O3 coating. (C) 2010 Elsevier B.V. All rights reserved.

Effect of anionic surfactant and short-chain alcohol mixtures on adsorption at quartz/water and water/air interfaces and the wettability of quartz

Zdziennicka, Anna; Janczuk, Bronislaw

JOURNAL OF COLLOID AND INTERFACE SCIENCE, 354, 1, 396-404

Measurements of the advancing contact angles for aqueous solutions of sodium dodecyl sulfate (SDDS) or sodium hexadecyl sulfonate (SHS) in mixtures with methanol, ethanol, or propanol on a quartz surface were carried out. On the basis of the obtained results and Young and Gibbs equations the critical surface tension of quartz wetting, the composition of the surface layer at the quartz-water interface, and the activity coefficients of the anionic surfactants and alcohols in this layer as well as the work of adhesion of aqueous solutions of anionic surfactant and alcohol mixtures to the quartz surface were determined. The analysis of the contact angle data showed that the wettability of quartz changed visibly only in the range of alcohol and anionic surfactant concentration at which these surface-active agents were present in the solution in the monomeric form. The analysis also showed that there was a linear dependence between the adhesion and the surface tension of aqueous solutions of anionic surfactant and alcohol mixtures. This dependence can be described by linear equations for which the constants depend on the anionic surfactant and alcohol concentrations. The slope of all linear dependence between adhesion and surface tension was positive. The critical surface tension of quartz wetting determined from this dependence by extrapolating the adhesion tension to the value equal to the surface tension (for contact angle equal zero) depends on the assumption whether the concentration of anionic surfactant or alcohol was constant. Its average value is equal to 29.95 mN/m and it is considerably lower than the quartz surface tension. The positive slope of the adhesion-surface tension curves was explained by the possibility of the presence of liquid vapor film beyond the solution drop which settled on the quartz surface and the adsorption of surface-active agents at the quartz/monolayer water film-water interface. This conclusion was confirmed by the work of adhesion of aqueous solutions of anionic surfactants and short-chain alcohol mixtures to the quartz surface determined on the basis of the contact angle data and molar fraction of anionic surfactants and alcohols and their activity coefficient in the surface layer. (C) 2010 Elsevier Inc. All rights reserved.

The Self-Propagating High-Temperature Synthesis of a Nanostructured Titanium Nitride Powder with the Use of Sodium Azide and Haloid Titanium-Containing Salt

Shiganova, L. A.; Bichurov, G. V.; Amosov, A. P.; Titova, Yu. V.; Ermoshkin, A. A.; Bichurova, P. G.

RUSSIAN JOURNAL OF NON-FERROUS METALS, 52, 1, 91-95

The use of the "ammonium hexafluorotitanate (NH(4))(2)TiF(6)-sodium azide NaN(3)" system during self-propagating high-temperature synthesis (SHS) allows researchers to obtain nanostructured titanium nitride powder. Nanopowders of silicon, boron, and aluminum nitrides are formed from similar "halogenide of nitrided element-sodium azide" systems by SHS. It is confirmed that the use of compounds rather than pure elements in the starting powder mixtures for SHS makes it possible to substantially decrease the dimensionality of the combustion products and obtain them in the form of nanostructured particles, nanofibers, and nanopowders.

STRUCTURE PARAMETERS AND MAGNETIC PROPERTIES OF Me2W1 COBALT-CONTAINING HEXAFERRITE SYSTEMS SYNTHESIZED BY THE SHS METHOD

Naiden, E. P.; Zhuravlev, V. A.; Suslyaev, V. I.; Minin, R. V.; Itin, V. I.; Korovin, E. Yu.

RUSSIAN PHYSICS JOURNAL, 53, 9, 974-982

Optimal conditions for synthesis of BaCo2-hZnhFe16O27 system hexaferrite powders fabricated using novel energy-saving technology of self-spreading high-temperature synthesis (SHS) with preliminary mechanical activation are determined. The phase composition and morphology of the synthesized materials are investigated by the method of x-ray structural and phase analysis. Values of specific saturation magnetization, crystal magnetic anisotropy field, spin reorientation transition temperature, and Curie's temperature are determined based on static and dynamic measurements of the magnetic properties. Spectra of the magnetic permeability and dielectric permittivity are measured in the microwave range.

Effect of reactive sintering conditions on microstructure of in situ titanium aluminide and silicide composites

Novak, P.; Popela, T.; Kubasek, J.; Serak, J.; Vojtech, D.; Michalcova, A.

POWDER METALLURGY, 54, 1, 50-55

In this work, the dependence of microstructure of in situ titanium aluminide and silicide composites on chemical composition and conditions of reactive sintering was studied. It was found that the rate of reactive sintering process increases with growing silicon content. In addition, heating rate strongly affects the structure of Ti-Al-Si alloys with lower content of silicon represented by TiAl23Si10 alloy. The structure consisting of homogeneously distributed Ti(5)Si(3) particles in TiAl matrix can be obtained by rapid heating over 250 K min(-1) in this material. TiAl15Si15 alloy forms the desired two phase TiAl-Ti(5)Si(3) structure when a heating rate of at least 10 K min(-1) and temperature over 750 degrees C are applied. Replacement of aluminium and silicon powders by Al-Si alloy positively affects the reactive sintering process. The structure of these materials can be refined by milling of Al-Si master alloy powder to the < 100 mu m fraction, reducing the size of Ti(5)Si(3) particles and porosity significantly.

Effect of composition of starting materials of Mo-Si on self-propagating high temperature SHS reaction

Feng, P. Z.; Liu, W. S.; Islam, S. H.; Wu, J.; Zhang, S.; Niu, J. N.; Qiang, Y. H.

POWDER METALLURGY, 54, 1, 79-83

An experimental study of the self-propagating high temperature synthesis of Mo-Si alloys was conducted from elemental powder compacts. Test specimens with seven compositions, including Mo/Si=1 : 1.25, 1 : 1.50, 1 : 1.75, 1 : 2.00, 1 : 2.25, 1 : 2.50 and 1 : 2.75 respectively, were employed. Experimental evidence showed that a combustion wave featuring a spinning reaction zone can be observed. When the powder compacts are from Mo : 1.25Si to Mo : 1.75Si, the combustion temperature and the propagation velocity of combustion wave increase with increasing silicon in the sample, and the combustion products are composed of MoSi(2), Mo(5)Si(3) and Mo. However, when the powder compacts are from Mo : 2.25Si to Mo: 2.75Si, the combustion temperature and the propagation velocity decrease rapidly as the silicon in the compact increases, and the combustion products are composed of MoSi(2) and Si. The sample with Mo/Si=1 : 2.00 possesses the highest combustion temperature (1628.9 K) and propagation velocity (3.13 mm s(-1)). A single-phase MoSi(2) is synthesised by the Mo/Si=1 : 2.00 sample.

A study on ultrafine powders of gadolinia doped ceria prepared by gel-combustion method

Chaubey, Nityanand; Chattopadhyaya, M. C.

JOURNAL OF THE INDIAN CHEMICAL SOCIETY, 88, 2, 217-224

In this paper ultrafine powder of gadolinia doped ceria was prepared by a combustion synthesis method using metal nitrates, both as a precursor and oxidizer and glycine as fuel for combustion. The influence of glycine to metal molar ratio on the characteristics of the powders has been studied. Characterization of the powder samples was performed using, FTIR spectroscopy, TG/DTA analysis, X-ray diffractometry, Small angle X-ray scattering (SAXS) technique and scanning electron microscopy. The ultrafine powders prepared by glycine to metal ratio 1.2 gives the best powder properties. The indexing of diffraction pattern shows that the gadolinia doped ceria powders have face centered cubic symmetry.

Stokes and anti-Stokes blue light emissions of thermal-evaporated silica sub-micron wires

Tao, Chuanyi; Li, Xueming; Feng, Wenlin; Yang, Jianchun; Li, Wulin; Li, Yongfu; Yang, Wenjing

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 208, 2, 466-470

Based on the thermal evaporation of silicon monoxide at high temperature, an improved method has been developed for large-scale synthesis of ultralong amorphous silica sub-micron wires using polished p-Si wafers as substrates. The synthesis was done with and without thermite. The morphology and structure of the silica wires was investigated through field-emission scanning electron microscope equipped with energy dispersive X-ray spectroscopy, and X-ray diffractometer. Almost uniform sub-micron wires with average diameters of 300 nm and length up to hundreds of micrometers were obtained in presence of thermite while sub-micron wires with many curved segments were obtained in absence of the thermite. Both forms of silica wires emitted blue lights at 478 nm (similar to 2.6 eV) under excitation at 351 nm (similar to 3.5 eV), while intense anti-Stokes blue emissions at 464 nm(similar to 2.7 eV) were observed under the 694 nm(similar to 1.8 eV) excitation due to the upconversion effect. This effect is associated with defect centers arising from high oxygen deficiency. The emissions from oxygen deficiency centers might be caused by multistep energy transfer from nonbridging oxygen hole centers to oxygen deficiency centers. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Synthesis of inside-out core-shell perovskite-type oxide nanopowder

Mazar, Omri; Schroeder, Michael; Tsur, Yoed

CHEMICAL ENGINEERING JOURNAL, 166, 3, 1139-1143

Core-shell perovskite-type oxides, with a relatively pure core and highly donor-doped shell, are widely investigated for, e.g., multilayer ceramic capacitors. Acceptor doped perovskite oxides are also widely investigated due to their applications as proton conductors. In the quest for new materials with novel properties we try to reverse both traits and form an inside-out core-shell structure with a highly donor-doped core and nominally undoped shell.A highly donor-doped core is expected to result in very few oxygen vacancies in this volume, due to self-compensation. The originally undoped shell, if thin enough, may behave as an acceptor doped area due to the migration of metal vacancies outwards. This may provide interesting properties resulting from internal electrical junctions and space charge. A possible synthesis route for the creation of such particles is the coating of previously synthesized nanoscaled donor-doped perovskite powder with undoped perovskite material. The synthesis route and the characterization of such inside-out core-shell (IOCS) nanopowder of Nb-doped BaCeO(3) core and an undoped BaCeO(3) shell are presented here. (C) 2010 Elsevier B.V. All rights reserved.

Novel synthesis of NixZn1-xFe2O4 (0 <= x <= 1) nanoparticles and their dielectric properties

Bhattacharjee, K.; Ghosh, C. K.; Mitra, M. K.; Das, G. C.; Mukherjee, S.; Chattopadhyay, Kalyan Kumar

JOURNAL OF NANOPARTICLE RESEARCH, 13, 2, 739-750

Nanocrystalline Ni (x) Zn1-x Fe2O4 (0 a parts per thousand currency sign x a parts per thousand currency sign 1) ferrite powders with average particle size 15-20 nm have been successfully prepared at a very low temperature (180 A degrees C) by a novel auto combustion process using citric acid and ethylenediamine as a coordinating agent and bridging ligand, respectively. Phase purity of the solid solutions has been confirmed by X-ray diffraction. Morphological characterizations of the prepared samples were performed by high resolution transmission electron and field emission scanning electron microscopy. Extensive Fourier transformed infrared spectroscopic characterization has been carried out to identify the plausible mechanism of the synthesis process. Composition-dependent electrical properties (resistivity and dielectric constant) of the synthesized solid solution have been investigated. Interestingly, a non-linear variation of dielectric permittivity with respect to composition has been observed. The room temperature electrical resistivity as well as the dielectric permittivity of Ni0.5Zn0.5Fe2O4 was found to decrease with the decrease of particle size.

Highly Insensitive/Reactive Thermite Prepared from Cr2O3 Nanoparticles

Gibot, Pierre; Comet, Marc; Eichhorn, Alfred; Schnell, Fabien; Muller, Olivier; Ciszek, Fabrice; Boehrer, Yannick; Spitzer, Denis

PROPELLANTS EXPLOSIVES PYROTECHNICS, 36, 1, 80-87

Thermites prepared from nanoparticles are currently the subject of growing interest due to their increased performances compared to classical micrometer-sized thermites. Here, we studied the combustion behavior of energetic composite composed of Al and chromium (III) oxide (Cr2O3) as function of the oxide particle size. Homogeneous composites were prepared by mixing Al nanoparticles (Phi approximate to 50 nm) with Cr2O3 micro- and nanoparticles (Phi approximate to 20 ), respectively, in hexane solution. The dried Cr2O3/Al composite powders were ignited by using a CO2 laser beam. The use of nanosized Cr2O3 particles incontestably improves the energetic performances of the Al/Cr2O3 thermite since the ignition delay time was shortened by a factor 3.5 (16 +/- 2 vs 54 +/- 4 ms) and the combustion rate (340 +/- 10 mm s(-1)) was significantly accelerated in contrast to those reported until now. Interestingly, the sensitivity to friction of the Al-based thermites formulated from Cr2O3 is two orders of magnitude lower than the thermite prepared from other metal oxide nanoparticles (MnO2, WO3). Finally, our study shows that the decrease of Cr2O3 particle size has an interesting and beneficial effect on the energetic properties of Cr2O3/Al thermites and appears as an alternative to tune the properties of these energetic materials.

Synthesis of ZnO nanoparticles through the impregnated layer combustion synthesis process

Deorsola, F. A.; Vallauri, D.

JOURNAL OF MATERIALS SCIENCE, 46, 3, 781-786

Zinc oxide nanopowders were synthesized by a solution combustion technique named impregnated layer combustion synthesis (ILCS), involving the impregnation of an active layer with the reactant solution and subsequently the combustion of the impregnated system. In this work three different organic fuels and two different ignition modes were tested in order to optimize the final microstructure and specific surface area (SSA) of the ZnO nanopowders. In particular, the ignition mode was found to significantly affect the final products, discriminating between an explosion procedure (flame combustion) and a self-propagating mode (smoldering combustion). The nitrate-glycine mixture and the smoldering combustion way were found to be the most suitable conditions, giving rise to softly agglomerated nanopowders with an average size of 20 nm and a very high SSA, without the need of any further crystallization treatment.

Thermoelectric Properties of Nanocrystalline Ca3-xCuxCo4O9 (0 <= x <= 0.32) for Power Generation

Nam, S. W.; Lim, Y. S.; Choi, S-M.; Seo, W-S.; Park, K.

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 11, 2, 1734-1737

We successfully synthesized nano-sized Ca3-xCuxCo4O9 (0 <= x <= 0.32) powders by solution combustion process. Plate-like grains and porous structure were observed in the sintered Ca3-xCuxCo4O9 ceramics. The sintered Ca3-xCuxCo4O9 showed a monoclinic symmetry. The electrical conductivity of the Ca3-xCuxCo4O9 increased with increasing temperature, indicative of a semiconducting behavior. The added Cu led to a significant increase in the electrical conductivity. The Seebeck coefficient of the Cu-added Ca3-xCuxCo4O9 was much higher than that of the Cu-free Ca3Co4O9. The highest power factor (9.99 x 10(-4) Wm(-1) K-2) was obtained for Ca2.76Cu0.24Co4O9 at 800 degrees C.

Combustion synthesis of La0.7Sr0.3Co0.5Fe0.5O3 (LSCF) porous materials for application as cathode in IT-SOFC

da Conceicao, Leandro; Silva, Amanda M.; Ribeiro, Nielson F. P.; Souza, Mariana M. V. M.

MATERIALS RESEARCH BULLETIN, 46, 2, 308-314

La0.7Sr0.3Co0.5Fe0.5O3 (LSCF) porous materials have attracted a substantial interest for application as cathode in solid oxide fuel cells of intermediate temperature (IT-SOFC). This work investigates the effect of different propellants (urea, glycine, citric acid and sucrose) in the preparation of LSCF powders by the combustion method and also the influence of the sintering temperature on the porosity and electrical conductivity. TGA profiles of the as-prepared samples showed a lower weight loss for the sample prepared with glycine, associated with the higher combustion temperature. XRD patterns presented characteristic reflections of LSFC perovskite and a small formation of secondary phases, with nanometric crystallite sizes (9-20 nm). SEM analysis revealed the loose and porous structure of the powder materials. Densification studies were carried within 950-1100 degrees C, showing that porosity decreased with increasing sintering temperature. Electrical conductivity was measured in the temperature range 300-800 degrees C and correlated with the sintering temperature. (C) 2010 Elsevier Ltd. All rights reserved.

Strong infrared-to-visible frequency upconversion in Er3+-doped Sr2CeO4 powders

Rakov, Nikifor; Guimaraes, Renato B.; Maciel, Glauco S.

JOURNAL OF LUMINESCENCE, 131, 2, 342-346

Efficient upconversion (UC) luminescence is demonstrated in Er3+ Sr2CeO4 powders prepared by combustion synthesis and exposed to near-Infrared (similar to 975 nm) radiation The UC emission lines observed at similar to 530 similar to 550 and similar to 665 nm correspond respectively to H-2(11/2)-> I-4(15/2) (4)s(3/2)-> I-4(15/2) and F-4(9/2)-> I-4(15/2) 4f-4f transitions of Er3+ X-ray powder diffraction data showed that the SrCO3 phase (impurity) is dramatically reduced when Sr2+ is partially substituted by Mg2+ ions The UC phenomenon was investigated by use of continuous wave and pulsed laser excitation and the UC mechanism was attributed to energy transfer between excited Er3+ ions (C) 2010 Elsevier B V All rights reserved

Solar-grade silicon powder prepared by combining combustion synthesis with hydrometallurgy

Won, C. W.; Nersisyan, H. H.; Won, H. I.

