A novel cost-effective method for combustion synthesis of AIN powders

Wang-Fei; Ge-Changchun(Taiyuan Univ. of Technol., Taiyuan, China)

Rare-Metal-Materials-and-Engineering. Aug. 2007: 192-5

A novel cost-effective method for combustion synthesis of AiN powders was reported. The effects of nitrogen pressure and the addition of ammonium halides on the combustion reaction process without inert diluents and the phase composition of the combustion products were investigated. It was found that single-phase fine AIN powders with high purity and low oxygen content could be synthesized without using of inert diluents. Furthermore, the nitrogen pressure greatly influences the nitridation degree of aluminum and the microstructure of the combustion products.

A multilayer model for self-propagating high-temperature synthesis of intermetallic compounds

Baras-F; Kondepudi-D(CNRS-Univ. de Bourgogne, Dijon, France)

Journal-of-Physical-Chemistry-B. 14 June 2007; 111(23): 6457-68

Self-propagating high-temperature synthesis of intermetallic compounds is of wide interest. We consider reactions in a binary system in which the rise and fall of the temperature during the reaction is such that one of the reacting metals melts but not the other. For such a system, using the phase diagram of the binary system, we present a general theory that describes the reaction taking place in a single solid particle of one component surrounded by the melt of the second component. The theory gives us a set of kinetic equations that describe the propagation of the phase interfaces in the solid particle and the change in composition of the melt that surrounds it. In this article, we derive a set of equations for one- and two-layer systems in which each layer is a binary compound in the phase diagram. The system of equations is numerically solved for Al - Ni to illustrate the applicability of the theory. The method presented here is general and, depending on the complexity of the phase diagram, it could be used to obtain similar equations for systems with more layers.

Combination of SHS and SPS techniques for fabrication of fully dense ZrB₂-ZrC-SiC composites

Licheri-R; Orru-R; Musa-C; Cao-G(Univ. degli Studi di Cagliari, Cagliari, Italy)

Materials-Letters. 15 Feb. 2008; 62(3): 432-5

A novel method for the fabrication of fully dense ZrB₂-ZrC-SiC ultra high temperature ceramic (UHTC) materials is proposed. It consists of first synthesizing ZrB₂-40 vol.% ZrC-12 vol.% SiC powders by Self-propagating high-temperature synthesis (SHS) and subsequently consolidating them by spark plasma sintering (SPS). Specifically, when starting from Zr, B₄C, Si, and graphite, the SHS technique leads to the complete conversion of reactants to the desired product. In addition, the use of the SPS apparatus allows for the full consolidation of the SHS powders. This result is achieved under the optimal conditions of 10 min total time and with a maximum temperature of 1800 degrees C. The proposed method is particularly rapid and convenient as compared to other techniques available for the preparation of analogous materials and for the consolidation of commercial ZrB₂, ZrC, and SiC, using the same SPS conditions. [All rights reserved Elsevier].

Surfactant effects on hydrate formation in an unstirred gas/liquid system: an experimental study using methane and sodium alkyl sulfates

Okutani-K; Kuwabara-Y; Mori-YH(Keio Univ., Yokohama, Japan)

Chemical-Engineering-Science. Jan. 2008; 63(1): 183-94

This paper reports an experimental study on the effects of surfactant additives on the formation of a clathrate hydrate in a quiescent methane/liquid-water system, which was initially composed of a 300-cm³ aqueous phase and an ~640-cm³ methane-gas phase, then successively provided with methane such that the system pressure was held constant. The surfactants used in the present study were three sodium alkyl sulfates appreciably different in the alkyl chain length-they were sodium dodecyl sulfate (abbreviated as SDS), sodium tetradecyl sulfate (abbreviated as STS) and sodium hexadecyl sulfate (abbreviated as SHS). For each surfactant added to water up to, at most, 1.82-3.75 times the solubility, we performed visual observations of hydrate formation simultaneously with the measurements of methane uptake due to the hydrate formation. The qualitative hydrate-formation behavior thus observed was almost the same irrespective of the species as well as the initial concentration of the surfactant used; i.e., thick, highly porous hydrate layers were formed and grew on the horizontal gas/liquid interface and also on the test-chamber wall above the level of the gas/liquid interface. In each experimental operation, hydrate formation continued for a limited time (from ~6 to ~25 h) and then practically ceased, leaving only a small proportion (typically 15% or less) of the aqueous solution unconverted into hydrate crystals. The variations in the time-averaged rate of hydrate formation (as measured by the rate of methane uptake) and the final water-to-hydrate conversion ratio with the initial concentration of each surfactant were investigated. Moreover, we examined the promotion of hydrate formation with the aid of a water-cooled cold plate, a steel-made flat-plate-type heat sink, vertically dipped into the aqueous phase across the gas/liquid interface. [All rights reserved Elsevier].

The impact of lipid on contact angle wettability

Lorentz-H; Rogers-R; Jones-L(Univ. of Waterloo, Waterloo, Canada)

Optometry-and-Vision-Science. Oct. 2007; 84(10): 946-53

The purpose of this paper is to analyze the effect of in vitro lipid doping on conventional hydrogel (CH) and silicone hydrogel (SH) lens wettability, assessed by sessile drop contact angle (CA) measurement. Nine contact lens materials, five SHs and four CH, were incubated with two different lipid tear solutions (Lt) containing cholesterol, cholesteryl oleate, oleic acid, oleic acid methyl ester, and triolein. The first LTS was a "low" concentration solution, which was close to human values, and the second was a "high" concentration. Lenses were soaked in the two LTS types for 2 or 5 days and compared with lenses soaked in phosphate buffered saline (PBS) only. After soaking, advancing CAs were measured on a customized computerized device using a sessile drop method. Compared with PBS, CAs for untreated SHs were unaffected by soaking in the LTS, with typical CA values of >95 degrees (p > 0.05). The surface-treated SH materials exhibited markedly reduced CAs after lipid exposure, with the high concentration LTS reducing the CA to <5 degrees (p < 0.01). The CH materials all exhibited lower CAs after soaking, with values typically decreasing to 35 degrees , which was significantly lower than that seen with PBS (p < 0.01). Exposure to lipid may improve the wettability of certain SH and CH materials, particularly those SH materials that are surface treated. This may help to explain why certain SH materials appear to improve in comfort for some patients during the first few hours or days of wear.

Properties of TiB₂/Al₂O₃ composites synthesized by SHS method

Fang-Shuangquan; Qiao-Yingjie; Jiang-Peng; Huang-Mian; Yang-Jijun(Harbin Eng. Univ., Harbin, China)

Rare-Metal-Materials-and-Engineering. Aug. 2007: 98-101

TiB₂/Al₂O₃ composite powder was synthesized using commercial TiO₂ as raw material with Al powder and B₄C by self-propagating high-temperature synthesis (SHS) method. Reaction mechanism among TiO₂, Al and B₄C was determined by DTA analysis and some mechanical properties of TiB₂/Al₂O₃ composite powder were also measured. Mechanical test showed that its compression strength was 87.2 MPa and bending strength was 104.3 MPa. SEM analysis indicated that lots of gas phase or pore existed in product and micro-region of product distributed uniformly. Main fracture mode of the samples was brittle fracture and obvious cleavage fracture was observed. Grain size of product was submicron order.

Study on the synthesis mechanism of titanium-nickel yellow pigment by the process of self-propagating high-temperature

Zhang-Bo; Cui-Xuemin(Guangxi Univ., Nanning, China)

Rare-Metal-Materials-and-Engineering. Aug. 2007: 17-19

The synthesis mechanism of titanium-nickel yellow pigment by self-propagating high-temperature (SHS) was studied by SEM, XRD and XPS. Titanium-nickel yellow pigment is a limit substitutional solid solution. The SHS process for this pigment begins with combustion of Ti powder, which release heat for the following reactions. Ti⁴⁺ ions leave their balance place during the heating process, while Ni²⁺ ions enter into the TiO₂ crystal lattice to replace Ti⁴⁺ partly. Rutile crystal lattice changes and then presents yellow color. Sb⁵⁺ ions balance the electric charges. Yellow color of the pigment can't appear completely through the SHS process, so that later heat treatment at high temperature is necessary. During the reheat process, reaction of replacement will be more complete, and yellow color fully appears.

Influence of Eu²⁺ content on the spectral characteristics of BaMgAl₁₀O₁₇ : Eu²⁺ phosphors

Chen-Zhe; Xie-Hong; Yan-You-wei(Huazhong Univ. of Sci. & Technol., Wuhan, China)

Spectroscopy-and-Spectral-Analysis. April 2007; 27(4): 657-59

Nanocrsytalline Ba_1-xMgAl₁₀O₁₇ : xEu²⁺ (0. 05x0.4) blue-emitting phosphor was successfully prepared by low- temperature combustion synthesis. The influence of different Eu content on the spectral characteristics of Bai-xMgAl₁₀O₁₇ : xEu²⁺ was mainly investigated. The results of XRD and SEM analysis show that the sample is single phase and its average grain size is about 30 nm. The luminescence property of Bai-xMgAl₁₀O₁₇ : xEu²⁺ phosphor is considerably influenced by Eu²⁺ concentration. In an appropriate Eu²⁺ doping concentration range, the intensity of the fluorescence of Bai-xMgAl₁₀O₁₇ : xEu²⁺ was increased obviously with increasing the Eu²⁺ doping concentration, owing to adding the number of luminescent centers and enhancing the energy transfer between Eu²⁺ ions. The optimum emission intensity was reached at x = 0. 2. However, as the Eu²⁺ doping concentration was higher than 0. 2, the intensity of the fluorescence was reduced, due to the concentration quenching occurrence.

Physical properties of ceramic layer prepared by SHS in centrifugal field

Jaeryeong-Lee; Le-MT; Chung-HS(Kangwon Nat. Univ., Kangwon-do, South Korea)

Materials-Transactions. Nov. 2007; 48(11): 2960-3

The inner surface of a steel pipe could be lined with ceramics by means of a SHS reaction under centrifugal force. Some physical characteristics of the ceramic layer were investigated with the change of filling ratio (thermit mixture, Fe₂O₃ and Al) and the addition of silica. Two compositions, alpha -Al₂O₃ and FeAl₂O₄, were detected in the dispersed phase. The size of alumina grains became larger towards the pipe innermost side at high mixture filling ratios. Additionally, it was found that amorphous silicate materials formed by the addition of silica makes the layer dense significantly. The apparent density and hardness of the ceramic layer were improved from 2.9 g/cm³ and 1,430 Hv to 3.7 g/cm³ and 1,700 Hv with the effect of additive, silica.

Studies on nanocrystalline (Sr,Pb)TiO₃ solid solutions prepared via a facile self-propagating combustion method

Hun-Xue; Zhaohui-Li; Xuxu-Wang; Xianzhi-Fu(Fuzhou Univ., Fuzhou, China)

Journal-of-Physics-and-Chemistry-of-Solids. Dec. 2007; 68(12): 2326-31

Macroporous nanocrystalline (Sr,Pb)TiO₃ solid solutions were prepared by a facile self-propagating combustion method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectrum (EDS) and X-ray photoelectron spectroscopy (XPS). (Sr,Pb)TiO₃ solid solutions showed enhanced photocatalytic activity for the degradation of methyl orange (MO) than pure SrTiO₃ and an optimum performance was observed for Sr2932/Pb₃32/TiO₃. The possible mechanism for the enhanced photocatalytic activity on (Sr,Pb)TiO₃ solid solutions was proposed. [All rights reserved Elsevier].

Improving thermal efficiency by reducing cooling losses in hydrogen combustion engines

Shudo-T(Hokkaido Univ., Sapporo, Japan)

International-Journal-of-Hydrogen-Energy. Dec. 2007; 32(17): 4285-93

Hydrogen can be readily used in spark ignition engines as a clean alternative to fossil fuels. However, the higher burning velocity and shorter quenching distance of hydrogen compared with hydrocarbons cause a larger heat transfer from the burning gas to the combustion chamber walls. Because of this cooling loss, the thermal efficiency of hydrogen-fueled engines is sometimes lower than that of conventionally fueled engines. Therefore, reducing the cooling loss is a crucial element in improving the thermal efficiency of hydrogen combustion engines. Previous research by the author and others has proposed the direct injection stratified charge as a technique for reducing the cooling loss in hydrogen combustion and shown its effect in reducing cooling loss through experiments in a constant volume combustion vessel. However, it is known that a reduction in cooling loss does not always improve thermal efficiency due to a simultaneous increase in the exhaust heat loss. This paper explains the relation between cooling loss reduction and thermal efficiency improvements by the direct injection stratified charge in hydrogen combustion engines. [All rights reserved Elsevier].

Preparation of Pr_0.35Nd_0.35Sr_0.3MnO_3-delta/YSZ composite cathode powders for tubular solid oxide fuel cells by microwave-induced monomer gelation and gel combustion synthesis process

Dehua-Dong; Jianfeng-Gao; Mingfei-Liu; Genbai-Chu; Juan-Diwu; Xingqin-Liu; Guangyao-Meng(Univ. of Sci. & Technol. of China, Hefei, China)

Journal-of-Power-Sources. 3 Jan. 2008; 175(1): 436-40

A microwave-induced monomer gelation and gel combustion synthesis process was successfully developed to synthesize well-dispersed Pr_0.35Nd_0.35Sr_0.3MnO_3-delta (PNSM)/YSZ composite cathode powders for tubular solid oxide fuel cells (SOFCs). The thermo-gravimetric (TG) analysis of as-prepared ash indicated the decomposition process of most of metal nitrates during gel combustion. The X-ray diffraction (XRD) pattern of the powders calcined at 1000 degrees C showed only pure PNSM and YSZ phase. Transmission electron microscopy (TEM) revealed that the morphology of powders was characterized with the YSZ particles enwrapped by fine PNSM particles so that PNSM/YSZ composite powders were much better-dispersed compared with the powders made simply by mechanical mixing process. The cell made from PNSM/YSZ composite powder showed lower cathode ohmic resistance and polarization resistance, and produced higher power density subsequently.[All rights reserved Elsevier].

Characteristics of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-delta-La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-delta composite cathode for solid oxide fuel cell

Bangwu-Liu; Yue-Zhang; Limin-Zhang(Univ. of Sci. & Technol. Beijing, Beijing, China)

Journal-of-Power-Sources. 3 Jan. 2008; 175(1): 189-95

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-delta-La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-delta composite cathodes are prepared successfully using combustion synthesis method. Microstructure, chemical compatibility and electrochemical performance have been investigated and analyzed in detail. SEM micrographs show that a structure with porosity and well-necked particles forms after sintering at 1000 degrees C in the composites. Grain growth is suppressed by addition of La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-delta phase and grain sizes decrease with increasing weight percent of La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-delta phase in the composites. Phase analysis demonstrates that chemical compatibility between Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-delta and La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-delta is excellent when the weight percent of La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-delta in the composite is not more than 40%. Through fitting ac impedance spectra, it is found that the ohmic resistance and polarization resistance decrease with increasing La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-delta content. The polarization resistance reaches a minimum at about 30 and 40 wt.% La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-delta in the composite. [All rights reserved Elsevier].

Synthesis of SrAl₂O₄: Eu²⁺, Dy³⁺, Gd³⁺ phosphor by combustion method and its phosphorescence properties

Huajie-Song; Donghua-Chen; Wangjun-Tang; Yuhua-Peng(South Central Univ. for Nat., Wuhan, China)

Displays-. Jan. 2008; 29(1): 41-4

Eu²⁺, Dy³⁺ and Gd³⁺ co-doped strontium aluminate yellow-green phosphor was synthesized by combustion method using urea as reducer at 600 degrees C. The crystallization, particles size and luminescence properties of the sample have been investigated. The results are as follows: Eu²⁺, Dy³⁺ and Gd³⁺ doped into the phosphor do not change the crystalline structure of strontium aluminate. The average size of particles is about 100 nm. The excitation and emission spectra are broad bands with the peaks at 348 and 515 nm, respectively. Compared with SrAl₂O₄: Eu²⁺, Dy³⁺ phosphor, the initial brightness improved and the afterglow time prolonged. [All rights reserved Elsevier].

Photoluminescence analysis of alpha -Al₂O₃ powders doped with Eu³⁺ and Eu²⁺ ions

Rakov-N; Maciel-GS(Univ. Federal do Vale do Sao Francisco, Petrolina, Brazil)

Journal-of-Luminescence. Dec. 2007; 127(2): 703-6

Alumina (Al₂O₃) powders doped with europium trivalent (Eu³⁺) were prepared by a low-temperature (~280 degrees C) combustion synthesis technique. When the powder was heat treated at 1200 degrees C for 2 h in the presence of flowing ammonia (NH₃), alpha -Al₂O₃ crystalline ceramic powders was obtained. The analysis of the luminescence showed that Eu³⁺ was reduced to europium divalent (Eu²⁺) after the heat-treatment process. Under ultraviolet (UV) lamp excitation ( lambda = 254 nm) these powders containing sub-microcrystalline structures present bright red (Al₂O₃:Eu³⁺) and green (Al₂O₃:Eu²⁺) luminescence indicating that this material is a potential candidate for applications in phosphor technology.[All rights reserved Elsevier].

NO_x formation pathways in lean-premixed-pre-vapourized combustion of fuels with carbon-to-hydrogen ratio between 0.25

Rutar-T; Lee-JCY; Dagaut-P; Malte-PC; Byrne-AA(Seattle Univ., Seattle, USA)

Proceedings-of-the-Institution-of-Mechanical-Engineers,-Part-A-Journal-of-Power-and-Energy. May 2007; 221(A3): 387-98

NO_x measurements in jet-stirred reactor (JSR) combustion of seven fuels are modelled using three complete chemical kinetic mechanisms. The two JSRs are operated at 1790 K, 1 atm, 2-4 ms, and the fuel-air equivalence ratio of 0.61. The modelled fuels are methanol, methane, ethane, ethene, propane, n-butane, and toluene. The experimental database also includes C1-C4 alkane mixtures, two light naphtas, four number two diesel oils, and benzene. The fuels and air are premixed, prevapourized, and preheated with a temperature-staged preva- pourizer-premixer and an air-heater. Experiments show NO_x and CO increase when burning fuels with increasing carbon-to-hydrogen ratio (from 0.25 to 0.88). The data are analysed using three complete chemical kinetic mechanisms: GRI 3.0 Mech., CNRS' C1-C4 hydrocarbon oxidation mechanism, and CNRS' toluene oxidation mechanism. The modelling shows that the increase in NO_x with the fuel carbon-to-hydrogen ratio is because of the increase in the NO formation via NNH, Zeldovich, and nitrous oxide pathways. The NNH pathway produces between 25 and 45 per cent of the NO formed. GRI 3.0 Mech. tends to favour this pathway since it forms more O, H, and NNH reactive species than the CNRS' C1-C4 hydrocarbon mechanism. Several rate constants for NNH + O to NH + NO are considered and best agreement using two and three perfectly stirred reactor schemes is found with the rate constant k = 7 x 10¹³ cm³/mol/s.

Process for SHS ultra-fast densification of ceramics

Fu-Zhengyi(Wuhan Univ. of Technol., Wuhan, China)

Journal-of-the-Chinese-Ceramic-Society. Aug. 2007; 35(8): 948-54

Combining self-propagation high-temperature synthesis (SHS) with hydraulic quick pressing (QP) in a single processing operation, dense ceramics can be fabricated rapidly. Immediately after SHS, when the sample is still red-hot and soft, a quick and large mechanical force is applied to the sample. The densification of the sample can be achieved in several minutes. The mechanism of densification in such a short time is still not clear. In this paper, the SHS/QP densification mechanism for ceramics is discussed. The processes for the making of multi-phase ceramics, layered materials and nano-ceramics were studied. The results show that dense ceramics with finer grains can be obtained by the SHS/QP technique. The process also revealed the densification mechanism based on plastic deformation.

Mechanical and electrical properties of Al₂O₃/Ce_0.8Y_0.2O_1.9 composite electrolytes

Hongmei-Xu; Hongge-Yan; Zhenhua-Chen(Hunan Univ. of Sci. & Technol., Xiangtan, China)

Materials-Science-and-Engineering-B. 20 Dec. 2007; 145(1-3): 85-90

The Al₂O₃/Ce_0.8Y_0.2O_1.9 composites, with Al₂O₃ concentration ranging from 0 to 10 mol%, were prepared by a low-temperature combustion process. The effects of Al₂O₃ addition on the flexural strength and electrical conductivity of Y³⁺-doped ceria were investigated, and the mechanism was analyzed. The experimental results showed that Al₂O₃ enhanced significantly the flexural strength of the as-sintered Ce_0.8Y_0.2O_1.9. The flexural strength was 270 MPa for the specimen containing 10 mol% Al₂O₃ while the flexural strength of the undoped Ce_0.8Y_0.2O_1.9 specimen was only 121 MPa. Impedance analysis showed that ionic conductivity of the Al₂O₃/Ce_0.8Y_0.2O_1.9 composite electrolytes decreased and the activation energy increased when the concentration of Al₂O₃ was within the solubility. When the content of Al₂O₃ was above its solubility limit in Ce_0.8Y_0.2O_1.9, the bulk resistance was constant and the grain boundary conductivity increased because of the "scavenging" effect of Al₂O₃. When the concentration of Al₂O₃ was over 5 mol%, the grain boundary conductivity began to reduce because of the "blocking" effect of Al₂O₃ particles at the grain boundaries. The activation energy for the bulk conductivity and the grain boundary conductivity retained constant when the concentration of Al₂O₃ was over its solubility limit in Ce_0.8Y_0.2O_1.9. [All rights reserved Elsevier].

Humidity-sensitive electrical resistivity of MgFe₂O₄ and Mg_0.9Sn_0.1Fe₂O₄ porous ceramics

Rezlescu-N; Doroftei-C; Popa-PD(Inst. of Tech. Phys., Iasi, Romania)

Romanian-Journal-of-Physics. 2007; 52(3-4): 353-60

Pure and Sn substituted Mg ferrites have been prepared by sol-gel autocombustion method. This method offers the advantage to prepare ultra-fine, homogeneous and reproducible ferrite powders using aqueous solutions of constituent ions (metal nitrates) salts. Sn ion partially substituted Mg ion to improve the humidity sensitivity of Mg polycrystalline ferrite. The phase composition and lattice parameters were determined by X-ray diffraction (XRD), and the effect of Sn substitution on the granular structure was investigated by scanning electron microscopy (SEM). We have found that Sn ions affect crystallite size, surface area and porosity. Sn ions assure a nanocrystalline structure of Mg_0.9Sn_0.1Fe₂O₄ ferrite. The average grain size changes from 500 nm to 100 nm by partial substituting Mg with Sn ions in MgFe₂O₄. Also, Sn ions enhance the humidity sensitivity of Mg ferrite. For Sn substituted ferrite, the electrical resistivity decreases by about three orders of magnitude, from 10⁹ Omega cm to 10⁶ Omega cm when the relative humidity increases from 11 % to 85%. These results show that the promoting effect of Sn ions on humidity sensitivity of Mg ferrite can be related with the changes in porosity and specific surface area. Further investigations are necessary to shorten response time to humidity variations.

Methods for research and testing of fuel oil miniaturised combustion (part 2)

Ghiea-VV)

Revue-Roumaine-des-Sciences-Techniques,-Serie-Electrotechnique-et-Energetique. July-Sept. 2007; 52(3): 383-94

Using the graphologic method and interpreting the combustion oscillogram (COS) supported by flame infrared thermo-gram (FIT) special economical results can be obtained. It is detailed the improving of symbiotic technologies, combustion of water-in-heavy fuel oil emulsion (CWHFOE) and combustion with additived air (CWAA). By establish of new criteria for optimum operation variant, in fact are predicted the very advantageous solutions, and thus avoiding many expensive industrial experiments. Also theoretical bases of phenomena which determine the industrial advantageous results are analysed and scientifically explained for boiler furnace operation. Are presented the perspectives and results in other applications, as well the differences and similitude between the proposed methods.

Microstructure and electrical transport in nano-grain sized Ce_0.9Gd_0.1O_2-delta ceramics

Ruiz-Trejo-E; Santoyo-Salazar-J; Vilchis-Morales-R; Benitez-Rico-A; Gomez-Garcia-F; Flores-Morales-C; Chavez-Carvayar-J; Tavizon-G(Univ. Nacional Autonoma de Mexico, Mexico, Mexico)

Journal-of-Solid-State-Chemistry. Nov. 2007; 180(11): 3093-100

An enhancement of the electrical conductivity has been found in nano-grain sized Ce_0.9Gd_0.1O_2-delta ceramics when measured in N₂ (p_O2=3.5x10^-6 atm) in comparison with the most commonly accepted values of bulk ionic conductivity. We first present the synthesis and characterisation of the nanoparticles later used for the preparation of dense nanoceramics of Gd-doped CeO₂. The nanoparticles were characterised by X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The good sintering properties of these nanopowders allowed us to obtain very dense ceramics (>90% theoretical density) while keeping the grain size close to 100 nm. The microstructure of these nanoceramics was analysed by AFM and scanning electron microscopy (SEM) while the electrical characterisation was performed by the 4-point dc technique between 500 and 950 degrees C in air or N₂ and ac impedance between 150 and 400 degrees C in air and or argon. We briefly discuss the possibilities of electron vs. oxygen ion conduction and grain boundary vs. bulk conductivity. The features exhibited by these ceramics represent an increased potential to process solid electroceramics materials with specific levels of electronic and/or ionic conductivities for a variety of electrochemical devices.An enhancement of the electrical conductivity has been found in nano-grain sized Ce_0.9Gd_0.1O_2-delta ceramics in comparison with the most commonly accepted values of bulk ionic conductivity. We present the microstructural characterisation of the nanoparticles and the nanoceramics of Ce_0.9Gd_0.1O_2-delta and then we briefly discuss the possibilities of electron vs. oxygen ion conduction and grain boundary vs. bulk conductivity. [All rights reserved Elsevier].

Al₂O₃/ZrO₂ (Y₂O₃) self-growing composites prepared by combustion synthesis under high gravity

Zhongmin-Zhao; Long-Zhang; Yigang-Song; Weiguo-Wang(Inst. of Adv. Mater., Shijiazhuang, China)

Scripta-Materialia. Feb. 2008; 58(3): 207-10

Al₂O₃/ZrO₂ (Y₂O₃) plates were prepared by combustion synthesis under high gravity (>200g) and the ceramics were composed of randomly orientated colonies containing a triangular dispersion of orderly nano-submicrometer t-ZrO₂ fibers, surrounded by inter-colony regions containing micrometer size t-ZrO₂ spherical grains. The high strength (close to 1.6 GPa) of the ceramics was attributed to small-size defect and high fracture toughness (close to 15.0 MPa m¹2/) dependent on an intensive coupled toughening mechanism. [All rights reserved Elsevier].

Hard tribological Ti-Cr-B-N coatings with enhanced thermal stability, corrosion- and oxidation resistance

Shtansky-DV; Kiryukhantsev-Korneev-PV; Sheveyko-AN; Kutyrev-AE; Levashov-EA(Moscow State Inst. of Steel & Alloys, Moscow, Russia)

Surface-and-Coatings-Technology. 15 Dec. 2007; 202(4-7): 861-5

Corrosion and oxidation resistance are of great importance for hard tribological coatings when it concerns thermal stability under severe cutting conditions. A comparative investigation of Cr-doped Ti-B-N coatings deposited by DC magnetron sputtering of TiCrB targets with 20, 30 and 40 wt.% of chromium in a gaseous mixture of argon and nitrogen is presented. The TiCrB composite targets were synthesized using combined force SHS-pressing technology. The structure, elemental and phase composition were studied by means of X-ray diffraction, transmission and scanning electron microscopy, as well as focused ion beam equipped with secondary ion mass spectrometer. To evaluate the thermal stability and oxidation resistance, the Ti-Cr-B-N coatings were annealed at 600, 800, and 1000 degrees C in vacuum and at 600, 700, 800, and 900 degrees C in air, respectively. The potentiodynamic polarization tests of the Ti-Cr-B-N coatings were carried out and compared with those for the Ti-B-N, Ti-Si-B-N, and Ti-Al-Si-B-N reference coatings. From the results obtained it can be concluded that the magnetron sputtering of TiCrB composite targets under controlled deposition parameters resulted in the growth of strongly (100) textured Ti-Cr-B-N coatings with high hardness and wear resistance, superior thermal stability up to 1000 degrees C, improved oxidation resistance up to 900 degrees C, and enhanced corrosion resistance in 1 N H₂SO₄ solution.[All rights reserved Elsevier].

Photoproduction of clean H₂ or O₂ from water using oxide semiconductors in presence of sacrificial reagent

Ekambaram-S(PhosphorTech Corp., Lithia Spring, USA)

Journal-of-Alloys-and-Compounds. 10 Jan. 2008; 448(1-2): 238-45

It is aimed to describe importance of oxide semiconductors with layered or bulk structures for photoproduction of clean H₂ or O₂ from water at room or near room temperature. To achieve this property of semiconductors, either H₂ or O₂ production, sacrificial reagents are employed. First, this short review is started with applications and principle of photocatalysts for water splitting. Followed by soft-chemical synthesis and characterization of layered semiconductor nanocomposites are discussed. Clean production of hydrogen from water using the semiconductor nanocomposites is demonstrated. Then, aqueous combustion synthesis, characterization and clean oxygen production using transition metal-incorporated ZnO are explained. Finally, potential new directions required in this area of research are highlighted.[All rights reserved Elsevier].

Combustion synthesis of Fe-Ti-C system by electric field inducement: effect of electric current on the synthesis products

Wang-Hongliang; Yang-Yi; Feng-Keqin; Lin-Huimin; Wang-Wenjuan(Sichuan Univ., Chengdu, China)

Rare-Metal-Materials-and-Engineering. Aug. 2007; 36(8): 1483-6

The reaction of combustion synthesis was occurred by electric field inducement for Fe-Ti-C system by using Gleeble-1500D thermal simulation apparatus, and the effect of electric field on the synthetical products was researched by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that there were TiC phase in all the products, but Fe₂Ti phase only in the special stage, with the current increasing, the particle size of synthesis products decreases in different extents. Through the investigation and analysis, the conclusion is obtained that the applied electric field can promote the nuclear formation and growth of reactant particle by solid diffusion, and ultimately influencing the phase composition and particle size of synthesis products.

On applicability of the kinetics of diffusion-controlled interaction to SHS modeling

Khina-BB; Formanek-B(Nat. Acad. of Sci., Minsk, Belarus)

Heat-Transfer-Research. 2007; 38(3): 197-209

Sequential analysis of a diffusion model, widely applied for describing the kinetics of heat-release in SHS of refractory compounds, using real values of diffusion coefficients and experimental data for synthesis of titanium carbide, was made. Variation of the reaction cell geometry in melting of the metallic reagent is taken into account. The condition for breaking the primary product crust, resulting in the flow of the liquid metal in the SHS wave, was determined. It was shown that the quasiequilibrium theory of diffusion-controlled interaction does not provide sufficient heat release to maintain the combustion wave, and only hollow particles of interstitial (carbides, nitrides, and borides) can generate within its framework. Qualitative nonequilibrium mechanism of phase formation, allowing explanation of experimental results, was proposed.

Analysis of structured highlight stereo imaging for shape measurement of specular objects

Graves-K; Nagarajah-R; Stoddart-PR(Swinburne Univ. of Technol., Hawthorn, Australia)

Optical-Engineering. Aug. 2007; 46(8): 1-11

Structured highlight stereo (SHS) is a technique for the measurement of specular objects, and is based on viewing the reflection of a structured highlight pattern from multiple directions. This paper reports the results of a simulation and experimental analysis of the approach in order to further understand the accuracy and limitations of SHS. In particular, this paper describes two important findings related to this technique. Firstly, it is shown that the search region containing a consistent set of candidate highlights may be minimized using epipolar constraints. Secondly, an analysis is presented to quantify the accuracy of the SHS approach for different surface curvatures. The results indicate that, although it is possible to accurately measure the surface height of planar specular objects, the accuracy is reduced for objects with curved surface profiles. The measurement error occurs because in general it is not possible to measure the same surface location with both cameras, which then leads to an inconsistency between the surface normal estimates for each camera. The measurement error increases in relation to both the distance between measurement locations on the surface and the surface curvature.

Study on processing of silicon nitride by combustion synthesis at low cost

Chen-Yixiang; Lin-Zhiming; Yang-Yun; Li-Jiangtao(Chinese Acad. of Sci. Beijing, Beijing, China)

Rare-Metal-Materials-and-Engineering. July 2007; 36(7): 1267-71

The feasibility of Mechanical-Activation (MA) assisted combustion synthesis of silicon nitride was demonstrated by using silicon/ammonia chloride as reactants under nitrogen pressure below 2 MPa. The MA treatment enhances the reactivity significantly and promotes the nitridation of silicon effectively. The increase of ammonia chloride content in the green mixture stimulates the increase of alpha -silicon nitride content in the product. Silicon nitride with alpha -phase content up to 90.6 wt% was obtained. The temperature difference between the centre and the edge of the sample was calculated by a simple analytical model. Such a temperature difference was caused mainly by the heat loss due to heat radiation, responsible for the differences in phase composition and morphology of the products.

Compression behavior of micro-scale truss structures formed from self-propagating polymer waveguides

Jacobsen-AJ; Barvosa-Carter-W; Nutt-S(LLC Malibu, Malibu, USA)

Acta-Materialia. Dec. 2007; 55(20): 6724-33

The structure-property relationships in newly developed polymer micro-truss structures were investigated, correlating compressive behavior with structural features, including density, cell size and truss angle. These open-cellular polymer micro-truss structures were formed from an interpenetrating array of self-propagating polymer waveguides. Compression experiments verified that the effective modulus scaled linearly with the measured relative density of the micro-trusses and was reliably predicted from a simple analytical model. However, the measured peak strength at initial truss member buckling was well below the values predicted from inelastic buckling theory, which was attributed to imperfections in the structure and the nonlinear compressive behavior of the solid polymer. In addition, a micro-truss structure was post cured at a higher temperature in an oxidizing environment which suppressed the tendency for truss members to prematurely buckle. The polymer modulus increased by approximately 40% and the peak strength of the micro-truss structure nearly doubled to 5.9 MPa.[All rights reserved Elsevier].

A policy proposal for the introduction of solar home systems in East Timor

Bond-M; Fuller-RJ; Lu-Aye(Melbourne Univ., Melbourne, Australia)

Energy-Policy. Dec. 2007; 35(12): 6535-45

The Government of East Timor aims to increase the rate of household electricity service from 20% to 80% over the next 20 years. With a largely rural population living in sparsely populated, remote locations, solar home systems (SHS) will play an important role in meeting the off-grid component of rural electrification in East Timor. This paper describes current experience and trials in East Timor with solar photovoltaic (PV) technology. It examines the East Timorese context against six key features identified by the World Bank as typically included in solar PV projects: delivery infrastructure; access to finance; rural electrification policy; guarantees for minimum quality; understanding of customer needs; and scaling up capacity building. Of these issues, the authors contend that selection of the delivery infrastructure model is the most critical decision, and that for East Timor, in its present stage of development, a market-driven approach for SHS is unlikely to be successful. A model which subsidises capital costs but seeks full recovery of operating costs is recommended. Irrespective of the delivery infrastructure model, for sustainability, capacity must be developed in a range of other areas, particularly the commercial availability of high-quality components and spare parts; creation of a pool of skilled technicians for installation and maintenance; and development of a robust fee collection and maintenance infrastructure. [All rights reserved Elsevier].

Combustion synthesis of narrow UVB emitting rare earth borate phosphors

Sonekar-RP; Omanwar-SK; Moharil-SV; Dhopte-SM; Muthal-PL; Kondawar-VK(Sant Gadgebaba Amravati Univ., Amravati, India)

Optical-Materials. Dec. 2007; 30(4): 622-5

Narrow UVB emitting phosphors are important for production of phototherapy lamps. The light output is in the form of a narrow line around 310 nm. Synthesis of Gd activated borate phosphors exhibiting such photoluminescence is described here.[All rights reserved Elsevier].

Influences of mechanical Vibration on Al₂O₃/ZrO₂ (3Y) self-toughening composite ceramics prepared by combustion synthesis

Zhao-Zhongmin; Zhang-Long; Yang-Runze; Xu-Baocai(Ordnance Eng. Coll., Shijiazhuang, China)

Rare-Metal-Materials-and-Engineering. Aug. 2007: 724-6

The mechanical vibration has been utilized to fabricate Al₂O₃/ZrO₂ (3Y), and the influences of mechanical vibration on the microstructures and mechanical properties of Al₂O₃/ZrO₂ (3Y) have been investigated. The results show that mechanical vibration with increasing frequency can promote ceramic densification by introducing the inertia force to increase actual temperature of the melts. Meanwhile, mechanical vibration with increasing frequency can not only make the composite ceramics reinforced by increasing under-cooling degree and solidification rate of the ceramic melts to refine rod-shaped grains and reduce the size of nano-micron fibers in rod-shaped grains, but also make the composite ceramics toughened by refining rod-shaped grains and increasing their aspect ratios to enhance toughening contribution from crack-bridging and pull-out of rod-shaped grains.

Colloidal behaviour of mullite powders produced by combustion synthesis

Burgos-Montes-O; Moreno-R(CSIC, Madrid, Spain)

Journal-of-the-European-Ceramic-Society. 2007; 27(16): 4751-7

The combustion synthesis method is very attractive to produce homogeneous powders of pure or mixed oxidic ceramics without further thermal treatment. Previous work reports the synthesis of monophasic mullite powders by a suspension combustion process using two combustions aids, ammonium nitrate and hydrogen peroxide, and an excess of colloidal silica suspension.The combustion synthesis leads to coarse, agglomerated powders that must be crushed. The effect of attrition milling on both particle size and morphology was studied. Aqueous suspensions of the milled powders were prepared using two dispersants: citric acid and a polyacrylic acid-based polyelectrolyte. The stability of the powders was studied by measuring the zeta potential. The effect of the dispersants on the rheological behaviour of concentrated suspensions was also studied. The sintered densities and the microstructures of specimens obtained by slip casting were studied, demonstrating that mullite powders obtained by a single step combustion process can be processed through conventional shaping routes.[All rights reserved Elsevier].

Aberration evaluation of alignment optics in lithographic tools by use of a step-height structure highly sensitive to the asymmetry of an optical image

Ina-H; Takeda-M(The Univ. of Electro-Commun., Tokyo, Japan)

Applied-Optics. 10 June 2007; 46(17): 3485-92

To satisfy the increasing demand for extremely tight overlay accuracy in semiconductor manufacturing processes, all the measurement error factors in alignment systems and overlay measurement tools need be identified and eliminated. The principle of most alignment systems is based on image processing of target marks on the wafer under bright-field illumination. Although the phenomenon that the sensitivity to the alignment error varies with the step height (SH) of the mark has been known and used for evaluating the performance of the alignment optics, no investigation has been made into the origin and the physical mechanism of the phenomenon. We propose a simplified optical model that can account for the origin of the asymmetric image and clarify its relation to the SHs. The model is validated with simulation and experimental results. The improved performance of an alignment system using marks with optimally designed SHs is demonstrated.

Structure and optical absorption of combustion-synthesized nanocrystalline LiCoO₂

Ghosh-P; Mahanty-S; Raja-MW; Basu-RN; Maiti-HS(Central Glass & Ceramic Res.Inst., Kolkata, India)

Journal-of-Materials-Research. May 2007; 22(5): 1162-7

Nanocrystalline LiCoO₂ powders (10-50 nm) were synthesized by a citrate-nitrate combustion process followed by calcination at different temperatures (300-800 degrees C) in air. Thermogravimetric analyses indicated a sharp combustion at a low temperature of 225 degrees C, producing fine crystallites. Quantitative phase analyses from the x-ray diffractograms showed that while annealing at 500 degrees C produced mixed phases of cubic and rhombohedral LiCoO₂, annealing at 800 degrees C resulted in single-phase rhombohedral LiCoO₂. Electronic transitions related to the Co 3d bands were investigated by ultraviolet-visible reflectance spectra in absorbance mode and were ascribed to the Co 3d intra-band transition involving t_2g and e_g orbitals. The d-d transitions underwent a blue shift of about 0.3 eV as the cubic LiCoO₂ transformed into the rhombohedral structure with band gap values of about 1.4 and 1.7 eV.

Mechanoactivation of SHS systems and processes

Levashov-EA; Kurbatkina-VV; Rogachev-AS; Kochetov-NA(Moscow State Inst. of Steel & Alloys (MSISA), Moscow, Russia)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. Jan.-March 2007; 16(1): 46-50

Data on the mechanoactivation (MA) of SHS processes and systems obtained over the past 15 years are overviewed. Analysis of these data is used to formulate some recommendations for appropriate application of MA to SHS.

Carbon combustion synthesis of nanostructured perovskites

Martirosyan-KS; Iliev-M; Luss-D(Univ. of Houston, Houston, USA)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. Jan.-March 2007; 16(1): 36-45

A novel, economical, and energy-efficient process to produce nanostructured particles of several perovskite oxides, such as ferroelectrics BaTiO₃, SrTiO₃ and LiNbO₃, is described. This process, referred to as carbon combustion synthesis of oxides (CCSO) is a modified SHS process that uses carbon as a fuel instead of a pure metal. In CCSO of nanostructured materials, the exothermic oxidation of carbon nanoparticles (~5 nm) with a surface area of 80 m²/g generates a thermal reaction wave with temperature of up to 1200 degrees C that propagates through the solid submicron reactant mixture, converting it to the desired complex oxide product. The carbon is not incorporated in the solid product since it is released in a gaseous form (CO₂) from the sample. The quenching front method combined with XRD and Raman spectroscopy revealed that crystalline tetragonal BaTiO₃ particles formed in the early stage of the combustion, before the temperature reached its maximum. A major difference between the thermal transport processes during CCSO and conventional SHS is the extensive emission of CO₂. The release of CO₂ enables synthesis of highly porous (up to 70%) powders having a particle size in the range of 60-80 nm with a surface area of up to 12.4 m²/g.

Novel approaches to solution-combustion synthesis of nanomaterials

Mukasyan-AS; Dinka-P(Univ. of Notre Dame, Notre Dame, USA)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. Jan.-March 2007; 16(1): 23-35

Solution-combustion is an attractive approach to synthesis of nanomaterials for a variety of applications, including catalysts, fuel cells, and biotechnology. In this paper, several novel methods based on the combustion of a reactive solution are presented. These methods include self-propagating sol-gel combustion and combustion of impregnated inert and active supports. It was demonstrated that, based on the fundamental understanding of the considered combustion processes, a variety of extremely high surface area materials could be synthesized. The controlling process parameters are defined and discussed. Examples of materials synthesized by the above methods are presented. For the first time, a continuous technology for production of nano- powders by using the solution combustion approach is demonstrated.

Time-resolved X-ray diffraction study of SHS-produced NiAl and NiAl-ZrO₂ composites

Tingaud-D; Stuppfler-L; Paris-S; Vrel-D; Bernard-F; Penot-C; Nardou-F(Univ. de Limoges, Limoges, France)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. Jan.-March 2007; 16(1): 12-17

NiAl and NiAl-ZrO₂ intermetallic composites were prepared from pressed elemental powders by SHS in a dynamic vacuum. The effect of diluent properties (such as conductivity and grain size) on the parameters of the SHS reaction has been investigated by time-resolved X-ray diffraction (TRXRD). By decreasing the reactivity of the green mixture, these nonreactive additives not only slow down the velocity of combustion front propagation but can also give rise to local melting of the product. Synchrotron radiation was also used to elucidate the reaction mechanism. It has been found that the combustion synthesis of NiAl is triggered by aluminum melting and proceeds via the formation of two transient intermetallic phases, NiAl₃ and Ni₂Al₃. In the final product, only the NiAl phase has been detected.

Creation of redox adsorption sites by Pd²⁺ ion substitution in nanoTiO₂ for high photocatalytic activity of CO oxidation, NO reduction, and NO decomposition

Roy-S; Hegde-MS; Ravishankar-N; Madras-G(Indian Inst. of Sci., Bangalore, India)

Journal-of-Physical-Chemistry-C. 14 June 2007; 111(23): 8153-60

The present study aims at developing a new photocatalyst for NO reduction and CO oxidation by creating redox adsorption sites and utilizing oxide ion vacancy in titania. For this purpose, PDX ion-substituted TiO₂, Ti_1-xPd_xO_{2- delta} was synthesized for the first time by solution combustion method. The photocatalytic activity was investigated with increasing Pd substitution and the optimum concentration was found to be 1 atom % Pd ion in TiO₂. The reduction of NO was carried out both in the presence and in the absence of CO. Despite competitive adsorption of NO and CO on the Pd²⁺ sites, the reduction of NO was 2 orders of magnitude higher than unsubstituted TiO₂. High rates of photooxidation of CO with O₂ over Ti_1-xPd_xO_{2- delta} are observed at room temperature. It was shown that enhanced CO oxidation at Pd²⁺ ion site and O₂ or NO photo dissociation at oxide ion vacancy is responsible for the enhanced catalytic activity.

Effect of citric acid on spinel LiMn₂O₄ prepared by solution combustion synthesis

Liu-Guiyang; Guo-Junming; Dai-Zhifu; Zhang-Lili; Chen-Kexin; Zhou-Heping(Honghe Univ., Mengzi, China)

Rare-Metal-Materials-and-Engineering. Aug. 2007: 115-17

The effects of amounts of citric acid and concentrations of nitric acid on spinel LiMn₂O₄ prepared by liquid combustion synthesis using manganese acetate, lithium acetate as raw materials and citric acid as fuel were studied. The results indicated that there are main phase of LiMn₂O₄ and a little Mn₂O₃ when mole ratio of citric acid/Mn²⁺0.5, and main phase of Mn₂O₃ and a little LiMn₂O₄ when mole ratio of citric acid/Mn²⁺>0.5. The content of LiMn₂O₄ increased with the increasing of HON₃ concentration. Pure LiMn₂O₄ with good crystallinity but non-uniform crystal size distribution was obtained when the mole ratio of citric acid/Mn²⁺=0.1 and HNO₃ concentration of 2 mol/L.

Suspension combustion synthesized SiO₂ and Its spherical shaping mechanism

Zhu-Yuan; Ren-Kegang; Chen-Kexin; Zhou-Heping(Tsinghua Univ., Beijing, China)

Rare-Metal-Materials-and-Engineering. Aug. 2007: 196-8

Spherical and fine-sized SiO₂ powders were directly prepared using suspension combustion at 1000 degrees C from Si powders. The spherical powders had broad peaks at around 22 degrees in the XRD spectrum. The shape of the prepared SiO₂ powders was spherical and the mean size of them was 100 nm. Both above could be seen by SEM. Furthermore, spherical shape mechanism of powders in suspension combustion is discussed.

In situ synchrotron investigation of MoSi₂ formation mechanisms during current-activated SHS sintering

Cabouro-G; Chevalier-S; Gaffet-E; Vrel-D; Boudet-N; Bernard-F(Univ. de Bourgogne, Dijon, France)

Acta-Materialia. Oct. 2007; 55(18): 6051-63

The development and control of the mechanically activated spark plasma sintering (MASPS) process is the main objective to be achieved in producing bulk nano-organized materials with perfectly controlled composition and microstructure. Consequently, it was essential to develop original experiments, such as time resolved X-ray diffraction with the X-ray synchrotron beam (D2AM-BM2, ESRF Grenoble) coupled to IR thermography to monitor in situ structural and thermal evolution during the current-activated SHS sintering process in the Mo-Si system. A new sample holder was designed in order to reproduce the synthesis conditions of the MASPS process, obviously without the consolidation step. The versatility of the set-up and the new possibilities offered by the design of new sample holders allow a new interpretation of MoSi₂ formation mechanisms during current-activated SHS sintering.[All rights reserved Elsevier].

Hydrogen storage Mg₂Ni alloy produced by induction field activated combustion synthesis

Kodera-Y; Yamasaki-N; Yamamoto-T; Kawasaki-T; Ohyanagi-M; Munir-ZA(Ryukoku Univ., Ohtsu, Japan)

Journal-of-Alloys-and-Compounds. 31 Oct. 2007; 446-447: 138-41

It is difficult to obtain pure Mg₂Ni alloy by conventional melting method because of the large difference in vapor pressure and melting point between Mg and Ni. However, Mg₂Ni with high purity and fine properties as a hydrogen storage material was successfully synthesized from elemental Mg and Ni powders by Induction Field Activated Combustion Synthesis (IFACS). The IFACSed Mg₂Ni showed convenient hydrogen properties as same as the reference. The effect of Mechanical Grinding (MG) on the hydrogen storage behavior in Mg₂Ni is also described. The MG process developed the applicability of Mg₂Ni as a hydrogen storage material by decreasing the absorption pressures and enhancing the reaction kinetics.[All rights reserved Elsevier].

Hydriding combustion synthesis of TiFe

Saita-I; Sato-M; Uesugi-H; Akiyama-T(Hokkaido Univ., Sapporo, Japan)

Journal-of-Alloys-and-Compounds. 31 Oct. 2007; 446-447: 195-9

Titanium iron (TiFe) is one of the most attractive metal hydrides because of abundant and low cost raw materials and moderate conditions for hydrogenation and dehydrogenation; however, it has not been practically used due to time-consuming and energy-consuming activation treatment. Aiming to improve the initial activity of TiFe, we applied hydriding combustion synthesis (HCS), which has attractive advantages for the direct production of metal hydride; time saving, energy saving, and highly pure product that is highly hydrogenated and does not require the activation treatments for metal hydride production, to the TiFe production. In the experiments, hydrogen storage reaction of titanium (Ti + H₂ = TiH₂ + 144 KJ) was utilized for HCS of TiFe because the adiabatic flame temperature of this reaction was estimated to be 2000 degrees C, which is enough high for melting both iron and titanium. The raw material of Ti and Fe powders mixed with 1:1 molar ratio was covered with additional Ti powders from above and placed in hydrogen atmosphere. After the Ti powders were ignited by electrically heated carbon filament, the TiFe synthesis reaction (Ti + Fe = TiFe + 40 kJ) occurred successfully. The HCSed TiFe was activated easily and stored hydrogen approximately 1.7 mass% indicating improved initial activity for hydrogen storage.

Global reaction route mapping on potential energy surfaces of C₂H₇⁺ and C₃H₉⁺

Watanabe-Y; Maeda-S; Ohno-K(Tohoku Univ., Sendai, Japan)

Chemical-Physics-Letters. 15 Oct. 2007; 447(1-3): 21-26

Dissociation and isomerization channels of C₂H₇⁺ and C₃H₉⁺ have been globally explored by the scaled hypersphere search (SHS) method, which discloses reaction routes in an automatic way by following the anharmonic downward distortion on the potential energy surfaces. New structures have been discovered in addition to all of reported ones. Branching ratios leading to C₂H₅⁺+CH₄toC₃H₉⁺toC₃H₇⁺+H₂ have been calculated based on microcanonical rate constants of all transition state structures elucidated by the SHS method. Generation of cyclic C₃H₇⁺ has been predicted to be responsible for this reaction in a certain collision energy range. [All rights reserved Elsevier].

Hydrogen storage properties of Mg_100-xNi_x (x = 5, 11.3, 20, 25) composites prepared by hydriding combustion synthesis followed by mechanical milling (HCS + MM)

Xiaofeng-Liu; Yunfeng-Zhu; Liquan-Li(Nanjing Univ. of Technol., Nanjing, China)

Intermetallics-. Dec. 2007; 15(12): 1582-8

We reported the structure and the notable hydrogen storage properties of the composites Mg_100-xNi_x (x = 5, 11.3, 20, 25) prepared from metallic powder mixtures of magnesium and nickel by the process of HCS + MM, i.e., the hydriding combustion synthesis (HCS) followed by mechanical milling (MM). X-ray diffraction (XRD) and scanning electron microscopy (SEM) results demonstrated that mechanical milling led to drastic pulverization and grain refinement of the composite produced by HCS. All the composites with different compositions showed a remarkable decline in dehydriding temperature comparing with that of the hydride mixtures prepared only by HCS. Furthermore, the hydriding rates of these composites were excellent. At 313 K the composite Mg₈₀Ni₂₀ showed the highest hydrogen capacity of 2.77 wt.% within 600 s among these four composites. The Mg₉₅Ni₅ showed maximum capacity of 4.88 wt.% at 373 K and 5.41 wt.% at 473 K within only 100 s. Some factors contributing to the improvement in hydriding rates were discussed in this paper.[All rights reserved Elsevier].

Low-temperature auto-combustion synthesis and magnetic properties of cobalt ferrite nanopowder

Shun-Hua-Xiao; Wei-Fen-Jiang; Long-Yu-Li; Xin-Jian-Li(Zhengzhou Univ., Zhengzhou, China)

Materials-Chemistry-and-Physics. 15 Nov. 2007; 106(1): 82-7

Cobalt ferrite (CoFe₂O₄) nanopowder was prepared by a low-temperature, auto-combustion method. The thermal evolution of the precursor, as well as the microstructure, morphology and magnetic properties of as-synthesized powder were studied. The results revealed that the synthetic process was a thermally induced redox reaction with carboxyl group as reductant and NO _3-1 ions as oxidant. The grains observed in as-burnt powder were proved to be CoFe₂O₄ nanocrystallites with high dispersibility and low agglomeration. Both the saturation magnetization (Ms) and the remnant magnetization (Mr) were found to be highly depending upon the annealing temperature. The highest coercivity (1373 Oe) was achieved by the sample annealed at 400 degrees C. Our results indicate that this method might provide a promising option for synthesizing high-quality CoFe₂O₄ nanopowder. [All rights reserved Elsevier].

Nanostructured Nd:YAG powders via gel combustion: the influence of citrate-to-nitrate ratio

Jiang-Li; Yubai-Pan; Fagui-Qiu; Yusong-Wu; Jingkun-Guo(Chinese Acad. of Sci., Shanghai, China)

Ceramics-International. Jan. 2008; 34(1): 141-9

Nanostructured neodymium doped yttrium aluminum garnet (Nd:YAG) powders were synthesized at low temperature by a gel combustion method with citric acid as fuel and nitrate as oxidizer. The method involves exothermic decomposition of an aqueous citrate-nitrate gel. The decomposition is based on a thermally induced anionic redox reaction. A variety of 1.0 at% Nd:YAG powders with different agglomerate structures were obtained by altering the citrate-to-nitrate ratio gamma . The gel with gamma =0.277 yielded nanocrystalline Nd:YAG at 800 degrees C without the formation of any intermediate phase. For other gels nanostructured Nd:YAG powders were obtained at 850 degrees C. The gel with gamma =0.1 yielded nanostructured Nd:YAG powder with an average particle size of ~40 nm. The stoichiometric citrate-to-nitrate ratio ( gamma =0.277) gave the lowest amount of agglomeration. The decomposition of the gel was investigated by TG-DSC and FTIR. The produced ashes and calcined powders were characterized by XRD, BET and FETEM analysis.[All rights reserved Elsevier].

Activated combustion features in the Mo-Si-C-promoter system and synthesis of MoSi₂-SiC composite powders

Hambartsumyan-AA; Khachatryan-HL; Harutyunyan-AB; Kharatyan-SL(Nat. Acad. of Sci., Yerevan, Armenia)

Materials-Research-Bulletin. 4 Dec. 2007; 42(12): 2082-9

Opportunities on combustion synthesizing the MoSi₂-SiC ceramic composites in a wide range of compositions under the chemical activated mode were studied. Molybdenum, silicon powders and carbon black were used as initial reagents, and Teflon was used as an activating additive. It was established that Teflon displays a dual (kinetic and thermal) impact on the interaction between reagents. The phasic character of the combustion process evolution, being characterized by low- and high-temperature regimes, was revealed. The end-products were subjected to SEM, XRD and chemical analyses.[All rights reserved Elsevier].

Microstructural study of titanium carbonitride produced by combustion synthesis

Carole-D; Frety-N; Paris-S; Vrel-D; Bernard-F; Marin-Ayral-R-M(Univ. de Montpellier II, Montpellier, France)

Ceramics-International. Dec. 2007; 33(8): 1525-34

The self-propagating high-temperature synthesis (S.H.S.) process, which is promising for the fabrication of ceramic materials, was chosen to elaborate titanium carbonitride materials. The influence of parameters such as nitrogen gas pressure and carbon ratio on the microstructure was studied. A single phase product of Ti(C,N) is obtained for a carbon ratio under 15at.% and a nitrogen pressure of 36 MPa. The increase of the carbon ratio corresponds to a decrease of the maximum temperature reached during the synthesis. Time resolved X-ray diffraction measurements (TRXRD) with the synchrotron radiation were used to determine the reaction mechanisms. We could observe that the synthesis of Ti(C,N) is preceded by the formation of titanium nitride. This reaction is initiated by the allotropic transition of alpha -Ti phase into beta -Ti. In the final material the presence of sub-stoichiometric phases such as Ti₂N and alpha -Ti was observed.[All rights reserved Elsevier].

Synthesis and characterization of Ba₂YSbO₆ nanoparticles through a modified combustion process

Vijayakumar-C; Kumar-HP; Thomas-JK; Wariar-PRS; Koshy-J(Univ. Coll., Trivandrum, India)

Materials-Letters. Nov. 2007; 61(27): 4924-7

Nanoparticles of Yttrium Barium Antimonate (Ba₂YSbO₆), a complex perovskite ceramic oxide have been synthesized using an auto ignition combustion process for the first time. The particle size and properties of the nanocrystals have been characterized by X-ray diffraction, thermo gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The XRD studies have shown that the as-prepared powder is phase pure Ba₂YSbO₆ and has a complex cubic perovskite (A₂BB'O₆) crystalline structure with lattice constant a = 8.402 A. Transmission electron microscopy study has shown that the particle size of the as-prepared powder was in the range 20-50 nm. The nanocrystals of Ba₂YSbO₆ synthesized by the combustion technique could be sintered to 97% of the theoretical density at a temperature of 1550 degrees C for 4 h. The combustion synthesis has a definite advantage that the phase pure Ba2YSbO6 nanopowder could be obtained by a single step process without the need of a calcination step.[All rights reserved Elsevier].

Combustion synthesis and luminescent properties of a new material Li₂(Ba_0.99,Eu_0.01)SiO₄:B³⁺ for ultraviolet light emitting diodes

Shanshan-Yao; Donghua-Chen(South Central Univ. for Nat., Wuhan, China)

Optics-and-Laser-Technology. April 2008; 40(3): 466-71

Using urea as fuel and boric as flux, a novel bluish green emitting phosphor Li₂(Ba_0.99,Eu_0.01)SiO₄:B³⁺ has been successfully synthesized using a combustion method. The material has potential application as the fluorescent material for ultraviolet light-emitting diodes (UV-LEDs). The dependence of the properties of Li₂(Ba_0.99,Eu_0.01)SiO₄:B³⁺ phosphors upon urea concentration, boric acid doping and initiating combustion temperature were investigated. The crystallization and particle sizes of Li₂(Ba_0.99,Eu_0.01)SiO₄:B³⁺ have been investigated by using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Luminescence measurements showed that the phosphors can be efficiently excited by ultraviolet (UV) to visible region, emitting a bluish green light with peak wavelength of 490 nm. The results showed that the boric acid was effective in improving the luminescence intensity of Li₂(Ba_0.99,Eu_0.01)SiO₄ and the optimum molar ratio of boric acid to barium nitrate was about 0.06. The optimized phosphors Li₂(Ba_0.99,Eu_0.01)SiO₄:B³⁺_0.06 showed 160% improved emission intensity compared with that of the Li₂(Ba_0.99,Eu_0.01)SiO₄ phosphors under UV ( lambda _ex = 350 nm) excitation. [All rights reserved Elsevier].

Insights on the nanoparticle formation process in counterflow diffusion flames

Seung-Hyun-Chung; Violi-A(Michigan Univ., Ann Arbor, USA)

Carbon-. Oct. 2007; 45(12): 2400-10

This paper reports on a new version of the multiscale atomistic model for particle inception (AMPI) code to study the effect of oxidation on nanoparticle structures formed in counter-flow, propene diffusion flames. The code has been expanded with 158 new oxidation reactions and the potential for the Molecular Dynamics module has been expanded to describe systems containing C, H and O. The rate of nanoparticle mass growth is modeled in two different flame configurations to address the influence of combustion environments on the inception process. In the case of high temperature and abundant radicals, the AMPI code successfully predicts the nanoparticle formation. In these conditions, the particle loading is mainly associated with the formation of high-molecular structures through polymerization reactions. In the case of low temperature and high polycyclic aromatic hydrocarbons (PAH) concentrations, the combined mechanism of chemical reactions described by the AMPI code and coagulation of PAH and nanoparticles contribute to particle growth. Structural properties of the particles, such as aspect ratio, oxygen content and H/C ratio are computed in the two configurations. [All rights reserved Elsevier].

PTFE, an effective additive on the combustion synthesis of silicon nitride

Yixiang-Chen; Zhiming-Lin; Jiangtao-Li; Jisheng-Du; Shuliang-Yang(Chinese Acad. of Sci., Beijing, China)

Journal-of-the-European-Ceramic-Society. 2008; 28(1): 289-93

Combustion synthesis (CS) of Si₃N₄ with the addition of polytetrafluoroethylene (PTFE) was carried out at a relatively low N₂ pressure of 2 MPa. It was found that the additive PTFE promoted the nitridation of Si. The alpha -Si₃N₄ contents in the periphery of the combustion-synthesized products showed great dependence on the contents of PTFE added in the reactants, which reached 77.7wt.% with 4wt.% PTFE addition. The residual silicon in the center of the combustion-synthesized products could be completely nitrided by further heat treatment at 1300 degrees C for 1 h in N₂. The temperature difference between the center and the edge of the samples was responsible for the discrepancy in both phase composition and morphology of the products. [All rights reserved Elsevier].

Reaction chemistry during self-propagating high-temperature synthesis (SHS) of H₃BO₃-ZrO₂-Mg system

Khanra-AK(IIT, Kharagpur, India)

Materials-Research-Bulletin. 4 Dec. 2007; 42(12): 2224-9

In the present investigation, the ZrB₂ powder is produced by SHS of mixture containing H₃BO₃, ZrO₂ and Mg. The thermal analysis and XRD study reveal the reaction mechanism of ZrB₂ formation by SHS process. Synthesis of H₃BO₃-Mg system results in formation of Mg₃(BO₃)₂ and MgB₄ phases, whereas ZrO₂ is partially reduced to Zr₃O and Zr during synthesis of ZrO₂-Mg system. The reaction between elemental Zr and MgB₄ results in ZrB₂ formation. The particle size of ZrB₂ is found to decrease with the addition of SHS diluent.[All rights reserved Elsevier].

Magnetic properties of nanosize NiFe₂O₄ particles synthesized by sol-gel auto combustion method

Azadmanjiri-J; Seyyed-Ebrahimi-SA; Salehani-HK(Islamic Azad Univ., Damavand, Iran)

Ceramics-International. Dec. 2007; 33(8): 1623-5

A nitrate-citrate gel was prepared from metal nitrates and citric acid by sol-gel auto combustion process, in order to synthesize NiFe₂O₄ ferrite. X-ray diffraction showed the formation of NiFe₂O₄ and the inclusion of alpha -Fe₂O₃. However, with increasing the calcination temperature, this inclusion phase ( alpha -Fe₂O₃) decreased. TEM was also used to characterize the microstructure of the nanosize NiFe₂O₄. Magnetization hysteresis of the nickel ferrite powders was performed at room temperature. It is shown that this powder which is composed of crystalline NiFe₂O₄ monophase, exhibited M_s = 54 (emu/g) at magnetic field of 2 (kOe). [All rights reserved Elsevier].

Effect of citric acid on the synthesis of nano-crystalline yttria stabilized zirconia powders by nitrate-citrate process

Singh-KA; Pathak-LC; Roy-SK(Indian Inst. of Technol., Kharagpur, India)

Ceramics-International. Dec. 2007; 33(8): 1463-8

The role of citric acid on the preparation of nano-crystalline cubic YSZ powder using a citrate-nitrate solution combustion technique is reported. Thermo-gravimetric analyses reveal that the exothermic peak of nitrate-citrate redox reaction disappears with the increase in citric acid content. The crystallite size of the cubic YSZ powder initially increases with the increase in citric acid content and then decreases upon further addition of citric acid. Particle coarsening has been found to significantly increase upon increase in calcination temperature from 650 degrees C (11.1 nm) to 800 degrees C (65.3 nm). Transmission electron microscopic studies in conjunction with XRD analyses indicate a low degree of agglomeration in the synthesized powder. Microwave heating of the solution can control the particle size and yield c-YSZ powder having sizes ~15 nm. [All rights reserved Elsevier].

Resistive lambda -sensors based on ball milled Fe-doped SrTiO₃ nanopowders obtained by self-propagating high-temperature synthesis (SHS)

Neri-G; Bonavita-A; Micali-G; Rizzo-G; Licheri-R; Orru-R; Cao-G(Univ. of Messina, Messina, Italy)

Sensors-and-Actuators:-B-Chemical. 20 Sept. 2007; 126(1): 258-65

A series of SrTi₁-_xFe_xO_3- delta (STO or STFO) powders, with x ranging from 0 to 0.6, were prepared by self-propagating high-temperature synthesis (SHS) starting from SrO₂, Ti, TiO₂ and Fe. A ball-milling (BM) treatment was subsequently carried out for further structure refinement and size reduction. Morphological and microstructural characteristics of both untreated and ball-milled SHS samples were investigated by SEM and XRD. Screen-printed SrTi₁-_xFe_xO_{3- delta} SHS powders on alumina substrate were investigated for resistive oxygen sensors operating at high operating temperature (450-650 degrees C). STFO powders have shown better performances with respect to the corresponding undoped STO ones. Moreover, when STFO powders were subjected to BM treatment, both temperature-independent resistance characteristics and sensor response greatly improved. On the basis of the reported data, it can be suggested that the ball milling treatment likely acts: (i) stabilizing the formation of non-equilibrium structures; (ii) decreasing the particle size, increasing surface defects and hence surface reactivity; (iii) favouring the substitution of titanium by iron in the SrTiO₃ perovskite structure.[All rights reserved Elsevier].

Synthesis of cobalt ferrite nanoparticles using combustion waves

de-Biasi-RS; Figueiredo-ABS; Fernandes-AAR; Larica-C(Instituto Militar de Engenharia, Rio de Janeiro, Brazil)

Solid-State-Communications. Oct. 2007; 144(1-2): 15-17

Nanocrystalline particles of cobalt ferrite (CoFe₂O₄) were prepared by a combustion wave method, based on the self-propagating high temperature synthesis technique (SHS), using iron nitrate, Fe(NO₃)₃9H₂O, cobalt nitrate, Co(NO₃)₂6H₂O, and glycine, C₂H₅NO₂. The average particle size, determined by means of X-ray diffraction, was found to depend on the glycine-nitrate ratio and varied between 2.7 and 17 nm. By measuring at several temperatures the relative intensity of the Mossbauer spectra due to superparamagnetic particles and to ferrimagnetic particles, we determined the size distribution of the nanoparticles in one of the samples. It was found to be a log-normal distribution with a most probable diameter D_m=1.8 nm and a full width at half-height Delta D=2.6 nm.[All rights reserved Elsevier].

Mechanism of the high activity of Mg₂NiH₄ produced by hydriding combustion synthesis based on the analysis of phase composition, particle characteristic and grain size

Dongming-Liu; Yunfeng-Zhu; Liquan-Li(Nanjing Univ. of Technol., Nanjing, China)

International-Journal-of-Hydrogen-Energy. Sept. 2007; 32(13): 2455-60

Hydriding combustion synthesis (HCS) is well known as an innovative processing to produce magnesium-based hydrogen storage alloys, and the product Mg₂NiH₄, as synthesized, possesses excellent activity without any activation process. In this paper, the mechanism of the high activity of Mg₂NiH₄ produced by HCS emphasized mainly on microstructure is discussed based on the analysis of phase composition, particle characteristic, crystal grain size and hydriding reaction by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and pressure composition temperature (PCT). It is indicated that pure composition, loose and porous morphology, a large number of microfissures and small grain size are the intrinsic reasons for the high activity of Mg₂NiH₄ produced by the process of HCS. The result is very helpful for us to control and improve the hydrogen storage properties of HCS product based on the microstructure further. [All rights reserved Elsevier].

Hydriding characteristics of Mg₂Ni prepared by mechanical milling of the product of hydriding combustion synthesis

Xiaofeng-Liu; Yunfeng-Zhu; Liquan-Li(Nanjing Univ. of Technol., Nanjing, China)

International-Journal-of-Hydrogen-Energy. Sept. 2007; 32(13): 2450-4

Hydriding combustion synthesis (HCS) and mechanical milling (MM) are both well-known methods for production of magnesium-based hydrogen storage alloys. The former can produce high active hydride by a simple process, and the latter can synthesis various metastable hydrogen storage materials such as nanocrystalline, amorphous and extended solid solutions phases with excellent hydrogen sorption properties. In the present study, HCS and MM were combined, aiming to decrease sorption temperature for Mg₂Ni . The high active Mg₂NiH₄, synthesized by HCS, was mechanically milled for 0.5, 6, 40 and 80h with 5wt% of graphite under argon atmosphere. The effect of the milling process on the morphology and crystal structural of Mg₂NiH₄ were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The hydrogen storage properties were examined by a Sieverts type apparatus. The nanocrystalline Mg₂NiH₄ milled for 40h has the best sorption kinetics, which can absorb 2.4wt% hydrogen at 303K within 100s in the first cycle. Several reasons are considered to explain the improvement in hydriding kinetics.[All rights reserved Elsevier].

Crystal defect analysis and surface characteristics of Mg₂NiH₄ produced by hydriding combustion synthesis

Dongming-Liu; Yunfeng-Zhu; Liquan-Li(Nanjing Univ. of Technol., Nanjing, China)

International-Journal-of-Hydrogen-Energy. Sept. 2007; 32(13): 2417-21

The mechanism of the high activity of Mg₂NiH₄ produced by the process of hydriding combustion synthesis (HCS) was discussed for the first time based mainly on the crystal defects and surface characteristics examined by means of high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). A large number of crystal defects (lattice distortions, dislocations, stacking faults and microtwins) observed in the as-dehydrogenated product of Mg₂NiH₄ and an outmost layer of Mg(OH)₂, instead of MgO determined on the surface of the as-synthesized Mg₂NiH₄, as well as a large amount of fresh surfaces in Mg₂Ni particles that was generated in the dehydriding process of the as-synthesized Mg₂NiH₄ prior to the first hydrogenation were revealed and considered as the intrinsic reasons contributing to the high activity of Mg₂NiH₄ produced by the process of HCS. These results are helpful to control and improve the hydrogen storage properties of the HCS product further.[All rights reserved Elsevier].

A novel combustion method to prepare tetrapod nano-ZnO

Liang-Chen; Wulin-Song; Changsheng-Xie; Lufeng-Lin; Jianguo-Wang(Huazhong Univ. of Sci. & Technol., Wuhan, China)

Materials-Letters. Sept. 2007; 61(23-24): 4603-5

Tetrapod nano-ZnO was prepared based on a novel combustion method: melting-combustion method (MCM). Industrial pure zinc was melted and then ignited by the flame of acetylene and oxygen gas mixture at a proper ratio. Nano-ZnO was obtained by condensation of the combusting product, and then was examined by XRD showing that the production was pure zinc oxide without other impurities. FESEM, TEM and HRTEM were used to characterize the structure features and appearance of the product. The results showed that the zinc oxide was largely tetrapod of 20-30 nm in diameter and 200-300 nm long in the four legs and a bottleneck phenomenon was also observed on several legs. Based on these analyses, growth mechanism was further discussed. [All rights reserved Elsevier].

Solution combustion synthesized oxygen carriers for chemical looping combustion

Erri-P; Varma-A(Purdue Univ., West Lafayette, USA)

Chemical-Engineering-Science. Sept.-Oct. 2007; 62(18-20): 5682-7

Chemical looping combustion is an attractive method for CO₂ capture in power plants, while maintaining high energy efficiency. The cyclic nature of the process, however, places significant demands on the redox and mechanical characteristics of the oxygen carrier. In this work, NiO/NiAl₂O₄ and (NiO)_1-y(MgO)_y/Ni(_1-x)Mg_xAl₂O₄ were synthesized by solution combustion and investigated in two forms: porous extruded and dense pressed pellets. The pressed oxygen carriers of both compositions exhibited excellent stability during thermogravimetric analysis at temperatures 800-1200 degrees C with cycling of oxidizing/reducing gases while, due to sintering effects, the extruded pellets showed deteriorating performance. The addition of magnesium to the structure decreased reduction of the spinel, thus stabilizing the support. Attrition tests revealed superior performance of the (NiO)_0.21(MgO)_0.79/Ni_0.62Mg_0.38Al₂O₄, exceeding that of commercially available sintered iron oxide reference. [All rights reserved Elsevier].

Preparation and regeneration of a catalytic diesel particulate filter

Cauda-E; Fino-D; Saracco-G; Specchia-V(Politecnico di Torino, Torino, Italy)

Chemical-Engineering-Science. Sept.-Oct. 2007; 62(18-20): 5182-5

A 1% Pt on CeO₂-promoted PrCrO₃ perovskite catalyst has been synthesized over a wall-flow monolith by the in situ solution combustion synthesis (SCS) method. The role of the catalyst, highly active towards diesel particulate combustion, has been studied during the regeneration phase as a function of the inlet trap temperature at which the regeneration is induced. The final aim of this study is to improve the knowledge on the catalytic regeneration process, with reference to the main operating parameters, in order to optimize the fuel penalties during the regeneration and to minimize the CO₂ emissions added by the post-injection and combustion of fuel. [All rights reserved Elsevier].

Feasibility study on the controlled hydriding combustion synthesis of Mg-La-Ni ternary hydrogen storage composite

Qian-Li; Xiong-Gang-Lu; Kuo-Chih-Chou; Kuang-Di-Xu; Jie-Yu-Zhang; Shuang-Lin-Chen(Shanghai Univ., Shanghai, China)

International-Journal-of-Hydrogen-Energy. Aug. 2007; 32(12): 1875-84

The feasibility of using the controlled hydriding combustion synthesis (CHCS) under a high magnetic field to prepare the Mg-La-Ni ternary hydrogen storage alloys was studied. Comparison was made between the conventional hydriding combustion synthesis (HCS) and the CHCS. The influence of a high magnetic field on the physicochemical properties (thermodynamic and kinetic characteristics, hydrogen absorption/desorption (A/D) properties, thermal behavior, phase composition and morphology) of the Mg-La-Ni composite was analyzed and the results suggested that a high magnetic field can change the microstructure and phase compositions, decrease the hydriding/dehydriding (H/D) temperature and the particle size of the composite, and increase the H/D rates. Based on this study, the lower-temperature metal hydrides prepared by CHCS seem to be technically feasible for lab-scale and it could represent a possible and attractive alternative to prepare the hydrogen storage materials.[All rights reserved Elsevier].

Lithium battery properties of LiNi_0.5Mn_1.5O₄ powders synthesized by internal combustion type spray pyrolysis apparatus using gas burner

Mukoyama-I; Myoujin-K; Nakamura-T; Ozawa-H; Ogihara-T; Uede-M(Univ. of Fukui, Fukui, Japan)

Key-Engineering-Materials. 2007; 350: 191-4

Spherical LiNi_0.5Mn_1.5O₄ powders were prepared by internal combustion type spray pyrolysis apparatus using gas burner. The powder production capacity was 1 kg/h by this equipment. After calcinations of as-prepared powders contained Ni at different temperatures from 800 to 1200 degrees C in air for 10h, LiNi_0.5Mn_1.5O₄ powders were obtained. As-prepared particles have a porous microstructure with an average diameter of about 5 mu m with narrow size distribution. XRD showed that LiNi_0.5Mn_1.5O₄ powders were well crystallized to a spinel structure with Fd3 m space group. LiNi_0.5Mn_1.5O₄ powders calcined at 1000 degrees C show good cycle performance with after 30 cycles discharge capacity of 112 mAh/g and 95% retention after 400 cycles between 3.5 V and 5 V.

Up-conversion in Yb,Er-doped Y₂O₃ nanoparticles for cell imaging

Bessiere-A; Pelle-F; Mathieuu-C; Viana-B; Vermaut-P(CNRS UMR7574, Paris, France)

Materials-Science-Forum. Sept. 2006; 555: 383-8

Y₂O₃:19%Yb,1%Er nanoparticles were synthesized with the aim of imaging the luminescent cell. Coprecipitation and combustion synthesis were used to obtain particulate sizes ranging from 25 up to 140 nm. The powders showed predominant red upconversion and the emission efficiency is controlled by the particle size. A colloidal route was also followed and 2-5 nm-large agglomerated nanoparticles were obtained. In that case, the luminescence of Er³⁺ was only observed by direct excitation and no upconversion tight has been detected on these very small particles.

Oxygen-release/storage properties of Ce_0.5M_0.5O₂ (M = Zr, Hf) oxides: interplay of crystal chemistry and electronic structure

Baidya-T; Hegde-MS; Gopalakrishnan-J(Indian Inst. of Sci., Bangalore, India)

Journal-of-Physical-Chemistry-B. 17 May 2007; 111(19): 5149-54

Fluorite-type Ce_0.5Zr_0.5O₂ and Ce_0.5Hf_0.5O₂ have been synthesized by a solution combustion route, and their oxygen release and reduction have been investigated up to 850 degrees C. On reduction, the zirconium system forms two pyrochlore phases, Ce₂Zr₂O₇ (pyrochlore-I) and Ce₂Zr₂O_6.2 (pyrochlore-II), while the hafnium system forms only a disordered fluorite phase with the composition Ce_0.5Hf_0.5O_1.77, under the same experimental conditions. The crystal structures of the reduction products have been characterized by powder X-ray diffraction and Rietveld refinement, and their electronic structures have been investigated by photoelectron spectroscopy and electrical conductivity measurements. Pyrochlore-I (a = 10.6727(4) A) is a semiconductor, while pyrochlore-II (a = 10.6463(8) A) is a good conductor (with a nearly temperature independent resistivity of ~2.5 ohmcm in the 400-1000 K range). X-ray photoelectron spectroscopy (XPS) shows an admixture of Ce(5d,6s) with Zr(4d) and O(2p) and a significant density of states near E_F in the highly reduced pyrochlore-II phase. The changes have been rationalized in terms of a qualitative energy band scheme that brings out the special role of zirconium vis-a-vis hafnium in the reduction/oxygen release properties of Ce_0.5Zr_0.5O₂ and Ce_0.5Hf_0.5O₂.

Simulation of Fe₂O₃/Al combustion: sensitivity analysis

Brito-P; Duraes-L; Campos-J; Portugal-A(Sch. of Technol. & Manage., Braganca, Portugal)

Chemical-Engineering-Science. Sept.-Oct. 2007; 62(18-20): 5078-5083

The sensitivity of a one-dimensional model, built to simulate the non-steady radial combustion propagation on thin circular samples of Fe₂O₃/aluminium thermite mixtures, was tested in relation to its least reliable thermophysical properties and to non-homogeneities in the initial reactant media. Zero order kinetics and conductive/radiative heat transfer were considered. The model is quite insensitive to variations of most of the properties studied. The highest sensitivity detected concerned aluminium conductivity. The non-uniform reactant mixing significantly affected the results, suggesting that experimental variability is partially explained by this feature.[All rights reserved Elsevier].

Photoluminescence and structural characteristics of Lu₂O₃:Eu³⁺ nanocrystallites in silica matrix

Sokolnicki-J(Univ. of Wrocław, Wroclaw, Poland)

Journal-of-Solid-State-Chemistry. Aug. 2007; 180(8): 2400-8

Two silica ceramics were obtained by mixing nanocrystalline Lu₂O₃:Eu³⁺ with silica sol using the sol-gel technique. The synthesis procedure for both samples differed in the pH of the sol and time of the sol condensation before substrates were mixed together, which implied their different optical properties. The first one has the same spectroscopic properties as Lu₂O₃:Eu³⁺ nanocrystallites with an exception of small lowering of the charge transfer (CT) band intensity. This feature is preserved up to about 950 degrees C. Above this temperature, nanocrystallites of Lu₂O₃:Eu³⁺ react with the silica matrix synthesis pyrosilicate (Lu₂Si₂O₇). The Eu³⁺ ions occupy only one crystallographic site in the crystal lattice for low concentration of the activator (1%) and two sites for higher concentration (10%). The second sample exhibits different Eu³⁺ emission than Lu₂O₃:Eu³⁺ nanocrystallites and, additionally, a broad band of the matrix originating at the green region of the spectrum. Sintering the sample at higher temperatures leads to disappearance of this broad emission and continuous changes of the Eu³⁺ emission because of the progressive conversion of the Lu₂O₃:Eu³⁺ to pyrosilicate. At 1300 degrees C for both samples, the reaction of synthesis lutetium pyrosilicate is completed. Structural characteristic of the samples is presented and correlate with the decay profile of the Eu³⁺ emission.The combination of the solution combustion synthesis and the sol-gel technique allows to obtain a silica ceramic containing nanocrystalline Lu₂O₃:Eu³⁺. The sample treated in temperatures up to 950 degrees C exhibits almost the same optical properties as compared to nanocrystalline Lu₂O₃:Eu³⁺. The material displays effective red emission under X-ray excitation and no afterglow, and is very promising phosphor for X-ray imaging. At 1300 degrees C, nanocrystalline Lu₂O₃:Eu³⁺ is converted to lutetium pyrosilicate, Lu₂Si₂O₇:Eu³⁺. Its overall optical performance makes them a good candidate for a cathode-ray phosphor. [All rights reserved Elsevier].

FEM analysis of conventional and square bird-beak SHS joint subject to in-plane bending moment - experimental study

Christitsas-AD; Pachoumis-DT; Kalfas-CN; Galoussis-EG(Democritus Univ. of Thrace, Xanthi, Greece)

Journal-of-Constructional-Steel-Research. Oct. 2007; 63(10): 1361-72

This paper presents the results of an experimental study of square hollow section joints subject to in-plane bending moment. A theoretical model of an X-type traditional joint and the same one with the chord rotated through 45 degrees about its longitudinal axis is considered. Models are analysed with the finite element method and the results are compared with those obtained from the experimental study. The geometry, the material and the overall parameters concerned are in agreement with the general requirements of the EC3. A classification of joints due to their stiffness and M- phi diagram is examined according to the last CIDECT guide No. 9 and Part 1.8 of EC3. The results showed that EC3 underestimates the design resistance of the conventional joints about 50%-70% and joints with beta to0.5 according to the rotational stiffness are classified almost as pinned while those with beta to1.0 react as semi-rigid connections. Chord orientation showed that has a very important effect in joints with beta <0.85 and increases their strength up to double when beta to0.50. In this same area for ratio beta , connections react as rigid while for beta to1.0 they have strength almost equal to the conventional ones and behave as semi-rigid connections. [All rights reserved Elsevier].

A new method for estimating insolation based on PV-module currents in a cluster of stand-alone solar systems

Nieuwenhout-F; van-der-Borg-N; van-Sark-W; Turkenburg-W(Energy Res. Centre of the Netherlands, Petten, Netherlands)

Progress-in-Photovoltaics:-Research-and-Applications. Aug. 2007; 15(5): 387-404

In order to evaluate the performance of solar home systems (SHSs), data on local insolation is a prerequisite. We present a new method to estimate insolation if direct measurements are unavailable. This method comprises estimation of daily irradiation by correlating photovoltaic (PV) module currents from a number of SHSs, located a few kilometres apart. The method was tested with a 3-year time series for nine SHS in a remote area in Indonesia. Verification with reference cell measurements over a 2-month period showed that our method could determine average daily irradiation with a mean bias error of 1-3%. Daily irradiation figures showed a standard error of 5%. The systematic error in this method is estimated to be around 10%. Especially if calibration with measurements during a short period is possible, the proposed method provides more accurate monthly insolation figures compared with the readily available satellite data from the NASA SSE database. An advantage of the proposed method over satellite data is that irradiation figures can be calculated on a daily basis, while the SSE database only provides monthly averages. It is concluded that the new method is a valuable tool to obtain information on insolation when long-term measurements are absent.

Nanostructured La(Sr)CrO₃ through gel combustion: sintering and electrical behavior

Nair-SR; Purohit-RD; Sinha-PK; Tyagi-AK(Bhabha Atomic Res. Centre, Mumbai, India)

Journal-of-Nanoscience-and-Nanotechnology. Aug. 2007; 7(8): 2904-8

Nanostructured La(Sr)CrO₃ (LSC) powders was prepared through glycine-nitrate gel combustion process. It was shown for the first time that the use of relatively inexpensive CrO₃ as a starting material for chromium has a potential for the bulk preparation of sinter-active LSC powder. As- prepared powder when calcined at 700 degrees C resulted in LSC along with a small amount of SrCrO₄ as a secondary phase. The powder was found to be composed of soft agglomerates with a particle size of approximately=70-270 nm. The average agglomerate size was found to be 0.95 mu m. The cold pressing and sintering of the LSC powder at 1450 degrees C resulted in mono-phasic La_0.8Sr_0.2CrO₃ with 94% of its theoretical density. This is the lowest sintering temperature ever reported for La_0.8Sr_0.2CrO₃. The conductivity of the sintered La_0.8Sr_0.2CrO₃ at 1000 degrees C was found to be approximately=18 S cm^-1.

Improved properties of SrFe₁₂O₁₉ synthesised by gel self-propagating combustion technique with glycol as solvent

Pan-XF; Mu-GH; Chen-N; Gan-KK; Yang-K; Gu-MY(Shanghai Jiaotong Univ., Shanghai, China)

Materials-Science-and-Technology. 2007; 23(7): 865-8

In this work SrFe₁₂O₁₉ is synthesised by gel self-propagating combustion technique with glycol as solvent. The morphology, crystal structure and magnetic properties of the as fabricated powders are investigated with X-ray diffraction, field emission scanning electron microscopy, thermo- gravimetric analysis/differential scanning calorimetry and vibrating sample magnetometry. The results show that the coercivity and specific saturation magnetisation of the as fabricated SrFe₁₂O₁₉ are increased to 528 kA m^-1 and 59-6 EMU g^-1, in comparison with 404 kA m^-1 and 57-6 EMU g^-1 using water as solvent. The 528 kA m^-1 is the highest Hc value recorded for isotropic SrFe₁₂O₁₉.

Effect of C/Ti ratio on the laser ignited self-propagating high-temperature synthesis reaction of Al-Ti-C system for fabricating TiC/Al composites

Li-YX; Hu-JD; Liu-YH; Yang-Y; Guo-ZX(Jilin Univ., Changchun, China)

Materials-Letters. Sept. 2007; 61(22): 4366-9

TiC/Al composite was successfully synthesized utilizing laser ignited self-propagating high-temperature synthesis (SHS) of Al-C-Ti system with the different C/Ti molar ratio. When the molar ratio of C to Ti is below 1:1 in the starting materials, in addition to fine TiC particulates, a large amount of Al₃Ti phase was found in the composites; however, when the molar ratio of C to Ti is 1:1 in the starting materials, the Al₃Ti phase was almost completely eliminated and the distribution of TiC particulates generally appeared to be more homogeneous throughout the products synthesized. [All rights reserved Elsevier].

The magnetic properties of strontium hexaferrites with La-Cu substitution prepared by SHS method

Liang-Qiao; Lishun-You; Jingwu-Zheng; Liqiang-Jiang; Jiawei-Sheng(Zhejiang Univ. of Technol., Hangzhou, China)

Journal-of-Magnetism-and-Magnetic-Materials. Nov. 2007; 318(1-2): 74-8

La-Cu substituted strontium hexaferrites with the chemical composition of Sr_1-xLa_xFe_12-xCu_xO₁₉ were prepared by self-propagating high-temperature synthesis. The effects of La-Cu substitution on the microstructure and magnetic properties of Sr-ferrites were studied. The XRD results show that all the samples are single SrM-type phase for x<0.4. Compared with the samples without La-Cu substitution, the magnetic properties of the samples with the composition of Sr_1-xLa_xFe_12-xCu_xO₁₉ are remarkably improved for x<0.4. The possibility that the substitution of Sr²⁺ by La³⁺ in the Sr-layer makes the Cu²⁺ preferably substitutes the Fe³⁺ in 4f₂ sites is predicted to be associated with the improvement of the magnetic properties of La-Cu substituted samples.[All rights reserved Elsevier].

Cr_2-xTi_xO₃ (x0.5) as CH₃COCH₃ sensitive resistors

Pokhrel-S; Yang-Ming; Lihua-Huo; Hui-Zhao; Shan-Gao(Heilongjiang Univ., Harbin, China)

SENSORS-AND-ACTUATORS-B:-CHEMICAL. 8 Aug. 2007; 125(2): 550-5

Fine powders of Cr_2-xTi_xO₃ (x=0-0.5, CTO) were prepared by combustion technique, followed by heat treatment at 1000 degrees C in ambient air. The XRD results showed the presence of a solid solution of TiO₂ in Cr₂O₃ as the major phase along with CrTiO₃ as the minor phase for x0.4. EDAX studies on Cr_2-xTi_xO₃ (x=0.1 and 0.3) suggested the composition of the oxides close to the theoretical values. The XPS studies showed the presence of Cr³⁺ and Ti⁴⁺species on the surface. Ti⁴⁺ inclusion in the eskolait Cr₂O₃ had significant influence on the activation energy for conduction (E_a) at 100-700 degrees C in air. The commercial Taguchi sensors coated with CTO, when subjected to acetone in ambient air, showed an abrupt change in resistance within 10s and took the same time for recovery at 400 degrees C. Different humidity levels were achieved by various water vapor buffers thermostated at room temperature where sensor response decreased nearly by 40% at 80% RH. The stability test indicated the first order exponential decay to a constant sensor potential value of 4.7. The origin of the gas response was attributed to the surface reaction of (CH₃)₂CO to form an intermediate geminal diol, followed by formation of an unstable ethanoyl radical and then final product CH₃COOH, which was desorbed as a gas at 400 degrees C.[All rights reserved Elsevier].

Porosity development in carbons derived from scrap automobile tires

Suuberg-EM; Aarna-I(Brown Univ., Providence, USA)

Carbon-. Aug. 2007; 45(9): 1719-26

The problem of disposal of scrap automotive tires has led to many investigations of possible processes leading to high value added products, including those yielding activated carbons. This study examines the porous nature of such carbons, and how it develops under oxidizing conditions that model "physical activation" or combustion types of conditions. The characterization of porosity is based upon information obtained from nitrogen and carbon dioxide adsorption isotherms. Up to a certain degree of conversion, remarkably similar patterns of porosity development are seen during burnoff in oxygen, carbon dioxide and nitric oxide, but this gives way to more unique behaviors in the different gases at high conversions. The implication is that there is imprinted during pyrolysis a certain pattern of porosity development that is initially followed, regardless of activation conditions (within the intrinsic chemical reaction rate controlled regime), but that this gradually gives way to development that is more heavily dictated by particular reaction conditions. [All rights reserved Elsevier].

Photoluminescence characteristics of pure and Dy-doped ZnNb₂O₆ nanoparticles prepared by a combustion method

Yuanyuan-Zhou; Zifeng-Qiu; Mengkai-Lu; Qian-Ma; Aiyu-Zhang; Guangjun-Zhou; Haiping-Zhang; Zhongsen-Yang(Shandong Univ., Jinan, China)

Journal-of-Physical-Chemistry-C. July 2007; 111(28): 10190-3

Pure and Dy-doped ZnNb₂O₆ nanoparticles have been prepared by a sol-gel combustion method using citric acid as a fuel and complexing agent and nitrates as oxidants at a relatively low temperature as compared to solid-state reaction methods. X-ray diffraction patterns of the pure ZnNb₂O₆ samples show that the ZnNb₂O₆ nanoparticles exhibit an orthorhombic phase. Photoluminescence (PL) properties of all the undoped and Dy-doped samples are studied in detail. For the pure ZnNb₂O₆ samples, a strong blue emission band centered at 445 nm and two weak emission bands centered at 525 and 625 nm, respectively, can be observed. For Dy- doped ZnNb₂O₆ samples, the luminescence of Dy³⁺ is observed with the host blue emission remaining and the host emission intensity varying with the Dy-doping concentrations. This novel PL characteristic of the doped samples may be attributed to the energy transfer between Dy³⁺ and niobate groups (NbO₂).

Technology parameters of ultra-fine beta -SiC powder by combustion synthesis

Zhang-Lifeng; Yan-Qingzhi; Shen-Weiping; GE-Changchun(Univ. of Sci. and Technol. Beijing, Beijing, China)

Journal-of-the-Chinese-Ceramic-Society. July 2007; 35(7): 817-21

Ultra-fine beta -SiC powder has been obtained by two methods, direct combustion synthesis and preheating combustion synthesis, in nitrogen atmosphere using Si, carbon, activated carbon as raw materials and teflon (-C₂F₄-)_n as additive. The crystallites of combustion products measured by a scanning electron microscopy showed that they are global and the average diameters are about 100 nm. Pure and ultra-fine beta -SiC powders can be obtained on direct combustion when the mass fraction(the same below) of additive is more than 5%. The theoretic preheating-temperature can decrease from 1 023 K to 673 K by decreasing the amount of additive to 2% and thus saving the cost. The same time, using activated carbon as substitution of carbon, the effect on combustion products of two batches of mole ratio of Si to active C with 1:1 and 1:1.25 was compared, it illustrated that the substitution of purer active C for carbon as raw material in preparing the beta -SiC is possible. Three methods of preheating combustion synthesis, combustion synthesis in nitrogen atmosphere and chemical stimulation combustion synthesis were successfully combined, and the material introduce from pressed block to powdery spread, the ultra-fine beta -SiC powders were fabricated through combustion synthesis in 60 L reactor with a single load of more than 1 kg materials. It makes the needs of pilot-plant.

Microstructure evolution of Fe-Ti-C system synthesized by low temperature combustion induced in electric field

Feng-Keqin; Bai-Chenguang; Yang-Yi(Chongqing Univ., Chongqing, China)

Rare-Metal-Materials-and-Engineering. 2007; 36(6): 1020-3

The microstructure evolution of Fe-Ti-C system synthesized by low temperature combustion in electric field was studied using the mixture powders compacts of 55 wt%(Ti+C)-45 wt%Fe heated to 250~800 degrees C by an analytical experiment of Gleeble-1500D thermal simulation equipment. The results show that the ignition temperature of Fe-Ti-C system can be greatly decreased under the action of electric field and high thermal density. Firstly, the microstructure changes with the heating temperature from 250 degrees C to 350 degrees C although no reaction occurred in the system. The system can be ignited so that the phenomenon of "thermal explosion" occurred from 350 degrees C to 470 degrees C, with a prior TiC synthesis reaction. As the temperature increased continuously from 470 degrees C to 670 degrees C, the TiC synthesis reaction followed by another Fe₂Ti synthesis reaction. But a part of Fe₂Ti can be decompounded when heated to 670~800 degrees C, so that the TiC synthesis reaction went on and finished completely at 800 degrees C. As a result, the synthesized products consisted of Fe, TiC and a little of Fe₂Ti. In addition, the microstructure showed that fine TiC spherical particles were uniformly distributed in the Fe matrix.

Comparison of carbon monoxide emissions and electricity consumption of modulating and non-modulating pellet and solar heating systems

Fiedler-F; Bales-C; Persson-T; Nordlander-S(Dalarna Univ. Coll., Borlange, Sweden)

International-Journal-of-Energy-Research. Aug. 2007; 31(10): 915-30

Emission and electricity consumption are important aspects of a pellet heating system. Low noxious emissions, particularly carbon monoxide, are a measure of a well-performing system. High carbon monoxide emissions are often caused by unnecessary cycling of the burner, poor adjustment of the combustion air and insufficient maintenance. The carbon monoxide output, the thermal performance and the electricity consumption for modulating and non-modulating operation mode have been investigated by simulations of four stoves/boilers as part of combined solar and pellet heating systems. The systems have been modelled with the simulation programme TRNSYS and simulated with the boundary conditions for space heating demand, hot water load and climate data as used in earlier research projects. The results from the simulations show that operating the pellet units with modulating combustion power reduces the number of starts and stops but does not necessarily reduce the carbon monoxide output. Whether the carbon monoxide output can be reduced or not, it depends very strongly on the reduction of starts and stops and how much the carbon monoxide emissions increase with decreased combustion power which are in turn dependent on the particular settings of each pellet burner and how the heat is transferred to the building. However, for most systems the modulating operation mode has a positive impact on carbon monoxide emissions. Considering the total auxiliary energy demand, including the electricity demand of the pellet units, the modulating combustion control is advantageous for systems 1 and 4 for the used boundary conditions. The study also shows that an appropriate sizing of the stove or boiler has a huge potential for energy saving and carbon monoxide emission reduction.Emission and electricity consumption are important aspects of a pellet heating system. Low noxious emissions, particularly carbon monoxide, are a measure of a well-performing system. High carbon monoxide emissions are often caused by unnecessary cycling of the burner, poor adjustment of the combustion air and insufficient maintenance. The carbon monoxide output, the thermal performance and the electricity consumption for modulating and non-modulating operation mode have been investigated by simulations of four stoves/boilers as part of combined solar and pellet heating systems. The systems have been modelled with the simulation programme TRNSYS and simulated with the boundary conditions for space heating demand, hot water load and climate data as used in earlier research projects. The results from the simulations show that operating the pellet units with modulating combustion power reduces the number of starts and stops but does not necessarily reduce the carbon monoxide output. Whether the carbon monoxide output can be reduced or not, it depends very strongly on the reduction of starts and stops and how much the carbon monoxide emissions increase with decreased combustion power which are in turn dependent on the particular settings of each pellet burner and how the heat is transferred to the building. However, for most systems the modulating operation mode has a positive impact on carbon monoxide emissions. Considering the total auxiliary energy demand, including the electricity demand of the pellet units, the modulating combustion control is advantageous for systems 1 and 4 for the used boundary conditions. The study also shows that an appropriate sizing of the stove or boiler has a huge potential for energy saving and carbon monoxide emission reduction.

Electrochemistry and dynamic ionography of self-propagating high-temperature synthesis (SHS)

Kuznetsov-MV; Morozov-YG; Parkin-L(Russian Acad. of Sci., Moscow, Russia)

Materials-Science-Forum. Sept. 2006; 555: 73-81

The results of a new potentiometric technique for in situ diagnostics of self-propagating high-temperature synthesis (SHS) of different complex oxides are presented. This technique is based on electrochemical processes. The characteristic peaks attributed to the electric responses from cation streams of alkali, alkaline-earth and some elements of group VI are discovered and the respective routes of the corresponding chemical reactions found.

Study on densification of laser ignited reaction sintering of Ni-Al-Cu powder

Liu-YH; Guo-ZX; Shen-P; Wang-HY; Hu-JD(Jilin Univ., Changchun, China)

Science-of-Sintering. Jan-April 2007; 39(1): 31-7

The mechanisms of densification during laser ignited reaction sintering of Ni-Al-Cu powder materials were studied. With the addition of Cu, densification of Ni-Al-Cu specimens made of big particles was realized under laser rapid ignition and sintering without signification change of the final products. Filling of the mixture of liquid and disintegrated small grains or particles was regarded as the dominant mechanism for the final densification.

Fabrication of alloy nanopowders by the electrical explosion of electrodeposited wires

Wonbaek-Kim; Je-Shin-Park; Chang-Yul-Suh; Hankwon-Chang; Jae-Chun-Lee(Korea Inst. of Geoscience and Mineral Resources, Taejeon, South Korea)

Materials-Letters. Aug. 2007; 61(21): 4259-61

Electrical wire explosion technique has been successful in the production of various pure metal powders. However, the process has the obvious limitation that alloy and intermetallic powders are difficult to produce due to the unavailability of their thin wire form. In this study, a novel method by which various alloys and compounds can be produced was suggested utilizing electrodeposition and wire explosion process. Al-Cu and Cu-Ni alloy nanopowders were fabricated by the electrical explosion of Cu-deposited Al and Ni wires. Ni-Cu nanopowders were composed of Ni- and Cu-solid solutions. Al-Cu wire explosion produced various phases in the order of Al, Al₂Cu, Al₃Cu₄ as the copper layer became thicker. It is demonstrated that the suggested method could provide means to produce numerous alloys and intermetallic nanopowders. [All rights reserved Elsevier].

Combustion synthesis of TiO₂ nanoparticles as photocatalyst

Kitamura-Y; Okinaka-N; Shibayama-T; Mahaney-OOP; Kusano-D; Ohtani-B; Akiyama-T(Hokkaido Univ., Japan)

Powder-Technology. 20 July 2007; 176(2-3): 93-8

This paper describes a new type of combustion synthesis of metal oxide nanoparticles, in which the adiabatic flame temperature of the solid phase reaction is beyond the boiling point of the product, and its implementation for the synthesis of titanium dioxide as photocatalyst. In this study, raw materials comprising titanium particles of different sizes and sodium perchlorate were intensively mixed and ignited by an electrical heating foil to produce titanium dioxide through the following reaction: Ti+NaClO₄toTiO₂+NaCl. The shape and crystal structure of the titanium dioxide product significantly depended on the particle size of the titanium used as raw material. That is, the smaller titanium particles (average size (AS) of 10 mu m) resulted in rutile with an irregular shape, whereas the larger particles (AS of 25 mu m) resulted in spheres of anatase. The photocatalytic activities of these samples were evaluated using the photocatalytic reactions of aqueous titanium dioxide suspensions containing methanol and acetic acid by irradiation at 298 K in argon atmosphere or in air. The activity of the rutile-rich sample was significantly larger than that of the anatase-rich one in both photocatalytic reactions.A new type of combustion synthesis and the conventional combustion synthesis are two methods used for producing oxide (AO). This paper describes a new type of combustion synthesis of metal oxide nanoparticles, in which the adiabatic flame temperature of the solid phase reaction is beyond the boiling point of the product, and its implementation for the synthesis of titanium dioxide as photocatalyst.[All rights reserved Elsevier].

Synthesis, characterization, photoluminescence and EPR investigations of Mn doped MgAl₂O₄ phosphors

Singh-; Chakradhar-RPS; Rao-JL; Dong-Kuk-Kim(Kyungpook Nat. Univ., Daegu, South Korea)

Journal-of-Solid-State-Chemistry. July 2007; 180(7): 2067-74

MgAl₂O₄:Mn phosphors have been prepared at 500 degrees C by combustion route. Powder X-ray diffraction (XRD) indicated the presence of mono-MgAl₂O₄ phase. Scanning electron microscopy showed that the powder particle crystallites are mostly angular. Fourier transform infrared spectroscopy confirmed the presence of AlO₆ group which makes up the MgAl₂O₄ spinel. Photoluminescence studies showed green/red emission indicating that two independent luminescence channels in this phosphor. The green emission at 518 nm is due to ⁴T₁ to ⁶A₁ transition of Mn²⁺ ions. The emission at 650 nm is due to the charge-transfer deexcitation associated with the Mn ion. EPR spectrum exhibits allowed and forbidden hyperfine structure at g=2.003. The gapproximately=2.00 is due to Mn²⁺ ion in an environment close to tetrahedral symmetry. It is observed that N and chi increase with decrease of temperature obeying the Boltzmann law. The variation of zero-field splitting parameter (D) with temperature is evaluated and discussed. MgAl₂O₄:Mn phosphors have been prepared at 500 degrees C by combustion route and are well characterized by PXRD, SEM and FTIR. Photoluminescence studies showed green/red emission indicating two independent luminescence channels in this phosphor. EPR spectrum exhibits allowed and forbidden hyperfine structure at g=2.003. From EPR spectra the spin-Hamiltonian parameters have been evaluated and discussed.[All rights reserved Elsevier].

Nitride nuclear fuel production using combustion synthesis

Donohoue-C; Reigel-M; Burkes-D; Moore-J; Kennedy-JR(Sch. of Mines, USA)

Transactions-of-the-American-Nuclear-Society. 24-28 June 2007; 96: 695-6

The retention of transuranic elements in the fuel pellet is the primary focus of this study. Plutonium and americium, in particular, have high vapor pressures resulting in significant losses of material while undergoing traditional fuel pellet manufacturing techniques such as melting or sintering. The exothermic combustion synthesis method, termed self-propagating high-temperature synthesis (SHS), to produce high density, readily reproducible, ceramic nuclear fuels in conjunction with the fabrication of transmutation fuels. Combustion synthesis offers an alternative process for the synthesis of nitride nuclear fuels whereby the rapid heating and cooling rates minimize material loss and maximize production efficiency.

Primary study on mixture freezing phenomena for fast reactor analysis by simulation of THEFIS experiment

Wang-Z; Cao-XW(Shanghai Jiaotong Univ., Shanghai, China)

Transactions-of-the-American-Nuclear-Society. 24-28 June 2007; 96: 601-2

This paper summarizes the simulation and verification study of the problems of liquid penetration inside the particle blockage based on an analysis of a series of thermite freezing in structure (THEFIS) experiments with particles. Simulation results show that the melt/particle mixture viscosity models have a capability to reproduce a penetration behavior inside a particle blockage and freezing behavior of a flowing melt with solid particles. However, the simulation results of melt penetration, especially in the intermediate initial particle bed heights, show that validity of melt/particle mixture viscosity equation depends on the initial particle bed height. Hence, these freezing phenomena and relating models are needed to be further investigated.

Synthesis of bulk nano-Al₂O₃ dispersed Cu-matrix composite using ball milled precursor

Das-D; Samanta-A; Chattopadhyay-PP(Bengal Eng. & Sci. Univ., Howrah, India)

Materials-and-Manufacturing-Processes. March 2007; 22(3-4): 516-24

Kinetics of solid-state reduction reaction during ball milling of CuO-AI and CuO-prealloyed Cu(Al) powder blends in dry and wet condition has been investigated by using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM) techniques. Direct reduction of CuO by Al has resulted into Al₂O₃ dispersed Cu-matrix composite through a self-propagating reaction only during milling in dry condition. However, indirect reduction of CuO by prealloyed Cu(Al) resulted into formation of nano-Al₂O₃ dispersed Cu-matrix composite either by continued ball milling in dry condition or by subsequent thermal treatment of wet milled powder precursor. The influence of milling conditions, that is, milling speed, and milling media, on the occurrence of reduction of CuO by elemental Al or Al in prealloyed Cu(Al) during ball milling have been explained by considering their effects on the rise of powder temperature due to collisions between balls and powder particles, and the rate of reduction of ignition temperature of the reaction due to microstructural refinement. TEM investigation has revealed that the size of Al₂O₃ particles in the composite power blend formed by the indirect reaction route (CuO-prealloyed Cu(Al)) is much finer than the same in case of direct reaction route (CuO-AI). It is suggested that the kinetics of the reduction reaction in the indirect reaction route is relatively sluggish in nature and amenable to processing of large amount of nano-Al₂O₃ dispersed Cu-matrix composite powder for industrial purpose.

A comparative study on combustion synthesis of Ta-Si compounds

Yen-CL; Wang-HJ(Da-Yeh Univ., Changhua, Taiwan)

Intermetallics-. 2007; 15(10): 1277-84

A comparative study on the preparation of tantalum silicides (including TaSi₂, Ta₅Si₃, Ta₂Si, and Ta₃Si) in the Ta-Si system was conducted by self-propagating high-temperature synthesis (SHS) from elemental powder compacts of corresponding stoichiometries. For the powder compacts of Ta:Si=5:3 and 2:1, upon ignition a planar combustion front traversing the entire sample was easily achieved even without prior heating. In contrast, a preheating temperature of 300 degrees C was required for the samples of Ta:Si=3:1 and 1:2 to establish the propagation of a planar reaction front in a self-sustaining manner. It was found that the flame-front propagation velocity and combustion temperature were increased by increasing the preheating temperature and sample compaction density. Among the test samples of different compositions, the reactant compact of Ta:Si=5:3 exhibited the highest flame speed, followed sequentially by the powder compacts of Ta:Si=2:1, 3:1, and 1:2. The variation of combustion temperature with starting stoichiometry of the reactant compact was in a manner consistent with that of the flame-front velocity. According to the XRD analysis, a complete conversion yielding single-phase disilicide TaSi₂ was achieved from the sample compact of Ta:Si=1:2. The silicides phases Ta₅Si₃ and Ta₂Si were obtained in relatively pure form through combustion reactions of the powder compacts with Ta:Si=5:3 and 2:1, respectively. However, a poor degree of phase transformation was observed in the case of Ta:Si=3:1, which produced a multiphase product composed mostly of Ta₂Si and Ta₅Si₃, along with small amounts of Ta₃Si and elemental Ta. In addition, based upon the temperature dependence of combustion wave velocity established in this study, the activation energies associated with combustion synthesis of Ta₅Si₃, Ta₂Si, and TaSi₂ were determined to be 105.2, 65.5, and 153.8 kJ/mol, respectively. [All rights reserved Elsevier].

Combustion synthesis and EIS characterization of TiO₂-SnO₂ system

Chinarro-E; Moreno-B; Jurado-J(CSIC, Madrid, Spain)

Journal-of-the-European-Ceramic-Society. 2007; 27(13-15): 3601-4

TiO₂ is an insulator, but using specific dopants, can modify sharply its electronic structure towards semiconducting behavior. This type of response is widely applied in many electrochemical and electrocatalytical devices, namely chlorine production, hydrocarbon oxidation, CO and CO₂ hydrogenation and as electroactive substrata for biological cell growth.Combustion synthesis is a very simple, rapid and clean method for material preparation, which will be used in the preparation of the (1-x)TiO₂-xSnO₂, x=0.05-0.3. Tin oxalate and titanium isopropoxide are used as precursors for the synthesis. The as-prepared powders are fine and homogeneous, the average particle size is in the range of 5-10nm, powders and ceramic compact bodies are characterized by DRX, SEM-TEM-EDX, DTA-TG and EIS. The impedance spectroscopy of the sample 10mol% of SnO₂ indicates the presence of several phases which promote a matrix composite based in an electrical TiO₂ insulator compatible with an electronic conducting phase tin rich. This could be attributed to the spinodal decomposition effect observed in TiO₂-SnO₂ system. [All rights reserved Elsevier].

Magnetic and structural properties of nanosize Ni-Zn-Cr ferrite particles synthesized by combustion reaction

Gama-L; Hernandez-EP; Cornejo-DR; Costa-AA; Rezende-SM; Kiminami-RHG; Costa-ACF(Federal Univ. of Campina Grande, Campina Grande, Brazil)

Journal-of-Magnetism-and-Magnetic-Materials. 2007; 317(1-2): 29-33

This paper reports on Cr³⁺-doped and undoped Ni-Zn nanosize ferrite obtained by reaction combustion synthesis. The powders resulting from this synthesis were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and their magnetic properties examined with an alternative gradient magnetometer (AGM) and by ferromagnetic resonance (FMR). The XRD results confirmed the formation of Ni_0.5Zn_0.5Fe₂O₄ bulk spinel and small quantities of second phase hematite ( alpha Fe₂O₄) to the powders without chromium. However, the powders containing 0.1mol of chromium showed only a Ni-Zn ferrite cubic phase. The Ni_0.5Zn_0.5Fe₂O₄ and Ni_0.5Zn_0.5Fe_1.9Cr_0.1O₄ showed average crystallite sizes of 20.7 and 22.7nm, respectively. The SEM micrographs of the powders to the sample without chromium reveals nanoparticles with a regular morphology without pre-sintering and with the presence of soft agglomerations. The powder with 0.1mol of chromium displays homogeneous and finer nanoparticles, which are more reactive and hence more agglomerated. Saturation magnetization of the phase without Cr³⁺ was 61.97emu/g, while that of the powder with chromium was 40.56emu/g. The inclusion of chromium caused the magnetization index to drop by 34% and decreased the coercive field, H_c, by 77%. It is known that the inclusion of chromium is advantageous for high-frequency transformer applications. [All rights reserved Elsevier].

Synthesis of nanosized Nd:YAG powders via gel combustion

Jiang-Li; Yubai-Pan; Fagui-Qiu; Yusong-Wu; Wenbin-Liu; Jingkun-Guo(Chinese Acad. of Sci., Shanghai, China)

Ceramics-International. april 2006; 33(6): 1047-52

Nanosized Nd:YAG powders with different doping concentrations were synthesized at a significantly low temperature by a gel combustion method with citric acid as fuel and nitrate as oxidizer. It is found that the precursor is composed of hydroxycarbonate and dehydrates at below 500 degrees C to form carbonate. Mono-phase Nd:YAG crystallites can be formed without any intermediate phase at 850 degrees C. The value of crystallite size of the 850 degrees C calcined 1.0 at% Nd:YAG powder is 59 nm and the average particle size is 86 nm. The doping of neodymium into YAG garnets increases the lattice constant and the fluorescent intensity decreases drastically when the neodymium concentration is higher than 3 at% because of the fluorescent quenching effect.

Preparation of SiC and SiC/ZnO nanocomposites and its properties

Hongyang-Zhu; Haibin-Yang; Kai-Du; Wuyou-Fu; Lianxia-Chang; Xiaofen-Pang; Yi-Zeng; Guangtian-Zou(Jilin Univ., Changchun, China)

Materials-Letters. 2007; 61(21): 4242-5

SiC/ZnO nanocomposites were synthesized via a two-stage process. SiC nanoparticles were synthesized by electrical explosion method, and using the SiC nanoparticles as precursor, SiC/ZnO nanocomposites were synthesized by co-precipitation processes. The SiC/ZnO nanocomposites exhibit energy tuning of band-to-band transitions. In addition to the UV emission, the green and orange emissions were also observed. To our interest the green and orange emissions decreased at first and then increased with increasing annealing temperature. The underlying mechanism is elucidated.[All rights reserved Elsevier].

An investigation on physical properties of strontium hexaferrite nanopowder synthesized by a sol-gel auto-combustion process with addition of cationic surfactant

Hasab-MG; Ebrahimi-SAS; Badiei-A(Univ. of Tehran, Tehran, Iran)

Journal-of-the-European-Ceramic-Society. 2007; 27(13-15): 3637-40

In this study a novel sol-gel auto-combustion method, using n-decyltrimethylammonium bromide as a cationic surfactant, has been used to synthesize strontium hexaferrite nanocrystalline powder. The dried nitrate-citrate gel, prepared from a solution of ferric nitrate, strontium nitrate, citric acid, trimethylamine and cationic surfactant, exhibited an auto-combustion behavior after ignition in air. The formation reaction temperature, phase identification, crystallites size, particles size distribution and morphology of resultant strontium hexaferrite powder were investigated by DTA/TGA, FTIR, XRD, LPSA, TEM and SEM techniques. The results showed that in presence of the cationic surfactant, the combustion intensity increases and the crystallite size decreases. The crystallite size of strontium hexaferrite powder in sample with surfactant calcined at 800 degrees C was 27.2nm. [All rights reserved Elsevier].

A new route to synthesize beta -Si_6-z/Al_zO_zN_8-z powders

Aoyagi-K; Hiraki-T; Sivakumar-R; Watanabe-T; Akiyama-T(Hokkaido Univ., Sapporo, Japan)

Journal-of-Alloys-and-Compounds. 2007; 441(1-2): 236-40

beta -Sialons (Si_6-z/Al_zO_zN_8-z) of z values ranging between 1 and 4 were tried for combustion synthesis using mechanically activated powders of Si, Al and Al₂O₃ with desired mixing ratio in a pressurized nitrogen atmosphere of 1MPa. The starting materials were milled to 18 min using a planetary ball mill for mechanical activation (MA). Unsuccessful propagations of z values 1 and 2 were explained in terms of amount of Al present in the raw material. Waste Si, of 94.8 mass% in purity, obtained from semiconductor industry was also introduced as a raw material to replace commercially available Si for the combustion synthesis. [All rights reserved Elsevier].

Adaptive credit scoring with kernel learning methods

Yingxu-Yang(SHS VIVEON, Munich, Germany)

European-Journal-of-Operational-Research. 2007; 183(3): 1521-36

Credit scoring is a method of modelling potential risk of credit applications. Traditionally, logistic regression and discriminant analysis are the most widely used approaches to create scoring models in the industry. However, these methods are associated with quite a few limitations, such as being instable with high-dimensional data and small sample size, intensive variable selection effort and incapability of efficiently handling non-linear features. Most importantly, based on these algorithms, it is difficult to automate the modelling process and when population changes occur, the static models usually fail to adapt and may need to be rebuilt from scratch. In the last few years, the kernel learning approach has been investigated to solve these problems. However, the existing applications of this type of methods (in particular the SVM) in credit scoring have all focused on the batch model and did not address the important problem of how to update the scoring model on-line. This paper presents a novel and practical adaptive scoring system based on an incremental kernel method. With this approach, the scoring model is adjusted according to an on-line update procedure that can always converge to the optimal solution without information loss or running into numerical difficulties. Non-linear features in the data are automatically included in the model through a kernel transformation. This approach does not require any variable reduction effort and is also robust for scoring data with a large number of attributes and highly unbalanced class distributions. Moreover, a new potential kernel function is introduced to further improve the predictive performance of the scoring model and a kernel attribute ranking technique is used that adds transparency in the final model. Experimental studies using real world data sets have demonstrated the effectiveness of the proposed method. [All rights reserved Elsevier].

Pure and doped lanthanum manganites obtained by combustion method

Berger-D; Matei-C; Papa-F; Macovei-D; Fruth-V; Deloume-JP(Univ. of Bucharest, Bucharest, Romania)

Journal-of-the-European-Ceramic-Society. 2007; 27(13-15): 4395-8

Pure and strontium-doped lanthanum manganite nanopowders were obtained by solution combustion method using metal nitrates as oxidants and different organic compounds as fuel ( alpha -alanine, glycine, urea and semioxamazide). Different molar ratios, fuel/oxidant, were chosen to study the effect of the fuel content on the phase formation and powder properties. The complex precursors isolated before ignition of the system, were characterized by FT-IR spectroscopy and thermal analysis. After ignition, the as-synthesized powders were calcined at different temperatures for obtaining single phases. Lanthanum manganite powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), specific surface area and magnetic measurements. [All rights reserved Elsevier].

Fe₂O₃/aluminum thermite reaction intermediate and final products characterization

Duraes-L; Costa-BFO; Santos-R; Correia-A; Campos-J; Portugal-A(Univ. of Coimbra, Coimbra, Portugal)

Materials-Science-and-Engineering-A. 2007; 465(1-2): 199-210

Radial combustion experiments on Fe₂O₃/aluminum thermite thin circular samples were conducted. A stoichiometric (Fe₂O₃+2Al) and four over aluminized mixtures were tested. The combustion products were characterized by X-ray diffraction and Mossbauer spectroscopy and the influence of Fe₂O₃/aluminum ratio on their composition was assessed. The main products were identified as alumina ( alpha -Al₂O₃) and iron (Fe). A significant amount of hercynite (FeAl₂O₄) was detected, decreasing with the aluminum excess in the reactants. Close to the sample/confinement interface, where reaction quenching occurs, a non-stoichiometric alumina (Al_2.667O₄) was observed, being its XRD intensity correlated to the hercynite amount. Fe₃Al intermetallic phase was found in the products of over aluminized mixtures. A reaction mechanism was proposed comprising: (i) Fe₂O₃ reduction to Fe₃O₄ and FeO; (ii) Al oxidation to Al₂O₃; (iii) interaction of the remaining Al with Fe₃O₄ and FeO with formation of iron-aluminates (hercynite) and iron; (iv) for the over aluminized mixtures, incorporation of Al into the iron-aluminates takes place with the formation of iron and alumina and, in parallel, Al reacts with iron to produce intermetallics. [All rights reserved Elsevier].

Supported Pd-perovskite catalyst for CNG engines' exhaust gas treatment

Fino-D; Russo-N; Saracco-G; Specchia-V(Politecnico di Torino, Torino, Italy)

Progress-in-Solid-State-Chemistry. 2007; 35(2-4): 501-11

Perovskite-type oxides of the series La_1-xA_xMn_1-yB_yO₃ (A = Sr; B = Fe or Co) were prepared by solution combustion synthesis and characterized by X-ray diffraction, specific surface analysis, transmission electron microscopy and field emission scanning electron microscopy techniques. Their activity towards the combustion of methane was evaluated in a temperature programmed combustion microreactor. The LaMn_0.9Fe_0.1O₃ catalyst was found to provide the best performance. The half-conversion temperature of methane over the LaMn_0.9Fe_0.1O₃ catalyst was 398 degrees C with a W/F = 0.12 g s/cm³ and a methane feed concentration of 0.4 vol% under oxygen excess. Via temperature programmed oxygen desorption (TPD) analysis as well as catalytic combustion runs, the prevalent activity of the LaMn_0.9Fe_0.1O₃ catalyst could be explained by its higher and increased capability to desorb suprafacial, weakly chemisorbed oxygen species. Further catalyst development allowed to maximise the catalytic activity of this compound by promoting it with CeO₂ (1:1 molar ratio) and with 1 wt% Pd. This promoted catalyst was lined on cordierite monoliths in a gamma -Al₂O₃-supported form (catalyst weight percentage: 15 wt%) and then tested in a lab-scale test rig under realistic conditions for compressed natural gas-vehicles' exhaust gas treatment. Half methane conversion was achieved at 340 degrees C (gas high space velocity = 10 000 h^-1), nearly the same but with a fourfold lower amount of the expensive noble metal than that used in commercial 4wt%Pd- gamma -Al₂O₃ catalysts. [All rights reserved Elsevier].

Preparation and characterization of BiFeO₃ ceramic

Fruth-V; Mitoseriu-L; Berger-D; Ianculescu-A; Matei-C; Preda-S; Zaharescu-M(Romanian Acad., Bucharest, Romania)

Progress-in-Solid-State-Chemistry. 2007; 35(2-4): 193-202

From the technological point of view, the mutual control of electric and magnetic properties is an attractive possibility, but the number of candidate materials is limited. One of them, BiFeO₃, has critical conditions for synthesizing single phase since the temperature stability range of the phase is very narrow. Hence, various aspects of BiFeO₃ system have to be studied.Fine particles of BiFeO₃ are obtained using a wet chemical route (combustion technique) and compared with the same product prepared by classic solid state reaction. The sintering programs have been varied in order to investigate the mechanism reactions and to show the relation between the microstructures and the magnetoelectric behavior.The samples are characterized by using various techniques: X-ray diffraction (XRD) study is carried out for phase determination and lattice parameter calculations; scanning electron microscopy (SEM-EDX) and TEM to find out grain size and morphology; differential thermal analysis (DTA) to determine transformations of the starting materials. The obtained bulk materials were characterized (density, porosity, etc.) and correlated with the phase composition present in the samples. Electric and magnetic properties were evaluated.This study underlines the role of the preparation route on the structural and morphological characteristic of the obtained materials and their influence on the magnetoelectric behavior. [All Rights Reserved. Elsevier].

Pure and doped lanthanum cobaltites obtained by combustion method

Berger-D; Matei-C; Papa-F; Voicu-G; Fruth-V(Politehnica Univ. of Bucharest, Bucharest, Romania)

Progress-in-Solid-State-Chemistry. 2007; 35(2-4): 183-91

We report the synthesis of La_1-xSr_xCoO₃ nanopowders by solution combustion method using metal nitrates and alpha -alanine (alanine method) or urea (urea method) as fuel. The influence of metal nitrates/organic substance molar ratio and the type of fuel was investigated. The isolated complex precursors were characterized by atomic absorption spectroscopy (AAS), FT-IR spectra and DTA-TG analysis. The La_1-xSr_xCoO₃ (x=0-0.3) powders were characterized by X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive X-ray analysis (SEM-EDX), as well as by specific surface area measurements. XRD patterns indicate the formation of single-phase LaCoO₃ (rhombohedral) when as-synthesized powders were calcined at 873 K, 3 h in the case of the alanine method and at 1073 K, 3 h for urea-based system. Also, strontium doped lanthanum cobaltites obtained by both methods at 1273 K are single phase with rhombohedral perovskite-like structure as XRD data have proved. SEM investigation of pure and doped lanthanum cobaltites reveal that the samples prepared by both methods have fine particles with tendency of agglomerates formation with different shapes, spongy aspect and high porosity. La_1-xSr_xCoO₃ nanopowders obtained by alanine method have larger specific surface area values than those prepared by urea method. [All rights reserved Elsevier].

Synthesis and characterisation of a green NiO/La(Sr)PO_4-delta cermet anode for phosphate based solid oxide fuel cells

Colomer-MT; Gallini-S; Jurado-JR(CSIC, Madrid, Spain)

Journal-of-the-European-Ceramic-Society. 2007; 27(13-15): 4237-40

Cermets are commonly used as anode in fuel cells. NiO/La(Sr)PO_4-delta has not been synthesized before and it could be a good anode for high-temperature protonic fuel cells. In this article, the preparation of NiO/La(Sr)PO_4-delta by combustion synthesis using nitrates, ammonium phosphate and urea is described. In this preliminary work, we are more concerned to understand the calcined powder reduction pattern with in situ electrochemical impedance spectroscopy (EIS) experiments. The as-prepared powder is structurally analysed by XRD, also after each calcination treatment in air and in reducing atmosphere, and before and after the electrical measurements were carried out. The electrical characteristics of a green pellet of NiO/La(Sr)PO_4-delta are studied by impedance spectroscopy as a function of temperature (50-800 degrees C) in a reducing atmosphere (10^-20 atm). The reducing process of NiO to Ni is also followed by EIS. Finally, the morphology of this composite material analysed by EIS was observed by means of SEM/EDX. The morphology of this composite material indicates the presence of two compatible phases. One corresponds to the La(Sr)PO₄ phase and the second one to a Ni phase, according to EDX data. The low electrical conductivity values indicate that nickel agglomerates are not totally percolated in the calcined pellet as it was expected. Higher conductivity values are expected when total Ni percolation occurs after sintering. [All rights reserved Elsevier].

Combustion synthesis and characterisation of Ni-MO-YSZ (M=Mg, Ca, Al₂3/) cermet anodes for SOFCs

Chinarro-E; Figueiredo-K; Mather-GC; Jurado-JR; Frade-JR(Inst. de Ceramica y Vidrio, Madrid, Spain)

Journal-of-the-European-Ceramic-Society. 2007; 27(13-15): 4233-6

The performance of Ni-yttria-stabilised zirconia (YSZ) cermet anodes can deteriorate with time and on redox and thermal cycling due to coarsening and/or oxidation of the Ni particles. Small additions of a second oxide phase may arrest degradation. In this work, Ni-YSZ-MO compositions (M=Mg, Ca, Al₂3/, respectively, NZM, NZC, NZA) were prepared by combustion. Phase composition and microstructural characteristics were assessed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Powders calcined at 1450 degrees C consist of mixtures of Ni(Mg)O-YSZ, NiO-YSZ-CaZrO₃ and NiO-YSZ-NiAl₂O₄ particles for NZM, NZC and NZA, respectively. The sintered and reduced cermets are composed of a homogeneous and well-dispersed distribution of Ni, YSZ and secondary oxide components. [All rights reserved Elsevier].

Synthesis of ceria-based electrolyte nanometric powders by urea-combustion technique

Chinarro-E; Jurado-JR; Colomer-MT(Inst. de Ceramica y Vidrio, Madrid, Spain)

Journal-of-the-European-Ceramic-Society. 2007; 27(13-15): 3619-23

Ceria-doped electrolytes have been extensively studied because they are promising candidates for intermediate temperature solid oxide fuel cells (ITSOFCs). In this work, the powder synthesis by the urea-combustion technique is used. The combustion synthesis is a really suitable synthesis route to achieve, at low temperatures, finely, homogeneous, and reactive powders for ceria-based electrolytes. This work describes the combustion synthesis of binary and ternary compositions of the (CeO₂)_0.92(Ln₂O₃)_0.04(CaO)_0.04 systems, being Ln=Y, Gd and Sm. The characterisation of the as-prepared combustion products showed that the combustion synthesis provides a straightforward method for the achievement of solid solutions of these materials as nanometric powder. [All rights reserved Elsevier].

Al-Ni intermetallics obtained by SHS; a time-resolved X-ray diffraction study

Curfs-C; Turrillas-X; Vaughan-GBM; Terry-AE; Kvick-A; Rodriguez-MA(European Synchrotron Radiat. Facility, Grenoble, France)

Intermetallics-. 2007; 15(9): 1163-71

Intermetallic compounds in the Al-Ni system were prepared by Self-propagating high-temperature synthesis (SHS). The front high speed in the range of 1-100 mm/s - typical of these processes made necessary the use a very intense synchrotron source (ESRF) coupled to a very fast acquisition system. Finely divided powders of Ni and Al were intimately mixed in a 1:1 mole ratio, and then compressed to form compact cylindrical of the right density to assure a steady combustion front. Diffraction patterns were acquired every 100 ms. As the reaction proceeded, patterns from the preheated, reaction front, post-heated and cooling zones were sampled. The crystal phases appearing were identified. Similarly, reaction mechanisms and nucleation kinetics were established. Also, high speed pyrometers were used to obtain combustion front temperature profiles and its propagation was video recorded. Finally, SEM images were taken to characterize the microstructure of end products. [All rights reserved Elsevier].

Nitrate-citrate combustion synthesis of Ce_1-xGd_xO_2-x2/ powder and its characterization

Cheng-Peng; Zhen-Zhang(South China Univ. of Technol., Guangzhou, China)

Ceramics-International. april 2006; 33(6): 1133-6

The structure, thermal expansion coefficients, and electric conductivity of Ce_1-xGd_xO_2-x2/ (x=0-0.6) solid solution, prepared by the gel-combustion method, were investigated. The uniform small particle size of the gel-combustion prepared materials allows sintering into highly dense ceramic pellets at 1300 degrees C, a significantly lower temperature compared to that of 1600-1650 degrees C required for ceria solid electrolytes prepared by traditional solid state techniques. XRD showed that single-phase solid solutions formed in all the investigated range. The maximum conductivity, sigma _{600 degrees C}=5.26x10^-3 S/cm, was found at x=0.2. The thermal expansion coefficient, determined from high-temperature X-ray data, was 8.125 x 10^-6 K^-1 at x=0.2. [All rights reserved Elsevier].

The application of self-propagating high-temperature synthesis of engineered porous composite biomedical materials

Ayers-R; Burkes-D; Gottoli-G; Yi-HC; Moore-JJ(Colorado Sch. of Mines, Golden, USA)

Materials-and-Manufacturing-Processes. 2007; 22(3-4): 481-8

The term "self-propagating high-temperature synthesis" (SHS), or "combustion synthesis", refers to an exothermic chemical reaction process that utilizes the heat generated by the exothermic reaction to ignite and sustain a propagating combustion wave through the reactants to produce the desired product(s). The products of combustion synthesis normally are extremely porous: Typically 50 percent of theoretical density. Advantages of combustion synthesis over traditional processing routes, e.g., sintering, in the production of advanced materials such as ceramics, intermetallic compounds and composites include process economics, simplicity of operation, and low energy requirements. However, the high exothermicity and rapid combustion propagation rates necessitate a high degree of control of these reactions. One research area being conducted in the Center for Space Resources (ISR) at the Colorado School of Mines (CSM) is the application of SHS to synthesize advanced, engineered porous TiB-Ti, NiTi, NiTi-TiC, TiC-Ti, and multiphase/heterogeneous calcium phosphate (HCaP) for bone tissue engineering and drug delivery systems. Processing conditions, such as reaction stoichiometry, green density, and gasifying agent, greatly affect the structure and properties of the SHS porous products. In general, all porous composite materials produced in this work for tissue engineering, including NiTi, NiTi+TiC, TiC+Ti, TiB+Ti, and multiphase/heterogeneous calcium phosphate (HCaP), appear to be biocompatible with no overt toxicity observed either in vitro or in vivo. An example of an SHS reaction is Ni + Ti = NiTi. The extent of the porosity and the size of the pores can be controlled using certain 'gasifying agents' such as B₂O₃, CaCO₃ The article discusses the synthesis of porous TiB-Ti, NiTi, Ni₃Ti-TiC, TiC-Ti, and multiphase/heterogeneous calcium phosphate (HCaP) for bone tissue engineering and drug delivery systems.

Photoluminescence of NiNb₂O₆ nanoparticles prepared by combustion method

Yuanyuan-Zhou; Mengkai-Lu; Zifeng-Qiu; Aiyu-Zhang; Qian-Ma; Haiping-Zhang; Zhongsen-Yang(Shandong Univ., Jinan, China)

Materials-Science-and-Engineering-B. 2007; 140(1-2): 128-31

Pure and Dy³⁺-doped NiNb₂O₆ nanoparticles have been prepared by a sol-gel combustion method using citric acid as fuel and complexing agent and nitrates as oxidants at a relatively low temperature compared to solid-state reaction method. The photoluminescence properties of these NiNb₂O₆ nanoparticles were studied in detail. For the pure NiNb₂O₆ nanoparticles, a blue emission band centered at 445 nm is observed. For NiNb₂O₆:Dy³⁺ nanoparticles, no characteristic luminescence of Dy³⁺ can be observed while the host blue emission enhances. It is suggested that energy transfer from Dy³⁺ to niobate groups maybe occurs. [All rights reserved Elsevier].

Preparation of zinc oxide (ZnO) powders with different types of morphology by a combustion synthesis method

Cheng-Shiung-Lin; Chyi-Ching-Hwang; Wei-Hua-Lee; Wei-Yin-Tong(NDU, Taoyuan, Taiwan)

Materials-Science-and-Engineering-B. 2007; 140(1-2): 31-7

A combustion synthesis process has been established for preparation of ZnO powders with different types of morphologies (that is, agglomerated particles, rod-like structures, and tetrapod whiskers) in air ambience. Metallic zinc and glycine (NH₂CH₂COOH) powders were used as the fuels, whereas zinc nitrate acted as the oxidant. These reactants were mixed and pressed into a compact. The compact was wrapped up with an igniting agent (i.e., Mg+Fe₃O₄) and the synthesis reaction was triggered by the combustion of the igniting agent. Both the combustion temperature and the product properties were affected by the reactant composition. A possible reaction mechanism based on thermodynamic calculations and experimental results was proposed that explains the effects of the reactant composition on the combustion reaction.

Enhanced magnetostrictive properties of CoFe₂O₄ synthesized by an autocombustion method

Bhame-SD; Joy-PA(Nat. Chem. Lab., Pune, India)

Sensors-and-Actuators:-A-Physical. 2007; 137(2): 256-61

The magnetostrictive properties of sintered cobalt ferrite derived from nanocrystalline powders synthesized by three different low-temperature methods (citrate, coprecipitation and autocombustion) and the high-temperature ceramic method have been compared. A strong dependence of the magnetostrictive strain is observed on the initial morphology of the ferrite particles and the microstructure of the final sintered product. The nanoparticles synthesized by the autocombustion method, with a flaky and porous morphology, give a sintered material with small grains. Maximum magnetostriction is found to be decreased with increasing grain size. However, no correlation is observed between the initial particle size of the powders or the sintered density and magnetostriction. Maximum magnetostriction values of 197, 184, 159, and 135 ppm are obtained for the sintered samples with average grain sizes of 8 mu m (combustion), 17 mu m (citrate), 23 mu m (coprecipitation), and >25 mu m (ceramic), respectively.

Mechanical-activation-assisted combustion synthesis of SiC powders with polytetrafluoroethylene as promoter

Kun-Yang; Yun-Yang; Zhi-Ming-Lin; Jiang-Tao-Li; Ji-Sheng-Du(Chinese Acad. of Sci., Beijing, China)

Materials-Research-Bulletin. 2007; 42(9): 1625-32

Mechanical-activation-assisted combustion synthesis of SiC has been conducted with polytetrafluoroethylene (PTFE) as promoters. The mechanical activation of the Si-C reactants with the addition of NH₄Cl as process controlling agent during the high-energy attrition milling could substantially decrease the content of PTFE promoter, which is needed for inducing the Si-C combustion reaction. Ultra-fine beta -SiC powders with spherical particles were synthesized at PTFE content as low as 6 wt.%. The combustion synthesized SiC powders have a narrow particle size distribution in the range of 0.5-1 mu m.

In situ observation of the formation of TiC from the elements by neutron diffraction

Winkler-B; Wilson-DJ; Vogel-SC; Brown-DW; Sisneros-TA; Milman-V(Univ. Frankfurt, Frankfurt am Main, Germany)

Journal-of-Alloys-and-Compounds. 2007; 441(1-2): 374-80

In situ neutron diffraction has been employed to investigate the formation of TiC_x from the elements at relatively low temperatures, beginning at T ~ 1073 K. Slow heating of the mixture of the elements precludes the generation of sufficient heat to induce a self-propagating high temperature synthesis (SHS), reported in the literature for this system. We observe that the reaction starts well before the alpha - beta transition in Ti occurs, which implies that in this case this transition does not serve as a trigger mechanism for SHS. An extensive coexistence of both polymorphs of titanium suggests that a significant amount of carbon diffuses into the hexagonal alpha -Ti lattice and stabilizes it with respect to the cubic beta -phase. This is supported by the observation of an anomalous increase of the c-lattice parameter of the alpha -Ti lattice above the transition temperature for pure alpha -Ti. Density functional theory (DFT) based calculations support this interpretation. The energetics of the carburization of alpha -Ti have been obtained from the DFT calculations. [All rights reserved Elsevier].

Microwave-assisted combustion synthesis of CoFe₂O₄ with urea, and its magnetic characterization

Kasapoglu-N; Baykal-A; Koseoglu-Y; Toprak-MS(Fatih Univ., Istanbul, Turkey)

Scripta-Materialia. 2007; 57(5): 441-4

A microwave-assisted combustion method has been utilized to prepare nanophased powders of CoFe₂O₄ using urea as fuel. The process takes only a few minutes to obtain as-received CoFe₂O₄. Structural and magnetic properties of the products were investigated by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and vibrating sample magnetometry. Magnetization measurements showed that, at the lowest temperature investigated, the coercivity of Co-ferrite is much larger than that of bulk and this is attributed to exchange anisotropy due to spin disorder at the particle surface. [All rights reserved Elsevier].

The effects of induction heating rate on properties of Ni-Al based intermetallic compound layer coated on ductile cast iron by combustion synthesis

Han-Young-Lee; Ikenaga-A; Sung-Hoon-Kim; Kwang-Bae-Kim(Keimyung Univ., Daegu, South Korea)

Intermetallics-. 2007; 15(8): 1050-6

Applying brittle intermetallic compound coating on metals can enlarge the range of their use. In this instance, the properties of the coating layer are influenced by the constituent phases of intermetallic compound coating layer.In this study, the mixtures of Ni and Al powder have been reacted at different heating rates in an induction furnace in order to obtain the intermetallic compound coating layer with a single phase structure on a ductile cast iron. The microstructures and mechanical properties of the coating layer are investigated and the effects of heating rate in the induction furnace on the properties of intermetallic compound coating layers are evaluated.It was found that the ignition temperature and the maximum temperature increase significantly with increasing heating rate. It was also found that the coating layer is composed of single phase NiAl corresponding to the initial composition of mixed powder and adhesion qualities with substrate are improved with increasing heating rate.

Combustion synthesis and luminescent properties of CaTiO₃:Pr, Al persistent phosphors

Shengyu-Yin; Donghua-Chen; Wanjun-Tang(South Central Univ. for Nat., Wuhan, China)

Journal-of-Alloys-and-Compounds. 2007; 441(1-2): 327-31

Using urea as fuel and boric acid as flux material, red persistent phosphors CaTiO₃:Pr, Al have been successfully synthesized by combustion method. The process lasted for less than 5 min and led to the formation of voluminous white powder. The photoluminescence, crystallinity and particle morphology of persistent phosphors were investigated by using luminescence spectrometer, X-ray diffractometer (XRD) and transmission electron microscopy (TEM), respectively. The results showed that the boric acid was effective in improving the photoluminescence intensity of CaTiO₃:Pr, Al phosphor particles and the optimum molar ratio of boric acid to calcium nitrate was about 0.4. The luminescent properties and crystallinity of phosphors increased with increasing initiating temperature. [All rights reserved Elsevier].

Self-propagating high-temperature synthesis of Sr-doped LaMnO₃ perovskite as oxidation catalyst

Hirano-T; Purwanto-H; Watanabe-T; Akiyama-T(Hokkaido Univ., Sapporo, Japan)

Journal-of-Alloys-and-Compounds. 2007; 441(1-2): 263-6

Sr-doped LaMnO₃ perovskite oxide has been focused on as one of the alternative catalysts to precious metals such as platinum that are used for cleaning automotive emission gas. The conventional Solid-state reaction method is a popular productive process for perovskite oxide, however, it is time and energy consuming process because it requires repeated prolonged heat treatment at high temperatures. Therefore, the purposes of this work are to produce Sr-doped LaMnO₃ perovskite by using Self-propagating high-temperature synthesis (SHS) and experimentally examine the oxidation catalytic activity of the product for cleaning automotive emission gas. In the SHS, powders of La₂O₃, SrCO₃, Mn and NaClO₄ were well mixed at the desired ratio and poured in a graphite crucible, where at one end it was ignited by using an electrically heated carbon foil. The wave of exothermic reaction due to oxidation of manganese propagated to the other end in a short time. The obtained products were characterized by means of XRD, FE-SEM, BET and particle size distribution analysis and then evaluated via catalytic oxidation tests by using propane in a fixed bed reactor at several temperatures. From the XRD analysis, the products had the desired composition of La_1-xSr_xMnO₃ (x=0, 0.1, 0.2 and 0.4) perovskite, in which the replacing ratio x of La and Sr in the products was easily controlled by changing the mixing ratio of raw materials. The catalytic activity test showed that the samples exhibited good catalytic activity for propane oxidation over 200 degrees C, although the products had a relatively small surface area. SHS showed the potential for the production of a relatively inexpensive catalytic converter. [All rights reserved Elsevier].

Formation and control of mechanism for the preparation of ultra-fine barium strontium titanate powders by the citrate precursor method

Chaoliang-Mao; Xianlin-Dong; Tao-Zeng; Genshui-Wang; Si-Chen(Chinese Acad. of Sci., Shanghai, China)

Materials-Research-Bulletin. 2007; 42(9): 1602-10

A modified citrate precursor method, combining the advantages of the nitrate autocombustion method by introducing the nitric acid, was successfully used to synthesize ultrafine Ba_0.70Sr_0.30TiO₃ powders. Slight agglomerated and homogenized BST powders, with an average particle size of 20 nm, were obtained at 800 degrees C. Combining the results of TG/DTA and XRD, it can be concluded that the formation of BST powders takes place via two reaction mechanisms: decomposition of an intermediate oxycarbonate mechanism (DIOm) at low temperature, and solid-state reaction mechanism (SSRm) between nanocrystalline carbonates and amorphous TiO₂ at high temperature. TEM shows higher amount of CA led to BST powders of better quality in morphology. Based on results of chemical analysis, it is suggested that higher amount of CA drives the mechanism to tend to DIOm. By simply adjusting the ratio of reagents, the reaction mechanism can be dominated and we can greatly control the final morphology of the powders.

Ignition mechanism of nickel-coated aluminum particles

Andrzejak-TA; Shafirovich-E; Varma-A(Purdue Univ., West Lafayette, USA)

Combustion-and-Flame. 2007; 150(1-2): 60-70

The use of nickel-coated aluminum particles (10-100 mu m) as a fuel component in propellants is expected to improve the performance characteristics of solid rocket motors. They can also be used for combustion synthesis of nickel aluminides. The ignition mechanism of such particles, however, is not well understood. In this study, to provide sufficient spatial and time resolution, single ~2.5-mm Ni-coated Al particles were laser-heated in argon and carbon dioxide atmospheres. The ignition process was investigated using a high-speed digital video camera, thermocouple measurements, and analysis of particles quenched at different preignition stages. It was shown that the particle ignition temperature is ~1325 degrees C and does not depend on atmosphere (Ar or CO₂) or Ni content. The established ignition mechanism includes exothermic intermetallic reactions and phase transformations of different Ni-Al compounds. Specifically, the melting of NiAl3 at 854 degrees C plays a critical role in particle ignition. [All rights reserved Elsevier].

Combustion synthesis and photoluminescence of perovskite PbTiO₃ nanopowders

Suwen-Liu; Zhiliang-Xiu; Jian'an-Liu; Fengxiu-Xu; Weina-Yu; Jie-Pan; Xiaopeng-Cui; Jiaoxian-Yu(Shandony Inst. of Light Ind., Jinan, China)

Journal-of-Alloys-and-Compounds. 2007; 441(1-2): L7-L9

Perovskite PbTiO₃ nanopowders were synthesized by citric acid sol-gel combustion method using citric acid (CA) as a reductant/fuel and nitrate as an oxidant at 700 degrees C. The particle sizes were in the range of 40-50 nm observed by transmission electron microscopy (TEM). The photoluminescence (PL) spectrum revealed that an intense emission at 415 nm was ascribed to the Pb²⁺ ion ³P₁-⁶S₀ transition. [All rights reserved Elsevier].

Synthesis of dense TiC-based cermets by electro-thermal explosion under pressure with confinement

Ali-Rachedi-M; Hendaoui-A; Vrel-D; Bounour-W; Amara-A; Guerioune-M(Universite Badji Mokhtar, Annaba, Algeria)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(4): 308-13

The Electro-Thermal Explosion under Pressure with Confinement (ETEPC) mode of Self-propagating high-temperature synthesis (SHS) has been studied for TiC and TiC + 20 wt% Ni from the elemental powders. The entire ETEPC procedure was performed in open air. X-ray diffraction shows the formation of TiC in both cases without oxide traces. Scanning electron microscopy shows that the application of a moderate pressure of 19.5 MPa leads to considerable improvement of the product final density when compared to the combustion wave mode of SHS. The addition of 20 wt% Ni to the Ti-C system improves the densification of the samples and leads to the formation of the Ti₂Ni intermetallic compound. These reactions lead to the refinement of the grain size of TiC as compared to the precursors, <20 mu m without Ni, and around 120 nm with the addition of 20 wt% Ni.

Self-propagating high-temperature synthesis of a nuclear reactor core melt for safety experiments

Mwamba-K; Piluso-P; Eyries-D; Journeau-C(Commissariat a I'Energie Atomique, St Paul les Durance Cedex, France)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(4): 284-96

Under nuclear accident and severe accident conditions for the water-cooled reactors, the materials of the nuclear reactor (nuclear fuel, cladding, metallic alloys, structural materials, concrete, etc.) could melt to form complex mixtures called corium. This paper presents for the SHS (Self Propagating High temperature Synthesis) process applied to the prototypic corium synthesis by thermitic reaction, an example of the selection of the promising raw powders mixtures and the calculation of some characteristics temperatures (i.e. Adiabatic, liquidus and solidus temperatures) of the charge. The thermodynamic predictions and computations have been performed using the GEMINI2 code and the relevant European Nuclear Thermodynamic Data-bases NUCLEA version05. The GEMINI2 code with NUCLEA is successfully applied on a regular basis to the corium melting experiments carried out on the PLINIUS platform of CEA. An accurate analysis of the ANL (Argone National Laboratory) corium thermitic experiments (ACE-MACE programs) using the GEMINI 2 code with NUCLEA 05 method has permitted to obtain two important results: (i) the adiabatic temperature T_adiabatic is always lower than the liquidus temperature T_liquidus for the ANL tests. This result means the initial corium load would be partially melted (below liquidus temperature). (ii) GEMINI 2 calculates successfully the equilibrium phases for specific temperatures (T_adiabatic, T_liquidus or T_solidus) regarding thermitic process as well as the composition. Special investigations concerning the SiO₂ effect on the thermitic reactions have been conducted for Cr-based and for Fe-based corium prototypic load. Experiences are presently conducted at small scale in VITI facilities (on the CEA PLINIUS platform) in order to verify the thermodynamic prediction for the most promising raw powders mixtures selected on the basis of this preliminary work.

Self-propagating high-temperature synthesis. a "TriNot" concept

Merzhanov-AG(Russian Acad. of Sci., Moscow, Russia)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(4): 269-83

The article considers the problems of equilibrium, stability, and controllability of self-propagating high-temperature synthesis (SHS) processes. The combination of these problems is a "TriNot" (triple negation) concept. The authors show that SHS processes can be (i) both essentially non-equilibrium and quasiequilibrium and in both cases equilibrium or quasiequilibrium products can be formed; (ii) stable and unstable dependent on the parameters and practically always there in the achievable parametric region, within which SHS processes are stable; (iii) regulated by the choice of parameters (periodic processes) and with the use of monitoring systems (continuous processes).

Characterization of quasi-nano-crystalline Li-Cu ferrite powders prepared by using self-propagating high temperature synthesis

Choi-Y; Choi-KS; Cho-NI(Sunmoon Univ., Asan, South Korea)

Journal-of-the-Korean-Physical-Society. June 2007; 50(6): 1719-21

Li_xCu_1-xFe₂O₄ ferrites with different initial compositions of Li₂O₃ and CuO were prepared by using self-propagating high-temperature synthesis (SHS) at an oxygen partial pressures of 0.1MPa. Spinel peaks of Li-Cu ferrite were clearly observed by X-ray diffractometry. The combustion temperature and the propagating rate increased with the molar ratio of lithium oxide to copper oxide. The ferrite particle size was less than about 200 nm. As the molar ratio of Li₂O₃ to CuO increased from 0.25 to 4.0, the maximum magnetization (Ms), the residual magnetization (Mr), and the coercive force (iHc) of the ferrites increased by about 14%, 40%, and 63%.

Synthesis and characterization of Gd₂O₃:Eu nano phosphors for application as X-ray image detectors

Kim-S-Y; Cho-S-H; Shin-J-W; Park-J-K; Kang-S-S; Nam-S-H(Inje Univ., Gimhae, South Korea)

Journal-of-the-Korean-Physical-Society. June 2007; 50(6): 1774-8

In this study, Gd₂O₃:Eu nano phosphor particles were synthesized by using a low- temperature solution-combustion method and their structural and optical characteristics were investigated for various sintering temperatures and europium concentrations. The XRD and FE-SEM results showed that the phosphor particles had a spherical 30 ~ 40 nm size. The photoluminescence showed a new line that was not observed for the bulk phosphor at about 610 nm, and when the particle size decreased, the intensity of the 611-nm peak decreased while the intensity of the 610-nm peak increased. In addition, the luminescence efficiency was revealed to be influenced by the concentration of europium and was highest at 5 wt%. When sintered at a temperature of 500 degrees C, the phosphor exhibited an X-ray peak that corresponded to the cubic phase structure of Gd₂O₃, and when the sintering temperature was increased to 700 degrees C, a new monoclinic phase structure along with the cubic phase of Gd₂O₃ was identified. In the decay time measurement, the mean lifetime, 2.3 ms ~ 2.6 ms, was relatively higher than the 1 ms for commercialized bulk phosphor. From the result of the X-ray absorption measurement, the Gd₂O₃:Eu nano phosphor, which was sintered at 500 degrees C, had about a 1.4 times higher efficiency than the same thickness Gd₂O₃:Eu bulk phosphor. As the results above show, Gd₂O₃:Eu nano phosphor may be applicable for use in high-efficiency, high- resolution medical X-ray image detectors.

Neutron diffraction analysis of fibrous titanium carbide of nano-size diameter formed by using self-propagating high temperature synthesis

Choi-Y; Seong-BSS(Sun Moon Univ., Asan, South Korea)

Journal-of-the-Korean-Physical-Society. June 2007; 50(6): 1632-5

Fibrous titanium carbides of less than 50 nm in diameter were synthesized by using a self-propagating high temperature synthesis (SHS) method. Neutron diffraction analysis showed that the non-stoichiometric numbers of titanium carbide were in the range of 0.89 and 0.94. The Rietveld refinement of each pattern converged to good agreement (0.49 < chi ²< 0.73). The formation mechanism of the carbide is related to a liquid-solid reaction including the preferential diffusion process of carbon atoms into liquid titanium.

Cathode performance of nanostructured La_1-aSr_aCo_1-bFe_bO_3-x on a Ce_0.8Sm_0.2O₂ electrolyte prepared by citrate-nitrate autocombustion

Deganello-F; Esposito-V; Miyayama-M; Traversa-E(Inst. for the Study of Nanostructured Mater., Italian Nat. Res. Council, Palermo, Italy)

Journal-of-the-Electrochemical-Society. Feb. 2007; 154(2): A89-96

Nanostructured La_1-aSr_aCo_1-bFe_bO_3-x (a=0.3-0.5; b=0-0.2) and Ce_0.8Sm_0.2O₂ powders were successfully prepared by citrate-nitrate autocombustion synthesis and were characterized by scanning electron microscopy and X-ray diffraction analysis. Electrochemical impedance spectroscopy measurements on symmetric cells were performed to evaluate the applicability of La_1-aSr_aCo_1-bFe_bO_3-x as a cathode material for intermediate temperature solid oxide fuel cells based on Sm doped-ceria electrolytes. Our results demonstrated that strontium has a positive effect while iron shows a slightly negative effect on the interfacial resistance. The effect of the electrode sintering temperature was investigated by varying the temperature from 850 to 1250 degrees C, and the best sintering temperature was found to be 900 degrees C. The best characteristics as cathode at intermediate operating temperatures were found for the composition with a=0.4 and the minimum iron doping, b=0.05; at 700 degrees C, an area specific resistance of 0.13 Omega cm² was measured.

Critical phenomena and structural effects in combustion of disordered heterogeneous mixtures

Grinchuk-PS; Rabinovich-OS(National Acad. of Sci., Minsk, Belarus)

Heat-Transfer-Research. 2007; 38(1): 57-69

Numerical modeling methods were applied to investigate propagation of combustion waves in two-component heterogeneous media. The main attention was paid to identification of the role of a random distribution of the combustible mixture components in the propagation of combustion waves. Mixtures of the "fuel-inert filler" type and two-reagent mixtures were analyzed. It was shown that the random structure of such mixtures manifests itself most strongly in critical phenomena, characteristic of combustion processes, above all, within the concentration and thermal limits of combustion. Taking into account the random nature of the internal structure of mixtures allows a natural description of the experimentally observed percolating mode of the combustion wave propagation over an "infinite" cluster, formed by combustible elements of the mixture. A single criterion, combining physico-chemical and structural characteristics of the medium, has been found; a value of this criterion determines the transition from the frontal mode of the combustion wave propagation to the percolation mode.