SOLAR ENERGY MATERIALS AND SOLAR CELLS, 95, 2, 745-750

Solar-grade silicon microparticles have been prepared by a two-stage technique consisting of a combustion process in a SiO(2)+alpha Mg (alpha is the mole number of Mg) system in an inert atmosphere and the hydrometallurgical treatment of the combustion product. It has been shown that the refining behavior of the metallic impurities from combustion-synthesized silicon (CS-Si) is better than that of metallic impurities from metallurgical-grade silicon (MG-Si) since CS-Si particles have a unique microporous network structure, which makes the hydrometallurgical treatment process very efficient. Inductively coupled plasma (ICP) analysis results indicate that silicon of purity greater than 99.99% can be obtained by the developed technique. The principle of the hydrometallurgical purification of CS-Si is discussed in the context of particle morphology and a comprehensive explanation for porous structure formation is provided. (C) 2010 Elsevier B.V. All rights reserved.

Preparation, Characterization, Decomposition Mechanism and Non-Isothermal Decomposition Reaction Kinetics of the Super Thermite Al/CuO Precursor

An Ting; Zhao Feng-Qi; Yi Jian-Hua; Fan Xue-Zhong; Gao Hong-Xu; Hao Hai-Xia; Wang Xiao-Hong; Hu Rong-Zu; Pei Qing

ACTA PHYSICO-CHIMICA SINICA, 27, 2, 281-288

The super thermite Al/CuO precursor was prepared using Cu(NO3)(2)center dot 3H(2)O, C2H5OH, 1,2-epoxy propane and nano-Al as raw materials under ultrasonic conditions by the sol-gel method. Our results show that the precursor components are Al and Cu-2(OH)(3)NO3. The thermal behavior and thermal decomposition mechanism of the nano super thermite Al/CuO precursor were investigated by thermogravimetric-differential scanning colorimetric-Fourier transform infrared spectrum-mass spectrometry analysis (TG-DSC-FTIR-MS). The decomposition reaction kinetics of the precursor was investigated by TG-DTG analysis at different heating rates and the kinetic parameters were calculated using six kinetic analytical methods. The activation energy, reaction order, frequency factor and other kinetic parameters were obtained and the kinetic equation of the decomposition process could be expressed as: d alpha/dt=10(14.0)x4 alpha(3/4)xexp(-2.0x10(4)/T).

Effects of Pd on enhancement of oxidation activity of LaBO3 (B = Mn, Fe, Co and Ni) pervoskite catalysts for pollution abatement from natural gas fueled vehicles

Ziaei-Azad, Hessam; Khodadadi, Abbasali; Esmaeilnejad-Ahranjani, Parvaneh; Mortazavi, Yadollah

APPLIED CATALYSIS B-ENVIRONMENTAL, 102, 41306, 62-70

The effect of Pd on activity enhancement of perovskite catalysts for oxidation of CH4 and CO emitted from natural-gas fueled vehicles is investigated using a synthetic stoichiometric exhaust gas mixture. Various LaBO3 and LaBPd0.05O3 (B = Mn, Fe, Co and Ni) perovskite-type nanocatalysts were prepared via a solution combustion synthesis, calcined at 700 degrees C for 5 h, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). BET specific surface area measurement, H-2 temperature programmed reduction (TPR) and O-2 temperature programmed desorption (TPD). XRD results, confirms the presence of PdO in Pd-containing samples, which is highly active for CO and CH4 oxidation. TPR and TPD results show that Pd significantly facilitates the reducibility of B in LaBPd0.05O3 pervoskites and enhances the mobility of lattice oxygen in the prepared samples, which results in activity enhancement for Pd-containing catalysts. Oxidation activity results reveal that Pd effect is more pronounced for CO oxidation as compared to that for CH4, probably due to the Pd transition from PdO to metallic Pd and/or its incorporation into the pervoskite structure occurred at elevated temperatures, which both seem to reduce its activity. Among the prepared samples, LaFePd0.05O3 catalyst shows the highest activity for CO and CH4 oxidation, T-90 of which occur at 165 and 558 degrees C, 191 and 40 degrees C lower than that for LaFeO3 respectively. (C) 2010 Elsevier B.V. All rights reserved.

Nonlinear Dynamics of Emotion-Cognition Interaction: When Emotion Does not Destroy Cognition?

Afraimovich, Valentin; Young, Todd; Muezzinoglu, Mehmet K.; Rabinovich, Mikhail I.

BULLETIN OF MATHEMATICAL BIOLOGY, 73, 2, 266-284

Emotion (i.e., spontaneous motivation and subsequent implementation of a behavior) and cognition (i.e., problem solving by information processing) are essential to how we, as humans, respond to changes in our environment. Recent studies in cognitive science suggest that emotion and cognition are subserved by different, although heavily integrated, neural systems. Understanding the time-varying relationship of emotion and cognition is a challenging goal with important implications for neuroscience. We formulate here the dynamical model of emotion-cognition interaction that is based on the following principles: (1) the temporal evolution of cognitive and emotion modes are captured by the incoming stimuli and competition within and among themselves (competition principle); (2) metastable states exist in the unified emotion-cognition phase space; and (3) the brain processes information with robust and reproducible transients through the sequence of metastable states. Such a model can take advantage of the often ignored temporal structure of the emotion-cognition interaction to provide a robust and generalizable method for understanding the relationship between brain activation and complex human behavior. The mathematical image of the robust and reproducible transient dynamics is a Stable Heteroclinic Sequence (SHS), and the Stable Heteroclinic Channels (SHCs). These have been hypothesized to be possible mechanisms that lead to the sequential transient behavior observed in networks. We investigate the modularity of SHCs, i.e., given a SHS and a SHC that is supported in one part of a network, we study conditions under which the SHC pertaining to the cognition will continue to function in the presence of interfering activity with other parts of the network, i.e., emotion.

alpha-Fe2O3 nanoparticles: An efficient, inexpensive catalyst for the one-pot preparation of 3,4-dihydropyrano[c]chromenes

Nagabhushana, H.; Saundalkar, S. Sandeep; Muralidhar, L.; Nagabhushana, B. M.; Girija, C. R.; Nagaraja, D.; Pasha, M. A.; Jayashankara, V. P.

CHINESE CHEMICAL LETTERS, 22, 2, 143-146

This paper describes the combustion synthesis of alpha-Fe2O3 nanopowder at much lower temperature and its catalytic activity for the one-pot preparation of 3,4-dihydropyrano[c]chromenes. The combustion derived alpha-Fe2O3 nanopowder was characterized by powder X-ray diffraction (PXRD), Braunauer, Emmett and Teller (BET) surface area, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Highly efficient, three-component condensation of aromatic aldehyde, malanonitrile and 4-hydroxycoumarin catalyzed by alpha-Fe2O3 nanoparticles at room temperature is described. The method offers an excellent alternative to the synthesis of 3,4-dihydropyrano[c]chromenes. The reactions are rapid, clean, and the products with good yield and high purity. (C) 2010 Published by Elsevier B.V. on behalf of Chinese Chemical Society.

Study of NiCuZn ferrite powders and films prepared by sol-gel method

Gao Liang-Qiu; Yu Guo-Jian; Wang Ying; Wei Fu-Lin

CHINESE PHYSICS B, 20, 2, 27503-

This paper reports that a series of NiCuZn ferrite powders and films are prepared by using sol-gel method. The effects of raw material composition and the calcinate temperature on magnetic properties of them are investigated. The NiCuZn ferrite powders are prepared by the self-propagating high-temperature synthesis method and subsequently heated at 700 degrees C similar to 1000 degrees C. The results show that NiCuZn ferrite powders with single spinel phase can be formed after heat-treating at 750 degrees C. Powders obtained from Ni(0.4)Cu(0.2)Zn(0.4)Fe(1.9)O(4) gel have better magnetic properties than those from gels with other composition. After heat-treating at 900 degrees C for 3 h, coercivity H(c) and saturation magnetization M(s) are 9.7 Oe (1 Oe = 80 A/m) and 72.4 emu/g, respectively. Different from the powders, NiCuZn films produced on Si (100) from the Ni(0.4)Cu(0.2)Zn(0.4)Fe(2)O(4) gel formed at room temperature possess high properties. When heat-treating condition is around 600 degrees C for 6 min, samples with low H(c) and high M(s) will be obtained. The minimal H(c) is 16.7 Oe and M(s) is about 300 emu/cm(3). In comparison with the films prepared through long-time heat treating, the films prepared through short heat-treating time exhibits better soft magnetic properties.

Microstructure and mechanical properties of Ni3Al and Ni3Al-1B alloys fabricated by SHS/HE

Guo, J. T.; Sheng, L. Y.; Xie, Y.; Zhang, Z. X.; Ovcharenko, V. E.; Ye, H. Q.

INTERMETALLICS, 19, 2, 137-142

The well-densified Ni3Al alloys without and with boron addition were fabricated by self-propagation high-temperature synthesis and hot extrusion (SHS/HE) technology. Microstructure investigation showed that Ni3Al and Ni3Al-1B alloys contained fine grain structure. Analysis of X-ray spectra as well as transmission electron microscopy studies revealed that three phases present in all alloys: gamma-Ni, Ni3Al and dispersoids of alpha- Al2O3 and gamma- Al2O3. However, beta-NiAl, Ni3B phase and twinned Ni3Al crystal are observed in the Ni3Al-1B alloy. In addition, dislocations with high density exist in all alloys. The mechanical test showed that the B addition leads to obvious improvement in yield strength and compressive ductility, and compared with the ones synthesized by combustion, SHS/HE synthesized Ni3Al and Ni3Al-1B alloys exhibit more excellent mechanical properties. (C) 2010 Elsevier Ltd. All rights reserved.

Hydrogen production via sulfur-based thermochemical cycles: Part 1: Synthesis and evaluation of metal oxide-based candidate catalyst powders for the sulfuric acid decomposition step

Karagiannakis, George; Agrafiotis, Christos C.; Zygogianni, Alexandra; Pagkoura, Chrysoula; Konstandopoulos, Athanasios G.

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 4, 2831-2844

The present work concerns the synthesis of various single and mixed oxide materials and their study as catalysts for the sulfuric acid dissociation reaction via which the production of SO(2) and O(2) is achieved. This is the most energy intensive step of sulfur-based thermochemical cycles for the production of hydrogen. Commercial (i.e. FeO, Fe(3)O(4), Fe(2)O(3), CuO, Cr(2)O(3), gamma-Al(2)O(3), Pt/gamma Al(2)O(3)) and in-house binary and ternary compositions of the Cu-Fe-Al system as well as Fe-Cr mixed oxide materials prepared by the Solution Combustion Synthesis (SCS) technique were comparatively tested. The materials were studied in powder form, in a fixed bed reactor at 850 degrees C and ambient pressure. The feedstock was concentrated liquid sulfuric acid (95-98% wt) and all tests were performed at a Liquid Hourly Space Velocity-LHSV of 50-52 h(-1). It was found that systems of both in-house synthesized mixed oxide families (Cu-Fe-Al and Fe-Cr) with proper composition could achieve SO(3) conversions comparable to that of the reference Pt/gamma Al(2)O(3) system, being at the same time much less expensive. The results, in combination with characterization results of fresh and spent catalysts are employed to identify possible mechanisms of the reaction and streamline the synthesis of more efficient catalytic systems. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Electrochemical performance of unsintered Ba0.5Sr0.5Co0.8Fe0.2O3-delta, La0.6Sr0.Co-4(0).8Fe0.2O3-delta, and La0.8Sr0.2MnO3-delta cathodes for metal-supported solid oxide fuel cells

Kim, Yu-Mi; Kim-Lohsoontorn, Pattaraporn; Baek, Seung-Wook; Bae, Joongmyeon

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 4, 3138-3146

The electrochemical performances of Ba0.5Sr0.5Co0.8Fe0.2O3-delta, La0.6Sr0.Co-4(0).8Fe0.2O3-delta, and La0.8Sr0.2MnO3-delta (LSM) cathodes fabricated without pre-sintering were studied. The BSCF starting powder prepared by the glycine nitrate method exhibited a single perovskite structure and no secondary phase was detected using XRD. SEM images revealed that the unsintered BSCF particles were highly agglomerated even before exposure to the operating temperature of the solid oxide fuel cell (SOFC). Unlike the LSM and LSCF cathodes, the BSCF cathode could be sintered at the SOFC operating temperature of 1073 K, and therefore exhibited porosity and good connectivity among particles. As determined using electrochemical impedance spectroscopy measurements, the lowest polarization resistances were found to be 0.13 Omega cm(2) for unsintered BSCF, 0.22 Omega cm(2) for unsintered LSCF, and 3.19 Omega cm(2) for unsintered LSM. The single-cell power density curves had maximal power densities of 0.91 W cm(-2), 0.77 W cm(-2), 0.60W cm(-2) for anode-supported SOFCs using unsintered BSCF, LSCF, and LSM cathodes, respectively. For practical aspect, the power densities of 0.72, 0.6 and 0.5 W cm(-2) were obtained at 0.7 V from anode-supported SOFCs with unsintered BSCF, LSCF and LSM cathodes, respectively. The metal-supported cells having unsintered BSCF cathode had maximum power densities at 0.82 W cm(-2), and a power density of 0.74 W cm(-2) at 0.7 V was observed. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Photocatalytic activity of BiVO4 nanospheres obtained by solution combustion synthesis using sodium carboxymethylcellulose

Garcia Perez, U. M.; Sepulveda-Guzman, S.; Martinez-de la Cruz, A.; Ortiz Mendez, U.

JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL, 335, 41306, 169-175

BiVO4 nanospheres were obtained through solution combustion synthesis (SCS) in presence of sodium carboxymethylcellulose (CMC). The CMC polymer had a double function, as a fuel and as a protecting agent in the particles growth process. The formation and characterization of oxide was carried out by simultaneous thermal analysis (TGA/DTA), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), and surface analysis (BET). The as-prepared BiVO4 nanospheres calcined at 300 degrees C exhibited higher photocatalytic activity under visible-light irradiation than BiVO4 samples prepared by coprecipitation and solid-state reaction methods in the degradation of rhodamine B (rhB). This behavior could be associated to their higher specific surface area (BET) and morphology. The analysis of the total organic carbon showed that the mineralization of rhB over a BiVO4 photocatalyst is feasible (43% after 100 h of irradiation). A mechanism of formation of BiVO4 nanospheres is also discussed. (C) 2010 Elsevier B.V. All rights reserved.

Magneto-optical properties of polycrystalline CoCrFeO4 films

Polyakova, K. P.; Polyakov, V. V.; Seredkin, V. A.; Patrin, G. S.

TECHNICAL PHYSICS LETTERS, 37, 2, 109-111

A methods of obtaining polycrystalline CoCrFeO4 films based on solid-phase reactions in Cr2O3/Co/Fe layer structures in the regimes of isothermal annealing and self-propagating high-temperature synthesis (SHS) is described. The magneto-optical properties of the obtained films have been studied. It is established that the spectra of magneto-optical characteristics depend on the solid-phase reaction regime and synthesis temperature. The Faraday rotation angle exhibits a local maximum (2 theta(F) = 5 deg/mu m) at a wave-length of 630 nm.

Application of the powder of porous titanium carbide ceramics to a reusable adsorbent for environmental pollutants

Moriwaki, Hiroshi; Kitajima, Shiori; Shirai, Koji; Kiguchi, Kenji; Yamada, Osamu

JOURNAL OF HAZARDOUS MATERIALS, 185, 41335, 725-731

The aim of this study is to investigate the utilization of the powder of porous titanium carbide (TiC) ceramics as a novel adsorbent or a material for solid-phase extraction (SPE). The adsorption and elution of inorganic and organic pollutants, Pb(II), 2,4,6-trichlorophenol (TCP), perfluorooctane sulfonate (PFOS), and perfluorooctanoic acid (PFOA), to the material were evaluated. The cartridge packed with TiC ceramics powder was used for the extraction test of pollutants. The solution containing pollutants at 1.0 mu g mL(-1) was passed through the TiC cartridge, and the substances were almost quantitatively removed. Furthermore, the pollutants retained in the cartridge were eluted with 3 N HCl for Pb(II) and with methanol for organic pollutants. The recoveries of pollutants were over 80%. In addition, we used the TiC cartridge for the solid-phase extraction of water samples (500 mL each of the distilled water and the river water) by adding pollutants at determined concentrations. Every pollutant was adsorbed almost quantitatively, and eluted by 3 N HCl or methanol. From these results, we concluded that the powder of porous TiC ceramics is a useful reusable adsorbent for the water cleanup and solid-phase extraction. (C) 2010 Elsevier B.V. All rights reserved.

Fe-Al phase formation around SHS reactions under isothermal conditions

Pochec, Ewelina; Jozwiak, Stanislaw; Karczewski, Krzysztof; Bojar, Zbigniew

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 4, 1124-1128

This study investigates the phenomena preceding and accompanying the SHS reaction between Fe and Al elemental powders during sintering SEM and XRD analysis were used to observe the mechanisms of formation of Fe-Al intermetallic phases The analysis of sintered material Just before the SHS reaction demonstrates that in addition to the well-known Fe(2)Al(5) phase and the low-aluminum solid solution of iron the high-aluminum phases FeAl(2) and FeAl(3) are formed The kinetics of phase transformations under Isothermal conditions were investigated by DSC using the JMA (Johnson-Mehl-Avrami) model This approach allowed us to calculate Avrami coefficients which characterize the speed and the manner of particular phase transformations (C) 2010 Elsevier B V All rights reserved

Microwave assisted solution combustion synthesis of alumina-zirconia, ZTA, nanocomposite powder

Tahmasebi, K.; Paydar, M. H.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 4, 1192-1196

In the present study the effect of microwave heating in producing alumina-20 wt% zircoma (ZTA) nanocomposite powder through metal nitrate solution combustion synthesis method using urea as fuel was studied For comparison ZTA nanocomposite powder is also synthesized using conventional heating method To characterize the products and evaluate the effect of microwave heating system on them X-ray diffractometry TEM SEM surface area analysis (BET) and TG/DTA analysis were used The results showed that both ZTA powder synthesized in microwave and furnace were nanocrystalline fine and brittle in which zircoma particles were homogeneously dispersed in the alumina matrix The results also proved that the powder produced in microwave was finer (<20 nm) with narrower size distribution and had better homogeneity of zircoma particles in alumina matrix but lower specific surface area in comparison with the sample which was synthesized in furnace (C) 2010 Elsevier B V All rights reserved

The structure and properties of NiAl formed by SHS using induction heating

Zhu, X.; Zhang, T.; Marchant, D.; Morris, V.