Modeling of energy transfer during combustion of low-gas thermal compositions in systems with intensive heat removal

Enaleev-RSh; Abdullin-IA; Dimukhametov-RR; Kachalkin-VA(Kazan State Technol. Univ., Russia)

Heat-Transfer-Research. 2007; 38(1): 21-31

Models of heat and mass transfer during combustion of pyrotechnical compositions in systems with an inert substrate are analyzed. A design of a scanning cylindrical calorimeter for experimental investigation of energy transfer processes during combustion of pyrotechnical compositions is given. Methods of measuring the transfer potentials in the combustion wave and thermal decomposition products are presented. Thermal balance components, including time-integrated establishment of the equilibrium temperature in the "thermal composition-substrate" system and front-differentiated combustion wave, are assessed. The modeling results of the process of combustion of iron-magnesium thermite in a cylindrical metal shell are discussed.

Effect of Zn²⁺ and Li⁺ codoping ions on nanosized Gd₂O₃:Eu³⁺ phosphor

Mu-Gu; Bingjie-Liu; Xiaolin-Liu; Chen-Ni; Di-Wang; Lihong-Xiao; Riu-Zhang(Lab. of Waves & Microstructure Mater., Tongji Univ., Shanghai, China)

Journal-of-Alloys-and-Compounds. 16 Aug. 2007; 440(1-2): 341-5

Nanosized Gd_1.92-x-yZn_xLi_yEu_0.08O_3-delta phosphor was fabricated by combustion synthesis. The effect of Zn²⁺ and Li⁺ ions on the crystallization behavior, morphology, and luminescence property of Gd₂O₃:Eu³⁺ was investigated. The results indicated that incorporation of Zn²⁺ and Li⁺ ions into Gd₂O₃:Eu³⁺ nanoparticles (NPs) could lead to a remarkable increase of photoluminescence or X-ray excited luminescence, and the intensity at 612nm was increased by a factor of 7.1 or 21.5 in comparison with that of undoped sample. The enhanced luminescence was regarded as the results of the creation of oxygen vacancies due to the Gd³⁺ sites occupied by Li⁺ ions, the alteration of the crystal field surrounding the activator Eu³⁺ ions owing to the incorporation Zn²⁺ ions into interstitial sites, and the flux effect of Zn²⁺ and Li⁺ ions. The Zn- and Li-codoped Gd₂O₃:Eu³⁺ phosphor with highly enhanced luminescence is very encouraging for applications in high-resolution display devices. [All rights reserved Elsevier].

Combustion synthesis of phosphors for plasma display panels

Moharil-SV; Mahakhode-JG; Dhoble-SJ; Joshi-CP(Dept. of Phys., Nagpur Univ., India)

Journal-of-Alloys-and-Compounds. 12 July 2007; 438(1-2): 293-7

Combustion synthesis of phosphors for plasma display panels (PDP) is reported. They include phosphors which are already in commercial use like BaMgAl₁₀O₁₇:Eu²⁺ and BaAl₁₂O₁₉:Mn²⁺ as well as some recently reported aluminates like SrMgAl₁₀O₁₇:Eu²⁺ and GdCaAl₃O₇: Eu³⁺. The phosphors so prepared were characterized by XRD, PL and X-ray excited luminescence (XEL) techniques. XRD studies confirmed formation of all the aluminates except Sr₃Al₁₀SiO₂ in a single step. PL spectra were also in good agreement with the literature results. [All rights reserved Elsevier].

Combustion synthesis of MoSi₂ and MoSi₂-Mo₅Si₃ composites

Yeh-CL; Chen-WH(Dept. of Mech. & Autom. Eng., Da-Yeh Univ., Changhua, Taiwan)

Journal-of-Alloys-and-Compounds. 12 July 2007; 438(1-2): 165-70

An experimental study on the preparation of molybdenum disilicide (MoSi₂) and MoSi₂-Mo₅Si₃ composites was conducted by self-propagating high-temperature synthesis (SHS) from elemental powder compacts of different stoichiometries. Test specimens with six compositions including Mo:Si=6:5, 1:1, 9:11, 3:4, 2:3, and 1:2 (corresponding to the Si content in the range of 45.5-66.7at.%) were employed in this study. Experimental evidence shows that the propagation mode of the reaction front, combustion wave velocity, and reaction temperature are significantly influenced by starting stoichiometry and preheating temperature (T_p) of the reactant compact. In the cases of preheating at 200 and 300 degrees C, self-sustaining combustion featuring a spinning reaction zone was observed for the compacts of Mo:Si=6:5, 1:1, and 9:11, and the reaction temperatures lower than the melting point of Si (1410 degrees C) were detected. On the other hand, a planar combustion front propagating in a steady manner was achieved in the samples with Mo:Si=3:4, 2:3, and 1:2 at T_p=200 and 300 degrees C, and the reaction temperatures exceeding 1410 degrees C were found. However, the planar reaction font was no longer stable in the case of without preheating or at T_p=100 degrees C, and therefore was transformed into a localized reaction zone propagating in a spinning mode. According to the XRD analysis, formation of MoSi₂-Mo₅Si₃ composites from the reactant compacts of Mo:Si=6:5, 1:1, 9:11, 3:4, and 2:3 was confirmed, but a significant amount of elemental Mo left unreacted was found in the cases of Mo:Si=6:5 and 1:1. The unreacted Mo was considerably decreased by increasing the Si content in the reactant compact. For the sample of Mo:Si=2:3, the residual Mo containing in the synthesized composite was in a small quantity. In addition, a single-phase product composed of the disilicide MoSi₂ was yielded from the sample of Mo:Si=1:2. [All rights reserved Elsevier].

Microstructure evolution and reaction mechanism during reactive joining of TiAl intermetallic to TiC cermet using Ti-Al-C-Ni interlayer

Feng-JC; Cao-J; Li-ZR(State Key Lab of Adv. Welding Production Technol., Harbin Inst. of Technol., China)

Journal-of-Alloys-and-Compounds. 14 June 2007; 436(1-2): 298-302

This study reports on a new approach for joining of TiAl intermetallic to TiC cermets by self-propagating high-temperature synthesis. The adiabatic combustion temperature in the Ti-Al-C-Ni system was calculated and the composition of the reactants was determined by the calculated result. For a typical microstructure of the joint, two continuous grey reaction layers were found near the TiAl substrate and massive Ni-rich zones were observed adjacent to the TiC cermet. It was noted that the voids were inevitable in the reaction products. The crack was always formed at the interface between the interlayer and TiC cermet due to the residual stress. The interfacial joining between TiC cermet and the interlayer depended on the formation of Ni-rich layer. The joining between the TiAl and the interlayer was simplified as the reaction between liquid Al and solid TiAl. The SHS reaction in Ti-Al-C-Ni system was ignited at the melting point of Al. The first reaction took place between liquid Al and solid Ti to form TiAl₃. With the increase of the temperature, Ti reacted with C to form TiC phase. [All rights reserved Elsevier].

Low elastic modulus metals for joint prosthesis: Tantalum and nickel-titanium foams

Gil-FJ; Arciniegas-M; Aparicio-C; Manero-JM(Biomed. & Biomech. Res. Centre, Tech. Univ. of Catalonia, Barcelona, Spain)

Journal-of-the-European-Ceramic-Society. 2007; 27(11): 3391-8

In order to allow the ingrowth of the living tissue and increase the mechanical anchorage of the implant, Ta and NiTi foams were obtained with similar microstructure to cancellous bone and mechanically characterized. The Ta foams were produced by chemical vapour deposition and the NiTi foams by self-propagating high temperature synthesis (SHS). The mechanical and microstructural characterization was developed using a servohydraulic testing machine and microscopy techniques. In both materials, pores in an appropriate range of sizes and interconnectivity were observed, comparable with the nature bone morphology. Moreover, the foams showed an excellent biomechanical compatibility and compressive fatigue limit. The fatigue endurance limit set at 10⁸ cycles showed an approximate endurance limit of 7.5 and 13.2MPa, for the NiTi and Ta foams, respectively. These results indicate that the studied materials provide an adequate structural support, showing mechanical properties similar to the cancellous bone, especially for the Ta foam. [All rights reserved Elsevier].

Al₂O₃-WC synthesis by high-energy reactive milling

Pallone-EMJA; Martin-DR; Tomasi-R; Filho-WJB(Univ. Sao Francisco, Sao Paulo, Brazil)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 25 Aug. 2007; 464(1-2): 47-51

Like most carbide-based composites, the two main characteristics of alumina-tungsten carbide (Al₂O₃-WC) composites are high hardness and high wear resistance. These features confer the composites important engineering applications, in particular when they are used as cutting tools. The present research involved a study of Al₂O₃-WC nanometric powders obtained through reactive milling. In this process, high-energy milling promotes the reaction in a mixture of reactive powders. The material was milled in a high-energy SPEX 8000 Mixer/Mill, using WO₃, Al and C precursor powders. The highly exothermic self-propagating high-temperature synthesis (SHS) type reaction was self-sustained, producing a temperature peak that was detected by a thermocouple attached to the external surface of the vessel. Using stoichiometric proportions of the reagents to reduce the WO₃ and to obtain WC, and adding Al₂O₃ as diluent, the SHS reaction occurred up to a limit of 0.8mols of diluent, forming not only alumina but also a W₂C mixture with little WC. To obtain only WC it was required the addition of more than 0.8mols of C, which indicates that the reaction may have occurred through a gaseous phase reaction mechanism. [All rights reserved Elsevier].

Study of rare-earth oxide sintering aid systems for AlN ceramics

Xueli-Du; Mingli-Qin; Farid-A; Humail-IS; Xuanhui-Qu(Inst. of Powder Metall., Univ. of Sci. & Technol. of Beijing, China)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 15 July 2007; 460-461: 471-4

In the present work, effects of Y₂O₃ and Dy₂O₃ sintering aid systems on density and thermal conductivity of AlN ceramics sintered at low temperature were investigated. The AlN powder synthesized by self-propagating high-temperature synthesis (SHS) was mixed individually with six different sintering aids, which were Y₂O₃, Dy₂O₃, CaF₂-Y₂O₃, CaF₂-Dy₂O₃, CaF₂-Li₂CO₃-Y₂O₃ and CaF₂-Li₂CO₃-Dy₂O₃, and then fabricated by employing press forming technique. The specimens were sintered at 1650 degrees C in nitrogen atmosphere at atmospheric pressure for 4h. X-ray diffraction (XRD) was used to identify the secondary phases. The microstructure of the specimen was observed by scanning electron microscopy (SEM). The thermal diffusivity at room temperature was measured by a laser flash technique. Density of sintered specimen was measured by Archimedes displacement method. The result reveals that the density and thermal conductivity of AlN ceramics sintered with one component sintering aids were lower than those of sintered with multiple components sintering aids. The thermal conductivity of AlN ceramics sintered with CaF₂-Li₂CO₃-Y₂O₃ and CaF₂-Dy₂O₃ were 141Wm^-1K^-1 and 142Wm^-1K^-1, which were higher than that of any others. [All rights reserved Elsevier].

Freeform fabrication of titanium metal and intermetallic alloys by three-dimensional micro welding

Miyamoto-Y; Katou-M; Oh-J; Matsuura-K; Kudoh-M(Joining & Welding Res. Inst., Osaka Univ., Japan)

Materials-and-Design. 2007; 28(7): 2093-8

3D micro welding (3DMW) is a new freeform fabrication method which combines tungsten inert gas (TIG) welding, rapid prototyping (RP), and self-propagating high temperature synthesis (SHS). The optimization of forming parameters such as arc peak current, bead diameter and contact angle was investigated. As the arc peak current increased, the height and the contact angle of a titanium bead were decreased, but the width increased. 3D titanium pins with needle-like dendritic microstructure of alpha -phase titanium were formed by continuous stacking and welding of titanium beads. Simple intermetallic alloy pin objects of Ni-Al, Ti-Ni and Ti-Fe systems were also formed by alternate stacking of their component wires. No pore and crack was observed but the uniform composition was observed. The exothermic SHS reactions should take place and assist the intermetallic alloy formation. 3D titanium objects of ring and double helix shapes were formed directly from their computer models without using molds or dies. [All rights reserved Elsevier].

Study on the preparation of IT-SOFC electrolyte and electrode material by citric acid-nitrate method

Li-Yan; Wu-Jin-xing; Zhao-Da-zhi; Wei-Xin-li(Sch. of Chem. Eng., Zhengzhou Univ., China)

Journal-of-Zhengzhou-University-Engineering-Science. March 2007; 28(1): 106-9

Electrode and electrolyte material fitting to IT-SOFC were synthesized by the combination of sol gel and citric acid-nitrate low temperature self-propagating combustion method. Ce_0.9Gd_0.10_1.95 ( GDC ) and La_0.7Sr_0.3Co_0.3Fe_0.7O₃ (LSCF) are used as electrolyte and cathode material respectively, while NiO-Ce_0.8Sm_0.2O_1.9(NiO-SDC)is a perfect anode precursor material. The crystal structure and reaction progress were investigated with XRD and TG-DTA. The results show that the electrode and electrolyte material with the diameter of tens of nm can be synthesized using sol gel and citric acid-nitrate low temperature self-propagating combustion method. Crystal growth and crystal structure depends strongly on pH value and the sinter temperature.

Effects of Tb doping on the photoluminescence of Y₂O₃:Tb nanophosphors

Muenchausen-RE; Jacobsohn-LG; Bennett-BL; McKigney-EA; Smith-JF; Valdez-JA; Cooke-DW(Mater. Sci. & Technol. Div., Los Alamos Nat. Lab., NM, USA)

Journal-of-Luminescence. Oct. 2007; 126(2): 838-42

The effects of Tb doping on the photoluminescence (PL) of Y₂O₃:Tb nanophosphors have been investigated. Nanophosphors were prepared by the glycine-nitrate solution combustion technique using yttria and terbia powders as precursors. PL excitation spectra at room temperature consist of two overlapping bands centered at 277 and 304nm, whereas emission spectra comprise several groups of lines corresponding to the ⁵D₄to⁷F_J (J=1-6) 4f electronic transitions of the Tb⁺³ ions. A direct comparison of nanophosphor and bulk concentration-quenching curves was obtained by annealing the nanophosphor powder and converting it to bulk material without altering the Tb concentration. The peak in the nanophosphor concentration-quenching curve occurs at a concentration ~3 times higher than that of the bulk. [All rights reserved Elsevier].

The enhancement of weakly exothermic polymerization fronts

Comissiong-DMG; Gross-LK; Volpert-VA(Center. for Math., Coimbra Univ., Portugal)

Journal-of-Engineering-Mathematics. April 2007; 57(4): 423-35

The propagation of one-dimensional waves resulting from chemical reactions in a sandwich-type two-layer setting is considered. One layer, termed the polymerization layer, contains the monomer and initiator molecules needed for the initiation of a self-propagating polymer front. The other layer will be referred to as the enhancement layer, and it contains the necessary reactants to support a highly exothermic self-propagating reaction wave. Heat exchange occurs between the layers, and as a result, there is a net diffusion of heat away from the region undergoing the more exothermic reaction. As frontal polymerization (FP) reactions are known not to be very exothermic, an overall transfer of heat from the enhancement layer into the polymerization layer takes place. An analysis of the basic state of the system is carried out to investigate the effect of heat transfer on the polymerization reaction. An enhancement layer is shown to promote FP. This analysis is applicable to the manufacture of thin polymer films by FP.

Effects of platinum concentration on combustion synthesis of NiAl: application in repairing Ni based superalloys

De-Jouvancourt-H; Record-MC; Marin-Ayral-RM(Lab. de Physico-chimie de la Matiere Condensee, Univ. Montpellier II, France)

Materials-Science-and-Technology. May 2007; 23(5): 593-9

The present work is a study on the effect of platinum concentration on the synthesis of NiAl in the 'SHS build-up process' under high gas pressure. It has been reported in previous work that this process can be used to repair damaged turbine blades, however a further step is necessary to protect them before use. The aim of the present investigation was to show the feasibility of this process for simultaneous repairing and coating. Good results were obtained for a content of 18 at.-%Pt. The Pt aluminide coatings are free of PtAl₂ precipitates and porosity. A good joining is ensured along the superalloy which does not show any damage.

Rapid densification of nano-grained alumina by high temperature and pressure with a very high heating rate

Fancheng-Meng; Zhengyi-Fu; Jinyong-Zhang; Hao-Wang; Weimin-Wang; Yucheng-Wang; Qingjie-Zhang(State Key Lab of Adv. Technol. for Mater. Synthesis & Process., Wuhan Univ. of Technol., China)

Journal-of-the-American-Ceramic-Society. April 2007; 90(4): 1262-4

A novel method for producing full-dense nano-grained alumina was reported. The heat generated by the combustion reaction (or self-propagating high-temperature synthesis (SHS)) was applied to act as a heating source. An alumina compact was loaded inside the combustion reactants. After reaction, the temperature of the alumina compact was increased at a heating rate of 1600 degrees C/min. A large mechanical pressure was applied, when the temperature reached the maximum. Two kinds of alpha -Al₂O₃ powders (200 and 600 nm) were used as the raw materials. The rapid densification process was performed within 2 min. Microstructure analysis indicated that the grains had no significant growth.

Preparation and characterisation of NiCo ferrite nanoparticles

Rajendran-V; Shobana-MK; Jeyasubramanian-K; Kumar-NS(Centre for Nano Sci., Technol. K S Rangasamy Coll. of Technol., Tamil Nadu, India)

Materials-Letters. May 2007; 61(13): 2616-19

The NiCo ferrite has been prepared using sol-gel combustion technique making use of source materials like metal nitrates of Ni, Co and Fe. In order to reduce agglomeration, the polyvinyl alcohol has been added as a reducing agent. The characterisation studies such as XRD and TEM have been carried out to explore the particle size. An increase in particle size with an increase in calcination temperature was noticed. Similarly, the FTIR study confirms the presence of metal oxide. The above studies reveal that the sol-gel combustion technique can be used to produce a wide range of nanoparticles for different applications. [All rights reserved Elsevier].

Sol-gel combustion hybrid method for nanooxide synthesis

Chi-Hwan-Han; Sang-Do-Han; Gwak-J(Photo- & Electro-Mater. Res. Center, Korea Inst. of Energy Res., Daejeon, South Korea)

2007-2nd-IEEE-International-Conference-on-Nano/Micro-Engineered-and-Molecular-Systems-IEEE-Cat.-No.07EX1515. 2007: 3 pp.

Nanopowders were synthesized employing a new route sol-gel combustion hybrid method using acetylene black as a fuel. The dried gels exhibited auto-catalytic combustion behavior. ITO and FTO nanopowders with narrow size distribution were obtained at 750 degrees C. Crystal structures were examined by powder X-ray diffraction (XRD) and particle morphology as well as crystal size was investigated by scanning electron microscopy (SEM). The size of nanopowder was found to be in the range of 16nm to 33 nm.

Preparation of MoB and MoB-MoSi₂ composites by combustion synthesis in SHS mode

Yeh-CL; Hsu-WS(Dept. of Mech. & Autom. Eng., Da-Yeh Univ., Changhua, Taiwan)

Journal-of-Alloys-and-Compounds. 16 Aug. 2007; 440(1-2): 193-8

Combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) was carried out in the Mo-B and Mo-B-Si systems for the preparation of molybdenum boride MoB and the composite of MoB-MoSi₂ from elemental powder compacts. Under a preheating temperature above 150 degrees C, the reaction of Mo with boron in the sample compact of Mo:B=1:1 is characterized by a planar combustion front propagating in a self-sustaining and steady manner. As the preheating temperature or sample compaction density increased, combustion temperature was found to increase and the propagation rate of the combustion front was correspondingly enhanced. Moreover, the XRD analysis provides evidence of yielding nearly single-phase alpha -MoB from the Mo-B sample at equiatomic stoichiometry. In the synthesis of MoB-MoSi₂ composites, the starting stoichiometry of the Mo-B-Si powder compact was varied so as to produce the final composites containing 20-80mol% MoB. It was also found the increase of flame-front velocity and combustion temperature with increasing MoB content formed in the composite. The composition analysis by XRD shows excellent conversion from the Mo-B-Si powder compact to the MoB-MoSi₂ composite through the SHS reaction; that is, in addition to a small amount of Mo₅Si₃, the as-synthesized composite is composed entirely of MoB and MoSi₂. [All rights reserved Elsevier].

Solid-state NMR and XRD study of alpha -SiAlON powders prepared by combustion synthesis

Kexin-Chen; Guanghua-Liu; Huaguang-Yu; Feng-Deng; Heping-Zhou; Kegang-Ren; Pereira-C; Ferreira-JMF(Dept. of Mater. Sci. & Eng., Tsinghua Univ., Beijing, China)

Journal-of-Alloys-and-Compounds. 31 July 2007; 439(1-2): 268-74

²⁷Al and ²⁹Si solid-state NMR spectra and X-ray diffraction (XRD) patterns were obtained for alpha -SiAlON powders prepared by combustion synthesis, according to which the phase transformation and structure evolution of alpha -SiAlON were studied. It was found that in alpha -SiAlON ²⁹Si chemical shift values (-48< delta _Si<-47) were close to those in beta -Si₃N₄ and alpha -Si₃N₄, indicating that Si atoms kept SiN₄ coordination to a large extent in alpha -SiAlON despite the presence of O atoms. Dissimilarly, ²⁷Al chemical shift values in alpha -SiAlON deviated clearly from that corresponding to AlN₄ coordination ( delta _Al~112) and occurred in a range from delta _Al 95.5 to 99.9, which should be assigned to tetrahedral AlO_xN_4-x (0x4) coordination. The broadening effect of AlO_xN_4-x peaks was noticed, which was suggested to induced by slight dispersion of alpha -SiAlON compositions. ²⁷Al resonances assigned to AlO₄ or AlO₆ were also observed, revealing the existence of glassy phase in combustion products. By comparing the intensities of AlO₄ and AlO₆ resonance peaks, it was found that the composition and structure of the co-existing liquid assisting alpha -SiAlON formation were not constant but varied with temperature in combustion synthesis. In addition, with CaF₂ used as Ca-source alpha -SiAlON with low oxygen contents (n

Mechanical-thermal synthesis of chromium carbides

Capocchi-JDT; Cintho-OM; Favilla-EAP(Dept. of Metall. & Mater. Eng., Univ. of Sao Paulo, Brazil)

Journal-of-Alloys-and-Compounds. 31 July 2007; 439(1-2): 189-95

The present investigation deals with the synthesis of chromium carbides (Cr₃C₂ and Cr₇C₃), starting from metallic chromium (obtained from the reduction of Cr₂O₃ with Al) and carbon (graphite). The synthesis was carried out via high energy milling, followed by heat-treating of pellets made of different milled mixtures at 800 degrees C, for 2h, under an atmosphere of argon. A SPEX CertPrep 8000Mixer/Mill was used for milling under argon atmosphere. A tool steel vat and two 12.7mm diameter chromium steel balls were used. The raw materials used and the products were characterized by differential thermal analysis, thermo gravimetric analysis, X-ray diffraction, electronic microscopy and X-ray fluorescence chemical analysis. The following variables were investigated: the quantity of carbon in the mixture, the milling time and the milling power. Mechanical activation of the reactant mixture depends upon the milling power ratio used for processing. The energy liberated by the reduction of the chromium oxide with aluminium exhibits a maximum for milling power ratio between 5:1 and 7.5:1. Self-propagating reaction occurred for all heat-treated samples whatever the carbon content of the sample and the milling power ratio used. Bearing carbon samples exhibited hollow shell structures after the reaction. The level of iron contamination of the milled samples was kept below 0.3% Fe. The self-propagated reaction caused high temperatures inside the samples as it may be seen by the occurrence of spherules, dendrites and whiskers. The carbon content determines the type of chromium carbide formed. [All rights reserved Elsevier].

Investigation of the SHS mechanisms of titanium nitride by in situ time-resolved diffraction and infrared thermography

Frety-N; Carole-D; Paris-S; Vrel-D; Bernard-F; Marin-Ayral-R-M(UMR CNRS, Univ. de Montpellier, France)

Journal-of-Alloys-and-Compounds. 14 June 2007; 436(1-2): 181-6

The self-propagating high-temperature synthesis (SHS) or combustion synthesis is a promising process to produce advanced ceramics due to the high purity of the elaborated materials and the very short synthesis time. Titanium nitride has been synthesised from pressed titanium powder and a nitrogen gas flow under a 0.1MPa pressure. The influence of the addition of a TiN diluent was investigated. For the first time, SHS reaction mechanisms were determined from in situ time-resolved X-ray diffraction (TRXRD) experiments using the synchrotron radiation. These experiments were coupled with infrared thermography to study the propagation of the combustion reaction. It appeared that the initiation of the combustion reaction is due to the alpha -Ti to beta -Ti phase transformation. A single delta -TiN phase was then produced from pressed titanium powder. The addition of a TiN diluent resulted in the synthesis of a multiphase material with the presence of the alpha -Ti, Ti₂N and TiN phases. The combustion reaction propagates in a surface mode at a velocity ranging from 6.4 to 7.4mm/s. [All rights reserved Elsevier].

Influence of an electric field on combustion synthesis process and microstructures of TiC-Al₂O₃-Al composites

Youwei-Yan; Qiaodan-Hu; Peng-Luo(State Key Lab. of Plastic Forming Simulation & Die & Mould Technol., Huazhong Univ. of Sci. & Technol., Wuhan, China)

Journal-of-Alloys-and-Compounds. 31 July 2007; 439(1-2): 132-6

In order to achieve combustion synthesis (CS) of high-density and fine-structured TiC-Al₂O₃-Al composites, the activation of combustion reactions of 3TiO₂-3C-(4+x) Al system with x10mol was conducted by means of external electric field. During the field-activated combustion synthesis (FACS), liquid Al in excess stoichiometric amount was generated and it infiltrated into the synthesized TiC-Al₂O₃ ceramic matrix with porosities, which directly results in a dense TiC-Al₂O₃-Al composites. The influence of electric field on CS process of the reactive system and the resulting microstructures of TiC-Al₂O₃-Al composites was investigated. The results show that an external electric field can effectively improve the adiabatic combustion temperature of the reactive system. Therefore a self-sustaining combustion of the system can be induced thermodynamically. In the experiments, both practical combustion temperature and propagation velocity of combustion wave were obviously enhanced with increasing field strength, whereas sizes of the synthesized TiC and Al₂O₃ particles were significantly decreased at the same time. Under an electric field of 25Vcm^-1, TiC-Al₂O₃-Al composites with a relative density of 92.5% was successfully fabricated through the combustion reaction in the system with x=14mol, in which TiC and Al₂O₃ particles possess fine-structured sizes of 0.2-1.0 mu m, with uniform distribution in metal Al. [All rights reserved Elsevier].

Comparison of the mechanical properties between tantalum and nickel-titanium foams implant materials for bone ingrowth applications

Gil-FJ; Sevilla-P; Aparicio-C; Planell-JA(CREB Dpto. Ciencia de los Mater. e Ingenieria Metalurgica, Univ. Politecnica de Cataluna, Barcelona, Spain)

Journal-of-Alloys-and-Compounds. 31 July 2007; 439(1-2): 67-73

Metallic porous materials are designed to allow the ingrowth of living tissue inside the pores and to improve the mechanical anchorage of the implant. In the present work, tantalum and nickel-titanium porous materials have been characterized. The tantalum foams were produced by vapour chemical deposition (CVD/CVI) and the NiTi foams by self-propagating high temperature synthesis (SHS). The former exhibited an open porosity ranging between 65 and 73% and for the latter it ranged between 63 and 68%. The pore sizes were between 370 and 440 mu m for tantalum and between 350 and 370 mu m for nickel-titanium. The Young's modulus in compression of the foams studied, especially for tantalum, were very similar to those of cancellous bone. This similitude may be relevant in order to minimize the stress shielding effect in the load transfer from the implant to bone. The strength values for NiTi foam are higher than for tantalum, especially of the strain to fracture which is about 23% for NiTi and only 8% for tantalum. The fatigue endurance limit set at 10⁸ cycles is about 7.5MPa for NiTi and 13.2MPa for tantalum. The failure mechanisms have been studied by scanning electron microscopy. [All rights reserved Elsevier].

An experimental investigation on combustion synthesis of transition metal silicides V₅Si₃, Nb₅Si₃, and Ta₅Si₃

Yeh-CL; Chen-WH(Dept. of Mech. & Autom. Eng., Da-Yeh Univ., Changhua, Taiwan)

Journal-of-Alloys-and-Compounds. 31 July 2007; 439(1-2): 59-66

Preparation of transition metal silicides V₅Si₃, Nb₅Si₃, and Ta₅Si₃ was conducted by self-propagating high-temperature synthesis (SHS) from elemental powder compacts at their stoichiometries. The propagation mode of self-sustaining reactions, flame-front velocity, combustion temperature, and phase composition of end products were extensively studied. For the reactant compacts from the mixtures of V:Si=5:3 and Ta:Si=5:3, a planar flame front propagating in a steady manner was observed, with or without sample preheating. On the other hand, a preheating temperature of 200 degrees C or above was required by the Nb-Si powder compact to initiate the self-sustaining combustion. Moreover, it was found that the planar reaction font was not stable in the samples of Nb:Si=5:3 and was transformed into a localized reaction zone propagating in a spinning mode. For all three types of the samples, as the sample density and preheating temperature increased, the combustion temperature was found to increase and the flame-front velocity was correspondingly enhanced. According to the XRD analysis, formation of single-phase silicides V₅Si₃ and Nb₅Si₃ from the reactant compacts of 5V+3Si and 5Nb+3Si, respectively, was confirmed. The samples of 5Ta+3Si yielded predominantly the silicide Ta₅Si₃, along with an intermediate phase Ta₂Si in a small amount. Based upon the temperature dependence of combustion wave velocity, the activation energies associated with combustion synthesis of V₅Si₃, Nb₅Si₃, and Ta₅Si₃ were determined to be 111.5, 259.2, and 105.2kJ/mol, respectively. [All rights reserved Elsevier].

Microstructural observation of titanium wires heated by combustion nitridation in liquid nitrogen

Shibuya-M; Despres-JF(Dept. of Electron Chem., Tokyo Inst. of Technol., Yokohama, Japan)

Journal-of-Alloys-and-Compounds. 14 June 2007; 436(1-2): 195-9

Microstructures of titanium wires heated in liquid nitrogen have been made clear by scanning and transmission electron microscopy to investigate the effects of the combustion nitridation of Ti with liquid N₂. High density N₂ generated from liquid N₂ strongly reacts with Ti wire during heating. Microstructural observations revealed the precipitation of TiN at the surface and the several alpha phases at the inside of the wire. The heated Ti wire was aligned in order of the TiN thin film, the primary- alpha phase and the alpha -acicular phase from the wire surface. The region of the primary- alpha phase which indicates high solubility of N₂ into Ti was increased by the nitridation with liquid N₂. An increase in the primary- alpha phase leads to the accelerated nitridation. [All rights reserved Elsevier].

Synthesis and characterizations of Al-doped Zn_0.95Ni_0.05O nanocrystals

Changtai-Xia; Guangqing-Pei; Linjun-Wang; Xing-Li; Xinbing-Jiao; Jun-Xu(Shanghai Inst. of Opt. & Fine Mech., Chinese Acad. of Sci., China)

Scripta-Materialia. June 2007; 56(11): 967-70

Nanocrystalline Zn_0.95-xNi_0.05Al_xO (x=0.01, 0.02, 0.05 and 0.10) diluted magnetic semiconductors have been synthesized by an autocombustion method. X-ray absorption spectroscopy, high-resolution transmission electron microscopy, energy-dispersive spectrometry and Ni 2p core-level photoemission spectroscopy analyses revealed that some of the nickel ions were substituted for Zn²⁺ into the ZnO matrix while others gave birth to NiO nanoclusters embedded in the ZnO particles. The Zn_0.95Ni_0.05O sample showed no enhancement of room-temperature ferromagnetism after Al doping. [All rights reserved Elsevier].

Photoluminescence properties of La₃PO₇:Eu³⁺ nanoparticles synthesized by a combustion method

Jin-Ye; Qin-Wei-ping; Zhang-Ji-sen; Wang-Yan; Cao-Chun-yan; Zhang-Ji-shuang; Ren-Xin-guang; Zhu-Pei-fen; Wei-Guo-dong; Wang-Li-li; Wang-Guo-feng(Key Lab. of Excited State Processes, Chinese Acad. of Sci., Changchun, China)

Chinese-Journal-of-Luminescence. April 2007; 28(2): 214-18

Eu²⁺-doped oxyphosphate (La₃PO₇) nanoparticles were synthesized by a straightforward combustion method. The synthesis procedure is similar to that of preparing oxide nanomaterials by the combustion method, but here (NH₄)₂HPO₄ is used in producing phosphate nanoparticles. Firstly, La(NO₃)₃ was prepared by putting appropriate molar rate La₂O₃ (1.5 mmol) and Eu₂O₃ into the thin HNO₃, stirring to a transparent solution. Excess water was evaporated and made it condensed while heating to obtain the solid La(NO₃)₃. Then, put into 10 mL thin HNO₃. At the same time, 0.1321 g (NH₄)₂HPO₄ and 0.2703 g glycine were dissolved in deioned water (10 mL). Thirdly, the solution of (NH₄)₂HPO₄ and glycine were added into that of the La( NO₃)₃ with vigorous stirring. The precursor solution was formed. Then, the precursor solution was heated until the white foam was obtained. The reaction took place in a few minutes and all the reactions happened in a wide-mouth beaker. A monoclinic lattice was verified in them by the investigation of X-ray diffraction (XRD). In the emission spectra of Eu³⁺, the ⁵D₀to⁷F₀ transition is often observed when Eu³⁺ is in low site symmetry because it is forbidden based on the group theory. The ⁵D₀to⁷F₁ transition is parity-allowed magnetic dipole transition, which is slightly affected by the symmetry of the Eu³⁺ site. The ⁵D₀to⁷F₂ transition is a parity forbidden electric dipole transition and strong emission only occurs in a non-inversion symmetry site. Under 254 nm excitation, La₃PO₇:Eu³⁺ nanoparticles emitted mainly red fluorescence, assigned to the ⁵D₀to⁷F₂ transition of Eu³⁺ ions and revealed the Eu³⁺ ions occupied asymmetric sites in the oxyphosphate host. After annealing at different temperatures from 400 degrees C to 1 200 degrees C , we found that the higher the annealing temperature, the better the samples crystallized and the bigger the intensity ratio of I(⁵D₀-⁷F₂)/I(⁵D₀-⁷F₁). In comparison with LaPO₄:Eu³⁺, an orange phosphor with stronger ⁵D₀to⁷F₁, emission, La₃PO₇:Eu³⁺ has prominent red luminescence under the same excitation and maybe become a promising red phosphor for PDPs and Hg-free fluorescent lamp in the future.

Effect of concentration on the luminescence of Eu³⁺ ions in nanocrystalline La₂O₃

HuangQing-Liu; LingLing-Wang; ShuQuang-Chen; Bingsuo-Zou(Dept. of Appl. Phys., Hunan Univ., Changsha, China)

Journal-of-Luminescence. Oct. 2007; 126(2): 459-63

Nanocrystalline powders with various Eu³⁺ concentration (from 1 to 10mol %) doped La₂O₃ were prepared via a combustion route. Their structure and morphology were characterized using X-ray diffraction (XRD) and High-resolution transmission electron microscopy. The emission spectra of the as-synthesized samples show that the strongest emission position is centered at 626nm corresponding to ⁵D₀to⁷F₂ transition of Eu³⁺ ions and the intensity change of 626nm emission is considered as a function of ultraviolet (240nm) irradiation time. The excitation spectra at 626nm monitoring indicate that the charge transfer state band is varies with different Eu³⁺ ion concentration. These results are attributed to the surface defects of the nanocrystals. [All rights reserved Elsevier].

Effect of different host on the luminescent property of YAG:Ce³⁺ crystallite formed by combustion

Yang-Zhi-ping; Li-Xu; Li-Xing-min; Yang-yong; Li-Pan-lai(Coll. of Phys. Sci. & Technol., Hebei Univ., Baoding, China)

Journal-of-Synthetic-Crystals. Feb. 2007; 36(1): 191-4

YAG:Ce³⁺ crystallite used for white LED was prepared by combustion method under low temperature. The crystal lattice was found changing when substituting B³⁺, Ga³⁺ for Al³⁺ and La³⁺, Gd³⁺ for Y³⁺ through XRD patterns. The morphology was observed by SEM. The excitation and emission spectra were measured and the emission peak changed with the host. Evident red shift or blue shift occurred when part or all of Y³⁺ or Al³⁺ ions were substituted by other ions, which can match different need for wavelength.

Synthesis of CaAl₂O₄:Eu,Nd long persistent phosphor by combustion processes and its optical properties

Donghua-Chen; Changliang-Zhao(Hubei Key Lab. for Catalysis & Mater. Sci., South-Central Univ. for Nat.ities, Hubei, China)

Materials-Letters. July 2007; 61(17): 3673-5

Eu²⁺,Nd³⁺ co-doped calcium aluminate with high brightness and long persistent luminescence was prepared by the combustion method. The luminescent properties of CaAl₂O₄-based luminescent materials have been studied systematically. The phosphor powders were further investigated by X-ray diffractometer (XRD), photoluminescence excitation and emission spectra (PL) and brightness meter. The analytical results indicated that the phase of CaAl₂O₄ was formed when the initiating combustion temperature was 400 degrees C. The broad band UV excited luminescence of the CaAl₂O₄:Eu²⁺,Nd³⁺ was observed at the blue region ( lambda _max=440 nm) due to transitions from the 4f⁶5d¹ to the 4f⁷ configuration of the Eu²⁺ ion. The decay time of the persistence indicated that the persistent luminescence phosphor has bright phosphorescence and maintains a long duration. [All rights reserved Elsevier].

Moderate temperature synthesis of single-walled carbon nanotubes on alumina supported nickel oxide catalyst

Mohamed-AR; Siang-Piao-Chai; Zein-SHS(Sch. of Chem. Eng., Univ. Sains Malaysia, Pulau Pinang, Malaysia)

Materials-Letters. June 2007; 61(16): 3519-21

A simple nickel oxide catalyst has been developed in synthesizing single-walled carbon nanotubes (SWNTs) at moderate temperature. The catalyst used in the experiment was without a preceding reduction in hydrogen flow. The synthesis of SWNTs was performed at a temperature of 700 degrees C, which represents a moderate reaction temperature. The presence of SWNTs on the catalyst was confirmed by transmission electron microscope (TEM) and Raman spectroscope. The Raman spectrum shows a strong intensity at the radial breathing mode, indicating that the occurrence of SWNTs was dominant. Raman data further reveals that the synthesized SWNTs had the diameters in the range from 0.58 to 2.02 nm. [All rights reserved Elsevier].

Effect of Ti/C ratio on the SHS reaction of Cr-Ti-C system

Jiang-QC; Zhang-WN; Wang-HY; Yin-SQ(Dept. of Mater. Sci. & Eng., Jilin Univ., Changchun, China)

Materials-Letters. June 2007; 61(14-15): 3075-8

The effect of Ti/C molar ratio on the SHS reaction of the Cr-Ti-C system was investigated. With the Ti/C ratio increasing, the type of products synthesized by SHS varied, and the amount of solid solution (Ti,Cr)C_ss increased in the final products; furthermore, also the lattice parameter of (Ti,Cr)C_ss increased due to the reduction in the solubility of Cr in TiC. Moreover, the combustion temperature increased, resulting in the increase of average grain size of (Ti,Cr)C_ss from ~1 mu m to ~5 mu m as well as the grain shape looked more and more like spherical. [All rights reserved Elsevier].

Modeling of chemical kinetics of kerosene/LOX combustion for gas generator

Changjin-Lee; Jungmin-Yu; Yungwhan-Byun; Sung-Taick-Lee(Sch. of Mech. & Aerosp. Eng., Konkuk Univ., Seoul, South Korea)

Proceedings-of-Asian-Joint-Conference-on-Propulsion-and-Power-2006. 2007: 5 pp.

Gas generator is the device to produce high enthalpy gases needed to drive turbo-pump system in liquid rocket engine. And, the combustion temperature in gas generator should be kept below around 1,000K to avoid any possible thermal damages to turbine blade by using either fuel rich combustion or oxidizer rich combustion. Thus, non-equilibrium chemical reaction is dominant in the gas generator. Meanwhile, Kerosene is a compounded fuel mixed with various types of hydrocarbon elements and difficult to model the chemical kinetics. This study focus to model the non-equilibrium chemical reaction of kerosene/LOX with detailed kinetics developed by Dagaut using PSR (perfectly stirred reactor) assumption. In Dagaut's surrogate model for kerosene, chemical kinetics of kerosene consists of 2350 reaction steps with 298 chemical species. Also, droplet evaporation time is taken into account in the PSR calculation by changing the residence time of droplet in the gas generator. The results could provide very reliable and accurate numbers in the prediction of combustion gas temperature, species fraction and material properties.

Characterization of boride ceramic powders prepared by SHS

Yu-Zhi-qiang; Yang-Zhen-guo(Dept. of Mater. Sci., Fudan Univ., Shanghai, China)

Journal-of-Aeronautical-Materials. April 2007; 27(2): 62-7

Self-propagating high-temperature synthesis (SHS) method with reductive process was used to produce TiB₂, TiB₂-Al₂O₃ and ZrB₂-Al₂O₃, etc. borides and composite ceramic powders. X-ray diffraction, XPS, SEM and TEM analysis means were used to analyse microstructure of the synthesized powders. The results showed that TiB₂, ZrB₂ and Al₂O₃ as primary crystalline phase existed in synthesized powders, respectively. By comparison, the particle size distribution of TiB₂ monolithic powder was wider. Owing to the high temperature of SHS, most of them formed aggregates and made the macroscopical particle size big (>5 mu m). While the particles size distribution of TiB₂-Al₂O₃ and ZrB₂-Al₂O₃ composite powders was obviously narrow and free-agglomerate, and the composite particles decreased in the particle size. It could be suggested that it was mainly related to the good interface formation between the different particles in composite powders during the synthesis reaction.

Influence of combustion additive on the structure and properties of Pr-CeO₂ powder prepared by low-temperature combustion synthesis (LCS)

Zhu-Zhen-feng; Wang-Bao-li; Li-Jing-ping; He-Xuan-meng; Yang-Jun; Ma-Jian-zhong(Sch. of Mater. Sci. & Eng., Shanxi Univ. of Sci. & Technol., Xi'an, China)

Journal-of-Synthetic-Crystals. April 2007; 36(2): 443-7

Ce_0.95Pr_0.05O₂ nano-crystallites were prepared by low-temperature combustion synthesis (LCS) using citric acid and acetic ammonium as combustion additive and Ce(NO₃)₃ < middle-dot > 6H₂O and Pr₆O₁₁ as raw materials. The ignition temperature, crystalline structure, morphologies and the coloring properties of the as-prepared nano-crystallites were characterized by DSC, XRD, SEM and colorimeter. Results show that the ignition temperature of the two kinds of precursors prepared by using acetic ammonium and citric acid as combustion additive is about 250 degrees C and 300 degrees C respectively. The Ce_0.95Pr_0.05O₂ solid solutions prepared from the two precursors both exhibit a fluorite crystal structure. Their average crystallite size is about 20-30 nm and 10-15 nm from Scherrer formula, and the particle size of Ce_0.95Pr_0.05O₂ powder is about 200-300 nm. Comparing with the crystallites prepared by using citric acid as combustion additives, the crystallinity, color performance, Pr ion content in CeO₂ crystal lattice and the agglomerates of those crystallites prepared by using acetic ammonium are obviously improved. The best mol ratio of acetic ammonium/cerium nitric and citric acid/cerium nitric is 2:1 and 3:1 respectively.

Synthesis of alpha -Al₂O₃ ultrafine powder by spray combustion method

Zhang-Hai-jun; Jia-Quan-li; Zhai-Peng-liang(Inst. of High Temp. Ceramics, Zhengzhou Univ., China)

Journal-of-Synthetic-Crystals. April 2007; 36(2): 419-23

Using aluminum nitrate and ethanol as starting materials, alpha -Al₂O₃ powder was prepared by spray combustion method. The effects of ethanol amount, the addition of fine alpha -Al₂O₃ seeds and ZnF₂, annealing temperature on the formation of alpha -Al₂O₃ were studied. The structure and microstructure of alpha -Al₂O₃ powder were analyzed by means of XRD and SEM. It shows that with increasing of ethanol amount, the addition of alpha -Al₂O₃ seeds have a clearly positive effect on the synthesis of alpha -Al₂O₃ powder.

Combustion synthesis of long-persistent luminescent MAl₂O₄: Eu²⁺, R³⁺ (M=Sr, Ba, Ca, R=Dy, Nd and La) nanoparticles and luminescence mechanism research

Mengkai-Lu; Zifeng-Qiu; Yuanyuan-Zhou; Aiyu-Zhang; Qian-Ma(State Key Lab. of Crystal Mater., Shan Dong Univ., Jinan, China)

Acta-Materialia. May 2007; 55(8): 2615-20

Eu²⁺, R³⁺ co-doped alkaline earth aluminates MAl₂O₄: Eu²⁺, R³⁺ (M=Sr, Ba and Ca; R=Dy, Nd and La) nanoparticles with high brightness and long afterglow have been prepared by solution-combustion synthesis at 600 degrees C without a post-annealing process for the first time. The morphologies and the phase structures of the products have been characterized by transmission electron microscopy and X-ray diffraction. The excitation and emission spectra of the products have been measured by an Edinburgh FLS920 spectrometer at room temperature. The characteristic luminescence of the as-prepared sample has been evaluated, and the reason why the wavelength changed from yellow-green to blue-green and then to blue-purple in visible range when the composition changed from SrAl₂O₄: Eu²⁺, Dy³⁺ to BaAl₂O₄: Eu²⁺, Nd³⁺ and then to CaAl₂O₄: Eu²⁺, La³⁺ has been explained. Furthermore, a new persistent luminescence mechanism was proposed in this article. [All rights reserved Elsevier].

Application of ceramic coat synthesized by in-situ combustion synthesis to BF tuyere

Yang-Da-zheng; Guan-Yong; Zhang-Yue; Li-Jing; Hu-Jun-ge; Li-Wen-zhu(Sch. of Mater. Sci. & Eng., Beijing Univ. of Sci. & Technol., China)

Journal-of-Iron-and-Steel-Research-International. March 2007; 14(2): 70-2

A novel technology of tuyere protection is introduced. The ceramic coat is synthesized by using in-situ combustion process as the internal, external, and nose protecting coat of BF tuyeres. It can effectively protect the tuyeres and reduce heat loss by cooling water. The technology is quick-acting, easy to use, energy-saving and can make tuyeres have long service life. The feasibility of the application of the tuyere ceramic coat is discussed and the energy-saving effect of the tuyere is compared with that of the tuyeres lined with refractory.

The effect of catalyst calcination temperature on the diameter of carbon nanotubes synthesized by the decomposition of methane

Mohamed-AR; Siang-Piao-Chai; Zein-SHS(Sch. of Chem. Eng., Univ. Sains Malaysia, Pulau Pinang, Malaysia)

Carbon-. June 2007; 45(7): 1535-41

The effect of catalyst calcination temperature on the uniformity of carbon nanotubes (CNTs) diameter synthesized by the decomposition of methane was studied. The catalysts used were CoO-MoO/Al₂O₃ without prior reduction in hydrogen. The results show that the catalyst calcination temperature greatly affects the uniformity of the diameter. The CNTs obtained from CoO-MoO/Al₂O₃ catalysts, calcined at 300 degrees C, 450 degrees C, 600 degrees C, and 700 degrees C had diameters of 13.4< plus-or-minus sign >8.4, 12.6< plus-or-minus sign >5.1, 10.7< plus-or-minus sign >3.2, and 9.0< plus-or-minus sign >1.4nm, respectively, showing that an increase in catalyst calcination temperature produces a smaller diameter and narrower diameter distribution. The catalyst calcined at 750 degrees C was inactive in methane decomposition. Transmission electron microscopy (TEM) studies showed that CNTs grown on the catalyst calcined at 700 degrees C were of uniform diameter and formed a dense interwoven covering. High-resolution TEM shows that these CNTs had walls of highly graphitized parallel graphenes. [All rights reserved Elsevier].

Effects of transverse welds on aluminum alloy columns

Young-B; Zhu-J-H(Dept. of Civil Eng., Univ. of Hong Kong, China)

Thin-Walled-Structures. March 2007; 45(3): 321-9

This paper investigates the effects of transverse welds on aluminum alloy columns. The materials of the specimens were 6063-T5 and 6061-T6 heat-treated aluminum alloys. Various coupon tests were performed to obtain the non-welded and welded material properties of aluminum alloys. An accurate and reliable finite element model (FEM) was used for the simulation of aluminum alloy stub columns of square and circular hollow sections (SHS, CHS) in this study. The stress-strain relationships obtained from the coupon tests were incorporated in the FEM. A parametric study was conducted that included 48 columns of different section shapes with and without transverse welds at the ends of the columns. This study focused on the effects of transverse welds on column strengths with respect to the section slenderness. Hence, the parametric study was performed on stub columns of SHS and CHS in constant column length. The European Code for aluminum structures uses the heat-affected zone (HAZ) softening factor to consider the weakening effects of transverse welds on column strength. The HAZ softening factors obtained from the parametric study were compared with the corresponding values specified in the European Code. HAZ softening factors were proposed in this study. [All rights reserved Elsevier].

In situ laser cladding of Al₂O₃ bearing coatings on aluminium alloy 7075 for improvement of wear resistance

Yue-TM; Huang-KJ; Man-HC(Dept. of Ind. & Syst. Eng., Hong Kong Polytech. Univ., China)

Surface-Engineering. March 2007; 23(2): 142-6

The wear properties of Al₂O₃ bearing coatings, produced by in situ laser induced thermite reactions fabricated on aluminium alloy 7075, were examined. The thermite reactions were initiated by the laser cladding of mixed powders of CuO-Al, Cr₂O₃-Al and TiO₂-Al. In order to improve the quality of the laser formed coatings, the laser cladding involved two passes of melting. The results of the XRD and XPS analyses showed that in all the three reaction systems, a reaction layer which comprised mainly Al₂O₃ and Al phases was formed. Under dry sliding conditions, the wear resistance, in terms of weight loss, of the laser cladded specimens was considerably higher than that of the uncladded specimens. The predominant wear mechanism of the former specimens was found to be characterised by abrasive, while with the latter specimens, it was the adhesive wear that prevailed.

Characteristics of CoY_xFe_2-xO₄ ferrite powders synthesized by sol-gel self-combustion

Meng-Xiangdong; Liu-Mei; Chen-Jingyan; Hua-Jie; Li-Haibo; Zong-Zhanguo(Coll. of Phys., Jiling Normal Univ., China)

Journal-of-the-Chinese-Ceramic-Society. 2007; 35(5): 550-3

CoY_xFe_2-xO₄ (x=0, 0.1, 0.2, 0.3) ferrite powders were synthesized by the sol-gel self-combustion method. The thermal reaction process of amorphous gelatin was studied by thermogravimetric-differential thermal analysis and Fourier transform infrared spectrometry. The structure, crystallite size and magnetic properties of powders were investigated by X-ray diffraction and vibrating sample magnetometer. The results indicate that a single-spinel phase powder with a grain size between 10 and 22 nm is formed after self-combustion synthesis or heat treatment. With the gradual increase in rare-earth Y content, the lattice constants, the size and saturation magnetization of the particles decrease, and the coercivity increases for the samples after self-combustion synthesis. After the heat treatment, the lattice constants, the size and saturation magnetization of the particles increase, and the coercivity first increases and then decreases.

Sintering of beta -Si₃N₄ powder prepared by self-propagating high-temperature synthesis (SHS)

Bai-L; Zhao-SY; Ge-CC(Lab. of Special Ceramics & Powder Metall., Univ. of Sci. & Technol. Beijing, China)

Materials-Science-Forum. 2007: 2179-82

Sintering of the Self-Propagating High-Temperature Synthesis (SHS) of beta -Si₃N₄ powder with 6.67 wt.% Y₂O₃ and 3.33 wt.% Al₂O₃ as sintering additives has been emphatically investigated using hot-press sintering process. The relative density of hot-pressed beta -Si₃N₄ reached near to the full densification (99.43%) at 1700 degrees C. The similar micrographs with self-reinforcing rod-like beta -Si₃N₄ grains forming an interlocking structure were observed. The better mechanical properties of hot-pressed Si₃N₄. such as the hardness (16.73GPa), fracture toughness (5.72 MPa< middle-dot >m¹2/) and bending strength (611.72MPa) values, were obtained at 1700 degrees C. The results indicate that good sinter ability can be obtained with the cheaply SHS of silicon nitride powder for preparing silicon nitride materials, which will make the cost of silicon nitride materials lowered.

Microstructures and mechanical properties of porous Ti₅₁Ni_49-xMo_x shape memory alloys

Jiang-HC; Rong-LJ(Inst. of Metal Res., Chinese Acad. of Sci., Shenyang, China)

Materials-Science-Forum. 2007: 2127-32

Porous Ti₅₁Ni_49-xMo_x (x = 0, 0.7, 1.0, 1.2) shape memory alloys were successfully fabricated by the self-propagating high-temperature synthesis (SHS) method. The effect of Mo content on microstructures, transformation characteristics and compressive properties of porous TiNiMo alloys was investigated systemically. It has been found that Mo doping into porous TiNi alloys will induce R phase transformation. A small amount of Mo addition (0.7at.%) improves compressive properties of porous TiNiMo alloy due to Mo solution strengthening and the obvious ductile fracture is observed on the fracture photography. However, the compressive strength and compressive strain of porous TiNiMo alloys with excessive Mo content decrease sharply and the failure manner turned into brittle fracture mode, which results from a large amount of Ti₂Ni and Ti₄Ni₂O phases precipitated at grain boundary. Porous Ti₅₁Ni_48.3Mo_0.7 alloy with suitable transformation temperature and high compressive strength is very promising for use as biomaterial and damping material.

Study on combustion synthesis and densification process for titanium diboride and iron layered materials

Kun-Wang; Jianping-Liu; Zhengyi-Fu; Weimin-Wang; Hao-Wang; Jinyong-Zhang; Yong-Peng; Qingjie-Zhang(State Key Lab. of Adv. Technol. for Mater. Synthesis & Process., Wuhan Univ. of Technol., China)

Materials-Science-Forum. 2007: 1401-8

The combustion synthesis and densification process for titanium diboride and iron layered materials in the process of self-propagating high-temperature synthesis of titanium diboride, variation of the initial temperature, amount of diluent and particle size of raw materials had effect on the adiabatic temperature, fraction of melted product and propagation rate of the combustion process, were studied by theoretical calculation and experimental analysis. The result showed that divided by a combustion temperature 3050K, either in the high temperature range or in the low temperature range, the calculated process activation energies were 140 KJ/mol or 355 KJ/mol respectively, which revealed two different reaction process mechanisms. Interfacial bonding between TiB₂+Fe cermet and Fe substrate was analyzed by EPMA, which showed interfacial bonding of two-layered product was obtained by the dissolution and the diffusion of Ti in the Fe substrate and joining of Fe binder with Fe substrate. The fractures of joints took place in the TiB₂+Fe cermet layer rather than at the interface.

Reaction mechanisms of combustion synthesis of Si₃N₄-SiC-TiN ceramics

Xuejun-Zhang; Yongting-Zheng; Jiecai-Han; Xinhong-Yang(Centre for Composite Mater., China)

Materials-Science-Forum. 2007: 1615-18

DSC/TG analysis was used to investigate the change of TiSi₂-SiC-N₂ system in the temperature range from room temperature to 1400 degrees C. The relationships between Delta G and T about the reactions possible occurring in TiSi₂-N₂ system during combustion synthesis were calculated. In order to study the combustion process in detail, the reaction of TiSi₂-SiC-N₂ system was stopped at different stages by quenching the samples. The composition and microstructure in different reaction zones were analyzed by means of XRD and SEM, accordingly, reaction kinetic model of TiSi₂-SiC-N₂ combustion system was established. The result showed that TiSi₂ firstly reacted with N₂ to form TiN and Si, and subsequently Si were nitrified.

Aluminum-doped TiO₂ nano-powders for gas sensors

Bose-S; Young-Jin-Choi; Seeley-Z; Bandyopadhyay-A; Akbar-SA(Sch. of Mech. & Mater. Eng., Washington State Univ., Pullman, WA, USA)

Sensors-and-Actuators-B-Chemical. 10 June 2007; 124(1): 111-17

Nano-powders of pure and Al-doped TiO₂ ceramics were synthesized using a citrate-nitrate auto combustion method. Powders were then used to make thick film gas sensors to measure selectivity and sensitivity in CO and O₂ environment. Titanyl nitrate solution was prepared using commercial TiO₂ powder, hydrofluoric acid (HF) and concentrated nitric acid (HNO₃). An optimized ratio of citrate to nitrate was used to produce TiO₂ nanoparticles. Powder X-ray diffraction data showed that synthesized TiO₂ nano-powders, pure as well as Al-doped, had stable anatase phase up to 800 degrees C. X-ray fluorescence confirmed the Al concentrations in synthesized nano-powders. BET surface area analysis showed a decrease at 5wt.% Al addition, followed by an increase at 7.5wt.% in specific average surface area. Particle size analysis showed particles below 100nm for both pure and doped TiO₂ even after calcination at 800 degrees C. The resistance of Al-doped TiO₂ samples was found to be lower than that of pure TiO₂ in O₂ and CO environment. Al-doped TiO₂ gas sensors were more selective and sensitive to CO and O₂ at an operating temperature of 600 degrees C than pure TiO₂ powders. [All rights reserved Elsevier].

Fabrication of Al-added TiN materials by the combination of double self-propagating high-temperature synthesis and pulsed electric-current pressure sintering

Nakane-S; Hikawa-S; Endo-T; Kato-M; Hirota-K; Miyauchi-H; Hioki-T(Nippon Electr. Glass Co. Ltd., Shiga, Japan)

International-Journal-of-Applied-Ceramic-Technology. 2007; 4(2): 175-83

Crystalline phases of Al-added TiN, denoted as (Ti_1-xAl_x)N_y (0 x 0.10, 0.8 < y < 1.0), prepared from a mixture of Ti and Al powders by self-propagating high-temperature synthesis (SHS) in a nitrogen atmosphere, have been investigated. By repeating SHS twice, in the region of 0.0 < x 0.02 cubic (Ti_1-xAl_x)N_y solid solutions, and in the region of 0.02 < x 0.10 composites consisting of (Ti_1-xAl_x)N_y and hexagonal Ti₂AlN were formed. After powder characterization, they were consolidated to dense materials ( > 97% of theoretical) by pulsed electric-current pressure sintering. With increasing Al addition, the optimum sintering temperatures were lowered, followed by reduction of grain size. Their mechanical properties, that is, three-point bending strength delta _b, Vickers hardness H_v, and fracture toughness K_1C were evaluated as a function of Al content.

Synthesis of manganese oxide/carbon nanotube nanocomposites using wet chemical method

Zein-SHS; Loon-Chong-Yeoh; Siang-Piao-Chai; Mohamed-AR; Mahayuddin-MEM(Sch. of Chem. Eng., Univ. Sains Malaysia, Pulau Pinang, Malaysia)

Journal-of-Materials-Processing-Technology. 23 July 2007; 190(1-3): 402-5

Novel material with peculiar properties can be obtained by introducing foreign materials into the inner cavity of carbon nanotubes. It has been suggested that the materials encapsulated into the hollow regions of carbon nanotubes could result in a significant change of the properties of these small particles, forming new hybrid composites with extraordinary properties. In this short communication, filling of carbon nanotubes with manganese oxide by wet chemical method is demonstrated. Transmission electron microscopy (TEM) result showed the hollow structure of carbon nanotubes were filled with manganese oxide. Energy dispersive X-rays (EDX) spectra elucidate the presence of manganese oxide in the filled carbon nanotubes whereas SEM result showed that manganese oxide is not crystallized at the outer surface of carbon nanotubes. [All rights reserved Elsevier].

SiC powder for casting from aqueous suspension

Stobierski-L; Lis-J; Gubernat-A(Fac. of Mater. Sci. & Ceramics, AGH-Univ. of Sci. & Technol., Krakow, Poland)

11th-International-Ceramics-Congress. 2006: 6 pp.

The activation of silicon carbide by boron and carbon is required to obtain dense monophase sintered body from SiC powder. The presence of carbon renders casting from aqueous suspension impossible. The SiC powders with boron and extra carbon were prepared by combustion method (SHS), where carbon was bound to SiC particles in a stable way. The experiments showed that this powder could be used for processing by casting of aqueous suspension. Finally nearly dense polycrystals were obtained by pressureless sintering.

Effects of fuel compositions on the structure and yield of flame synthesized carbon nanotubes

Camacho-J; Choudhuri-AR(Dept. of Mech. & Ind. Eng., Texas Univ., El Paso, TX, USA)

Fullerenes,-Nanotubes,-and-Carbon-Nanostructures. March-April 2007; 15(2): 99-111

Flame synthesis of carbon nanostructures including nanotubes on galvanized steel was investigated utilizing laminar diffusion flames of different types of fuel. Methane (CH₄), propane (C₃H₈) and acetylene (C₂H₂) were used as fuels. Distinctive carbon nanostructures were produced depending on fuel types and fuel flow rates. The qualitative and quantitative analysis of many transmission electron microscope (TEM) and scanning electron microscope (SEM) images were performed. Methane produced thin multi wall carbon nanotubes as well as nanorods and nanofibers within the fuel flow rate range of 7.18E-07 m³/s to 9.57E-07 m³/s. Propane yielded nanotubes only at the fuel flow rate of 4.20E-07 m³/s. The nanotubes synthesized by acetylene flames were of different types that included helically coiled and twisted nanotubes.

Tailoring of phase assemblage and grain morphology of (Nd,Dy)-containing SiAlON powders prepared by combustion synthesis

Kexin-Chen; Guanghua-Liu; Heping-Zhou; Jin-H; Pereira-C; Agrathopoulos-S; Ferreira-JMF(Dept. of Mater. Sci. & Eng., Tsinghua Univ., Beijing, China)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 25 April 2007; 454-455: 310-13

(Nd,Dy)-containing SiAlON powders were prepared by combustion synthesis, where it was proved that the phase assemblage and grain morphology of final products could be tailored by controlling the relative contents of the two rare-earth elements. When the molar ratio of Dy/(Nd+Dy) was increased, the phase content of alpha -SiAlON was promoted and beta -SiAlON was reduced. At the same time, the grain morphology of combustion products varied from elongated prismatic crystals to fine isotropic grains. It was also found that the lattice parameters of both alpha - and beta -SiAlON were affected by Dy/(Nd+Dy) ratios. The experimental results were discussed by considering the different ability of Dy³⁺ and Nd³⁺ to stabilize alpha -SiAlON structure. [All rights reserved Elsevier].

Fabrication of BN-AlN-TiB₂ compound conductive ceramics by self-propagating high temperature synthesis and hot isostatic pressing

Zhou-Lijuan; Zheng-Yongting; Du-Shanyi(Center for Composite Mater., Harbin Inst. of Technol., China)

Key-Engineering-Materials. 2007: 786-9

BN-AlN-TiB₂ compound conductive ceramics from powder mixtures of BN, Al, and TiB₂ was fabricated by self-propagating high temperature synthesis (SHS) and hot isostatic pressing (HIP). The powder mixtures were shaped by isostatic cool pressing at 5-10MPa and the combustion reaction was carried at 100-200 MPa N₂ by an ignitor. XRD experiments confirmed that the reaction was complete and only AlN, BN and TiB₂ were detected. Optical microscopy as well as SEM with an electron probe microanalysis was used for microstructural analysis and revealed a relatively uniform distribution of particulates. The temperature-dependence and composition-dependence of the electrical resistivity of BN-AlN-TiB₂ ceramics were studied. The results showed that the optimum composition was 5-10wt% BN, 30-55wt% Al and 60-40wt% TiB₂, and the products had the density of 90% of the theoretical, resistivity of 80-1000 mu Omega < middle-dot >cm and bending strength of 100-200 MPa.

Microstructure and electrical conductivity of Ni-YSZ cermets prepared by combustion synthesis method

Tiesong-Lin; Dechang-Jia; Kening-Sun(Inst. for Adv. Ceramics, Harbin Inst. of Technol., China)

Key-Engineering-Materials. 2007: 437-9

Ni-YSZ cermets were prepared by combustion synthesis of Y(NO₃)₃, Zr(NO₃)₄, Ni(NO₃)₂ and urea followed by hydrogen reduction at 800 degrees C. The microstructure and electrical conductivity of Ni-YSZ cermets were investigated as contrasted to those of the cermets with the same Ni contents prepared by mechanically mixing method. The cermets prepared by combustion synthesis method had better homogeneity of Ni distributed in YSZ than those prepared by mechanically mixed method; thus, both Ni and YSZ phases formed, to a certain extent, a continuous network structure. The electrical conductivity of the cermets prepared by combustion synthesis method was always better than that obtained with the samples prepared by mechanically mixed method.

Nitrate-citrate combustion synthesis and properties of Ce_1-xGd_xO_2-x2/ solid solutions

Cheng-Peng; Zhen-Zhang(Dept. of Appl. Chem., South China Univ. of Technol., Guangzhou, China)

Key-Engineering-Materials. 2007: 401-4

The structure, thermal expansion coefficients, and electric conductivity of Ce_1-xGd_xO_2-x2/ (x = 0 ~ 0.6) solid solutions, prepared by gel-combustion method, were investigated. The uniform small particle size of the gel-combustion prepared materials allows sintering of the samples into highly dense ceramic pellets at 1300 degrees C, a significantly lower temperature, compared to that of 1600~1650 degrees C required for ceria solid electrolytes prepared by traditional solid state techniques. XRD showed that single-phase solid solutions have been formed in all investigated range. The maximum conductivity, sigma _{600 degrees C}= 5.26 x 10^-3 S/cm, was found at x = 0.2. The thermal expansion coefficient, determined from high-temperature X-ray data is 8.125 x 10^-6 K^-1 at x = 0.2.

Preparation and microwave permittivity of SiC-AlN solid solution powders

Xiaokui-Liu; Wancheng-Zhou; Fa-Luo; Dongmei-Zhu(State Key Lab. of Solidification Process., Northwestern Polytech. Univ., Xi'an, China)

Key-Engineering-Materials. 2007: 310-12

SiC-AlN solid solution powders were prepared from the mixtures of aluminum, silicon and carbon black in a nitrogen atmosphere with preheating self-propagating high temperature synthesis (SHS) method. The powders synthesized with different ratios of Al/Si were mixed with paraffin wax and the microwave permittivity of the mixtures was measured at the frequency of 8.2~12.4 GHz. The results were contrasted with that of SiC powders synthesized by preheating SHS in argon and nitrogen atmosphere respectively. The epsilon ', epsilon ", and the tg delta ( epsilon "/ epsilon ') of the mixture of SiC prepared in a nitrogen atmosphere are highest, followed with those of the SiC-AlN solid solution powders and the SiC powders prepared in an argon atmosphere. Along with the increase of atomic ratio of Al/Si, the epsilon ', epsilon ", and tg delta of SiC-AlN solid solution decrease. We believe that, with the increase of AlN dissolved, the concentration of carriers and the effect of dielectric relaxation will decrease because of the two contrary dopants.

Synthesis of ultrafine Lu₂Hf₂O₇/Tb phosphor by solution combustion process

Yikun-Liao; Danyu-Jiang; Yunpeng-Xu; Jianlin-Shi(Shanghai Inst. of Ceramics, Chinese Acad. of Sci., Shanghai, China)

Key-Engineering-Materials. 2007: 640-2

Ultrafine terbium-doped Lu₂Hf₂O₇/Tb phosphor powders are prepared by a solution combustion process using glycine and urea as fuel. Phase evolution of the synthesized powder is determined by X-ray diffraction (XRD) techniques. Single-phase cubic Lu₂Hf₂O₇/Tb crystalline powder is obtained by calcining the amorphous materials at 800 degrees C and no intermediate phase is observed. Transmission electronic microscope (TEM) morphology shows that the resultant Lu₂Hf₂O₇/Tb powders have uniform size and good homogeneity. The photoluminescence (PL) spectra of Tb³⁺ substituted for Lu³⁺ in Lu₂Hf₂O₇ with different content has been measured on samples calcined at 1000 degrees C.

Defect and its influence on mechanical property of titanium diboride-copper matrix composite

Li-Xu; Jiecai-Han; Xinghong-Zhang(Center for Composite Mater. & Struct., Harbin Inst. of Technol., China)

Key-Engineering-Materials. 2007: 1414-16

The TiB₂-40Cu-8Ni composite prepared by combustion synthesis is investigated. Both 2D digital radiography (DR) and 3D computed tomography (CT) are used to test the specimens non-destructively. The result shows that ceramic phase aggregation is the main defect. Then the mechanical properties of samples are assessed by means of three-point-bend test. It appears that mechanical properties are related with the distribution of TiB₂ phase and Cu phase. The scanning electron microscope (SEM) is also used to observe the crack growth of the bending test sample.

Preparation of TiB₂ nanoparticles reinforced Cu-matrix composite by direct combustion synthesis

Qiang-Xu; Xinghong-Zhang; Jiecai-Han; Xiaodong-He(Sch. of Mater. Sci. & Eng., Beijing Inst. of Technol., China)

Key-Engineering-Materials. 2007: 1339-41

Titanium diboride nanoparticles reinforced copper matrix composite by combustion synthesis technology from titanium, boron and copper powders without other activated methods. Thermodynamics of the system was calculated theoretically. It was found that TiB₂ was stable phase in the composite and TiCu interphase compound can convert into stable phase. The phases of the synthesized product were identified using X-ray diffraction and the results showed that only TiB₂ and Cu phases, no other phases existed in the product. It is consistent with the calculated result of thermodynamics. SEM microstructural characterization showed that a homogenous distribution of the titanium diboride nanoparticles in the copper matrix.

Mechanical properties and microstructure of Al₂O₃-TiC composite by hot-pressing

Suilin-Shi; Lingzhen-Zhang(Shijiazhuang Mech. Eng. Coll., China)

Key-Engineering-Materials. 2007: 1424-5

In this study, Al₂O₃-TiC composite was prepared at 1600 degrees C for 1 h by hot-pressing using the Al₂O₃-TiC composite powder synthesized from self-propagating high-temperature synthesis (SHS) process. Mechanical properties of the composite were investigated, such as bulk density, Vickers hardness, fracture toughness and bending strength. The microstructure of the composite was also investigated by scanning electron microscopy (SEM).

Microstructure of ceramic layer in composite pipe made by SHS-gravitational process

Tao-Lin; Fenge-Cui; Sheng-Yin; Zhimeng-Guo(Dept. of Powder Metall., Sci. & Technol. Univ. Beijing, China)

Key-Engineering-Materials. 2007: 1722-4

SHS-gravitational process was developed to synthesize the ceramic lined steel pipe, especially for elbow, conical pipe, three-way and four-way pipe and pipe with a small diameter. In SHS-gravitational process, the molten ceramic, which separated out from the reaction products due to their density difference, solidified to form the ceramic lined layer in the steel pipe when contacted with the steel pipe wall. With an X-ray diffractometer and a scanning electron microscope, it can be found that the ceramic layer is composed of alpha -Al₂O₃ and FeAl₂O₄. A small amount of iron also remains in the ceramic layer. There is a thin equiaxed grain area of alumina near the steel pipe wall, and then alumina was grown in form of dentrite to the surface of ceramic layer. FeAl₂O₄ distributes among alumina dentrite. Although the ceramic layer was solidified from one end to another end of a pipe, the microstructure of ceramic layer was almost uniform throughout the whole length of the pipe.

Thermal shock resistance and ablation behavior of TiB₂-Cu-Ni composite via combustion synthesis

Zhang-Yong; Xinghong-Zhang; Qiang-Xu(Center for Composite Mater., Harbin Inst. of Technol., China)

Key-Engineering-Materials. 2007: 1513-16

TiB₂-Cu-Ni cermet composite was fabricated by self-propagating high-temperature synthesis combined with Pseudo Hot Isostatic Pressing. The microstructure of the composite is fine and uniform. The thermal shock resistance and ablation behavior of the TiB₂-Cu-Ni composite was investigated by heating it for twenty seconds using a plasma torch arc heater. Fatal breakup took place in the monolithic TiB₂ ceramic once the plasma arc flow faced the surface of the ceramic. Only a small crack was found on the ablation surface of the TiB₂-Cu-Ni composite. The thermal stress fracture resistance parameter, R, and the critical energy release rate G_IC of TiB₂-Cu-Ni composite are at the same order with that of the W/Cu alloy. It showed that the properties of thermal shock resistance and the ablation of the composite are good. The fraction of mass loss of the homogeneous composite was 2.32%, which was similar to that of traditional W/Cu alloy. The volatilization of the metal binder and mechanical erosion was the main mechanisms of the ablation.

Preparation of porous Si₃N₄ based ceramics by combustion synthesis

Wenkui-Li; Junhuai-Xiang; Baolin-Zhang(Jiangxi Key Lab. of Surface Eng., Jiangxi Sci. & Technol. Normal Univ., Nanchang, China)

Key-Engineering-Materials. 2007: 1087-9

This paper presents the results of combustion synthesis of porous Si₃N₄ based ceramics from silicon powders, with fine alpha -Si₃N₄ and BN powders as diluents, under high nitrogen pressure. The effect of addition of BN on the morphology is investigated. The results revealed that the strength decreased and the porosity increased with the addition of BN, which is strongly depended on the final morphology of the products.

The effect of diluent on combustion synthesis of Si₃N₄-SiC-TiN ceramics with small diameter

Xuejun-Zhang; Yongting-Zheng; Jiecai-Han(Centre for Composite Mater., Harbin Inst. of Technol., China)

Key-Engineering-Materials. 2007: 1084-6

Si₃N₄-TiN-SiC multiphase ceramics was synthesized from TiSi₂ and SiC powders by combustion synthesis. The effect of dilute content on conversion percentage was calculated in theory assuming that there is no penetration of nitrogen gas, and combustion synthesis was carried under different conditions. The results show that the increase of diluent content in certain extent is helpful for nitrification of TiSi₂ and free silicon were detected in the 30wt% and 40wt% SiC-diluted samples with 45vol% porosity while no silicon were found in 50vol% porosity green parts. The increase in diluent content and porosity of the compacts are favorable for the development of rod-like beta -Si₃N₄ and the long-diameter ratio of beta -Si₃N₄ is increase as the increase of these two values.

Combustion synthesis of magnesium silicon nitride powders in the Mg-Si-N system

Fei-Wang; Wei-Ping-Shen; Ling-Bai; Chang-Chun-Ge(Lab. of Special Ceramics & Powder Metall., Univ. of Sci. & Technol. Beijing, China)

Key-Engineering-Materials. 2007: 935-8

A combustion synthesis process was developed for the synthesis of magnesium silicon nitride powders in the Mg-Si-N system. The effects of ammonium halide addition and the nitrogen pressure on the phase composition and microstructure of the final product were discussed in detail. It was found that ammonium halides were helpful to enhance the nitrogen infiltration, decrease the agglomeration degree and improve the nitridation reaction. Furthermore, the nitrogen pressure greatly influenced the reaction process and the properties of the final MgSiN₂ products, especially the phase composition. MgSiN₂ powders with low level of impurities (MgO and free Si) could be synthesized through combustion synthesis process in the Mg-Si-N system.

Preparation of (Ca+M) (M = Mg, Yb, Sr) co-doped alpha -SiAlON powders by combustion synthesis

Liu-GH; Chen-KX; Zhou-HP; Ren-KG; Pereira-C; Ferreira-JMF(Dept. of Mater. Sci. & Eng., Tsinghua Univ., Beijing, China)

Key-Engineering-Materials. 2007: 930-2

In this paper, alpha -SiAlON powders co-doped with (Ca+M) (M = Mg, Yb, Sr) were prepared by combustion synthesis. The effect of Ca incorporation on the phase composition and grain morphology of reaction products was discussed. The experimental results showed that Ca incorporation promoted the growth of rod-like alpha -SiAlON crystals in (Ca+Mg) and (Ca+Yb) systems. For (Ca+Sr) system, the addition of Ca assisted Sr into alpha -SiAlON crystal lattice and increased the relative content of alpha -SiAlON in reaction product.

Effects of different debinding atmosphere on the properties of powder injection molded AlN ceramics

Xueli-Du; Mingli-Qin; Humail-IS; Peizhong-Feng; Xuanhui-Qu(Sch. of Mater. Sci. & Eng., Univ. of Sci. & Technol. Beijing, China)

Key-Engineering-Materials. 2007: 1028-30

In the present work the influence of two different thermal debinding atmosphere, vacuum and air, on the properties of 5wt% Y₂O₃-doped aluminum nitride (AlN) ceramics was investigated. The AlN powder as a raw material was synthesized by self-propagating high-temperature synthesis (SHS) and compact was fabricated by employing powder injection molding technique. The polymer-wax binder consists of 60wt% paraffin wax (PW), 35wt% polypropylene (PP) and 5wt% stearic acid (SA). The binder was removed through debinding process in two steps, solvent debinding followed by thermal debinding. After the removal of binder, specimens were sintered at 1850 degrees C in nitrogen atmosphere at atmospheric pressure. The result reveals that debinding atmosphere has significant effect on the thermal conductivity and densification of AlN ceramics. The microstructure and secondary phase identification was determined by scanning electron microscopy and X-ray diffraction. The thermal conductivity and density of injection molded AlN ceramics are 177.3 W< middle-dot >m^-1< middle-dot >K^-1 and 3.31 g< middle-dot >cm^-3 in the air and 200.8 W< middle-dot >m^-1< middle-dot >K^-1 and 3.28 g< middle-dot >cm^-3 in the vacuum.

On the progress of combustion synthesis of Si₃N₄ ceramic: from laboratory research to industrial production

Jiang-Tao-Li; Yun-Yang; Hai-Bo-Jin(Tech. Inst. of Phys. & Chem., Chinese Acad. of Sci., Beijing, China)

Key-Engineering-Materials. 2007: 911-15

The progress on the combustion synthesis of Si₃N₄ powders during the past decades was summarized with the emphasis on the recently developed mechano-chemically activated combustion synthesis (MACS) method. The effects of processing parameters such as the addition of diluent and ammonium salts into the green mixtures, the variation of nitrogen pressure as well as the mechanical activation treatment on the degree of Si to alpha -Si₃N₄ conversion was evaluated. The combination of mechanical activation and chemical stimulation was effective in enhancing the reactivity of Si powder reactants, which was responsible for the extension of the minimum nitrogen pressure normally required for the combustion synthesis of Si₃N₄. This breakthrough indicates that nitriding combustion of silicon in pressurized nitrogen could be promoted by activating the solid reactants instead of by increasing the pre-exerted nitrogen pressure. The MACS process was successfully applied to the industrial production of Si₃Ni₄ powders, the regularities for the large-scale synthesis were reported, and the as-synthesized Si₃N₄ powder products were systematically characterized.

A comparison study on microstructure and mechanical properties of Si₃N₄ ceramic prepared from MACS powders

Ren-KG; Chen-KX; Jin-HB; Ning-XS; Zhou-HP(Dept. of Material Sci. & Eng., Tsinghua Univ., Beijing, China)

Key-Engineering-Materials. 2007: 1179-81

In present work, ultra-fine powders with alpha phase content higher than 95 wt% and specific surface area of 15.33 m²/g were prepared by mechanical activated combustion synthesis (MACS) process. The sinterability of as-fabricated Si₃N₄ as well as the microstructure and mechanical properties of the sintered bulk were investigated by comparing with a kind of commercial available Si₃N₄ powders used as diluents in MACS process. Employing hot-pressing method, both powders were sintered equally by using Y₂O₃ and Al₂O₃ as sintering aids. Results showed that smaller particle size and higher specific surface area were obtained by MACS process when compared with the commercial one. Bulk Si₃N₄ appeared approximately the same relative density, hardness, strength and fracture toughness, however, proved to be higher while using MACS powders.

Fatigue tests and design of thin CHS-plate T-joints under cyclic in-plane bending

Mashiri-FR; Zhao-XL(Sch. of Eng., Univ. of Tasmania, Hobart, Tas., Australia)

Thin-Walled-Structures. April 2007; 45(4): 463-72

A review of existing fatigue design guidelines has been undertaken and shows that there are no fatigue design recommendations for circular hollow section-to-plate T-joints subjected to in-plane bending. This paper therefore reports on the high cycle fatigue behaviour of welded thin-walled circular hollow section (CHS) tubes of thicknesses less than 4mm that are fillet-welded onto a plate to form a base plate moment connection. The resultant thin CHS-Plate T-joints are subjected to cyclic in-plane bending load to determine their fatigue strength at different stress ranges. The S-N data from the failed thin CHS-Plate T-joints is analysed using the least-squares method of statistical analysis to obtain a design S-N curve. The derived design S-N curve for the thin CHS-Plate T-joints is compared to existing design S-N curves and also that of square hollow section (SHS)-to-plate T-joints under in-plane bending in current fatigue design guidelines. The thin CHS-Plate T-joints are found to have a better fatigue strength compared to the existing S-N curve for SHS-Plate T-joints under in-plane bending. An appropriate design S-N curve from the group of existing design S-N curves is adopted for the design of thin CHS-Plate T-joints. [All rights reserved Elsevier].

Sintering of mixed-conducting composites for hydrogen membranes from nanoscale Co-synthesized powders

Canfield-NL; Crum-JV; Matyas-J; Bandyopadhyay-A; Weil-KS; Pederson-LR; Hardy-JS(Pacific Northwest Nat. Lab., Richland, WA, USA)

Materials-Science-Forum. 2007: 1415-20

The potential for highly selective, nongalvanic permeation of hydrogen through dense mixed conducting composites at elevated temperatures makes them attractive as hydrogen separation membranes. The glycine-nitrate combustion synthesis technique has been used to co-synthesize a cation-doped barium cerate protonic conducting phase together with a metallic nickel electronic conducting phase (15-35 vol% Ni). Co-synthesis of these phases results in an intimately mixed powder with particle sizes on the order of 10 nm. DTA/TGA of all as-synthesized compositions determined that a calcination temperature of 1000 degrees C was required for full reaction of the cerate components. DTA/TGA and sintering shrinkage dilatometry were performed on calcined powders to determine that a sintering temperature of 1250 degrees C would be adequate for achieving >90% relative density in all compositions. Bars of the material containing 25 vol% Ni were reduced at three different points in the heat treatment process (e.g., before, during, or after sintering). It was determined that there was less porosity in the sample reduced during sintering than any other. It was also seen on SEM that the primary grain size, regardless of when reduction occurred compared to sintering of the material, is less than 5 mu m.

Synthesis and sintering behavior of nano crystalline Gd-doped ceria

Jo-Seung-Hwan; Kim-Jong-Ho; Kim-Do-Kyung(Dept. of Material Sci. & Eng., Korea Adv. Inst. of Sci. & Technol., Daejeon, South Korea)

Materials-Science-Forum. 2007: 1373-8

Two kinds of nano crystalline Gd-doped CeO₂ particles were successfully synthesized via glycine-nitrate combustion and neutral precipitation with subsequent hydrothermal crystallization. It was revealed that the surface modification of nano particles significantly affected sintering behaviors and resulting physical properties. Glycine/nitrate ratio was a key parameter to control the surface state of nano particles in the glycine-nitrate process, but, in the neutral precipitation process, the solvent was important. To obtain the GDC nano particles with chemically and physically favorable properties, the effect of the surface state of nano particles on the sintering behavior was discussed with consideration of aggregation property and surface-adsorbed substances on nano particles.

Intelligent simulation of traffic flow in port area with MAS and SHS

Yang-Shen-hua; Shi-Chao-jian; Guan-Ke-ping; Ying-Shi-jun(Merchant Marine Coll., Shanghai Maritime Univ., China)

Journal-of-System-Simulation. Jan. 2007; 19(2): 289-92, 299

Applying the theory and technology of multi-agent system (MAS), an intelligent simulation system of traffic flow in port area was developed on shiphandling simulator (SHS) platform. Algorithms for port dispatch and ship automatic navigation were proposed for reasonable simulation. The system defines distinct agents for arrival ship, port dispatch operation, berth and fairway respectively. Solutions were determined with the intelligent character of agents and through the interaction among agents. The system was applied to the assessment of proposed plan of Qianwan area of Qingdao port. It simulated the future situation of vessel traffic flow in the port area. The experimental data were compared with that calculated with queueing theory. The system provides a more reasonable result for the assessment and demonstration of port planning.

Self-propagating combustion preheating and explosive consolidation of Mo/Cu functionally gradient material

Wang-Pengfei; Shen-Weiping; Zhang-Qiang; Zhang-Ke; Jiang-Zhiming; Chen-Pengwan(Beijing Univ. of Sci. & Technol., China)

Rare-Metal-Materials-and-Engineering. April 2007; 36(4): 652-5

Mo/Cu functionally gradient material (FGM) was prepared by self-propagating combustion preheating and bidirectional explosive consolidation with buffer action of water. The density, hardness and electric conductivity of each layer were measured: the relative density increased, the hardness decreased and the electric conductivity increased with the increase of Cu content in Mo/Cu FGM. The microstructure of Mo/Cu FGM was observed by SEM. The relative density of each layer in Mo/Cu FGM increased from 94.2% of Mo layer to 98.4% of Cu layer. The relative density of integral Mo/Cu FGM attained 95.5%. The shearing strength between the first layer and the second layer of the Mo/Cu FGM was 214.8 MPa. The thermal conductivities of third layer and fourth layer were 204.76 W < middle-dot > m^-1 < middle-dot > K^-1 and 249.71 W < middle-dot > m^-1 < middle-dot > K^-1, respectively.

TiC/Ni₃Al coating on steel via combustion synthesis during casting

Wang-SQ; Li-XX; Chen-KM; Jin-HJ(Dept. of Mater. Sci. & Eng., Jiangsu Univ., Zhenjiang, China)

Materials-Letters. May 2007; 61(11-12): 2531-4

TiC-reinforced Ni₃Al intermetallic matrix composite coating on steel was fabricated successfully using the combustion synthesis reaction of 3Ni-Al-Ti-C system during casting. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectrum (EDS) are used to analyze phases, microstructure and composition of the coating and the interface. The results show that the coating is composed of Ni₃Al and TiC. In the coating, TiC particulates with dimension of 1-2 mu m are relatively uniformly distributed in Ni₃Al matrix. The coating is compactly formed on steel with a metallurgical bonding interface. The wear resistance of the coating is 4.3 and 23.4 times higher than that of steel substrate at the room temperature and 400 degrees C respectively. [All rights reserved Elsevier].

Understanding localized-scanning worms

Zesheng-Chen; Chao-Chen; Chuanyi-Ji(Sch. of Electr. & Comput. Eng., Georgia Inst. of Technol., Atlanta, GA, USA)

2007-IEEE-International-Performance,-Computing-and-Communications-Conference-IPCC-'07-IEEE-Cat-No.-07CH37894. 2007: 186-93

Localized scanning is a simple technique used by attackers to search for vulnerable hosts. Localized scanning trades off between the local and the global search of vulnerable hosts and has been used by Code Red II and Ninida worms. As such a strategy is so simple yet effective in attacking the Internet, it is important that defenders understand the spreading ability and behaviors of localized-scanning worms. In this work, we first characterize the relationships between vulnerable-host distributions and the spread of localized-scanning worms through mathematical modeling and analysis, and compare random scanning with localized scanning. We then design an optimal localized-scanning strategy, which provides an upper bound on the spreading speed of localized-scanning self-propagating codes. Furthermore, we construct three variants of localized scanning. Specifically, the feedback localized scanning and the ping-pong localized scanning adapt the scanning methods based on the feedback from the probed host, and thus spread faster than the original localized scanning and meanwhile have a smaller variance.

Microstructure and property of TiB₂-dispersed Cu-matrix composites

Ji-Soon-Kim; Jong-Won-Kum; Eun-Hee-Kang; Dang-Thuy-Nguyen; Jin-Chun-Kim; Yong-Soon-Kwon(Sch. of Mater. Sci. & Eng., Ulsan Univ., South Korea)

2006-International-Forum-on-Strategic-Technology-IEEE-Cat-No.-06EX1401C. 2006: 366-8

In the present work, the microstructure and properties of Cu-based composites with 4.5 vol.% dispersed TiB₂ particles developed by a combined process of mechanical alloying (MA), self-propagate high temperature synthesis (SHS) and spark-plasma sintering (SPS) will be reported. The microstructure of the composites revealed that the TiB₂ dispersoids with the particle size of smaller than 250 nm uniformly distributed in Cu matrix. The sintered samples obtained approximately 99% in relative density after sintering at 650 degrees C for 5 min. The fine dispersed TiB₂ dispersoids in Cu matrix was the main reason to improve the mechanical properties of the composites. The hardness reached a value of 74 H_rB. The result of tensile test showed that the ultimate tensile strength, yield strength and Young modulus increased from 187 MPa, 158 Mpa and 119 GPa for pure Cu to 485.7 MPa, 355.3 MPa and 157 GPa for the composites, whereas the electrical conductivity remained a high value of 83 % IACS. After soaking at 850, 900 and 950 degrees C, the hardness of composites decreased to 62, 61 and 55 H_rB, respectively. The softening temperature was determined to be higher than 900 degrees C.

The influence of sintering temperature on particle size/shape and photoluminescence characteristics of CaIn₂O₄:xTb synthesized by combustion process

Khatkar-SP; Sang-Do-Han; Taxak-VB; Sharma-G; Kumar-D(Maharshi Dayanand Univ., India)

Optical-Materials. July 2007; 29(11): 1362-6

Terbium doped CaIn₂O₄ green phosphor was prepared by combustion synthesis and the first ever attempt to study the influence of sintering temperature upon particle size/shape, especially the effect on the photoluminescence characteristics of the same has been made in the present study. Scanning electron microscopy (SEM) investigations were carried out to understand surface morphological features and the particle size. The crystal structure and quality of phosphors sintered at different temperatures were checked by XRD. The crystal structure did not change with an increase of sintering temperature but the particle size and PL intensity increased rapidly. The sintered phosphors on excitation at 254nm emit green luminescence with the main peak at 545nm and the phosphor sintered at 1100 degrees C was having maximum PL intensity. Energy dispersive X-ray analysis (EDAX) was also carried out. [All rights reserved Elsevier].

Synthesis, photoluminescence, thermoluminescence and electron spin resonance investigations of CaAl₁₂O₁₉:Eu phosphor

Jun-jie-Zhu; Singh-V; Rao-TKG(Dept. of Chem., Nanjing Univ., China)

Journal-of-Luminescence. Sept. 2007; 126(1): 1-6

The present paper describes the synthesis of europium-doped calcium aluminate phosphor using the combustion method. An efficient blue emission phosphor can be prepared at reaction temperatures as low as 500 degrees C in a few minutes by this method. Characterization of the powder was done by X-ray diffraction, transmission electron microscopy, scanning electron microscope analysis and the optical properties were studied by photoluminescence spectra. Thermoluminescence (TL) studies also have been carried out on CaAl₁₂O₁₉:Eu²⁺ phosphor. The TL glow curve shows peaks at 174 and 240 degrees C. Defect centres formed in irradiated phosphor have been studied using the technique of electron spin resonance. Step annealing measurements indicate that one of the annealing stages of a defect centre appear to correlate with the release of carriers resulting in TL peak at 174 degrees C. The centre is characterized by an isotropic g-value of 2.0046 and is assigned to a F⁺ centre. [All rights reserved Elsevier].

Densification mechanism of TiB₂ ceramics prepared by the self-propagating high-temperature synthesis/quick pressing method

Meng-Fancheng; Fu-Zhengyi; Zhang-Jinyong; Wang-Weimin; Wang-Hao; Wang-Yucheng; Zhang-Qingjie(State Key Lab. of Adv. Technol., Wuhan Univ. of Technol., China)

Journal-of-the-Chinese-Ceramic-Society. 2007; 35(4): 430-4

Titanium diboride ceramics were prepared by the self-propagating high temperature synthesis/quick pressing (SHS/QP) method. The morphologies of the ceramics produced were characterized by scanning electron microscopy and transmission electron microscopy. The densification mechanism was discussed based on dynamic analysis of the densification process and experimental observations of the structure formation. The results indicate that both the re-arrangement and high-temperature plastic deformation of grains are operative during SHS/QP processing.

Nanocrystalline CaO as adsorbent to remove COD from paper mill effluent

Nagappa-B; Chandrappa-GT(Dept. of Chem., Central Coll. Bangalore Univ., India)

Journal-of-Nanoscience-and-Nanotechnology. March 2007; 7(3): 1039-42

Porous nanocrystalline CaO has been prepared by the solution combustion process using calcium nitrate as oxidizer and glycine as a fuel. As prepared calcium oxide has been characterized using powder X-ray diffraction (XRD), BET surface area, and scanning electron microscopy (SEM). The powder XRD pattern confirms the crystallinity and phase purity of the powder. The particle size of the powder obtained from Scherrer's formula lies in the range of 37-53 nm. The particles are loosely agglomerated and spherical in shape as observed by SEM. The specific surface area of the powder is 18.5 m²/g and the average pore diameter obtained from N₂-desorption isotherm is ~5.2 nm. Batch shaking process was performed using CaO as adsorbent with effluent collected from pulp and paper mill to remove chemical oxygen demand (COD). The COD removal capacity of the CaO is ~93%.

Thermodynamic study of impurity forming in preparing La_1-xSr_xMnO₃ by self-propagating high-temperature synthesis method

Zhu-Baojun; Tao-Ying; Gong-Tao; Tang-Yuanhong; Wang-Ping(Coll. of Mater. Sci. & Eng., Hunan Univ., Changsha, China)

Rare-Metal-Materials-and-Engineering. March 2007; 36(3): 513-16

Through thermodynamic calculation and experiment analysis, the cause of impurity forming in preparing La_1-xSr_xMnO₃ by self-propagating high-temperature synthesis (SHS) was studied and the suggestion was given in this paper to avoid or diminish it. The results show that La₂SrO₄ impurity was produced inevitably in the products synthesized by SHS because the Gibbs free energy of La₂SrO₄ forming reaction is equivalent to that of SrMnO₃ forming reaction when MnO₂ was adopted as dilution. When La_1-xSr_xMnO₃ was used as dilution, La₂SrO₄ forming could be avoided. The over-dilution of La₂Sr_xMnO₃ resulted in Mn₃O₄ impurity forming, which could be avoided by adjusting the proportion of dilution and controlling the reaction speed and system temperature of SHS process.

Gravity effects on reactive settling of transition metals in liquid aluminum under SHS conditions

Munir-ZA; Unuvar-C; Fredrick-DM; Anselmi-Tamburini-U; Shaw-BD; Manerbino-A; Guigne-JY(Dept. of Chem. Eng. & Mater. Sci., Univ. of California, Davis, CA, USA)

Acta-Materialia. May 2007; 55(9): 2965-75

The reactive settling of W, Ta, Ni, and Ti in liquid aluminum was investigated under terrestrial and microgravity conditions. Settling occurred in some systems and total dissolution occurred in others. Analyses were made based on Stoke's settling time relative to dissolution time based on two approaches: dissolution based on a diffusion-controlled process and based on solubility limit. The experimental results are in agreement with the solubility model. The effect of solid volume fraction was also investigated. The results showed a critical volume fraction of about 20vol.%, in agreement with literature values. Effect of particle size was investigated and the observations are consistent with the analysis of settling and dissolution times, indicated above. The absence of settling of the intermetallic phases in all systems was attributed to solid skeleton formation, and confirmed by results on low solid content experiments. [All rights reserved Elsevier].

Photocatalytic recovery of Ag ions from wastewater using ZnO nanopowders immobilized on microporous alumina substrates

Sung-Park; Hye-Jung-Park; Kang-Yoo; Ju-Hyeon-Lee; Jae-Chun-Lee(Dept. of Mater. Sci. & Eng., Myongji Univ., Kyunggi-Do, South Korea)

Colloids-and-Surfaces-A-Physicochemical-and-Engineering-Aspects. 1 June 2007; 300(1-2): 30-4

ZnO nanopowders were synthesized by solution combustion method (SCM) and their average particle size was about 30nm. They were immobilized on microporous alumina substrates by spray coating. The microporous alumina substrates were prepared by anodization and the average pore size was about 150nm. Ag ions were tried to be recovered from waste photograph developing solution by photocatalytic reaction. Three kinds of samples were prepared to compare their photocatalytic efficiency: commercial ZnO powders (slurry type reaction), SCM ZnO powders immobilized on normal alumina substrates and SCM ZnO powders immobilized on anodized alumina substrates. The commercial ZnO powders without immobilization did not show any photocatalytic reaction even though they have maximum surface area. This is probably ascribed to their poor crystalline quality. However, the Ag ion recovery rate by SCM ZnO powders immobilized on anodized alumina substrates was about 2.5 times higher than that by SCM ZnO powders immobilized on normal alumina substrates. This big difference in photocatalytic efficiency is probably due to the large surface area of the anodized alumina. This result was correspondent to photoluminescence measurement results. [All rights reserved Elsevier].

Preparation of nano-sized TiO₂ particles by self-propagating-high-temperature synthesis

Wang-CM; Chung-SL(Dept. of Chem. Eng., Nation Cheng Kung Univ., Tainan, Taiwan)

11th-International-Ceramics-Congress. 2006: 6 pp.

This investigation was aimed at preparing nanocrystalline TiO₂ powder by self-propagating-high-temperature synthesis. Titanium (IV) n-butoxide was hydrolyzed to obtain titanyl hydroxide [TiO(OH)₂], and titanyl nitrate [TiO(NO₃)₂] was obtained by reaction of TiO(OH)₂ with nitric acid. Finally, the aqueous solution containing titanyl nitrate [TiO(NO₃)₂] and a fuel, urea, were mixed and combusted to obtain the nano-sized titania. The anatase TiO₂ nanocrystalline (~56nm) with high BET surface area( 280 m²g^-1) and narrow band gap energy( 2.7 eV) were thus obtained.

Self-propagating high-temperature synthesis: non-equilibrium processes and equilibrium products

Merzhanov-AG(Inst. of Struct. Macrokinetics & Mater. Sci., Chernogolovka, Russia)

11th-International-Ceramics-Congress. 2006: 9 pp.

The nature of SHS process was studied, and conditions under which equilibrium and non-equilibrium regimes take place for wave propagation and structure formation of SHS products are under consideration. The important role of cooling down time is shown. Depending on its magnitude, either autoannealing or autoquenching processes can take place in the products after combustion front propagation. The correlation between transition from non-equilibrium to equilibrium state of the product with prolongation of cooling time was examined as well as character of products and processes was indicated in dependence on relationship between the characteristic times of combustion, time of cooling down, and structure formation in SHS product.

SHS of doped LaGaO₃ perovskite oxide

Ishikawa-H; Enoki-M; Ishihara-T; Akiyama-T(Center for Adv. Res. of Energy Conversion Mater., Hokkaido Univ., Japan)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(3): 259-67

Self-propagating high-temperature synthesis was used to produce strontium and magnesium doped LaGaO₃ perovskite oxide (LSGM) electrolyte under a nitrogen or argon atmosphere. The electrical conductivity of LSGM was measured to evaluate the property of the SOFC electrolyte. It was found that electrical conductivity increased by decreasing the mixing mole ratio of magnesium and it was stable across a wide range of oxygen partial pressures. The value was the same as that of the product obtained by the conventional calcination-sintering method. The total processing time and energy consumption in the LSGM production by the combustion synthesis was reduced to half of those in the conventional calcination-sintering method.

Effect of nickel addition on the Ti-C reaction process and microstructural evolution by SHS

Bounour-W; Benaldjia-A; Ouari-A; Guerioune-M; Vrel-D(LEREC, Badji Mokhtar Univ., Annaba, Algeria)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(3): 247-57

We studied the synthesis of stoichiometric titanium carbide using SHS, with various additives. Nickel (Ni) has been used, either as a pure powder or as a 3Ni + Al₂O₃ powder mixture. It is incorporated into an equimolar Ti/C reactant mixture, in order to study the effect of the addition on the combustion reaction between titanium and carbon, with a powder granulometry lower than 10 mu m. The final product was analyzed by X-ray diffraction and scanning electron microscopy. As the amount of nickel incorporated was increased from 0 to 20 wt.% the grain size of TiC decreased to approximately 2 mu m. It was also observed that most of nickel in TiC-Ni composite was distributed on the surface of almost spherical TiC grains. For the addition of the 3Ni + Al₂O₃ mixture, the ignition time increases with the percentage added, therefore making the SHS reaction of the titanium-carbon system more difficult. The combustion process is therefore directly affected and the propagation mode becomes unstable.

Mechanochemically and thermally activated combustion of the B-TiN system

Bilyan-TsS; Manukyan-KhV; Kharatyan-SL; Puszynski-JA(Dept. of Chem. Phys., Yerevan State Univ., Armenia)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(3): 235-45

Interaction in the B-TiN system under the thermally and mechanochemically activated combustion mode was investigated. Combustion laws for n(Ti-2B)-(3B-TiN) and n(B-0.5N₂)-(3B-TiN) systems were revealed. It was shown that phase composition and microstructure of final products are strongly dependent on the type of activation, initial mixture composition, density of the initial samples and reactive (or inert) gas pressure. Optimum conditions for synthesizing TiB₂/BN composite powders with various content of BN were revealed.

The phenomenon of multilimit combustion in the silicon-melamine-promoter system

Khachatryan-HL; Kharatyan-SL(Dept. of Chem. Phys., Yerevan State Univ., Armenia)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(3): 229-34

In this work, self-propagation high temperature synthesis (SHS) was used to synthesize the Si₃N₄-SiC composites. To carry out simultaneous nitridation and carbidization at comparatively low pressures and with the dominating role of alpha -Si₃N₄ phase in the products promoters, basically nitrogen containing organic solid compounds was used. It was established that both the nitrogen penetrating to the reaction zone from the outside (by filtration) and the nitrogen contained in melamine act jointly and depending on the conditions, one of the two can dominate. It was discovered that in this system there subsist three combustion limits. The existence of three combustion limits in the melamine concentration in the Si-N₂-Teflon-melamine system was caused by variation in the reaction mechanism.

Advanced diagnostic techniques for experimental study of the self-propagating high-temperature synthesis (SHS)

Merzhanov-AG; Rogachev-AS(Inst. of Struct. Macrokinetic & Mater. Sci., Russian Acad. of Sci., Moscow, Russia)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(3): 215-27

Self-propagating high temperature synthesis (SHS) is a promising method for the synthesis of a wide variety of advanced materials in the combustion mode. Therefore, fundamental and applied study of this process must include not only common characteristics of combustion (such as propagating velocity, temperature profiles etc.), but also main features of the product structure formation. In the present work, both traditional and novel methods of experimental diagnostics of the SHS processes are considered. Methods of image recording traditionally play an important role in the combustion science. Modern problems of these methods, from photography to high-speed digital video recording, are discussed. Various methods for temperature profile measurement (micro-thermocouples, micro-pyrometry) are examined from the viewpoint of withdrawing kinetic information from the profile. Quenching of the SHS wave provides unique possibility to obtain data concerning dynamics of microstructure formation of the products. A novel powerful method for in situ study of the crystal structure evolution, time resolved X-ray diffraction (TRXRD) is considered.

Numerical simulation of initiation of SHS reactions in a powder mixture in a gap between heat-conducting metal sheets

Kovalev-OB; Manaichev-KA(Inst. of Theor. & Appl. Mech., Novosibirsk, Russia)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(3): 203-13

A mathematical model for in-depth fusion of metal sheets joined by laser welding is described in the paper. The model is based on a physicochemical mechanism of fusion of the welding joints with the use of the energy of chemical interaction of high temperature synthesis (SHS) powder systems. The reacting mixture placed in a narrow gap between two heat-conducting sheets is initiated by a focused laser beam moving continuously along the boundary between the sheets. Numerical simulations yield a spatial distribution of the temperature field in a chemically active zone and in the metal proper, as well as the position of the inner fusion boundary and the shape of the fused region. The power of the laser radiation and physicochemical properties of the reacting powder necessary to ensure a sufficient magnitude of welding velocity and fusion depth are determined. The computational experiments performed made it possible to theoretically justify the possibility of laser SHS welding of aluminum sheets in a stable regime with the velocity of the gasless combustion front in the powder mixture not exceeding the welding velocity.

Studies on Eu doped Ba and Zn aluminate phosphors prepared by combustion synthesis

Jun-Jie-Zhu; Singh-V; Natarajan-V(Key Lab of Anal. Chem. for Life Sci., Nanjing Univ., China)

Optical-Materials. July 2007; 29(11): 1447-51

BaAl₂O₄:Eu²⁺ and ZnAl₂O₄:Eu³⁺ phosphors were prepared by urea combustion route. The formation of crystalline aluminates was confirmed by X-ray diffraction. The X-band EPR spectra of BaAl₂O₄:Eu²⁺ showed the presence of Eu²⁺ ions, while in the case of ZnAl₂O₄:Eu³⁺, no signal attributable to Eu²⁺ was observed. The broad band UV excited luminescence of BaAl₂O₄:Eu²⁺ was observed at the blue region ( lambda _max=439nm) due to transitions from the 4f⁶5d¹ to the 4f⁷ configuration of the Eu²⁺ ion, whereas ZnAl₂O₄:Eu³⁺ gave an emission at 613nm attributed to ⁵D₀-⁷F₂ transition of Eu³⁺ ions. [All rights reserved Elsevier].

Microstructure and wear behaviour of laser-induced thermite reaction Al₂O₃ ceramic coating on AA7075 aluminum alloy

Kaijin-Huang; Xin-Lin; Changsheng-Xie; Yue-TM(State Key Lab. of Plastic Forming Simulation & Mould Technol., Huazhong Univ. of Sci. & Technol., Wuhan, China)

Journal-of-Materials-Science-and-Technology. 2007; 23(2): 201-6

The microstructure and wear behaviour of the thermite reaction coating produced by the hybrid laser cladding-remelting on AA7075 aluminum alloy for the systems of Al-CuO-SiO₂, Al-Cr₂O₃-SiO₂, Al-Fe₂O₃-SiO₂, and Al-TiO₂-SiO₂ were studied. The results of the X-ray diffraction (XRD) analysis show that in all the four reaction coatings, alpha -Al₂O₃ and gamma -Al₂O₃ phases were present at the top surface, together with various intermetallic phases, the corresponding reduced metal and Al phase in the fusion zone. Under the dry sliding condition, the wear resistance, in terms of weight loss, of the laser-clad specimens was considerably higher than that of the untreated specimen. The predominant wear mechanism of the former specimens was abrasive wear, while for the latter, it was the adhesive wear that prevailed.

Radiative properties of MoO₃ and Al nanopowders from light-scattering measurements

Begley-SM; Brewster-MQ(Mech. Sci. & Eng. Dept., Univ. of Illinois, Urbana, IL, USA)

Transactions-of-the-ASME-Journal-of-Heat-Transfer. May 2007; 129(5): 624-33

The combustion behavior of nanometer-scale energetic materials is much different than micron size or larger materials. Burning rates up to 950 m/s have been reported for a thermite composition of nanosized aluminum and molybdenum trioxide. The energy transport mechanisms in the reactive wave are still uncertain. The relative contribution of radiation has not yet been quantified. To do so analytically requires dependent scattering theory, which has not yet been fully developed. Radiative properties for nanoaluminum and nanomolybdenum-trioxide were obtained experimentally by comparing light scattering measurements on a one-dimensional slab of powder with multiple-scattering simulations using Monte Carlo and discrete ordinate methods. The equivalent isotropic-scattering extinction coefficient for close-packed molybdenum trioxide (MoO₃) nanopowder was found to be 5900< plus-or-minus sign >450 cm^-1; the equivalent isotropic-scattering albedo was 0.97< plus-or-minus sign >0.035. Aluminum (Al), which proved to be more difficult to work with, had an albedo of 0.35 and 0.38 from two tests. The radiative conductivity based on the MoO₃ results is two orders of magnitude less than the diffusive thermal conductivity, indicating that radiation is not a dominant heat transfer mode for the reactive wave propagation of nanothermites under optically thick conditions

Synthesis and magnetic properties of Mn doped ZnO nanowires

Joy-PA; Deka-S(Phys. & Mater. Chem. Div., Nat. Chem. Lab., Pune, India)

Solid-State-Communications. April 2007; 142(4): 190-4

Mn doped ZnO nanowires have been synthesized using a simple autocombustion method. The as-synthesized Mn doped ZnO nanowires were characterized by X-ray diffraction and transmission electron microscopy. An increase in the hexagonal lattice parameters of ZnO is observed on increasing the Mn concentration. Optical absorption studies show an increment in the band gap with increasing Mn content, and also give evidence for the presence of Mn²⁺ ions in tetrahedral sites. All Zn_1-xMn_xO (0x0.25) samples are paramagnetic at room temperature. However, a large increase in the magnetization is observed below 50 K. This behavior, along with the negative value of the Weiss constant obtained from the linear fit to the susceptibility data below room temperature, indicate ferrimagnetic behavior. The origin of ferrimagnetism is likely to be either the intrinsic characteristics of the Mn doped samples, or due to some spinel-type impurity phases present in the samples that could not be detected. [All rights reserved Elsevier]

Combustion synthesis and photocatalytic properties of transition metal-incorporated ZnO

Ekambaram-S; Iikubo-Y; Kudo-A(PhosphorTech Corp., Lithia Spring, GA, USA)

Journal-of-Alloys-and-Compounds. 16 May 2007; 433(1-2): 237-40

This paper describes the combustion synthesis and photocatalytic production of oxygen at room temperature from water using visible light in the presence of sacrificial reagent. The combustion synthesis photocatalysts have been characterized by powder XRD, DRS, BET method, and SEM. Powder XRD of all the transition metal-incorporated ZnO reveals crystalline nature of as-prepared powder whereas DRS of Mn and Co incorporated exhibit absorption peaks and absorption band in the visible regions. Photocatalytic study performed on all the photocatalysts results in production of oxygen and among them, cobalt doped zinc oxide is the best photocatalyst for oxygen production from water in presence of AgNO₃ sacrificial reagent. [All rights reserved Elsevier]

Effects of Si₃N₄ addition on formation of aluminum nitride by self-propagating combustion synthesis

Yeh-CL; Liu-EW(Dept. of Mech. & Autom. Eng., Da-Yeh Univ., Changhua, Taiwan)

Journal-of-Alloys-and-Compounds. 16 May 2007; 433(1-2): 147-53

An experimental study on the preparation of aluminum nitride (AlN) by self-propagating high-temperature synthesis (SHS) was conducted with powder compacts under nitrogen pressures of 0.79-4.24MPa. Reactant compacts were diluted by 30-50wt% of AlN to avoid the melting of aluminum during combustion. In addition, silicon nitride (Si₃N₄) was adopted as a solid source of nitrogen in the reactant compacts and its contribution to the improvement of nitride formation was explored. For the AlN-diluted compacts with no Si₃N₄ addition, a preheating temperature of 200 degrees C is shown to be required to achieve the self-propagating reaction in nitrogen and a large content (i.e., 50wt%) of AlN dilution is needed to obtain a high degree of nitridation about 90%. The self-sustaining reaction proceeds with a distinct combustion front traversing the entire sample in a steady mode. The flame-front propagation velocity was found to increase with nitrogen pressure, but to decrease with diluent content. After the passage of the flame front, further nitridation caused by continuous infiltration of nitrogen gas leads to the emergence of afterburning glows. On the other hand, the addition of Si₃N₄ in the reactant compacts not only activates the self-sustaining reaction under the condition without prior heating, but also brings about a high product yield up to 90% in the compacts with a low content (i.e., 30wt%) of AlN dilution. The morphology of synthesized products from AlN-diluted samples exhibits formation of AlN particles and AlN whiskers, and the former dominates in the case of diluting with 50wt% AlN. The addition of Si₃N₄ was also shown to favor the production of AlN with a particulate structure. [All rights reserved Elsevier]

Novel photoluminescence of SrZrO₃ nanocrystals synthesized through a facile combustion method

Mengkai-Lu; Aiyu-Zhang; Shufen-Wang; Guangjun-Zhou; Shumei-Wang; Yuanyuan-Zhou(State Key Lab. of Crystal Mater., Shan Dong Univ., Jinan, China)

Journal-of-Alloys-and-Compounds. 16 May 2007; 433(1-2): L7-11

Strontium zirconate (SrZrO₃) nanocrystals with an average size of 19nm were prepared by a simple sol-gel combustion method. The combustion reaction was induced just at 300 degrees C. Under conventional UV excitation, the SrZrO₃ nanocrystals showed a strong violet emission at 400nm. The number of luminescent zirconates is small, especially of those with visible emission. The novel luminescence was tentatively attributed to the existence of defect levels. Further study was carried out corresponding the size dependence of the luminescence property. [All rights reserved Elsevier]

Synthesis of nanosize-necked structure alpha - and gamma -Fe₂O₃ and photocatalytic activity

Apte-SK; Naik-SD; Sonawane-RS; Kale-BB; Baeg-JO(Ministry of Information & Commun. Technol., Center for Mater. for Electron. Technol., Pune, India)

Journal-of-the-American-Ceramic-Society. Feb. 2007; 90(2): 412-14

Highly dispersed nanometer-sized alpha -Fe₂O₃ (hematite) and gamma -Fe₂O₃ (maghemite) iron oxide particles were synthesized by the combustion method. Ferric nitrate was used as a precursor. X-ray diffractometer study revealed the phase purity of alpha - and gamma -Fe₂O₃. Both the products were characterized using field emission scanning electron microscope and transmission electron microscope for particle size and morphology. Necked structure particle morphology was observed for the first time in both the iron oxides. The particle size was observed in the range of 25-55 nm. Photodecomposition of H₂S for hydrogen generation was performed using alpha and gamma -Fe₂O₃. Good photocatalytic activity was obtained using alpha - and gamma -Fe₂O₃ as photocatalysts under visible light irradiation

Monophasic nanostructured powders of niobium, tantalum, and hafnium carbonitrides synthesized by a mechanically induced self-propagating reaction

Cordoba-JM; Sayagues-MJ; Alcala-MD; Gotor-FJ(Instituto de Ciencia de Materiales de Sevilla, Centro mixto CSIC-US, Sevilla, Spain)

Journal-of-the-American-Ceramic-Society. Feb. 2007; 90(2): 381-7

Niobium, tantalum, and hafnium carbonitride nanopowders were obtained by high-energy ball milling of elemental metal and graphite in a nitrogen atmosphere. By adjusting milling parameters, a mechanically induced self-propagating reaction was observed during the formation of carbonitride phases. The stoichiometry of transition metal carbonitrides was controlled by fixing the starting metal-to-carbon molar ratio. Ignition of the reactant mixture was determined by the combined effect of nitrogen and carbon, gas, and solid reagents, respectively. The composition and lattice parameters were determined by X-ray diffraction measurements. Microstructural characterization showed a nanophase structure with a homogeneous chemical composition

Fabrication of machinable silicon nitride/boron nitride composite ceramics

Zhang-Qiang; Shen-Weiping; Gu-Shuyuan(Beijing Univ. of Sci. & Technol., China)

Journal-of-the-Chinese-Ceramic-Society. 2007; 35(3): 337-41

Machinable silicon nitride/hexahedral boron nitride (Si₃N₄/h-BN) composite ceramics with silicon (Si) powders and hexahedral boron nitride (h-BN) as raw materials were synthesized in-situ in a nitrogen pressure by combustion synthesis gas-solid reaction. The effect of volume fraction (the same below) of h-BN on machinable properties Of Si₃N₄/BN composite ceramics was investigated. The results show that Si powders were fully nitrified under the experimental conditions and no residual free silicon was found. Columnar crystals of beta -Si₃N₄ are the main phase and acicular crystals of h-BN disperse intergranular position of beta -Si₃N₄. With increase of the volume content of h-BN, the machinability of the composite ceramics increases, but the bending strength first decreases and then increases. The lowest point of bending strength is at 25% of h-BN

A novel preparation method of active materials for the lithium secondary battery

Ho-Gi-Kim; Seung-Beob-Yi; Hoon-Taek-Chung(Dept. of Mater. Sci. & Eng., Korea Adv. Inst. of Sci. & Technol., Daejeon, South Korea)

Electrochemistry-Communications. April 2007; 9(4): 591-5

LiNi_0.8Co_0.2O₂ is a promising candidate to replace LiCoO₂. The present paper describes the preparation of LiNi_0.8Co_0.2O₂ compounds from nitrate sources and sucrose (or sugar) by the sucrose combustion process (SCP), which involves application of a conventional combustion method. In the proposed approach, sucrose serves as a fuel, a dispersing agent, and a precipitation suppressant. Precursors were made via a combustion reaction, and LiNi_0.8Co_0.2O₂ was subsequently synthesized by heat treatment at 800 degrees C for 16h in oxygen atmosphere. The initial discharge capacity was 175mAh/g when a cell was operated at 2.7-4.3V at 0.5C-rate. Furthermore, it shows good cycling stability. When increased amount of sucrose were added as a start material, the final calcined powder displayed smaller particle size and better discharge capacity. It is expected that optimization of the heat treatment conditions would yield LiNi_0.8Co_0.2O₂ with excellent properties. Furthermore, SCP is expected to be applicable to the production of various materials. [All rights reserved Elsevier]

Size shrinkage of GaN nanocrystalline grains induced by Eu doping

Nyk-M; Podhorodecki-A; Kudrawiec-R; Misiewicz-J; Strek-W(Inst. of Phys., Wroclaw Univ. of Technol., Poland)

Electrochemical-and-Solid-State-Letters. July 2007; 10(7): H203-5

Undoped nanocrystalline GaN grains with the size changing from ~11 to ~31 nm have been obtained by the combustion method, where grain size was controlled by the nitridation temperature changing from 850 to 1050 degrees C. The same procedure has been applied in order to obtain Eu-doped GaN powders. It has been observed that the introduction of Eu ions reduces the size of GaN grains by 30< plus-or-minus sign >10%. In photoluminescence spectra, in addition to the Eu-related emission, strong UV bands (associated with the GaN bandgap-related emission) and VIS bands (associated with the GaN defect/surface-related emission) have been clearly observed. After the Eu-ion incorporation into GaN nanocrystals, the relative intensity of UV and VIS bands changes in favor of VIS emission because of the Eu-induced size shrinkage, i.e., the surface-to-volume ratio increase

Electrochemical properties of V₃TiNi_0.56Al_0.2 hydrogen storage materials

Li-Rong; Zhou-Shang-qi; Liang-Guo-ming; Liu-Shou-ping; Fu-Wen-sheng(Coll. of Chem., Chongqing Normal Univ., China)

Chinese-Journal-of-Nonferrous-Metals. Feb. 2007; 17(2): 222-7

The storage hydrogen alloy V₃TiNi_0.56Al_0.2 was prepared by self-propagating high-temperature synthesis (SHS). The microstructure and electrochemical properties of alloy were investigated from the viewpoint of experiments. The results show that the maximal discharge capacity of as-cast alloy V₃TiNi_0.56Al_0.2 is 350 mAh/g. The activation performance is relatively good, the diffusion coefficient of the hydrogen is little, while the cyclic and discharge capacity are not good. The reason why the alloy lost the activity is that the main phase of vanadium-based solid solution alloy is dissolved in the electrolyte during cyclic course. The cyclic and discharge capacity could be improved by vacuum melting manage

Effect of argon atmosphere on the formation of MoSi₂ by self-propagating combustion method

Jianguang-Xu; Houan-Zhang; Jianhui-Yan; Baolin-Zhang; Li-W(Sch. of Electromech. Eng., Hunan Univ. of Sci. & Technol., China)

International-Journal-of-Refractory-Metals-and-Hard-Materials. July 2007; 25(4): 318-21

The effect of argon atmosphere on the formation of MoSi₂ by self-propagating combustion method has been detailedly investigated in present work by comparing SHS reaction between Mo and Si in argon atmosphere with that in vacuum. The SHS procedure in argon atmosphere could produce higher heating rate and maximum temperature than that in vacuum. The particle size distribution of synthesized products has been studied by light transmission sedimentation method. More homogeneous particle size distribution of the molybdenum disilicide by SHS method in argon atmosphere was achieved than it in vacuum. And it also can be observed in SEM photographs of synthesized products. Compared with SHS method in vacuum, a purer product was indicated by XRD and X-fluorescence analysis results while reaction in argon atmosphere. [All rights reserved Elsevier]

Synthesis of titania films by combustion flame spray pyrolysis technique and its characterization for photocatalysis

Kavitha-R; Meghani-S; Jayaram-V(Dept. of Metall., Indian Inst. of Sci., Bangalore, India)

Materials-Science-and-Engineering-B-Solid-State-Materials-for-Advanced-Technology. 15 May 2007; 139(2-3): 134-40

The phase composition, texture and roughness of titania films deposited using combustion flame pyrolysis technique are studied as a function of substrate temperature, deposition time and precursor concentration. In this process, a liquid precursor feedstock that results in TiO₂ film is injected into a combustion flame and the film is deposited onto a silica substrate. The resulting film has anatase at low substrate temperature, rutile at high substrate temperature and a mixture of these two phases at intermediate temperatures. A large decrease in the average size of the primary particles that constitute the film is observed with low precursor concentration. The band gap energy of titania films with different phase compositions is measured using UV spectrophotometer. ZnO films are deposited from sprayed droplets of an aqueous zinc acetate solution by using this process and comparison of TiO₂ and ZnO films on the photocatalytic degradation of remazol brilliant blue is investigated. [All rights reserved Elsevier]

Development of aluminium composites with in situ formed AlTiSi reinforcements through infiltration

Zhao-YG; Jiang-QC; Qin-QD; Liu-C; Zhou-W(Dept. of Mater. Sci. & Eng., Jilin Univ., Changchun, China)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 15 July 2007; 460-461: 604-10

An in situ AlTiSi ternary phase local reinforced aluminum MMCs composite was successfully fabricated by combustion synthesis and nonpressure infiltration course. XRD results show that the reinforced region of the composite is composed of Al and ternary AlTiSi phase with the composition closing to Ti(Al_0.8Si_0.2)₃. The volume fraction of reinforcement can be controlled by adjusting Al content in compacts. SEM results show that the morphologies of the AlTiSi particles are polygonal and/or spherical. There exists some residual Ti surrounding by AlTiSi phase in the composites. In addition, there is some residual Si in the matrix in the form of Al-Si binary eutectic. The wettability between AlTiSi reinforcement and Al matrix is very good, and the reinforcement lies in the center of alpha -Al dendritic. [All rights reserved Elsevier]

Finite element analysis of residual thermal stress in ceramic-lined composite pipe prepared by centrifugal-SHS

Zhen-Guo-Yang; Yu-Fei-Wang(Dept. of Mater. Sci., Fudan Univ., Shanghai, China)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 15 July 2007; 460-461: 130-4

The ceramic-lined composite pipe is a kind of high-performance, wear-resisting and anti-corrosion pipe. It is widely used in many fields such as electricity, petrochemical industry, metallurgy, chemical industries, etc. In this study, the centrifugal-SHS process to prepare ceramic-lined composite pipe was briefly introduced. The temperature distribution and transformation during the cooling process of the ceramic-lined composite pipe preparation were emphatically analyzed with finite element numerical simulation. With the function of transient thermal analysis and thermal-structure coupling of ANSYS, the residual thermal stress of the composite pipe was numerically simulated. The effect of the thickness of SHS-layer on the performance of the ceramic-lined composite pipe was investigated as well. The results of numerical analysis indicate that reasonable adjustment of the thickness of SHS-layer could reduce the interfacial stress between any two layers so that the service life, safety and reliability of the ceramic-lined composite pipe would be improved. [All rights reserved Elsevier]

Alanine-assisted low-temperature combustion synthesis of nanocrystalline LiMn₂O₄ for lithium-ion batteries

Basu-RN; Raja-MW; Mahanty-S; Ghosh-P; Maiti-HS(Fuel Cell & Battery Sect., Central Glass & Ceramic Res. Inst., Kolkata, India)

Materials-Research-Bulletin. 7 Aug. 2007; 42(8): 1499-506

Nanocrystalline LiMn₂O₄ powders have been synthesized by combustion process in a single step using a novel fuel, l-alanine. Thermogravimetric analysis and differential thermal analysis of the gel indicate a sharp combustion at a temperature as low as 149 degrees C. Quantitative phase analysis of X-ray diffraction data shows about 97% of phase purity in the as-synthesized powder, which on further calcination at 700 degrees C becomes single phase LiMn₂O₄. High Brunauer, Emmett, and Teller surface area values obtained for ash (53m²/g) and calcined powder (23m²/g) indicate the ultrafine nature of the powder. Average crystallite size is found to be ~60-70nm from X-ray diffraction analysis and transmission electron microscopy. Fourier transformed infra-red spectrum shows two strong bands at 615 and 511cm^-1 originating from asymmetrical stretching of MnO₆ octahedra. A nominal composition of Li_0.88 Mn₂O₄ is calculated from the inductive coupled plasma analysis. From UV-vis spectroscopy, an optical band gap of 1.43eV is estimated which is assigned to a transition between t_2g and e_g bands of Mn 3d. Electrochemical charge-discharge profiles show typical LiMn₂O₄ behavior with a specific capacity of 76mAh/g. [All rights reserved Elsevier]

Higher catalytic activity of nano-Ce_1-x-yTi_xPd_yO_2-delta compared to nano-Ce_1-xPd_xO_2-delta for CO oxidation and N₂O and NO reduction by CO: role of oxide ion vacancy

Baidya-T; Marimuthu-A; Hegde-MS; Ravishankar-N; Madras-G(Solid State & Struct. Chem. Unit, Indian Inst. of Sci., Bangalore, India)

Journal-of-Physical-Chemistry-C. 18 Jan. 2007; 111(2): 830-9

The Nano-Ce_0.73Ti_0.25Pd_0.02O_2-delta solid solution, prepared by solution combustion method, has been synthesized. The catalyst has been characterized by XRD, HRTEM and XPS. Synergistic interaction of Pd with Ti/Ce is very strong because of ionic substitution. The reducibility of Ce_0.73Ti_0.25Pd_0.02O_2-delta is about 5 times higher compared to that of Ce_0.98Pd_0.02O_2-delta below 140 degrees C. The easy removal of oxygen from the more reducible Ti containing support plays a major role in showing higher catalytic activity of this material for CO oxidation and N₂O and NO reduction by CO. The catalyst shows 100% N₂ selectivity above 240 degrees C and high reaction rates compared to other catalysts reported in the literature. It has been shown that oxide ion vacancy creation in the support promotes the adsorption and dissociation of NO or N₂O at a lower temperature. Kinetic models based on a bifunctional mechanism were used to determine the reaction rate coefficients

A fuzzy decision tree-based duration model for Standard Yoruba text-to-speech synthesis

Wong-SHS; Odejobi-OA; Beaumont-AJ(Comput. Sci., Aston Univ., Birmingham, UK)

Computer-Speech-and-Language. April 2007; 21(2): 325-49

In this paper, we present syllable-based duration modelling in the context of a prosody model for Standard Yoruba (SY) text-to-speech (TTS) synthesis applications. Our prosody model is conceptualised around a modular holistic framework. This framework is implemented using the Relational Tree (R-Tree) techniques. An important feature of our R-Tree framework is its flexibility in that it facilitates the independent implementation of the different dimensions of prosody, i.e. duration, intonation, and intensity, using different techniques and their subsequent integration. We applied the Fuzzy Decision Tree (FDT) technique to model the duration dimension. In order to evaluate the effectiveness of FDT in duration modelling, we have also developed a Classification And Regression Tree (CART) based duration model using the same speech data. Each of these models was integrated into our R-Tree based prosody model. We performed both quantitative (i.e. Root Mean Square Error (RMSE) and Correlation (Corr)) and qualitative (i.e. intelligibility and naturalness) evaluations on the two duration models. The results show that CART models the training data more accurately than FDT. The FDT model, however, shows a better ability to extrapolate from the training data since it achieved a better accuracy for the test data set. Our qualitative evaluation results show that our FDT model produces synthesised speech that is perceived to be more natural than our CART model. In addition, we also observed that the expressiveness of FDT is much better than that of CART. That is because the representation in FDT is not restricted to a set of piece-wise or discrete constant approximation. We, therefore, conclude that the FDT approach is a practical approach for duration modelling in SY TTS applications. [All rights reserved Elsevier]

The structure and magnetic properties of Zn_1-xNi_xFe₂O₄ ferrite nanoparticles prepared by sol-gel auto-combustion

Zhang-BF; Zhang-HE; Wang-GF; Dong-XH; Gao-Y(Dept. of Appl. Phys. Fac. of Sci., Tianjin Univ., China)

Journal-of-Magnetism-and-Magnetic-Materials. May 2007; 312(1): 126-30

Zn_1-xNi_xFe₂O₄ ferrite nanoparticles were prepared by sol-gel auto-combustion and then annealed at 700 degrees C for 4h. The results of differential thermal analysis indicate that the thermal decomposition temperature is about 210 degrees C and Ni-Zn ferrite nanoparticles could be synthesized in the self-propagating combustion process. The microstructure and magnetic properties were investigated by means of X-ray diffraction, scanning electron microscope, and Vibrating sample magnetometer. It is observed that all the spherical nanoparticles with an average grain size of about 35nm are of pure spinel cubic structure. The crystal lattice constant declines gradually with increasing x from 0.8435nm (x=0.20) to 0.8352nm (x=1.00). Different from the composition of Zn_0.5Ni_0.5Fe₂O₄ for the bulk, the maximum M_s is found in the composition of Zn_0.3Ni_0.7Fe₂O₄ for nanoparticles. The H_c of samples is much larger than the bulk ferrites and increases with the enlarging x. The results of Zn_0.3Ni_0.7Fe₂O₄ annealed at different temperatures indicate that the maximum M_s (83.2emu/g) appears in the sample annealed at 900 degrees C. The H_c of Zn_0.3Ni_0.7Fe₂O₄ firstly increases slightly as the grain size increases, and presents a maximum value of 115Oe when the grains grow up to about 30nm, and then declines rapidly with the grains further growing. The critical diameter (under the critical diameter, the grain is of single domain) of Zn_0.3Ni_0.7Fe₂O₄ nanoparticles is found to be about 30nm. [All rights reserved Elsevier]

Mechanically activated combustion synthesis of beta -Si_6-zAl_zO_zN_8-z (z = 1-4))

Aoyagi-K; Hiraki-T; Sivakumar-R; Watanabe-T; Akiyama-T(Center for Adv. Res. of Energy Conversation Mater., Hokkaido Univ., Sapporo, Japan)

Journal-of-the-American-Ceramic-Society. Feb. 2007; 90(2): 626-8

Fine beta -sialon (Si_6-z/AL_zO_zN_8-z, 1 < z < 4) was prepared by mechanical-activated combustion synthesis (CS) using raw materials such as Si, Al, and SiC₂ in a nitriding atmosphere of 1 MPa. Mechanical activation by planetary milling for only 18 min led to the formation of beta -sialon after combustion synthesis. Comparative experiments with ball milling showed that the relative amount of beta -sialon was considerably increased to 66% when planetary milled to 18 min after CS. The raw material Si was replaced by waste Si of 94.8 mass% in purity, and was combustion synthesized successfully under the same processing parameters for cost-effective measures

Crystal growth of TiC grains during SHS reactions

Dubois-S; Cochepin-B; Gauthier-V; Vrel-D(Lab. de Metallurgie Phys., UMR CNRS, Futuroscope-Chasseneuil Du Poitou, France)

Journal-of-Crystal-Growth. 15 June 2007; 304(2): 481-6

The microstructure formation of TiC during self-propagating high-temperature synthesis (SHS) reactions is investigated thanks to the quenching method. The morphology and chemical composition of titanium carbide grains are characterized, during the growth phase, from X-ray diffraction (XRD), scanning electron microscopy (SEM) and wavelength dispersion spectroscopy (WDS) analyses. It is demonstrated that TiC_x grains nucleate with a great deficit in carbon; the carbon composition evolves towards the stoichiometry during the growth phase. The TiC grain sizes are then coupled to thermal data acquired by infra red (IR) thermography. It is shown that the convolution of the temperature and of the time elapsed in the temperature range T_max-1000K constitute a pertinent parameter to give account of the variation of TiC grain sizes. [All rights reserved Elsevier]

Synthesis and optical characterization of Co₃O₄ nanocrystals

Chunzhong-Li; Feng-Gu; Yanjie-Hu; Ling-Zhang(Sch. of Mater. Sci. & Eng., East China Univ. of Sci. & Technol., Shanghai, China)

Journal-of-Crystal-Growth. 15 June 2007; 304(2): 369-73

Cobalt oxide (Co₃O₄) nanocrystals have been synthesized successfully via a facile combustion method. The Li ions incorporated into the Co₃O₄ lattice should serve as a self-promoter for the crystallization, resulting in the drastic increase of particle size. The Li addition can complex the structure of the energy band gap. The optical absorption spectra indicate that the direct band gap of Co₃O₄ varied from 3.11 and 1.62 to 3.29-3.98eV after introducing Li ions. This approach provides economically viable route for large-scale synthesis of this kind of nanomaterials. [All rights reserved Elsevier]

Novel processing of porous titanium composite for producing open cell structure

Kanetake-N; Kobashi-M(Dept. of Material Sci. & Eng., Nagoya Univ., Japan)

Materials-Science-Forum. 2007; 539-543: 1004-9

Processing technique to produce open-cell porous titanium composite was developed. One of the outstanding benefits of porous titanium composite is both physical and mechanical properties can be controlled widely by changing the metal/ceramic fraction and cell structures. in this work, porous titanium composite was fabricated by a chemical reaction between titanium powder and boron carbide (B₄C) powder. The reactions between titanium and B₄C generates a large amount of latent heat and, therefore, it was a combustion and self-propagating mode. Precursors were made by compacting the starting powder blend (Ti and B₄C), and heated in an induction furnace to induce the reaction. The reaction was strongly exothermic and, therefore, the precursor was sintered by its latent heat when the Ti/B₄C blending ratio was appropriate. The reaction products were titanium boride (TiB and/or TiB₂) and titanium carbide (TiC). By controlling the Ti/B₄C blending ratio, it was possible to control the volume fraction of reaction products in titanium matrix. The combustion synthesized titanium composite was porous and its cell structure was strongly affected by the processing condition of the precursor (porosity and Ti/B₄C blending ratio). High porosity with open pores was obtained with small Ti/B₄C ratios and high porosity of the precursor, while the cell structure was closed and spherical with high Ti/B₄C ratio. The cell-wall size was varied from several tens of microns to about 500 microns by changing the combustion temperature

Synthesizing carbon nanotubes and carbon nanofibers over supported-nickel oxide catalysts via catalytic decomposition of methane

Mohamed-AR; Siang-Piao-Chai; Zein-SHS(Sch. of Chem. Eng., Univ. Sains Malaysia, Pulau Pinang, Malaysia)

Diamond-and-Related-Materials. Aug. 2007; 16(8): 1656-64

Supported-NiO catalysts were tested in the synthesis of carbon nanotubes and carbon nanofibers by catalytic decomposition of methane at 550 degrees C and 700 degrees C. Catalytic activity was characterized by the conversion levels of methane and the amount of carbons accumulated on the catalysts. Selectivity of carbon nanotubes and carbon nanofiber formation were determined using transmission electron microscopy (TEM). The catalytic performance of the supported-NiO catalysts and the types of filamentous carbons produced were discussed based on the X-ray diffraction (XRD) results and the TEM images of the used catalysts. The experimental results show that the catalytic performance of supported-NiO catalysts decreased in the order of NiO/SiO₂>NiO/HZSM-5>NiO/CeO₂>NiO/Al₂O₃ at both reaction temperatures. The structures of the carbons formed by decomposition of methane were dependent on the types of catalyst supports used and the reaction temperatures conducted. It was found that Al₂O₃ was crucial to the dispersion of smaller NiO crystallites, which gave rise to the formation of multi-walled carbon nanotubes at the reaction temperature of 550 degrees C and a mixture of multi-walled carbon nanotubes and single-walled carbon nanotubes at 700 degrees C. Other than NiO/Al₂O₃ catalyst, all the tested supported-NiO catalysts formed carbon nanofibers at 550 degrees C and multi-walled carbon nanotubes at 700 degrees C except for NiO/HZSM-5 catalyst, which grew carbon nanofibers at both 550 degrees C and 700 degrees C. [All rights reserved Elsevier]

Study of hydrogen storage by carbonaceous material at room temperature

Zein-SHS; Hassan-NHA; Mohamed-AR(Sch. of Chem. Eng., Univ. Sains Malaysia, Pulau Pinang, Malaysia)

Diamond-and-Related-Materials. Aug. 2007; 16(8): 1517-23

Recently, many studies have been reported about a variety of carbon materials in adsorbing hydrogen. Regarding that, hydrogen adsorption in different carbonaceous materials was investigated at room temperature, 298 K and three different pressures which were 6.5, 8.5 and 9.5 bar. Pressure drop of hydrogen was measured and the amount it adsorbed was calculated by using ideal gas law and it was presented in weight percent, wt.%. In this paper, the effect of a purification process on hydrogen adsorption was also discussed. Along with that, pretreatment also gave a major influence in hydrogen adsorption because it affected the adsorption behavior of the carbon nanotubes surfaces. The highest result obtained during this work was 0.195 wt.% for purified carbon nanotubes. [All rights reserved Elsevier]

Study on the effect factor of combustion synthesizing Mg₂Ni

Chen-Xiujuan; Xia-Tiandong; Liu-Xuelong; Zhao-Wenjun; Liu-Tianzuo(State Key Lab. of Gansu Adv. Non-Ferrous Metal Mater., Lanzhou Univ. of Tech., China)

Rare-Metal-Materials-and-Engineering. March 2007; 36(3): 450-3

The effect of some parameters in combustion synthesis on the products was studied by means of XRD and SEM. The results showed that Mg₂Ni can be synthesized by the thermal explosion mode at over 440 degrees C of preheat temperature, and the larger the preheat rate, the more dense the combustion-synthesized product. Using too high dense green, the combustion temperature of the reaction was decreased gradually, which brought unsatisfied reaction between Mg and Ni. In contrast, the too fine Mg powder would lead a higher combustion temperature of the reaction, resulting in oversintering of the products. In addition, heating the product to a proper temperature and holding a proper time would be beneficial to improve the purity of Mg₂Ni

Synthesis and characterization of LaCoO₃ based cathode and its chemical compatibility with CeO₂ based electrolytes for intermediate temperature solid oxide fuel cell (ITSOFC)

Nesaraj-AS; Raj-IA; Pattabiraman-R(Dept. of Chem., Karunya Univ., Coimbatore, India)

Indian-Journal-of-Chemical-Technology. March 2007; 14(2): 154-60

The use of alternate cathode materials with improved performance and without any chemical reaction with adjoining electrolyte is required for a reduction in operating temperature of SOFC from 1273 K to about 1073 K (ITSOFC). Cobalt containing perovskite oxides such as LaCoO₃ tend to exhibit a higher ionic conductivity due to a greater concentration of oxygen vacancies than other perovskite oxides. The mixed ionic and electronic conducting cathode of the La_1-xSr_xCoO_3-delta systems has shown the lowest cathodic overpotential for an SOFC air electrode. In this research work, fine powders of La_0.70Sr_0.30CoO_3-delta (LSC) cathode and Ce_0.90Gd_0.10O_2-delta (GDC) and Ce_0.80Sm_0.20O_2-delta (SDC) are synthesized by glycine nitrate combustion synthesis and systematically characterized by XRD and particle characteristics. The electrical properties of LSC cathode and GDC and SDC electrolytes are also studied. But, the crucial requirement for applicability of LSC cathode is its chemical compatibility in conjunction with the alternate solid electrolytes, GDC and SDC without any phase formation. The XRD studies showed no reaction products when the La_0.70Sr_0.30CoO_3-delta cathode is mixed and calcined with GDC and SDC electrolyte at 1573 K. Hence, the LSC cathode may be combined with CeO₂ based electrolytes in ITSOFC application

Interaction of a ceramic material based on hematite with molten iron produced by an aluminothermic reaction

Udalov-YuP; Mikhailov-MN; Fil'chakov-IF(St. Petersburg State Technol. Inst., Russia)

Glass-Physics-and-Chemistry. March-April 2007; 33(2): 174-9; Original: Fizika-i-Khimiya-Stekla. March-April 2007; 33(2)

The problems regarding the use of hematite-based ceramics as sacrificial ceramic materials are considered. The interaction of hematite with an iron melt produced by a self-propagating high-temperature reaction is investigated. It is revealed that the hematite-based ceramic material containing activating additives of 3d element oxides is wet by the iron melt. This leads to an intense redox reaction at the iron-ceramic interface

One step synthesis and consolidation of nanostructured ZrSi₂-SiC composite and its mechanical properties

In-Jin-Shon; Hyun-kuk-Park; In-Yong-Ko; Jin-Kook-Yoon; Kyung-Tae-Hong(Eng. Res. Inst., Chonbuk Nat. Univ., Jeonbuk, South Korea)

Diffusion-and-Defect-Data-Part-B-Solid-State-Phenomena. 2007; 124-126: 1149-52

Dense nanostructured ZrSi₂-SiC composite was synthesized by high frequency induction heated combustion synthesis (HFIHCS) method within 1 minute in one step from powders of ZrC and 3Si. Simultaneous combustion synthesis and densification were accomplished under the combined effects of an induced current and mechanical pressure. Highly dense ZrSi₂-SiC with relative density of up to 98% were produced under simultaneous application of a 60 MPa pressure and the induced current. The average grain size and mechanical properties (hardness and fracture toughness) of the composite were investigated

Criterion of microroughness for self-propagating wafer bonding

Ma-Ziwen; Tang-Zirong; Liao-Guanglan; Shi-Tielin(Wuhan Nat. Lab. for Optoelectron., Huazhong Univ. of Sci. & Technol., Wuhan, China)

Chinese-Journal-of-Semiconductors. March 2007; 28(3): 465-9

The criterion of microroughness for self-propagating wafer bonding is studied according to JKR contact theory, where the microroughness model is based on a sinusoidal distribution for gap height and gap length. Our analysis shows that the criterion for self-propagating wafer bonding is relevant to the dimensionless parameter. In silicon wafer bonding, using the dimensionless parameter as a measure, three regions of silicon wafer bonding can be identified: self-propagating silicon wafer bonding ( alpha >1.065), external pressure assisted silicon wafer bonding (0.57< alpha <1.065), and silicon wafer bonding with voids ( alpha <0.57). Experimental data are in reasonable agreement with this theory

Detonation synthesis of nanosized titanium dioxide powders

Yandong-Qu; Xiaojie-Li; Xiaohong-Wang; Dahui-Liu(Dept. of Eng. Mech., Dalian Univ. of Technol., China)

Nanotechnology-. 23 May 2007; 18(20): 5 pp.

Utilizing titanyl sulfate as a TiO₂ source, via a novel synthesis method-the detonation method-nanosized TiO₂(n-TiO₂) powders were prepared. The results showed that the as-prepared n-TiO₂ powders did not have enough time to grow into large and fine crystallites, and that the characteristics of high temperature, high pressure and high cooling were helpful in the synthesis of nanosized materials. The anatase phase appeared to be the stable form of nanocrystalline TiO₂ at small crystallite sizes to some extent and part of the rutile phase could transform to the anatase phase when the detonation products were oxidized to eliminate the impurities via the combined action of chromic anhydride (CrO₃) and concentrated nitric acid. The main reason resulting in the reversal of stability of anatase and rutile could be the differences in the surface energy of anatase and rutile at small crystallite sizes

Conditions for combustion synthesis in nanosized Ni/Al films on a substrate

Rabinovich-OS; Grinchuk-PS; Andreev-MA; Khina-BB(A.V.Luikov Heat & Mass Transfer Inst., Minsk, Belarus)

Physica-B. 15 April 2007; 392(1-2): 272-80

The conditions for self-sustaining combustion synthesis in nanosized multilayer Ni/Al films deposited on a substrate are studied based on a 2D model. The model considers two conjugate processes, i.e. propagation of the synthesis wave in a multi-layer Ni/Al system and propagation of the accompanying thermal wave into the substrate. It is shown that the boundary between the regimes of self-sustaining reaction and annealing is determined by the number of binary layers of reactants (at a given heater temperature, stoichiometric ratio of the reactants and ration of film and substrate thermal diffusivities), but it does not depend on the bilayer thickness. The distinctive features of synthesis in the thermal explosion mode and in the annealing regime are studied as well. [All rights reserved Elsevier]

A novel synthesis of B-Al-Ca-O-(N) glasses by self-propagating high-temperature combustion method

Shingo-Nakane; Kobayashi-Y; Yoshinaka-M; Hirota-K; Yamaguchi-O(Nippon Electr. Glass Co. Ltd., Shiga, Japan)

Materials-Research-Bulletin. 18 Jan. 2007; 42(1): 46-55

Glasses in the B-Al-Ca-O-(N) system have been prepared by self-propagating high-temperature combustion synthesis (SHS) directly from mixed powders of B, Al and CaO under pressurized dry-air of 3MPa. The nitrogen content of the SHS product is 0.63mass%, the value of which is about 30 times higher than that of conventional molten glass fabricated in air. Their initial reactants, B and Al when ignited, transform instantaneously into oxides, nitrides and oxynitride with a high exothermic heat of reaction. Sequentially the reacted products in a liquid state solidify into a glass material by rapid cooling. The glass forming region is similar to that of the same oxide glass system prepared by the conventional melting method. [All rights reserved Elsevier]

Thermoelectric properties of combustion-synthesized lanthanum-doped strontium titanate

Lihua-Zhang; Tsuyoshi-Tosho; Noriyuki-Okinaka; Tomohiro-Akiyama(Graduate Sch. of Eng., Hokkaido Univ., Sapporo, Japan)

Materials-Transactions. May 2007; 48(5): 1079-83

The possibility of combustion synthesis of perovskite-oxide thermoelectric materials with the attendant saving of energy and time and without deterioration in the thermoelectric properties was investigated by evaluating the thermoelectric properties of lanthanum-doped strontium titanate (Sr_1-xLa_xTiO₃, 0x0.1). The materials were successfully combustion synthesized and spark plasma sintered with 98.0-99.6% of true density, and their thermoelectric properties were evaluated from room temperature to 850 K. The optimal lanthanum doping amount ratio x in the considered temperature range was from 0.06 to 0.08. in which Sr_0.92La_0.08TiO₃ sample showed the maximum ZT of 0.22 at 800 K. This value was close to the highest recorded ZT at the same temperature up to now. and the ZT of most samples are higher than those synthesized by the conventional solid state reaction method. Thus, combustion synthesis is promising for producing perovskite-oxide thermoelectric materials for high-temperature application

Plastic mechanism analysis of steel SHS strengthened with CFRP under large axial deformation

Bambach-MR; Elchalakani-M(Dept. of Civil Eng., Monash Univ., Clayton, Vic., Australia)

Thin-Walled-Structures. Feb. 2007; 45(2): 159-70

Carbon fibre reinforced polymer (CFRP) strengthening of structures has been gaining increasing interest, traditionally in application with concrete structures, and more recently in application with steel structures. This paper presents experiments and plastic mechanism analysis of steel square hollow section (SHS) tubes strengthened using externally bonded CFRP, deforming in an axi-symmetric collapse mode under quasi-static large deformation axial compression. The fold formation process of the stub column was such that the flat sides formed the well-known roof mechanism. The collapse proceeded progressively by folding about concentrated hinge lines and yielding of the four corners. An expression for the plastic collapse axial load was obtained by equating the total energy absorbed in bending and yielding to the external work carried out during deformation of the composite tube. The predicted instantaneous post-buckling and mean collapse loads are shown to compare well with the experimental results. [All rights reserved Elsevier]

Carbon combustion synthesis and magnetic properties of cobalt ferrite nanoparticles

Martirosyan-KS; Chang-L; Rantschler-J; Khizroev-S; Luss-D; Litvinov-D(Dept. of Chem. Eng., Houston Univ., TX, USA)

IEEE-Transactions-on-Magnetics. June 2007; 43(6): 3118-20

Cobalt ferrite CoFe₂O₄ crystalline nanoparticles (50-100 nm) were produced by carbon combustion synthesis of oxides (CCSO). In this combustion synthesis process, the exothermic oxidation of carbon generates a thermal reaction wave that propagates through the solid reactants mixture of CoO and Fe₂O₃ converting it to cobalt ferrite. The extensive emission of CO₂ increased the porosity and friability of the product. The quenching front method combined with XRD and VSM characterization revealed that crystalline CoFe₂O₄ particles formed in the early stage of the combustion, before the temperature reached its maximum. The maximum value of the coercivity of the quenched product within the front region was 940 Oe with a magnetization of 15 emu/g. The as-synthesized ferrites had hard magnetic properties with coercivity of 700 Oe and saturation magnetization of up to 47 emu/g

The phase evolution of the TiC cermet fabricated by spark plasma sintering

Ahn-In-Shup; Bae-Sung-Yeal; Sung-Tek-Kyung; Park-Dong-Kyu(Div. of Adv. Mater. Sci. & Eng., Gyeong Sang Nat. Univ., Chinju, South Korea)

Materials-Science-Forum. 2007; 539-543: 2755-60

The TiC cermet widely used for high hardness working dies and tool materials was fabricated by carbo-thermic reduction of titania-precusor or self-propagating high temperature synthesis(SHS) reaction. In this paper, the titanium hydride, carbon and iron alloy(D'AE) powders which were mixed for uniform microstructure by spex mill was sintered directly in the spark plasma sintering(SPS) furnace. The nano TiC powders which were fabricated by mechanical alloying using TiH₂ powders mixed with carbon powder were sintered also in the SPS furnace. The effects of mechanical alloying time and sintering procedure on the phase changes of sintered microstructure were evaluated with X-ray diffraction, electron microscopy, EDS, and hardness tester. As-milled powders for 5 hours were successfully synthesized to the TiC phase of 300 nm mean particle size. The microstructure of spark plasma sintered TiC/Fe cermet using TiC powders fabricated by 5 hours milling shows lower density in compare with the spark plasma sintered cermet using mixed powders. The nano size TiC particles were formed homogeneously during spark plasma sintering by the self propagating synthesis reaction

Combustion synthesis of TiB₂ particle dispersed metal matrix composites

Matsuura-K; Obara-Y(Div. of Mater. Sci. & Eng., Hokkaido Univ., Sapporo, Japan)

Materials-Science-Forum. 2007; 539-543: 809-13

FeAl-TiB₂ composites have been combustion synthesized from mixtures of Fe, Al, Ti and B powders. When the powder mixture was heated in vacuum to approximately 900 K, an abrupt increase in temperature was observed, indicating that the combustion synthesis reactions occurred in the powder mixture. X-ray diffraction analyses revealed that the combustion-synthesized sample consisted of only FeAl and TiB₂. Metallographic investigations using a scanning electron microscope revealed that fine TiB₂ particles were dispersed in FeAl matrix phase. As the volume fraction of the TiB₂ particles increased from 0.3 to 0.8 by controlling the powder mixture composition, the average TiB₂ particle size increased to 1 to 7 mu m and the average Vickers hardness of the composites increased from 800 to 1600. This method has been applied to the fabrication of some other ceramic particle dispersed metal matrix composites such as Fe-TiC and FeAl-TiC systems

Highly sinter-active (Mg-Cu)-Zn ferrite nanoparticles prepared by flame spray synthesis

Vital-A; Angermann-A; Dittmann-R; Graule-T; Topfer-J(Empa, Swiss Fed. Labs. for Mater. Testing & Res., Duebendorf, Switzerland)

Acta-Materialia. April 2007; 55(6): 1955-64

Nanoscale ZnFe₂O₄, Mg_0.5Zn_0.5Fe₂O₄ and Mg_0.2Cu_0.2Zn_0.62Fe_1.98O_3.99 powders were prepared for the first time by flame spray synthesis (FSS). Solutions of metal beta -diketonates in organic solvents were used as precursor. Crystalline particles of spinel structure with 6-13nm primary particle size resulted from the flame process. Particle and crystallite size depended on the flow rate of the atomizing gas, the precursor and its molarity. Compacts prepared from Mg-Cu-Zn ferrite nanoparticles revealed an extremely high sinter-activity. A sintered density of 5.05gcm^-3 was achieved after firing for 2h at 900 degrees C without any sintering additives, while a maximum density of 4.91gcm^-3 was obtained with particles from the conventional ceramic route. The permeability of the sintered Mg-Cu-Zn ferrite nanopowder compacts reached mu =600 at 1MHz and the saturation magnetisation was 80emug^-1. The outstanding sintering activity of the flame-made ferrite powders is attributed to their small primary particle size. [All rights reserved Elsevier]

Characteristics of ZnGa₂O₄ phosphors synthesized by solution combustion method

Sung-Park; Yun-Joong-Chung; Jae-Chun-Lee; Kang-Yoo; Byoung-Woo-Kim; Ju-Hyeon-Lee(Dept. of Mater. Sci. & Eng., Myongji Univ., Kyunggi-do, South Korea)

Journal-of-Electroceramics. Dec. 2006; 17(2-4): 827-30

ZnGa₂O₄ phosphors were synthesized by both SCM (solution combustion method) and SSRM (solid state reaction method). The characteristics of the both ZnGa₂O₄ phosphors were investigated by TGA (thermogravimetric analysis), SEM (scanning electron microscope), BET (Brunauer Emmett Teller), PL (photoluminescence) and XRD (X-ray diffraction). The particle size of SCM phosphor was about one-hundredth of SSRM phosphor. The PL intensity of SCM phosphor was about 1.5 fold higher than that of SSRM phosphor. The SCM phosphor was also tried to be doped with Mn⁺² ions. The highest PL peak was observed with Mn⁺² ions of 0.003 mole fraction. The peak was shifted from blue (470 nm) to green (513 nm) color. These results might be very useful for high efficiency phosphors for displays such as field emission displays and plasma display panels

A radio through X-ray study of the hot spots, active nucleus, and environment of the nearby FR II radio galaxy 3C 33

Kraft-RP; Birkinshaw-M; Hardcastle-MJ; Evans-DA; Croston-JH; Worrall-DM; Murray-SS(Harvard-Smithsonian Center for Astrophys., Cambridge, MA, USA)