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 528, 3, 1251-1260

Intermetallic NiAl has the potential to be used for elevated temperature applications. To date different ignition techniques have been utilized to synthesize NiAl and produce coatings. Self-propagating high-temperature synthesis (SHS) has been developed as a relatively simple route to obtain intermetallics. This paper considers using induction heating to preheat and ignite the synthesis directly and investigates the effect of processing parameters on the phase transformation, microstructures and properties of Ni/Al compacts synthesized by SHS. The results show that single phase NiAl can be produced by induction heating whilst processing parameters such as heating rates and green densities have a significant effect on the properties and structures of sintered products. (C) 2010 Elsevier B.V. All rights reserved.

Effect of boron doping on microwave dielectric properties of SiC powder synthesized by combustion synthesis

Li, Zhimin; Zhou, Wancheng; Su, Xiaolei; Luo, Fa; Huang, Yunxia; Wang, Cheng

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 3, 973-976

Boron-doped SiC powders were synthesized from the Si/C/B system in a nitrogen atmosphere by combustion synthesis. Results showed that boron benefited the crystallization of beta-SiC, and that SiC solid solution with B acceptor doping was generated in combustion process. In the frequency range of 8.2-12.4 GHz, it was found that both real parts' and imaginary part epsilon '' of complex permittivity of siC samples decreased firstly, and then increased with increasing B content. (C) 2010 Elsevier B.V. All rights reserved.

Effects of Al and Al4C3 contents on combustion synthesis of Cr2AlC from Cr2O3-Al-Al4C3 powder compacts

Yeh, C. L.; Kuo, C. W.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 3, 651-655

Preparation of the ternary carbide Cr2AlC was conducted by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) from the Cr2O3-Al-Al4C3 powder compact. Effects of the contents of Al and Al4C3 on the product composition and combustion behavior were studied by formulating the reactant mixture with a stoichiometric proportion of Cr2O3:Al:Al4C3 = 3:5x:y, where x and y varied from 1.0 to 1.5. When compared to those of the powder compact with Cr2O3:Al:Al4C3 = 3:5:1 (i.e., x = y = 1.0), the combustion temperature and reaction front velocity increased with content of Al, but decreased with that of Al4C3. Besides Cr2AlC and Al2O3, the final products always contained a secondary phase Cr7C3 that was substantially reduced by adopting additional Al and Al4C3 in the reactant compacts. For the sample with Cr2O3:Al:Al4C3 = 3:7.5:1 (x = 1.5), solid state combustion reached a peak temperature of 1245 degrees C and yielded Cr2AlC with a trivial amount of Cr7C3. Although Cr7C3 was lessened by introducing extra Al4C3, the increase of Al4C3 from y = 1.1 to 1.5 produced almost no further reduction of Cr7C3 in the final product. This is partly attributed to the low combustion temperature in the range of 1065-1095 degrees C for the samples with additional Al4C3, and in part, due to the role of Al4C3 which might react with Cr to form Cr7C3, Cr2Al, and Cr2AlC. (C) 2010 Elsevier B.V. All rights reserved.

Heat flow calorimetry and SEM investigations to characterize the hydration at different temperatures of different 12CaO.Al2O3 (C(12)A(7)) samples synthesized by solid state reaction, polymer precursor process and glycine nitrate process

Raab, B.; Poellmann, H.

THERMOCHIMICA ACTA, 513, 41306, 106-111

Mayenite was synthesized using the conventional solid-state reaction and two low temperature synthesis methods a self-combustion method and a polymeric precursor process. Using the low temperature methods the metastable phase 5CaO center dot 3Al(2)O(3) (C(5)A(3)) crystallizes at 1173 K (2 h) instead of C(12)A(2). After forming pure crystalline 12CaO center dot 7Al(2)O(3) (C(12)A(2)) at 1373 K (2 h) the hydration was monitored at 283 K. 288 K, 293 K, 298 K and 301 K by heat flow calorimetry. During hydration the first calorimetric peak correlates with the formation of layers around the C(12)A(2) grains and the second peak corresponds to further hydration reactions and crystallization of lamellar calcium aluminate hydrates C(2)AH(8 +/- x) showing different hydration steps of 8.2H(2)O, 8.0H(2)O and 7.5H(2)O depending on temperature. At higher temperatures the formation of hydrate shells is increased and consequently the further hydration reaction is hindered. (c) 2010 Elsevier B.V. All rights reserved.

Synthesis and crystal structures and luminescent properties of divalent europium-doped Ba2ZnSi2O7 and BaZn2Si2O7

Yao, Shan-shan; Xue, Li-hong; Yan, You-wei

PHYSICA B-CONDENSED MATTER, 406, 2, 250-253

The monoclinic Ba2ZnSi2O7:Eu2+ blue-green-emitting phosphor and the orthorhombic BaZn2Si2O7:Eu2+ green-emitting phosphor were prepared by combustion-assisted synthesis method as the fluorescent materials for ultraviolet-light-emitting diodes (UV-LEDs) performed as a light source. The crystallinity and luminescence were investigated using X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy. Pure monoclinic Ba2ZnSi2O7 and orthorhombic BaZn2Si2O7 crystallize completely at 1100 degrees C. The doped Eu2+ ions did not cause any significant change in the host structure. The emission spectra presented an emission position red shift of up to 16 nm from Ba2ZnSi2O7:Eu2+ to BaZn2Si2O7:Eu2+. The excitation spectra of Ba2ZnSi2O7:Eu2+ and BaZn2Si2O7:Eu2+ were broad-banding, extending from 260 to 465 nm, which match the emission of UV-LEDs. (C) 2010 Elsevier B.V. All rights reserved.

Barium hexaferrite nanoparticles: Synthesis and magnetic properties

Martirosyan, K. S.; Galstyan, E.; Hossain, S. M.; Wang, Yi-Ju; Litvinov, D.

MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 176, 1, 8-13

Carbon combustion synthesis is applied to rapid and energy efficient fabrication of crystalline barium hexaferrite nanoparticles with the average particle size of 50-100 nm. In this method, the exothermic oxidation of carbon nanoparticles with an average size of 5 nm with a surface area of 80 m(2)/g generates a self-propagating thermal wave with maximum temperatures of up to 1000 degrees C. The thermal front rapidly propagates through the mixture of solid reactants converting it to the hexagonal barium ferrite. Carbon is not incorporated in the product and is emitted from the reaction zone as a gaseous CO(2). The activation energy for carbon combustion synthesis of BaFe(12)O(19) was estimated to be 98 kJ/mol. A complete conversion to hexagonal barium ferrite is obtained for carbon concentration exceeding 11 wt.%. The magnetic properties H(c)similar to 3000 Oe and M(s)similar to 50.3 emu/g of the compact sintered ferrites compare well with those produced by other synthesis methods. (C) 2010 Elsevier B.V. All rights reserved.

Effect of nickel nano-particle sintering on methane reforming activity of Ni-CGO cermet anodes for internal steam reforming SOFCs

Prasad, D. Hari; Ji, H. -I.; Kim, H. -R.; Son, J. -W.; Kim, B. -K.; Lee, H. -W.; Lee, J. -H.

APPLIED CATALYSIS B-ENVIRONMENTAL, 101, 41367, 531-539

In the present study, a single step synthesis of nano-sized NiO-Ce(0.9)Gd(0.1)O(2) (NiO-CGO) composite powder was successfully accomplished by a glycine-nitrate-process (GNP) and its catalytic activity for steam reforming of methane (SRM) was investigated in the absence of electrochemical effects. From XRD, SEM and CHN analysis on the spent Ni-CGO cermet catalysts after the test with different flow rates and SIC ratios, we found that the main reason for the decrease in the reforming activity was not due to oxidation or sintering of bulk Ni catalyst and carbon formation on the catalyst surface. Time-on-stream analysis at 800 degrees C for 80 h showed a continuous decease in the reforming activity for steam rich conditions (S/C = 1.5) whereas a constant and moderate reforming activity was observed for steam lean conditions (S/C = 0.5). From TEM analysis it is clearly evidenced that the reason for continuous decrease in the reforming activity under steam rich conditions was due to nickel nano-particle sintering whereas no sintering occurred under steam lean conditions which indicated that the steam was primary cause for nickel nano-particle sintering. Furthermore, TEM/EDS analysis confirmed that the nickel nano-particles were mainly located on the surface of the CGO support which can suppress the carbon formation by maintaining good metal (Ni)-support (CGO) interaction even under steam lean conditions. (C) 2010 Elsevier B.V. All rights reserved.

A Self-Propagating Matrix Metalloprotease-9 (MMP-9) Dependent Cycle of Chronic Neutrophilic Inflammation

Xu, Xin; Jackson, Patricia L.; Tanner, Scott; Hardison, Matthew T.; Roda, Mojtaba Abdul; Blalock, James Edwin; Gaggar, Amit

PLOS ONE, 6, 1, e15781-

Background: Chronic neutrophilic inflammation is a poorly understood feature in a variety of diseases with notable worldwide morbidity and mortality. We have recently characterized N-acetyl Pro-Gly-Pro (Ac-PGP) as an important neutrophil (PMN) chemoattractant in chronic inflammation generated from the breakdown of collagen by the actions of MMP-9. MMP-9 is present in the granules of PMNs and is differentially released during inflammation but whether Ac-PGP contributes to this ongoing proteolytic activity in chronic neutrophilic inflammation is currently unknown.Methodology/Principal Findings: Utilizing isolated primary blood PMNs from human donors, we found that Ac-PGP induces significant release of MMP-9 and concurrently activates the ERK1/2 MAPK pathway. This MMP-9 release is attenuated by an inhibitor of ERK1/2 MAPK and upstream blockade of CXCR1 and CXCR2 receptors with repertaxin leads to decreased MMP-9 release and ERK 1/2 MAPK activation. Supernatants obtained from PMNs stimulated by Ac-PGP generate more Ac-PGP when incubated with intact collagen ex vivo; this effect is inhibited by an ERK1/2 pathway inhibitor. Finally, clinical samples from individuals with CF demonstrate a notable correlation between Ac-PGP (as measured by liquid chromatography-tandem mass spectrometry) and MMP-9 levels even when accounting for total PMN burden.Conclusions/Significance: These data indicate that ECM-derived Ac-PGP could result in a feed-forward cycle by releasing MMP-9 from activated PMNs through the ligation of CXCR1 and CXCR2 and subsequent activation of the ERK1/2 MAPK, highlighting for the first time a matrix-derived chemokine (matrikine) augmenting its generation through a discrete receptor/intracellular signaling pathway. These findings have notable implications to the development unrelenting chronic PMN inflammation in human disease.

Effects of alpha-Si3N4 and AlN addition on formation of alpha-SiAlON by combustion synthesis

Yeh, C. L.; Sheng, K. C.

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 2, 529-534

Preparation of Yb alpha-SiAlON was investigated by self-propagating high-temperature synthesis (SHS) from alpha-Si3N4- and alpha-Si3N4/AlN-diluted powder compacts under nitrogen of 2.17 MPa. For the AlN-free samples, the molar ratio of Si3N4/Si varies between 0.22 and 0.5. The starting stoichiometry of the AlN-added samples comprises a constant proportion of Si3N4/Si equal to 0.22, but a broad range of AlN/Al from 0.33 to 1.0. The self-sustaining combustion wave propagated in the spinning mode on account of highly diluted samples adopted in this study. The overall reaction exothermicity increases with Si3N4/Si ratio for the AlN-free samples, while decreases with AlN/Al ratio for the AlN-added powder compacts. As a result, the amount of unreacted Si left in the final product was significantly reduced and the formation of nearly single-phase Yb alpha-SiAlON was achieved in the sample with Si3N4/Si = 0.5. Moreover, the growth of elongated alpha-SiAlON grains was enhanced in the samples with high contents of Si3N4. In contrast, the nitridation of Si was only improved to a certain extent with the addition of AlN and no further improvement was attained by increasing the AlN content. Due to the lack of sufficient liquid phases during combustion and the weak reaction exothermicity, the samples with high contents of AlN were inclined to produce alpha-SiAlON grains in a fine equiaxed form. (C) 2010 Elsevier B.V. All rights reserved.

Energy release characteristics of impact-initiated energetic aluminum-magnesium mechanical alloy particles with nanometer-scale structure

Wang, Yi; Jiang, Wei; Zhang, Xianfeng; Liu, Hongying; Liu, Yaqing; Li, Fengsheng

THERMOCHIMICA ACTA, 512, 41306, 233-239

Aluminum-magnesium alloys, fabricated by bi-directional rotation ball milling, were used as a kind of promising solid fuel in "reactive material" that can be ignited by impact to release a large quantity of heats. Different percentages of Mg were added to Al to yield Al(90%)-Mg(10%) and Al(70%)-Mg(30%) alloys in order to probe the effect of Mg content on the microstructure and thermal reactivity of Al-Mg alloys. Structural characterization revealed that a nanometer-scale structure was formed and oxidation of as-fabricated alloy powders was faint. Moreover, as the Mg percentage increased, the particle size of alloy decreased with increasing brittleness of Al-Mg. TGA/DSC curves of the [Al(70%)-Mg(30%)]-O(2) system exhibited an intense exothermic peak before melting with reaction heat of 2478 J g(-1) and its weight increase reached 90.16% of its theoretical value, which contrasted clearly with 181.2 J g(-1) and 75.35% of [Al(90%)-Mg(10%)]-O(2) system, respectively. In addition, other than [Al(90%)-Mg(10%)]-Fe(2)O(3) system, the [Al(70%)-Mg(30%)]-Fe(2)O(3) system exhibited a considerable solid-solid reaction and a low activation energy. Finally, target penetration experiments were conducted and the results confirmed that a projectile composed of [Al(70%)-Mg(30%)]-Fe(2)O(3) displayed a more complete ignition of target than that of Al-Fe(2)O(3) formulation. (C) 2010 Elsevier B.V. All rights reserved.

The mechanism of combustion synthesis of (TiCxNy-TiB2)/Ni from a Ni-Ti-C-BN system

Zhan, Lei; Shen, Ping; Jiang, Qichuan

POWDER TECHNOLOGY, 205, 41334, 52-60

The combustion reaction mechanism of the Ni-Ti-C-BN system was investigated by a combustion front quenching method. The results showed that the SHS reaction in the Ni-Ti-C-BN system starts with the formation of TiNx and TiB from the solid-state reaction between Ti and BN. Meanwhile, the solid-state reaction between Ni and Ti occurs at some locations to form Ni3Ti. Subsequently, the resultant TiNx reacts with Ni to form the Ni-Ti compounds such as NiTi and Ni3Ti. As the temperature increases further, Ni-Ti liquid appears between NiTi and Ni3Ti, and some B atoms that diffused away from BN could dissolve into the Ni-Ti liquid to form TiB2. The heat generated from these reactions promotes the further dissolution of the C, B and N atoms in the Ni-Ti liquid to form the Ni-Ti-B-N-C liquid. As the B. N and C atoms in the liquid become sufficiently supersaturated, precipitation of plenty of TiB2 and TiCxNy grains occurs. In addition, the reasons for the prior formation of TiB2 over TiCxNy and separated residence of the TiB2 and TiCxNy grains in the microstructure were discussed. (C) 2010 Elsevier B.V. All rights reserved.

The effect of Si-Bi2O3 on the ignition of the Al-CuO thermite

Ilunga, K.; del Fabbro, O.; Yapi, L.; Focke, W. W.

POWDER TECHNOLOGY, 205, 41334, 97-102

The ignition temperature of the Al-CuO thermite was measured using DTA at a scan rate of 50 degrees C min(-1) in a nitrogen atmosphere. Thermite reactions are difficult to start as they require very high temperatures for ignition, e.g. for Al-CuO thermite comprising micron particles it is ca. 940 degrees C. It was found that the ignition temperature is significantly reduced when the binary Si-Bi2O3 system is added as sensitizer. Further improvement is achieved when the reagents are nano-sized powders. For the composition Al + CuO + Si + Bi2O3 (65.3:14.7:16:4 wt.%), with all components nano-sized, the observed ignition temperature is ca. 613 degrees C and a thermal runaway reaction is observed in the DTA. (C) 2010 Elsevier B.V. All rights reserved.

A fundamental measure theory for the sticky hard sphere fluid

Hansen-Goos, Hendrik; Wettlaufer, J. S.