Astrophysical-Journal. 20 April 2007; 659(2): 1008-21

We present results from Chandra ACIS-S, Spitzer, XMM-Newton, HST, and VLA observations of the radio hot spots, extended environment, and nucleus of the nearby (z = 0.0597) FR II radio galaxy 3C 33. This is a relatively low power FR II radio galaxy, so we expect, a priori, to detect a significant X-ray synchrotron component to the emission from the hot spots. We detect X-ray emission coincident with the two knots of polarized optical emission from the southern hot spot (SHS), as well as along the northwest arm of this hot spot. We also detect X-ray emission from two compact regions of the northern hot spot (NHS), as well as diffuse emission behind the radio peak. The X-ray flux density of the region at the tip of the southern hot spot, the most compact radio feature of the southern lobe, is consistent with the synchrotron self-Compton (SSC) process. The X-ray flux densities of the other three regions of the SHS and the two compact regions of the NHS are an order of magnitude or more above the predictions from either the SSC or inverse Compton scattering of the CMB (IC/CMB) mechanisms, thus strongly disfavoring these scenarios unless they are far from equipartition (B ~ 4-14 times smaller than the equipartition values). We conclude that the X-ray emission is synchrotron emission from multiple populations of ultrarelativistic electrons. There must be complex, unresolved substructure within each region. The detection of X-ray emission from both hot spots combined with the large absorbing column toward the primary power-law component of the nucleus conclusively demonstrate that the jets must lie relatively close to the plane of the sky and that relativistic beaming cannot be important

Safety analysis of sugar cataract development using stochastic hybrid systems

Riley-D; Koutsoukos-X; Riley-K(Vanderbilt Univ., Nashville, TN, USA)

Hybrid-Systems:-Computation-and-Control.-10th-Internationa-Conference,-HSCC-2007.-Proceedings-Lecture-Notes-in-Computer-Science-Vol.4416. : 758-61

Modeling and analysis of biochemical systems are important tasks because they can unlock insights into the complicated dynamics of systems which are difficult or expensive to test experimentally. In this paper we model sugar cataract development (SCD) as a SHS, and we present a probabilistic verification method for computing the probability of sugar cataract formation for different chemical concentrations. An accumulation of sorbitol in the eye is theorized to be the main factor in the SCD process. Understanding the exact conditions that lead to the development of sugar cataracts help scientists better predict and prevent the condition. The chemical reactions and kinetic constants for the system have been previously studied. The stochastic dynamics for biochemical processes can be accurately modeled by the chemical master equation which, however, is impossible to solve for most practical systems. The stochastic simulation algorithm (SSA) is equivalent to solving the master equation based on a discrete model by simulating one reaction at a time, but if the number of molecules of any of the reactants is large, the SSA is not efficient. For verification, it is computationally intractable to enumerate all possible states of the model employed by the SSA. Our approach suggests starting with the continuous stochastic dynamics and generating discrete approximations with coarser (and variable) resolution unlike the fixed, overly-fine resolution of the SSA. The discrete approximations can then be used for verification of reachability properties

Finite-element model of temperature conditions in self-propagating high-temperature synthesis of cylindrical blanks

Kvanin-VL; Balikhina-NT; Krasnoshchekov-PI; Radchenko-VP; Fedotov-AF(Samara State Tech. Univ., Russia)

Journal-of-Engineering-Physics-and-Thermophysics. Sept.-Oct. 2006; 79(5): 905-14; Original: Inzhenerno-Fizicheskii-Zhurnal. Sept.-Oct. 2006; 79(5): 64-73

Two-dimensional, nonstationary heat-conduction problems in a system of four finite bodies with an internal mobile heat source of the first kind (burning front) have been solved by the finite-element method. The influence of basic technological factors on the temperature-field parameters in the process of synthesis of TiB-40% Ti alloys has been investigated. It has been shown that for a real technological cycle the temperature field in a blank and a sand shell can be considered to be stationary and homogeneous

Photoluminescence studies on Eu²⁺-activated Li₂SrSiO₄ - a potential orange-yellow phosphor for solid-state lighting

Pardha-Saradhi-M; Varadaraju-UV(Dept. of Chem., Indian Inst. of Chem. Technol. Madras, Chennai, India)

Chemistry-of-Materials. Oct. 2006; 18(22): 5267-72

A series of Eu²⁺-activated Li₂SrSiO₄ orange-yellow phosphor compositions exhibiting intense emission under 400-470 nm excitation are synthesized by solid-state reaction, and their luminescence properties are investigated as a function of activator concentration (Eu²⁺). The critical concentration is found to be 0.005 mol of Eu²⁺ (R_c = 34 A) per formula unit. The composition containing 0.005 mol of Eu²⁺ is also synthesized by a combustion technique followed by postannealing at different temperatures. The luminescence emission intensity of a combustion-synthesized sample increases with increasing annealing temperature. This is attributed to increased crystallinity and improved distribution of activator in the lattice in the combustion-synthesized sample. Attempts are made to develop white light-emitting diodes by combining an InGaN blue LED chip (420 nm) and a Li₂SrSiO₄:Eu²⁺ phosphor. Two distinct emission bands from the InGaN and Li₂SrSiO₄:Eu²⁺ (562 nm) are observed that combine to give a spectrum that appears white to the naked eye. The values of the CIE coordinates indicate that the Li₂SrSiO₄:Eu²⁺-coated LED has improved red emission compared to the commercial YAG:Ce phosphor

Consolidation and mechanical properties of nanostructured 2MoSi₂-SiC composite synthesized by high-frequency induction heated combustion

In-Jin-Shon; Dong-Ki-Kim; In-Yong-Ko; Jin-Kook-Yoon; Munir-ZA(Dept. of Mater. Eng., Chonbuk Nat. Univ., Jeonbuk, South Korea)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 25 May 2007; 457(1-2): 368-72

Dense nanostructured 2MoSi₂-SiC composite was synthesized by high-frequency induction heated combustion synthesis (HFIHCS) method within 1min in one step from powders of Mo₂C and 5Si. Simultaneous combustion synthesis and densification were accomplished under the combined effects of an induced current and mechanical pressure. Highly dense 2MoSi₂-SiC with relative density of up to 96.5% was produced under simultaneous application of a 60MPa pressure and the induced current. The average grain size of MoSi₂ and SiC were about 50 and 40nm, respectively. The hardness and fracture toughness values obtained were 1540kg/mm² and 4.6MPam¹2/, respectively. [All rights reserved Elsevier]

Local structure characterization of superconducting MgCNi₃ prepared by SHS technique

Paolone-A; Castellano-C; Palumbo-O; Cordero-F; Cantelli-R; Martinelli-A; Ferretti-M(Dipt. di Fisica, Univ. di Roma "La Sapienza", Italy)

Physica-C. 15 April 2007; 454(1-2): 77-81

Extended X-ray absorption fine structure measurements at the Ni K absorption edge on MgCNi₃ prepared by an alternative method based on the self-propagating high-temperature synthesis (SHS) technique are reported in the temperature range from 5 up to 300K. The temperature dependence of the interatomic Ni-Ni and Ni-Mg distances is in agreement with the values reported for samples obtained by the common solid state route, which has been largely used up to now. The Ni-Ni and Ni-Mg Debye-Waller factors can be well described by a correlated Debye model, with theta _D=287K. The present measurements confirm the good quality of the samples produced by the SHS method. [All rights reserved Elsevier]

Microstructural transformation during combustion synthesis of MgB₂ superconductor

Xiujuan-Chen; Tiandong-Xia; Mingjing-Wang; Wenjun-Zhao; Tianzuo-Liu(Coll. of Mater. Sci. & Eng., Lanzhou Univ. of Technol., China)

Physica-C. 15 April 2007; 454(1-2): 38-42

To investigate the phase transformation behaviors of combustion synthesis of MgB₂, a mixture of Mg, B was used for a combustion front quenching test, and the microstructural evolution in the quenched sample was observed by scanning electron microscopy (SEM) and electron probe microanalyzer (EPMA). The temperature-time profile of the combustion was measured, and the phase constituents of the different zones of the quenched sample were inspected by X-ray diffraction (XRD). Based on these experimental results, the transformation behaviors in the SHS-synthesized superconductor MgB₂ was analyzed, and a solid phase diffusion and dissolution-precipitation mechanism was proposed. [All rights reserved Elsevier]

Synthesis of the ceramic-metal catalysts (PtRuNi-TiO₂) by the combustion method

Moreno-B; Chinarro-E; Fierro-JLG; Jurado-JR(Inst. de Ceramica y Vidrio, Madrid, Spain)

Journal-of-Power-Sources. 10 June 2007; 169(1): 98-102

Electrocatalysis on the anode side of PEM fuel cells (PEMFC) has been widely studied, however, little information has been published on cermet catalysts, probably due to the very low or negligible power density registered when a ceramic oxide is blended with Pt based powders. In spite of this, there exists an advantage in the use of oxides, such as TiO₂. This type of oxide can exhibit a bifunctional catalytical effect, as a Pt protecting matrix in the hydrogen oxidation reaction (H.O.R.) which increases CO oxidation and also promotes hydroxide formation, thus improving the oxidation of hydrogen. In this work, a trimetallic composition of 50mol% (Pt-Ru-Ni, 60:30:10)-50mol% TiO₂ is investigated as anode catalyst for a PEMFC. For the preparation of this catalyst, combustion synthesis was the route selected, which allows us to achieve a powder composite with trimetallic (PtRuNi) and ceramic (TiO₂) phases. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and polarisation curves (after MEA construction) are used to evaluate the catalytic activity of this type of powder. The catalyst obtained shows a single trimetallic phase with an average particle size of 8nm. The TiO₂ was found mainly as anatase phase with an average particle size of 2-3nm. No reaction was detected between the two phases. The high power density exhibited (107mWcm^-2) with this cermet may be attributable to by a bifunctional effect on the CO and hydrogen oxidation reactions which occur during the single cell operation. [All rights reserved Elsevier]

A study on the heat-treatments of nanocrystalline nickel substituted BaW hexaferrite produced by low combustion synthesis method

Agarwala-V; Sharma-R; Agarwala-RC(Metall. & Mater. Eng. Dept., Indian Inst. of Technol. Roorkee, Uttaranchal, India)

Journal-of-Magnetism-and-Magnetic-Materials. May 2007; 312(1): 117-25

The novel low temperature combustion synthesis (LCS) method for the preparation of nanocrystalline W-type BaW hexaferrite i.e. BaNi₂Fe₁₆O₂₇ has been carried out by citrate precursor using the sol-to-gel (S-G) followed by gel-to-nanocrystalline (G-N) conversion. Decomposition behaviors and the phases associated therein are investigated by means of thermal analysis (DTA/DTG/TG) and XRD, respectively. Atomic absorption spectroscopy (AAS) has been used to determine the elemental analysis in different conditions. Surface morphology of the nonporous ultra fine particles have been examined by SEM. The TEM micrographs show that the particles of the size of 10nm were seemed to be agglomerated in the `as synthesized' condition. Room temperature Fe-57 Mossbauer spectrum, MS has showed doublet of `as synthesized' nanocrystalline powder that indicates the superparamagnetic behavior of the material. This effect is further confirmed by vibrating sample magnetometer (VSM) wherein it was noticed that the magnetic field (10KG max) did not have any effect on the material. The material was annealed at 400, 700 and 1000 degrees C in the furnace for 4h. The grain size is found to increase from 10 to 70nm after annealing at 1000 degrees C for 4h. MS after annealing at 700-1000 degrees C for 4h, showed that the doublets of `as synthesized' is further resolved into broad sextets due to the presence of both superparamagnetic and ferrimagnetic particles, in the wide size range from 10 to 70nm. Only slight increase in particle size (from 10 to 15nm) is noticed after the heat-treatment for 1-3 and 5min in microwave oven (2.45GHz with 760W) but with predominant phase changes. TEM after the heat treatment revealed the presence of microcrystalline nature of grains of the size ~70nm. The transformation of the magnetic properties i.e. from superparamagnetic to ferrimagnetic behaviour after heating in microwave oven has been revealed by hysteresis loops under VSM study. The saturation magnetisation, M_s after heat treatment has been seen to increase from 26.7 to 44.5emu/gm. Remanence and coercivity have also increased four and seven times, respectively. M_s of the as synthesised hexaferrite nano powder and heat-treated powder in microwave oven for 5min show doublets, confirming the presence of superparamagnetic relaxation in the nano particles as only slight increase in the particle size is associated with the heat treatment. [All rights reserved Elsevier]

Spark plasma sintering behavior of Fe-TiC composite materials fabricated by mechanical alloying

Cho-Ho-Jung; Bae-Sung-Yeal; Ahn-In-Shup; Park-Dong-Kyu(Sch. of Nano & Adv. Mater. Eng., Gyeongsang Nat. Univ, Jinju, South Korea)

Materials-Science-Forum. 2007; 544-545: 825-8

TiC-based cermets attract much attention because of their excellent wear-resistance, high hardness at high temperature, good chemical stability, superior thermal deformation resistance. Therefore, titanium carbide is mainly used for cutting tools, grinding wheels, coated cutting tips and coated steel tools. In this research, Fe-TiC composite materials were fabricated by spark plasma sintering (SPS) after mechanical alloying. TiH₂ and graphite powders were used to synthesize TiC phase. In order to compare the properties of sintered materials using mixture powder (D'AE+TiH₂+graphite), commercial TiC powder was mixed with Distaloy AE (D'AE) powder as a same mechanical alloying method. Then, the shape of each mixture powder (D'AE+TiFh+graphite, D'AE+TiC (commercial)) and sintering properties were compared. TiC phase was synthesized by self-propagating high-temperature synthesis (SHS) reaction during spark plasma sintering. It was confirmed by using X-ray diffraction (XRD), energy dispersive spectrometry (EDS) and scanning electron microscopy (SEM) were used to observe shape of mixture powders and also sintering properties were examined such as hardness, relative density. In case of sintered material for 10 min holding time at 1373 K after mechanical alloying for 1 hour with D'AE, TiH₂ and graphite, it indicated higher hardness value 49H_R-C than a case using D'AE and TiC powder

In-situ joining of combustion synthesized Ni₃Al intermetallic compounds with AZ91D Mg alloy

Cho-GS; Lee-KR; Choe-KH; Lee-KW; Kim-KY(Adv. Mater. Res. & Dev. Center, Korea Inst. of Ind. Technol., Incheon, South Korea)

Materials-Science-Forum. 2007; 544-545: 383-6

We focused on the surface reinforcement of light weight casting alloys with Ni3Al intermetallic compounds by in-situ combustion reaction to improve the surface properties of nonferrous casting components. In the present work, by setting the mixture of elemental Ni and Al powders in a casting mold, the powder mixture reacted to form Ni3Al intermetallic compound by SHS reaction ignited by the heat of molten AZ91D Mg alloy and simultaneously bonded with the Mg casting alloy. The AZ91D Mg alloy bonded with the Ni3Al intermetallic compound was sectioned and observed by optical microscopy and scanning electron microscopy(SEM). The chemical composition of intermetallic compounds and diffusion layer formed around bonding interface were identified by energy dispersive spectroscopy(EDS). X-ray diffraction analysis(XRD) and electron probe micro analyzer(EPMA). The main intermetallic compound was Ni3Al phase and a little Ni2Al3 intermetallic compound was formed from the Ni and Al powder mixtures. Residual pores were observed in the synthesized intermetallic compound. The AZ91D Mg alloy and Ni3Al intermetallic compound were bonded very soundly by the interdiffusion of Mg, Ni and Al elements, but some cracks were observed around the bonded interface on the interdiffusion layer. The diffusion length formed between AZ91D Mg alloy and Ni3Al was different depending on the diffusivity of Ni and Al elements into the molten Mg alloy. Ni was more deeply diffused into the Mg alloy than Al. The diffusion layer was about 200 mu m thickness and various phases were formed by the interdiffusion of Mg. Ni and Al. From this challenge we have successfully produced a coating layer based on nickel aluminide on light weight Mg alloy using molten metal heat without any additional process. On the basis of the results obtained, it is concluded that near-net shaped nickel aluminide coating layer can be formed using this unique process

Crystalline phases and particle characteristics of the combustion-synthesized TiO₂ nanoparticles

Gyo-Woo-Lee; Shang-Min-Choi(Div. of Mech. & Aerosp. Syst. Eng., Chonbuk Nat. Univ., Jeonju, South Korea)

Materials-Science-Forum. 2007; 544-545: 39-42

TiO₂ nanoparticles were synthesized with using N₂-diluted and O₂-enriched coflow hydrogen diffusion flames. We investigated the effects of the flame temperature on the crystalline phases and particle characteristics of the TiO₂ nanoparticles that were formed. For the higher temperature conditions, the maximum centerline temperatures that were measured were greater than approximately 1,600 K, and TiO₂ nanoparticles, which had spherical shapes with diameters of approximately 60 nm, were synthesized. For the lower temperature conditions, the maximum centerline temperatures that were measured were less than approximately 1,600 K, and the diameters of the nanoparticles that were formed had unclear boundaries that ranged from 35 to 50 nm. From the XRD analyses, it was believed that the crystalline structures of the nanoparticles that were formed were divided into two types. For the higher temperature cases, the fractions of the TiO₂ nanoparticles that were synthesized, which had anatase-phase crystalline structures, increased with the increase of the flame temperatures. On the contrary, for the lower temperature cases, the fraction of anatase-phase nanoparticles increased with the decrease of the flame temperatures

Morphology and luminescence performance of the nano-sized BaMgAl₁₀O₁₇:Eu²⁺ phosphor with PEG as additive

Chen-Zhe; Xie-Hong; Yan-You-wei(State Key Lab. of Die & Mould Technol., Huazhong Univ. of Sci. & Technol., Wuhan, China)

Journal-of-Synthetic-Crystals. Dec. 2006; 35(6): 1277-82

Starting from the aqueous solutions of metal nitrates with polyethylene glycol (PEG) as additives, the blue emitting BaMgAl₁₀O₁₇:Eu²⁺ (BAM) phosphor for PDP application was prepared by solution combustion method. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) , transmission electron microscopy (TEM) and photoluminescence spectra were used to characterize the resulted BAM phosphor. The obtained BAM phosphor particles have spherical shape, nanometer size (20-40 nm) and its average grain size is about 30 nm. In this paper, the effect of PEG on the morphology and luminescence performance of the BAM phosphor was mainly investigated. The results show that adequate amount of PEG was necessary for obtaining spherical particles, and the optimum emission intensity was achieved when the concentration of PEG (MW = 10000) was 5.0 wt% in the precursor solution

The effect of preset heating rate on combustion synthesis of Fe-V-C system under an electric field

Lin-Huimin; Feng-Keqin; Yang-Yi; Bai-Chenguang; Wang-Wenjuan; Wang-Hongliang(Sichuan Univ., Chengdu, China)

Rare-Metal-Materials-and-Engineering. Jan. 2007; 36(1): 50-3

The effect of preset heating rate on the combustion synthesis of Fe-V-C system under an electric field was investigated using Gleeble thermal simulation apparatus. The phase structure and microstructure of samples under different heating rates were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM) etc. The results showed that under the effect of electric field, the starting temperature of synthesis reaction was relatively low, on this condition, the effect of preset heating rate on the synthetic process presented a change like stepladder, that is, when the preset heating rates were 600 degrees C/s and 1000 degrees C/s, only a little changes in both the progress and the products took place during the synthesis, and when the preset heating rate was 1400 degrees C/s, the ignition temperature and the delay time decreased, and the sizes of the synthetic products reduced, and the hardness increased

Remote femtosecond laser induced breakdown spectroscopy (LIBS) in a standoff detection regime

Brown-CG; Bernath-R; Fisher-M; Richardson-MC; Sigman-M; Walters-RA; Miziolek-A; Bereket-H; Johnson-LE(Laser Plasma Lab., Univ. of Central Florida, Orlando, FL, USA)

Proceedings-of-the-SPIE-The-International-Society-for-Optical-Engineering. 2006; 6219(1): 62190B-1-7

The need for robust, versatile, and rapid analysis standoff detection systems has emerged in response to the increasing threat to homeland security. Laser Induced Breakdown Spectroscopy (LIBS) has emerged as a novel technique that not only resolves issues of versatility, and rapid analysis, but also allows detection in settings not currently possible with existing methods. Several studies have shown that femtosecond lasers may have advantages over nanosecond lasers for LIBS analysis in terms of SNR. Furthermore, since femtosecond pulses can travel through the atmosphere as a self-propagating transient waveguide, they may have advantages over conventional stand-off LIBS approaches¹. Utilizing single and multiple femtosecond pulse laser regimes, we investigate the potential of femtosecond LIBS as a standoff detection technology. We examine the character of UV and visible LIBS from various targets of defense and homeland security interest created by channeled femtosecond laser beams over distances of 30m or more

Combustion synthesis and luminescent properties of phosphor BaMgAl₁₀O₁₇:Eu²⁺

Zhang-Ran; Zhu-Wei-hua; Zhou-Tao-jun; Xia-Chun-yan; Wang-Jin-feng(Sch. of Chem. & Chem. Eng., Jiangsu Univ., China)

Chinese-Journal-of-Liquid-Crystals-and-Displays. Feb. 2007; 22(1): 32-6

The aluminate phosphor BaMgAl₁₀O₁₇:Eu²⁺(BAM) was successfully synthesized by rapid combustion process at 600 degrees C furnace temperature. The phosphor was characterized by XRD and fluorescence spectra. The effect of urea and the ratio of Sr²⁺ were inspected. The results showed that the emission spectrum of BaMgAl₁₀O₁₇:Eu²⁺ peaking at 450 nm was assigned to the Eu²⁺ 4f⁶5d¹-4f⁷. The luminescence intensity of the phosphor depended on the concentration of Eu²⁺ highly and reached a maximum at 10 %(mole fraction). Additionally the study also indicated that the amount of urea had a great effect on the crystal performance and luminescent property of phosphor. The luminescence intensity of the phosphor was the strongest when the value of urea:NO₃^- was 2.5:1. The luminescence intensity of the phosphor would increase with doping rare earth ions, including Dy³⁺, Er³⁺, Nd³⁺ and Pr³⁺. The crystal performance and luminescent property had a great change when Sr²⁺ ions was doped in BAM

Combustion synthesis and photoluminescence of nanocrystalline Gd₂O₃:Eu³⁺

Peng-Zhi-Wei; Wang-Ling-Ling; Liu-Huang-Qing; Huang-Wei-Qing; Zou-Bing-Suo(Dept. of Appl. Phys., Hunan Univ., Changsha, China)

Acta-Physica-Sinica. 2007; 56(2): 1162-6

Nanocrystalline Gd₂O₃:Eu³⁺ was prepared by modified combustion synthesis using citric acid as the fuel and metal nitrates as oxidants. By using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and fluorescence spectrophotometry, the structural, morphological and luminescent properties of the nanocrystals were investigated. The results showed that Gd₂O₃:Eu³⁺ nanocrystal with pure cubic phase was produced after the samples prepared using different citric acid-to-metal nitrate (C/M) molar ratios were calcined at 800 degrees C for 1 hour. The grain size was approximately 30 nm and the size distribution was narrow. The Gd₂O₃:Eu³⁺ nanocrystals with C/M ratio 1.0 had the best crystallinity and strongest photoluminescence. The main emission peak of Gd₂O₃:Eu³⁺ nanocrystal was 612 nm, being attributed to ⁵D₀to⁷F₂ transition. The charge transfer state had an obvious red shift in the excitation spectrum. The efficient energy transfer from Gd³⁺ to Eu³⁺ was also observed. In addition, the influences of C/M molar ratio on crystallinity and luminescent properties were studied and discussed

Generation of hydrogen gas by reforming biomass with superheated steam

Yamada-O(Dept. of Mech. Eng. for Transp., Osaka Sangyo Univ. Nakagaito, Daito Osaka, Japan)

Thin-Solid-Films. 19 June 2006; 509(1-2): 207-11

Various kinds of new porous materials, such as non-oxide ceramics and intermetallic compounds, can be rapidly manufactured by combustion synthesis methods. Since combustion-synthesized materials have good electroconductivity, porosity with three-dimensional network skeletal structure, and heat and corrosion resistance, they are suitable for use in heating elements, filters, catalysts, sensors, biomaterials, heat exchangers, and electrode materials for fuel cells and electrolysis of water. By using combustion-synthesized materials of NiAl intermetallic compounds for a heater, it is possible to generate high temperature superheated steam. We have been able to generate superheated steam at 1000 degrees C by sending low temperature saturated steam at 100 degrees C from the bottom of a quartz tube filled with porous NiAl pellets that are heated by an electromagnetic induction coil wound outside the tube. It was confirmed that substantial amounts of hydrogen gas can be generated by reforming grass biomass with high temperature superheated steam at 900 degrees C. This method would also be effective for decomposition of toxic organic substances such as dioxin. [All rights reserved Elsevier]

Convective heat transfer in the processes of "gas-free" combustion (by an example of Ti + C system combustion)

Seplyarskii-BS; Vadchenko-SG(Inst. of Struct. Macrokinetics & Problems of Material Sci., Russian Acad. of Sci., Moscow, Russia)

Heat-Transfer-Research. 2007; 38(2): 123-33

This work presents, for the first time, an experimental verification of the hypothesis on the convective-conductive mechanism of combustion wave propagation for fast-burning "gas-free" systems, containing an easily melted reagent. According to this hypothesis, the velocity of movement of the melt, ensuring convective heat transfer, in reality represents the velocity of combustion wave propagation. The main factors affecting the velocity of melt movement were determined. It was found that, despite the opinion existing in the scientific literature, elongation of burning specimens, compressed from a stoichiometric mixture of titanium and soot, occurs beyond the heating area. It was demonstrated, for the first time, that thermal vacuum processing of initial specimens not only leads to an increase of the combustion rate, but also modifies the qualitative character of the dependence of the combustion rate on the density: the combustion rate monotonously increases with density. The experiments showed that for specimens, compressed from a stoichiometric mixture of titanium and soot, the combustion rate increases more than twofold with an increase of the specimen thickness. The range of experimental investigations, made by the authors, confirms the hypothesis about a convective-conductive mechanism of the combustion wave propagation for fast-burning "gas-free" systems, containing an easily melted reagent

Effect of the microstructure of heterogeneous mixture on regularities of gas-free combustion

Kochetov-NA; Rogachev-AS; Emelianov-AN; Illarionova-EV; Shkiro-VM(Inst. of Struct. Macrokinetics & Problems of Material Sci., Russian Acad. of Sci., Moscow, Russia)

Heat-Transfer-Research. 2007; 38(2): 95-106

We performed a series of experiments on investigation of the microstructure of the initial charge for gas-free combustion, including investigation of compressibility, electroconductivity, thermal conductivity, rate of charge burning, as well as metallographic investigations. The determining role of the shape of particles and their capacity of formation of a continuous skeleton, as well as their impact on regularities of gas-free combustion have been identified. It has been shown that the velocity and mode of propagation of the gas-free combustion front are determined by the transfer of heat between metal particles in the initial reaction mixture, with the limiting role being played by contacts between particles. The method of atomic tunnel microscopy was used to study the micro relief of the surface of particles and determine the most probable width of micro gaps between the particles at the point of their contact. The presence of these gaps leads to a strong dependence of the mixture heat conduction on the gaseous atmosphere (vacuum, helium and air)

Use of BN as a reactant in combustion synthesis of TiNTiB₂ composites under nitrogen pressure

Yeh-CL; Teng-GS(Dept. of Mech. & Autom. Eng., Da-Yeh Univ., Changhua, Taiwan)

Journal-of-Alloys-and-Compounds. 29 June 2006; 417(1-2): 109-15

An experimental study on direct formation of TiNTiB₂ composites by self-propagating high-temperature synthesis (SHS) was conducted using compacted samples of titanium (Ti) and boron nitride (BN) powders ignited in gaseous nitrogen. Effects of sample green density, nitrogen pressure, starting stoichiometry of reactant compacts, and diluent content on the degree of conversion and combustion characteristics were investigated. With the addition of TiN as a diluent in the sample, TiNTiB₂ composites with the TiB₂ content ranging from 12.5 to 33.3mol.% were produced at relatively low pressures of nitrogen. Experimental results showed that the TiN-33.3mol.% TiB₂ composite was directly synthesized from SHS reaction of the 1.5Ti+BN sample in argon. Moreover, combustion of a 60% TMD sample made up of 2Ti+BN achieved complete nitridation in nitrogen of 1.48MPa and yielded a composite of TiN-25mol.% TiB₂. However, due to the melting of reactant compacts in combustion the degree of nitridation was relatively low for the undiluted samples of 3Ti+BN and 4Ti+BN, implying that the addition of diluent TiN was required in order to achieve the full conversion. For the reactant compacts of 60% TMD, the TiN-diluted samples of 2.5Ti+BN+0.5TiN and 3Ti+BN+TiN reached complete nitridation at 1.14MPa of nitrogen and produced TiNTiB₂ composites with the TiB₂ concentrations of 16.7 and 12.5mol.%, respectively. For the end products of incomplete conversion, XRD analysis identified not only desired phases of TiN and TiB₂, but intermediate compounds of Ti₂N and TiB. [All rights reserved Elsevier]

Failure assessment of cracked square hollow section T-joints

Yang-ZM; Lie-ST; Gho-WM(Maritime Res. Centre, Nanyang Technol. Univ., Singapore, Singapore)

International-Journal-of-Pressure-Vessels-and-Piping. April 2007; 84(4): 244-55

Three full-scale static strength tests were carried out on pre-cracked square hollow section (SHS) T-joints. In accordance with the experimental results, an accurate crack model for welded SHS joints is proposed in this paper. Based on this numerical model, the load-displacement curves and the stress intensity factors (SIFs) along the crack front are calculated. It is found that the SIF varies greatly along the crack front, and the highest value is located at the brace corner. From Charpy V-notch impact test results, anisotropic fracture toughness was found, and influenced the failure behavior of the damaged joints. Ductile tearing was found to initiate from the crack front parallel to the chord side wall where the fracture toughness was smaller, and not from the crack front at the corner where the SIF value was the highest. Using the plastic collapse load obtained via the twice elastic compliance technique and the fracture toughness obtained from the Crack tip opening displacement (CTOD) tests, the BS7910 Level 2A Failure Assessment Diagrams (FAD) for the three cracked joints are plotted. It is confirmed that the standard BS7910 Level 2A curve gives a conservative assessment for cracked SHS T-joints under brace end axial loads. [All rights reserved Elsevier]

Combustion synthesis of silicate phosphors

Bhatkar-VB; Omanwar-SK; Moharil-SV(Dept. of Phys., Amaravati Univ., Amravati, India)

Optical-Materials. April 2007; 29(8): 1066-70

Silicate materials are useful for various applications. Combustion synthesis of some silicate phosphors is described. The synthesis is based on the exothermic reaction between urea and ammonium nitrate and subsequent heat transfer to the reactants. It is argued that the combustion synthesis is a simple and fast method for preparing silicate materials. [All rights reserved Elsevier]

Microstructure and mechanical properties of multilayer-lined composite pipes prepared by SHS centrifugal-thermite process

Meng-QS; Chen-SP; Zhao-JF; Zhang-H; Zhang-HX; Munir-ZA(Coll. of Mater. Sci. & Eng., Taiyuan Univ. of Technol., China)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 15 May 2007; 456(1-2): 332-6

Using a self-propagating high-temperature synthesis centrifugal-thermite process, pipes were lined with a multiphase ceramic layer. The ceramic layer was metallurgically joined with an intermediate intermetallic layer, situated between the base metal and the ceramic layer. The microstructures of the intermetallic layer, the multiphase ceramic layer, and the interfaces between them were investigated. The results showed that ceramic layer was composed of Al₂O₃, TiO₂, and TiC while the intermediate layer contained AlFe, AlCrFe, and NiFe. Under the action of the centrifugal force, the phase TiC settled in the interface between the intermetallic and ceramic layers. The good wettability of TiC by ferrous metals and by Al₂O₃, the intermetallic layer and ceramic layer resulted in a good bond with improved bonding strength. Mechanical characterization of the pipes showed a significant improvement over conventional thermite self-propagating high-temperature synthesis (SHS) methods. [All rights reserved Elsevier]

Assisted self-sustaining combustion reaction in the Fe-Si system: Mechanical and chemical activation

Gras-Ch; Zink-N; Bernard-F; Gaffet-E(MaNaPi Group, Univ. of Burgundy, Dijon, France)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 15 May 2007; 456(1-2): 270-7

This work presents original investigations carried out to improve the activated self-propagating high-temperature synthesis (SHS) process in the Fe-Si system: different ignition modes are tested (volume heating as opposed to a local ignition source), and the use of additive is considered in order to enhance the SHS type reactivity in the Fe-Si system. When 20wt.% of KNO₃ is added to the reactive mixture, the fast (>20mms^-1), stable and self-sustaining combustion reaction produces a very fine FeSi+ alpha -FeSi₂ structure. Infrared thermography (IR) as well as post-mortem analysis (SEM, EDXS, XRD) was used to understand the mechanism behind the chemical activation process when KNO₃ was used as an additive. [All rights reserved Elsevier]

Phase behaviour of polydisperse sticky hard spheres: analytical solutions and perturbation theory

Gazzillo-D; Fantoni-R; Giacometti-A(Dipt. di Chimica Fisica, Univ. di Venezia, Italy)

Molecular-Physics. 20 Nov.-20 Dec. 2006; 104(22-24): 3451-9

We discuss the phase coexistence of polydisperse colloidal suspensions in the presence of adhesion forces. The combined effect of polydispersity and Baxter's sticky-hard-sphere (SHS) potential, describing hard spheres interacting via strong and very short-ranged attractive forces, give rise, within the Percus-Yevick (PY) approximation, to a system of coupled quadratic equations which, in general, cannot be solved either analytically or numerically. We review and compare two recent alternative proposals that have attempted to by-pass this difficulty. In the first, truncating the density expansion of the direct correlation functions, we have considered approximations simpler than the PY one. These C_n approximations can be systematically improved. We have been able to provide a complete analytical description of polydisperse SHS fluids using the simplest two orders C₀ and C₁. Such a simplification comes at the price of a lower accuracy in the phase diagram, but has the advantage of providing an analytical description of various new phenomena associated with the onset of polydispersity in phase equilibria (e.g., fractionation). The second approach is based on a perturbative expansion of the polydisperse PY solution around its monodisperse counterpart. This approach provides a sound approximation to the real phase behaviour, at the cost of considering only weak polydispersity. Although a final determination of the soundness of the latter method would require numerical simulations for the polydisperse Baxter model, we argue that this approach is expected to correctly take into account the effects of polydispersity, at least qualitatively

Effect of titanium diluent on the fabrication of Al₂O₃-ZrB₂ composite by SHS dynamic compaction

Mishra-SK; Rupa-PKP; Das-SK; Shcherbakov-V(Nat. Metall. Lab., Jamshedpur, India)

Composites-Science-and-Technology. June 2007; 67(7-8): 1734-9

An investigation on the effect of titanium as diluent (5-20wt%) on the Al₂O₃-ZrB₂ composite by self-propagating high temperature synthesis (SHS) dynamic compaction was carried out. Addition of titanium during the SHS synthesis could vary percentage of phases and microstructure. Small percentage addition (5wt%) of titanium diluent helps in inhibition of grain growth of borides but further increase in diluent addition leads to formation of oxide phases and also titanium diboride. The vickers microhardness first increased with the addition of 5-wt% titanium and then decreased for further additions of titanium diluent up to 20wt%. The maximum hardness was found as 2800Hv_0.025. [All rights reserved Elsevier]

Effective stiffness of nano and transformation composite ceramics

Xiaobo-Lu; Xiequan-Liu; Xinhua-Ni; Shuqin-Zhang(Mech. Eng. Coll., Shijiazhuang, China)

Key-Engineering-Materials. 2007; 336-338: 2528-31

The composite ceramics that contain nano-fibers and transformation particles, fabricated through SHS process, are performed with high fracture toughness and high plasticity. The matrix of composite ceramics was mainly composed of fiber eutectics with nano-fibers. The transformation particles were distributed along boundaries of the fiber eutectic structures. First, Mori-Tanaka method was used to predict the stiffness of the fiber eutectic. The fiber eutectic is transversely isotropic and has five independent elastic constants. Then, considering random orientation of the fiber eutectic, the Young's modulus and Poisson's ratio of the matrix is determined by even strain. The matrix is isotropic. Finally, assuming the transformation particles as spheres distributed in the matrix, the effective stiffness for composite ceramics was computed. When the volume fraction of fibers and particles increase, the Young's modulus of composite ceramics decrease and are little smaller than the volume average value, the Poisson's ratio of composite ceramics decrease and are little bigger than the volume average value

Cracking stress of nano-fibers composite ceramics

Xinhua-Ni; Zhanjun-Yao; Xiequan-Liu; Junying-Wang(Mech. Eng. Coll., Shijiazhuang, China)

Key-Engineering-Materials. 2007; 336-338: 2432-5

Recent experiment showed that nano-fibers composite ceramics, fabricated through SHS process, could acquire high toughening and strengthening. Composite ceramics are mainly composed of fiber eutectic with random orientation, in which nanometer sized zirconia fibers are dispersed within the alumina matrix. First, it can be visualized that tensile force is transmitted from the matrix to the nano-fiber by means of shear stress that develop along the fiber- matrix interface. Then the shear stress on the surface of the fiber eutectic is obtained. It related to the volume fraction and slenderness ratio of the nano-fibers, and external strain of the fiber eutectic. The maximum shear stress is at the ends of the fiber eutectic perpendicular to applied tensile stress. As maximum shear stress on the surface of the fiber eutectic is equal to the critical shear stress, the composite ceramics would crack. So the applied tensile stress on composite ceramics arousing the surface crack of the fiber eutectic is gotten

Synthesis and luminescence properties of nanocrystalline Gd₂O₃:Eu³⁺ by combustion process

Yanhong-Li; Guangyan-Hong(Sch. of Mater. Sci. & Eng., Shenyang Inst. of Chem. Technol., China)

Journal-of-Luminescence. June 2007; 124(2): 297-301

The nanocrystalline Gd₂O₃:Eu³⁺ powders with cubic phase were prepared by a combustion method in the presence of urea and glycol. The effects of the annealing temperature on the crystallization and luminescence properties were studied. The results of XRD show pure phase can be obtained, the average crystallite size could be calculated as 7, 8, 15, and 23nm for the precursor and samples annealed at 600, 700 and 800 degrees C, respectively, which coincided with the results from TEM images. The emission intensity, host absorption and charge transfer band intensity increased with increasing the temperature. The slightly broad emission peak at 610nm for smaller particles can be observed. The ratio of host absorption to O^2--Eu³⁺ charge transfer band of smaller nanoparticles is much stronger compared with that for larger nanoparticles, furthermore, the luminescence lifetimes of nanoparticles increased with increasing particles size. The effects of doping concentration of Eu³⁺ on luminescence lifetimes and intensities were also discussed. The samples exhibited a higher quenching concentration of Eu³⁺, and luminescence lifetimes of nanoparticles are related to annealing temperature of samples and the doping concentration of Eu³⁺ ions. [All rights reserved Elsevier]

Preparation and luminescent properties of cubic Eu³⁺:Y₂O₃ nanocrystals and comparison to bulk Eu³⁺:Y₂O₃

Siyuan-Zhang; Zuoling-Fu; Shihong-Zhou; Tianqi-Pan(Lab. of Rare Earth Chem. & Phys., Graduate Sch. of the Chinese Acad. Sci., Changchun, Taiwan)

Journal-of-Luminescence. June 2007; 124(2): 213-16

Y₂O₃:Eu³⁺ nanocrystals were prepared by combustion synthesis. The particle size estimated by X-ray powder diffraction (XRD) was about 10nm. A blue-shift of the charge-transfer (CT) band in excitation spectra was observed in Y₂O₃:Eu³⁺ nanocrystals compared with bulk Y₂O₃:Eu³⁺. The electronic structure of Y₂O₃ is calculated by density functional method and exchange and correlation have been treated by the generalized gradient approximation (GGA) within the scheme due to Perdew-Burke-Ernzerhof (PBE). The calculated results show that the energy centroid of 5d orbital in nanocrystal has increasing trend compared with that in the bulk material. The bond length and bond covalency are calculated by chemical bond theory. The bond lengths of Y₂O₃:Eu³⁺ nanocrystal are shorter than those of the bulk counterpart and the bond covalency of Y₂O₃:Eu³⁺ nanocrystal also has an increasing trend. By combining centroid shift and crystal-field splitting, the blue-shift of the CT band is interpreted. [All rights reserved Elsevier]

Glycine-nitrates combustion synthesis and properties of nano-sized Ce_1-xGd_xO_2-delta solid solution for solid oxide fuel cell viewpoint

Singh-K; Acharya-SA; Bhoga-SS(Amaravati Univ., India)

Indian-Journal-of-Engineering-and-Materials-Sciences. Dec. 2006; 13(6): 525-30

Nanocrystalline gadolinium-doped ceria powders for solid electrolytes have been successfully prepared via glycine nitrate combustion synthesis and characterized by TGA/DTA, XRD and SEM. Using these powders; highly dense ceramics have been prepared by sintering at 1100 degrees C which is much lower temperature than 1600 degrees C usually required for ceria solid electrolytes prepared by conventional ceramic technique. The effect of compositions on structure and conductivity has also been studied

Preparation and luminescence properties of nanocrystalline La₂O₃:Eu phosphor

HuangQing-Liu; LingLing-Wang; Weiqing-Huang; ZhiWei-Peng(Dept. of Appl. Phys., Hunan Univ., Changsha, China)

Materials-Letters. April 2007; 61(10): 1968-70

Powders La₂O₃ doped with 1 mol% Eu were prepared via a combustion route using different reducers (urea, glycine and citric acid). The structure and morphology were determined with XRD and HRTEM measurement. The main emission positions centered at 626 nm for ⁵D₀to⁷F₂ transition are observed. The variation of CT band with different reducers is observed. The intensity of ⁵D₀to⁷F₂ transition centered at 626 nm with respect to that of ⁵D₀to⁷F₁ transition is a function of the energy difference Delta E between the two CT band positions. [All rights reserved Elsevier]

Effects of concentration of catalyst precursors on carbon nanostructures

Jin-Cheng; Xiaoping-Zou; Fei-Li; Hongdan-Zhang; Pengfei-Ren(Beijing Information Technol. Inst., Res. Center for Sensor Technol., Beijing, China)

Diffusion-and-Defect-Data-Part-B-Solid-State-Phenomena. 2007; 124-126: 1245-8

It is very important to study the effects of various factors on synthesis of carbon nanomaterials for controlled synthesis, which plays a significant role in realizing desired nanostructures or nanodevices for applications. In this report, we employed iron nitrate solution with different concentration, such as 1 mol/l, 0.1 mol/l, 0.01 mol/l, and saturated iron nitrate solution as catalyst precursor solution and studied the effects of concentration of catalyst precursor solution on carbon nanostructures that were synthesized by ethanol catalytic combustion (ECC) process. We have characterized the as-grown carbon nanostructures by employing scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for deep understanding

Rapid transformation of alpha -alumina nanocomposite powders by microwave assisted combustion

Young-Mi-Jung; Sang-Woo-Kim(Nano-Mater. Res. Center, Korea Inst. of Sci. & Technol., Seoul, South Korea)

Diffusion-and-Defect-Data-Part-B-Solid-State-Phenomena. 2007; 124-126: 823-6

The microwave-assisted combustion synthesis as a route to obtain ultrafine alpha -alumina and magnesium aluminate composite powders starting from the ammonium aluminum carbonate hydroxide precursor was investigated. The synthetic temperature and the crystallite size of the alpha -alumina nanocomposite powder were significantly affected by the environmental atmosphere in the microwave assisted combustion. The alpha -alumina and spinel composite powder was obtained by the microwave-assisted combustion at temperature of 1000 degrees C under H₂/N₂, but at 1150 degrees C by the normal heat process under air. The rapid transformation from gamma - to alpha -phase was achieved by microwave assisted nucleation at low temperature of 900 degrees C under H₂/N₂ atmosphere. The least crystallite size of 26.2 nm was obtained under H₂/N₂ atmosphere at 1000 degrees C for 10 min

Microwave-assisted combustion synthesis of NiAl intermetallics in a single mode applicator: Modeling and optimisation

Veronesi-P; Poli-G; Sola-R(Dept. of Mater. & Environ. Eng., Univ. of Modena & Reggio Emilia, Italy)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 15 Dec. 2006; 441(1-2): 149-56

The microwave-assisted combustion synthesis of NiAl intermetallics in a single mode applicator has been simulated numerically and performed with the aim of achieving the highest yields, energy efficiency and process reproducibility. The electromagnetic field modeling of the microwave system allowed to chose the proper experimental set-up and the materials more suitable for the application, minimising the reflected power and the risks of arcing. In all the experimental conditions tested, conversions of 3-5g 1:1 atomic ratio Ni and Al powder compacts into NiAl ranged from 98.7% to 100%, requiring from 30 to 180s with power from 500 to 1500W. The optimisation procedure allowed to determine and quantify the effects of the main process variables on the ignition time, the NiAl yields and the specific energy consumption, leading to a fast, reproducible and cost-effective process of microwave-assisted combustion synthesis of NiAl intermetallics. [All rights reserved Elsevier]

Fabrication of steel matrix composites locally reinforced with different ratios of TiC/TiB₂ particulates using SHS reactions of Ni-Ti-B₄C and Ni-Ti-B₄C-C systems during casting

Qi-chuan-Jiang; Ya-feng-Yang; Hui-yuan-Wang; Yun-hong-Liang; Ru-yi-Zhao(Dept. of Mater. Sci. & Eng., Jilin Univ., Changchun, China)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 15 Feb. 2007; 445-446: 398-404

Steel matrix composites locally reinforced with different molar ratios of in situ TiC/TiB₂ particulates (2:1, 1:1 and 1:2, respectively) have been fabricated successfully utilizing the self-propagating high-temperature synthesis (SHS) reactions of Ni-Ti-B₄C and Ni-Ti-B₄C-C systems during casting. Differential thermal analysis (DTA) and X-ray diffraction (XRD) results reveal that the exothermic reactions of the Ni-Ti-B₄C and Ni-Ti-B₄C-C systems proceed in such a way that Ni initially reacts with B₄C and Ti to form Ni₂B and Ti₂Ni compounds, respectively, with heat evolution at 1037degC; Subsequently, the external heat and the evolved heat from these exothermic reactions promote the reactions forming TiC and TiB₂ at 1133degC. In the composites reinforced with 1:2 molar ratio of TiC/TiB₂, almost all TiB₂ grains have clubbed structures, while TiC grains exhibit near-spherical morphologies. Furthermore, TiB₂ grain sizes decrease, with the increase of TiC content. In particular, in the composites reinforced with 2:1 molar ratio of TiC/TiB₂, it is difficult to find the clubbed TiB₂ grains. Macro-pores and blowholes are absent in the local reinforcing region of the composites reinforced with 1:1 and 1:2 molar ratios of TiC/TiB₂, while a few macro-pores can be observed in the composite reinforced with 2:1 molar ratio of TiC/TiB₂. Moreover, the densities of the composites reinforced with 1:1 and 1:2 molar ratios of TiC/TiB₂ are higher than that of the composite reinforced with 2:1 molar ratio of TiC/TiB₂. The composite reinforced with 1:2 molar ratio of TiC/TiB₂ has the highest hardness and the best wear resistance. [All rights reserved Elsevier]

Reaction process of Al-TiO₂-C-Ti-Fe multiphase system during combustion synthesis

Songhe-Meng; Xinghong-Zhang; Weifang-Zhang(Center for Composite Mater., Harbin Inst. of Technol., China)

Key-Engineering-Materials. 2007; 336-338: 2340-3

The reaction process and kinetics of Al-TiO₂-C-Ti-Fe system were investigated by differential scanning calorimetry (DSC) analysis, X-ray diffraction (XRD) analysis and scanning electron microscope (SEM). In order to obtain the information of reaction process for complicated system, the reaction characteristics of Al-TiO₂, Al-TiO₂-C and Al-TiO₂-C-Ti systems are explored firstly. The results show that the reaction process varies with temperature in Al-TiO₂-C-Ti-Fe system. At the lower temperature, the dominating reaction in Al-TiO₂-C-Ti-Fe system is that between Al and Ti, Al and Fe, and so TiAl_x, FeAl_x, and Ti₂Fe intermetallic compounds form. With the temperature increasing, the intermetallic compounds are decomposed. Then the decomposed Ti and Al react with C and TiO₂ respectively and the stable TiC, Al₂O₃ and Fe three phases form in the final product

Microstructures and properties of Al₂O₃/ZrO₂ composite ceramics from in-situ growth in the melts produced by combustion synthesis

Zhongmin-Zhao; Long-Zhang; Hongbai-Bai; Jian-Zheng; Jiang-Wu(Inst. of Adv. Mater., Mech. Eng. Coll., Shijiazhuang, China)

Key-Engineering-Materials. 2007; 336-338: 2260-3

By introducing ZrO₂(3Y) micron powder into the thermit, Al₂O₃/18%, 21%, 24%, 27% and 30%ZrO₂ composite ceramics were obtained from in-situ growth in the melts produced by combustion synthesis. As the volume fraction of ZrO₂ is below 27%, the ceramics is comprised of lath-shaped and rod-shaped alpha-Al₂O₃ matrix, within the rod-shaped grain the nano-micron fibers are oriented in essentially the same direction. As volume fraction of ZrO₂ is over 27%, the ceramics is mainly composed of lamina-shaped grains with alternating a-Al₂O₃ and t-ZrO₂ layers. The flexural strength and the fracture toughness measured simultaneously the maximum values with increasing volume fraction of ZrO₂ to 24%, indicating that flexural strength and fracture toughness are simultaneously under the control of rod-shaped grains in which ZrO₂ nano-micron monocrystal fibers are embedded

Microstructures and multi-toughening of ZrO₂ nano-micron fibers self-toughening Al₂O₃ ceramics from in-situ growth in the melts produced by combustion synthesis

Long-Zhang; Zhongmin-Zhao; Jian-Zheng; Hongbai-Bai; Jiang-Wu(Inst. of Adv. Mater., Mech. Eng. Coll., Shijiazhuang, China)

Key-Engineering-Materials. 2007; 336-338: 2257-9

Al₂O₃/24%ZrO₂ composite, which is mainly composed of lath-shaped and rod-shaped alpha-Al₂O₃ matrix containing ZrO₂ nano-micron fibers, was obtained from in-situ growth in the melts produced by combustion synthesis. The results from XRD, SEM and EPMA showed that, besides the rod-shaped and lath-shaped alpha-Al₂O₃ grains, there are also t-ZrO₂ or m-ZrO₂ independent phases and Cr metallic particles at the boundaries of rod-shaped grains. The strength and toughness were measured to be 1186 MPa and 12.8 MPamiddotm^0.5 respectively. The procedure for toughening ceramics relies on coordinated action of multiple toughening mechanisms involving reinforcement-induced toughening by ZrO₂ nano-micron fibers, deflection-induced toughening, stress-induced transformation toughening, crack-bridging toughening by lath-shaped alpha-Al₂O₃ grains as well as deformation-induced toughening by Cr metallic particles, and promises the occurrence of a sharp rising R-curved behavior

Coloring mechanism of Pr-CeO₂ nano-crystalline red lanthanide pigments prepared by low-temperature combustion synthesis

Zhu-ZF; Zhou-Y; Wang-RL(Sch. of Mater. Sci. & Eng., Shaanxi Univ. of Sci. & Technol., Xianyang, China)

Key-Engineering-Materials. 2007; 336-338: 2068-70

Pr-CeO₂ nano-crystalline red lanthanide pigments were prepared from cerium (III) nitrate hexahydrate and praseodymium oxide by low-temperature combustion synthesis. Its ignited temperature was approximately 250 degC. The prepared pigments were characterized by DSC, XRD, SEM and XPS. The results showed that the crystallite size decreases with increasing Pr mol concentration. The valence of praseodymium in the pigments and its coloring mechanism were also investigated. The trivalent Pr entered into CeO₂ crystal lattice and formed Pr-CeO₂ solid solution, which was based on the fluorite structure. It substituted trivalent Pr for tetravalent Ce in CeO₂ crystal and was compensated by oxygen vacancies, which caused the distortion and the defection of the crystal lattice. Therefore the pigments can absorb the light with the wavelength of approximately 600 nm and present the red tonality

Local structure of nanocrystalline Lu₂O₃:Eu studied by X-ray absorption spectroscopy

Zeming-Qi; Miao-Liu; Yonghu-Chen; Guobin-Zhang; Mei-Xu; Chaoshu-Shi; Weiping-Zhang; Min-Yin; Yanin-Xie(Nat. Synchrotron Radiat. Lab., Univ. of Sci. & Technol. of China, Hefei, China)

Journal-of-Physical-Chemistry-C. 8 Feb. 2007; 111(5): 1945-50

Eu-doped nanocrystalline Lu₂O₃ with different particle sizes was prepared by combustion synthesis. The local structures around the rare-earth Lu and Eu ions were studied by using both Lu and Eu L₃ edge X-ray absorption spectroscopy. According to the extended X-ray absorption fine structure (EXAFS) analysis, detailed local structure information such as coordination numbers, bonding length, and disorder has been obtained. The results showed that the samples with a particle size larger than 5 nm keep the cubic structure and the disorder increases with decreasing size. However, when the particle size is smaller than 5 nm, the existence of considerable amorphous components accounts for the rough interface and the obvious change of the local structure around the rare-earth ions. A new type of coordination environment around Eu was formed, and the most probable symmetry of the Eu³⁺ site was determined by combining the real-space self-consistent field full multiple scattering X-ray absorption near edge structure (XANES) calculation and the EXAFS result. The local structure information obtained from EXAFS and XANES was used to explain the size-dependent luminescent properties of the nanocrystalline Lu₂O₃:Eu. The decreasing intensity ratio between the host absorption band and the Eu³⁺-O^2- charge-transfer state (CTS) band with decreasing particle size can be attributed to a larger disorder and more defects in the small sized samples, while the red shift of the CTS band in the smaller size particles can be ascribed to the longer Eu-O bond length and the higher coordination number

Disperse-strengthening by nanoparticles advanced tribological coatings and electrode materials for their deposition

Levashov-EA; Vakaev-PV; Zamulaeva-EI; Kudryashov-AE; Kurbatkina-VV; Shtansky-DV; Voevodin-AA; Sanz-A(Moscow State Inst. of Steel & Alloys, Russia)

Surface-and-Coatings-Technology. 26 March 2007; 201(13): 6176-81

Two types of electrode materials were developed using self-propagating high-temperature synthesis (SHS) and powder metallurgy: 1- composite with nanosized additives; 2- nanostructured cemented carbide WC-Co. Electrospark deposition (ESD) was applied to produce tribological coatings which were disperse-strengthened by incorporation of nanosized particles. Nanostructured electrodes of cemented carbides WC-8% Co provide increasing density, thickness, hardness, Young's modulus, and wear resistance of ESD-coatings. Positive effects of nanostructural state of the electrodes on the deposition process and structure/properties of the coatings are discussed. In that case the tungsten carbide phase becomes predominant in the coatings. A mechanism of the dissolution reaction of WC in Ni at the contact surface of the electrode was proposed. It was shown that formation of the coating structure is initiated on the electrode and accomplished on the substrate. [All rights reserved Elsevier]

Performance of Gd-Ba-Cu-O superconductor bulks with ultrafine Gd₂BaCuO₅ powders prepared by low-temperature combustion synthesis

Ma-XH; Su-XT; Yan-QZ; Jiao-YL; Xiao-L; Ge-CC(Lab. of Special Ceramics & Powder Metall., Sci. & Technol. Univ. Beijing, China)

Materials-Science-Forum. 2007; 546-549: 2111-14

This paper describes the details on synthesizing nanocrystalline Gd₂BaCuO₅ (Gd211) using low-temperature combustion synthesis(LCS). The morphology and structure of the powders are characterized by field emission scanning electron microscopy (FESEM) and XRD. The size of obtained powders by this method calcined at 800 degC is about 100nm, which is much smaller than the powders synthesizing by conventional solid state route. Besides, the Gd211 powders synthesizing by LCS have a low calcination temperature with a high-purity. The microstructure of melt-textured samples is also observed by FESEM, the result shows that the size of Gd211 particles trapped in GdBaCu₃O₇ (Gd123) matrix could be refined by using ultrafine Gd211 powder as a precursor. The refined Gd211 particles with a good distribution resulted in the improvement of Jc values in this system

Microstructures and toughening mechanisms of Y₂O₃ doped Al₂O₃/ZrO₂ eutectic composite ceramics prepared by SHS melt-growth process

Long-Zhang; Zhongmin-Zhao; Yigang-Song; Weiguo-Wang(Inst. of Adv. Mater., Mech. Eng. Coll., Shijiazhuang, China)

Materials-Science-Forum. 2007; 546-549: 1619-22

By introducing ZrO₂(4Y) powder of suitable content into the thermit and based on oxidation-reduction reaction of the thermit and liquid-liquid phase separation of ceramics/metal under gravity, Al₂O₃/ZrO₂ composite ceramics have been prepared through melt-growth with eutectic reaction under high degree of undercooling from SHS process. It has been found that the ceramics were composed of major rod-shaped sapphires with 8.0-12.0 aspect ratios and minor plate-like alpha-Al₂O₃ grains, and within the sapphires t-ZrO₂ nanomicron fibers were embedded. Flexural strength and fracture toughness were measured to be 1256 MPa and 13.2 MPamiddotm^frac12. It was obtained that a number of low energy interfaces (the interface distance on nanomicron scale) between two Al₂O₃/ZrO₂(4Y) phases and the strong compressive residual stress in the sapphires made the sapphires reinforced, forcing the crack to propagate along the rod-shaped sapphires; meanwhile, crack-bridging and pull-out of the sapphires, crack-bridging and frictionally interlocked effects of plate-like alpha-Al₂O₃ grains in the wake of crack tip also rendered the crack stabilization to arise

Fabrication of AlN-SiC-TiB₂ ceramics by self-propagating high temperature synthesis and hot isostatic pressing

Iijuan-Zhou; Yongting-Zheng; Shanyi-Du; Hongbo-Li(Center for Composite Mater., Harbin Inst. of Technol., China)

Materials-Science-Forum. 2007; 546-549: 1505-8

The fabrication of AlN-SiC-TiB₂ ceramics with powder mixtures of Al, 6H-SiC and TiB₂ was investigated by self-propagating high temperature synthesis (SHS) and hot isostatic pressing (HIP). The powder mixtures were shaped by isostatic cool pressing method and the combustion reaction was carried at the pressure of 100-200 MPa N₂ by an ignitor. The compositions and morphologies of the combustion product were studied by XRD and SEM. The determined bending strength and the fracture toughness of the ceramics were 350 MPa and 3.5 MPamiddotm^frac12 respectively

Modifying effect of Al-Ti-C-P master alloy on hypereutectic Al-Si alloy

Chunxiang-Xu; Liping-Liang; Binfeng-Lu; Yongjun-Xue; Jinshan-Zhang; Liang-Wei(Sch. of Mater. Sci. & Eng., Taiyuan Univ. of Technol., China)

Materials-Science-Forum. 2007; 546-549: 947-51

Al-Ti-C-P master alloy has been successfully fabricated by SHS-melting technology. Microstructures and phase constituent of Al-Ti-C-P master alloy were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and EDS. The results show that Al-Ti-C-P master alloy comprises TiAl₃, TiC, AlP and alpha-Al matrix. After adding 2.0 wt% Al-Ti-C-P master alloy, microstructure and mechanical properties (after T₆ treating) of ZL117 alloy has been improved dramatically: The average grain size of primary silicon decreases from 260 to 35 mum, edges and angles of primary silicon are passivated, the morphology of eutectic silicon changes from large needle-like one to fine rod-like or particle-like one, and the microstructures are noticeably refined. Room temperature tensile strength changes from 168 to 260 MPa while elevated temperature tensile strength (at 300degC) varies from 88 to 125 MPa. Impact toughness and macro-hardness(HB) increases to 17 J/cm² and 97 from the original 6.5 J/cm² and 92

Fabrication of metal/intermetallic compound laminate composites by thin foil hot press process

Kim-JK; Chung-Dong-Seok(Dept. of Nanosystem & Nanoprocess Eng., Pusan Nat. Univ., Miyrang, South Korea)

Diffusion-and-Defect-Data-Part-B-Solid-State-Phenomena. 2007; 124-126: 1099-102

Thin foil hot press process was used to fabricate metal/intermetallic compound laminate composites to induce self-propagating high-temperature (SHS) reaction between different pure metal sheets. In the present study, Ni/Ni-aluminide and Ti/Ti-aluminide laminate composites were fabricated through diffusion bonding, reaction synthesis and post-heat treatment of alternatively stacked pure Ni/Al and Ti/Al foils, respectively. Thick intermetallic layers of NiAl and TiAl₃ were formed by a self-propagating high-temperature synthesis (SHS) reaction, and thin continuous layers of Ni₃Al and TiAl were formed by a solid-state diffusion. Also, Ni/Ni-aluminide//Ti/Ti-aluminide laminate composite, considered as a functionally gradient material, was manufactured from stacked foils of pure Ni, Ti and Al in order of Ni/Al/Ni/.../Ni/Al /Ti/.../Ti/Al/Ti. Nb/Nb-aluminide laminate composite was manufactured with pure Nb and Al multilayered foils, consisting of fine Nb/Nb₃Al/Nb₂Al/NbAl₃ layer structure

Microwave-assisted combustion synthesis of alpha-alumina and magnesium aluminate spinel nanocomposite powders

Young-Mi-Jung; Sang-Woo-Kim(Nano-Mater. Res. Center, Korea Inst. of Sci. & Technol., Seoul, South Korea)

Diffusion-and-Defect-Data-Part-B-Solid-State-Phenomena. 2007; 119: 191-4

Microwave-assisted combustion synthesis of alpha-alumina-magnesium spinel nanocomposite powders from a route using ammonium aluminum carbonate hydroxide (AACH) as a precursor was studied. gamma- to alpha-phase transformation temperature of microwave-assisted alumina composite powders is lowered by 100degC compared to that of normal heat-treated alumina composite powders. The crystallite size of the microwave-assisted composite powders was considerably decreased from 42 nm to 29 nm compared to that of the normal heat treated composite powders. Nanosized alpha- alumina-magnesium aluminate composite powders were successfully synthesized by microwave-assisted combustion under nitrogen atmosphere at 1050degC

Synthesis and dilatometric study of Ca(Sr, La)TiO₃ prepared by solution combustion synthesis (SCS)

Choong-Hwan-Jung; Ji-Yeon-Park; Woo-Seog-Ryu(Nucl. Mater. Technol. Dev. Div., Korea Atomic Energy Res. Inst., Daejeon, South Korea)

Diffusion-and-Defect-Data-Part-B-Solid-State-Phenomena. 2007; 119: 107-10

La and Sr have recognized as elements of high level radioactive wastes immobilized by solid solution with CaTiO₃. For forming solid solution with CaTiO₃, the solution combustion synthesis (SCS) process was applied and the powder characteristics and sinterability were investigated. The proper selection of the type and the composition of fuels are important to get the crystalline of CaTiO₃. When glycine or the mixtures of urea+citric acid with stoichiometric composition was used, the solid solutions of Ca(La, Sr)TiO₃ were entirely produced. The combustion synthesized powder seemed to have a good sinterability with the linear shrinkage of more than 23% up to 1400degC, while that of the solid state reacted powder was less than 19% at the same conditions

Magnetic properties of Bi(Fe_1-xCr_x)O₃ synthesized by a combustion method

Li-J-B; Rao-GH; Liang-JK; Liu-YH; Luo-J; Chen-JR(Beijing Nat. Lab. for Condensed Matter Phys., Chinese Acad. of Sci., Beijing, China)

Applied-Physics-Letters. 16 April 2007; 90(16): 162513-1-3

Single-phase samples of Bi(Fe_1-xCr_x)O₃ with x=0, 0.1, and 0.2 were synthesized by a combustion method. X-ray diffraction reveals that the lattice parameters of Bi(Fe_1-xCr_x)O₃ perovskites decrease linearly with the Cr content, indicating that Cr ions substitute for Fe ions to form a solid solution. X-ray photoelectron spectroscopy investigation shows that Cr ions have the Cr³⁺ valence state in Bi(Fe_1-xCr_x)O₃. The frequency dependence of dielectric constants was investigated at room temperature. Magnetic measurements show hysteresis loops at both 5 and 300 K and the substitution of Cr for Fe enhances the magnetization

Morphology control and VUV photoluminescence characteristics of BaMgAl₁₀O₁₇:Eu²⁺ phosphors

Youwei-Yan; Zhe-Chen(State Key Lab of Die & Mould Technol., Huazhong Univ. of Sci. & Technol., Wuhan, China)

Physica-B. 15 April 2007; 392(1-2): 1-6

BaMgAl₁₀O₁₇:Eu²⁺ (BAM) phosphors for plasma display panel application were successfully prepared by a novel solution combustion synthesis method. Morphology control of BAM phosphor particles in the process was attempted by using polyethylene glycol (PEG) as additive. The crystallinity, particle size, morphology and luminescent properties were characterized by XRD, FE-SEM and vacuum ultraviolet (VUV) irradiation derived synchrotron radiation, respectively. It was found that BAM phosphors resulted from PEG additive have nearly spherical morphology, narrow size distribution and strong blue emission under VUV light excitation compared to those without PEG additive. [All rights reserved Elsevier]

Reaction mechanism in self-propagating high temperature synthesis of TiC-TiB₂/Al composites from an Al-Ti-B₄C system

Qichuan-Jiang; Ping-Shen; Binglin-Zou; Shenbao-Jin(Dept. of Mater. Sci. & Eng., Jilin Univ., Changchun, China)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 25 April 2007; 454-455: 300-9

The reaction sequence and phase formation mechanism in self-propagating high temperature synthesis (SHS) processing of the Al-Ti-B₄C compacts were explored through a delicate microstructure and phase analysis on the combustion-wave quenched samples in combination with differential thermal analysis. The reaction sequence could be described as Al+Ti+B₄CrarrTiAl₃+Ti+B₄CrarrTiAl_n+B₄CrarrTiAl_n+B₁₃C₂+TiC_x+Ti$ daAl_bC_crarrTiAl_n+TiC_x+TiB₂+Ti_aAl_bC_crarrAl+TiC_x+TiB₂. The phase formation mechanism could be ascribed to the displacive reaction between B₄C and the Ti-Al melt and is essentially dependent on the dissociation and diffusion rates of carbon and boron from the B₄C crystal. The reasons for the prior formation of TiC_x over TiB₂ and the separated residence of the TiC_x and TiB₂ grains in the microstructure were addressed. [All rights reserved Elsevier]

Sintering behaviour of ultra-fine titanium diboride powder prepared by self-propagating high-temperature synthesis (SHS) technique

Khanra-AK; Godkhindi-MM; Pathak-LC(Dept. of Metall. & Mater. Eng., Indian Inst. of Technol., Kharagpur, India)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 25 April 2007; 454-455: 281-7

A systematic study on the sintering behaviour of titanium diboride (TiB₂) powder of different particle sizes prepared by a SHS route is carried out in the temperature range of 1973-2173K. The decrease of particle size increases the densification of the TiB₂ powder compacts and a maximum densification of 93% of the theoretical density is achieved after sintering at 2173K. The activation energies for sintering are observed to vary within ~76 to 85kJ/mol for the different particle sizes that indicate the boron diffusion in Ti as the possible rate-controlling process for sintering. The time dependent variation of densification under isothermal condition indicates the surface diffusion or vapour phase condensation mechanisms operative in the system. The microstructure and microhardness of different sintered samples reflect the densification behaviour of sintered pellets. [All rights reserved Elsevier]

Effect of different fuels on the strontium hexaferrite nanopowder synthesized by a surfactant-assisted sol-gel auto-combustion method

Ebrahimi-SAS; Ghobeiti-Hasab-M; Badiei-A(Center of Excellence in Magnetic Mater., Univ. of Tehran, Sch. Of Metall. And Mater. Eng., Iran)

Journal-of-Non-Crystalline-Solids. 15 April 2007; 353(8-10): 814-16

In this research a sol-gel auto-combustion route has been proposed to synthesize strontium hexaferrite nanopowder, using metal nitrates, ammonia as pH adjusting agent, n-decyltrimethylammonium bromide as a cationic surfactant and different fuels such as citric acid, glycine, acetylacetone and oxalic acid. The formation temperature of strontium hexaferrite and its crystallite size in presence of different fuels were compared together. The results showed the lowest formation temperature as well as the smallest crystallite size in the presence of citric acid as 900degC and 37.3nm respectively. [All rights reserved Elsevier]

Combustion synthesis, powder characteristics, and shrinkage of a gadolinia-ceria system

Lenka-RK; Mahata-T; Sinha-PK; Sharma-BP(Energy Conversion Mater. Sect., Bhabha Atomic Res. Centre, Mumbai, India)

Journal-of-the-American-Ceramic-Society. Dec. 2006; 89(12): 3871-3

Pure and gadolinia-doped nanocrystalline ceria powders were prepared through the gel combustion route. Analysis of crystallite size, surface area, and particle size indicates that the powders are agglomerates of nanosize primary particles. The degree of agglomeration increases with increase in the gadolinia content. The shrinkage behavior on firing of the powders was studied using a dilatometer. Although the shrinkage starts at a lower temperature, the densification completes at a higher temperature as the gadolinia content increases. The wider temperature range required for shrinkage in high gadolinia content ceria is attributed to the wider distribution of interparticle pore size in the green compact

Gas-phase and heat-exchange effects on the ignition of high- and low-exothermicity porous solids subject to constant heating

Shah-AA; Brindley-J; Mclntosh-AC; Griffiths-J(Dept. of Appl. Math., Leeds Univ., UK)

Journal-of-Engineering-Mathematics. Oct. 2006; 56(2): 161-77

This article investigates the ignition of low-exothermicity reactive porous solids exposed to a maintained source of heat (hotspot), without oxygen limitation. The gas flow within the solid, particularly in response to pressure gradients (Darcy's law), is accounted for. Numerical experiments related to the ignition of low-exothermicity porous materials are presented. Gas and solid products of reaction are included. The first stage of the paper examines the (pseudo-homogeneous) assumption of a single temperature for both phases, amounting to an infinite rate of heat exchange between the two. Isolating the effect of gas production and flow in this manner, the effect of each on the ignition time is studied. In such cases, ignition is conveniently defined by the birth of a self-sustained combustion wave. It is found that gas production decreases the ignition time, compared to equivalent systems in which the gas-dynamic problem is effectively neglected. The reason for this is quite simple; the smaller heat capacity of the gas allows the overall temperature to attain a higher value in a similar time, and so speeds up the ignition process. Next, numerical results using a two-temperature (heterogeneous) model, allowing for local heat exchange between the phases, are presented. The pseudo-homogeneous results are recovered in the limit of infinite heat exchange. For a finite value of heat exchange, the ignition time is lower when compared to the single-temperature limit, decreasing as the rate of heat exchange decreases. However, the decrease is only mild, of the order of a few percent, indicating that the pseudo-homogeneous model is in fact a rather good approximation, at least for a constant heat-exchange rate. The relationships between the ignition time and a number of physico-chemical parameters of the system are also investigated

Effect of nickel addition on the exothermic reaction of titanium and boron carbide

Yang-YF; Wang-HY; Liang-YH; Zhacx-RY; Jiang-QC(Dept. of Mater. Sci. & Eng., Jilin Univ., Changchun, China)

Journal-of-Materials-Research. Jan. 2007; 22(1): 169-74

Exothermic reaction path of the Ni-Ti-B₄C system in the differential thermal analysis apparatus proceeded in such a way that Ni initially reacted with B₄C and Ti to form Ni-B compounds and Ti₂Ni with heat release, respectively; subsequently, the formation of Ni-B eutectic liquid between Ni₂B and Ni₄B₃, and the appearance of Ni-Ti eutectic liquid phase between Ti₂Ni and Ti were followed, which enabled the diffusion of Ni, B, C, and Ti in solution to form Ni-Ti-B-C liquid more easily and quickly at a low temperature; finally, TiC and TiB₂ were precipitated out of the liquid. The addition of Ni provided an easier route for reactant mass transfer and accelerated the occurrence of complete reaction

A novel combustion route for the preparation of perovskite-type oxygen permeable materials

Wang-R; Liu-M; Li-DF; Liang-DT(Innovation Center, Nanyang Technol. Univ., Singapore, Singapore)

Materials-Chemistry-and-Physics. 15 April 2007; 102(2-3): 132-9

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-delta perovskite-type oxygen permeable materials were prepared by a novel complexation/combustion (CC) method, where oxygen/air was introduced externally to assist combustion instead of adding an extra oxidant into a precursor solution. This method offers the advantages of facilitating the crystallization of perovskite phase and easy sample treatment. Compared with various self-propagating combustion systems, such as glycerol/nitrates (GlN), glycine nitrates (GN) and EDTA/citrate nitrates (ECN) routes, the CC method yields perovskite products with minimum phase contamination and the highest crystallinity. Additionally, the oxygen permeation tests and SEM studies revealed that the disc-shape membrane made from the CC powder exhibit less structure defects and higher oxygen permeation flux. The complexation/combustion method developed here is an attractive technique for synthesizing perovskite-type oxygen permeable materials. [All rights reserved Elsevier]

Influence of Ba/Mg ratio on crystal structure and luminescent characteristics of Eu²⁺-doped (Ba_xMg)₂(x+1)/Al₁₀O₁₇ blue-emitting phosphors

Chen-Zhe; Xie-Hong; Yan-Youwei(State Key Lab. of Die & Mould Technol., Huazhong Univ. of Sci. & Technol., Wuhan, China)

Acta-Optica-Sinica. Jan. 2007; 27(1): 111-15

The (Ba_xMg)₂(x+1)/ Al₁₀O₁₇:Eu²⁺ (0.6lesrles1.2) (BAM) phosphors with different Ba/Mg ratio were successfully prepared by solution combustion method at 600degC. The influence of Ba/Mg ratio on the crystal structure and luminescent properties of the obtained samples were mainly investigated. The results show that the samples are of single phase, and the lattice parameters increase with the Ba/Mg ratio. Moreover, the intensity of the fluorescence of the resulting phosphors increases obviously with the Ba/Mg ratio, and the maximum emission intensity is reached at Ba/Mg=0.9. However, as Ba/Mg ratio was higher than 0.9, the intensity of the fluorescence is reduced reversely. Furthermore, with the decrease of the Ba/Mg ratio, the emission peak of the phosphors shifts to the longer wavelength due to the crystal field enhancement and electron cloud expansion. Moreover the luminescent property of BAM phosphor is considerably influenced by Eu²⁺ concentration. In an appropriate Eu²⁺ doping concentration range, the intensity of the fluorescence of BAM increase obviously with Eu²⁺ doping concentration and reaches a maximum, owing to more luminescent centers and faster energy transfer between Eu²⁺ ions. However, as the Eu²⁺ doping concentration is higher than a critical value, the intensity of the fluorescence is reduced reversely, due to the concentration quenching as the energy transfer rate between Eu²⁺ ions exceeds the emission rate

Hafnium reactivity below 1500degC in search of better processing of HfB₂/SiC UHTC composites

Blum-YD; Young-S; Hui-D; Alvarez-E(SRI Int., Menlo Park, CA, USA)

Mechanical-Properties-and-Performance-of-Engineering-Ceramics-and-Composites-II.-A-Collection-of-Papers-Presented-at-the-30th-International-Conference-on-Advanced-Ceramics-and-Composites. 2006: 617-28

Ultra-high-temperature ceramics (UHTC) have regained significant interest as materials of choice for aerospace and energy applications. UHTCs are based on composites consisting of borides, carbides and nitrides of hafnium and zirconium combined with a silicon carbide phase. The current hot-press processing of UHTCs is a major obstacle in incorporating such composites into component designs and ultra-high-temperature protective coatings. This article further explores exothermic chemical reactions and behavior of Hf metal that may lead to processes that are performed under pressureless conditions or below 1500degC. Such reactions have rarely been studied outside the context of self-propagating high-temperature synthesis (SHS). This article reports a local micro-melting phenomenon at the surface of Hf strips after interacting with powders containing B and/or C powders. The melting is observed at temperatures more than 1000degC below the actual melting point of Hf (2227degC), due to confined energy release derived from the very exothermic reactions intriguing displacement reactions between the Hf surface and boron-containing compounds (B₄C and BN) are also reported, which demonstrate the powerful reactivity of the metal even in the presence of minimal contact area between the reactants. The presence of distinct large crystallites after the reactions with the boron compounds means long-range diffusivities of the elements in the molten and solid phases of the Hf

SHS hydrogenation and following dehydrogenation of titanium sponge

Ratnikov-VI; Borovinskaya-IP; Prokudina-VK(Inst. of Struct. Macrokinetics & Mater. Sci., Russian Acad. of Sci., Moscow, Russia)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(2): 193-202

In this work, some conditions for SHS-hydrogenation of titanium sponge were considered. This process allows one to obtain titanium hydride with high contents of hydrogen at the pilot-industrial scale. Design features of a special (non-standard) reactor patented in Russia for safe SHS-hydrogenation were given. The modes for disintegration of hydrogenated sponges and operation procedures for an installation for dehydrogenation of disintegrated sponge were considered. Chemical composition and size distribution of SHS titanium hydride and titanium powder produced by its dehydrogenation were presented

Combustion synthesis of ultra fine BN/AlN and BN/B₄C composite powders: role of gasifying compounds

Hobosyan-MA; Khachatryan-HL; Kharatyan-SL; Puszynski-JA(Dept. of Chem. Phys., Yeravan State Univ., Armenia)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(2): 181-91

Aluminum diboride was chosen as an initial reagent to obtain BN/AlN composites with high homogeneity. By comparing the specific surface area of products, it was established that this parameter can be increased (up to 10-24 m²/g) by increasing the amount of boron nitride. The gasifying compounds have essential influence on the formation of submicron particles in products. Even at their negligible amounts the specific surface area can increase by a factor of 2, and at higher amounts (close to the combustion limit) by 4 times. The maximum value for specific surface area (86 m²/g) was obtained for the 80%BN+20%AlN composite. It was established that it is impossible to obtain BN-B₄C composite by direct interaction between elements (B, C and N₂). Therefore another way was developed aimed at synthesizing BN-B₄C composite under the activated combustion mode. Organic nitrogen containing compounds (ONCC) were used as sources for both the carbon and nitrogen

Metastability route to obtain nanocomposites by SHS

Vallauri-D; Atias-Adrian-IC; Deorsola-FA; Amato-I; DeBenedetti-B(Dept. of Mater. Sci. & Chem. Eng., Politecnico di Torino, Turin, Italy)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(2): 169-79

The trend in today's industry toward improving the performance and durability of components stimulates the design and development of advanced materials. In this context, the fabrication of nanostructured materials by competing technologies like SHS represents an attractive possibility. The processing based on metastable transformations represents an attractive route for this aim. Nanostructured powders of the TiC_1-x-TiB₂ system are obtained through combustion processes based on the concept of metastability. The process is based on the rapid cooling by quench of the SHS products immediately after the reaction, yielding inherently nanostructured powder agglomerates. The degree of metastability of the composite powders is evaluated by thermal treatments

Role of the additive components in self-propagating high-temperature synthesis of silicon nitride

Pradeilles-N; Record-MC; Marin-Ayral-RM(Lab. de Physico-chimie de la Matiere Condensee, Univ. Montpellier II, France)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(2): 157-67

Silicon nitride (Si₃N₄), was prepared by SHS under high nitrogen gas with different additives. The aim of this work was to understand the role of the additives components on the SHS reaction. The influence of two experimental parameters (composition of the reactant mixture and nitrogen pressure) was studied. The SHS sample were characterized by using X-ray diffraction and SEM analysis. Rietveld refinement was performed on recorded diffractograms in order to determine the composition of the SHS products. From our results, a mechanism of formation for Si₃N₄ was suggested and the role of additives was shown. This study also allows us to explain ambiguous results previously reported in the literature

Combustion of gasless systems with a variable porosity and an external gas exchange

Prokofiev-VG; Smolyakov-VK(Tomsk Sci. Center, Siberian Branch of the Russian Acad. of Sci., Tomsk, Russia)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(2): 133-55

The investigation of stationary and self-oscillatory combustion regimes in gasless systems with an external gas exchange is based on a two-temperature and two-velocity model of gasless combustion accounting for structural transformations caused by an in-pore forced gas infiltration, liquid-phase sintering, and bulk alteration of the condensed phase during chemical conversions. It has been shown that structural transformations exert a strong effect on the character and regularities of the combustion front propagation. The main structural parameters affecting the synthesis wave structure, velocity, and stability are the initial sample porosity, diameter, and the particle size. The results of numerical calculations are compared to the available experimental data

A new mechanism for formation of spatial oscillations in SHS of Ni/Al bilayer foils

Washington-EBK; Aurongze-D; Berg-JM; Osbourne-D; Holtz-M; Pantoya-M; Temkin-H(Dept. of Mech. Eng., Texas Tech. Univ., Lubbock, TX, USA)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(2): 121-32

We investigate the self-propagating high-temperature synthesis of Ni/Al foils, in order to gain insight into the mechanisms of combustion and product formation, and to better understand how these products might be used. The study is motivated by the observation of fine spatial oscillations in combusted freestanding foils. Previous researchers have recounted oscillations in the reacted foil parallel to the flame front velocity vector, which they attributed to periodic variation in the flame front velocity. In contrast we report fine-scale spatial oscillations normal to the flame front velocity vector. The reacted foils were further characterized by magnetic force microscopy, atomic force microscopy, and X-ray diffraction. The results are consistent with directional solidification as the mechanism for the formation of these spatial oscillations. Understanding of this mechanism has immediate consequences for modeling the combustion and solidification process, and for utilizing the combustion products

A simulation approach to the combustion synthesis of silicides

Gennari-S; Maglia-F; Anselmi-Tamburini-U; Spinolo-G(Dept. of Phys. Chem., Univ. of Pavia, Italy)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(2): 105-20

The work describes the application of a computer simulation approach developed by the authors to the study of the SHS of some disilicides MeSi₂ (Me=Mo, Nb, Ta, Ti). The method is specifically oriented towards the study of the reaction mechanism and of the heterogeneous aspects of the SHS process and takes into account solid/liquid phase transitions, diffusion-controlled dissolution of the high melting metal and nucleation/precipitation of the compound. When combined with experimental measurements, the computer approach is able to outline the effect of the various process variables, to obtain a microscopical insight of the reaction mechanism and to determine the onset of different dynamic behaviors. The reported results are compared with experimental literature data with particular attention to the effect of starting reactant grain size and of the effective thermal conductivity of the powder mixture

Synthesis of barium hexaferrite nano-particles via mechano-combustion route

Ataie-A; Zojaji-SE(Sch. of Metall. & Mater. Eng., Univ. of Tehran, Iran)

Journal-of-Alloys-and-Compounds. 4 April 2007; 431(1-2): 331-6

Nano-size particles of barium hexaferrite have been synthesized by what is termed mechano-combustion after milling of intermediate products obtained in the sol-gel combustion process using nitrate-citrate gels prepared from metal nitrates and citric acid. The effects of precursor milling conditions on the phase evolution, crystallite size and annealing behavior of the products were investigated using XRD technique. The XRD results indicate the presence of gamma-Fe₂O₃ as a major phase and BaCO₃ as a minor phase in as-burnt powder. Analysis of the XRD patterns also confirms the transformation of gammato alpha-Fe₂O₃ via mechanical milling; the rate of this transformation is strongly affected by milling conditions. Barium hexaferrite starts to form at 700degC and fully formed at 1000degC for milled sample under the optimum milling conditions. XRD and DTA/TGA results showed that an intermediate precursor milling accelerates the formation of magnetic phase. SEM micrograph of the sample milled for 120h and then annealed at 1000degC exhibited nano-size particles of BaFe₁₂O₁₉ with mean particle size of around 100nm. [All rights reserved Elsevier]

Preparation, characterization and luminescence of nanocrystalline Y₂O₃:Ho

Biljan-T; Gajovic-A; Meic-Z; Mestrovic-E(Dept. of Chem., Univ. of Zagreb, Croatia)

Journal-of-Alloys-and-Compounds. 4 April 2007; 431(1-2): 217-20

Nanocrystalline Y₂O₃:Ho was synthesized by solution combustion method with ethylene glycol as fuel. Material was characterized using powder X-ray diffraction and transmission electron microscopy (TEM). X-ray diffraction and TEM showed that the material is nanostructured. Luminescence properties were studied using Raman spectrometers with excitation in near infrared (NIR) and visible regions. The visible and NIR luminescence spectra of nanocrystalline Y₂O₃:Ho show some important differences from those of bulk material. The convenience of using Raman instruments for studying luminescence of lanthanide ions is demonstrated. [All rights reserved Elsevier]

Preparation, electronic structure and photocatalytic activity of the In₂TiO₅ photocatalyst

Fu-Qiang-Huang; Wen-Deng-Wang; Cun-Ming-Liu; Xin-Ping-Lin; Jian-Lin-Shi(State Key Lab. of High Performance Ceramics & Superfine Microstructure, Chinese Acad. of Sci., Shanghai, China)

Materials-Science-and-Engineering-B-Solid-State-Materials-for-Advanced-Technology. 25 April 2007; 139(1): 74-80

Indium titanate In₂TiO₅ powder was prepared by a low-temperature combustion synthesis method and characterized by X-ray powder diffraction, UV-vis diffuse reflectance spectrum and field-emission scanning electron microscope. The only ternary In/Ti/O compound In₂TiO₅, composed of the octahedral [TiO₆] and [InO₆] motifs, was selected to be a photocatalyst containing both early-transition metal (d⁰) and p-block metal (d¹⁰). The absorption spectrum indicates that In₂TiO₅ has an optical gap of 3.02eV. The photocatalytic property of the sample was evaluated by using the photodegradation of methyl orange (MO). The photocatalytic activity of In₂TiO₅ for the complete degradation of MO was higher than that of TiO₂ (P25). Band calculations reveal that the high photocatalytic activity is tightly related to the electronic structure and the open crystal structure of In₂TiO₅. [All rights reserved Elsevier]

Fine powders of SrFe₁₂O₁₉ with SrTiO₃ additive prepared via a quasi-dry combustion synthesis route

Chyi-Ching-Hwang; Cheng-Shiung-Lin; Ting-Han-Huang; Gaw-Pying-Wang; Cheng-Hsiung-Peng(Dept. of Appl. Chem. & Mater. Sci., Chung Cheng Inst. of Technol., Taoyuan, Taiwan)

Materials-Science-and-Engineering-B-Solid-State-Materials-for-Advanced-Technology. 25 April 2007; 139(1): 24-36

This study presents a successful preparation of fine powders of strontium ferrite, SrFe₁₂O₁₉, with different contents of SrTiO₃ additive (i.e., SrFe₁₂O₁₉+xSrTiO₃, x=0.00, 0.05, 0.10, 0.15 and 0.20) through a quasi-dry combustion synthesis route using Sr(NO₃)₂, Fe(NO₃)middot9H₂O, glycine (NH₂CH₂COOH), and Ti powder as reactants. The synthesis route included mixing and dehydration procedures to produce a flammable, homogenous dried reactant mixture with its subsequent combustion at room temperature to form a voluminous loose product. The as-synthesized powder was calcined at various temperatures to study the effects of temperature on phase development and products' properties. Characterizations of the products were evaluated based on the X-ray diffraction, morphology observations, and magnetic properties studied using various instrumental analyses. Nearly Pure, single magnetic domain SrFe₁₂O₁₉ powder with crystalline size ranging from 55 to 75nm was produced when x=0.00 at 1050degC. It had a maximum intrinsic coercivity (iH_c) of 4.92kOe, a magnetization value (M_max) of 60.13emu/g, and a remanence magnetization (M_r) of 34.75emu/g. Calcination at 1200degC was found to increase the M_max to 64.52emu/g but to decrease the iH_c. Experimental results suggested a possible mechanism for the formation of SrFe₁₂O₁₉. The as-synthesized powders and the calcined ones with different x values were introduced into thermal polyurethane (TPU) matrix to prepare a composite. The relative complex permittivity (epsiv_r=epsiv'-jepsiv") and permeability (mu_r=mu'-jmu") of the composite specimens were measured within a frequency range of 1-12GHz using a network analyzer. Adding SrTiO₃ to SrFe₁₂O₁₉ was demonstrated not only to improve the epsiv_r but also to modify the mu_r. This similar effect was observed when adjusting the calcination temperature. [All rights reserved Elsevier]

Evaluation of NiFe₂O₄ ferrite nanocrystalline powder synthesized by a sol-gel auto-combustion method

Ebrahimi-SAS; Azadmanjiri-J(Center of Excellence in Magnetic Mater., Univ. of Tehran, Iran)

Journal-of-Non-Crystalline-Solids. 15 April 2007; 353(8-10): 802-4

Nanocrystalline NiFe₂O₄ ferrite powder was prepared by a sol-gel auto-combustion method from metal nitrates and citric acid. The combustion process is an oxidation-reduction reaction in which the NO₃^- ion is oxidant and the carboxyl group is reductant. The thermal analysis of nitrate-citrate gels and the phase evolution of as-burnt powder with the different ratios of Fe/Ni and calcined powder were investigated by DTA/TG and XRD techniques respectively. SEM and Hysteresigraph were also used to characterize the microstructure and magnetic properties of the products. The results revealed that the nitrate-citrate gel exhibits a self-propagating combustion behavior. By using this novel auto-combustion method, NiFe₂O₄ ferrite powder was obtained with crystallite size of 20-40nm and suitable soft magnetic properties. [All rights reserved Elsevier]

Surface peculiarities of detonation nanodiamonds in dependence of fabrication and purification methods

Mitev-D; Dimitrova-R; Spassova-M; Minchev-Ch; Stavrev-S(Space Res. Inst., Bulgarian Acad. of Sci., Bulgaria)

Diamond-and-Related-Materials. April-July 2007; 16(4-7): 776-80

A variety of post-treatments, such as thermal annealing and liquid phase oxidation, were used to determine the surface properties of six blasting synthesized nanodiamond powders, produced by various purification conditions. Methods of FTIR-spectroscopy, oxidative titration and pH-measurement were applied for comparing the surface functional groups. All spectra exhibited the characteristic IR-bands of detonation diamond in the regions 3400-2700 cm^-1 and 1000-400 cm^-1. The differences were revealed by the dissimilarity of the bands in the region 2000-1000 cm^-1. The nanodiamond powder annealing up to 600 degC in air most fully revealed the specificity of the attached groups on diamond surface. The chemical oxidation with H₂O₂ modified nanodiamond surface groups and prevented them from further oxidative attack during thermal treatment. [All rights reserved Elsevier]

Microstructure and magnetic properties of Ni_1-xZn_xFe₂O₄ synthesized by combustion reaction

Costa-ACFM; Morelli-MR; Kiminami-RHGA(Dept. of Mater. Eng., Fed. Univ. of Paraiba, Campina Grande, Brazil)

Journal-of-Materials-Science. Feb. 2007; 42(3): 779-83

An investigation was made of samples having a chemical formula of Ni_1-xZn_x-Fe₂O₄, where x = 0.3, 0.5 and 0.7. The samples were prepared by the reaction combustion synthesis method and sintered at 1200degC/2 h in a static air atmosphere. The influence of the Zn concentration on the relative density, microstructure and magnetic properties of the samples was studied. X-ray diffraction, scanning electron microscopy and magnetic hysteresis loop tracer were used to analyze the compositions. The samples were found to have a spinel cubic structure, sintered density of 92.9%-98.8% of the corresponding X-ray density, homogeneous microstructure with grain size ranging from 1.37 to 3.36 mum, maximum flux density of 0.160.35 T, field coercivity ranging from 17 to 168 A/m, and loss hysteresis of 1.5-105 W/kg. Increased grain growth, with fine pores inside the grains, was found to occur as the Zn concentration increased. The overall findings are discussed here in light of the existing understanding of these systems

Spark plasma sintering of ZrB₂-ZrC powder mixtures synthesized by MA-SHS in air

Tsuchida-T; Yamamoto-S(Div. of Mater. Sci. & Eng., Hokkaido Univ., Sapporo, Japan)

Journal-of-Materials-Science. Feb. 2007; 42(3): 772-8

Mechanical activation-assisted self-propagating high-temperature synthesis (MA-SHS) in air was successfully applied to the synthesis of the powder mixtures of ZrB₂ and ZrC as a precursor of the ZrB₂ZrC composite. When the powder mixtures of Zr/B/ C = 4/2/3-6/10/1 in molar ratio were mechanically activated (MA) by ball milling for 45-60 min and then exposed to air, they self-ignited spontaneously and the self-propagating high-temperature synthesis (SHS) was occurred to form ZrB₂ and ZrC. The ZrB2-ZrC composites were produced from these MA-SHS powders by spark plasma sintering (SPS) at 1800degC for 5-10 min and showed the fine and homogeneous microstructure composed of the <5 mum-sized grains. The mechanical properties of the composites evaluated by Vickers indentation method showed the values of Vickers hardness of 13.6-17.8 GPa and fracture toughness of 2.9-5.1 MPamiddotm¹2/, depending on the molar ratio of ZrB₂/ZrC. Thus, the better microstructure and mechanical properties of the ZrB2-ZrC composites were obtained from the MA-SHS powder mixtures, compared with those obtained from the MA powder, the mixing powder and the commercial powder mixtures

A numerical study of the effect of heterogeneities in composition on micropyretic synthesis

Li-HP(Jin-Wen Univ. of Sci. & Technol., Taipei, Taiwan)

Journal-of-Materials-Science. Feb. 2007; 42(4): 1177-83

Micropyretic synthesis is a technique whereby a material is synthesized by the propagation of a combustion front across a powder. Composition variations in reactants and diluent are common during micropyretic synthesis when powders are mixed and the conventional modeling treatments thus far have only considered uniform systems. Composition variations arc thought to result in the local variations of such thermophysical/chemical parameters for the reactant as density, heat capacity, and thermal conductivity; the result is changes in the combustion temperature, propagation velocity, and propagation pattern of a combustion front. This study investigates the impact of composition variations during micropyretic synthesis with Ni + Al. Correlations of variations in the reactants and diluent with the propagation velocity and combustion temperature are both studied by a numerical simulation

Rapid gold ion recovery from wastewater by photocatalytic ZnO nanopowders

Sung-Park; Kang-Yoo; Hye-Jung-Park; Jae-Chun-Lee; Ju-Hyeon-Lee(Dept. of Mater. Sci. & Eng., Myongji Univ., Kyunggi-do, South Korea)

Journal-of-Electroceramics. Dec. 2006; 17(2-4): 831-4

In this study, ZnO nanopowder was synthesized by solution-combustion method (SCM). The photocatalytic gold recovery efficiency by this SCM ZnO nanopowder was about 6 fold higher compared to the case by the state of the art commercial TiO₂ nanopowder. The purity of recovered gold was about 99.6% in weight% and 98.8% in atomic%. Furthermore, the ZnO nanopowder synthesis method and gold recovery process are very cost-effective. Especially, in this study it was tried to recover gold metal ions from not simulated wastewater but real plating wastewater. This technology is therefore very viable to obtain high purity gold from plating wastewater

Influence of nanocrystalline Ni-Ti reaction agent on self-propagating high-temperature synthesized porous NiTi

Lim-CS; Goh-CW; Gu-YW; Tay-BY(Biomed. Eng. Res. Center, Nanyang Technol. Univ., Singapore, Singapore)

Intermetallics-. April 2007; 15(4): 461-7

Nanocrystalline Ni-Ti was used in self-propagating high-temperature synthesis (SHS) to fabricate porous NiTi. The SHS of porous NiTi using elemental powders was also prepared for comparison. Results showed that the main phase was NiTi with unreacted Ni when using elemental powders, which is detrimental to medical use. A large amount of Ti₂Ni secondary phase was also detected. By employing mechanically alloyed nanocrystalline Ni-Ti as a reaction agent, the secondary intermetallic phase (i.e. Ti₂Ni) was significantly reduced and the unreacted Ni was eliminated. The addition of 25wt% nanocrystalline Ni-Ti reaction agent produced porous NiTi with an average porosity of 52-55vol% and a general pore size of 100-600mum under preheating temperatures of 200 and 300degC. This general pore size in the range of 100-600mum is beneficial to biomedical application for osseointegration. By further increase of the reaction agent to 50wt% in the reactant, a porous NiTi part was produced at ambient temperature (i.e. no preheating was necessary) and a dense part was formed at preheated temperature of 200degC due to the large amount of energies in the nanocrystalline reaction agent. This revealed that the use of nanocrystalline reaction agent effectively lowered the activation barriers for combustion synthesis reaction. [All rights reserved Elsevier]

Properties and microstructure of B-N-Al-Ti composite ceramics produced by self-propagating high-temperature synthesis

Kobyakov-VP; Bunin-VA; Borovinskaya-LP(Inst. of Struct. Macrokinetics & Mater. Sci., Russian Acad. of Sci., Moscow Oblast, Russia)

Inorganic-Materials. Dec. 2006; 42(12): 1397-403; Original: Neorganicheskie-Materialy. Dec. 2006; 42(12): 1525-32

Nitride-boride composite ceramics differing in BN, AlN, and TiB₂ contents have been prepared by self-propagating high-temperature synthesis in filtration combustion mode (high nitrogen pressure), and their physical properties have been studied by a variety of techniques. The influence of starting-mixture composition and preparation conditions on the properties of the ceramics has been analyzed

Properties of barium hexaferrite prepared by electric field assisted self-propagating high-temperature synthesis

Busurin-SM; Morozov-YuG; Kuznetsov-MV; Chernega-ML; Chobko-AA(Inst. of Struct. Macrokinetics & Mater. Sci., Russian Acad. of Sci., Moscow Oblast, Russia)

Inorganic-Materials. Dec. 2006; 42(12): 1374-8; Original: Neorganicheskie-Materialy. Dec. 2006; 42(12): 1503-7

We have prepared ferromagnetic barium hexaferrite powders by self-propagating high-temperature synthesis (SHS) in an electric field applied by a contactless method. Our results indicate that the field strength has a significant effect on the phase composition of the synthesis product. This effect is interpreted in terms of the decomposition kinetics of the solid oxidant and reactant diffusion. Microstructural examination demonstrates that an electric field has a marked effect on the morphology of SHS materials. The magnetic properties of the synthesized powders depend significantly on both the strength and direction of the applied field

Ferrite with extraordinary electric and dielectric properties prepared from self-combustion technique

Qian-Chen; Piyi-Du; Wenyan-Huang; Lu-Jin; Wenjian-Weng; Gaorong-Han(Dept. of Mater. Sci. & Eng., Zhejiang Univ., Hangzhou, China)

Applied-Physics-Letters. 26 March 2007; 90(13): 132907-1-3

Nickel-zinc ferrites (Ni_0.5Zn_0.5Fe₂O₄) with extraordinary electric and dielectric properties were prepared by self-combustion technique. The resistivity of ferrite in the ferric citrate system is on the order of 10¹⁰ Omega cm, which is about four orders higher than that of ferrite in the ferric nitrate system as well as that of ferrite prepared by the conventional method. The dielectric loss of sample in the ferric citrate system is only 0.008. The amorphous phase and its encapsulation well around the grains have played most important roles in both high resistivity and low dielectric loss of ferrite in the ferric citrate system

Catalytic combustion of methane over Mn-substituted Ba-La-hexaaluminate nanoparticles

Xiaolai-Wang; Shunqing-Li(State Key Lab. for Oxo Synthesis & Selective Oxidation, Chinese Acad. of Sci., Lanzhou, China)

Journal-of-Alloys-and-Compounds. 25 April 2007; 432(1-2): 333-7

Mn-substituted Ba-La-hexaaluminate rod-like nanoparticles with high surface area in the range between 45 and 73m²/g have been prepared using the alumina sol as the (NH₄)₂CO₃ co-precipitation precursor and the supercritical drying (SCD) method. The properties and microstructures of the catalysts are determined by the ion mobility at high calcination temperature. The nature of the large cation in the mirror plane can affect the Mn²⁺/Mn³⁺ redox process. The Ba_0.2La_0.8MnAl₁₁O_19-alpha catalyst possesses the highest catalytic activity owing to the excellent performance of activating oxygen. [All rights reserved Elsevier]

Systematic investigations into SrSnO₃ nanocrystals (I) synthesis by using combustion and coprecipitation methods

Mengkai-Lu; Shumei-Wang; Guangju-Zhou; Yuanyuan-Zhou; Aiyu-Zhang; Zhongsen-Yang(State Key Lab. of Crystal Mater., Shandong Univ., Jinan, China)

Journal-of-Alloys-and-Compounds. 25 April 2007; 432(1-2): 265-8

Strontium stannate (SrSnO₃) nanocrystals have been synthesized by using an efficient combustion method for the first time. The corresponding nanorods integrated with nanoparticles are also obtained with the coprecipitation method. X-ray diffraction, transmission electron micrograph and scanning transmission electron micrograph are used to illustrate the crystal structure, phase purity and morphology of the synthesized nanocrystals. The growth mechanisms are investigated in detail. [All rights reserved Elsevier]

Formation of titanium silicides Ti₅Si₃ and TiSi₂ by self-propagating combustion synthesis

Yeh-CL; Chen-WH; Hsu-CC(Dept. of Mech. & Autom. Eng., Da-Yeh Univ., Changhua, Taiwan)

Journal-of-Alloys-and-Compounds. 25 April 2007; 432(1-2): 90-5

Preparation of titanium silicides Ti₅Si₃ and TiSi₂ from elemental powder compacts of their corresponding stoichiometries was conducted by self-propagating high-temperature synthesis (SHS) in this study. Effects of the sample green density, preheating temperature, and starting stoichiometry on combustion characteristics, as well as on product composition were studied. Experimental evidence indicated that a self-sustained combustion front was established upon ignition and subsequently traversed the entire sample in a steady manner. After the passage of the flame front, further phase transformation taking place in the sample led to the emergence of afterburning glows. As a result of the combustion temperatures exceeding the lowest eutectic point (1330degC) of the Ti-Si binary mixture, formation of Ti₅Si₃ from the stoichiometric powder compact is primarily dominated by the solid-liquid mechanism, which involves the dissolution of solid reactants and the precipitation of silicide products. Moreover, complete conversion yielding a single-phase silicide Ti₅Si₃ was achieved in this study. On the contrary, the interaction between reactant elements within the Ti+2Si compacts is governed by a solid-state mechanism, due to their low reaction temperatures less than the Ti-Si eutectic point 1330degC. The XRD analysis identifies the disilicide TiSi₂ as the major composition in the final products of Ti+2Si samples. In addition to TiSi₂, however, small amounts of TiSi and Si were detected in the products obtained from the samples of Ti:Si=1:2. It is believed that different reaction mechanisms are responsible for the significantly higher propagation velocity of the reaction front observed in the 5Ti+3Si compacts than in the samples of Ti:Si=1:2. Based upon the dependence of flame-front velocity on combustion temperature, the activation energies in association with formation of Ti₅Si₃ and TiSi₂ by SHS were determined to be 205.2 and 165.4kJ/mol, respectively. [All rights reserved Elsevier]

Mechanical-activation-assisted combustion synthesis of alpha-SiAlON in air

Kexin-Chen; Guanghua-Liu; Heping-Zhou; Jiangtao-Li; Pereira-C; Ferreira-JMF(Dept. of Mater. Sci. & Eng., Tsinghua Univ., Beijing, China)

Materials-Research-Bulletin. 5 June 2007; 42(6): 989-95

With the assistance of mechanical activation, yttrium-stabilized alpha-SiAlON was prepared by combustion synthesis in air, instead of high-pressure N₂ atmosphere for the first time. The reaction activity of metallic particles was remarkably enhanced by mechanical activation, which conduced the reduction of grain size, increased the total surface area and formation of fresh surface. The formation of alpha-SiAlON by combustion synthesis in air was explained by a kinetically induced reaction mechanism, in which both initial formation of alpha-SiAlON and following avoidance of oxidation were fulfilled by the retardation of O₂ infiltration owing to the short reaction period and fast cooling rate. [All rights reserved Elsevier]

Chromium vaporization of bare and of coated iron-chromium alloys at 1073 K

Kurokawa-H; Jacobson-CP; DeJonghe-LC; Visco-SJ(Mater. Sci. Div., Lawrence Berkeley Nat. Lab., CA, USA)

Solid-State-Ionics,-Diffusion-and-Reactions. Feb. 2007; 178(3-4): 287-96

Suppression of chromium vaporization from oxidation scales formed on ferritic stainless steel, when used on the cathode side of Solid Oxide Fuel Cells (SOFC), is a most important issue, since gaseous chromium species cause deposition of chromium oxide on electrolyte or electrode materials. This phenomenon leads to deterioration of the cell performance. The chromium vaporization rates of bare and of coated iron-chromium alloys were measured at 1073 K. The effect of ceramic coating layers, deposited by low-cost aerosol spraying or by dip coating, was evaluated and the morphology of the coating layer was observed. Lanthanum strontium manganese oxide (LSM: La_0.65Sr_0.3MnO₃), lanthanum strontium cobalt iron oxide (LSCF: La_0.6Sr_0.4Co_0.8Fe_0.2O₃) and manganese cobalt oxide (MCO: MnCo₂O₄) coatings, formed from submicron powders, decreased chromium vaporization by a factor of as much as 21-40 at 1073 K. Manganese cobalt oxide and lanthanum strontium chromium oxide (La_0.7Sr_0.3CrO₃) coating, formed from powders prepared by a glycine nitrate combustion synthesis, reduced chromium vaporization by factors of only 2-3 because the coating layers were porous. [All rights reserved Elsevier]

Cadmium- and indium-doped zinc oxide by combustion synthesis using dopant chloride precursors

Yogeeswaran-G; Chenthamarakshan-CR; deTacconi-NR; Rajeshwar-K(Mate. Sci. & Eng. Program, Texas Univ., Arlington, TX, USA)

Journal-of-Materials-Research. Dec. 2006; 21(12): 3234-41

Cadmium-doped ZnO was prepared for the first time by combustion synthesis using CdCl₂ as a dopant precursor, with zinc nitrate and urea as the combustion mixture. Unlike previous studies of combustion synthesis of ZnO in the presence of an indium nitrate precursor, which resulted in (ZnO)_mIn₂O₃ (m=3 or 4) compound formation, In-doped ZnO was prepared by combustion synthesis in this study using an InCl₃ precursor. The doped samples were compared and contrasted with undoped ZnO using scanning electron microscopy, x-ray powder diffraction, energy-dispersive X-ray analyses, and X-ray photoelectron spectroscopy. Diffuse reflectance spectroscopy showed the optical band gap of ZnO to shrink from 3.14 to 3.07 eV and 3.02 eV on Cd and In doping, respectively. Finally, the doped samples showed an improved photoelectrochemical response relative to undoped ZnO over the wavelength range from ~300 to ~450 nm

Self-propagating, high-temperature combustion synthesis of rhombohedral AlPt thin films

Adams-DP; Rodriguez-MA; Tigges-CP; Kotula-PG(Sandia Nat. Labs., Albuquerque, NM, USA)

Journal-of-Materials-Research. Dec. 2006; 21(12): 3168-79

Sputter-deposited, Al/Pt multilayer thin films of various designs exhibited rapid, self-propagating, high-temperature reactions. With reactant layers maintained at ~21degC prior to ignition and films adhered to oxide-passivated silicon substrates, the propagation speeds varied from approximately 20 to 90 m/s depending on bilayer dimension and total film thickness. Contrary to current Al-Pt equilibrium phase diagrams, all multilayers reacted in air and in vacuum transformed into rhombohedral AlPt having a space group R-3(148). Rietveld refinement of AlPt powder (generated from thin film samples) yielded trigonal/hexagonal unit cell lattice parameters of a=15.634(3) Aring and c=5.308(1) Aring; the number of formula units=39. Rhombohedral AlPt was stable to 550degC with transformation to a cubic FeSi-type structure occurring above this temperature

Combustion synthesis, characterization and metal-insulator transition studies of nanocrystalline La_1-xCa_xMnO₃ (0.0lesxles0.5)

Chandrappa-GT; Nagabhushana-BM; Chakradhar-RPS; Ramesh-KP; Shivakumara-C(Dept. of Chem., Bangalore Univ., India)

Materials-Chemistry-and-Physics. 15 March 2007; 102(1): 47-52

Nanocrystalline CMR materials La_1-xCa_xMnO₃ (0.0lesxles0.5) are prepared by a low temperature, self-propagating combustion synthesis. As-formed and heat treated calcium doped lanthanum manganites are crystalline, showing cubic symmetry. However, as-formed cubic LaMnO₃ on calcination at 900degC for 6h, transformed into rhombohedral phase. The microstructure and morphology of the compounds show that the particles are nearly spherical in shape and are agglomerated. Differential thermal analysis (DTA) curve reveals a broad exothermic peak around 900degC, while the thermogravimetric (TG) curve exhibits a gradual weight loss from 650degC onwards, corresponding to reduction of Mn⁴⁺ to Mn³⁺. The surface area of manganites increases from 12.5 to 24m²g^-1 with increase in calcium content. Both undoped and doped lanthanum manganites show two IR active vibrational modes at 400 and 600cm^-1, corresponding to bending (nu_b) and stretching modes (nu_s) of the Mn-O-Mn bond, respectively. The metal-insulator transition temperatures (T_M-I) are found to lie in the range 117-235K for combustion derived samples, which are low compared to those prepared by ceramic route. [All rights reserved Elsevier]

Effect of PVA with various combustion fuels in sol-gel thermolysis process for the synthesis of LiMn₂O₄ nanoparticles for Li-ion batteries

Subramania-A; Angayarkanni-N; Vasudevan-T(Dept. of Ind. Chem., Alagappa Univ., Karaikudi, India)

Materials-Chemistry-and-Physics. 15 March 2007; 102(1): 19-23

LiMn₂O₄-based spinels are of great interest as positive electrode materials for lithium-ion batteries. The single-phase LiMn₂O₄ nanoparticles have been synthesized by a novel sol-gel thermolysis process using poly vinyl alcohol (PVA) with three different combustion fuels such as urea, hexamine and citric acid to know the effect on structure, particle size and electrochemical properties of LiMn₂O₄ nanoparticles. Among the three combinations, the polymeric gel precursor obtained by using PVA-urea has generate complete crystallization at lower temperature than other two combinations are confirmed by TG/DTA analysis. But all the three combinations generate phase pure LiMn₂O₄ nanoparticles are confirmed by XRD studies. The particle size and electrochemical properties are confirmed by TEM analysis and charge/discharge studies, respectively. It reveals that LiMn₂O₄ obtained by using PVA-urea has smaller nanoparticles and better electrochemical performance than the nanoparticles obtained by using other two combinations such as PVA-hexamine and PVA-citric acid. [All rights reserved Elsevier]

The influence of surfactant on ZnO varistors

Ravi-V; Dhage-SR; Navale-SC(Phys. & Mater. Chem. division, Nat. Chem. Lab., Pune, India)

Ceramics-International. March 2007; 33(2): 289-91

ZnO varistors with and without surfactant such as sodium dodecyl sulphate (SDS) are prepared by nitrate-combustion process. The samples were identically heat treated and sintered at 1000degC for 12h to study the influence of the surfactant on the nonlinear electrical properties of polycrystalline ZnO. It is observed that the nonlinear coefficient decreases marginally (alpha=35) for samples prepared with surfactant, whereas breakdown field (E_b=130V/mm) decreased significantly. The corresponding parameters for the samples synthesized without surfactant are alpha=45 and E_b=400V/mm. Hence, this method can be used for the manufacture of varistors with low to moderate breakdown fields. [All rights reserved Elsevier]

Synthesis of strontium zirconate as nanocrystals through a single step combustion process

Thomas-JK; Kumar-HP; Pazhani-R; Solomon-S; Jose-R; Koshy-J(Dept. of Phys., Mar Ivanios Coll., Kerala, India)

Materials-Letters. March 2007; 61(7): 1592-5

Nanocrystals of strontium zirconium oxide (SrZrO₃), a high dielectric constant (epsi'=60) ceramic, were synthesized using an auto-igniting combustion of a precursor solution containing metal ions, oxidant, and a fuel. Phase-purity and particulate properties of the as-prepared powder were examined using X-ray diffraction, differential thermal and thermogravimetric analyses, Fourier-transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopic techniques. As-prepared powder was single phase, crystalline, and composed of uniform particles with sizes of ~15-25 nm. These nanocrystals were sintered to high density (~98% of the theoretical density) at 1470 degC for 4 h. [All rights reserved Elsevier]

Low temperature solid-phase synthesis of tetragonal BaTiO₃ powders and its characterization

Nersisyan-HH; Won-HI; Won-CW(Rapidly Solidified Mater. Res. Center, Chungnam Nat. Univ., Daejeon, South Korea)

Materials-Letters. March 2007; 61(7): 1492-6

We report an alternative synthesis route for tetragonal and submicron barium titanate particles through a low temperature isothermal heat treatment of a precursor powder obtained from the BaO₂-TiO₂-C mixture utilizing combustion synthesis technique. Effort has been concentrated on the investigation and optimization of the synthesis process including combustion temperature and velocity, heat treatment procedure, and the characteristics of the powder obtained. It was shown that precursor powder prepared by the combustion method easily transformed to the tetragonal BaTiO₃ starting from 700 degC. Characterization of the products was performed by powder X-ray diffraction, scanning electron microscopy (SEM) and BET. From the results, it has been found that the formation of tetragonal BaTiO₃ powder at low temperature is conditioned by high chemical activity and specific characteristics of combustion products. The BaTiO₃ specimens were found to possess high dielectric constant and low dissipation factor at room temperature. [All rights reserved Elsevier]

Layered growth of Ti₂AlC and Ti₃AlC₂ in combustion synthesis

Kexin-Chen; Guanghua-Liu; Heping-Zhou; Junming-Guo; Kegang-Ren; Ferreira-JMF(Dept. of Mater. Sci. & Eng., Tsinghua Univ., Beijing, China)

Materials-Letters. Feb. 2007; 61(3): 779-84

In Ti-Al-C system two ternary carbides of Ti₂AlC and Ti₃AlC₂ were prepared by combustion synthesis. Laminated grain morphology and a terraced structure consisting of several parallel laminated layers were observed. On the basis of SEM and TEM results, a layered growth mechanism was proposed to describe the formation of the terraced structure. In this mechanism, the ternary carbide grains will undergo a preferential growth, i.e. each layer grows fast and expands quickly in the basal plane and all the layers are successively stacked along the normal direction identical to the c-axis in the hexagonal structure. This preferential growth characterized by the terraced structure was widely observed in this study and hence may be a common behavior during the growth of Ti₂AlC and Ti₃AlC₂ crystals in combustion synthesis. [All rights reserved Elsevier]

White upconverted luminescence of rare earth ions codoped Gd₂(MoO₄)₃ nanocrystals

Zhang-QY; Pan-YX(Key Lab. of Special Functional Mater., South China Univ. of Technol., China)

Materials-Science-and-Engineering-B-Solid-State-Materials-for-Advanced-Technology. 15 March 2007; 138(1): 90-4

The synthesis and upconversion luminescence (UL) of combustion method derived multiple rare earth ions doped gadolinium molybdate Gd₂(MoO₄)₃ nanocrystals have been presented. The monoclinic and orthorhombic Gd₂(MoO₄)₃ nanocrystals have been achieved by sintering the complex precursors respectively at 600 and 900degC. The room temperature normal emission spectra and excitation spectra of Er³⁺, Tm³⁺, Ho³⁺ codoped monoclinic Gd₂(MoO₄)₃ nanocrystals with sensitizer Yb³⁺ excited by xenon source have been investigated. The UL properties of Er³⁺, Tm³⁺, Ho³⁺ respectively doped monoclinic Gd₂(MoO₄)₃ nanocrystals pumped by 980nm laser diode have been examined. White light is produced in these multiple rare earth ions doped gadolinium molybdates when pumped either by 808nm or 980nm laser diode (LD). The CIE color coordinates of these white lights are close to the white light region. [All rights reserved Elsevier]

Study on the self sustained reactions in an Al-TiO₂ composite powder produced by high-energy mechanical milling

Zhiguang-Liu; Raynova-S; Deliang-Zhang; Gabbitas-B(Sch. of Mater. Sci. & Eng., Harbin Inst. of Technol., China)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 25 March 2007; 449-451: 1107-10

A mixture of Al and TiO₂ powders after high-energy mechanical milling was submitted to self sustained reactions to understand the influence of mechanical activation on the kinetics and products of the reactions. It has been found that mechanical milling the powders significantly lowered the ignition temperature of the reactions by refining the Al/TiO₂ composite structure. Shorter milling time leads to the formation of more amounts of metastable phases and coarse microstructure, which is in the similar scale in the mechanical milled samples. In contrast, equilibrium phases and a fine microstructure were found in the samples having a fine Al/TiO₂ composite structure produced with a longer milling time. Mechanical milling has greatly improved the kinetics of the reactions between the two components. [All rights reserved Elsevier]

Influence of (Zr,C) content on microstructure and properties of Zr₅₅Al₁₀Ni₅Cu₃₀ alloy prepared by laser-induced self-propagating reaction synthesis

Wang-CS; Chi-LN; Dong-C(State Key Lab. of Mater. Modification, Dalian Univ. of Technol., China)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 25 March 2007; 449-451: 609-12

Based on large negative enthalpy of mixing among major components of bulk metallic glass forming alloy systems, a new technique to fabricate amorphous-based composite materials using laser-induced self-propagating reaction synthesis (LSRS) was developed. The LSRS of a Zr₅₅Al₁₀Ni₅Cu₃₀ (numbers indicate at.%) alloy with different (Zr,C) content shows that the products mainly consist of amorphous phase and the Zr₃Al₂ and Zr₂Cu intermetallic phases. However, the content of amorphous phase in the products is closely related to the (Zr,C) content: the higher the content of (Zr,C), the lower the content of the amorphous phase. The microhardness and wear resistance of the samples increase with increasing (Zr,C) content. [All rights reserved Elsevier]

Improved luminescence of Zn₂SiO₄:Mn Green phosphor prepared by gel combustion synthesis of ZnO:Mn-SiO₂

Thiyagarajan-P; Kottaisamy-M; Rao-MSR(Mater. Sci. Res. Centre, Indian Inst. of Technol. Madras, Chennai, India)

Journal-of-the-Electrochemical-Society. April 2007; 154(4): H297-303

A bright green light emitting Zn₂SiO₄:Mn phosphor has been prepared at low temperature 800degC through gel combustion synthesis using zinc nitrate, manganese acetate, urea in a silica gel matrix. The structure and morphology of the phosphors using scanning electron microscopy along with thermogravimetric analysis/differential thermal analysis/Fourier transform infrared study along with X-ray diffraction, diffuse reflectance spectroscopy, and photoluminescence (PL) data show interesting trends with respect to the phase evaluation of Zn₂SiO₄:Mn phosphor. Photoluminescent and crystalline properties are examined as a function of firing temperature and Mn concentration. Maximum PL intensity is observed at lambda_em=522 nm for 0.03 Mn²⁺ concentration, which can be attributed to the ⁴T₁(G)-⁶A₁(S) transition of Mn²⁺ under short ultraviolet excitation. The PL emission intensity of these phosphors is found to be more superior to that of the corresponding samples prepared using the conventional solid state method implying the suitability of this route for the preparation of device worthy phosphor materials

Nanoparticles and nanograin-sized Y-doped CeO₂ ceramics

Ruiz-Trejo-E; Benitez-Rico-A; Gomez-Reynoso-S; Angeles-Rosas-M(Dept. de Fisica y Quimica Teorica, Univ. Nacional Autonoma de Mexico, Mexico)

Journal-of-the-Electrochemical-Society. April 2007; 154(4): A258-62

In this article we discuss the synthesis of nanoparticles and the preparation of dense nanoceramics of Y-doped CeO₂. We prepared the nanoparticles by combustion synthesis and characterized the nanopowders by X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy. The good sintering properties of these nanopowders allowed us to obtain very dense ceramics of Y-doped CeO₂ (>90% theoretical density) and keep the grain size small, in some cases around 100 nm, by using sintering temperatures as low as 1250degC and very short annealing times between 5 and 60 min. The microstructure of these nanoceramics was analyzed by atomic force microscopy and SEM. The most interesting feature of these nanoceramics is that the electrical measurements in N₂ (p_O2=3.5times10^-6 atm) carried out by the four-point dc technique showed a considerable increase in total conductivity in comparison with the measurements in air or oxygen in the range 700-900degC. This conductivity enhancement might be associated with the electronic contribution to the total conductivity and it is clearly higher than the ionic conductivity in the same temperature range

A hybrid model for worm simulations in a large network

Eul-Gyu-Im; Jung-Sik-Kim; In-Woo-Noh; Hyun-Jun-Jang(Coll. of Inf. & Commun., Hanyang Univ., Seoul, South Korea)

Intelligence-and-Security-Informatics.-Pacific-Asia-Workshop,-PAISI-2007.-Proceedings-Lecture-Notes-in-Computer-Science-Vol.4430. 2007: 301-6

Internet becomes more and more popular, and most companies and institutes use Web services for e-business and many other purposes. As results, Internet and Web services become core infrastructure for a company or an institute and become more and more important. With the explosion of Internet, the occurrence of cyber terrorism has grown very rapidly. It is difficult to find and close all security-flaws in a computer system that is connected to a network. Internet worms take advantages of these security flaws, and attack a large number of hosts with self-propagating techniques. It is quite challenging to simulate very large-scale worm attacks. This paper propose a hybrid model for large-scale simulations, and the proposed model will be both detailed enough to generate realistic packet traffic, and efficient enough to model a worm spreading through the Internet

Enhanced white light emission from GdAl₃(BO₃)₄:Dy³⁺,Ce³⁺ nanorods

Zhang-QY; Yang-CH; Pan-YX(Key Lab of Specially Functional Mater. of Minist. of Educ. & Inst. of Opt. Commun. Mater., South China Univ. of Technol., Guangzhou, China)

Nanotechnology-. 11 April 2007; 18(14): 5 pp.

GdAl₃(BO₃)₄ nanorods doped with rare-earth ions have been obtained via a combustion synthesis. The nanorods have been characterized by x-ray diffraction, micro-Raman spectra, various microscopy techniques and fluorescence measurements. The results show that the nanorods are of straight morphology and smooth surface with an average diameter of 60 nm. The GdAl₃(BO₃)₄:Dy³⁺ nanorods show intense emissions centred at 480, 575, and 665 nm upon excitation by both ultraviolet-blue and infrared light, which are associated with the typical transitions of ⁴F₉2/rarr⁶H₁₅2/, ⁴F₉2/rarr⁶H₁₃2/ and ⁴F₉2/rarr⁶H₁₁2/ of Dy³⁺, respectively. The presence of Ce³⁺ in the nanorods resulted in an enhancement of the Dy³⁺ emission intensity by a factor of ~2. Furthermore, the values of yellow-to-blue integral intensity of the nanorods decrease rapidly with an increase of Ce³⁺ concentration, which indicates that the emitted light approaches the Commission Internationale de I'Eclairage (CIE) ideal white conditions

Synthesis of alpha-Si₃N₄ using low-alpha-phase Si₃N₄ diluent by the seeding technique

Jiang-Tao-Li; Yun-Yang; Yi-Xiang-Chen; Zhi-Ming-Lin(Tech. Inst. of Phys. & Chem., Chinese Acad. of Sci., Beijing, China)

Scripta-Materialia. March 2007; 56(5): 401-4

An iterative method, called the seeding technique, was introduced into the traditional combustion synthesis process to synthesize alpha-Si₃N₄ powders, using low-alpha-phase Si₃N₄ diluent. The effect of the reaction thermodynamics and kinetics on the alpha-phase content of the synthesized product was discussed by calculating the conversion ratio of Si to alpha-Si₃N₄. The optimal conditions to obtain alpha-Si₃N₄ through the seeding technique have been determined. [All rights reserved Elsevier]

Experimental investigations on in-vessel corium retention through inherent gap cooling mechanisms

Kyoung-Ho-Kang; Rae-Joon-Park; Kil-Mo-Koo; Sang-Baik-Kim; Hee-Dong-Kim(Korea Atomic Energy Res. Inst., Daejeon, South Korea)

Journal-of-Nuclear-Science-and-Technology. Dec. 2006; 43(12): 1490-500

In-vessel retention (IVR) of corium is considered as one of the most attractive severe accident management strategies in that the success of the IVR can considerably reduce the concerns about containment failure and associated risks. Among the various measures to attain the IVR, inherent gap cooling through the in-vessel flooding is very useful since it requires no additional engineering features for the IVR. In this study, simulant melt experiments using thermite melt (Al₂O₃/Fe or Al₂O₃ only) were performed to technically validate the concept of in-vessel gap cooling. The experimental results indicate that a gap could form between the debris and the vessel lower head which could be attributed to the difference of materials between the debris and the vessel, the existence of water inside the lower plenum and the internal pressure load. The heat removal capacity in the gap was determined by the possibility of a water ingression into the gap. In the case of a small gap size, effective heat removal to the extent of the vessel bottom could not be achieved due to the difficulties of water ingression induced by the counter current flow limits (CCFL). Therefore, for an application of the in-vessel gap cooling concept to the real accident sequences, the regime for an effective gap cooling should be mapped according to the relocated melt mass and the gap size

Modeling nonisothermal interaction kinetics in the condensed state: a diagram of phase formation mechanisms for the Ni-Al system

Khina-BB(Physico-Tech. Inst., Nat. Acad. of Sci., Minsk, Belarus)

Journal-of-Applied-Physics. 15 March 2007; 101(6): 63510-1-11

Nonisothermal interaction in condensed Ni-Al system takes place during combustion synthesis (CS) or the so-called self-propagating high-temperature synthesis, which is characterized by a high heating rate, high final temperature, fast accomplishment of interaction, and unconventional, nonequilibrium phase formation mechanisms. In this work, a kinetic model for phase formation during CS of nickel monoaluminide in a layered Ni-Al system is developed basing on the diffusion-controlled growth of a solid product layer in strongly nonisothermal conditions. The model includes competition between the growth of NiAl and its dissolution in the parent phases (Al-base melt and solid or liquid Ni-base solution). For numerical calculations, real values of diffusion parameters in NiAl and the Ni-Al phase diagram are used. Simulation has revealed the existence of critical heating rates that correspond to a transition from the common diffusion-controlled growth mechanism to quasiequilibrium dissolution-precipitation pattern and then to nonequilibrium crystallization route. Thereby the existence of uncommon interaction pathways during CS of intermetallics, which were observed experimentally and debated in literature, is proved theoretically ex contrario. A map of phase formation mechanisms for reaction Ni+AlrarrNiAl in nonisothermal conditions is constructed, which defines the applicability domains of previously known theoretical approaches and permits predicting the interaction route

Combustion synthesis route to carbon-encapsulated iron nanoparticles

Bystrzejewski-M; Huczko-A; Lange-H; Cudzilo-S; Kicinski-W(Dept. of Chem., Warsaw Univ., Poland)

Diamond-and-Related-Materials. Feb. 2007; 16(2): 225-8

A new self-induced and efficient route to carbon-encapsulated iron nanocrystallites (ca. 30-60 nm in diameter) using the thermolysis of sodium azide-chlorocarbon mixtures in the presence of ferrocene is presented. The product was purified and its composition and morphology were studied by means of HR SEM, HR TEM, XRD, and DTA/TG. The magnetic properties (the coercivities ca. 60-70 Oe and the saturation magnetization ca. 21-22 emu/g) of encapsulates were measured. This autothermal process has inherent advantages, including the use of low cost materials and the simplicity of the production protocol, and can be also used to obtain other nanoencapsulates. [All rights reserved Elsevier]

Synthesis of La_0.7Ca_0.3CrO₃ SOFC interconnect using a chromium source

Ghosh-S; Das-Sharma-A; Basu-RN; Maiti-HS(Fuel Cell & Battery Sect., Central Glass & Ceramic Res. Inst., Kolkata, India)

Electrochemical-and-Solid-State-Letters. Nov. 2006; 9(11): A516-19

A chromium source, ammonium dichromate, has been used to synthesize ultrafine La_0.7Ca_0.3CrO₃ interconnect powder for solid oxide fuel cells (SOFCs)by combustion synthesis technique. Ammonium dichromate is the replacement of conventional chromium nitrate which is hygroscopic and relatively expensive. Besides being a chromium source, ammonium dichromate acts as a fuel in the auto combustion reaction. The La_0.7Ca_0.3CrO₃ powders as derived from dichromate source can be sintered to near theoretical density at a temperature as low as 1400degC and the properties of the samples are at par with those prepared using the conventional chromium nitrate under identical processing conditions

Studies of nanosized LiNi_0.5Mn_0.5O₂-layered compounds produced by self-combustion reaction as cathodes for lithium-ion batteries

Markovsky-B; Kovacheva-D; Talyosef-Y; Gorova-M; Grinblat-J; Aurbach-D(Dept. of Chem., Bar-Ilan Univ., Ramat-Gan, Israel)

Electrochemical-and-Solid-State-Letters. Oct. 2006; 9(10): A449-53

We report here on the synthesis of layered nanosized LiNi_0.5Mn_0.5O₂ compound by a modified self-combustion reaction and the studies of its electrochemical behavior as a cathode material for Li cells. Capacities up to 180-200 mAh/g could be reached during cycling of these electrodes even at 60degC in LiPF₆/alkyl-carbonate solutions. The nano-LiNi_0.5Mn_0.5O₂ material exhibits remarkable stability during prolonged aging and cycling at elevated temperatures. Surface films developed on the nano-LiNi_0.5Mn_0.5O₂ particles in the course of cycling/aging contain polycarbonates, LiF, nickel and manganese oxides, and fluorides, and lead to efficient passivation and stabilization of the electrodes

Dissolution and precipitation under gravitational conditions in the W-Al system

Munir-ZA; Unuvar-C; Fredrick-DM; Anselmi-Tamburini-U; Shaw-BD; Manerbino-A; Guigne-JY(Dept. of Chem. Eng. & Mater. Sci., Univ. of California, Davis, CA, USA)

Intermetallics-. March 2007; 15(3): 363-70

Dissolution and precipitation in the system Al-W was investigated under different gravitational conditions and applied electric fields. An intermetallic phase, WAl₄, precipitates after the dissolution of W into liquid Al. Settling of WAl₄ precipitates was absent under all gravity and electric current conditions and a homogenous distribution of WAl₄ with random alignment was observed in all cases. The size of the precipitates was found to increase with gravity. The electric current had a very small effect on the precipitate size in terrestrial gravity. However, under reduced gravity, the application of current resulted in a marked increase in precipitate size. Increasing gravity was found to increase the dissolution rate of W, which was discussed in terms of the stirring effect, created by the settling of W grains. Similar enhancement in the dissolution rate was observed with increasing electric current. [All rights reserved Elsevier]

Putting solar home system programmes into perspective: What lessons are relevant?

van-der-Vleuten-F; Stam-N; van-der-Plas-R(Solar Orange Group, Eindhoven, Netherlands)

Energy-Policy. March 2007; 35(3): 1439-51

Solar Home Systems (SHSs) have gradually become a household name in Africa. Pioneering efforts to make a new technology available to rural households have over the years developed into a few mass markets for the "base of the pyramid". This paper focuses on the lessons that can be learned from these experiences. Have policy makers and donors supported SHSs in an efficient way? Are they a luxury item or an essential element in the development process? Can they trigger or facilitate rural electrification? The answer to these questions is that photovoltaic (PV) systems can play a useful role for rural development and rural electrification purposes, but the desire to deploy them on a more massive scale to rural Africans demands a new type of energy policy support, creating new partnerships with local SMEs. [All rights reserved Elsevier]

Preparation and characterization of yttrium iron garnet (YIG) nanocrystalline powders by auto-combustion of nitrate-citrate gel

Hosseini-HRM; Vajargah-SH; Nemati-ZA(Mater. Sci. & Eng. Dept., Sharif Univ. of Technol., Tehran, Iran)

Journal-of-Alloys-and-Compounds. 14 March 2007; 430(1-2): 339-43

The nitrate-citrate gel exhibits auto-catalytic behavior, which can be used to synthesize nanocrystalline YIG powders. In this study, yttrium iron garnet (Y₃Fe₅O₁₂) nanocrystalline powders were prepared by a sol-gel auto-combustion process. The influence of metal nitrates to citric acid molar ratio (MN/CA) of the precursor solution on the combustion behavior and crystallite size of synthesized powders was investigated by scanning electron microscopy (SEM), thermal analyses (DTA/TGA) and X-ray diffraction (XRD). The results show that with increasing MN/CA value, the combustion rate increases and the single-phase YIG forms at a higher temperature. The crystallite size of the single phase YIG prepared with different MN/CA values and calcined at 800degC for 3h are in the range of 38-70nm. In addition, the crystallite size of the powders increased with increasing the calcination temperature. [All rights reserved Elsevier]

Bimodal size distribution and shape anisotropy in ball-milled nano-sized alpha-Al₂O₃

Deb-AK; Chatterjee-P; Sen-Gupta-SP(Dept. of Mater. Sci., Indian Assoc. for the Cultivation of Sci., Kolkata, India)

Materials-and-Manufacturing-Processes. 2006; 21(7-8): 641-3

alpha-Al₂O₃ prepared by combustion technique was ball-milled in a planetary mill in toluene medium at 300 rpm in ZrO₂ pot with a ball to powder ratio 10:1 for 1, 5, 10, 15, and 20hours. X-ray diffraction pattern from the milled materials showed super-Lorentzian peak shapes for alpha-Al₂O₃ peak profiles. The super-Lorentzian peak shape has been attributed to the bimodal size distribution of the alpha-Al₂O₃ particles. Rietveld analysis using two different phase fractions of alpha-Al₂O₃ with different microstructural features yielded a low goodness-of-fit of the X-ray data indicating the suitability of the assumed model. The phase fraction of alpha-Al₂O₃ particles with smaller size increases with the milling time. Further the particles shapes were observed to be cylindrical in this case with the cylinder axis along the crystallographic c-axis. The cylinder diameter and the length were obtained to be 86 Aring and 140 Aring respectively after 20hrs of milling. The alpha-Al₂O₃ particles of larger size are isotropic. It is, thus, proposed that milling induces bimodal size distribution in the initial hours of milling

Synchrotron X-ray diffraction study of the tetragonal-cubic phase boundary of nanocrystalline ZrO₂-CeO₂ synthesized by a gel-combustion process

Lamas-DG; Fuentes-RO; Fabregas-IO; Fernandez-de-Rapp-ME; Lascalea-GE; Casanova-JR; Walsoe-de-Reca-NE; Craievich-AF(CINSO, Pcia. De Buenos Aires, Argentina)

Journal-of-Applied-Crystallography. Dec. 2005; 38(6): 867-73

The crystal structures of a number of nanocrystalline ZrO₂-CeO₂ solid solutions, synthesized by a pH-controlled nitrate-glycine gel-combustion process, were studied. By using a synchrotron X-ray diffractometer, small peaks of the tetragonal phase, which correspond to forbidden reflections in the case of a perfect cubic fluorite structure, were clearly detected. By monitoring the most intense of these reflections, 112, as a function of the CeO₂ content, the tetragonal-cubic phase boundary was found to be at 85 (5) mol% CeO₂. For a CeO₂ content up to 68 mol%, a tetragonal phase with c/a>1 (known as the t' form) was detected, whereas, between 68 and 85 mol% CeO₂, the existence of a tetragonal phase with c/a=1 and oxygen anions displaced from their ideal positions in the cubic phase (the t" form) was verified. Finally, solid solutions with higher CeO₂ contents exhibit the cubic fluorite-type phase

Crystallization of amorphous silicon by self-propagation of nanoengineered thermites

Hossain-M; Subramanian-S; Bhattacharya-S; Yuanfang-Gao; Apperson-S; Shende-R; Guha-S; Arif-M; Mengjun-Bai; Gangopadhyay-K; Gangopadhyay-S(Dept. of Electr. & Comput. Eng., Univ. of Missouri, Columbia, MO, USA)

Journal-of-Applied-Physics. 1 March 2007; 101(5): 54509-1-6

Crystallization of amorphous silicon (a-Si) thin film occurred by the self-propagation of copper oxide/aluminum thermite nanocomposites. Amorphous Si films were prepared on glass at a temperature of 250degC by plasma enhanced chemical vapor deposition. The platinum heater was patterned on the edge of the substrate and the CuO/Al nanoengineered thermite was spin coated on the substrate that connects the heater and the a-Si film. A voltage source was used to ignite the thermites followed by a piranha solution (4:1 of H₂SO₄:H₂O₂) etch for the removal of residual products of thermite reaction. Raman spectroscopy was used to confirm the crystallization of a-Si

Microstructure of Si₃N₄-TiN-SiC ceramics during combustion synthesis process

Zhang-Xuejun; Zheng-Yongting; Han-Jiecai(Center for Composite Mater., Harbin Inst. of Technol., China)

Journal-of-the-Chinese-Ceramic-Society. 2006; 34(11): 1295-300

Si₃N₄-TiN-SiC multiphase ceramics were synthesized from TiSi₂ and SiC powders by combustion synthesis. In order to study the combustion process of the TiSi₂-SiC-N₂ system in details, the reaction was stopped at different stages by quenching the samples. The composition and microstructure in different reaction zones were analyzed by X-ray diffraction and scanning electron microscopy. The results show that the main phase of product after complete reaction is whisker-like Si₃N₄, others are TiN and SiC During the combustion synthesis, TiSi₂ particles melt and enwrap on the surface of SiC particles first. As a result, the contact area of TiSi₂ and N₂ increases, and TiN and Si are formed after the reaction. The mid-product, silicon melts or evaporates under high combustion temperature. At the same time, liquid free silicon and unreacted TiSi₂ are completely miscible. Finally, free silicon reacts with nitrogen to form Si₃N₄ crystal nuclei and grow up. Si₃N₄ whiskers are formed during the combustion reaction as a result of the combined effect of vapor-liquid-solid, vapor-solid and evaporation-agglomeration mechanisms

Structure characteristic of lanthanum chromites nano-powder by low-temperature combustion synthesis

Liu-Weiming; Li-Jing; Li-Shengli; Li-Shigang; Zhu-Xinde; Li-Hong(Coll. of Mater. Sci. & Eng., Shandong Univ., Jinan, China)

Journal-of-the-Chinese-Ceramic-Society. 2006; 34(10): 1279-82

Nano-powder of lanthanum chromites were synthesized by low-temperature combustion method. The powders were composed of La_1-xCa_xCrO₃, a little of LaCrO₄, La₂CrO₆ and organic compounds measured by X-ray diffraction and scanning electron microscopy analysis. The phase of LaCrO₄, as an inter-phase, was resulted from incomplete decomposition of the gel, and the formation of La₂CrO₆ was related to incomplete complexation of cations. The products synthesized are as a film-like material with thickness about 80 nm. During the film calcined at high temperature, volatilization of organic compounds and the decomposition of LaCrO₄ and La₂CrO₆ lead to the film broken into the nano powders with average particle size about 80 nm. The powders synthesized are uniform in size, but there are partially hard particle agglomerates in the powders

Influence of different additives on the luminescence properties of SrAl₂O₄:(Eu,Dy) phosphors

Shen-Yi; Zhang-Ping; Zheng-Zhentai; Qu-Yuanfang(Key Lab. for Adv. Ceramics & Machining Technol. of Ministry of Educ., Tianjin Univ., China)

Journal-of-the-Chinese-Ceramic-Society. 2006; 34(10): 1187-90

Strontium aluminate co-doped with Eu²⁺, Dy₃₊ phosphor powders were rapidly prepared at lower temperatures by combustion synthesis. The influence of P₂O₅, CaF₂, H₃BO₃ and NaF additives on the luminescence properties of SrAl₂O₄:(Eu, Dy) phosphors was studied. The results indicate that the luminescence properties Of SrAl₂O₄:(Eu, Dy) phosphors are improved by doping of the H₃BO₃ and P₂O₅, but suppressed by doping of CaF₂ and NaF. The main emission peaks on the emission spectra doped with the additives tend to blue shift compared to that without additives. According to the results, the mechanism of the additives in phosphors was analyzed

Influence of high-energy milling and sintering cycle on obtaining from elemental Ti and Al powders

Esteban-PG; Gordo-E; Ruiz-Navas-EM(Dept. of Mater. Sci. & Eng., Univ. Carlos III de Madrid, Leganes, Spain)

Materials-Science-Forum. 2007; 534-536: 813-16

The present work studies the influence of high-energy milling (HEM) and sintering cycle of Ti and Al powders on the obtainment of TiAl. This study shows that HEM modifies the diffusion processes during the sintering stage. The ignition temperature of the exothermic reaction (SHS) that occurs between Ti and Al, was considered as the key parameter of the sintering process, leading to the study of sintering cycles that avoid uncontrolled processes caused by the SHS reaction. The samples were obtained by cold uniaxial and isostatic pressing, pre-sintered at different temperatures, and then heated up to the sintering temperature. This study also shows the effect of powder additions processed by HEM on the sintering behavior of blended elemental Ti and Al powder compacts

Fabrication of nanocrystalline TaSi₂-SiC composite by high frequency induction heated combustion synthesis and its mechanical properties

In-Jin-Shon; Dong-Ki-Kim; In-Yong-Ko; Jin-Kook-Yoon; Kyung-Tae-Hong(Div. of Adv. Mater. Eng., Chonbuk Nat. Univ., Jeonbuk, South Korea)

Materials-Science-Forum. 2007; 534-536: 525-8

By the high frequency induction heated combustion synthesis (HFIHCS) method, dense nanostructured TaSi₂-SiC composite was synthesized within 2 minutes and in a single step from powders of TaC and 3Si. Simultaneous combustion synthesis and densification were accomplished under the combined effects of an induced current and mechanical pressure. Highly dense TaSi₂-SiC with relative density of up to 97% were produced under a 60 MPa pressure and induced current. The average grain size and mechanical properties (hardness and fracture toughness) of the composite were investigated

Effect of the preparation methods of Me+Al powder blends on the compaction behavior, structure, phase transformations, and properties of the compacted aluminides of transition metals

Povarova-KB; Kazanskaya-NK; Drozdov-AA; Morozov-AE; Nikolaev-AG(Baikov Inst. of Metall. & Mater. Sci., Russian Acad. of Sci., Moscow, Russia)

Materials-Science-Forum. 2007; 534-536: 513-16

The effect of the methods for preparing powder blend by conventional milling (Me+Al particles), attriting (Me/Al/ Me/Al composite particles), and plating of Me by Al (Me/Al composite particles) on the structure, internal stress level, and compactability of the powder blends as well as the structure and phase composition of the MeAl compacts was investigated. The Me+AlrarrMeAl exothermic reaction of these powders occurs at Tges650degC. The reaction sintering (RS) or high-temperature self-propagation synthesis (HTSPS) occurs through the formation of Al melt (liquid-phase reaction) and lower-melting MeAl₃, Me₂Al₃, Me₃Al aluminides. An increase in the level of internal stresses (IS) upon attritting activates RS at lower temperatures and decreases the value of high-temperature exoeffect. This suppresses the HTSPS development. A large high-temperature exoeffect ensures the intensity and completeness of the reaction interaction, and the application of pressure upon RS or HTSPS provides a high, near-theoretical density of the compacted material

Combustion behaviors resulting from bimodal aluminum size distributions in thermites

Moore-K; Pantoya-ML; Son-SF(Texas Tech. Univ., Lubbock, TX, USA)

Journal-of-Propulsion-and-Power. Jan.-Feb. 2007; 23(1): 181-5

Studies that replace a portion of the micron-size aluminum (Al) with nano-Al particles in an energetic formulation demonstrate significant performance enhancement. Little is known, however, about the critical level of nano-sized fuel particles needed to enhance the performance of the energetic composite. Ignition sensitivity and combustion velocity experiments were performed using a thermite composed of Al and molybdenum trioxide (MoO₃). Both loose powders and compressed pellets were examined. A bimodal Al particle size distribution was prepared using 4 or 20-mum-diam Al fuel particles that were replaced in 10% increments by 80-nm-diam Al particles until the fuel was 100% nano-Al. Results show that with only 20% nano-Al content, the mixtures showed reduced ignition delay times by up to 2 orders of magnitude. The combustion velocity was shown to dramatically increase as more nano-Al particles replace micron-Al particles within the mixture. This increasing trend was attributed to incomplete reactions of the micron-Al particles or significantly slower reactions such that the micron-Al particles promote cooling or quenching of the reaction

Novel wet-chemical synthesis and characterization of nanocrystalline CeO₂ and Ce_0.8Gd_0.2O_1.9 as solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications

Rambabu-B; Ghosh-S; Jena-H(Dept. of Phys., Southern Univ., Louisiana, USA)

Journal-of-Materials-Science. Nov. 2006; 41(22): 7530-6

Novel wet-chemical methods of synthesis have been adopted to synthesize nano-crystalline CeO₂ and Gd-substituted compositions aiming to explore an efficient oxide ion conducting solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. Nano-crystalline CeO₂ powders were synthesized by combustion method using redox mixture of cerric ammonium nitrate or cerium nitrate and maleic acid or 1,3-dimethylurea and compared with high surface area CeO₂ powders prepared by hydrothermal technique with microwave precipitated precursor from aqueous solutions of (NH₄)₂Ce(NO₃)₆ and urea. The grain size achieved by the hydrothermal technique is ~7 nm which is smaller than that of commercial nano CeO₂ powders. Conventional or microwave sintering was used to prepare dense Ce_0.8Gd_0.2O_1.9 pellets from the ceria powders made of redox mixture of cerium nitrate, 1,3-dimethylurea (DMU) and Gd₂O₃ as the starting ingredients. The samples were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and ac impedance spectroscopy. The ionic conductivity measured for the pellet sintered at 1400degC is 1times10^-2 and 2.4times10^-2 S/cm at 700degC and 800degC respectively

Production of single and multi-walled carbon nanotubes using natural gas as a precursor compound

Bonadiman-R; Lima-MD; de-Andrade-MJ; Bergmann-CP(Dept. of Mater. Eng., Univ. Fed. do Rio Grande do Sul, Porto Alegre, Brazil)

Journal-of-Materials-Science. Nov. 2006; 41(22): 7288-95

In this work, the Catalytic Chemical Vapor Deposition (CCVD) technique was used to synthesize carbon nanotubes (CNT). Natural gas (NG) was employed as a carbon source for the growing of CNT, while magnesium oxide was used as a catalyst support for the nanotubes synthesis. Two systems were utilized. The Fe-Mo/MgO system was obtained by the impregnation technique through the dispersion of iron oxide, which is the catalyst, over magnesia (with molybdenum additions). This system was tested intending to optimize the parameters for the production of single-walled carbon nanotubes (SWCNT). Moreover, Mg_1-xFe_xMoO₄, which was prepared by the combustion synthesis method, was tested to produce multi-walled carbon nanotubes (MWCNT). The Fe-Mo/MgO tests were carried out under H₂/GN and Ar/GN atmospheres at 950 degC, whereas the Mg_1-xFe_xMoO₄ was submitted to 1,000 degC under H₂/GN atmosphere. The Fe-Mo/MgO catalyst produced better results regarding number of CNT and their diameters under Ar/NG atmospheres than under H₂/NG atmospheres. The system Mg_1-xFe_xMoO₄ produced MWCNT according to the expectations

Effects of calcium nitride and calcium carbonate gasifying agents on the porosity of Ni₃Ti-TiC composites produced by combustion synthesis

Burkes-DE; Milwid-J; Gottoli-G; Moore-JJ(Dept. of Metall. & Mater. Eng., Colorado Sch. of Mines, Golden, CO, USA)

Journal-of-Materials-Science. Dec. 2006; 41(23): 7944-53

Combustion synthesis or self-propagating high temperature synthesis (SHS) has been used to produce highly porous materials intended for biomedical applications. Two novel gasifying agents, calcium nitride and calcium carbonate, were employed to increase product porosity and pore size during the combustion synthesis reaction for two SHS chemical compositions. A greater increase in apparent porosity of the products was gained using calcium carbonate compared with calcium nitride. Conversely, a greater increase in the number of pores falling within a 101-500 mum range was gained using calcium nitride compared with calcium carbonate. A greater increase in product porosity and pore sizes was observed for the TiC-50 wt% Ni₃Ti than the TiC-30 wt% Ni₃Ti with both gasifying agents

Effects of TiAl₃ addition on combustion synthesis of Ti₃AlC

Guo-Junming; Chen-Kexin; Wang-Baosen; Zhang-Hong; Li-Xingquan; Zhou-Heping(Honghe Univ., Mengzi, China)

Rare-Metal-Materials-and-Engineering. Nov. 2006; 35(11): 1708-11

Using Ti, Al and C powders as starting materials, the effect of intermetallic compound TiAl₃ addition on the combustion synthesis of Ti₃AlC has been studied. The experiment results show that the main phase of the combustion product involves Ti₂AlC and TiC without Ti₃AlC, if the molar ratio of Ti, Al, C is equal to 3:1:1. However, the product Ti₃AlC is produced by combustion synthesis if a small amount of TiAl₃ is added to the starting mixtures without changing the overall stoichiometry. The Ti₃AlC becomes the main phase in the final product upon adding 23.5% TiAl₃ (mass fraction) in the raw mixtures. The amount of Ti₃AlC increases with increasing of addition of TiAl₃ in the raw mixtures. The above experimental phenomena were explained through thermodynamic and kinetic analysis

Combustion synthesis of cast intermetallic Ti-Al-Nb alloys in a centrifugal machine

Sanin-V; Yukhvid-V; Sytschev-A; Andreev-D(Inst. of Struct. Macrokinetics & Mater. Sci., Russian Acad. of Sci., Chernogolovka, Russia)

Metallic-Materials. Jan.-Feb. 2006; 44(1): 49-56; Original: Kovove-Materialy. Jan.-Feb. 2006; 44(1): 49-56

The effect of green powder composition and centrifugal overload n on combustion temperature, separation of metallic products from ceramic phases, chemical composition and microstructure of intermetallic Ti-Al-Nb alloys prepared by Self-propagating High-temperature Synthesis (SHS) in a centrifugal machine was investigated. It was found that SHS can be performed in a combustion mode by addition of energy-producing CaO₂+Al components into the product-forming Ti+Nb+Al or TiO₂+Nb₂O₅+Al powder mixtures. The yield of a metallic product increases, porosity decreases and microstructure significantly changes with increasing n. The presence of CaO in combustion products and centrifugal overload facilitates almost complete separation of ceramic phases from the metallic product. The uniform microstructure of metallic products and chemical composition close the targeted Ti-46Al-8Nb (at.%) can be achieved by an appropriate selection of SHS parameters

Thermal properties of MoSi₂ with minor aluminum substitutions

Umarji-AM; Dasgupta-T(Mater. Res. Centre, Indian Inst. of Sci., Bangalore, India)

Intermetallics-. Feb. 2007; 15(2): 128-32

Mo(Si_1-xAl_x)₂ compositions (x=0-0.1) have been prepared by a modified SHS route under uniaxial hydrostatic pressure. Oxidation studies carried out by thermal analysis and sheet resistivity indicate an improvement in the low temperature (700-900K) oxidation resistance with increasing aluminum addition. Dilatometric results show a decrease in the alpha value up to x=0.05 substitution. With the aluminum substitution, both thermal expansion coefficient and thermal conductivity show decrease in their values except in the biphasic region. The x=0.05 composition containing both C11_b and C40 phases is a promising material for high temperature thermal barrier coating as it shows higher oxidation resistance and a similar K/alpha value as compared to pure MoSi₂. [All rights reserved Elsevier]

Combustion synthesis and compaction of Si₃N₄-TiN composite powder

Blugan-G; Manukyan-KhV; Kharatyan-SL; Kuebler-J(Empa, Lab. of High Performance Ceramics, Duebendorf, Switzerland)

Ceramics-International. April 2007; 33(3): 379-83

The possibilities for combustion synthesis of TiN-Si₃N₄ composite powders were investigated using different titanium silicides (TiSi, Ti₅Si₃, TiSi₂) as initial raw materials. Thermodynamic analysis and relevant experiments have shown that at relatively low nitrogen pressure (up to 5MPa) Ti₅Si₃ is the most suitable compound for this purpose. Optimum experimental conditions for synthesizing two-phase silicon-free TiN-Si₃N₄ (containing 30-35wt.% TiN) composite powders with characteristic sizes of approximately 5-10mum were determined. Compact discs of 50mm diameter were fabricated using hot pressing technique. Microstructural features of the composite powder and hot pressed samples were investigated, i.e. biaxial flexure strength. [All rights reserved Elsevier]

Combustion synthesis of vanadium carbonitride from V-C powder compacts under nitrogen pressure

Yeh-CL; Chen-YD(Dept. of Mech. & Autom. Eng., Da-Yeh Univ., Changhua, Taiwan)

Ceramics-International. April 2007; 33(3): 365-71

An experimental investigation on the preparation of vanadium carbonitrides by self-propagating high-temperature synthesis (SHS) was conducted using compacted samples of the vanadium and carbon powder mixture ignited in gaseous nitrogen. Effects of the initial sample stoichiometry, nitrogen pressure, and dilution by vanadium nitride (VN) on the combustion characteristics and the degree of conversion were studied. Experimental observation shows that upon initiation the combustion process is characterized by the steady propagation of a self-sustained reaction front. The flame-front propagation velocity was found to decrease with an increase in the carbon content of the compact, due to the decrease of combustion temperature with increasing carbon content. For the reactants composed of V+0.3C and V+0.5C, after the passage of the flame front the nitridation continued lengthily in an afterburning stage. Because of a less amount of available vanadium to react with nitrogen, the compact of V+0.5C achieved a higher degree of nitridation than did the V+0.3C sample. However, the nitridation percentage of the V+0.7C sample was lower than that of the V+0.5C sample, mainly due to the absence of afterburning reaction in the V+0.7C powder compact. Moreover, it was found that diluting the V+0.3C sample by a small amount of VN as the sample of 0.9V+0.3C+0.1VN effectively enhanced the degree of nitridation, but a further increase in the diluent concentration provided no additional improvement. The XRD analysis indicates the formation of single-phase carbonitrides V(C,N) slightly rich with vanadium from the reactant compacts of V+0.5C, V+0.7C, and 0.9V+0.3C+0.1VN. For the sample of V+0.3C, due to the low degree of nitridation there exists an intermediate nitride phase of V₂N in addition to the dominant phase of V(C,N). [All rights reserved Elsevier]

Alumina precursors produced by gel combustion

Pan-Y; Jiang-Li; Yusong-Wu; Jingkun-Guo(State Key Lab of High Performance Ceramics & Superfine Microstruct., Chinese Acad. of Sci., Shanghai, China)