JOURNAL OF CHEMICAL PHYSICS, 134, 1, 14506-

We construct a density functional theory (DFT) for the sticky hard sphere (SHS) fluid which, like Rosenfeld's fundamental measure theory (FMT) for the hard sphere fluid [Y. Rosenfeld, Phys. Rev. Lett. 63, 980 (1989)], is based on a set of weighted densities and an exact result from scaled particle theory (SPT). It is demonstrated that the excess free energy density of the inhomogeneous SHS fluid (Phi)SHS is uniquely defined when (a) it is solely a function of the weighted densities from Kierlik and Rosinberg's version of FMT [E. Kierlik and M. L. Rosinberg, Phys. Rev. A 42, 3382 (1990)], (b) it satisfies the SPT differential equation, and (c) it yields any given direct correlation function (DCF) from the class of generalized Percus-Yevick closures introduced by Gazzillo and Giacometti [J. Chem. Phys. 120, 4742 (2004)]. The resulting DFT is shown to be in very good agreement with simulation data. In particular, this FMT yields the correct contact value of the density profiles with no adjustable parameters. Rather than requiring higher order DCFs, such as perturbative DFTs, our SHS FMT produces them. Interestingly, although equivalent to Kierlik and Rosinberg's FMT in the case of hard spheres, the set of weighted densities used for Rosenfeld's original FMT is insufficient for constructing a DFT which yields the SHS DCF. (c) 2011 American Institute of Physics. [doi:10.1063/1.3528226]

Microwave-assisted synthesis and characterization of Nd1.5Mg17Ni0.5-Fe3O4 hydrogen storage composite

Li, Qian; Ye, Li-Wen; Meng, Jie; Liu, Yang; Chou, Kuo-Chih

JOURNAL OF ALLOYS AND COMPOUNDS, 509, 1, 99-104

This work reports the preparation of Nd1.5Mg17Ni0.5-Fe3O4 hydrogen storage composite in a single mode 2.45 GHz microwave cavity. The physicochemical properties (thermodynamic and kinetic characteristics, hydrogen absorption/desorption properties, thermal behavior, phase composition and morphology) were characterized by pressure-composition isotherms, differential scanning calorimetry, X-ray diffraction, scanning electron microscope with an energy dispersive X-ray spectrometer, transmission electron microscopy, and laser granulometry. The proposed microwave synthesis, in contrast with conventional sintering method, offers rapid heating, makes homogenous composition and hence improves the hydrogen storage properties of the composite. (C) 2010 Elsevier B.V. All rights reserved.

SOLUTION COMBUSTION SYNTHESIS AND CHARACTERISTICS OF NANOSCALE MgO POWDERS

Bai, Jiahai; Meng, Fantao; Wei, Chuncheng; Zhao, Yunxia; Tan, Huihui; Liu, Juncheng

CERAMICS-SILIKATY, 55, 1, 20-25

Nanoscale MgO powders were fabricated via a microwave-induced solution combustion process using Mg(NO(3))(2) and starch as starting materials. Effects of the relative filet-to-oxidant ratios (phi(e) = 1.1, 1.0, 0.9 and 0.8, respectively) on characteristics of MgO nanoparticles were also investigated. The XRD analysis discloses that MgO nanocrystalline are successfully synthesized and the crystalline size of MgO increases remarkably with increasing of phi e from 0.8 to 1.1. TEM images reveal that nanoporous agglomerates of MgO nanocrystalline are formed in the powders. Experimental results show that the average particles' size of the powders decreases significantly as phi e increases from 0.8 to 1.1. However; the powders from the precursors with phi(e) equal to 1.0 exhibit larger specific surface area as compared the other powders.

Development of an Amperometric Hydrogen Peroxide Biosensor based on the Immobilization of Horseradish Peroxidase onto Nickel Ferrite Nanoparticle-Chitosan Composite

Yalciner, Furkan; Cevik, Emre; Senel, Mehmet; Baykal, Abdulhadi

NANO-MICRO LETTERS, 3, 2, 91-98

Nickel ferrite (NiFe2O4) nanoparticles have been dispersed in chitosan solution in order to fabricate nanocomposite films. Horseradish peroxidase (HRP) has been immobilized onto this chitosan-NiFe2O4 nanocomposite film via physical adsorption. The size of the NiFe2O4 nanoparticles has been estimated using X-ray diffraction pattern and scanning electron microscopy (SEM) to be 40 +/- 9 nm. The chitosan-NiFe2O4 nanocomposite film and HRP/chitosan-NiFe2O4 bioelectrode have been characterized using SEM technique. The HRP/chitosan-NiFe2O4 nanocomposite bioelectrode has a response time of 4s, linearity as 0.3 to 12mM of H2O2, sensitivity as 22 nA/mM. The effects of pH and the temperature of the immobilized HRP electrode have also been studied.

Conductivity Study of Polyaniline-Cobalt Ferrite (PANI-CoFe2O4) Nanocomposite

Tanriverdi, E. E.; Uzumcu, A. T.; Kavas, H.; Demir, A.; Baykal, A.

NANO-MICRO LETTERS, 3, 2, 99-107

In this investigation, the structural and electrical properties of nanocomposites of polyaniline (PANI) and cobalt ferrite synthesized by hydrothermal route are reported for the first time (with weight ratios of CoFe2O4/PANI 1:2 and 2:1). Synthesized nanomaterials have been characterized by XRD, FT-IR, SEM and TEM techniques. FT-IR results confirm the presence of CoFe2O4 and PANI in the samples. Their detailed conductivity measurements have been investigated. It has been found that PANI has a more effective conducting mechanism in CoFe2O4-PANI composites. These results are also consistent with the change in AC conductivity orders in composites.

The Effect of Condensation on the Morphology and Magnetic Properties of Modified Barium Hexaferrite (BaFe12O19)

Durmus, Z.; Sozeri, H.; Toprak, M. S.; Baykal, A.

NANO-MICRO LETTERS, 3, 2, 108-114

We present a comparison for the effect of condensation on the morphology and magnetic properties of oleic acid modified BaFe12O19 nanoparticles. Two different samples of BaFe12O19 nanoparticles were synthesized by dehydration (Z1) and rotary evaporation (Z2) method, respectively. Oleic acid was used as the surface modification agent to observe the morphological and magnetic changes. The nanoparticles were analyzed by XRD, FTIR, TGA, SEM, and VSM techniques for structural and physicochemical characteristics. Crystallographic analysis reveals the phase as hexaferrite and the average crystallite size of Z1 and Z2 is 21 +/- 3 nm and 17 +/- 2 nm, respectively. Rotary evaporator accelerates the condensation process in viscous gel (Z2). Due to the use of rotary evaporator, the coating with oleic acid for Z2 product has been accomplished very well, as compared with Z1. As a result, saturation magnetization of Z2 sample is much lower than that of Z1 sample.

Morphology and Phase Evolution in Microwave Synthesized Al/Fe3O4 System

Chuan, Lee Chang; Yoshikawaa, Noboru; Taniguchia, Shoji

JOURNAL OF MICROWAVE POWER AND ELECTROMAGNETIC ENERGY, 45, 3, 148-154

Thermite reaction between Al/Fe3O4 raised by microwave (MW) heating under N-2 atmosphere has been investigated, and compared with that by the electric furnace. In addition to the stoichiometric ratio for the production of metallic iron and alumina, mixture with slightly lower in Al content is also studied. As thermite reaction is highly exothermic, melting of reaction product and destruction of microstructure may occur, which corresponds to the enthalpy and adiabatic temperature of the reaction. Hence, to avoid this problem, reaction coupled with a smaller driving force by controlling the MW ignition condition at low temperature exotherm has been investigated. The phase and microstructure evolution during the reaction were analyzed by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Thermogram of the DTA analysis, irrespective of their mole ratio, recorded two exothermic peaks, one at similar to 1310 degrees C and another one at similar to 1370 degrees C. When heated by microwave at 955 degrees C, the main products were identified as Al, FeO and Fe, minor amount of Fe3O4 and some Fe and alumina were detected. When heating to 1155 degrees C, Al and Fe3O4 peaks disappeared, formation of Fe-Al alloy was observed. For sample heated at 1265 degrees C, a porous body was obtained. Micron sized metal particles with complex morphology, irregular in size and shapes were formed, uniformly distributed within the spinel hercynite and/or alumina matrix. In contrast, conventional heating produced no porous products. Formation of alumina is also observed around the metal particles. Controlling of the reaction progress was possible while heating the sample by MW around the low temperature exotherm region, whereas the combustion wave could not be self-propagated.

High density nanoparticle Mn-Zn ferrite synthesis, characterisation and magnetic properties

Tangsali, R. B.; Budkuley, J. S.; Keluskar, S. H.; Naik, G. K.; Watave, S. C.

INTERNATIONAL JOURNAL OF NANOTECHNOLOGY, 8, 41618, 948-962

The amazing magnetic properties exhibited by nanoparticles Mn-Zn ferrites and their promising technological and medical applications have attracted much interest in recent years. Nanoparticle Mn-x Zn(1-x) Fe2O4 spinel ferrites with x = 0.6/0.63/0.65/0.67/0.7 were synthesised by the nitrilotriacetate precursor method employing microwave combustion synthesis. Powder X-ray diffractometry (XRD) confirmed the formation of the ferrite phase in all samples. IR analysis was done to verify formation of spinel structure. Elemental analysis using EDS confirmed the nanoparticle composition. The crystallite size was calculated from peak widths using the Scherrer formula, yielding a size in the range of 10-25 nm. Transmission electron microscopy was also performed on the samples to testify formation of nanosized crystallites in the sample. Saturation magnetisation (Mr), retentivity (Ms) and coercivity (He) measurements were carried out on the samples using standard hysteresis loop tracer equipment. The saturation magnetisation values were found to be in the range of 58.6-63.2 emu/g with very low values for (Mr/Ms). Variation of specific magnetisation with temperature and Curie temperature measurements were carried out using pulse field AC susceptibility measuring equipment. These measurements indicated formation of single domain (SD) material with dependence of Curie temperature on Zn concentration. The density of the samples was found to be high.

CO oxidation by CeO2-Al2O3-CeAlO3 hybrid oxides

Deshpande, Parag A.; Aruna, S. T.; Madras, Giridhar

CATALYSIS SCIENCE & TECHNOLOGY, 1, 9, 1683-1691

A modified solution combustion technique was successfully used to synthesize sub-10 nm crystallites of hybrid CeO2-Al2O3-CeAlO3. The fuel in the solution combustion was tuned to obtain mixed oxides and solid solutions of the compound. The compounds were characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. XRD and TEM analysis showed the substitution of Al3+ ions in the CeO2 matrix when a combination of glycine, urea, hexamine and oxalyl dihydrazide was used as fuel for the synthesis. The compounds showed high activity for CO oxidation and the activity of the compounds was dependent upon the composition of the oxide.

In situ Synthesis of Nano-sized ZrC and Its Formation Mechanism by Combustion Synthesis from Zr-C-Cu System

Zhang, Mengxian; Hu, Qiaodan; Huang, Bing; Li, Junzheng; Li, Jianguo

ISIJ INTERNATIONAL, 51, 10, 1576-1579

Nano-sized ZrC was prepared by combustion synthesis (CS) from Cu-Zr-C elemental powder mixtures. The ZrC particle size greatly decreased from about 10 mu m with an irregular shape in free Cu addition to nano-meter order with a nearly spherical shape in Cu addition ranging from 10 wt.% to 30 wt.%. The formation mechanism of the nano-sized ZrC was discussed. The low dissolubility of C into Cu melt may greatly inhibit the growth of product ZrC, resulting in formation of ZrC particles as fine as nano-sized C. Melting of metallic Cu plays an important role in the formation mechanism of the nano-sized ZrC.

SYNTHESIS OF V-AL ALLOY BY MICROWAVE-ASSISTED SELF-PROPAGATING

Liu, Shouping; Li, Jin; Lv, Xuewei; Lun, Zhigang; Bai, Chenguang

METALURGIA INTERNATIONAL, 16, 12, 41-47

V-Al intermediate alloy was the main material for the preparation of Ti-V-Al alloy which is used in the field of aerospace, therefore it is especially meaningful for the study about preparation and constitution of the V-Al alloy. In this paper. V-Al alloy was produced by microwave-assisted Self-propagating High-temperature Synthesis (SHS) and the reaction feasibility was predicted through thermodynamic calculation. The effects of the amount of CaO, Al, the holding time of microwave heating on the recovery of Vanadium and the compositions of the alloy were studied. The phase compositions and the distribution of component of the V-Al alloy were detected by X-ray diffractometer and scanning electron inicroscopy respectively. The elements of V-Al alloy quantitatively described through energy disperse spectroscopy. The results show that the main phases of the V-Al intermediate alloy produced by microwave heat-assisted SHS process are V-Al compounds matrix, a small amounts of alumina and vanadium oxide inclusions. The recovery of vanadium increased and the content of nonmetallic inclusions decreased with the amount of Al increased and the holding time extended.

PMMA-Y2O3 (Eu3+) nanocomposites: optical and mechanical properties

Musbah, Salah S.; Radojevic, Vesna J.; Borna, Nadezda V.; Stojanovic, Dusica B.; Dramicanin, Miroslav D.; Marinkovic, Aleksandar D.; Aleksic, Radoslav R.

JOURNAL OF THE SERBIAN CHEMICAL SOCIETY, 76, 8, 1153-1161

The results of a study related to the processing and characterization of poly(methyl methacrylate) (PMMA)-Y2O3 (Eu3+) nanocomposites are presented herein. The nanocomposite samples were prepared using a laboratory mixing molder with different contents of Eu-ion doped Y2O3 nanophosphor powder. The influence of particle content on the optical and dynamic mechanical properties of the nanocomposites was investigated. The intensity of the luminescence emission spectra increased as the nanophosphor content in the composite increased. The results of dynamic mechanical analysis revealed that the storage modulus, loss modulus and glass transition temperature (T-g) of the polymer composites increased with increasing content of the nanophosphor powder. The microhardness data also confirmed that the hardness number increased with nanoparticles concentration in the PMMA nanocomposites. The obtained results revealed a relatively linear relationship between T-g and the Vickers hardness.

Modified Combustion Synthesis of gamma-Alumina Nano Powders

Norouzbeigi, R.; Edrissi, M.

ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS, 225, 8, 881-900

Alumina nano powders have been prepared by a chemical method named combustion synthesis using new fuels. The effect of key factors on the synthesis of nanoparticles was studied and optimized using Taguchi L(16) (4(5)) array design. The products were characterized by XRD, TGA, EDX, FESEM, and TEM analyses. Results show that aluminum oxide powders had crystal sizes between 7.2 nm and 13 nm and specific surface areas between 21 m(2) g(-1) and 70 m(2) g(-1). It was found that there is a good linear correlation (R(2) = 0.953) between crystallite size and specific surface area of the synthesized gamma-alumina. The surface area of the sample prepared under optimum condition was 72 m(2) g(-1) and its average particle size measured by DLLS was 81 nm. The synthesis of gamma-alumina was modified in order to achieve higher specific surface area (123 m(2) g(-1)). A network of nano-fibers was successfully obtained by the modified route. The length and diameter of fibers were about 160 nm and 10 nm respectively.

Near UV-Blue Excitable Green-Emitting Nanocrystalline Oxide

Rodriguez-Garcia, C. E.; Perea-Lopez, N.; Hirata, G. A.

ADVANCES IN MATERIALS SCIENCE AND ENGINEERING, , , 790517-

Green-emitting Eu-activated powders were produced by a two-stage method consisting of pressure-assisted combustion synthesis and postannealing in ammonia. The as-synthesized powders exhibited a red photoluminescence (PL) peak located at lambda = 616 nm when excited with lambda = 395 nm UV. This emission peak corresponds to the D-5(0) -> F-7(2) transition in Eu3+. After annealing in ammonia, the PL emission changed to an intense broad-band peak centered at lambda = 500 nm, most likely produced by 4f(6)5d(1) -> 4f(7) electronic transitions in Eu2+. This green-emitting phosphor has excitation band in the near UV-blue region (lambda = 300-450 nm). X-ray diffraction analysis reveals mainly the orthorhombic EuAlO3 and Al2O3 phases. Transmission electron microscopy observations showed that the grains are formed by faceted nanocrystals (similar to 4 nm) of polygonal shape. The excellent excitation and emission properties make these powders very promising to be used as phosphors in UV solid-state diodes coupled to activate white-emitting lamps.

Heterogeneous Combustion in Systems Containing Chemical Elements of Group III. Generation of Electric Potentials

Morozov, Yu G.; Kuznetsov, M. V.; Belousova, O. V.

COMBUSTION EXPLOSION AND SHOCK WAVES, 47, 1, 59-64

The behavior of frontally burning heterogeneous systems containing boron, aluminum, gallium, indium, yttrium, lanthanum, and ytterbium is studied by a potentiometric method. These systems are used for self-propagating high-temperature synthesis of some oxide materials. The peak values of the electromotive force of combustion arising between the combustion wave front and the synthesis products in systems with participation of triple-charged ions of these chemical elements are found to be directly proportional to the ionic potential of the chemical element and reach 150-400 mV. The use of two heteropolarly reacting systems as elements of the electromotive force of combustion in one array assembly allows the difference in potentials to be increased to 2.3 V.

Preparation and Property Evaluation of Co-Doped La0.8Sr0.2Ga0.8Mg0.2O3-partial derivative Electrolyte for IT- SOFC

Lee, Dokyol; Han, Ju-Hyeong

ELECTROCHEMICAL AND SOLID STATE LETTERS, 14, 9, B85-B88

Co doping was used to enhance the electrical conductivity of La0.8Sr0.2Ga0.8Mg0.2O3-partial derivative (LSGM). La0.8Sr0.2Ga0.8Mg0.2-xCoxO3-partial derivative (LSGMC) powders were synthesized using the glycine nitrate process for use as the electrolyte of solid oxide fuel cells. The powder X-ray diffraction patterns confirmed a single perovskite phase and the SEM images showed the dense grain microstructure of the sintered pellets. The electrical conductivity of LSGMC measured at 800 degrees C was observed to be 0.145 Scm(-1), which is higher than that of LSGM (0.127 Scm(-1)). In addition, the linear thermal expansion coefficient and chemical reaction were investigated. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3597839] All rights reserved.