Ceramics-International. April 2007; 33(3): 361-3

Alumina precursor produced by a gel combustion method using aluminum nitrate and citric acid as raw materials was investigated. Thermodynamic calculation of the combustion reaction shows that as the citrate-to-nitrate ratio gamma increases, the enthalpy of reaction and adiabatic flame temperatures also increase. The DSC analysis indicates that the combustion temperature of the gel decreases, as the citrate content in the gel increases in the fuel-lean condition. In the stoichiometric and fuel-rich conditions, combustion temperature remains ~160degC with increase of gamma. [All rights reserved Elsevier]

Synthesizing sulphides by a temperature gradient method

Tao-Liu; Jingkun-Yu; Min-Chen(Sch. of Mater. & Metall., Northeastern Univ., Shenyang, China)

Ceramics-International. April 2007; 33(3): 321-5

Metal sulphides were synthesized with a temperature gradient method by using metal and S as starting materials. The relationship among the amount of evaporating sulphur, volume of quartz tube, synthesis temperature and pressure in the quartz tube was studied. The results showed that the maximum amount of evaporating sulphur is 1.15g in the quartz tube under the experimental conditions, this confirming that the temperature gradient and heating-rate in the synthesis system were controlled. MgS, TiS₂, ZrS₂ and WS₂ were synthesized safely and in large amount: 56.37, 112.00, 155.36 and 247.97g, respectively. [All rights reserved Elsevier]

Polypropylene as a carbon source for the synthesis of multi-walled carbon nanotubes via catalytic combustion

Tao-Tang; Zhiwei-Jiang; Rongjun-Song; Wuguo-Bi; Jun-Lu(State Key Lab. of Polymer Phys. & Chem., Chinese Acad. of Sci., Changchun, China)

Carbon-. Feb. 2007; 45(2): 449-58

Multi-walled carbon nanotubes (MWCNTs) were efficiently synthesized by catalytic combustion of polypropylene (PP) using nickel compounds (such as Ni₂O₃, NiO, Ni(OH)₂ and NiCO₃middot2Ni(OH)₂) as catalysts in the presence of organic-modified montmorillonite (OMMT) at 630-830degC. Morphologies of the sample undergoing different combustion times were observed to investigate actual process producing MWCNTs by this method. The obtained MWCNTs were characterized by X-ray diffraction (XRD), transmission electron microscope and Raman spectroscopy. The yield of MWCNTs was affected by the composition of PP mixtures with OMMT and nickel compounds and the combustion temperature. The proton acidic sites from the degraded OMMT layers due to the Hoffman reaction of the modifiers at high temperature played an important role in the catalytic degradation of PP to supply carbon sources that are easy to be catalyzed by nickel catalyst for the growth of MWCNTs. The XRD measurements demonstrated that the nickel compounds were in situ reduced into the Ni(0) state with the aid of hydrogen gas and/or hydrocarbons in the degradation products of PP, and the Ni(0) was really the active site for the growth of MWCNTs. The combination of nickel compounds with OMMT was a key factor to efficiently synthesize MWCNTs via catalytic combustion of PP. [All rights reserved Elsevier]

Microstructure and kinetics of a functionally graded NiTi-TiC_x composite produced by combustion synthesis

Burkes-DE; Moore-JJ(Metall. & Mater. Eng. Dept., Colorado Sch. of Mines, Golden, CO, USA)

Journal-of-Alloys-and-Compounds. 14 March 2007; 430(1-2): 274-81

Production of a NiTi-TiC_x functionally graded material (FGM) composite is possible through use of a combustion synthesis (CS) reaction employing the propagating mode (SHS). The NiTi-TiC_x FGM combines the well-known and understood superelastic and shape memory capabilities of NiTi with the high hardness, wear and corrosion resistance of TiC_x. The material layers were observed as functionally graded both in composition and porosity with distinct interfaces, while still maintaining good material interaction and bonding. XRD of the FGM composite revealed the presence of TiC_x with equi-atomic NiTi and minor NiTi₂ and NiTi₃ phases. The TiC_x particle size decreased with increasing NiTi content. Microindentation performed across the length of the FGM revealed a decrease in hardness as the NiTi content increased. [All rights reserved Elsevier]

Telerehabilitation using a virtual environment improves upper extremity function in patients with stroke

Holden-MK; Dyar-TA; Dayan-Cimadoro-L(Dept. of Phys. Therapy, Northeastern Univ., Boston, MA, USA)

IEEE-Transactions-on-Neural-Systems-and-Rehabilitation-Engineering. March 2007; 15(1): 36-42

In this paper, we describe our experience in designing a virtual environment-based (VE) telerehabilitation system, and the results of a clinical study of the first 11 subjects with stroke to use the system. Our telerehabilitation system allows a therapist to conduct interactive VE treatment sessions remotely with a patient who is located at home. The system, software architecture, and development experience are described. Results of the clinical study on subjects with stroke showed significant improvements in upper extremity function following 30 1-h VE treatment sessions as measured by three standard clinical tests: Fugl-Meyer test of motor recovery (FM) (p<0.0001), Wolf motor test (WMT) (p=0.0097, and shoulder strength (ShS) (p=0.0027). Grip strength (GS) showed a trend toward improvement (p=0.025). These changes were maintained, for the most part, at four-months follow-up (FM +7.6, WMT -18.4 s, ShS, +169%, GS, +53%)

Synthesis of TiC by controlled ball milling of titanium and carbon

Lohse-BH; Calka-A; Wexler-D(Fac. of Eng., Wollongong Univ., NSW, Australia)

Journal-of-Materials-Science. Jan. 2007; 42(2): 669-75

Titanium and carbon powder mixtures with compositions of Ti_100-xC_x (x=50, 40, 30) were milled under a helium atmosphere using a magneto ball mill. Controlled ball milling was performed in a higher energy impact mode and a lower energy shearing mode. For Ti₅₀C₅₀ and Ti₆₀C₄₀ powder mixtures milled in impact mode, TiC was formed via a mechanically-induced self-propagating reaction (MSR). When milling Ti₇₀C₃₀ in impact mode, the reaction to form TiC proceeded gradually as milling progressed, indicating that, for milling conditions that lead to the formation of TiC via MSR, a minimum carbon content is required to sustain the self-propagating reaction to form TiC. Milling in shearing mode resulted in the gradual formation of TiC during milling. This study found that increasing the carbon content of the starting powder mixture slowed the milling process. Replacing the activated carbon starting powder with high purity graphite was found to have little effect on the ignition time, indicating that the slowing of the milling process is not due to graphite acting as a lubricant during milling. Rather, this slowing of the milling process is most likely due to an increased carbon content resulting in an increase in the volume of the powder mixture. This would have a similar effect during milling to decreasing the ball:powder weight ratio (BPR), which is known to slow the milling process

Unusual magnetic and transport properties of the CMR Pr_1-xCa_xMnO_3-y system

Yin-RZ; Yo-CH(Dept. of Chem., Yonsei Univ., Seoul, South Korea)

Journal-of-Materials-Science. Jan. 2007; 42(2): 660-8

The substituted nonstoichiometric perovskite Pr_1-xCa_xMnO_3-y compounds have been synthesized by a standard combustion technique, which show uniphase solid solutions. All samples of the Pr_1-xCa_xMnO_3-y system show an orthorhombic crystal system and the cell volumes are decreased with increasing the larger amounts of substituted atoms or the increasing x values. The mixed valence of Mn⁴⁺ ions is identified by the XAS (XANES/EXAFS) spectroscopy and the amounts of Mn⁴⁺ ions are determined by an iodometric titration method. Nonstoichiometric chemical formulas of the Pr_1-xCa_xMn_1-tau³⁺Mn_tau⁴⁺O_3-y compounds have been obviously formulated. Magnetic properties are investigated by SQUID and thus the Pr_1-xCa_xMnO_3-y (x=0.4, 0.6, and 0.8) compounds show the transition from antiferromagnetic state to paramagnetic state. The Pr_1-xCa_xMnO_3-y (x=0.0, 0.2, and 1.0) compounds show the transition from ferromagnetic state to paramagnetic state. The facts that Mn⁴⁺ contents play important roles in the magnetic ordering have been found out. The transport properties have been studied by the DC electrical conductivity measurement under magnetic fields of 0 G and 3 kG. Maximum and minimum MR ratios are 1016% of the Pr_0.6Ca_0.4MnO_2.846, and -77.5% of the PrMnO_3.021 compound, respectively

Study on phase transformation of MgB₂ after sintering

Han-Huanqing; Lu-Huimin; Qiu-Dingfan(Univ. of Sci. & Technol. Beijing, China)

Rare-Metal-Materials-and-Engineering. Oct. 2006; 35(10): 1602-4

MgB₂ powder was synthesized by self-propagating high-temperature method, and then was pressed into green compacts, which were sintered in Ar gas to get required samples. XRD, SEM and EDX methods analyzed the sample. It is found that MgB₂ was partially transformed into MgB₄ after sintering at 1050degC for 1 h in Ar. The amount of MgB₄ increased with increasing of sinter temperature. A part of MgB₂ was decomposed into metallic Mg and amorphous B. The grain morphology of MgB₄ was different with that of MgB₂

System design of spatial heterodyne spectrometer

Ye-Song; Fang-Yong-hua; Hong-Jin; Yang-Wei-feng; Qiao-Yan-li(Anhui Inst. of Opt. & Fine Mech., Chinese Acad. of Sci., Hefei, China)

Optics-and-Precision-Engineering. Dec. 2006; 14(6): 959-64

This paper analyses and studies the parameter design of a spatial heterodyne spectrometer (SHS). The basic concept and structure of SHvS is described and the dependence of resolution limit, power of resolution and spectral range on some critical parameters of optical components including grating parameters, pixels of detector, image lens and so on is introduced. By taking an integrated system design for example, the simulated result is presented. SHS system built and tested in the laboratory, the basic concepts and performance characteristics of the technique have been verified. Experimental results show that the achieved resolving power of the SHS system is 17 700 at 591 nm, and the spectral range is 574~591 nm. These results are coincident with the theoretical results well

Copyright infringement in a borderless world - does territoriality matter? Society of composers, authors and music publishers of Canada v. Canadian association of Internet providers [2004] 2 SCR 427

Leong-SHS; Saw-CL(Bus. Sch. Nat. Univ. of Singapore, Singapore)

International-Journal-of-Law-and-Information-Technology. Spring 2007; 15(1): 38-53

The recent decision of the Supreme Court of Canada in society of composers, authors and music publishers of Canada v Canadian association of Internet providers [2004] 2 SCR 427 is significant for two reasons: (a) the Canadian Supreme Court held that Internet service providers should be exempted from copyright liability as long as they provide only a conduit service in transmitting copyright materials between Internet users (a point which is consistent with many national copyright laws); (b) the majority of the Canadian Supreme Court arrived at the conclusion that the appropriate test to determine whether an infringement for the unauthorized transmission of online copyright material has occurred within the Canadian jurisdiction is the `real and substantial connection' test (LeBel J, however, dissented and was of the view that the correct test to apply is the `host server' test). This paper studies these two tests as propounded by the Canadian Supreme Court and assesses their strengths and weaknesses, especially in light of the territoriality principle in copyright law

Influence of hot pressing on microstructure and mechanical properties of combustion synthesized TiB₂-Cu-Ni composite

Hong-Changqing; Han-Jiecai; Zhang-Xinghong; Meng-Songhe(Center for Composite Mater., Harbin Inst. of Technol., China)

Journal-of-Materials-Processing-Technology. 23 March 2007; 183(2-3): 445-9

TiB₂-40Cu-8Ni ceramic-metal composite with the relative density of about 90% was prepared by combustion synthesis. In order to improve the mechanical properties, the hot pressing was conducted at 1200, 1250 and 1300degC, respectively. The microstructure, deformation behavior and mechanical properties were investigated. The results showed that the relative density and the flexural strength increased greatly after hot pressing. The morphology of titanium diboride (TiB₂) grain transformed from a near equal axis-like shape to a rod-like shape. The change of ceramic grain shape and the density have an important influence on the mechanical properties. The evolution of TiB₂ morphology and growth mechanism was analyzed according to TiB₂ crystal structure characteristics. [All rights reserved Elsevier]

Synthesis of pure powder of La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.825 by microwave-induced solution combustion method

Zhai-Yu-ling; Ye-Chang; Xiao-Jian-zhong(State Key Lab. of Die & Mould Technol., Huazhong Univ. of Sci. & Technol., Hubei, China)

Battery-Bimonthly. Oct. 2006; 36(5): 377-9

The method of microwave-induced solution combustion was used to prepare the powder of La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.825 (LS_0.1GM_0.2). For the more homogenous heating manner without thermal gradients in the microwave oven, the homogenous pure powder of LS_0.1GM_0.2 after calcination at 1400 degC for 9 h was obtained. The calcination behavior of the precursor powder was studied in the temperature range of 500~1400 degC. By this method, the desired perovskite phase with little secondary phases was existed before calcination. The grain size of the powder of LS_0.1GM_0.2 after calcination at 1400 degC for 9 h was about 2~3 mum. However, the density of the pellet was 5.43 g/cm³, lower than other reports for the mechanism of the combustion method itself

In-situ preparation of highly crystallized ZnO nanopowders by ultrasonic spraying combustion method

Lee-NH; Kim-JH; Oh-HJ; Kim-SJ(Dept. of Nano Sci. & Technol., Sejong Univ., South Korea)

Diffusion-and-Defect-Data-Part-B-Solid-State-Phenomena. 2007; 121-123: 1269-72

To obtain a mass production of nanocrystalline ZnO powders, equipment that combines the conventional self-sustaining combustion process (SCP) with the ultrasonic spraying combustion method (USCM) were applied. The droplet was sprayed into the reaction zone of the furnace to carry out USCM that produces softly agglomerated crystalline ZnO particle with spherical shape. It was confirmed that the ZnO powder was prepared from ultrasonic spraying combustion method having smaller primary particle size, spherical shape with weak agglomeration and larger specific surface area than from conventional self-sustaining combustion method. Synthesized nanocrystalline ZnO powders have primary particle size in a range of 20~30 nm, and specific surface area of about 20 m²/g under the optimum ultrasonic spray conditions

Mesomechanical strength model of nano-fibers composite ceramics

Liu-XQ; Ni-XH; Liu-YT; Han-BH(Mech. Eng. Coll., Hebei, China)

Diffusion-and-Defect-Data-Part-B-Solid-State-Phenomena. 2007; 121-123: 1157-60

Recent experiment showed that nano-fibers composite ceramics, fabricated through SHS process, can acquire high toughening and strengthening. Composite ceramics are mainly composed of fiber eutectic structures with random orientation, in which nanometer sized zirconia fibers are dispersed within the alumina matrix. First, it can be visualized that tensile force is transmitted from the matrix to the nano-fiber by means of shear stress that develop along the fiber- matrix interface. Then the mesomechanical strength model of the fiber eutectic structure is built. The longitudinal tensile stress of the fiber eutectic structure and shear stress on the surface of the fiber eutectic structure are obtained. They related to the volume fraction and slenderness ratio of the nano-fibers, and external strain of the fiber eutectic structure. Then considering random orientation of the fiber eutectic structure, as composite ceramics is subjected to tensile stress, external strain of the fiber eutectic structure can be determined. Finally, theoretical expression for the strength prediction of composite ceramics is gotten

Self-propagating high-temperature synthesis of La(Sr)Ga(Mg)O_3-delta for electrolyte of solid oxide fuel cells

Akiyama-T; Ishikawa-H; Enoki-M; Ishihara-T(Center for Adv. Res. of Energy Conversion Mater., Hokkaido Univ., Sapporo, Japan)

Journal-of-Alloys-and-Compounds. 14 March 2007; 430(1-2): 246-51

This paper describes self-propagating high-temperature synthesis (SHS) of an electrolyte for solid oxide fuel (SOFC), in comparison to a conventional solid-state reaction method (SRM). Doped-lanthanum gallate: La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-delta (LSGM9182) and LSGM9173 as the SOFC electrolyte, was prepared by the SHS and sintered at different temperatures, for measuring the electrical conductivity of the sintered LSGM and the power generating performance at 1073K, in comparison to the SRM. In the SHS, the LSGM powders with smaller size were obtained and easily sintered at the 100K-lower temperature, 1673K, than in the SRM. Most significantly, the electrical conductivity of the sintered LSGM9182 was as high as 0.11Scm^-1 and its maximum power density was a value of 245mWcm^-2 in the cell configuration of Ni/LSGM9182 (0.501mm in thickness)/Sm_0.5Sr_0.5CoO₃. The conclusion was that the proposed SHS-sintering method with many benefits of minimizing the energy requirement and the processing time in the production, easing temperature restriction for the sintering, and improving the electrolyte performance up to a conventional level is practicable for producing the LSGM-electrolyte of SOFC at an intermediate-temperature application. [All rights reserved Elsevier]

Stereo imaging and analysis of combustion process in a gas turbine combustor

Cheung-KY; Yang-Zhang(Sch. of Mech., Univ. of Manchester, UK)

Measurement-Science-and-Technology. Dec. 2006; 17(12): 3221-8

Quantitative digital 3D information extraction from a stereo imaging pair of a semi-transparent flame has been attempted in this paper. A semi-automatic image matching methodology has been adopted to overcome the very challenging problem of non-unique matching of semi-transparent flame. It is shown that the tracking of flame features in relation to the 3D position to the combustor wall surface is possible by combining optical 3D visualization and digital image reconstruction. Useful statistics can be obtained. 3D particle tracking has also been demonstrated. The complex 3D trajectory of a residual particle near one of the dilution holes of the combustor has been computed. A time-resolved analysis of flame positions from stable combustion mode to unstable mode has been carried out. The results show that the general flame in depth distribution is different under the stable, transition and unstable combustion modes. The most scattered in depth distribution is observed in the transition combustion mode. The technique is most suitable for practical devices with very limited optical access

Synthesis of Li(Co_0.8Ni_0.2-yAl_y)O₂ (yles0.02) by combustion method as a possible cathode material for lithium batteries

Kee-Suk-Nahm; Soo-Kyung-Jeong; Stephan-AM(Sch. of Chem. Eng. & Technol., Chonbuk Nat. Univ., Chonju, South Korea)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 15 Feb. 2007; 445-446: 657-62

The layered compounds, Li(Co_0.8Ni_0.2-yAl_y)O₂ (yles0.02) were synthesized by a self-sustaining solution combustion method with hexamethylenetetramine (HMTA) as a fuel. The prepared compounds were characterized by means of XRD, SEM and DSC studies. The precursors were also subjected to thermogravimmetry (TG) analysis. Li[Co_0.8Ni_0.2-yAl_y]O₂ (yles0.02)/Li cells have been assembled and were subjected to cycling studies at different C-rates. The substitution of Al³⁺-ions has considerably increased the structural and thermal properties of the compound. [All rights reserved Elsevier]

Seasonality indices for regionalizing low flows

Laaha-G; Bloschl-G(Inst. fur Angewandte Statistik, Univ. fur Bodenkultur Wien, Vienna, Austria)

Hydrological-Processes. 30 Nov. 2006; 20(18): 3851-78

In this study we examine three seasonality indices for their potential in regionalizing low flows. The indices are seasonality histograms (SHs) that represent the monthly distribution of low flows, a cyclic seasonality index (SI) that represents the average timing of low flows within a year, and the seasonality ratio (SR), which is the ratio of summer and winter low flows. The rationale of examining these indices is the recognition that summer and winter low flows are subject to important differences in the underlying hydrological processes. We analyse specific low flow discharges q₉₅, i.e. the specific discharge that is exceeded on 95% of all days at a particular site. Data from 325 subcatchments in Austria, ranging in catchment area from 7 to 963 km², are used in the analysis. In a first step, three seasonality indices are compared. Their spatial patterns can be interpreted well on hydrological grounds. In a second step, the indices are used to classify the catchments into two, three, and eight regions based on different combinations of the indices. In a third step, the value of the seasonality indices for low flow regionalization is examined by comparing the cross-validation performance of multiple regressions between low flows and catchment characteristics. The regressions make use of the three seasonality-based classifications. The results indicate that grouping the study area into two regions and three regions and separate regressions in each region gives the best performance. A global regression model yields the lowest performance and a global regression model that uses different calibration coefficients in each of the eight regions only performs slightly better. This suggests that separate regression models in each of the regions are to be preferred over a global model in order to represent differences in the way catchment characteristics are related to low flows

Fabrication of TiC-20mass%Ni cermet using MA-PCS process

Kobayashi-K; Ozaki-K(Mater. Res. Inst. for Sustainabie Dev., Nat. Inst. of Adv. Ind. Sci. & Technol., Nagoya, Japan)

Materials-Transactions. Oct. 2006; 47(10): 2561-5

Mechanical alloying and pulsed-current sintering were used to synthesize TiC-20mass%Ni cermet with ultra-fine TiC particles dispersed. The mixture, in which Ti and Ni elements were uniformly distributed, was prepared by mechanical alloying of Ti, Ni and graphite powders for 18 ks. TiC particles were produced in the mixture milled for longer than 18 ks through a combustion synthesis reaction during heating. Mechanically alloyed Ti-C-Ni composite powder milled for 18 ks was consolidated using pulsed-current sintering at 1223 K under 70 MPa pressure. The sintered compact consisted of TiC and Ni. The average grain size of TiC particles in the sintered body was 0.80 mum. The relative density of the sintered compact reached 92% of the theoretical one: its Vickers hardness was 2260 Hv

PRICM-5

Zhong-EZY; Saka-H; Kim-TH; Holm-EA; Han-YF; Xie-XS)

Materials-Science-Forum. 2006; 510-511: 1036

This indispensable work is the fifth in a series of international conferences devoted to advanced materials and processing. The conferences, which are held every three years, are jointly sponsored by the Chinese Society for Metals (CSM), the Japan Institute of Metals (JIM), the Korean Institute of Metals and Materials (KIM), and the Minerals, Metals and Materials Society (TMS), and organized by them in rotation. The purpose of this international conference, PRICM, is to provide a forum for the exchange of technical and scientific information, which is always of great benefit to researchers, manufacturers and end-users. The proceedings comprise 988 papers from 20 symposia, and the main topics covered are: structural materials, functional materials, materials processing and characterization. The five-volume set is further divided into carefully targeted sections: advanced ferrous alloys light metals; intermetallics composite materials; advanced ceramics; advanced nuclear materials; layered and graded materials; combustion synthesis; electronic materials; smart materials magnetic materials; biomaterials; hydrogen-absorbing materials; advanced melt processing, casting spray forming superplasticity modeling and simulation of materials and processes; amorphous, quasicrystalline and nanocrystalline materials; thin-film materials grain boundary, interface materials characterization & evaluation. Altogether, the set offers an incomparable wealth of up-to-date information concerning this whole field

Analysis on equivalent circuit of Ce_0.8Gd_0.2O_1.9 film

Xie-De-ming; Tong-Shao-ping; Shao-Hai-bo(MOE Key Lab. of Mech. Manuf. & Autom., Zhejiang Univ. of Technol., China)

Chinese-Journal-of-Power-Sources. 2006; 30(12): 993-6

The electrolyte Ce_0.8Gd_0.2O_1.9(CGO) for solid oxide fuel cell was prepared by combustion synthesis method of citric acid-nitrate. The complex impedance of CGO film was measured. The results show that the complex impedance spectroscopy is relevant to test temperature. The equivalent circuit model of the CGO film was recommended, and the complex impedance spectroscopy of the CGO film was analyzed at different test temperatures. The relationship between electrical conductivity and temperature was found and that was conformed to Arrhenius law. The conductivity of CGO pellet reaches to 0.044 Smiddotm^-1 at 800 degC

Porous Ni-Ti ignition and combustion synthesis

Zanotti-C; Giuliani-P; Terrosu-A; Gennari-S; Maglia-F(Milano Labs., IENI-CNR, Milano, Italy)

Intermetallics-. March 2007; 15(3): 404-12

The self-propagating high-temperature synthesis of Ni-Ti mixtures was investigated with particular attention to the ignition step. Ignition was performed using an integrated laser diode system which allows fine control of the heating and ignition processes. The experimental parameters controlling the ignition step such as thermal conductivity, surface absorbance, ignition temperature and energy were obtained both experimentally and by numerical simulation as a function of initial stoichiometry, reactants particle size, and heating cycle. Appropriate ignition conditions were searched in order to minimize the thermal gradients inside the pellet obtaining constant reaction temperature and velocity. Dependencies of reaction front velocity and reaction temperature on the pre-heating one were reported too. [All rights reserved Elsevier]

Gravity effects on reactive settling in the Al-W system in SHS

Munir-ZA; Unuvar-C; Fredrick-DM; Anselmi-Tamburini-U; Shaw-BD; Manerbino-A; Guigne-JY(Dept. of Chem. Eng. & Mater. Sci., Univ. of California, Davis, CA, USA)

Intermetallics-. March 2007; 15(3): 294-304

Reactive settling in the system Al-W was investigated under different gravitational conditions and applied electric field. Samples of 0.1W+1.0Al were reacted under conditions of 0, 0.16 (lunar gravity), 1.0, and 1.8g. Non-terrestrial gravity experiments were carried out onboard NASA KC-135 aircraft. The reactive settling involved a process of dissolution of W into liquid Al, the formation of WAl₄, and the settling of the partially reacted W particles. Settling of W was absent under 0g, partial settling was observed under 0.16g, and complete settling was observed under 1.0 and 1.8g conditions. The effect of temperature on settling and microstructural evolution was investigated. The results are interpreted in terms of competing processes of settling, reactivity, and nucleation of the aluminide. [All rights reserved Elsevier]

Shear initiated reactions in energetic and reactive materials

Mcuken-B; Martinez-Pacheco-M; Verbeek-HJ; Bouma-RHB; Katgerman-L(Security & Safety, TNO Defense, Rijswijk, Netherlands)

Multifunctional-Energetic-Materials.-Symposium-Materials-Research-Society-Symposium-Proceedings-Vol.896. 2006: 203-10

Deformation of energetic materials may cause undesired reactions and therefore hazardous situations. The deformation of an energetic material and in particular shear deformation is studied in this paper. Understanding of the phenomena leading to shear initiation is not only necessary to explain for example the response of munitions to intrusions or large deformations imposed in storage and transportation accidents. A fundamental understanding of shear initiation also provides the opportunity to initiate energetic materials in a different and controlled manner, and possibly with a tailored reaction rate of the material. Several small and large scale experiments have been performed in which a shear deformation is imposed onto high explosives as well as thermite based reactive materials. Experiments are numerically simulated in order to correlate small and large scale experiments and understand the initiation mechanisms

On-chip initiation and burn rate measurements of thermite energetic reactions

Apperson-S; Bhattacharya-S; Gao-Y; Subramanian-S; Hasan-S; Hossain-M; Shende-RV; Redner-P; Kapoor-D; Nicolich-S; Gangopadhyay-K; Gangopadhyay-S(Dept. of Electr. & Comput. Eng., Missouri Univ., Columbia, MO, USA)

Multifunctional-Energetic-Materials.-Symposium-Materials-Research-Society-Symposium-Proceedings-Vol.896. 2006: 81-6

Burn rates of various nano-energetic composites were measured by two techniques; on-chip method and conventional optical method. A comparison is presented to confirm the validity of on-chip method. On-chip initiators were prepared using platinum heater films and nanoenergetic composites. Thin film Pt heaters were fabricated with different dimensions and ignition delay was studied using a nano-energetic composite of CuO nano-rods and Al-nano-particles. The ignition delay as a function of electrical power is presented for the same energetic composite. Heater with smaller surface area is found to be more efficient, which may be due to the lower heat losses

The application of energetic SHS reactions in the synthesis of multi-functional bone tissue engineering and drug delivery systems

Ayers-R; Burkes-D; Gottoli-G; Yi-HC; Guigne-JY; Moore-JJ(Inst. for Space Resources, Colorado Sch. of Mines, Golden, CO, USA)

Multifunctional-Energetic-Materials.-Symposium-Materials-Research-Society-Symposium-Proceedings-Vol.896. 2006: 25-37

The term combustion synthesis, or self-propagating high temperature synthesis (SHS), refers to an exothermic chemical reaction process that utilizes heat generated within the reaction to ignite and sustain a propagating combustion wave through reactants to produce desired product(s). The products of combustion synthesis normally are extremely porous: typically 50 percent of theoretical density. Advantages of combustion synthesis over traditional processing routes, e.g., sintering, in the production of advanced materials such as ceramics, intermetallic compounds and composites include process economics, simplicity of operation, and low energy requirements. However, the high exothermicity and rapid combustion propagation rates necessitate a high degree of control of these reactions. One research area being conducted in the Institute for Space Resources (ISR) at the Colorado School of Mines (CSM) is the application of combustion synthesis (SHS) to synthesize advanced, engineered porous multiphase/heterogeneous calcium phosphate (HCaP), NiTi, NiTi-TiC, TiB-Ti, TiC-Ti for bone tissue engineering and drug delivery systems. Such material systems require a complex combination of properties that can be truly classified as multifunctional materials. The range of properties includes: an overall porosity of 40-60% with a pore size of 200-500 mum; mechanical properties (compression strength and Young's modulus) that match those of natural bone to avoid `stress shielding'; and a surface chemistry that is capable of facilitating bone growth and mineralization. The paper will discuss the synthesis of porous multiphase/heterogeneous calcium phosphate (HCaP), NiTi, NiTi-TiC, TiB-Ti, TiC-Ti for bone tissue engineering and drug delivery systems

Weld defect formation in rail thermite welds

Chen-Y; Lawrence-FV; Barkan-CPL; Dantzig-JA(Energy Technol. Div., Argonne Nat. Lab., IL, USA)

Proceedings-of-the-Institution-of-Mechanical-Engineers,-Part-F-Journal-of-Rail-and-Rapid-Transit. Dec. 2006; 220(F4): 373-84

A previously developed heat transfer model is used to study the influence of welding parameters on weld defect development in thermite welds. Weld defect formation maps are constructed from a series of heat transfer simulations. For the current normal rail thermite welding conditions, it is found that shrinkage cavity formation can be avoided but cold-lap and centre-line defects are likely to occur. This study also shows that increasing the preheating time or the liquid temperature can suppress the development of cold-lap and centre-line defects but can lead to a slightly higher microporosity content in the railhead as well. Alternatively, it is found that instead of increasing the preheating time or the liquid temperature, the same effect can be achieved by increasing the 25 mm weld gap (standard) to a slightly larger value

Self-propagating high-temperature synthesis of barium titanate and subsequent densification by spark plasma sintering (SPS)

Orru-R; Cao-G; Licheri-R; Fadda-S; Buscaglia-V(Dipt. di Ingegneria Chimica e Mater., Univ. degli Studi di Cagliari, Italy)

Journal-of-the-European-Ceramic-Society. 2007; 27(5): 2245-53

This paper describes the self-propagating high-temperature synthesis (SHS) of perovskitic oxides, specifically BaTiO₃, and their subsequent densification by spark plasma sintering. With the final goal of obtaining dense nanostructured materials, SHS products were mechanically treated at different milling time conditions, before densification. It was found that the grain size of ball milled powders decreases with increasing milling time, this effect being more evident at early stages of milling. Depending upon the ball milling (BM) conditions adopted, crystallite size in the range 15-70nm was obtained. After milling for 5h, the resulting powders (20-30nm) were sintered by SPS, at 700A, for different periods of time. By properly varying sintering time in the interval 70-140s, it is possible to obtain products with relative density in the range 66-99%, respectively. In particular, grain growth during sintering was found to be limited (below 50nm) if the electric current is applied for time intervals equal to or less than 100s. The observed dielectric properties are typical of a nanocrystalline BaTiO₃ ceramic. [All rights reserved Elsevier]

Enhanced white light emission from Dy³⁺/Ce³⁺ codoped GdAl₃(BO₃)₄ phosphors by combustion synthesis

Zhang-QY; Yang-CH; Pan-YX(Key Lab of Special Functional Mater., South China Univ. of Technol., Guangzhou, China)

Materials-Science-and-Engineering-B-Solid-State-Materials-for-Advanced-Technology. 25 Feb. 2007; 137(1-3): 195-9

Polycrystalline GdAl₃(BO₃)₄ sub-micrometer-sized phosphors doped with rare-earth ions has been prepared by combustion synthesis method with urea. The phosphors have been characterized by X-ray diffractometer, thermogravimetric analysis/different scanning calorimeter and scanning electron microscope. Intense emissions centred at 480, 573 and 664nm, originated from the transitions of ⁴F₉2/rarr⁶H₁₅2/, ⁴F₉2/rarr⁶H₁₃2/ and ⁴F₉2/rarr⁶H₁₁2/ of Dy³⁺, respectively, have been observed upon excitation of ultraviolet-blue light. Concentration quenching occurs when Dy³⁺ ions is beyond 3 mol.% due to the cross-relaxation of Dy³⁺. Codoping of Ce³⁺ has enhanced the luminescence of Dy³⁺ quite significantly and the optimum dopant concentration of Ce³⁺ is 7mol.%. It is noted that the values of yellow-to-blue integral intensity of codoped GdAl₃(BO₃)₄:Dy,Ce phosphors decrease with an increase of Ce³⁺ concentration. The chromaticity coordinates and colour temperatures of Dy³⁺ doped and/or Dy³⁺/Ce³⁺ codoped GdAl₃(BO₃)₄ have been calculated and analysed with Commission Internationale l'Eclairage (CIE) diagrams. [All rights reserved Elsevier]

Sol-gel auto-combustion synthesis of samarium-doped TiO₂ nanoparticles and their photocatalytic activity under visible light irradiation

Qi-Xiao; Zhichun-Si; Zhiming-Yu; Guanzhou-Qiu(Sch. of Resources Process. & Bioeng., Central South Univ., Changsha, China)

Materials-Science-and-Engineering-B-Solid-State-Materials-for-Advanced-Technology. 25 Feb. 2007; 137(1-3): 189-94

High photocatalytic activity of Sm³⁺-doped TiO₂ nanocrystalline under visible light has been successfully prepared by sol-gel auto-combustion technique. The samples were characterized by X-ray diffraction, UV-vis diffuse reflectance spectroscopy and photoluminescence (PL) spectra. UV-vis diffuse reflectance spectra showed a slight shift to longer wavelengths and an extension of the absorption in the visible region for almost all the samarium-doped samples, compared to the non-doped sample. The results of photocatalytic decomposition of methylene blue (MB) over 0.5mol% Sm³⁺-TiO₂ prepared at various calcinations temperatures show that the sample calcinated at 600degC consists of mixed phases with 51.61% rutile shows the highest photocatalytic activity, which suggests the existence of a synergistic effect between anatase and rutile powders under visible light. Doping with the samarium ions significantly enhanced the overall photocatalytic activity for MB degradation under visible light irradiation because the larger specific surface area and the higher separation efficiency of electron-hole pairs were obtained simultaneously for Sm³⁺-doped TiO₂ nanocrystalline. It was found that there were certain relationships between PL spectra and photocatalytic activity, namely, the stronger the PL intensity, the larger the content of oxygen vacancies and defects, the higher the photocatalytic activity. Therefore, in this study, 0.5mol% may be the most suitable content of Sm³⁺ in the titania, at which the recombination of photoinduced electrons and holes could be effectively inhibited and thereby the highest photocatalytic activity is formed. [All rights reserved Elsevier]

Superelastic property of Ti-Ni alloy produced by casting after SHS

Kitamura-K; Kuchida-T; Inaba-T; Tokuda-M; Yoshimi-Y(Dept. of Mechanical Eng., Nagano Nat. Coll. of Technol., Japan)

Materials-Transactions. Nov. 2006; 47(11): 2867-70

The superelastic properties of cast Ti-Ni shape memory alloy (SMA) were studied. Base materials were prepared as a melting method ingot and as a self-propagating high-temperature synthesis (SHS) ingot. The composition of these ingots was Ti-50.8 at%Ni. Each ingot was cast into a rod shape by centrifugal casting. The heat-treatment conditions were 773 K for - 1.8 ks and 773 K-1.8 ks rarr 873 K-3.6 ks. Shape memory characteristics were measured by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and a tensile test. All casting specimens have good shape memory characteristics. According to DSC measurements, the melt method specimens show gravity segregation

Synthesis and characterization of submicron-sized LiNi₁3/Co₁3/Mn₁3/O₂ by a simple self-propagating solid-state metathesis method

Zi-Feng-Ma; Yu-Shi-He; Xiao-Zhen-Liao; Yi-Jiang(Dept. of Chem. Eng., Shanghai Jiao Tong Univ., China)

Journal-of-Power-Sources. 1 Jan. 2007; 163(2): 1053-8

Submicron-sized LiNi₁3/Co₁3/Mn₁3/O₂ cathode materials were synthesized using a simple self-propagating solid-state metathesis method with the help of ball milling and the following calcination. A mixture of Li(ac)middot2H₂O, Ni(ac)₂middot4H₂O, Co(ac)₂middot4H₂O, Mn(ac)₂middot4H₂O (ac=acetate) and excess H₂C₂O₄middot2H₂O was used as starting material without any solvent. XRD analyses indicate that the LiNi₁3/Co₁3/Mn₁3/O₂ materials were formed with typical hexagonal structure. The FESEM images show that the primary particle size of the LiNi₁3/Co₁3/Mn₁3/O₂ materials gradually increases from about 100nm at 700degC to 200-500nm at 950degC with increasing calcination temperature. Among the synthesized materials, the LiNi₁3/Co₁3/Mn₁3/O₂ material calcined at 900degC exhibits excellent electrochemical performance. The steady discharge capacities of the material cycled at 1C (160mAg^-1) rate are at about 140mAhg^-1 after 100cycles in the voltage range 3-4.5V (versus Li⁺/Li) and the capacity retention is about 87% at the 350th cycle. [All rights reserved Elsevier]

Wire design influence on the melting behavior in the high velocity combustion wire spraying process

Wielage-B; Rupprecht-C; Wank-A; Zimmermann-S; Landes-K(Chemnitz Univ. of Technol., Germany)

Advanced-Engineering-Materials. July 2006; 8(7): 640-4

This paper evaluates the sprayability of cored wires. For this purpose 316L is chosen as coating material, because it is available in all different types of wire design. To verify the differences between conventional and high velocity combustion wire spraying both methods are carried out, and for process optimization HVCW spraying is researched concerning its characteristic by the use of a high speed camera. Also the melting behavior of the wire tip and the spray jet is monitored in order to evaluate the process stability. The particle velocities at the spraying distance are determined. Finally the wire design is correlated to the coating properties at different spraying distances to obtain information about effective application of the HVCW technology

Solid-state diffusion-dissolution-precipitation mechanism of combustion synthesis of Mg₂Ni

Chen-Xiu-juan; Liu-Xue-long(State Key Lab. of Gansu Adv. Non-ferrous Metal Mater., Lanzhou Univ. of Technol., China)

Chinese-Journal-of-Nonferrous-Metals. Oct. 2006; 16(10): 1771-7

The pure Mg₂Ni intermetallic was synthesized by self-propagating combustion mode, and thermal explosion mode, respectively. And the reaction process of thermal explosion was researched under different preheat temperatures. The results show that solid combustion exists at lower temperatures, and the reaction extent increases with decreasing preheat rate. Further more, the synthesis is incomplete for the weak exothermal system. A further experiment of combustion front quenching (CFQ) was brought to success in cylindrical steel die by adding some Al-Ti-C powder that was accepted high exothermic system on the top of Mg-Ni specimen. The phase structure changes of all region in the quenched sample during the combustion synthesis were observed by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffractometry. The results show that the synthesis of Mg₂Ni is direct rather than through other intermediates

Mechanical properties and high temperature oxidation behavior of La₂O₃-Mo₅Si₃/MoSi₂ composite

Yan-Jian-hui; Li-Yi-min; Zhang-Hou-an; Tang-Si-wen(State Key Lab. of Powder Metall., Central South Univ., Changsha, China)

Chinese-Journal-of-Nonferrous-Metals. Oct. 2006; 16(10): 1730-5

The MoSi₂-based composites containing La₂O₃ earth and different volume fractions of Mo₅Si₃ were synthesized by self-propagating high temperature synthesis. The mechanical properties of MoSi₂ matrix composites and high temperature oxidation behavior were studied. The results show that additions of La₂O₃ earth and Mo₅Si₃ refine the grain size of the MoSi₂ matrix composite and improve the flexure strength and fracture toughness at room temperature in contrast with pure MoSi₂. The strengthening mechanism of La₂O₃-MO₅Si₃/MoSi₂ is fine-grain strengthening, and the toughening mechanisms are fine-grain toughening, crack deflection, crack branching and crack microbridging. When the Mo₅Si₃ content does not exceed 30% (mole fraction) , the oxidation resistance of La₂O₃-Mo₅Si₃/MoSi₂ decreases with the increase of Mo₅Si₃ content. However, the RE-40% Mo₅Si₃MoSi₂ (mole fraction) composite occurs pesting because of the poor oxidation resistance of Mo₅Si₃, decrease of relative density and grain refinement of the composites. The La₂O₃-Mo₅Si₃/MoSi₂ composite has optimal mechanical properties and high temperature oxidation resistance with additions of 0.8% La₂O₃ (mass fraction) and 5% Mo₅Si₃ (mole fraction)

Synthesis and dielectric property of perovskite-type LaMnO₃ nanoparticle

Jie-Sun; Zhenhua-Zhang; Xiaohui-Cao(Sch. of Environ.& Chem. Eng., Shenyang Ligong Univ., China)

Diffusion-and-Defect-Data-Part-B-Solid-State-Phenomena. 2007; 121-123: 967-70

The perovskite-type nanocrystal LaMnO₃ was prepared using sol-gel auto-combustion method with citric acid as the chelating agent. Some analytical methods consisted of FT-IR, XRD, TEM and wave-guide method were used to characterize the gel and the final products. The metal ions coordination compound, obtained from nitrate and citrate, underwent an auto-combustion process and voluminous ashes formed when calcining the complex in the air. From the result of the dielectric property. It was shown that the dielectric coefficient curves and dielectric loss curve of LaMnO₃ nanocrystals were smooth in the range of 8-11 MHz. The dielectric loss can be observed obviously in the measured range

Flame synthesis and characterization of rare-earth (Er³⁺, Ho³⁺, and Tm³⁺) doped upconversion nanophosphors

Xiao-Qin; Yokomori-T; Yiguang-Ju(Dept. of Mech. & Aerosp. Eng., Princeton Univ., NJ, USA)

Applied-Physics-Letters. 12 Feb. 2007; 90(7): 73104-1-3

Rare-earth doped yttria upconversion nanophosphors were synthesized using a single-step gas-phase flame synthesis method. The phosphors were characterized by x-ray diffractometry, transmission electron microscopy, and fluorescence spectroscopy. The dependence of multiphoton emissions on excitation power was examined. The results show that particle size, morphology, and photoluminescence intensity are strongly affected by flame temperature. The as-prepared nanophosphors are mostly single crystallites with an average size less than 30 nm. Under laser diode excitation, bright blue, green, and red emissions are visible from these phosphors which show potential applications in biological imaging and photodynamic therapy

The effect of nanopowder attributes on reaction mechanism and ignition sensitivity of nanothermites

Puszynski-JA; Bulian-CJ; Swiatkiewicz-JJ(Dept. of Chem. & Biol. Eng., South Dakota Sch. of Mines & Technol., Rapid City, SD, USA)

Multifunctional-Energetic-Materials.-Symposium-Materials-Research-Society-Symposium-Proceedings-Vol.896. 2006: 147-58

Nanothermite composites have several properties that are not typical of conventional thermites. The nanoscale size of individual reactants is responsible for the significant differences in these properties, especially the rate of energy release and mechanism of combustion front propagation. Several thermite mixtures were investigated, including Al-Fe₂O₃, Al-CuO, Al-MoO₃, and Al-Bi₂O₃. Previous studies have reported on the behavior of these mixtures during unconfined burning and on the characterization of particle attributes such as particle size, surface area, and reactive metal content. This study was focused on several other attributes, including mixing of nanoreactants in water and measurements of reaction kinetics and combustion front propagation characteristics under confined conditions. The nanoscale nature of the thermite components also has an effect on the kinetics of the reaction. Differential scanning calorimetry was used to determine activation energy of these reacting systems. Several experimental setups were used to monitor the nanothermite mixtures during combustion. The mixtures were monitored during combustion in small diameter tubes using high speed video technology and a pressure sensor system. These tests were used to characterize combustion propagation under confined conditions and to determine the effect of pressure and mixture density on propagation rate. Experiments were also performed using both a closed volume pressure cell and recoil force cell to measure the reactive energy of the mixtures

Energetic decomposition of high-nitrogen metal complexes and the formation of low-density nano-structured metal monoliths

Tappan-BC; My-Hang-Huynh; Hiskey-MA; Chavez-DE; Luther-EP; Mang-JT; Son-SF(Los Alamos Nat. Lab., NM, USA)

Multifunctional-Energetic-Materials.-Symposium-Materials-Research-Society-Symposium-Proceedings-Vol.896. 2006: 15-24

Metal complexes of the energetic high-nitrogen ligand, bistetrazole amine (BTA) were ignited in inert environments and their decomposition characteristics were determined. These molecules were found to have the unique properties of a comparatively slow burning rate with very little pressure dependency, unlike most energetic, metal-containing molecules which tend to detonate, rather than burn steadily. This process resulted in unprecedented ultra-low-density, nano-structured, transition metal monoliths, useful as a self-propagating combustion synthesis technique. The resulting nanostructured metal monolithic foams formed in the post flame-front dynamic assembly have remarkably low densities down to 0.011 g cm^-3 and extremely high surface areas as high as 270 m² g^-1. In this work we discuss primary the production of iron monoliths, however have produced monolithic nano-porous metal foams via this method with cobalt, copper and silver metals as well. We expect to be able to apply this to many other metals and to be able to tailor the resulting structure significantly

In vitro corrosion resistance of porous NiTi intervertebral fusion devices

Schrooten-J; Assad-M; Van-Humbeeck-J; Leroux-MA(Dept. of Metall. & Mater. Eng., Katholieke Univ. Leuven, Belgium)

Smart-Materials-and-Structures. Feb. 2007; 16(1): S145-54

Porous titanium-nickel (PTN) intervertebral fusion devices, produced by self-propagating high-temperature synthesis, represent an alternative to traditional long-term implants in the orthopaedic field. PTN promotes tissue ingrowth and has succeeded short-term and long-term biocompatibility in vivo testing. In this in vitro study, the PTN morphology was characterized using microfocus computer tomography (muCT) in order to calculate the active PTN surface. Potentiodynamic polarization testing was then performed to evaluate the in vitro corrosion resistance of PTN devices in Hanks' based salt solution. Direct coupling experiments of PTN with Ti6Al4V were also performed in order to establish the galvanic corrosion resistance of PTN intervertebral implants in the presence of potential Ti6Al4V supplemental fixation devices. Compared to the behaviour of other orthopaedic biomaterials and solid NiTi devices, PTN devices showed a level of corrosion resistance that is comparable to other NiTi devices and acceptable for the intended orthopaedic application. Further improvement of the corrosion resistance is still possible by specific electrochemical surface treatments

Effect of heating rate on the crystal composition of ferroelectric lithium niobate crystallites

Dongfeng-Xue; Meinan-Liu(Dept. of Mater. Sci. & Chem. Eng., Dalian Univ. of Technol., China)

Journal-of-Alloys-and-Compounds. 16 Jan. 2007; 427(1-2): 256-9

A series of lithium niobate powders were synthesized by the combustion method at different heating rates. The effect of heating rate on the crystal composition of lithium niobate powders was investigated by powder X-ray diffraction measurements. It has been found that the lithium content in the as-synthesized lithium niobate powders increases with decreasing the heating rate. On the basis of the existed structure-property relationship of lithium niobate single crystals, it was concluded that high quality lithium niobate powders can be effectively synthesized at a lower heating rate (in the range of 5-10degC/min) by the combustion method. [All rights reserved Elsevier]

Multicomponent adhesive hard sphere models and short-ranged attractive interactions in colloidal or micellar solutions

Gazzillo-D; Giacometti-A; Fantoni-R; Sollich-P(Dipt. di Chimica Fisica, Univ. di Venezia, Italy)

Physical-Review-E-Statistical,-Nonlinear,-and-Soft-Matter-Physics. Nov. 2006; 74(5): 51407-1-14

We investigate the dependence of the stickiness parameters t_ij=1/(12tau_ij)-where the tau_ij are the conventional Baxter parameters-on the solute diameters sigma_i and sigma_J in multicomponent sticky hard sphere (SHS) models for fluid mixtures of mesoscopic neutral particles. A variety of simple but realistic interaction potentials, utilized in the literature to model short-ranged attractions present in real solutions of colloids or reverse micelles, is reviewed. We consider: (i) van der Waals attractions, (ii) hard-sphere-depletion forces, (iii) polymer-coated colloids, and (iv) solvation effects (in particular hydrophobic bonding and attractions between reverse micelles of water-in-oil microemulsions). We map each of these potentials onto an equivalent SHS model by requiring the equality of the second virial coefficients. The main finding is that, for most of the potentials considered, the size-dependence of t_ij(T,sigma_i,sigma_J) can be approximated by essentially the same expression, i.e., a simple polynomial in the variable sigma_isigma_J/sigma_ij², with coefficients depending on the temperature T, or-for depletion interactions-on the packing fraction eta₀ of the depletant particles

Europium luminescence enhancement in Al₂O₃:Eu³⁺ powders prepared by direct combustion synthesis

Rakov-N; Maciel-GS; B-WL; de-Araujo-CB(Univ. Fed. do Vale do Sao Francisco, Pernambuco, Brazil)

Journal-of-Applied-Physics. 1 Feb. 2007; 101(3): 36102-1-3

The luminescence properties of Eu³⁺:Al₂O₃ powders prepared via low temperature direct combustion synthesis was investigated. It was observed that the heat treatment of the powders modifies the dynamics of the radiative transition ⁵D₀rarr⁷F₂ of Eu³⁺ (1.0 mol %) and produces an enhancement of the luminescence intensity by nearly one order of magnitude. The luminescence enhancement is attributed to the presence of Eu³⁺ in alpha-Al₂O₃ crystalline phase as the heat treatment drastically reduces the amount of amorphous Al₂O₃ phases present in the powder

Electrochemical performance of anode-supported intermediate temperature solid oxide fuel cells fed with hydrogen sulfide

Tan-Wenyi; Zhong-Qin(Sch. of Chem. Eng., Nanjing Univ. of Sci. & Technol., China)

Journal-of-the-Chinese-Ceramic-Society. 2006; 34(8): 970-4

A glycine-nitrate combustion process was adopted to prepare samaria doped ceria [(CeO₂)_1-2x(Sm₂O₃)_x,SDC] electrolyte on NiO-SDC anode substrate. The electrochemical performance of H₂S-Air solid oxide fuel cells (SOFCs) was characterized at different intermediate temperatures and H₂S flow rates, r(H₂S). The results demonstrate that the open circuit voltage (OCV) of SOFCs increases exponentially with the H₂S flow rate, and the electrochemical performance is improved at higher flow rates except r(H₂S)=80 mL/min. The descent of voltage at r(H₂S)=80 mL/min appears in the higher current density range, which can be attributed to the concentrated polarization and the fact that Ni particles in anodes are corrupted by H₂S. The influence of temperature on OCV seems complicated, although the polarization curve of H₂S-Air SOFC based on ceria electrolyte is improved at elevated temperatures

Synthesis of red-emitting phosphors Ca_1-xSr_xS:Eu²⁺ used in white light emitting diodes by combustion

Yang-Zhiping; Li-Xu; Li-Xingmin; Yang-Yong; Liu-Yufeng; Xu-Xiaoling; Xiong-Zhijun(Coll. of Phys. Sci. & Technol., Hebei Univ., China)

Journal-of-the-Chinese-Ceramic-Society. 2006; 34(8): 966-9

The powder of Ca_1-xSr_xS:Eu²⁺ was synthesized using combustion with ignition temperatures of 500-550degC by oxidation-reduction reaction of the mixed metal nitrate and sulfourea. The products of Ca_1-xSr_xS:Eu²⁺ are an efficiency red phosphor using in white light emitting diodes. The X-ray diffraction patterns show that pure Ca_1-xSr_xS:Eu²⁺ phosphors are obtained; the excitation and emission spectra show that the phosphor is excited effectively by visible light from 430 nm to 500 nm and emitted red light from 600 nm to 650 nm. Compared with the solid-state method, the combustion method has the advantages of less time, lower temperature, and only a slight change in the emission spectra. Sulfourea was found to be an effective reducing agent because it enhances the reaction and is cheaper than other reducing agents

Structure and properties of MASHS titanium aluminide-based powder alloyed with chromium

Talaka-T; IIyuschenko-A; Letsko-A; Hasak-T(Powder Metall. Inst., Minsk, Belarus)

Materials-Science-Forum. 2007; 534-536: 1589-92

Structure and properties of MASHS powder Ti-46Al-8Cr, at. %, have been investigated. The powder is characterized by the multiphase dispersed strengthened structure with coherent precipitates/matrix bonding. Main structural constituents of the powder are titanium aluminides alloyed with chromium: gamma-TiAl(Cr), Al_0.67/Cr_0.08Ti_0.25 and alpha₂-Ti₃Al(Cr). Average powder microhardness is 313 H_v0.25. High-quality detonation coatings with high hardness (940-1100 H_v) and low porosity (less than 1%) have been obtained from the synthesized powder. The coatings exhibit good oxidation behaviour at 900degC

Ni₃Al-Fe-Cr alloy processed by combined mechanical alloying-reactive synthesis

Orban-RL; Lucaci-M(Cluj-Napoca Techn. Univ., Romania)

Materials-Science-Forum. 2007; 534-536: 1581-4

Property modification of Ni₃Al with alloying addition of Fe and Cr was investigated through MA and subsequent SHS processes. Fe addition brought about high temperature strengthening effect and formed a Ni-Fe compound in the liquid grain boundary phase of Ni₃Al structure and Cr addition showed a retarded homogenization. Homogenized Ni₃Al composition with Fe and Cr addition by MA and SHS showed better mechanical resistance and deformability in the compression tests at temperatures up to 800degC than the same composition processed by classical PM routes

Thermal stability and properties of Cu-TiB₂ nanocomposites prepared by combustion synthesis and spark-plasma sintering

Dae-Hwan-Kwon; Thuy-Dang-Nguyen; Dina-Dudina; Jong-Won-Kum; Pyuck-Pa-Choi; Ji-Soon-Kim; Young-Soon-Kwon(Res. Center for Machine Parts & Mater. Process., Ulsan Univ., South Korea)

Materials-Science-Forum. 2007; 534-536: 1517-20

In the present work, Cu-TiB₂ nanocomposite powders were synthesized by combining high-energy ball-milling of Cu-Ti-B mixtures and subsequent self-propagating high temperature synthesis (SHS). Cu-40wt.%TiB₂ powders were produced by SHS reaction and ball-milled. The milled SHS powder was mixed with Cu powders by ball milling to produce Cu-2.5wt.%TiB₂ composites. TiB₂ particles less than 250nm were formed in the copper matrix after SHS-reaction. The relative density, electrical conductivity and hardness of specimens sintered at 650-750 degC were nearly 98%, 83%IACS and 71H_rB, respectively. After heat treatment at 850 to 950 degC for 2 hours under Ar atmosphere, hardness was descended by 15%. Our Cu-TiB₂ composite showed good thermal stability at elevated temperature

Structure peculiarities of nanocomposite powder Fe40Al/Al₂O₃ produced by MASHS

Talaka-T; Grigorieva-T; Vitiaz-P; Lyakhov-N; Letsko-A; Barinova-A(Powder Metall. Inst., Minsk, Belarus)

Materials-Science-Forum. 2007; 534-536: 1421-4

Structure investigation results for MASHS powder Fe40Al/Al₂O₃ are presented. The powder structure formation proceeds via two stages. On the first step (mechanical activation) aluminothermal reaction takes plays in the system Fe+Al+Fe₂O₃, leading to formation of nanocomposite precursor Fe-Al-Al₂O₃. On the second step (SHS), iron and aluminum reacts, forming intermetallic FeAl. As-synthesized composite powder completely inherits the precursor structural morphology in spite of the phase transformations taking place during the production process. Such a production route provides the formation of intergrowth nanocomposite material structure with improved interfacial strength

Cold and detonation spraying of TiB₂-Cu nanocomposites

Lomovsky-OI; Dudina-DV; Ulianitsky-VYu; Zlobin-SB; Kosarev-VF; Klinkov-SV; Korchagin-MA; Kwon-DH; Kim-JS; Kwon-YS(Inst. of Solid State Chem. & Mechanochem., Novosibirsk, Russia)

Materials-Science-Forum. 2007; 534-536: 1373-6

TiB₂-43vol.%Cu nanocomposite powders with titanium diboride particle size 50-100 nm were cold and detonation sprayed in order to fabricate coatings on a copper substrate. The powders were produced by self-propagating high-temperature synthesis (SHS) followed by mechanical milling. The temperatures during spraying were calculated and the change in the nanostructure of the powders during spraying was studied: in cold sprayed coatings the size of TiB₂ particles was well retained, in detonation sprayed coatings the growth of the particles was observed, the mode of spraying greatly affecting the microstructure and the size of the particles. The hardness of cold sprayed coatings was higher compared to detonation sprayed coatings. This research shows the future potential for development of coatings with submicron and nanostructure by cold and detonation spraying of powders produced by mechanical milling

Determination of non-stoichiometry of tubular titanium carbide formed by self-propagating high temperature synthesis

Choi-Y; Cho-NI(Dept. of Electron. Mater. Eng., Sunmoon Univ., Chungnam, South Korea)

Materials-Science-Forum. 2007; 534-536: 1301-4

Titinium carbide (TiC_x) was produced by self-propagating high temperature synthesis (SHS) method. The morphology and non-stoichiometric number of the SHS product were observed by scanning electron microscopy and neutron diffractometry, respectively. Tubular titanium carbide with hole inside was formed with different non-stoichiometric number (x), which value increased with combustion temperature

Study on oxidation behavior of (W,Mo)Si₂ powders in air at 400, 500 and 600degC

Feng-Peizhong; Qu-Xuanhui; Wang-Xiaohong; Akhtar-Farid(Sch. of Mater. Sci. & Eng., Univ. of Sci. & Technol. Beijing, China)

Materials-Science-Forum. 2007; 534-536: 1289-92

The oxidation of (W,Mo)Si₂ powders has been examined at 400, 500 and 600degC for 12.0 hours in air. It was shown that the low temperature oxidation resistance of (W,Mo)Si₂ was worse than that of MoSi₂, and they showed great changes in mass, volume and colour. At 500degC, the amount of volume expansion of (W,Mo)Si₂ was as high as about 7~8 times and color changed from black to yellow after 4.0 h with MoO₃, WO₃, (W,Mo)O₃ and amorphous SiO₂ as main reaction products. It took about 8.0 h to obtain the same results for MoSi₂. The mass gain and oxidation rate were relatively slower at 400degC and 600degC than that at 500degC. These were probably due to the lower oxidation rate at 400degC and the protective silica glass on surface of powders formed from the volatilization of MoO₃, WO₃ and (W,Mo)O₃ at 600degC, which would restrain the diffusion of molybdenum from matrix to exterior and oxygen from outside to inside and the further accelerated oxidation

Neutron diffraction analysis of tungsten-molybdenum-disilicide powders formed by self-propagating high temperature synthesis

Choi-Y; Kim-YS(Dept. of Electron. Mater. Eng., Asan, South Korea)

Materials-Science-Forum. 2007; 534-536: 1277-80

Tungsten-molydisilicide W_xMo_1-xSi₂ was synthesized by self-propagating high temperature synthesis. The SHS product with the initial composition of (0.5Mo+0.5W+2Si) contains 23.9% MoSi₂, 40.89% WSi₂ with remaining 9.11% Mo, 9.16% Si and 16.94%W. Lattice parameters of the MoSi₂ and WSi₂ determined by Rietvelt analysis were a=0.3206 nm, c=0.7841 nm and a=0.3212 nm, c=0.7822 nm, respectively

Mechanical-activation-assisted combustion synthesis of SiC

Jiang-Tao-Li; Yun-Yang; Kun-Yang; Zhi-Ming-Lin(Tech. Inst. of Phys. & Chem., Chinese Acad. of Sci., Beijing, China)

Materials-Letters. Feb. 2007; 61(3): 671-6

Mechanical-activation-assisted combustion synthesis of SiC has been conducted with PVC as promoters. The mechanical activation of the Si-C reactants through high-energy attrition milling could result in substantial decrease of the ignition temperature and the incubation time for the Si-C combustion reaction. Ultra-fine beta-SiC powders with equiaxed grains were synthesized at the preheating temperature as low as 1050 degC. The specific surface area (SSA) of the combustion synthesized SiC powders was 4.36 m²/g, and the average particle size was less than 5 mum. [All rights reserved Elsevier]

Salt-assisted combustion synthesis of highly dispersed perovskite NdCoO₃ nanoparticles

Chen-W; Fengsheng-Li; Jiyi-Yu(Nat. Special Superfine Powder Eng. Res. Center, Nanjing Univ. of Sci. & Technol., China)

Materials-Letters. Jan. 2007; 61(2): 397-400

Highly dispersed perovskite NdCoO₃ nanoparticles with an average particle size of about 9 nm have been successfully prepared by a novel salt-assisted combustion process. The effects of NaCl content and calcination temperature on the characteristics of the products were investigated by XRD, TEM and BET nitrogen adsorption. The facile introduction of NaCl in the conventional combustion synthesis process was found to result in the formation of well-dispersed perovskite nanoparticles and increase specific surface area of the resultants from 1.70 to 43.22 m²middotg^-1. A mechanism scheme was proposed to illustrate the possible formation processes. [All rights reserved Elsevier]

Facile synthesis of nanocrystalline zinc ferrite via a self-propagating combustion method

Xianzhi-Fu; Hun-Xue; Zhaohui-Li; Xuxu-Wang(Res. Inst. of Photocatalysis, Fuzhou Univ., China)

Materials-Letters. Jan. 2007; 61(2): 347-50

Macroporous nanocrystalline zinc ferrite with single spinel-phase was prepared by a facile self-propagating combustion method using zinc nitrate, iron nitrate and glycine. The as-prepared ZnFe₂O₄ were characterized by X-ray diffraction (XRD) analysis, N₂ adsorption, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectrum (EDS). The magnetic properties of the prepared ZnFe₂O₄ were also studied. [All rights reserved Elsevier]

Preparation of nanostructured FeAl₂O₄-Al₂O₃-Fe composite coating by SHS plasma spraying technology

Niu-Er-Wu; Yan-Dian-Ran; He-Ji-Ning; Dong-Yan-Chun; Li-Xian-Zhi; Feng-Wen-Ran; Zhang-Jian-Xin; Zhang-Gu-Ling; Yang-Si-Ze(Mater. Sci. & Technol. Sch., Hebei Univ. of Technol., Tianjin, China)

Acta-Physica-Sinica. 2006; 55(10): 5535-8

In this paper, composite coating (about 400 mum thick) was prepared by SHS plasma spraying technology using micro-dimensional Fe₂O₃-Al composite feedstock, which was fabricated by mechanical agglomeration. The composition and microstructure of the coating were analyzed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Meanwhile, the microhardness, fracture toughness and wear resistance were also measured. It shows that the skeleton of the coating is mainly composed of nanostructured FeAl₂O₄ and Al₂O₃, and the dispersed phase is nanosized Fe. The composite coating possesses satisfactory microhardness of about Hv870. Compared with conventional alumina coating, the fracture toughness and wear resistance of composite coating are increased by one and 1.5 times, respectively

Processing of nano-structured barium hexaferrite by self-propagating high temperature synthesis (SHS) using nitrate precursor

Ataie-A; Nikkhah-Moshaie-R; Ebrahimi-SAS(Sch. of Metall. & Mater. Eng., Univ. of Tehran, Iran)

Journal-of-Alloys-and-Compounds. 21 Feb. 2007; 429(1-2): 324-8

Barium hexaferrite magnetic powder was produced by self propagating high temperature synthesis (SHS) route through putting a hot filament on top of the compact mixture of iron, iron oxide and barium nitrate powders with a Fe_(total)/Ba molar ratio of 12. Morphology, particle size distribution, thermal behavior, phase evolution, chemical analysis and magnetic properties of the products were investigated by SEM, LPSA, DTA/TGA, XRD, EDS and VSM techniques, respectively. EDS analysis confirmed the presence of barium hexaferrite in as-SHS sample. An exothermic peak appeared at 814degC in DTA/TGA traces seems to be due to the formation of barium hexaferrite. Single-phase barium hexaferrite was formed after annealing of SHS product at 1150degC for 2h. SEM micrograph of the sample annealed at 1150degC for 2h showed plate-like hexagonal particles of barium hexaferrite with mean size of 2mum. Saturation magnetization (Ms) and coercivity (Hc) for sample annealed at 1150degC for 2h were obtained 66emu/g and 192kA/m, respectively. The microstructure of as-SHS sample after it was pressed and then sintered at 1250degC for 3h exhibited nano-grains of barium hexaferrite with mean diameter of 200nm. [All rights reserved Elsevier]

Use of Si₃N₄ as a reactant in preparation of TiN-Ti₅Si₃ composites by solid-state SHS reactions

Yeh-CL; Teng-GS(Dept. of Mech. & Autom. Eng., Da-Yeh Univ., Changhua, Taiwan)

Journal-of-Alloys-and-Compounds. 21 Feb. 2007; 429(1-2): 126-32

An experimental study on in situ formation of TiN-Ti₅Si₃ composites with a wide range of compositions by self-propagating high-temperature synthesis (SHS) was conducted in two reaction systems. One adopted silicon nitride (Si₃N₄) as the solid source of nitrogen in a solid-state combustion system. The other employed both solid and gaseous reagents and performed the reactions of the Ti-Si powder compact under nitrogen pressures. Self-sustained reactions featuring a distinct combustion front were observed in both systems. TiN-Ti₅Si₃ composites containing Ti₅Si₃ from 20 to 80mol% were effectively produced by solid-state combustion synthesis of Ti-Si₃N₄ and Ti-Si₃N₄-Si powder compacts. This result verifies the contribution of Si₃N₄ to the formation of TiN and Ti₅Si₃. However, the solid/gas reaction of Ti-Si compacts with gaseous nitrogen was proved to be an inappropriate route in terms of product composition. For the production of a TiN-rich composite such as 80mol% TiN, it was found that the nitrogen uptake by the Ti-Si sample compact was inadequate, thus resulting in formation of a great amount of Ti₂N in the final product. On the contrary, when preparing the TiN-Ti₅Si₃ composite with a low TiN content like 20mol% or even 50mol%, Ti-Si powder compacts in gaseous nitrogen were subjected to excessive Ti nitridation and yielded a Si-rich silicide phase TiSi₂ in addition to TiN and Ti₅Si₃. [All rights reserved Elsevier]

Equal channel angular pressing followed by combustion synthesis of titanium aluminides

Morsi-K; Goyal-S(Dept. of Mech. Eng., San Diego State Univ., CA, USA)

Journal-of-Alloys-and-Compounds. 21 Feb. 2007; 429(1-2): L1-4

Titanium aluminides are one of the most promising intermetallics today. They have previously been processed using a variety of routes to generate different and unique microstructures. Recently, TiAl have been processed using severe plastic deformation by equal channel angular pressing (ECAP). However the temperature and energy requirements for this approach are high. Alternative lower energy approaches are therefore needed. The work presented in this paper investigates a new low energy approach consisting of ECAP of elemental titanium and aluminum powders (up to three passes) followed by combustion synthesis. The effect of number of passes during ECAP on the reaction characteristics, product homogeneity and microstructure are presented. [All rights reserved Elsevier]

The ECO steam explosion experiments

Cherdron-W; Kaiser-A(Inst. fur Reaktorsicherheit, Forschungszentrum Karlsruhe, Germany)

Atw-Internationale-Zeitschrift-fur-Kernenergie. Aug.-Sept. 2006; 51(8-9): 518-25

Analyses of LWR core melt accidents show that in case of a steam explosion the reactor pressure vessel experiences a considerable mechanical load which however remains below the capabilities of the vessel. The ECO experimental series is conducted with relevant melt masses (upto 18 kg) at the Forschungszentrum Karlsruhe to extend the data basis necessary for the analyses and to reduce the uncertainties (that had to be covered conservatively). Explosion pressures are measured as well as the energy conversion (ECO) under well-defined conditions. The facility consists in principle of a piston and cylinder system. Molten alumina (Al₂O₃) from a thermite reaction is used to simulate the high temperature core melt. The melt is injected from above into a water pool which is situated in the piston. Under the explosion pressure forces, the piston moves downwards compressing a stack of crushing material with known forces. The energy conversion ratio is considerably increased after the first few tests by changing essential test conditions. The water-to-melt mass ratio is decreased and the melt jet is partly fragmented before it penetrated into the water. Under these conditions, the short-term peak pressures exceeded the registration limits of 50 and 100 MPa while the energy conversion ratio reached about 3%

Spectroscopic properties of nano-sized cerium-doped lutetium aluminum garnet phosphors via sol-gel combustion process

Liu-X-J; Li-H-L; Xie-R-J; Yi-Zeng; Huang-L-P(Shanghai Inst. of Ceramics, Chinese Acad. of Sci., Shanghai, China)

Journal-of-Luminescence. May 2007; 124(1): 75-80

Nano-sized cerium-doped lutetium aluminum garnet (LuAG:Ce) phosphors were prepared via a sol-gel combustion process from a mixed aqueous solution of metal nitrates, using glycine as a fuel. The prepared LuAG:Ce phosphors were characterized by XRD, EPMA, and TEM, respectively. The spectroscopic properties of the phosphors were investigated. The as-prepared phosphors are agglomerated with a primary particle size of about 30nm and have a foamy-like morphology. The pure crystalline LuAG:Ce with uniform size of 40nm was obtained after calcined at 1000degC for 2h. The excitation spectrum shows two bands localized at 350 and 450nm due to transitions from the 4f ground state to the excited 5d band. Both the photoluminescence excited by UV and the radioluminescence excited by X-ray show the same two emission bands, corresponding to transitions from the lowest 5d excited state (²D) to the 4f ground state of Ce³⁺ (²F₅2/,²F₇2/). [All rights reserved Elsevier]

Preparation and optical properties of nanocrystalline Lu₂O₃:Eu³⁺ phosphors

Legendziewicz-J; Daldosso-M; Sokolnicki-J; Kepinski-L; Speghini-A; Bettinelli-M(Fac. of Chem., Univ. of Wroclaw, Poland)

Journal-of-Luminescence. Jan.-April 2007; 122-123: 858-61

New combustion technology of synthesis of nanosize phosphors have been described. Four series of nanocrystalline Lu₂O₃:Eu³⁺ have been prepared for different composition of fuel (glutamic acid:glycine)¹1Patented method using the combustion method. The concentration of Eu(III) varied from 0.05 to 15wt% and the size of the nanoparticles covered the range 6-10nm. The size effect on optical properties of the phosphors have been investigated and correlated with the decay profiles of the Eu(III) emission. It has been proved that composition of the fuel influences the size of nanocrystallines, and in consequence their optical properties. [All rights reserved Elsevier]

Photoluminescence and cathodoluminescence properties of Y₂O₃:Eu nanophosphors prepared by combustion synthesis

Nguyen-Vu; Tran-Kim-Anh; Yi-G-C; Strek-W(Inst. of Mater. Sci., Hanoi, Vietnam)

Journal-of-Luminescence. Jan.-April 2007; 122-123: 776-9

Eu-doped Y₂O₃ nanophosphors were prepared using combustion synthesis. In this method, urea was employed as a fuel. The particle size was estimated to be in the range of 10-20nm as determined by X-ray diffractometry and transmission electron microscopy. The photoluminescent and cathodoluminescent spectra are described by the well-known ⁵D₀rarr⁷F_J transition (J=0, 1, 2, etc.) of Eu³⁺ ions with the strongest emission for J=2. The optical properties of nanophosphors were compared with commercial with an order of micrometer size. The effects of urea-to-metal nitrate molar ratio and the other synthesis conditions on the particle size and luminescent properties will be discussed in detail. The red emission of Eu-doped Y₂O₃ nanophosphors is promising materials not only in high-resolution screen but also in telecommunication as well as in biosensor. [All rights reserved Elsevier]

The spectral properties of different structural centers in nanocrystalline Gd₂O₃:Eu³⁺

Chunxu-Liu; Shaozhe-Lu; Baojiu-Chen; Jiahua-Zhang; Junye-Liu(Key Lab. of Excited State Processes, Chinese Acad. of Sci., Changchun, China)

Journal-of-Luminescence. Jan.-April 2007; 122-123: 80-2

Monoclinic and cubic Gd₂O₃:Eu³⁺ were prepared by combustion synthesis. The optical and structural properties have been investigated using photoluminescence (PL), photoluminescence excitation (PLE), site-selective excitation (SSE) spectra as well as fluorescence lifetime measurement. Three nonequivalent C_s centers in monoclinic phase and C₂ center in cubic phase are distinguished. The energy transfers between three different C_s centers in monoclinic phase of nano-material were observed. The lifetime of ⁵D₀ of Eu³⁺ in the nano-material is longer than that in bulk lattice, due to the effective refractive index decreasing. [All rights reserved Elsevier]

High pure negative thermal expansion material ZrW₂O₈ powders synthesized by combustion method

Yan-Xuehua; Yang-Xinbo; Cheng-Xiaonong; Fu-Tingbo; Qiu-Jie; Liu-Hongfei(Sch. of Mater. Sci. & Eng., Jiangsu Univ., China)

Journal-of-the-Chinese-Ceramic-Society. 2006; 34(9): 1066-74

Isotropic ZrW₂O₈ powders material with negative thermal expansion were successfully synthesized via a combustion method at low temperature. The effects of the furnace temperature, the H₃BO₃ and (NH₂)₂CO content, and the molar ratio of W⁶⁺ and Zr⁴⁺ on the purity of the synthesized ZrW₂O₈ powders were investigated by X-ray diffraction, scanning electron microscopy and infrared spectrum. The results show that high purity ZrW₂O₈ powders with a mean particle size of 0.5 mum, can be obtained by the method under the following conditions: a furnace temperature of 500degC; a H₃BO₃ molar fraction of 10%; a 2:1 mass ratio of (NH₂)₂CO and (NH₄)₅H₅[H₂(WO₄)₆]middotH₂O added to ZrOCl₂middot8H₂O; and a 1:3.2 molar ratio of (NH₄)₅H₅[H₂(WO₄)₆middotH₂O and ZrOCl₂middot8H₂O. The linear thermal expansion coefficient of prepared ZrW₂O₈ material is -5.08 times 10^-6/degC in the temperature range from 50degC to 700degC. The equation for the relationship of thermal expansion to the temperature of the material is dL/L₀ = -1.4 times 10^-2-4.5times10^-4T

Combustion synthesis as a preparation method of perovskites with cerium for methane oxidation

Fraga-MA; Pereiraand-RA; Greca-MC(Laboratorio de Catalise, Instituto Nacional de Tecnologia, Rio de Janeiro, Brazil)

Materials-Science-Forum. 2006; 530-531: 696-701

The aim of this contribution was to evaluate the synthesis of perovskites containing cerium by the combustion synthesis methodology as well as their catalytic behaviour in the methane combustion. Cerium was introduced partially replacing lanthanum into A position of perovskites with general formula Ag_xA'_1-xCoO₃. The formation of cubic perovskites was confirmed by XRD. The powder containing only lanthanum and strontium in A sites showed a structure transition to orthorhombic at temperatures above 700degC. The addition of cerium, instead of strontium, induced a structural stabilisation and only a cubic phase was detected up to 1100degC. High cerium loadings led to the formation of cerium oxide, revealing its up limit into the structure. All samples showed to be active in methane combustion. The results indicated that over the perovskites loaded with cerium the oxygen adsorbed onto the catalyst surface plays a role in the reaction

Sintering of cobalt and strontium doped lanthanum chromite obtained by combustion synthesis

Setz-LFG; Correa-HPS; Paiva-Santos-CO; Mello-Castanho-SRH(Instituto de Pesquisas Energeticas e Nucleares, Cidade Universitaria, Sao Paulo, Brazil)

Materials-Science-Forum. 2006; 530-531: 671-6

Lanthanum chromite (LaCrO₃) is one of the most adequate materials for use as interconnector in solid oxide fuel cell (SOFC) applications, due to its intrinsic properties, namely its good electrical conductivity and resistance to environment conditions in fuel cell operations. Due to difficulties in sintering, additives are usually added to help in the densification process. In this paper, the influence of added cobalt and strontium, in the sintering of LaCrO₃ obtained by combustion synthesis was studied. The starting materials were respectively nitrates of chromium, lanthanum, cobalt and strontium, and urea was used as fuel. The results show that by increasing the strontium and cobalt concentrations it is possible to reduce the temperature of sintering. Using both additives, the sintering processes took place in lesser times than normally used for this material, as well as greater values of density were attained

Combustion synthesis of alpha-Al₂O₃ powders

Freitas-NL; Fagury-Neto-E; Lira-HL; Gama-L; Kiminami-RHGA; Costa-ACFM(Dept. of Mater. Eng., Fed. Univ. of Campina Grande, Brazil)