Orange Emission in Eu3+-Activated Mg2M (PO4)2(M = Sr and KNa) and KSrPO4 Phosphors

Shinde, K. N.; Pawade, V. B.; Dhoble, S. J.; Yawalkar, P. W.

SYNTHESIS AND REACTIVITY IN INORGANIC METAL-ORGANIC AND NANO-METAL CHEMISTRY, 41, 5, 517-524

This work concerns the photoluminescence (PL) studies of intense orange emission in phosphate based phosphors doped with trivalent europium. The present compounds were prepared by combustion synthesis, and the completion of the synthesis was confirmed by X-ray diffraction (XRD) pattern. The PL emission spectrum of Eu3+ in Mg2M(PO4)2 (M = Sr and KNa) and KSrPO4 phosphors was observed at around 590 nm orange region. The spectrum is due to 5D0 7F1 transitions at near UV excitation, i.e., 391 nm. The 300-400 nm is Hg free excitation (Hg excitation is 85% 254 nm wavelength of light and 15% are other wavelengths), which is characteristic of solid-state lighting phosphors. Hence, intense orange PL emissions suggest the possibility of the potential of phosphate based phosphors in warm white LED phosphors.

SYNTHESIS OF ZNS PHOSPHOR PARTICLES IN EXOTHERMIC FRONTAL WAVES

Won, C. W.; Nersisyan, H. H.; Won, H. I.; Jeon, D. Y.; Kirakosyan, A. G.

COMBUSTION SCIENCE AND TECHNOLOGY, 183, 9, 915-927

In this study, temperature profiles and combustion velocities of a Zn+S system in the presence of sodium halide (SH) as an inert diluent were investigated by combining combustion experiments with the thermocouple measurement technique. Flammability limits were determined experimentally by determining the limiting concentrations of sodium halides for which combustion can be initiated and propagated throughout the reaction pellet. The limiting concentration of NaCl was found to be higher than those of NaF and NaI, indicating that NaCl might be a more effective diluent for the Zn+S system. All reaction mixtures were characterized by low combustion temperature in the range 800-1350 degrees C and burning velocities in the range of 0.024-0.095 cmls. Depending on the combustion temperature, this synthetic route provides single-phase modified zinc sulfide powders of sphalerite and wurtzite. ZnS samples doped with halogen ions (H(-)) produced sky-blue emission (470 nm) under 340 nm excitation. ZnS samples codoped with Mn2(+) ions showed a red shift (588 nm) under 356 nm excitation. The relative emission intensity of ZnS:Mn(2+) phosphor increased as much as 3 times in the NaF -> NaI -> NaCl range.

Comparison of Combustion and Solid-State Reaction Methods for the Fabrication of SOFC LSM Cathodes

Yang, Seon-Ho; Kim, Kyung-Hwan; Yoon, Hyon-Hee; Kim, Woo-Jae; Choi, Hyung-Wook

MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 539, , 50-57

This study investigates the crystal phase and microstructure of LSM (La1-xSrxMnO3) cathode material synthesized by solid state reaction method and combustion synthesis. It measures and compares their electrical properties. LSM is a lanthanum ferrite-based cathode material. It has an ABO3 perovskite structure; the A in this structure was substituted by Sr in this research to synthesize the LSM cathode powder. An electrolyte pellet was prepared using 8mol% YSZ (yttria-stabilized zirconia) powder. The electrode was vapor deposited by screen printing. The crystal structure and morphology were measured by scanning electron microscopy (SEM) and X-ray diffraction (XRD) for the sintered samples collected. The complex impedance was measured in the temperature range 600-900 degrees C in air (Computer Impedance Grain-Phase Analyzer). The electrical conductivity and polarization resistance of LSM were characterized systematically.

IGNITION OF TITANIUM POWDER LAYERS BY ELECTROSTATIC DISCHARGE

Beloni, Ervin; Dreizin, Edward L.

COMBUSTION SCIENCE AND TECHNOLOGY, 183, 8, 823-845

Titanium powder heating and ignition by an electrostatic discharge (ESD) or spark was investigated. The effect of powder layer thickness and morphology was determined. Ti powder was chosen for these experiments because it is commonly found in energetic formulations, used for materials preparation by self-propagating high-temperature synthesis, and is extensively used in powder metallurgy. Two Ti powders were used: spherical powder with a volume mean diameter of 82 mu m and sponge powder with a volume mean diameter of 30 mu m. ESD current and voltage were measured in real time; powder ignition was characterized using an optical sensor and photographs of the produced burning particles. Different ignition modes were observed for powders with different morphologies and placed in layers with different thickness. For both spherical and sponge Ti powders prepared as monolayers, ESD initiation resulted in fragmentation of the initial particles. Produced particle fragments were ejected from the sample holder and burned as individual fine metal droplets. The burn times for such fragments were substantially shorter than expected for particles present in the starting Ti powders. Sponge powder placed in thicker layers ignited generating individual burning particles with combustion times close to those expected based on the particle size distribution. Spherical Ti powder placed in thicker layers was difficult to ignite and only a few short individual particle streaks were observed, which could be attributed to the finest particles present in the sample. When a titanium powder (either spherical and sponge) was placed in a layer with thickness greater than 0.1 mm, significant fusing of the particles was observed which reduced the powder heating by the discharge's Joule energy.

Impact-Driven Thermite Reactions with Iodine Pentoxide and Silver Oxide

Russell, R.; Bless, S.; Pantoya, M.

JOURNAL OF ENERGETIC MATERIALS, 29, 2, 175-192

Thermite reactions using aluminum (Al) fuel and either iodine pentoxide (I2O5) or silver oxide (Ag2O) were initiated by high-velocity impact or thermal initiation and examined for their flame propagation behavior. In the impact-ignition experiments, the Al-Ag2O reaction produced more energy than the Al-I2O5 reaction; in the thermal-ignition experiments, the I2O5 reaction produced higher flame propagation rates (1,305m/s compared with 531m/s). The energy released from impact-initiated reactions is significantly enhanced by reducing the size of the oxide particles. Results suggest that the reaction propagation mechanisms may be the same, even though ignition is spurred by two different stimuli (mechanically induced compaction versus thermal).

Temperature measurements of Al containing nano-thermite reactions using multi-wavelength pyrometry

Weismiller, M. R.; Lee, J. G.; Yetter, R. A.

PROCEEDINGS OF THE COMBUSTION INSTITUTE, 33, , 1933-1940

Thermite reactions with nano-scale particles have attracted much study due to their high flame temperatures and combustion velocities. The mechanism by which the reaction propagates is not well understood. The reaction temperature, the heating rate, and the reaction zone thickness are critical parameters to understanding the mechanism. Measurements of the reaction temperature for the Al/CuO, Al/MoO3, and Al/Fe2O3 nano-thermite systems were made using multi-wavelength pyrometry for two experimental configurations. In one experiment, the radiative emission from the reaction of a small, unconfined pile (similar to 10 mg) of reacting nano-thermite is collected over a 50 ms integration time and the temperature is measured. In a second experiment, the radiative emission was collected from a single spot, with a diameter of 1.5 mm, on a transparent tube filled with the nano-thermite as the combustion wave passes and the spectrum is temporally resolved using a streak tube and detected using an intensified CCD camera. Temperature traces from these experiments show a temperature ramping period followed by a plateau in temperature. For Al/CuO, the average temperature from the unconfined pile experiment was 2390 +/- 150 K, and the average plateau temperature for the temporally resolved measurements was approximately 2250 +/- 100 K. For Al/MoO3, the unconfined pile experiment yielded an average temperature of 2150 +/- 100 K, and the average plateau temperature was the same. The temperature measured from the Al/Fe2O3 unconfined pile experiment was 1735 +/- 50 K. The measured temperatures suggest that the gases generated during the reactions are primarily from the decomposition or vaporization of the various metal oxides. Furthermore, for Al/CuO and Al/MoO3, which can be classified as 'fast' nano-thermites, it was shown that the length scale associated with thed temperature rise is much longer than classical conduction driven reactions. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Spontaneous ignition temperature for the compacted mixture of Ti-Al system: Theory and experimental comparisons

Makino, Atsushi; Higuchi, R.; Hisamoto, A.; Koizumi, K.; Takada, H.

PROCEEDINGS OF THE COMBUSTION INSTITUTE, 33, , 1967-1974

Spontaneous ignition of compacted mixture has been examined not only experimentally but also theoretically, relevant to materials synthesis by combustion for Ti-Al system. By varying compact and particle sizes, mixture ratio, and degree of dilution, spontaneous ignition temperature has been measured, which is determined from the inflection-point of the temporal variations of the surface temperature. It is found that the spontaneous ignition temperature decreases with increasing aspect ratio, defined as the ratio of the sample height and compact diameter, due to an establishment of the stationary temperature distribution in the radial direction in the compacted mixture, as the sample height becomes tall. It is also found that the spontaneous ignition temperature decreases with increasing size ratio, defined as the ratio of compact and particle diameters, due to an increase in the particle surface per unit spatial volume of the compacted mixture, caused by a decrease in the particle diameter and/or an increase in the compact diameter. By further examining its dependence on mixture ratio and/or degree of dilution, it is confirmed that the limit of flammability also exerts influences on the spontaneous ignition temperature. In addition, a fair degree of agreement, shown in experimental comparisons with theoretical results, indicates that the present formulation has captured the essential features of the spontaneous ignition of compacted mixture. Since this kind of particle size effect, especially, relevant to the spontaneous ignition of compacted mixtures, has not been captured in the previous studies, its elucidation can be considered not only notable but also useful, especially, in manipulating combustion process in materials synthesis. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Effects of fuel and oxidizer particle dimensions on the propagation of aluminum containing thermites

Weismiller, M. R.; Malchi, J. Y.; Lee, J. G.; Yetter, R. A.; Foley, T. J.

PROCEEDINGS OF THE COMBUSTION INSTITUTE, 33, , 1989-1996

Results from combustion experiments, in which the fuel and oxidizer particle sizes of Al/CuO and Al/MoO3 thermites were varied between the nanometer and micrometer scale, are presented to gain further insight into the factors governing their rate of propagation. The experiments were performed with thermite mixtures loosely packed in an instrumented burn tube. Critical properties, including linear propagation rates, dynamic pressure, and spectral emission, were measured and compared to determine if the scale of one constituent had more influence over the rate of propagation than the other. It was found that, although nano-fuel/nano-oxidizer composites propagated the fastest for both the Al/CuO and Al/MoO3 thermites, composites containing micron-aluminum and a nano-scale oxidizer propagated significantly faster than a composite of nano-aluminum and a micron-scale oxidizer. The impact of nano-scale oxidizer versus nano-scale Al is twofold. Firstly, mixtures containing nano-aluminum have a greater mass percentage of Al2O3, which reduces reaction temperatures and propagation rates. Secondly, reactions in porous nano-thermites propagate through a convective mechanism; with heat transfer being driven by flow induced by large pressure gradients. Mixtures containing nano-scale oxidizer particles show faster pressurization rates. Because the majority of gas generation is due to the decomposition or vaporization of the oxide in these reactions, and oxide particles on the nano-scale have shorter heat-up times and smaller length scales for gas diffusion than micron particles, convective burning is greatly enhanced with the nano-scale oxidizer. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Mixture of fuels approach for solution combustion synthesis of nanoscale MgAl2O4 powders

Bai, Jiahai; Liu, Juncheng; Li, Chengfeng; Li, Guochang; Du, Qingyang

ADVANCED POWDER TECHNOLOGY, 22, 1, 72-76

Nanoscale MgAl2O4 powders were synthesized via a microwave-assisted solution combustion process using various mixtures of urea, glycine and starch as fuel. The effects of starch addition on characteristics (e.g. specific surface area and crystallite size) of the as-resulted powders were also investigated. The experimental results revealed that the specific surface area of the powders was significantly increased as the starch content rose from 0 to 35.6 wt.%, followed by a slight decrease when it was further raised to 54.7 wt.%. The scanning electron microscope micrographs disclosed that starch addition also affected the morphology of porous nanoparticles' agglomerates and was remarkably beneficial to dissipate the as-produced nanoparticles. Higher degree of dissipation and larger specific surface area of the powders resulted from starch addition were mainly attributed to a larger amount of gases evolved during combustion and/or lower combustion temperature. (C) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

Combustion-synthesized Ru-Al2O3 composites as anode catalyst layer of a solid oxide fuel cell operating on methane

Wang, Wei; Ran, Ran; Shao, Zongping

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 1, 755-764

Ru-Al2O3 composites with varied Ru contents were synthesized by a glycine nitrate combustion technique. Their potential application as anode catalyst functional layer of a solid oxide fuel cell operating on methane fuel was investigated. Catalytic tests demonstrated the 3-7 wt.% Ru-Al2O3 composites had high catalytic activity for methane partial oxidation and CO2/H2O reforming reactions, while 1 wt.% Ru-Al2O3 had insufficient activity. The 3 wt.% Ru-Al2O3 catalyst also showed excellent operation stability and good thermal mechanical compatibility with Ni-YSZ anode. H-2-TPR and TEM results indicated there was strong interaction between RuOx and Al2O3 in the as-synthesized catalysts, which may account for the good catalytic stability of 3 wt.% Ru-Al2O3 catalyst. O-2-TPO results demonstrated Ru-Al2O3 also had excellent coking resistance. Furthermore, the carbon deposited over Ru-Al2O3 had lower graphitization degree than that deposited over Ni-Al2O3, suggesting the easier elimination of potential carbon deposited over the Ru-Al2O3 catalysts. A cell with 3 wt.% Ru-Al2O3 catalyst functional layer was prepared, wh-ich delivered peak power densities of 1006, 952 and 929 mW cm(-2) at 850 degrees C, operating on methane-O-2, methane-H2O and methane-CO2 gas mixtures, respectively, comparable to that operating on hydrogen fuel. It highly promised 3 wt.% Ru-Al2O3 as a coking resistant catalyst layer for solid oxide fuel cells. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

The combustion processes in Ti-V-Cr-C-H system and synthesis of complex carbohydrides

Aghajanyan, N. N.; Dolukhanyan, S. K.; Ter-Galstyan, O. P.

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 36, 1, 1306-1308

Using the SHS method, the titanium, vanadium and chromium based multicomponent carbohydrides of variable compositions were synthesized. The synthesis of complex carbohydrides with Ti and Cr was conducted in one technological stage: xTi + (1 - x)Cr + yC mixture (0.4 <= x <= 0.8 and 0.4 <= y <= 0.6), was pressed to the tablet and ignited in the argon or hydrogen environment (P = 2 atm). At syntheses of complex carbohydrides including titanium, vanadium, and chromium, the metal/carbon compositions xTi + (1 - x) (V + Cr) + yC (0.6 <= x <= 0.9 and 0.35 <= y <= 0.6), were studied. The X-ray analysis demonstrated that in SHS mode, only carbohydrides with FCC lattice formed. It was demonstrated that at high content of titanium and carbon, monophase products formed. It was shown that at the vanadium insertion into the system, single-phase carbohydrides with FCC structure can be received possessing very low dissociation temperature. The temperatures of DTA decomposition were defined: within 360-530 degrees C in Ti-Cr-C-H system, but within 340-400 degrees C Ti-Cr-V-C-H system. The hydrogen liberation occurred with one endoeffect. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Photocatalytic Inactivation of Escherichia coli with LbL Fabricated Immobilized TiO2 Thin Films

Sontakke, Sharad; Modak, Jayant; Madras, Giridhar

JOURNAL OF ADVANCED OXIDATION TECHNOLOGIES, 14, 1, 86-92

Photocatalysis using semiconductor catalyst such as TiO2, in presence of UV light, is a promising technique for the inactivation of various microorganisms present in water. In the current study, the photocatalytic inactivation of Escherichia coli bacteria was studied with commercial Degussa Aeroxide TiO2 P25 (Aeroxide) and combustion synthesized TiO2 (CS TiO2) catalysts immobilized on glass slides in presence of UV irradiation. Thin films of the catalyst and polyelectrolytes, poly(allyl amine hydrochloride) and poly(styrene sulfonate sodium salt), were deposited on glass slides by layer by layer (LbL) deposition method and characterized by SEM and AFM imaging. The effect of various parameters, namely, catalyst concentration, surface area and number of bilayers, on inactivation was studied. Maximum inactivation of 8-log reduction in the viable count was observed with 1.227 mg/cm(2) of catalyst loaded slides. With this loading, complete inactivation was observed within 90 min and 75 min of irradiation, for Aeroxide and CS TiO2, respectively. Further increase in the catalyst concentration or increasing number of bilayers had no significant effect on inactivation. The effect of surface area on the inactivation was studied by increasing the number of slides and the inactivation was observed to increase with increasing surface area. It was also observed that the immobilized catalyst slides can be used for several cycles leading to an economic process. The study shows potential application of TiO2, for the inactivation of bacteria, in its fixed form by a simple immobilization technique.

Preparation of Nickel Thin Sheets with Nanosized Ferrites by Combustion Synthesis and Electroforming

Choi, Yong; Baik, Nam Ik

JAPANESE JOURNAL OF APPLIED PHYSICS, 50, 1, 01BE14-

Composite nickel sheets with nanosized nickel-zinc ferrite particles were prepared as electromagnetic shielding materials by electroforming in a modified nickel-sulfate bath with nickel-zinc ferrite particles. The nanosized nickel-zinc ferrites were prepared by combustion synthesis and mechanical milling. The combustion temperature and propagation rate were about 1150 degrees C and 8.9 mm/s, respectively. Neutron diffractometry revealed that the final nickel-zinc ferrites formed by combustion synthesis followed by mechanical milling were Ni0.42Zn0.58Fe2O4 with the crystal structure and lattice parameter of Fd3m and 0.84124 nm, respectively. Microstructure observation and chemical analysis by transmission electron microscopy and energy-dispersive spectroscopy respectively showed that nanosized nickel-zinc ferrite particles with a diameter of about 20 nm exist in the thin composite nickel sheet. Maximum magnetization (M-s), residual magnetization (M-r), and coercive force (H-i(c)) were 7.75 Wb/m(2)/kg, 0.88 m(3)/kg, and 1297 A/m, respectively. The complex permeability decreases with an increase in frequency, and its real value (mu(')(r)) has an maximum at about 0.65 GHz. (C) 2011 The Japan Society of Applied Physics

Study of the formation temperature of mixed LaREO3 (RE Dy, Ho, Er, Tm, Yb, Lu) and NdGdO3 oxides

Artini, C.; Costa, G. A.; Masini, R.

JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 103, 1, 17-21

Mixed LaREO3 (RE Dy, Ho, Er, Tm, Yb, Lu) and NdGdO3 oxides were prepared by thermal decomposition of the corresponding co-precipitated mixed oxalates. The decomposition of La/RE and Nd/Gd oxalates was studied by means of differential thermal analysis and thermogravimetric (DTA-TG) measurements; in particular the last step, consisting of the loss of a CO2 molecule from the corresponding oxycarbonate, has been thoroughly investigated, as it is particularly interesting for the study of the formation temperature of mixed rare earth oxides. After the release of CO2, the oxides crystallize in a distorted perovskitic cell or one of the structures typical of rare earth sesquioxides, depending on the cationic size difference and on the average cationic radius. The mixed rare earth oxycarbonate decomposition has been studied in comparison to the decomposition of single rare earth oxycarbonates. A trend of the mixed oxides formation temperature as a function both of the average cationic size and of the cationic sizes difference has been observed and compared to the behaviour of single rare earth oxides.

Energy Transfer Between Ce3+and Eu2+in Doped Sr5(PO4)3F Phosphor

Shinde, K. N.; Nagpure, I. M.; Dhoble, S. J.

SYNTHESIS AND REACTIVITY IN INORGANIC METAL-ORGANIC AND NANO-METAL CHEMISTRY, 41, 1, 107-113

Sr5(PO4)3F phosphor doped with Eu[image omitted] and Ce[image omitted] ion were prepared by combustion synthesis. Under UV excitation (254 nm) Sr5(PO4)3F:Ce exhibits Ce[image omitted] UV emission (355 nm) and under 354 nm, Sr5(PO4)3F:Eu exhibits Eu[image omitted] emission (440 nm). The aim of this article is to report energy transfer mechanism between Ce[image omitted]Eu[image omitted] ion in Sr5(PO4)3F:Ce,Eu phosphors, where Ce ion act as sensitizer and Eu act as activator. Ce emission energy band is in resonance with Eu excitation energy band. Their structures properties and photoluminescence spectra were systemically studied. This article includes synthesis of phosphor, XRD, EDS, SEM pattern of host lattice, photoluminescence behavior, and energy transfer mechanism between the two rare earth ions.

SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS OF SILICON-NITRIDE CERAMIC MIX USING FERRO-SILICON AND ILMENITE

Chukhlomina, L. N.; Vitushkina, O. G.; Vereshchagin, V. I.

GLASS AND CERAMICS, 67, 41556, 277-280

The results of an investigation of the high-temperature nitriding of a mixture of ferro-silicon - ilmenite using a complex method of differential-scanning calorimetry are presented. A ceramic mix with the composition Si(3)N(4)-TiN-Si(2)N(2)O-Fe is obtained by the method of self-propagating high-temperature synthesis using as the raw material dust-like ferro-silicon and ilmenite wastes.

Microstructure and mechanical behavior of nanostructured composite Cu60Fe40 alloy

Fu, Licai; Yang, Jun; Bi, Qinling; Liu, Weimin

PHILOSOPHICAL MAGAZINE LETTERS, 91, 2, 78-85

In this study, bulk nanostructured composite Cu60Fe40 alloy is prepared by a combustion synthesis technique. The prepared Cu60Fe40 alloy consists of Cu(Fe) solid solution and Fe(Cu) solid solution phases. The large-scaled compositional segregation in the Cu-rich and Fe-rich phases is not observed, respectively. A few micron-sized dendrite (Fe(Cu) solid solution) is embedded into the nanostructured matrix (Cu(Fe) solid solution). The grain size of the matrix is in the range 50-300 nm. The yield and fracture strength of the Cu60Fe40 alloy are 540 and 1050 MPa, respectively, and the fracture strain obtained from the compression test is about 20.9%. The Cu60Fe40 alloy displays notable work hardening in the compressive deformation.

Low-temperature synthesis of red-emitting nanostructured La(2)O(2)S(2):Eu(3+) phosphor

Bera, Debasis; Maslov, Sergey; Qian, Lei; Holloway, Paul H.

SOLID STATE COMMUNICATIONS, 151, 2, 164-168

An Eu(3+)-doped red emitting nanostructured La(2)O(2)S(2) phosphor was synthesized using a combustion process at 230 degrees C. The as-synthesized and heat-treated phosphors were characterized by a number of techniques, including scanning electron microscope to determine morphology and composition. The as-synthesized particles were porous with agglomerated particles of similar to 100 nm. X-ray diffraction (XRD) data showed that the crystallite size was 17.5 nm and pattern matched with tetragonal La(2)O(2)S(2). The lattice parameter was slightly smaller and consistent with the formation of La(2-x)Eu(x)O(2)S(2), where x reflects the concentration of Eu (0%-14.4%). The photoluminescence quantum yields of as-synthesized and heat-treated powder phosphors were found to be similar to 0% and 25%, respectively (excitation wavelength of 395 nm). (C) 2010 Elsevier Ltd. All rights reserved.

A sol-gel combustion synthesis method for TiO2 powders with enhanced photocatalytic activity

Chung, Shyan-Lung; Wang, Ching-Mei

JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 57, 1, 76-85

TiO2 photocatalytic powders were synthesized by a sol-gel combustion synthesis method in which urea was used as the fuel and titanyl nitrate was used as the oxidizer. Various fuel-to-oxidizer ratios were studied for their effects on the combustion phenomena and the properties of the synthesized TiO2. The fuel-to-oxidizer ratio was found to determine the maximum combustion temperature, which in turn affects the specific surface area, crystallite size, and weight fraction of anatase phase of the synthesized TiO2. The synthesized TiO2 all contain carbonaceous species and are either pure anatase or anatase-rutile mixed phase in crystalline structure. The photocatalytic activity of the TiO2 was found to correlate to a certain degree with the specific surface area, crystallite size, weight fraction of anatase phase, and visible and IR absorbances. The mixed phase TiO2 shows a higher photocatalytic activity than the pure anatase phase TiO2 when containing a small fraction (similar to 25 wt%) of rutile phase. The synthesized TiO2 all show higher photocatalytic activity than Degussa P25 TiO2. The enhanced photocatalytic activity was attributed mainly to sensitization by the carbonaceous species and larger amounts of hydroxyl group adsorbed on the TiO2 surface.

Wavefront Velocity Oscillations of Carbon-Nanotube-Guided Thermopower Waves: Nanoscale Alternating Current Sources

Abrahamson, Joel T.; Choi, Wonjoon; Schonenbach, Nicole S.; Park, Jungsik; Han, Jae-Hee; Walsh, Michael P.; Kalantar-zadeh, Kourosh; Strano, Michael S.

ACS NANO, 5, 1, 367-375

The nonlinear coupling between exothermic chemical reactions and a nanowire or nanotube with large axial heat conduction results in a self propagating thermal wave guided along the nanoconduct. The resulting reaction wave induces a concomitant thermopower wave of high power density (>7 kW/kg), resulting In an electrical current along the same direction. We develop the theory of such waves and analyze them experimentally, showing that for certain values of the chemical reaction kinetics and thermal parameters, oscillating wavefront velocities are possible. We demonstrate such oscillations experimentally using a cyclotrimethylene-trinitramine/multiwalled carbon nanotube system, which produces frequencies in the range of 400 to 5000 Hz. The propagation velocity oscillations and the frequency dispersion are well-described by Fourier's law with an Arrhenius source term accounting for reaction and a linear heat exchange with the nanotube scaffold.. The frequencies are in agreement with oscillations in the voltage generated by the reaction. These thermopower oscillations may enable new types of nanoscale power and signal processing sources.

Glycine-nitrate synthesis of Sr doped La2Zr2O7 pyrochlore powder

Orlovskaya, N.; Chen, Y.; Miller, N.; Abernathy, H.; Haynes, D.; Tucker, D.; Gemmen, R.

ADVANCES IN APPLIED CERAMICS, 110, 1, 54-57

Materials with A(2)B(2)O(7) (pyrochlore) structure have received significant attention for their applications as new protonic conductors and materials used in electronic devices. One of the unique synthesis routes for La2Zr2O7 (pyrochlore) powders is the glycine-nitrate combustion method, which shows superior properties of the synthesised powder using glycine as a complexing agent. The Sr doped La2Zr2O7 powders in pure pyrochlore structure were produced using this approach. Selected characteristics of the synthesised powders, such as crystal structure, lattice parameters, crystallite size, the vibrational properties, the morphology of the particles, along with the specific surface area and particle size, have been investigated. The dependence of some properties on annealing temperatures of the powders has been studied.

Amyloid Structure: Conformational Diversity and Consequences

Toyama, Brandon H.; Weissman, Jonathan S.

ANNUAL REVIEW OF BIOCHEMISTRY, VOL 80, 80, , 557-585

Many, perhaps most, proteins, are capable of forming self-propagating, beta-sheet (amyloid) aggregates. Amyloid-like aggregates are found in a wide range of diseases and underlie prion-based inheritance. Despite intense interest in amyloids, structural details have only recently begun to be revealed as advances in biophysical approaches, such as hydrogen-deuterium exchange, X-ray crystallography, solid-state nuclear magnetic resonance (SSNMR), and cryoelectron microscopy (cryoEM), have enabled high-resolution insights into their molecular organization. Initial studies found that despite the highly divergent primary structure of different amyloid-forming proteins, amyloids from different sources share many structural similarities. With higher-resolution information, however, it has become clear that, on the molecular level, amyloids comprise a wide diversity of structures. Particularly surprising has been the finding that identical polypeptides can fold into multiple, distinct amyloid conformations and that this structural diversity can lead to distinct heritable prion states or strains.

Chemical redox recovery of giant, small-gap and other fullerenes

Raebiger, James W.; Alford, John M.; Bolskar, Robert D.; Diener, Michael D.

CARBON, 49, 1, 37-46

A simple method for extracting otherwise insoluble fullerenes into organic solvents is presented The fullerenes are reduced to anionic charge states by contact with zinc in the presence of an alkylphosphonium salt in tetrahydrofuran The anionic fullerenes become soluble, and the non-fullerene carbon matrix is separated by filtration The anionic fullerenes can then be precipitated from solution by the action of a chemical oxidant such as iodine It is also shown that there are approximately as many fullerenes left behind in carbon arc soot after solvent extraction as are extracted by the solvent In contrast, more than twice as many fullerenes are left behind in combustion-produced fullerene soot as are solvent extracted Thus, approximately 70% of the total recovered carbon product from large scale combustion synthesis is fullerenes Conversely, no detectable amount of fullerenes can be recovered from conventional carbon blacks under the same conditions Analysis by single photon ionization mass spectrometry suggests that C-60 and Cm account for almost half of the fullerenes that were not solvent-extractable, suggesting that they are readily incorporated into toluene-insoluble fullerene polymers The redox process presented here is easily up scaled, and we routinely recover 100 g of heretofore insoluble fullerenes in 8 h (C) 2010 Elsevier Ltd All rights reserved

Activation energy of tantalum-tungsten oxide thermite reactions

Cervantes, Octavio G.; Kuntz, Joshua D.; Gash, Alexander E.; Munir, Zuhair A.

COMBUSTION AND FLAME, 158, 1, 117-122

The activation energy of a sol-gel (SG) derived tantalum-tungsten oxide thermite composite was determined using the Kissinger isoconversion method. The SG derived powder was consolidated using the high-pressure spark plasma sintering (HPSPS) technique at 300 and 400 degrees C. The ignition temperatures were investigated under high heating rates (500-2000 degrees C min(-1)). Such heating rates were required in order to ignite the thermite composite. Samples consolidated at 300 degrees C exhibit an abrupt change in temperature response prior to the main ignition temperature. This change in temperature response is attributed to the crystallization of the amorphous WO(3) in the SG derived Ta-WO(3) thermite composite and not to a pre-ignition reaction between the constituents. Ignition temperatures for the Ta-WO(3) thermite ranged from approximately 465 to 670 degrees C. The activation energies of the SG derived Ta-WO(3) thermite composite consolidated at 300 and 400 degrees C were determined to be 38 +/- 2 kJ mol(-1) and 57 +/- 2 kJ mol(-1), respectively. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Ignition and Combustion Characteristics of Nanoscale Al/AgIO3: A Potential Energetic Biocidal System

Sullivan, K. T.; Piekiel, N. W.; Chowdhury, S.; Wu, C.; Zachariah, M. R.; Johnson, C. E.

COMBUSTION SCIENCE AND TECHNOLOGY, 183, 3, 285-302

The authors investigated the ignition and reaction of Al/AgIO3 thermites for potential use in biocidal applications. Rapid-heating wire experiments were performed to measure the ignition temperature and investigate the thermal decomposition of the oxidizer using a T-Jump/TOF Mass Spectrometer and an optical emission setup. Combustion experiments inside a constant-volume pressure cell were also carried out, and the relative performance was compared with other thermite systems. The ignition temperature in air at atmospheric pressure was found to be 1215 +/- 40K. The AgIO3 was found to significantly outperform CuO and Fe2O3 oxidizers in pressurization tests, and this is attributed to the enhanced gas release as the AgIO3 thermally decomposes to release iodine in addition to oxygen. The reacted product was collected to investigate the final state of the products. Transmission electron microscopy and X-ray diffraction were performed to show that the major Ag product species was AgI, and not elemental Ag and I2. The AgI was found to be surface exposed to the environment, existing primarily as agglomerated spherical nanoparticles, and was found in some cases to coat the Al2O3 after the reaction.

CoMn2O4 spinel from a MOF: synthesis, structure and magnetic studies

Mahata, Partha; Sarma, Debajit; Madhu, C.; Sundaresen, A.; Natarajan, Srinivasan

DALTON TRANSACTIONS, 40, 9, 1952-1960

A hydrothermal reaction of Mn(OAc)(2)center dot 4H(2)O, Co(OAc)(2)center dot 4H(2)O and 1,2,4 benzenetricarboxylic acid at 220 degrees C for 24 h gives rise to a mixed metal MOF compound, [CoMn2{C6H3(COO)(3)}(2)], I. The structure is formed by the connectivity between octahedral CoO6 and trigonal prism MnO6 units connected through their vertices forming a Kagome layer, which are pillared by the trimellitate. Magnetic susceptibility studies on the MOF compound indicate a canted anti-ferromagnetic behavior, due to the large antisymmetric DM interaction between the M2+ ions (M = Mn, Co). Thermal decomposition studies indicate that the MOF compound forms a tetragonal mixed-metal spinel phase, CoMn2O4, with particle sizes in the nano regime at 400 degrees C. The particle size of the CoMn2O4 can be controlled by varying the decomposition temperature of the parent MOF compound. Magnetic studies of the CoMn2O4 compound suggests that the coercivity and the ferrimagnetic ordering temperatures are dependent on the particle size.

Novel borothermal process for the synthesis of nanocrystalline oxides and borides of niobium

Jha, Menaka; Ramanujachary, Kandalam V.; Lofland, Samuel E.; Gupta, Govind; Ganguli, Ashok K.

DALTON TRANSACTIONS, 40, 31, 7879-7888

A new process has been developed for the synthesis of nanocrystalline niobium oxide and niobium diboride using an amorphous niobium precursor obtained via the solvothermal route. On varying the ratio of niobium precursor to boron and the reaction conditions, pure phases of nanostructured niobium oxides (Nb(2)O(5), NbO(2)), niobium diboride (NbB(2)) and core-shell nanostructures of NbB(2)@Nb(2)O(5) could be obtained at normal pressure and low temperature of 1300 degrees C compared to a temperature of 1650 degrees C normally used. The above borothermal process involves the in situ generation of B(2)O(2) to yield either oxide or diboride. The niobium oxides and borides have been characterized in detail by XRD, HRTEM and EDX studies. The core-shell structure has been investigated by XPS depth profiling, EFTEM and EELS (especially to characterize the presence of boron and the shell thickness). The niobium diboride nanorods (with high aspect ratio) show a superconducting transition with the T(c) of 6.4 K. In the core-shell of NbB(2)@Nb(2)O(5), the superconductivity of NbB(2) is masked by the niobium oxide shell and hence no superconductivity was observed. The above methodology has the benefits of realizing both oxides and borides of niobium in nanocrystalline form, in high purity and at much lower temperatures.

Evaluation of the interaction between calcifying nanoparticles and human dental pulp cells: a preliminary investigation

Yang, Fang; Zeng, Jinfeng; Zhang, Wei; Sun, Xi; Ling, Junqi

INTERNATIONAL JOURNAL OF NANOMEDICINE, 6, , 13-18

Calcifying nanoparticles (CNPs, previously called nanobacteria) are self-propagating, cultivable macromolecular complexes. Their extraordinary characteristic is that they can aggregate carbonate apatite on their envelope from soluble calcium and phosphorus at physiologic concentrations and display cytotoxic effects on murine and human fibroblast cell lines. The question arises whether CNPs contribute to the degeneration of pulp tissue and thus result in clinically significant human dental pulp stones as nidies. This study evaluates CNPs' effects upon human dental pulp cells (HDPCs, the host cells in pulp tissue). We observed the ultrastructural variation of HDPCs attacked by CNPs. The spatial relationship of HDPCs and CNPs after coculture was also identified by immunofluroscence staining. Furthermore, it was verified by MTT viability assay that CNPs isolated from dental pulp stones exerted cytotoxic effect on HDPCs. Therefore, it could be concluded that the existence of CNPs might interfere with the normal physiologic function of the cells, and that might lead to dental pulp calcification. Elucidation of the cytotoxic characteristics of CNPs may offer a new perspective for understanding the etiology of human dental pulp stones.

Effect of mechanical activation on the production of SiC from silica sand

Raygan, Sh; Kondori, B.; Yangijeh, H. M.

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 1, 10-13

In this study the effect of 100 and 200 h low energy ball milling on the carbothermic reduction of SiO(2) and C powder mixture was investigated Microstructure studies of the mixture by SEM revealed that the particle size had been decreased and the SiO(2) particles had been covered by C particles due to the milling The results of thermal analysis (TG-DTA) of milled and unmilled mixtures clearly showed that the reduction temperature decreased due to milling process XRD pattern of 200 h activated mixture proved that beta SiC had been formed almost completely after reduction at 1500 C (C) 2010 Elsevier Ltd All rights reserved

Production of tungsten boride from CaWO4 by self-propagating high-temperature synthesis followed by HCl leaching

Yazici, Sertac; Derin, Bora

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS, 29, 1, 90-95

In this study the conditions of producing tungsten boride powder from calcium tungstate (CaWO4) by self-propagating high-temperature synthesis (SHS) followed by HCl leaching techniques were investigated In the first stage of the experimental study the SHS products consisting of borides and other compounds were obtained starting with different initial molar ratios of CaWO4 Mg and B2O3 It was found that increasing B2O3 content in the initial mixture resulted in an increase of W2B5/WB ratio along with MG(3)B(2)O(6) in the SHS product In the second step Mg and Ca containing byproducts (i e MgO Mg3B2O6 and Ca3B2O6) found in this SHS product were leached out by using aqueous HCl solution to obtain a clean tungsten boride product The effects of particle size temperature time acid concentration and solid/liquid ratio were selected as leaching parameters The acid leaching experiments of the SHS product synthesized at 1 8 2 5 initial molar ratio of CaWO4 Mg B2O3 showed that optimum leaching conditions could be achieved by using 2 85 M HCl at 1/10/S/L ratio and the temperature of 80 C for 60 min (C) 2010 Elsevier Ltd All rights reserved

Solution Combustion Synthesis of BiVO4 Nanoparticles: Effect of Combustion Precursors on the Photocatalytic Activity

Timmaji, H. K.; Chanmanee, W.; de Tacconi, N. R.; Rajeshwar, K.

JOURNAL OF ADVANCED OXIDATION TECHNOLOGIES, 14, 1, 93-105

This paper describes the solution combustion synthesis, solid-state characterization, photoelectrochemical behavior, and photocatalytic properties of bismuth vanadate (BiVO4). In particular, the influence of combustion precursor was addressed in this study. Bismuth nitrate pentahydrate was used as the bismuth precursor and either vanadium chloride or vanadium oxysulfate was used as the vanadium precursor. Urea, glycine, or citric acid was used as the fuel. Stoichiometric mixtures (1: 1) of the fuels and oxidants (with the Bi:V mole ratio also maintained at 1: 1) were subjected to solution combustion synthesis. The resultant samples were characterized by X-ray diffraction, high-resolution transmission electron microscopy, diffuse reflectance spectrophotometry, thermal analyses, and laser Raman spectroscopy. Methyl orange was used as a probe to test the photocatalytic attributes of the combustion-synthesized (CS) samples, and benchmarked against a commercial bismuth vanadate sample. The CS samples were superior to the commercial benchmark sample, and samples derived from vanadium chloride were superior to vanadium oxysulfate counterparts. The photoelectrochemical properties of the various CS samples were also studied and these samples were shown to be useful both for environmental photocatalytic remediation and water photooxidation applications.

Characterization of self-propagating formation reactions in Ni/Zr multilayered foils using reaction heats, velocities, and temperature-time profiles

Barron, S. C.; Knepper, R.; Walker, N.; Weihs, T. P.

JOURNAL OF APPLIED PHYSICS, 109, 1, 13519-

We report on intermetallic formation reactions in vapor-deposited multilayered foils of Ni/Zr with 70 nm bilayers and overall atomic ratios of Ni:Zr, 2 Ni:Zr, and 7 Ni:2 Zr. The sequence of alloy phase formation and the stored energy is evaluated at slow heating rates (similar to 1 K/s) using differential scanning calorimetry traces to 725 degrees C. All three chemistries initially form a Ni-Zr amorphous phase which crystallizes first to the intermetallic NiZr. The heat of reaction to the final phase is 34-36 kJ/mol atom for all chemistries. Intermetallic formation reactions are also studied at rapid heating rates (greater than 10(5) K/s) in high temperature, self-propagating reactions which can be ignited in these foils by an electric spark. We find that reaction velocities and maximum reaction temperatures (T-max) are largely independent of foil chemistry at 0.6 +/- 0.1 m/s and 1220 +/- 50 K, respectively, and that the measured T-max is more than 200 K lower than predicted adiabatic temperatures (T-ad). The difference between T-max and T-ad is explained by the prediction that transformation to the final intermetallic phases occurs after T-max and results in the release of 20%-30% of the total heat of reaction and a delay in rapid cooling. (C) 2011 American Institute of Physics. [doi:10.1063/1.3527925]

Synthesis, Characterization, Luminescence and Defect Centres in CaYAl3O7:Eu3+ Red Phosphor

Singh, Vijay; Watanabe, S.; Rao, T. K. Gundu; Kwak, Ho-Young

JOURNAL OF FLUORESCENCE, 21, 1, 313-320

CaYAl3O7:Eu3+ phosphor was prepared at furnace temperatures as low as 550A degrees C by a solution combustion method. The formation of crystalline CaYAl3O7:Eu3+ was confirmed by powder X-Ray diffraction pattern. The prepared phosphor was characterized by SEM, FT-IR and photoluminescence techniques. Photoluminescence measurements indicated that emission spectrum is dominated by the red peak located at 618 nm due to the D-5(0)-F-7(2) electric dipole transition of Eu3+ ions. Electron Spin Resonance (ESR) studies were carried out to identify the centres responsible for the thermoluminescence (TL) peaks. Room temperature ESR spectrum of irradiated phosphor appears to be a superposition of two distinct centres. One of the centres (centre I) with principal g-value 2.0126 is identified as an O- ion while centre II with an isotropic g-factor 2.0060 is assigned to an F+ centre (singly ionized oxygen vacancy). An additional defect centre is observed during thermal annealing experiments and this centre (assigned to F+ centre) seems to originate from an F centre (oxygen vacancy with two electrons). The F+ centre appears to correlate with the observed high temperature TL peak in CaYAl3O7:Eu3+ phosphor.

An analysis of Y2O3 center dot Eu3+ thin films for thermographic phosphor applications

Bosze, Eric J.; Hirata, Gustavo A.; McKittrick, Joanna

JOURNAL OF LUMINESCENCE, 131, 1, 41-48

A comparative study of the luminescent properties of Y2O3 Eu3+ phosphor powders and thin films sputtered from targets prepared from combustion synthesized powders is reported Thin films of (Yo(96)Eu(0 04))(2)O-3 were deposited on silicon substrates Films deposited at 600 degrees C had both monoclinic and cubic phases of Y2O3 which developed to an oriented cubic phase after annealing Films and powders showed a linear dependence of the intensity of the 5D(7)-> F-7(2) (611 nm) transition with temperature in the range 26-660 degrees C with an average rate of change of 18 x 10(-4) degrees C-1 The rate of change appears to be dependent on the Eu3+ concentration This work shows that these thin films can be used as thermographic phosphors for remote temperature measurements (c) 2010 Elsevier B V All rights reserved

Porosity driven photocatalytic activity of wormhole mesoporous TiO2-xNx in direct sunlight

Sivaranjani, Kumarsrinivasan; Gopinath, Chinnakonda S.

JOURNAL OF MATERIALS CHEMISTRY, 21, 8, 2639-2647

Results obtained by combining four important factors simultaneously, namely, wormhole mesoporosity with low diffusion length for charge carriers, high surface area, nanoparticles with high crystallinity, and visible light absorption due to N-doping, in titania (meso-TiO2-xNx) are reported. Meso-TiO2-xNx materials have been prepared by a combustion method within 10 min and by varying urea : Ti(NO3)(4) between 1 (UT1) and 10 (UT10). All of the prepared materials have been thoroughly characterised. Nanocrystalline anatase phase with high surface area (234 m(2) g(-1)), and type-IV H-3-mesoporosity is observed with UT10. Photocatalytic rhodamine-B degradation was employed to screen for the activity of the materials, and p-anisyl alcohol oxidation to p-anisaldehyde was carried out successfully in aqueous solution under direct sunlight. High photocatalytic activity of UT10 in direct sunlight, in spite of high band gap (3.24 eV), is attributed to the better utilization of holes due to the low charge diffusion barrier associated with wormhole mesoporosity along with highly crystalline, however, nanoparticulate TiO2-xNx.

Chemically modified graphene: flame retardant or fuel for combustion?

Shi, Yumeng; Li, Lain-Jong

JOURNAL OF MATERIALS CHEMISTRY, 21, 10, 3277-3279

Graphene oxide (GO), an oxidized form of graphene, has attracted lots of attention due to its solution processability and chemical reactivity from its functional groups. GO is known as a promising flame retarding nano-additive in polymers. Interestingly, a local hot spot can trigger a rapid and self-propagating reaction to convert GO into a more stable form, reduced-GO (r-GO). However, the presence of potassium salt impurities causes catastrophic reduction (carbon combustion) of GO (r-GO) once these chemically modified graphene materials are triggered by a hot spot. The self-propagating reduction from GO solids is due to its highly energetic nature, suggesting that caution needs to be adopted against a possible fire hazard.

Manganite perovskite nanoparticles for self-controlled magnetic fluid hyperthermia: about the suitability of an aqueous combustion synthesis route

Epherre, Romain; Duguet, Etienne; Mornet, Stephane; Pollert, Emil; Louguet, Stephanie; Lecommandoux, Sebastien; Schatz, Christophe; Goglio, Graziella

JOURNAL OF MATERIALS CHEMISTRY, 21, 12, 4393-4401

Unaggregated La0.82Sr0.18MnO3+delta perovskite nanoparticles with a mean crystallite size of 22 nm were successfully synthesized through an aqueous combustion process (Glycine Nitrate Process, GNP) which takes advantage of exothermic, fast and self-sustaining chemical reactions between metal nitrates and glycine as a suitable organic reducing agent. The influence of G/N molar ratio on the phase purity, crystallite size and manganese valency was screened. Fuel-rich conditions were selected to improve chelation of the cations in acidic pH and ensure an accurate control of the cationic composition. Fast calcination was optimized to enhance crystallinity of the nanoparticles and subsequent milling step was performed to favour their desaggregation. The manganite nanoparticles were thoroughly characterized by X-ray diffraction (XRD), elemental chemical analysis, Mohr salt titration and transmission electron microscopy (TEM). According to a process derived from the Stober's method, they were uniformly coated with a 5 nm thick silica shell, as evidenced by TEM, infrared spectroscopy, zeta potential measurements and dynamic light scattering experiments. Preliminary heating experiments in a ac magnetic field showed these core@shell nanoparticles fulfill the requirements for self-controlled magnetic fluid hyperthermia, considering their size (20-70 nm) and their maximum heating temperature (43 degrees C) which is controlled by the Curie temperature of the magnetic cores.

Nanoenergetic Gas-Generators: principles and applications

Martirosyan, Karen S.

JOURNAL OF MATERIALS CHEMISTRY, 21, 26, 9400-9405

Metastable Intermolecular Composites or so-called Nanoenergetic Materials have been widely touted for their potential to fulfill dreams in high density energetic materials and nanotechnology. They are likely to become the next-generation explosives, propellants and primes as they enable flexibility in energy density and power release through control of particle size, tunable stoichiometry and choice of fuel and oxidizer. Despite intense examination by scientists and engineers worldwide the temperature progress and velocity of the thermal front propagation on the nanostructured formulations, however, gas pressure evolution and rate of gas release are not well investigated and understood. This issue has seriously impeded realization of various potential emerging applications envisioned in rocket solid fuels and explosives, which require a high pressure discharge in a short period of time as well as in bio-defeat systems. This highlight describes principles and development of Nanoenergetic Gas-Generators (NGG) systems comprising high PV (pressure x volume) values and energy densities (up to 25.7 kJ cm(-3)) that may have several potential civil and military applications. Our recent study revealed that Al/Bi(2)O(3) and Al/I(2)O(5) nanocomposites can generate a transient pressure pulse more than three times larger than that during the explosion of traditional thermite reactive mixtures.

Combustion Synthesis of Large Bulk Nanostructured Ni65Al21Cr14 Alloy

Ma, Jiqiang; Yang, Jun; Bi, Qinling; Fu, Licai; Kang, Yonghai; Liu, Weimin

JOURNAL OF NANOMATERIALS, , , 934801-

A large bulk nanostructured Ni65Al21Cr14 alloy with dimensions of Phi 100 mm x 6 mm was produced by combustion synthesis technique followed with rapid solidification. The Ni65Al21Cr14 alloy was composed of gamma'-Ni3Al/gamma-Ni(Al, Cr) eutectic matrix and gamma-Ni(Al, Cr) dendrite. The eutectic matrix consisted of 80-150 nm cuboidal. gamma'-Ni3Al and 2-5 nm gamma-Ni(Al, Cr) boundary. The dentrite was comprised of high-density growth twins with about 3-20 nm in width. The nanostructured Ni65Al21Cr14 alloy exhibited simultaneously high fracture strength of 2200 MPa and good ductility of 26% in compression test.

Effect of Copper Oxide on the Structure of Nano-Sized Ni(x)Zn(y)Fce(2)O(4) Powders Prepared by Using Self-Propagating High Temperature Synthesis

Lee, Sang-Heon; Choi, Yong; Pirogov, Alexander

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 11, 1, 829-832

Nano-sized CuxNixZn1-x-yFe2O4 ferrites were prepared by using self-propagating high-temperature synthesis (SHS) and mechanical ball milling. As oxygen pressure increases and copper content decreases in the initial composition, average combustion temperature and combustion velocity increases in the ranges of 947 to 1150 degrees C and 4.2 to 6.5 mm/sec, respectively. The SHS products were agglomerated crystalline powders in which fine particles were present. The average particle of the pulverized SHS product was about 200 nm. Lattice parameters determined by neutron diffractometry are 8.4125 angstrom for Ni0.38Zn0.62Fe2O4 and a = 8.3540 angstrom for Cu0.29Ni0.28Zn0.43Fe2O4.

CuO-CeO2/Al2O3/FeCrAl monolithic catalysts prepared by in situ combustion synthesis method for preferential oxidation of carbon monoxide

Zeng Shanghong; Su Haiquan; Liu Yuan; Wang Yan; Wang Dongfang

JOURNAL OF RARE EARTHS, 29, 1, 69-73

This work described in situ combustion synthesis method for depositing CuO-CeO2 on the FeCrAl honeycomb supports. The influence of the solution concentration and the role of the additive were studied and analyzed by scanning electron microscopy (SEM), X-ray diffractometer (XRD), and temperature programmed reduction (TPR) techniques. The results showed that 200 g/L of the active solution was the most appropriate concentration for preparing the monolithic catalysts, and the additives of praseodymium and lanthanum improved the adhesion stability of the monolithic catalysts. The addition of Pr did not greatly affect the catalytic performance, but CO could not be totally converted into CO2 after the addition of La into the CuO-CeO2/Al2O3/FeCrAl catalysts.

A Comparative Study of Electrochemical Capacitive Behavior of NiFe2O4 Synthesized by Different Routes

Anwar, Shahid; Muthu, K. Sudalai; Ganesh, V.; Lakshminarasimhan, N.

JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 158, 8, A976-A981

The electrochemical capacitive behavior of NiFe2O4 ceramic powders prepared by combustion synthesis, polyol-mediated and sol-gel methods was studied. The phase formation and morphological characterizations of synthesized materials were carried out through thermal analysis (TG-DTA), powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrochemical performance of these electrode materials as capacitors was investigated in aqueous NaCl electrolyte using cyclic voltammetry (CV) and the corresponding specific capacitance (SC) values were determined. The observed electrochemical double layer capacitive (EDLC) behavior in NiFe2O4 depends on the morphology which can be controlled by the synthesis method adopted. NiFe2O4 synthesized by sol-gel method exhibited a specific capacitance of 97.5 F/g which is higher than the capacitance values of NiFe2O4 obtained through other synthesis methods. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3601863] All rights reserved.

Cation order enhancement in Sr2FeMoO6 by water-saturated hydrogen reduction

Calleja, Alberto; Capdevila, Xavier G.; Segarra, Merce; Frontera, Carles; Espiell, Ferran

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 31, 41306, 121-127

Sr2FeMoO6 (SFMO) double perovskite has been prepared from powders obtained by the polyacrylamide gel combustion synthesis After removing organic residues the precursor powder consists of a homogeneous submicronic blend of SrFeO3-x and SrMoO4 In order to crystallize SFMO an experimental setup consisting of injecting water-saturated Ar/5%H-2 gas flow in a crucible was used Results show that a high saturation magnetization of 3 9 mu(B)/formula unit, which accounts for 98% of the theoretical value, and Curie temperature of 415 K can be achieved in this way The Fe/Mo order was 98% by Rietveld refinement of best sample Furthermore no metallic iron was detected, even at long reducing treatments Lowering the reducing power of hydrogen with water is believed to be the main reason for improved synthesis (C) 2010 Elsevier Ltd All rights reserved

Combustion synthesis of LaSi3N5 Eu2+ phosphor powders

Zhou, You; Yoshizawa, Yu-ichi; Hirao, Kiyoshi; Lences, Zoltan; Sajgalik, Pavol

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 31, 41306, 151-157

LaSi3N5 Eu2+ phosphor powders were prepared by a highly efficient combustion synthesis method It was found that the compositions of the raw powder mixtures had great influences on the phase compositions and particle morphologies of the synthesized powders By selecting appropriate starting compositions and combustion parameters, single phase LaSi3N5 Eu2+ phosphors could be synthesized When excited by a UV light the LaSi3N5 Eu2+ phosphors emitted green light The wavelength and intensity of the emission spectra were affected by the amount of Eu2+ dopant With increasing amount of Eu2+ dopant, concentration quenching could occur and emission spectra shifted to longer wavelengths (C) 2010 Elsevier Ltd All rights reserved

The Influence of Oleic Acid to Metal Nitrate Ratio on the Particle Size and Magnetic Properties of Lanthanum Ferrite Nanoparticles by Emulsion Method

Chandradass, Jeyaseelan; Bae, Dong Sik; Balasubramanian, M.; Kim, Ki Hyeon

MATERIALS AND MANUFACTURING PROCESSES, 26, 2, 230-235

LaFeO3 nanoparticles of different sizes are prepared by varying the molar concentration of oleic acid to metal nitrate using emulsion combustion method. X-ray diffraction analysis confirms that LaFeO3 nanoparticles are crystalline in nature with an orthorhombic structure. The average particle size and saturation magnetization decreases from 56 to 32nm and 0.20 to 0.08emu/g, as molar concentration of oleic acid to metal nitrate increases from 0.25 to 1. The Fourier transform infrared (FTIR) spectra show the lower frequency bands are assigned to Fe-O stretching vibration (579cm-1) and O-Fe-O deformation vibration (475 and 400cm-1). The experimental results suggest that molar concentration of oleic acid to metal nitrate plays an important role in the particle size and magnetic property of combustion synthesized lanthanum ferrite nanoparticles.

Microstructure and Properties of TiC/Ni3Al Composites Prepared by Pressureless Melt Infiltration with Porous TiC/Ni3Al Preforms

He, Bo-Lin; Zhu, Yue-Feng

MATERIALS AND MANUFACTURING PROCESSES, 26, 4, 586-591

In this article, porous TiC/Ni3Al preforms were fabricated by self-propagating high-temperature combustion synthesis (SHCS). Then, the porous TiC/Ni3Al preforms were densified with infiltrated Ni3Al melt via the conventional pressureless infiltration, and TiC/Ni3Al composites were prepared. The composites were characterized by microstructure observation and mechanical property measurements. The results demonstrate that the wetting ability of liquid Ni3Al to porous TiC/Ni3Al preforms is better than that of liquid Ni3Al to TiC preforms. The porous TiC/Ni3Al preforms can be completely infiltrated by Ni3Al melt via pressureless infiltration technique, and then densified TiC/Ni3Al composites without defects can be obtained. During the infiltration process, both Ni3Al and TiC/Ni3Al preforms were thermally and chemically stable, and the infiltration resulted in no new phases. Comparing the similar composites prepared with TiC preforms infiltrated by melt Ni3Al via pressureless infiltration, bending strength of the TiC/Ni3Al composites of this work was much improved with higher reliability. The interfaces between TiC particles and the intermetallic compound Ni3Al were the main points of failure in the composites. Strengthening mechanism of the TiC/Ni3Al composites consisted of mainly pullout of TiC particles from the matrix and crack deflection surrounding Ni3Al particles.

Effect of Titanium-Aluminum Ratio on the Thermal Explosion Processing of TiAl-TiB0.6 Layered Composites

Kecskes, Laszlo; Butler, Brady; Oniashvili, George; Aslamazishvili, Zurab; Zakharov, Garegin; Peikrishvili, Akaki

MATERIALS AND MANUFACTURING PROCESSES, 26, 9, 1157-1163

Bi- and trilayer composites of titanium aluminides (Ti-Al) and substoichiometric titanium boride (TiB0.6) have been fabricated from green compacts placed under pressure. Ti-Al blends with ratios of 3:1, 1:1, or 1:3 have been prepared by ball milling. Subsequent to the preparation of the precursor blends, plate-shaped green compacts of Ti-Al and Ti-B-0.6 were pressed at room temperature. Green compacts were stacked in a layered geometry and were heated rapidly under a static pressure of about 10 bar. After the temperature reached 1300-1400 degrees C, the Ti-Al and TiB0.6 phases were synthesized by the conversion of the reactants into the product phases (also known as "thermal explosion" processing) and simultaneously consolidated and joined under a pressure of 80-100 bar.Scanning electron microscopy (SEM) examination showed that the Ti-Al layer was highly heterogeneous, and the extent of heterogeneity depended strongly on the respective elemental ratio of Ti to Al. Furthermore, the conversion from reactants to products was found to be determined by the overall heat available during the thermal explosion processing step. Unlike the Ti-Al, the TiB0.6 layer was more uniform; however, the combination of heat and pressure was found to be insufficient to fully densify the aluminide layer. These and other features of the layered intermetallic structures will be discussed.

Synthesis of Al2O3-(Co, Ni) Cermets via Thermal Explosion Method

Lu, Tao; Pan, Ye

MATERIALS AND MANUFACTURING PROCESSES, 26, 10, 1288-1292

Al2O3-(Co, Ni) cermets with different Co-Ni ratios in metal phases were successfully prepared by combustion synthesis in thermal explosion mode. The reaction process, microstructure, and magnetic properties of synthesized cermets were investigated. With a small uniaxial loading of similar to 1.28 MPa applying at the time of ignition, the dense cermets with relative density of 90%similar to 96.5% can be achieved. The microstructure was characterized by Co-Ni alloys with average particle size of less than 10 mu m dispersing homogeneously in the matrix. The transition phase of (Co, Ni)Al2O4 spinel is partly preserved in the Al2O3 matrix due to the rapid reaction process. The top saturation magnetization of synthesized ferromagnetic cermets is about 29 emu/g and the coercive force depends on the microstructure of cermets.

Ion dynamics in combustion synthesized Na3Cr2(PO4)(3) crystallites

Vijayan, Lakshmi; Cheruku, Rajesh; Govindaraj, G.; Rajagopan, S.

MATERIALS CHEMISTRY AND PHYSICS, 125, 41306, 184-190

Phase pure Na3Cr2(PO4)(3) crystallites of 41 nm are synthesized by novel solution combustion technique. Characterization methods like X-ray diffraction, Fourier transform infrared spectroscopy, UV-vis spectroscopy, Thermo gravimetric, differential thermal analysis and scanning electron microscopy with energy dispersive X-ray analysis are utilized to validate the structure and phase purity. These crystallites are stable in room temperature rhombohedral phase of R (3) over barc symmetry. Fascination of the material is because of its structural stability and high conductivity. Due to its structural stability, present study depicts the ion dynamics in the crystal lattice by analyzing the conductivity relaxation process. Interpretations from impedance representation fortify these conclusions and the dc conductivity activation energy is found to be 0.70 +/- 0.02 eV. Almost same value of activation energy for conductivity relaxation from modulus and conductivity representations show that while conducting and relaxing, ion has to overcome the same energy barrier. The conductivity and modulus isotherms are shown to be collapsed to a master curve upon appropriate scaling of the axes: indicating the temperature independent relaxation mechanism. It is evident that the scaling of conductivity and modulus spectra provides the same information on ion dynamics of this material. (C) 2010 Elsevier B.V. All rights reserved.

Isothermal oxidation behavior of reactive hot-pressed TiN-TiB2 ceramics at elevated temperatures

Yang, Zhen-Lin; Ouyang, Jia-Hu; Liu, Zhan-Guo

MATERIALS & DESIGN, 32, 1, 29-35

Isothermal oxidation behavior of reactive hot-pressed TiN-TiB2 ceramics with various TiN/TiB2 molar ratios of 2/1, 1/1 and 1/2 was evaluated in the temperature range of 500-800 degrees C in air. TiN-TiB2 ceramics have a relative density of 97-98.6%. The oxidation weight gains of TiN-TiB2 ceramics depend upon the composition, oxidation temperature and exposure time. The structure and morphology of oxidized layers of TiN-TiB2 ceramics were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). During isothermal oxidation of TiN-TiB2 ceramics, anatase and rutile-TiO2 form as the oxidized products at 500 degrees C. However, phase transformation from anatase to rutile occurs at temperatures between 500 and 600 degrees C, and therefore rutile-TiO2 becomes the only crystalline phase after oxidation at temperatures of 600-800 degrees C for 10 h. The oxidation mechanism was proposed with reference to thermodynamically feasible oxidation reactions. The influence of composition on oxidation behavior of TiN-TiB2 ceramics varies with temperature. (C) 2010 Elsevier Ltd. All rights reserved.

A novel red emitting phosphor CaIn2O4:Eu3+, Sm3+ with a broadened near-ultraviolet absorption band for solid-state lighting

Yan, Xiaosong; Li, Wanwan; Sun, Kang

MATERIALS RESEARCH BULLETIN, 46, 1, 87-91

Red phosphor of CaIn2O4:Eu3+, Sm3+ is synthesized by solid state reaction. The D-5(0) -> F-7(2) transition of Eu3+ is dominantly observed in the photoluminescence spectrum, leading to a red emission of the phosphor. The doped Sm3+ is found to be efficient to sensitize the emission of Eu3+ and be effective to extend and strengthen the absorption of near-UV light with wavelength of 400-405 nm, and the energy transfer from Sm3+ to Eu3+ occurs and is discussed. The effect of the molar concentration of Sm3+ on the emission intensities of the phosphor CaIn2O4:Eu3+, Sm3+ is investigated. The temperature quenching effect is also measured from room temperature to 425 K, and the emission intensity of the phosphor at 425 K shows about 85% of that at room temperature. Furthermore, the chromaticity coordinates, the emission intensities and the conversion efficiencies of CaIn2O4:Eu3+, Sm3+ are compared to those of the conventional red phosphor of Y2O2S:Eu3+. (C) 2010 Elsevier Ltd. All rights reserved.

An investigation of the SCOZA for narrow square-well potentials and in the sticky limit

Pini, D.; Parola, A.; Colombo, J.; Reatto, L.

MOLECULAR PHYSICS, 109, 41554, 1343-1361

We present a study of the self-consistent Ornstein-Zernike approximation (SCOZA) for square-well (SW) potentials of narrow width . The main purpose of this investigation is to elucidate whether, in the limit 0, the SCOZA predicts a finite value for the second virial coefficient at the critical temperature B2(Tc), and whether this theory can lead to an improvement of the approximate Percus-Yevick solution of the sticky hard-sphere (SHS) model due to Baxter [J. Chem. Phys. 49, 2770 (1968)]. For the SW of non-vanishing , the difficulties due to the influence of the boundary condition at high density, already encountered in an earlier investigation by Scholl-Paschinger et al. [J. Chem. Phys. 123, 234513 (2005)], prevented us from obtaining reliable results for 0.1. In the sticky limit, this difficulty can be circumvented, but then the SCOZA fails to predict a liquid-vapor transition. The picture that emerges from this study is that, for 0, the SCOZA does not fulfill the expected prediction of a constant B2(Tc) [J. Chem. Phys. 113, 2941 (2000)], and that, for thermodynamic consistency to be usefully exploited in this regime, one should probably go beyond the Ornstein-Zernike ansatz.

BAYESIAN INFERENCE OF ATOMIC DIFFUSIVITY IN A BINARY NI/AL SYSTEM BASED ON MOLECULAR DYNAMICS

Rizzi, F.; Salloum, M.; Marzouk, Y. M.; Xu, R. -G.; Falk, M. L.; Weihs, T. P.; Fritz, G.; Knio, O. M.

MULTISCALE MODELING & SIMULATION, 9, 1, 486-512

This work focuses on characterizing the integral features of atomic diffusion in Ni/Al nanolaminates based on molecular dynamics (MD) computations. Attention is focused on the simplified problem of extracting the diffusivity, D, in an isothermal system at high temperature. To this end, a mixing measure theory is developed that relies on analyzing the moments of the cumulative distribution functions (CDFs) of the constituents. The mixing measures obtained from replica simulations are exploited in a Bayesian inference framework, based on contrasting these measures with corresponding moments of a dimensionless concentration evolving according to a Fickian process. The noise inherent in the MD simulations is described as a Gaussian process, and this hypothesis is verified both a priori and using a posterior predictive check. Computed values of D for an initially unmixed system rapidly heated to 1500 K are found to be consistent with experimental correlation for diffusion of Ni into molten Al. On the contrary, large discrepancies with experimental predictions are observed when D is estimated based on large-time mean-square displacement (MSD) analysis, and when it is evaluated using the Arrhenius correlation calibrated against experimental measurements of self-propagating front velocities. Implications are finally drawn regarding extension of the present work and potential refinement of continuum modeling approaches.

Synthesis and ignition of energetic CuO/Al core/shell nanowires

Ohkura, Yuma; Liu, Shih-Yu; Rao, Pratap M.; Zheng, Xiaolin

PROCEEDINGS OF THE COMBUSTION INSTITUTE, 33, , 1909-1915

Energetic thermites (mixtures of Al and metal oxides), due to their high energy densities, have broad applications in propulsion, thermal batteries, waste disposal, and power generation for micro systems. Reducing the sizes of Al and metal oxides down to the nanoscale has been shown to be effective in increasing their reaction rates and reducing their ignition delays. However, it remains a challenge to create mixtures of Al and metal oxides with nanoscale uniformity. Here we report synthesis and ignition studies on thermites with a new nanostructure, i.e., CuO/Al core/shell nanowires (NWs). The CuO NW cores were synthesized by the thermal annealing of copper films and served as templates for the deposition of Al shells by subsequent sputtering. The advantage of such a core/shell NW structure is that CuO and Al are uniformly mixed at the nanoscale. The onset temperatures of the exothermic reaction of the core/shell NWs were similar to those of nanoparticle (NP)-based thermites in terms of magnitude, insensitivity to equivalence ratios and sensitivity to heating rates. Moreover, the core/shell NW thermites, compared to NP-based thermites, exhibit greatly improved mixing uniformity and reduced activation energy for the thermite reaction. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Preparation and Dielectric Spectroscopy Characterization of A(2)MnMoO(6) (A = Ca, Sr and Ba) Double Perovskites

Perianu, Elena-Adriana; Gorodea, Ioana Aurelia; Gheorghiu, Felicia; Sandu, Andrei Victor; Ianculescu, Adelina Carmen; Sandu, Ion; Iordan, Alexandra Raluca; Palamaru, Mircea Nicolae

REVISTA DE CHIMIE, 62, 1, 17-20

The aim of this work is to study the behavior of the perovskite-type complex oxides A(2)MnMoO(6) obtained by the citrate combustion synthesis method. We have prepared our samples of nanosized perovskite-type complex oxides A(2)MnMoO(6) (A = Ca, Sr and Ba) by citrate combustion method. The starting materials were CaCO3, SrCO3, BaCO3 (treated with HNO3 to form active nitrates) (NH4)(6)Mo7O24 center dot 4H(2)O, Mn powder and citric. acid in stoichiometric ratio. The precursors were presintered and sintered at different temperatures. The obtained powders were firstly characterised by infrared spectro photometry. The infrared spectra have revealed several novel aspects of the structure. The position of bands indicates that all nanosized materials are polymetalic oxides exhibiting perovskite-type structure. The complex impedance properties have also been determined and they are discussed in relationship with the composition of the samples.

Dry reforming of methane on porous membrane catalytic systems

Tsodikov, M. V.; Teplyakov, V. V.; Fedotov, A. S.; Kozitsyna, N. Yu.; Bychkov, V. Yu.; Korchak, V. N.; Moiseev, I. I.

RUSSIAN CHEMICAL BULLETIN, 60, 1, 55-62

A method of high-performance dry reforming of methane into syngas at temperatures below 650 degrees C on membrane catalytic systems was proposed. The membrane catalytic systems consist of porous inorganic membrane-supports, prepared by self-propagating high-temperature synthesis and modified by nanosized metallocomplex components, which are uniformly distributed inside membrane pores. The influence of the composition of the supported active components, temperature, and flow rate on the activity and selectivity of CH(4) and CO(2) transformations into syngas, as well as the dynamics of CH(4) and CO(2) conversion on the membrane catalytic systems were studied.

Combustion Synthesis of BaCO3 and its Application for Eu(III) Adsorption from Aqueous Solution

Granados-Correa, F.; Jimenez-Reyes, M.

SEPARATION SCIENCE AND TECHNOLOGY, 46, 15, 2360-2366

A combustion method using urea as fuel and barium nitrate as oxidant was applied for the synthesis of barium carbonate, which was characterized by XRD, IR, SEM, and BET. A batch technique was employed to study the Eu(III) adsorption from an aqueous solution using BaCO3. It was found that the adsorption process attains equilibrium within 3 hours and depends upon the pH, europium concentration, and temperature. The kinetic data of the process could be fitted by means of the pseudo-second order and the intraparticle mass transfer diffusion models, whereas the isotherm by means of the Langmuir equation. Thermodynamic parameters indicate that the process is spontaneous and endothermic in nature. These results suggest that BaCO3 is an effective material for Eu(III) adsorption from aqueous solutions. The findings of this study could be relevant for heterogeneous catalytic processes as well have an environmental impact.