Materials-Science-Forum. 2006; 530-531: 631-6

Among ceramic materials, the alumina has high importance because of its characteristics of resistance and refractory. The possibility to improve the final characteristics of this material opens possibilities for new applications. The aim of this paper is to synthesize alpha-Al₂O₃) alumina powders by combustion reaction and to evaluate the effect of the urea content in the final characteristics of the alpha-Al₂O₃ powders. Three compositions were studied: a) stoichiometric, b) with 10% of urea reduction and c) with 20% of urea reduction. The initial solution composition was based on the total valence of the reagents by using chemical concepts of the propellant. These powders were characterized by X-ray diffraction (XRD), granulometric determination by laser diffraction, nitrogen adsorption by BET, scanning electron microscopy (SEM), infrared spectroscopy (IR) and helium picnometer. The results showed that the urea reduction change the temperature of the reaction from 525 to 463degC , the characteristics of the powders, and principally the reduction of the particles size

Mechanical activation of Nb75Al mixtures using shaker and planetary ball mills

Rocha-CJ; Goncalves-VS; Leal-Neto-RM(Instituto de Pesquisas Energeticas c Nucleares, Centro de Ciencia e Tecnologia de Mater., Sao Paulo, Brazil)

Materials-Science-Forum. 2006; 530-531: 203-10

Different types of high-energy ball mills can be applied to promote mechanical activation of powders mixtures for further combustion synthesis of intermetallic compounds. In this work, Nb75Al powder mixtures (for NbAl₃ synthesis) were mechanically activated in shaker and planetary mills by 1 and 3 hours. Remarkable differences in shape and microstructure of the activated powders resulted in distinct reaction behaviors (e.g. ignition and combustion temperatures). Temperature profile of the samples during the reaction showed that mechanical activation was higher in the shaker mill. Higher densities were obtained with samples activated in shaker mill by 1h

Mechanical behavior of TiB₂ nanoparticles reinforced Cu matrix composites synthesized by in-situ processing

Dae-Hwan-Kwon; Khoa-Xuan-Huynh; Thuy-Dang-Nguyen; Pyuck-Pa-Choi; Myung-Gyu-Chang; Young-Jin-Yum; Ji-Soon-Kim; Young-Soon-Kwon(Sch. of Mater. Sci. & Eng., Ulsan Univ., South Korea)

Materials-Science-Forum. 2006; 510-511: 346-9

Cu-TiB₂ nanocomposite powders were in situ synthesized by combining high-energy ball milling of Cu-Ti-B elemental powder mixtures as precursors and subsequent self-propagating high temperature synthesis (SHS). Cu-40wt.% TiB₂ was produced after SHS reaction and then diluted by copper to obtain desired homogeneous composites with 2.5, 5 and 10wt.%TiB₂. Spark plasma sintering (SPS) was used to inhibit grain growth and thereby obtain fully Cu-TiB₂ sintered bodies with nanocomposite structure. After SHS reaction, only Cu and TiB₂ phases were detected in the SHS-product. Spheroidal TiB₂ particles smaller than 250 nm were formed in the copper matrix after SHS-reaction. Mechanical and electrical properties were investigated after SPS at 650degC for 30 min under 50 MPa. The electrical conductivity decreased from 75 to 54% IACS with increasing of TiB₂ contents from 2.5 to 10wt.%. However, hardness increased from 56 to 97 H_rB. In addition, the tensile strength increased with increasing the TiB₂ content

Optical properties of GaN nanocrystals embedded into silica matrices

Podhorodecki-A; Nyk-M; Kudrawiec-R; Misiewicz-J; Pivin-JC; Strek-W(Inst. of Phys., Wroclaw Univ. of Technol., Poland)

Superlattices-and-Microstructures. Oct.-Dec. 2006; 40(4-6): 533-6

The purpose of this work was to obtain GaN nanocrystals (GaN-nc) embedded into silica-based matrix and to investigate their optical properties by photoluminescence (PL) spectroscopy. GaN-nc have been obtained both by the sol-gel chemistry and by the combustion method (CM). The GaN-nc obtained by CM have been introduced into the silica-based matrix during the formation of the film in the spin-on technique. Strong emission at ~3.4 eV has been observed for the films doped by GaN-nc whereas no emission in UV has been observed for GaN-nc obtained by sol-gel chemistry. [All rights reserved Elsevier]

Flame spray synthesis under a non-oxidizing atmosphere: preparation of metallic bismuth nanoparticles and nanocrystalline bulk bismuth metal

Grass-RN; Stark-WJ(Inst. for Chem. & Bioeng., ETH Zurich, Switzerland)

Journal-of-Nanoparticle-Research. Oct. 2006; 8(5): 729-36

Metallic bismuth nanoparticles of over 98% purity were prepared by a modified flame spray synthesis method in an inert atmosphere by oxygen-deficient combustion of a bismuth-carboxylate based precursor. The samples were characterized by X-ray diffraction, thermal analysis and scanning electron microscopy confirming the formation of pure, crystalline metallic bismuth nanoparticles. Compression of the as-prepared powder resulted in highly dense, nanocrystalline pills with strong electrical conductivity and bright metallic gloss

Synthesis and optical properties of TiO₂ nanoparticles

Chunzhong-Li; Yin-Zhao; Xiuhong-Liu; Feng-Gu; Haibo-Jiang; Wei-Shao; Ling-Zhang; Ying-He(Sch. of Mater. Sci. & Eng., East China Univ. of Sci. & Technol., Shanghai, China)

Materials-Letters. Jan. 2007; 61(1): 79-83

Ultrafine TiO₂ particles have been synthesized successfully by a facile gas flame combustion method. The synthesized sample is characterized by X-ray diffraction (XRD), transmission electron micrograph (TEM), Fourier transform infrared (FTIR), and photoluminescence (PL) spectroscopy. The as-prepared TiO₂ nanoparticles appear to be a single anatase crystalline phase and the diameter is about 9 nm. Besides a sharp emission at 398 nm originating from the radiative annihilation of excitons, a weak broad band at about 434 nm from the defect-related emission is also discussed. [All rights reserved Elsevier]

Reaction of boron-containing materials with titanium during self-propagating high-temperature synthesis

Zhunkovskii-GL; Evtushok-TM; Kotenko-VA; Mazur-PV; Gordienko-SP(Inst. for Problems of Mater. Sci., Nat. Acad. of Sci., Kiev, Ukraine)

Powder-Metallurgy-and-Metal-Ceramics. March-April 2006; 45(3-4): 163-7; Original: Poroshkovaya-Metallurgiya. March-April 2006; 45(3-4): 67-72

We have studied the contact reaction of titanium, chromium, and tungsten borides with titanium. We have established that the materials react according to an exothermic solid-phase reaction mechanism with formation of titanium monoboride and diboride. The reaction is limited by diffusion of boron atoms through the layer of titanium monoboride formed. This makes it possible to successfully use reaction to effectively control the process for obtaining composite materials in the Ti - B₄C system under self-propagating high-temperature synthesis conditions

Effect of processing parameters on the luminescence intensity of Sr₃(VO₄)₂:Eu³⁺ nanocrystals via combustion synthesis

Mengkai-Lu; Haiping-Zhang; Zhongsen-Yang; Zhiliang-Xiu; Guangjun-Zhou; Shufen-Wang; Yuanyuan-Zhou; Shumei-Wang(State Key Lab. of Crystal Mater., Shandong Univ., Jinan, China)

Journal-of-Alloys-and-Compounds. 21 Dec. 2006; 426(1-2): 384-9

Sr₃(VO₄)₂:Eu³⁺ nanopowders were prepared by a combustion method using citric acid as a fuel/reductant and nitrates as oxidants. The effects of processing parameters, such as citric acid to nitrates ratio, calcination temperature and the amounts of the additive boric acid (HBO₃), on the powder characteristics and fluorescence properties of the resultant strontium orthovanadate doped with 5mol% Eu³⁺ were investigated. [All rights reserved Elsevier]

Consolidation of nanostructured NbSi₂-SiC composite synthesized by high-frequency induction heated combustion

In-Jin-Shon; Hyun-Kuk-Park; Jin-Kook-Yoon; Kyung-Tae-Hong(Dept. of Mater. Eng., Chonbuk Nat. Univ., Jeonbuk, South Korea)

Journal-of-Alloys-and-Compounds. 21 Dec. 2006; 426(1-2): 322-6

Dense nanostructured NbSi₂-SiC composite was synthesized by high-frequency induction heated combustion synthesis (HFIHCS) method within 2min in one step from powders of NbC and 3Si. Simultaneous combustion synthesis and densification were accomplished under the combined effects of an induced current and mechanical pressure. Highly dense NbSi₂-SiC with relative density of up to 99.8% were produced under simultaneous application of a 60MPa pressure and the induced current. The average grain size and mechanical properties (hardness and fracture toughness) of the composite were investigated. [All rights reserved Elsevier]

High-temperature oxidation of reactively processed nickel aluminide intermetallics

Moussa-SO; Morsi-K(Dept. of Chem., Ain Shams Univ., Cairo, Egypt)

Journal-of-Alloys-and-Compounds. 21 Dec. 2006; 426(1-2): 136-43

A detailed study of the high-temperature oxidation behavior of powder processed Ni₃Al (combustion synthesized (CS), reactively pressed (RP), and reactively extruded (RE)) in air at two different temperatures (1000 and 1200degC) for 400h was carried out. The weight gain per unit area (mg/cm²) due to oxide scale formation at a given exposure time t (h) and temperature was discussed. Thermodynamics and kinetics were used to explain the oxidation mechanism. The results indicated that Ni₃Al alloys processed using RE showed superior high-temperature oxidation resistance compared to either RP or CS-Ni₃Al at both 1000 and 1200degC. The oxide scales resulting from the high-temperature oxidation of Ni₃Al consisted of an internal layer of Al₂O₃ (major phase in the case of RE and RP), intermediate layer of NiAl₂O₄, and an external scale of NiO (major phase in the case of CS-Ni₃Al at 1000 and 1200degC). Both XRD and SEM/EDS-analysis were used to identify the oxide phases present after the high-temperature oxidation exposure at 1200degC of CS-Ni₃Al and RE-Ni₃Al in air after 400h. [All rights reserved Elsevier]

Combustion synthesis of chromium nitrides by SHS of Cr powder compacts under nitrogen pressures

Yeh-CL; Liu-EW(Dept. of Mech. & Autom. Eng., Da-Yeh Univ., Changhua, Taiwan)

Journal-of-Alloys-and-Compounds. 21 Dec. 2006; 426(1-2): 131-5

An experimental study on the preparation of chromium nitrides by self-propagating high-temperature synthesis (SHS) was conducted with powder compacts under nitrogen pressures of 0.45-4.24MPa. The SHS process is characterized by the steady propagation of a self-sustained combustion front, followed by prolonged afterburning reactions. Nitrogen pressure was demonstrated to play an important role in the combustion characteristics as well as in the phase composition of synthesized products. Experimental evidence indicated that combustion temperature and flame-front propagation velocity were substantially increased by increasing the nitrogen pressure. It was found that multiphase products consisting of two nitride phases Cr₂N and CrN were yielded by the self-sustained reactions conducted in this study. The combustion product contained only about 10mol% of CrN when the reaction was performed under a low nitrogen pressure of 0.79MPa. However, the CrN content was found to increase significantly with nitrogen pressure. Namely, the mole fraction of CrN in the final product increases up to about 54% at 1.83MPa of nitrogen, and finally approaches an asymptotical value around 80% in nitrogen of 4.24MPa. [All rights reserved Elsevier]

Experimental investigation on a combined sensible and latent heat storage system integrated with constant/varying (solar) heat sources

Velraj-R; Nallusamy-N; Sampath-S(Inst. for Energy Studies, Anna Univ., Chennai, India)

Renewable-Energy. June 2007; 32(7): 1206-27

The objective of the present work is to investigate experimentally the thermal behavior of a packed bed of combined sensible and latent heat thermal energy storage (TES) unit. A TES unit is designed, constructed and integrated with constant temperature bath/solar collector to study the performance of the storage unit. The TES unit contains paraffin as phase change material (PCM) filled in spherical capsules, which are packed in an insulated cylindrical storage tank. The water used as heat transfer fluid (HTF) to transfer heat from the constant temperature bath/solar collector to the TES tank also acts as sensible heat storage (SHS) material. Charging experiments are carried out at constant and varying (solar energy) inlet fluid temperatures to examine the effects of inlet fluid temperature and flow rate of HTF on the performance of the storage unit. Discharging experiments are carried out by both continuous and batchwise processes to recover the stored heat. The significance of time wise variation of HTF and PCM temperatures during charging and discharging processes is discussed in detail and the performance parameters such as instantaneous heat stored and cumulative heat stored are also studied. The performance of the present system is compared with that of the conventional SHS system. It is found from the discharging experiments that the combined storage system employing batchwise discharging of hot water from the TES tank is best suited for applications where the requirement is intermittent. [All rights reserved Elsevier]

Multifunctional biocompatible nanostructured coatings for load-bearing implants

Shtansky-DV; Gloushankova-NA; Bashkova-IA; Petrzhik-MI; Sheveiko-AN; Kiryukhantsev-Korneev-FV; Reshetov-IV; Grigoryan-AS; Levashov-EA(Moscow State Inst. of Steel & Alloys, Technol. Univ., Russia)

Surface-and-Coatings-Technology. 20 Dec. 2006; 201(7): 4111-18

To take advantage of the self-propagating high-temperature synthesis (SHS) technique, magnetron sputtering (MS), and ion implantation assisted magnetron sputtering (IIAMS), a new type of biocompatible nanostructured film was developed and studied. Films of Ti-Ca-C-O-(N), Ti-Ca-P-C-O-(N), Ti-Si-Zr-O-(N), and Ti-Zr-C-O-(N) were deposited by DC MS or IIAMS of SHS composite targets TiC_0.5+CaO, TiC_0.5+CaO+TiO₂, TiC_0.5+Ca₁₀(PO₄)₆(OH)₂, Ti₅Si₃+ZrO₂, and TiC_0.5+ZrO₂ in an Ar atmosphere or reactively in a gaseous mixture of Ar+14% N₂. The films were characterized in terms of their structure, chemical, mechanical, and tribological properties. The biocompatibility of the films was evaluated by both in vitro and in vivo experiments. In vitro studies involved the investigation of adhesion, spreading and proliferation of Rat-1 fibroblasts, MC3T3-E1 osteoblasts, and IAR-2 epithelial cells, morphometric analysis, actin cytoskeleton and focal contacts staining of the cells cultivated on the films. Alkaline phosphatase activity and von Kossa staining of osteoblastic culture were investigated. Three groups of the in vivo investigations were fulfilled. Teflon plates coated with the tested films were inserted subcutaneous in mice and analysis of the population of cells on the surfaces was performed. Implantation studies of Ti rings and Ti rods coated with tested films using rat calvarian and hip defect models were also fulfilled. The results obtained show that Ti-based multicomponent films possess a combination of high hardness and adhesion strength, reduced Young's modulus, low wear and friction, high corrosion resistance with bioactivity, biocompatibility and non-toxicity that makes the films promising candidates as tribological coatings to be used for various medical applications like orthopedic prostheses, materials for connective surgery and dental implants. [All rights reserved Elsevier]

Three-dimensional ageostrophic motion in mesoscale vortex dipoles

Pallas-Sanz-E; Viudez-A(Inst. de Ciencies del Mar, Barcelona, Spain)

Journal-of-Physical-Oceanography. Jan. 2007; 37(1): 84-105

The three-dimensional motion of mesoscale baroclinic dipoles is simulated using a nonhydrostatic Boussinesq numerical model. The initial conditions are two ellipsoidal vortices of positive and negative potential vorticity anomalies. The flow is moderately ageostrophic with a maximum absolute Rossby number equal to 0.71. The trajectory of the dipole is related to the maximum potential vorticity anomaly and size of the vortices. Three cases are considered depending on the curvature of the dipole trajectory: negative, close to zero, and positive. The ageostrophic flow strongly depends on the distance between the ellipsoidal vortices d₀. For small d₀ the vortices move steadily as a compact dipole, and the vertical velocity w has an octupolar three-dimensional pattern. The horizontal ageostrophic velocity is due to the advective acceleration of the flow, particularly the centripetal acceleration. The speed acceleration is only relatively important at the rear and front parts of the dipole axis, where the flow curvature is small but where the flow confluence and diffluence are, respectively, large. The geostrophy is maximal at the dipole center, on the dipole axis, where both curvature and speed acceleration are minimal. As d₀ increases, the dipole self-propagating velocity and the extreme values of | w | decrease, and vortex oscillations highly distort the octupolar pattern of w. Jn all cases, as is typical of balanced mesoscale geophysical flows, the vertical velocity is related to the advection of vertical vorticity by the horizontal shear velocity u_hz middot nabla_hzeta

Electrochemical capacitance of nano-sized nickel oxide derived from a gel-combustion process

Gao-Jia-hui; Wu-Meng-qiang; Zhang-Shu-ren(China Univ. of Electron. Sci. & Tech., Chengdu, China)

Journal-of-University-of-Electronic-Science-and-Technology-of-China. Dec. 2006; 35(6): 960-3

The nanocrystalline nickel oxide was prepared by a citrate-gel method. The results showed that the NiO_x prepared in the optimum condition (CA:Ni²⁺ mole ratio 1.3:1.0, annealing at 400degC for 1h). The electrochemical capacitive behaviors of the NiO_x, electrodes were characterized by cyclic voltammetry (CV), chronopotentiometry (CP) and A.C. impedance in 1 mol/L KOH aqueous solution. The electrochemical measurements indicated that the prepared samples exhibited high specific capacitance of 78.74 F/g, and excellent cyclability

Effects of dominant parameters on burning velocity and range of flammability in SHS process for Ti-Al system

Makino-A; Shibata-N(Institute of Space Technol. & Aeronaut., Tokyo, Japan)

JSME-International-Journal,-Series-B-Fluids-and-Thermal-Engineering. Aug. 2006; 49(3): 856-63

Relevant to the self-propagating high-temperature synthesis (SHS) process for the Ti-Al system, burning velocity and the range of flammability are examined theoretically. The heterogeneous theory for SHS flame propagation, presented in the literature is used. It is found that the effects of particle size, mixture ratio, degree of dilution, and initial temperature on the burning velocity and/or the range of flammability are the same as those for other representative systems. It has been confirmed that even for the Ti-Al system, a parameter defined as a product of the burning velocity and the particle size can be useful in correlating experimental results for flame propagation. It has also been confirmed that a parameter defined as the square of particle size divided by the compact diameter can be useful in correlating experimental results for flame extinction. In addition, it has been demonstrated that a fair degree of agreement exists between theoretical results and experimental data in the literature, as far as the trend and approximate magnitude are concerned

Robotised assistance for reduced mobility persons: resume of a project

de-Chaumont-F; Marhic-B; Delahoche-L; Remy-Neris-O)

Smart-Homes-and-Beyond.-ICOST-2006-4th-International-Conference-on-Smart-Homes-and-Health-Telematics. 2006: 90-7

This project deals with technical assistance for persons of reduced mobility. We propose to study the technical, psychological and clinical impact of an original approach which consists of mounting a prehensile arm on to a mobile base. The use of this mobile unit in relation to patient's wheelchair is carried out on a master-slave basis. This study therefore has a pluridisciplinary nature: science for the engineer (science pour i'ingenieur, known as "SPI"), human and social science (science humaine et sociale known as "SHS") and clinical. We present a short synthesis of the various points which were approached during the three years of research on the above-mentioned project

Deposition of alpha-alumina via combustion chemical vapor deposition

Carter-WB; Kelekanjeri-VSKG; Hampikian-JM(Sch. of Mater. Sci. & Eng., Georgia Inst. of Technol., Atlanta, GA, USA)

Thin-Solid-Films. 5 Dec. 2006; 515(4): 1905-11

Combustion chemical vapor deposition was used to synthesize alpha-alumina thin films. The deposition solutions were 0.0015 M aluminum acetylacetonate dissolved in isopropanol. Fused silica and nichrome (Ni-20Cr) served as substrates. Deposition temperatures were in the range of 1050 degC to 1125 degC. Crystalline films consisting of hexagonal alpha-grains were produced on both substrates. Some films on nichrome displayed preferred orientations of (113) and (116) normal to substrate surfaces, while films deposited on silica showed no preferred orientation. Films deposited on nichrome seemed denser than those on silica as the grains clustered together to provide a `cauliflower' appearance. The oxidation response of uncoated and alumina-coated nichrome specimens was measured by isothermal thermogravimetric analysis in pure flowing air at 900 degC, 1000 degC and 1100 degC. The coated specimens had significantly lower mass gain values and parabolic rate constants than their uncoated counterparts. [All rights reserved Elsevier]

Amyloid of the prion domain of Sup35p has an in-register parallel beta-sheet structure

Shewmaker-F; Wickner-RB; Tycko-R(Lab. of Biochem. & Genetics, Nat. Inst. of Health, Bethesda, MD, USA)

Proceedings-of-the-National-Academy-of-Sciences-of-the-United-States-of-America. 26 Dec. 2006; 103(52): 19754-9

The [PSI⁺] prion of Saccharomyces cerevisiae is a self-propagating amyloid form of Sup35p, a subunit of the translation termination factor. Using solid-state NMR we have examined the structure of amyloid fibrils formed in vitro from purified recombinant Sup35^1-253, consisting of the glutamine- and asparagine-rich N-terminal 123-residue prion domain (N) and the adjacent 130-residue highly charged M domain. Measurements of magnetic dipole-dipole couplings among ¹³C nuclei in a series of Sup35NM fibril samples, ¹³C-labeled at backbone carbonyl sites of Tyr, Leu, or Phe residues or at side-chain methyl sites of Ala residues, indicate intermolecular ¹³C-¹³C distances of ap0.5 nm for nearly all sites in the N domain. Certain sites in the M domain also exhibit intermolecular distances of ap0.5 nm. These results indicate that an in-register parallel beta-sheet structure underlies the [PSI⁺] prion phenomenon

Heat transfer modelling of rail thermite welding

Chen-Y; Lawrence-FV; Barkan-CPL; Dantzig-JA(Div. of Energy Technol., Argonne Nat. Lab., IL, USA)

Proceedings-of-the-Institution-of-Mechanical-Engineers,-Part-F-Journal-of-Rail-and-Rapid-Transit. Sept. 2006; 220(F3): 207-17

Rail thermite (or Thermitreg) welding is a valuable welding technology for the railway industry because of its simplicity, portability, and economy. Using the finite-element method, a heat transfer analysis is conducted in this study. Only the heat transfer by conduction was simulated explicitly in the model, the other thermally significant phenomena were included through the boundary and initial conditions. Despite these simplifications, the model can be used to analyse the thermal conditions during thermite welding with sufficient accuracy. The predicted temperature history, weld deposit, and HAZ profiles were in good agreement with the experimental measurements in laboratory welds. It is found that the weld gap is the most influential welding parameter for rail thermite welding. A wider-gap weld appears to be less sensitive to chance variations in the other welding parameters, and therefore fairly consistent thermal conditions can be obtained

High flux diffractometers on reactor neutron sources

Hewat-AW(Inst. Laue-Langevin, Grenoble, France)

Physica-B. 15 Nov. 2006; 385-386: 979-84

Continuous neutron sources such as reactors can deliver a very high time-averaged flux to the sample using a relatively wide band of wavelengths, while still retaining good resolution. For example, the D20 diffractometer at ILL Grenoble, the world's highest flux neutron powder machine, can collect complete patterns at 100ms intervals, and this has been important for the real time study of explosive SHS reactions. New very large 2D detectors, such as those recently installed on D2B and D19 at ILL, are up to an order of magnitude larger than previous designs, and will provide unmatched speed of data collection from very small samples, opening up new scientific perspectives for powder and single crystal diffraction. We will discuss future reactor based diffractometers designed for rapid data collection from small samples in special environments. [All rights reserved Elsevier]

Novel composite coatings containing (TiC-Al₂O₃) powder

Aal-AA; Zaki-ZI; Hamid-ZA(Central Metall. R&D Inst., Cairo, Egypt)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 25 Feb. 2007; 447(1-2): 87-94

Electroless plating technique has been applied on steel substrate to prepare novel Ni-P composite coatings containing (TiC-Al₂O₃) powder synthesized by self-propagation high temperature synthesis (SHS). The operating conditions for plating process, such as powder content, temperature and pH were optimized. The mechanism of the co-deposition process was also discussed. The results demonstrated that the powder particle incorporation in deposited electrolessed layer depends on pH, temperature and content of powder suspended in plating bath. The maximum (TiC-Al₂O₃) incorporation (approximately 61vol.%) could be obtained by addition of 10g/L of powder in the plating solution operating at pH 5.5 and temperature 85degC. The morphology of composite coatings has been investigated using scanning electron microscopy (SEM). Incorporation of (TiC-Al₂O₃) particles in deposited coating significantly improves the corrosion resistance, wear resistance and increases the hardness of deposited layer. [All rights reserved Elsevier]

Oxide films by combustion pyrolysis of solution precursors

Kavitha-R; Hegde-SR; Vikram-Jayaram(Dept. of Metall., Indian Inst. of Sci., Bangalore, India)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 25 Oct. 2003; A359(1-2): 1 pp.

A combustion pyrolysis technique has been developed to deposit oxide films onto metal and ceramic substrates. A precursor solution is atomised and injected into an oxy-acetylene flame where thermal decomposition takes place to directly yield a film on a substrate. This technique is used to deposit different kinds of films including Al₂O₃, ZnO, metastable solid solutions of ZnO-MgO and ZrO₂-Y₂O₃. The conditions that were necessary to obtain uniform and adherent films were established. Films were characterised by X-ray diffractometry, scanning electron microscopy and micro-hardness

Effects of processing parameters on pore morphology of combustion synthesized Al-Ni foams

Kobashi-M; Wang-R-X; Inagaki-Y; Kanetake-N(Dept. of Mater. Sci. & Eng., Nagoya Univ., Japan)

Materials-Transactions. Sept. 2006; 47(9): 2172-7

Intermetallic (Al-Ni) foams were fabricated by a combustion reaction of the blended powder compacts consisting of nickel and aluminum. The foaming agents (titanium and B₄C powders) were added to the nickel and aluminum blended powder to produce foams with high porosity by increasing the combustion temperature. The effects of the size of elemental powders (aluminum and nickel), the powder blending ratio, the amount of foaming agent and compacting conditions on the porosity and pore morphology of the foams were investigated. The size of nickel powder was an important factor to produce foams by the combustion synthesis and it should be small enough to achieve high porosity. The size of the aluminum powder was not such an important factor. The uniform pore morphology in the foam was obtained only when the powder blending ratio was adequate. The proper addition of the foaming agent increased the porosity and the size of pores, and also stabilized the uniformity of the pore morphology. There was a threshold density of the precursor to achieve sufficient foaming. The pore diameter of a synthesized foam is increased with increasing precursor compacting temperature and pressure. An attempt was made to disperse fine ceramic particles in the foam materials. It was revealed that the addition of ceramic particles did not affect the porous structure

Deposition and characterization of alumina films produced by combustion flame pyrolysis

Kavitha-R; Jayaram-V(Dept. of Metall., Indian Inst. of Sci., Bangalore, India)

Surface-and-Coatings-Technology. 4 Dec. 2006; 201(6): 2491-9

Alumina coatings have been deposited by combustion flame pyrolysis on amorphous silica and stainless steel substrates with the objective to study the effect of solvent composition, Fe³⁺ addition and determine the thermal fatigue lifetime. The effect of solvent composition on crystallinity, transformation temperature and hardness are studied, three different solvent compositions are chosen for preparing the aluminium nitrate solution. Using 100% water, as-deposited films are amorphous and transform to alpha-alumina only upon annealing, while this equilibrium phase is directly obtained but with a porous microstructure by using 100% methanol. The hardness of the coatings varies with the flammability of the solvents. The effect of Fe³⁺ addition on the crystallization of alumina is studied by combustion pyrolysis of aqueous solutions of Al³⁺ and Fe³⁺ nitrates. Small amount of ferric nitrate reduced the transformation temperature by 100 degC. Thermal cycling of as-deposited amorphous alumina on stainless steel substrate is carried out at different temperatures to determine the thermal fatigue lifetime. [All rights reserved Elsevier]

Microstructural analysis of iron aluminide formed by self-propagating high-temperature synthesis mechanism in aluminium matrix composite

Olszowka-Myalska-A; Maziarz-W(Silesian Univ. of Technol., Katowice, Poland)

Journal-of-Microscopy. Oct. 2006; 224: 1-3

An aluminium matrix composite with iron aluminide formed in situ as a result of self-propagated high-temperature synthesis was examined. The structural characteristics of the reinforcement investigated by scanning electron microscopy and transmission electron microscopy methods are presented. Iron aluminide particles with a very fine grain size and of two shapes, cubic and needle-like, were observed. No differences in their phase composition were found by the selective electron diffraction pattern method. The composite reinforcement formed in the early stage of self-propagating high-temperature synthesis consisted only of the Al₃Fe phase

Synthesis and luminescent properties of CaIn₂O₄:xTb nanocrystals

Sang-Do-Han; Khatkar-SP; Taxak-VB; Sharma-G; Kumar-D(Korea Inst. of Energy Res., Daejeon, South Korea)

Current-Applied-Physics. Aug. 2006; 6: e192-4

Terbium-activated CaIn₂O₄:xTb (x=0.12%, 0.5%, 1.0% and 2%) nanocrystals have been produced by combustion synthesis using glycine as a fuel in a preheated furnace at 500degC. The nanocrystals obtained were characterized by scanning electron microscopy and X-ray diffraction (XRD) techniques. The prepared nanocrystals under a UV source revealed green luminescence that was attributed to the transition from ⁵D₄ excited state to ⁷F₅ ground state of Tb³⁺ ions. In addition, the dependence of the luminescence intensity on Tb³⁺ concentration and effect of glycine to nitrate ratio on the particle size of the nanocrystals have also been discussed. [All rights reserved Elsevier]

Combustion oxidization synthesis of unique cage-like nanotetrapod ZnO and its optical property

Yu-Na-Zhao; Mao-Sheng-Cao; Hai-Bo-Jin; Xiao-Ling-Shi; Xiang-Li; Agathopoulos-S(Sch. of Mater. Sci. & Eng., Beijing Inst. of Technol., China)

Journal-of-Nanoscience-and-Nanotechnology. Aug. 2006; 6(8): 2525-8

Cage-like nano-tetrapod ZnO is a novel structure, which was successfully synthesized by combustion oxidation at 850degC. No catalyst or carrier gases were used. Thorough SEM and TEM analyses revealed that the linking legs of the tetrapod ZnO may or may not have an interface. The formation of an interface is discussed and it was attributed to different growth process of the cage-like ZnO nano-tetrapod. Enhanced UV emission peak at the wavelength of 375 nm, featuring high intensity and narrow width, indicates a highly crystalline structure. A green emission, recorded at 502 nm, was related to the defects of the surface of the branching configuration as well as to the ZnO nuclei of the cage-like nano-tetrapod ZnO

Modelling of electrical properties of Ni-YSZ composites

Marinsek-M; Pejovnik-S; Macek-J(Fac. of Chem. & Chem. Technol., Ljubljana, Slovenia)

Journal-of-the-European-Ceramic-Society. 2007; 27(2-3): 959-64

Ni-YSZ cermets with tailored microstructural characteristics are of interest in many solid-state electrochemical applications such as fuel cell electrode processes or oxygen sensors. In order to elucidate the role of microstructural parameters on overall Ni-YSZ electrical characteristics, different cermets were synthesized by the citrate-nitrate combustion route and their electrical characteristics were tested. The combustion derived samples exhibited fairly high electronic conductivity, even at a relatively low metal volume fraction of 24vol.% of Ni. To determine the electrical conductivity behaviour of the composites in a broad range of metal content and its relation to material porosity, the general effective media approach and the sine-wave approximation were used, respectively. [All rights reserved Elsevier]

MA-SHS of NbC and NbB₂ in air from the Nb/B/C powder mixtures

Tsuchida-T; Kakuta-T(Graduate Sch. of Eng., Hokkaido Univ., Sapporo, Japan)

Journal-of-the-European-Ceramic-Society. 2007; 27(2-3): 527-30

When the Nb/B/C powder mixture with different molar ratios was mechanically activated by grinding for 60-150min in a planetary ball mill and exposed to air, it self-ignited spontaneously and the self-propagating high-temperature synthesis (SHS) of NbC and NbB₂ was induced. This mechanical activation assisted SHS (MA-SHS in air process) depended strongly on the particle size of Nb metal, the mixing ratio of Nb/B/C and the weight ratio of sample to balls. The product of NbC and NbB₂ with fine, homogeneous microstructure is expected to be a promising candidate as precursor of NbC-NbB₂ composites. [All rights reserved Elsevier]

Varistors prepared by self-propagating combustion ZnO powders

Liu-Guixiang; Xu-Guangliang; Luo-Qingping(Coll. of Material Sci. & Eng., Southwest Univ. of Sci. & Technol., Sichuan, China)

Journal-of-the-Chinese-Ceramic-Society. 2006; 34(9): 1055-9

Using zinc nitrate, urea and additives as raw materials, doped ZnO nanopowders for varistors were prepared by the self-propagating combustion method. The powders were characterized by means of X-ray diffraction, scanning electron microscopy, specific surface area analysis and laser size analysis. The effects of addition amounts of urea on the properties of the powders and sintering temperature on the properties of ZnO varistors were studied. The mechanism of the reaction in the self-propagating combustion process was discussed. The results showed that doped ZnO powders prepared at 600degC when the mass ratio of urea and metal salts is 1, possess good properties. A ZnO varistor with the best electronic properties was prepared by the powders, which had a potential gradient of 745.21 V/mm, a nonlinear coefficient of 56.53 and a leakage current of 6 muA

Cell structure control of porous titanium composite synthesized by combustion reaction

Kobashi-M; Kuze-K; Kanetake-N(Dept. of Mater. Sci. & Eng., Nagoya Univ., Japan)

Advanced-Engineering-Materials. Sept. 2006; 8(9): 836-40

Porous titanium matrix composites were fabricated by a reaction between titanium powder and boron carbide (B₄C) powder. Precursors were made by compacting the elemental powder blend, and heated in an induction furnace to induce the reaction. The reaction was strongly exothermic and, therefore, it was a combustion mode when Ti/B₄C blending ratio of the precursor was appropriate. The reaction products were titanium boride (TiB or TiB₂) and titanium carbide (TiC). By controlling the Ti/B₄C blending ratio, it was possible to control the volume fraction of reaction products in the titanium matrix. The combustion synthesized material was porous and its cell structure was strongly affected by the processing condition of the precursor (porosity of the precursor and Ti/B₄C blending ratio). The open cell structure was made from precursors with low Ti/B₄C and high porosity. The cell size was varied from several tens of microns to about 500 microns by changing the combustion temperature

Sinterable La_0.8Sr_0.2CrO₃ and La_0.7Ca_0.3CrO₃ powders by sucrose combustion synthesis

Prabhakaran-K; Lakra-J; Beigh-MO; Gokhale-NM; Sharma-SC; Lal-R(Naval Mater. Res. Lab., Thane, India)

Journal-of-Materials-Science. Oct. 2006; 41(19): 6300-4

Air atmosphere sinterable La_0.8Sr_0.2CrO₃ [LSC] and La_0.7Ca_0.3CrO₃ [LCC] powders have been prepared by sucrose combustion synthesis. Aqueous solution containing stoichiometric quantities of the metal nitrates and sucrose (3 moles/mole of the metal ion) at pH ~1 was concentrated by heating on a hot plate into a viscous resin which on drying at 120degC produced a foam with interconnected pore structure. This foam ignited with a matchstick in a combustion set up fabricated in the laboratory produced ashes consisting of loose aggregate of LSC and LCC particles. The loose aggregates of LSC and LCC were powdered by planetary ball milling to submicron size particles with D₅₀ value 0.19 and 0.60 mum, respectively. The surface area of the LSC and LCC powders was 23 and 19 m²/g, respectively. Pellets prepared by cold compaction and sintering of LSC and LCC powders in air atmosphere showed density 96.8 and 98.8% of theoretical value respectively. Sintered LCC sample showed finer grains compared to the LSC sample under identical processing conditions

Nano-sized PDP phosphors prepared by solution combustion method

Zhe-Chen; Youwei-Yan(State Key Lab. of Die & Mould Technol., Univ. of Sci. & Technol., Wuhan, China)

Journal-of-Materials-Science. Sept. 2006; 41(17): 5793-6

Nanoscale BaMgAl₁₀O₁₇:Eu²⁺ phosphors are successfully grown by an improved facile combustion method. The solution combustion synthesis produces perfectly spherical, fine sized particles with high crystallinity and improved luminescence properties compared to those fabricated by conventional solid-state synthesis

Self-propagating high-temperature synthesis (SHS) of rotator mixed and mechanically alloyed Ni/Al powder compacts

Morsi-K; Shinde-S; Olevsky-EA(Dept. of Mech. Eng., San Diego State Univ., CA, USA)

Journal-of-Materials-Science. Sept. 2006; 41(17): 5699-703

The concepts of the theory of plasticity of porous materials are used to investigate the influence of mechanical alloying (MA) on the yield stress of Ni-Al compacts. MA process effects on self-propagating high temperature synthesis (SHS) characteristics as well as the influence of degassing-MA-SHS sequential order on the porosity of the products are also reported

Strengthening mechanisms of carbon element in in situ TiC/Ti-1100 composites

Fengcang-Ma; Weijie-Lu; Jining-Qin; Di-Zhang(State Key Lab. of Metal Matrix Composites, Shanghai Jiao Tong Univ., China)

Journal-of-Materials-Science. Aug. 2006; 41(16): 5395-8

In this paper, C element was added to Ti-1100 alloy to prepare TiC/Ti-1100 composites utilizing SHS technique. It was observed that C element can increase the strength of Ti-1100 alloy obviously at ambient temperature or at 800 K. But the strengthening mechanism is different at different temperatures. At ambient temperature, compared to Ti-1100 alloy the tensile strength increases mainly results from the solid solution C in matrix. At 873 K, compared to Ti-1100 alloy the tensile strength increases results from not only solid solution C in matrix but also formed TiC particles

Aerosol flame synthesis of catalysts

Strobel-R; Baiker-A; Pratsinis-SE(Dept. of Mech. & Process Eng., ETH Zurich, Switzerland)

Advanced-Powder-Technology. 2006; 17(5): 457-80

A review of synthesis and performance of flame-made catalytic materials is presented. Emphasis is placed on flame technology for its dominance in aerosol manufacturing of materials of high purity with minimal liquid byproducts. Flame aerosol processes are characterized in terms of the precursor state supplied to the flame. During the last decade, a better understanding of aerosol and combustion synthesis of materials contributed to the development of one-step, dry synthesis of catalysts that are prepared conventionally by multi-step wet-phase processes. This includes TiO₂-based photocatalysts, mixed oxides (e.g. V₂O₅/TiO₂, TiO₂/SiO₂, perovskites, etc.) as well as supported metals (e.g. Pt/TiO₂, Pd/Al₂O₃, Pt/CeO₂/ZrO₂, Pt/Ba/Al₂O₃, Ag/ZnO, Cu/ZnO/Al₂O₃ bimetallic Pd/Pt/Al₂O₃ and Au/TiO₂) made by single- or multi-nozzle flames. In general, highly crystalline and non-porous nanoparticles are formed during flame synthesis, resulting in materials with high thermal stability. Unique particle structures, only available through aerosol processes, lead to improved performance in various catalytic applications

Dynamics of reactive flame sprayed TiC/Fe composite coatings

Liu-Chang-song; Li-Zhi-wen; Huang-Ji-hua; Yin-Sheng(Sch. of Mech. Eng., Qingdao Technol. Univ., China)

Chinese-Journal-of-Nonferrous-Metals. Sept. 2006; 16(9): 1522-6

The TiC/Fe composite coatings were prepared by reactive flame spray using ferrotitanium, iron and graphite as the starting materials, which needs to ignite the self-propagation high-temperature synthesis (SHS) reaction of Fe-Ti-C system by oxygen-acetylene flame. The dynamics of this SHS reaction were studied. The ignition temperature is reduced by increasing Fe content and graphite content or by decreasing the size of reactive components. The degree of the complete reaction is affected by spray powder size, oxygen-acetylene flame power, spray distance and the composition of spray powder

Nonlinear luminescence in Eu³⁺-doped Y₂O₃ powders pumped at 355 nm

de-Araujo-CB; Rakov-N; Whualkuer-Lozano-B; Maciel-GS(Dept. de Fisica, Univ. Fed. de Pernambuco, Recife, Brazil)

Chemical-Physics-Letters. 8 Sept. 2006; 428(1-3): 134-7

Luminescence properties of Eu³⁺-doped Y₂O₃ powder prepared by combustion synthesis were studied. Nonlinear luminescence due to Eu³⁺:⁵D₀rarr⁷F₂ transition was observed for excitation at 355 nm. The dynamics of luminescence signal changes with the pump laser intensity showing that different regimes are present being faster at higher intensities. [All rights reserved Elsevier]

Development prospects of SHS technologies in Altai State Technical University

Evstigneev-VV; Guljaev-PJ; Miljukova-IV; Goncharov-VD; Vagner-VA; Gladkih-AA(Polzunov Altai State Tech. Univ., Barnaul, Russia)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(1): 99-103

The discovery of self-propagating high-temperature synthesis (SHS) gives a new impulse to searching and conception forming of physical and chemical combustion mechanisms in various substance aggregate states. First, it concerns combustion in a firm phase. The method of SHS provides the possibility of getting the materials with peculiar properties owing to specific synthesis conditions: considerable thermodynamic nonequilibrium, and high-temperature gradients

Study on the synthesis and structural characterization of the cermets TiC/Fe by self-propagating high-temperature and by thermal explosion

Bendjemil-B; Zemmour-K; Guerioune-M; Gunth-A; Leonhardt-A; Langlois-P; Vrel-D(Departement de Phys., Univ. Badji-Mokhtar Annaba, Algeria)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(1): 85-98

A study of the TiC/Fe cermets produced by self-propagating high-temperature synthesis and by thermal explosion with various quantities of added iron was performed. It was established that both the experimental and calculated adiabatic temperature of combustion and the propagation velocity of the reaction front decrease with the addition of iron in the reactants. The addition of iron was optimized at 30 wt.% to ensure the stability of the propagation. The products were characterized by X-ray diffraction (XRD); the reaction seems to start at the surface of the solid titanium particle and proceed by solid-state diffusion of iron and carbon to form TiFe and TiC/Fe cermets composite. The evolutions of the phases, size, and density of TiC grains during both kinetics reactions were highlighted by XRD and optical and scanning electronic microscopy equipped with microindentation and energy-dispersive X-ray spectroscopy, respectively

Synthesis of a single-phase RuAl intermetallic compound by reactive powder processing

Gobran-HA; Mucklich-F(Dept. of Mater. Sci., Saarlandes Univ., Saarbrucken, Germany)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(1): 71-83

Single-phase ruthenium-aluminum (RuAl) was synthesized from elemental powders by reactive sintering. The process involves a self-propagating exothermic reaction between the constituent powders to form an intermetallic compound. It was shown that the initial composition, density of the green compact, and Ru:Al particle-size ratio strongly affect the structure and density of the final material. An initial excess of aluminum of 1.5 at.% over the stoichiometric composition is necessary in order to compensate for Al loss during reactive sintering in vacuum

Titanium diboride-titanium aluminides composites prepared by SHS under normal and microgravity conditions: a microstructural study

Lemoisson-F; De-Wilde-J; Orru-R; Beloki-IA; Licheri-R; Sytchev-A; Rogachev-A; Cao-G; Jarvis-DJ; Froyen-L(Departement MTM, Katholieke Univ., Leuven, Belgium)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(1): 49-61

Within the frame of the Belgian Taxi flight mission ODISSEA, microgravity self-propagating high-temperature synthesis (SHS) experiments on the production of intermetallic matrix composites (IMCs) based on the Al-Ti-B system were performed on the International Space Station (ISS). Depending on the composition, different intermetallic compounds can be formed: titanium aluminides, which act as a matrix phase, and titanium diboride, which is present as a reinforcing particulate phase. The present experiments consist of cylindrical samples with a conical end, the last one integrated in a copper block with a conical cavity in order to perform combustion front quenching. The cylindrical part can be used to study the combustion process in a stationary regime. A comparative analysis is performed between samples processed in reduced gravity and normal gravity. Microstructure formation is a focal point. The elimination of gravity-dependent phenomena such as convection and spreading of molten components, buoyancy, and sedimentation of inert solid particles and droplet coalescence streamlines the research focus. Under certain conditions, gravity-dependent secondary processes may also occur in the heat-affected zone after combustion. Other phenomenon masked by gravity include diffusion and Marangoni convection. In the present paper, the effect on the microstructure of both gravity and initial composition are assessed in terms of morphology and composition of the matrix phase, as well as in terms of the size and morphology of the particulate phase

Synthesis of ceramics in an SHS reaction ignited with the other one

Guellati-O; Ali-rachedi-M; Bounour-W; Benaldjia-A; Guerioune-M; Vrel-D(Lab. d'Etude et de Recherche des Etats Condenses, Univ. Badji Mokhtar, Annaba, Algeria)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(1): 41-8

The necessity of developing new material with better properties has oriented investigations to advanced techniques such as self-propagating high-temperature synthesis (SHS). The present study first suggests synthesizing titanium carbide TiC in a direct SHS reaction. Then, using a thermite reaction, the exothermicity of which is even higher and the ignition temperature is smaller, we have ignited the Ti + C rarr TiC reaction. Finally, characterization of the synthesized products has been carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to determine compositions and microstructures

Influence of molybdenum and boron oxides on combustion in the Mo-B gasless system

Egishyan-AV; Manukyan-KhV; Harutyunyan-AB; Kharatyan-SL(Lab. of Kinetics of SHS Processes, Nat. Acad. of Sci., Yerevan, Armenia)

International-Journal-of-Self-Propagating-High-Temperature-Synthesis. 2006; 15(1): 33-40

Combustion laws in the Mo-B and Mo-B-MoO₃(B₂O₃) systems, as well as phase and microstructure formation, have been studied depending on the ratio of components in the initial charge and on the quantity of oxide additives. Based on experimental results obtained and detailed thermodynamic analysis, a possible mechanism on combustion wave propagation in the Mo-B system is suggested, according to which boron oxides are predominant in the mass exchange

Influence of synthesis route on morphology and electrical properties of LaNi_0.6/Fe_0.4O₃

Fornasiero-P; Bevilacqua-M; Montini-T; Tavagnacco-C; Vicario-G; Graziani-M(Chem. Dept., Univ. of Trieste & INSTM, Italy)

Solid-State-Ionics,-Diffusion-and-Reactions. 15 Nov. 2006; 177(33-34): 2957-65

Recently LaNi_1-xFe_xO₃ materials have been suggested as good candidates for cathodes for Intermediate Temperature Solid Oxide Fuel Cells. The electrical conductivity and the morphology of LaNi_0.6/Fe_0.4O₃ samples have been studied as a function of preparation route and calcination temperature. The conductivity, mainly electronic, strongly depends on the densification of the material, which is influenced by the preparation procedure. DFT calculations indicate that the conduction bands of LaNi_0.6/Fe_0.4O₃ are mainly made up of Fe and Ni 3d states and that there is a small bandwidth (2.3 eV) around the Fermi level. Moreover, a small polaron mechanism for the electronic conduction in this material is suggested by the simulations. Three different preparation methods have been investigated: the glycine-nitrate process, the gel-citrate complexation route and the coprecipitation route. The glycine-nitrate synthesis produces non-homogenous LaNi_0.6/Fe_0.4O₃ materials. Good specific conductivity is obtained only after high temperature treatments that homogenise and sinter the material. The gel-citrate complexation route leads to homogenous LaNi_0.6/Fe_0.4O₃ samples, which however are resistant to sinterization/densification. Finally, homogenous LaNi_0.6/Fe_0.4O₃ is obtained with coprecipitation synthesis. This synthesis is particularly promising since the morphology of the obtained precipitate favours the sinterization at low temperatures. These temperatures are low enough to prevent the undesirable reaction with ZrO₂-based electrolyte. [All rights reserved Elsevier]

Self-propagating high-temperature synthesis of Ti₃SiC₂: study of the reaction mechanisms by time-resolved X-ray diffraction and infrared thermography

Gauthier-V; Cochepin-B; Dubois-S; Vrel-D(Lab. de Metall. Phys., UMR CNRS, Poitiers, France)

Journal-of-the-American-Ceramic-Society. Sept. 2006; 89(9): 2899-907

Ti₃SiC₂ is synthesized by self-propagating high-temperature synthesis (SHS) of elemental titanium, silicon, and graphite powders. The reaction paths and structure evolution are studied in situ during the SHS of the 3Ti+Si+2C mixture by time-resolved X-ray diffraction coupled with infrared thermography. The proposed reaction mechanism suggests that Ti₃SiC₂ might be formed from Ti-Si liquid phase and solid TiC_x. Finally, the effect of the powders starting composition on the Ti₃SiC₂ synthesis is studied. For the investigated initial mixtures, TiC_x is always formed as a major impurity together with the Ti₃SiC₂ phase

Synthesis and characterization of mixed-metal oxide nanopowders along the CoO_x-Al₂O₃ tie line using liquid-feed flame spray pyrolysis

Azurdia-J; Marchal-J; Laine-RM(Dept. of Mater. Sci. & Eng., Michigan Univ., Ann Arbor, MI, USA)

Journal-of-the-American-Ceramic-Society. Sept. 2006; 89(9): 2749-56

We report here the use of liquid-feed flame spray pyrolysis (LF-FSP) to produce a series of nanopowders along the CoO_x-Al₂O₃ tie line. The process is a general aerosol combustion synthesis route to a wide range of lightly agglomerated oxide nanopowders. The materials reported here were produced by aerosolizing ethanol solutions of alumatrane [Al(OCH₂CH₂)₃N] and a cobalt precursor, made by reacting Co(NO₃)₂middot6H₂O crystals with propionic acid. The compositions of the as-produced nanopowders were controlled by selecting the appropriate ratios of the precursors. Nine samples with compositions (CoO)_y(Al₂O₃)_1-y, y = 0-1 along the CoO_x-Al₂O₃ tie line were prepared and studied. The resulting nanopowders were characterized by X-ray fluorescence, BET, scanning electron microscopy , high-resolution transmission electron micrographs, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and FTIR. The powders typically consist of single-crystal particles <40 nm diameter and specific surface areas (SSAs) of 20-60 m²/g. XRD studies show a gradual change in powder patterns from delta-Al₂O₃ to Co₃O₄. The cobalt aluminate spinel phase is observed at stoichiometries (21 and 37 mol%) not seen in published phase diagrams, likely because LF-FSP processing involves a quench of >1000degC in microseconds frequently leading to kinetic rather than thermodynamic products. Likewise, the appearance of Co₃O₄ rather than CoO as the end member in the tie line is thought to be a consequence of the process conditions. TGA studies combined with diffuse reflectance FTIR spectroscopic studies indicate that both physi and chemi-sorbed H₂O are the principal surface species present in the as-processed nanopowders. The only sample that differs is Co₃O₄, which has some carbonate species present that are detected and confirmed by a sharp mass loss event at ~250degC. The thermal behavior of the high cobalt content samples differs greatly from the low cobalt content samples. The latter behave like most LF-FSP-derived nanopowders exhibiting typical 1%-4% mass losses over the 1400degC range due mostly to loss of water and some CO₂. The high cobalt content samples exhibit a sharp mass loss event that can be attributed to the decomposition of Co₃O₄ to CoO

Efficient preparation of submicrometer alpha-alumina powders by calcining carbon-covered alumina

Pei-Wang; Chunming-Wang; Li-Lin; Yuexiang-Zhu; Youchang-Xie(State Key Lab. for Struct. Chem. of Unstable & Stable Species, Peking Univ., Beijing, China)

Journal-of-the-American-Ceramic-Society. Sept. 2006; 89(9): 2744-8

A simple method is described to prepare submicrometer alpha-alumina by burning carbon supported on the surface of gamma-alumina in oxygen flow at a temperature of 800degC. The burning of carbon generates a large amount of heat and leads to a rapid increase in the local temperature inside the pores of alumina. When the temperature is high enough for the phase transformation, alpha-alumina is obtained in a very short rime. It was found that, for carbon contents between 6 and 10 wt%, all the gamma-alumina could transform into alpha-alumina after burning of carbon in oxygen for a short time, and the transformed particle sizes of alpha-alumina were mostly no more than 1 mum

Formation of MgO powders by using a combustion method and the thermodynamics of gas adsorption

Seo-DH; Kim-CO; Lee-YP; Kim-JY; Choi-BI; Nham-HS(Div. of Adv. Res., Hanyang Univ., Seoul, South Korea)

Journal-of-the-Korean-Physical-Society. Sept. 2006; 49(3): 951-4

MgO and ZnO powders having highly uniform (100) surface exposure were synthesized by using a combustion method at an rf power. Mg or Zn pieces of a few millimeter size were mixed with carbon in a volume ratio of 2:1 and were placed in a carbon crucible. The quality of the powders was characterized by using X-ray and TEM investigations, which confirmed that the powders were a single phase with sizes smaller than a few hundred nanometers. The adsorption isotherms of Ar measured below the triple point (83.78 K) showed that 1) the amount of gas adsorbed on the MgO surface was approximately two times greater than that of the ZnO powder and that 2) the curvature of the isotherm step depended on the condition of the powder. These results demonstrate that the adsorption isotherm is strongly affected by the condition of the powder surface

KrF excimer laser-assisted combustion-flame deposition of diamond films

Han-YX; Ling-H; Lu-YF(Dept. of Electr. Eng., Univ. of Nebraska-Lincoln, Lincoln, NB, USA)

Journal-of-Applied-Physics. 15 Dec. 2006; 100(12): 124911-1-5

Cobalt (Co) composition has detrimental effects on the deposition of diamond films on cemented tungsten carbide (WC-Co) substrates. It decreases adhesion of the deposited films to the substrates and causes a transformation of sp³-bonded diamond to sp²-bonded graphite. In this study, a KrF excimer laser with a wavelength of 248 nm, a pulse width of 23 ns, and a pulse energy range of 84-450 mJ was used in the combustion-flame method to improve the quality of the deposited diamond films. Scanning electron microscopy, energy dispersive x-ray analysis, and Raman spectroscopy of the deposited films showed that a laser irradiation during combustion-flame deposition of diamond decreased the cobalt composition drastically. Based on the experimental results, the influence of the laser irradiation on the deposition process was analyzed

Lean and ultralean stretched propane-air counterflow flames

Pitz-RW; Zhongxian-Cheng; Wehrmeyer-JA(Mech. Eng. Dept., Vanderbilt Univ., Nashville, TN, USA)

Combustion-and-Flame. June 2006; 145(4): 647-62

Stretched laminar flame structures for a wide range of C₃H₈-air mixtures vs hot products are investigated by laser-based diagnostics and numerical simulation. The hot products are produced by a lean H₂-air premixed flame. The effect of stretch rate and equivalence ratio on four groups of C₃H₈-air flame structures is studied in detail by Raman scattering measurements and by numerical calculations of the major species concentration and temperature profiles. The equivalence ratio, phi, is varied from a near-stoichiometric condition (phi=0.86) to the sublean limit (phi=0.44) and the stretch rate varies from 90 s^-1 to near extinction. For most of these C₃H₈-air lean mixtures, hot products are needed to maintain the flame. The significant feature of these flames is the relatively low flame temperatures (1200-1800 K). For this temperature range, the predicted C₃H₈-air flame structure is sensitive to the specific chemical kinetic mechanism. Two types of flame structures (a lean self-propagating flame and a lean diffusion-controlled flame) are obtained based on the combined effect of stretch and equivalence ratio. Three different mechanisms, the M5 mechanism, the Optimized mechanism, and the San Diego mechanism, are chosen for the numerical simulations. None of the propane chemical mechanisms give good agreement with the data over the entire range of flame conditions. [All rights reserved Elsevier]

Investigation and simulation of the structural features of composites containing conducting nonstoichiometric titanium compounds

Ishkov-AV; Sagalakov-AM(Altai State Univ., Barnaul, Russia)

Technical-Physics-Letters. June 2006; 32(6): 474-6; Original: Pis'ma-v-Zhurnal-Tekhnicheskoi-Fizika. June 2006; 32(6)

The structure of polymer-based composite materials filled with conducting nonstoichiometric titanium compounds has been studied by the method of fractography, with determination of the fractal dimension of the filler cluster boundaries in the composite. A computer model of the formation of isotropic filler clusters is proposed. In terms of this model, the morphology of conducting structures has been studied and the reasons for additional structurization of the filler in the composite have been established

Self-propagating high-temperature synthesis for aluminum oxynitride (AlON)

Jaeryeong-Lee; Ikkyu-Lee; Hunsaeng-Chung; Jonggwan-Ahn; Dongjin-Kim; Byounggu-Kim(Div. of Miner. & Mater. Process., Korea Inst. of Geosci. & Miner. Resources, Daejeon, South Korea)

Materials-Science-Forum. 2006; 510-511: 662-5

As the result of combustion reaction in Al-Al₂O₃-N₂ system, AlON phase can be synthesized in the range of initial nitrogen pressure, from 1 to 5 MPa. On the occasion of r_m = 0.3, the unreacted Al was detected in the case of 1 MPa of P_N2. Its intensity decreases with an increase of nitrogen pressure. Ultimately, no peak of Al was observed in the product at nitrogen pressure of 5 MPa. In addition, the peak intensity of AlON in the products increases proportionally with the nitrogen pressure, while the intensities of AlN and Al₂O₃ decrease slightly with an increase of nitrogen pressure. The formation of AlON may be induced by successive two reactions. The former is the formation of AlN, and the latter is the reaction between AlN and Al₂O₃ in the after-burning period sustaining high temperature

In-situ joining of combustion synthesized Ni-Al alloys with Al casting alloy

Gue-Serb-Cho; Kang-Rae-Lee; Kyeong-Hwan-Choe; Kyong-Whoan-Lee; Akira-Ikenaga(Adv. Mater. R&D Center, Korea Inst. of Ind. Technol., Incheon, South Korea)

Materials-Science-Forum. 2006; 510-511: 178-81

We focused on the surface reinforcement of Al casting alloys with Ni-Al intermetallic compounds by in-situ combustion reaction to improve the surface properties of Al casting components. Microstructure and phase formation behavior of Ni-Al based intermetallic compounds synthesized by combustion reaction were investigated in terms of thermal and phase analysis using scanning electron microscope(SEM) equipped with energy dispersive X-ray spectrometer (EDS) and X-ray diffractometer (XRD) in Ni-Al intermetallic compounds. Three kinds of nickel aluminides, NiAl₃, NiAl and Ni₃Al, were synthesized by emission heat from the Al molten metal in order to form a coating layer of intermetallic phase simultaneously on the solidified Al alloy surface. The synthesized shapes and microstructures of nickel aluminides were varied by casting temperature, Si contents, and the mixing ratio of elemental powders. The synthesized reaction products formed in nickel aluminides were observed to be different depending on the mixing ratio of elemental powders. The reaction layer of about 25 mum thickness was formed at the interface, and it mainly consisted of NiAl₃ phase by the reaction between liquid molten Al alloy and solid Ni powders in green compact. With this information, we successfully produced a coating layer of Ni₃Al intermetallic compound onto the casting Al alloy surface using molten metal heat without any additional process. These findings led us to conclude that a near-net shaped nickel aluminide coating layer can be formed using this unique process

Silica-based composite and mixed-oxide nanoparticles from atmospheric pressure flame synthesis

Akurati-KK; Dittmann-R; Vital-A; Klotz-U; Hug-P; Graule-T; Winterer-M(Lab. for High Performance Ceramics, Swiss Federal Lab. for Mater. Testing & Res., Duebendorf, Switzerland)

Journal-of-Nanoparticle-Research. Aug. 2006; 8(3-4): 379-93

Binary TiO₂/SiO₂ and SnO₂/SiO₂ nanoparticles have been synthesized by feeding evaporated precursor mixtures into an atmospheric pressure diffusion flame. Particles with controlled Si:Ti and Si:Sn ratios were produced at various flow rates of oxygen and the resulting powders were characterized by BET (Brunauer-Emmett-Teller) surface area analysis, XRD, TEM and Raman spectroscopy. In the Si-O-Ti system, mixed oxide composite particles exhibiting anatase segregation formed when the Si:Ti ratio exceeded 9.8:1, while at lower concentrations only mixed oxide single phase particles were found. Arrangement of the species and phases within the particles correspond to an intermediate equilibrium state at elevated temperature. This can be explained by rapid quenching of the particles in the flame and is in accordance with liquid phase solubility data of Ti in SiO₂. In contrast, only composite particles formed in the Sn-O-Si system, with SnO₂ nanoparticles predominantly found adhering to the surface of SiO₂ substrate nanoparticles. Differences in the arrangement of phases and constituents within the particles were observed at constant precursor mixture concentration and the size of the resultant segregated phase was influenced by varying the flow rate of the oxidant. The above effect is due to the variation of the residence time and quenching rate experienced by the binary oxide nanoparticles when varying the oxygen flow rate and shows the flexibility of diffusion flame aerosol reactors

SHS process of Ti-B₄C-C reactive system in flame spraying

Wang-Jianjiang; Du-Xinkang; Fu-Yongxin; Xue-Jin; Lu-Daqin(Xi'an Jiaotong Univ., China)

Rare-Metal-Materials-and-Engineering. Aug. 2006; 35(8): 1258-62

Based on the SHS reactive flame spray technology, TiC-TiB₂ multiphase ceramic coatings were prepared in the Ti-B₄C-C reactive system. Water quenching experiments were used to intercept the intermediate states of the flying particles during the spray course. The macroscopical characteristics, composition, structure, and transforming course of the intermediate-stated reactive products in different flying distance were observed, and the flying combustion course and reactive mechanism of the spray agglomerates in the oxyacetylene flame were discussed. It was showed that there were four types of intermediate-stated reactive products according to their macroscopical characteristics, which were the fully molten solid and hollow ceramic beads, the ceramic particles with molten surface whereas the un-molten core and the completely un-molten ceramic particles. The flying combustion mechanism is studied. The SHS reaction began with the melting of Ti powders. The combustion synthesis of the relatively small spray agglomerates in the core of the oxyacetylene flame was controlled by the diffusion and capillary mechanism and took place in the deflagration mode, whereas the combustion synthesis of the relatively big spray agglomerates in the periphery of the oxyacetylene flame was controlled by the ingredient melting and separating out mechanism

Combustion front dynamics in the combustion synthesis of refractory metal carbides and di-borides using time-resolved X-ray diffraction

Wong-J; Larson-EM; Waide-PA; Frahm-R(Lawrence Livermore Nat. Lab., California Univ., USA)

Journal-of-Synchrotron-Radiation. July 2006; 13: 326-35

A compact diffraction-reaction chamber, using a 2-inch photodiode array detector, has been employed to investigate the chemical dynamics at the combustion front of a selected series of refractory metal carbides and di-borides from their constituent element reactants as well as binary products from B₄C as a reactant. These systems are denoted as (i) M + C rarr MC; (ii) M + 2B rarr MB₂; and (iii) 3M + B₄C rarr 2MB₂ + MC, where M = Ti, Zr, Nb, Hf or Ta. Time-resolved X-ray diffraction using intense synchrotron radiation at frame rates up to 10 frames s^-1 (or 100 ms frame^-1) was employed. The combustion reactions were found to complete within 200-400 ms. In contrast to the Ta + C rarr TaC combustion system studied earlier, in which a discernible intermediate sub-carbide phase was first formed, reacted further and disappeared to yield the final TaC product, no intermediate sub-carbide or sub-boride was detected in the current systems. Combustion for the Ti, Zr and Hf systems involved a liquid phase, in which the adiabatic temperatures T_ad are well above the melting points of the respective reactant metals and have a typical combustion front velocity of 5-6 mm s^-1. The Nb and Ta systems have lower T_ad, involving no liquid phase. These are truly solid combustion systems and have a lower combustion front velocity of 1-2 mm s^-1. The current study opens up a new avenue to chemical dynamics and macrokinetic investigations of high-temperature solid-state reactions

Preparation of carbon nanotubes over cobalt-containing catalysts via catalytic decomposition of methane

Mohamed-AR; Siang-Piao-Chai; Zein-SHS(Sch. of Chem. Eng., Univ. Sains Malaysia, Pulau Pinang, Malaysia)

Chemical-Physics-Letters. 4 Aug. 2006; 426(4-6): 345-50

Decomposition of methane into carbon nanotubes over CoO catalysts supported on various catalyst supports at 550 degC and 700 degC was investigated. The effect of catalyst promoters on the supported CoO catalysts at 700 degC was also examined. Electron microscope observations showed that among the various catalyst supports tested, alumina was found to be the most appropriate for CoO that CoO/Al₂O₃ catalyst grew carbon nanotubes with significant hollow cores. Experimental results further revealed that introducing FeO into CoO/Al₂O₃ catalyst resulted in the formation of carbon nanotubes with thin wall structure. Introducing MoO into CoO/Al₂O₃ catalyst increased the carbon capacity and the selectivity of CoO/Al₂O₃ catalyst in growing better quality carbon nanotubes

Mesoscale simulation of nanoparticle combustion synthesis

Zuccaro-G; Lapenta-G; Maizza-G(DISMIC, Politecnico di Torino, Italy)

IEEE-Conference-Record-Abstracts.-The-33rd-IEEE-International-Conference-on-Plasma-Science-IEEE-Cat.-No.-06CH37759. 2006: 342

Summary form only given. A coupled continuum-discrete numerical model is proposed to study complex physical systems composed by a set of clusters of different chemical species immersed in a matrix with which they interact. The overall model describes the transient of the basic mechanisms governing the processes of interaction in a two-dimensional micrometer size system. At each time step, the continuum (micrometer scale) model computes the macroscopic temperature field according to the prescribed boundary conditions. The continuum system is discretized with a desired number of uniform computational cells. Each cell contains a number of computational particles which represent the actual particles mixture. The particle-in-cell (discrete) model maps the macroscopic fields from the (continuum) cells to the particles. Chemical reactions and particle dynamics are followed using a molecular dynamics approach. We present results of a recent application of this approach to the simulation of nanoparticles formation in SHS reactors. To investigate the physical conditions under which this phenomenon takes place, we propose a statistical analysis based on the pair distribution function for the particles formed during the reaction. In particular, the dependence of this function on the interaction potential between particles has been investigated. As a demonstration of the effectiveness of the method some paradigmatic examples will be shown

Quasi one-dimensional ceramic nanostructures spontaneously formed by combustion synthesis

Huczko-A; Lange-H; Bystrzejewski-M; Rutkowska-A; Cudzilo-S; Szala-M; Wee-ATS(Dept. of Chem., Warsaw Univ., Poland)

Physica-Status-Solidi-B. Nov. 2006; 243(13): 3297-300

Inorganic quasi one-dimensional (quasi 1D) nanostructures (carbides, nitrides) were spontaneously and efficiently produced via a combustion synthesis. Silicon carbide (beta-SiC) nanofibres ca. 20-100 nm in diameter with the aspect ratio between 10² and 10³ were isolated (with a 98% purity) from the products resulting from redox reaction between Si-bearing compounds (mostly silicides) and perhalogenated hydrocarbons. The products were analysed by using XRD, Raman, and SEM/TEM techniques. The optical limiting performance of the nanofibres was evaluated

Novel faceted alpha-SiAlON micro-crystals prepared by combustion synthesis

Guanghua-Liu; Kexin-Chen; Heping-Zhou; Pereira-C; Ferreira-J(Dept. of Mater. Sci. & Eng., Tsinghua Univ., Beijing, China)

Journal-of-the-American-Ceramic-Society. Jan. 2006; 89(1): 364-6

Novel faceted alpha-SiAlON micro-crystals were prepared by combustion synthesis with proper additives. These crystals exhibited various end shapes, including smooth flat hexagonal faces, pyramids bounded by six small isosceles triangles, and partial pyramids with the sharp roofs removed. The formation mechanisms of different crystal shapes were discussed, and a terraced epitaxial nucleation mode for alpha-SiAlON was proposed. By this nucleation mode, two interesting crystal morphologies were formed: a terraced tower structure and a T-like shape. Transmission electron microscopy results showed that the fast growth direction of rod-like alpha-SiAlON crystals was parallel to the c-axis

Magnesium removal from TiC-TiB₂ SHS powders by controlled hot acid leaching

Delmas-F; Goncalves-L; Martins-I; Oliveira-M(Departamento de Mater. e Tecnologias de Producao, Instituto Nacional de Engenharia, Lisboa, Portugal)

Materials-Science-Forum. 2006; 514-516: 594-8

TiC and TiC-TiB₂ powder mixtures obtained directly from titanium (TiO₂) and boron (B₂O₃ or B₄C) raw-materials by reduction with magnesium by self propagating high temperature synthesis (SHS) contain, as impurity, large quantities of MgO under its periclase form, together in some cases with unreacted magnesium. Several leaching agents, namely hydrochloric acid, sulphuric acid, acetic acid and EDTA were tested aiming at removal of magnesium from these powders as required characteristic for further work. Several parameters as leachant concentration, pH, reaction time and temperature were evaluated. Alternative leaching methodologies were compared in order to achieve magnesium removal yields over 98% and minimising at the same time the expected high matrix losses due to TiC and/or TiB₂ co-solubilisation. As main conclusion it was established that strong hydrochloric acid (6M) is the most efficient medium to remove magnesium from these particular TiC-TiB₂ SHS mixtures. The leaching methodology used (controlled hot acid leaching under close conditions) allowed to minimise TiC and TiB₂ solubilisation losses. Sulphuric acid is not an effective leaching medium and contaminates the resulting powder mixture with unfriendly sulphur. Using acetic acid, magnesium removal yield is low and titanium losses are considerable. On the other hand, low aggressive EDTA complexant leaves TiC-TiB₂ matrix unalterable but residual MgO remains over 6%. The proposed process seems to have potential for application in the general field of semi-micro materials purification

Synthesis of IR sensitive material CaS:Eu, Sm by low-temperature combustion and its characterization

Lu-Liping; Zhang-Xiyan; Bai-Zhaohui; Wang-Xiaochun; Liu-Quansheng; Mi-Xiaoyun(Changchun Univ. of Sci. & Technol., China)

Rare-Metal-Materials-and-Engineering. Aug. 2006; 35(8): 1211-14

Infrared sensitive material CaS:Eu,Sm was synthesized by adding sublimate sulphur and using nitrate-urea as raw material system in a low-temperature combustion synthesis (LCS) method. The combustion process was discussed and the theoretical amount of urea adding was calculated according to the oxidation-reduction theory. It is found that the ignited temperature is 600degC, the reaction duration is 2 min~3 min and the product is red loose nano-powders with the size of 36 nm or so. XRD pattern shows that the product has a CaS crystal structure. Spectra analysis indicates that the sample can be excited effectively by natural light to store energy. The sample is sensitive to the infrared light of 800 nm~1600 nm and then emit a red light due to the transition 4f⁶5drarr4f⁷(⁸S₇2/) of Eu²⁺ ion

Estimating insolation based on PV-module currents in a cluster of stand-alone solar systems: Introduction of a new method

Nieuwenhout-F; van-der-Borg-N; van-Sark-W; Turkenburg-W(Energy research Centre of the Netherlands, Petten, Netherlands)

Solar-Energy. Sept. 2006; 80(9): 1220-2

In order to evaluate the performance of solar home systems (SHS), data on local insolation is a prerequisite. We present the outline of a new method to estimate insolation if direct measurements are unavailable. This method comprises estimation of daily irradiation by correlating photovoltaic (PV)-module currents from a number of solar home systems, located a few kilometres apart. The objective is to obtain reliable daily and monthly insolation figures that are representative for an area of a few square kilometres. [All rights reserved Elsevier]

Mechanism of combustion synthesis of Mg₂Ni

Chen-X-J; Tian-Dong-Xia; Liu-X-L; Tian-Zuo-Liu; Wen-Jun-Zhao(State Key Lab. of Gansu Adv. Non-ferrous Metal Mater., Lanzhou Univ. of Technol., China)

Journal-of-Alloys-and-Compounds. 21 Dec. 2006; 426(1-2): 123-30

To investigate the mechanism of combustion synthesis of Mg₂Ni, a mixture of Mg, Ni was used for a combustion front quenching test, and the microstructural evolution in the quenched sample was observed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The temperature-time profile of the combustion was measured, and the phase constituents of the different zones of the quenched sample were inspected by X-ray diffraction (XRD). Based on these experimental results, the mechanism of the combustion synthesis was analyzed, and a solid phase diffusion-dissolution-precipitation mechanism was proposed. An incompleteness of the combustion was found to be related to the usage of coarse reactant powders. [All rights reserved Elsevier]

Ni-YSZ SOFC anodes-Minimization of carbon deposition

Macek-J; Novosel-B; Marinsek-M(Fac. of Chem. & Chem. Technol., Univ. of Ljubljana, Slovenia)

Journal-of-the-European-Ceramic-Society. 2007; 27(2-3): 487-91

An advantage of solid oxide fuel cells (SOFC) over some other types of fuel cells is the extended range of fuels they can use. Besides hydrogen, hydrocarbons are often used. A problem that may arise on a prolonged operation of cells using hydrocarbons is the formation of carbon deposits on the anodes. These deposits deteriorate the cell performance by blocking the access of reactants to the anode surface and into its pores, thus changing the micromorphology of the anode. The behavior of anodic material during the extended contact with such fuels must be tested and if needed modifications must be made in its composition in order to reduce the rate of carbon deposition. Ni-YSZ cermet materials prepared by different processes (sol-gel and combustion synthesis) with variations in composition and presence of dopants were tested by exposing these materials to methane at elevated temperatures. The thermal dissociation of methane, which leads to carbon deposits on the cermet surface, was studied by the analysis of the gas phase using mass spectrometry and gas chromatography. The influence of anode composition and its microstructure on carbon deposition was studied as well as the influence of some dopants. The amount of the deposited carbon was determined by temperature programmed oxidation. [All rights reserved Elsevier]

Growth mechanisms for SiC-AlN solid solution crystals prepared combustion synthesis

Huabin-Wang; Northwood-DO; Jiecai-Han; Shanyi-Du(Dept. of Mech., Automotive & Mater. Eng., Windsor Univ., Ont., Canada)

Journal-of-the-American-Ceramic-Society. Feb. 2006; 89(2): 501-8

AlN-SiC solid solution particles with a variety of morphologies including faceted polyhedrons with or without ledges; hexagonal platelets; hexagonal columns with a hexagonal plate or a pyramidal cap; and interpenetrating cones, have been found in the combustion products of a mixture of Al, Si, and carbon black under a nitrogen pressure of 10 MPa. Combustion temperature (the growth temperature of crystals) is the most important factor controlling the morphology of crystals formed in the combustion product. When temperatures are close to the melting point of the solid solutions, a small driving force for nucleation and long distances of surface migration make nucleation on the basal plane difficult, and thus the solid solution particles tend to grow as platelets. Supersaturation is the second key factor influencing crystal growth. At relatively low temperatures, a low supersaturation at the large pores renders nucleation difficult and the solid solution particles tend to grow as platelets. At relatively low temperatures and high supersaturation, a relatively high driving force for nucleation and short mean distances of surface migration promote the growth of AlN-SiC solid solutions as polyhedrons. The formation of the ledges on the polyhedral particles is attributed to the differences in the evaporation rates and the deposition rates between Al and Si. At relatively low temperatures and an intermediate supersaturation, the solid solution particles grow as prismatic columns. The formation of the prismatic columns with a hexagonal plate, or a pyramidal cap, is attributed to a sudden change of temperature during combustion. A possible growth mechanism for the AlN-SiC solid solution cones is proposed

Synthesis of mullite powders through a suspension combustion process

Burgos-Montes-O; Moreno-R; Colomer-MT; Farinas-JC(Instituto de Ceramica y Vidrio, CSIC, Madrid, Spain)

Journal-of-the-American-Ceramic-Society. Feb. 2006; 89(2): 484-9

This work reports on the synthesis of mullite powders by a suspension combustion process. Aluminum nitrate, as a source of Al, and a colloidal silica suspension, as a source of Si, are used as reagents, and urea serves as the fuel. This colloidal suspension allows a complete mixing of the reactants, thus promoting a core-shell reaction to produce the mullite. The powders obtained need to be treated at a high temperature to form the mullite. However, when ammonium nitrate is also added as a combustion aid, the mullite phase is directly obtained without any further treatment. A chemical reaction involving all these compounds is proposed, and the thermodynamic parameters are calculated in order to predict the temperature reached during the combustion process. The addition of ammonium nitrate reduces the temperature of the reaction by ca. 150 degC. Once the conditions for the combustion reaction are optimized, the Al/Si ratio is modified in an attempt to obtain monophasic mullite

Effects of silica on the combustion synthesis and glass formation of TiB₂-containing calcium aluminate matrix composites

Hu-Chun-Yi; Guigne-JY; Robinson-LA; Manerbino-AR; Moore-JJ(Guigne Int. Ltd., Paradise, NF, Canada)

Journal-of-the-American-Ceramic-Society. Jan. 2006; 89(1): 162-70

Combustion synthesis has been used to study the combustion characteristics and microstructure in the TiB₂-CaO-Al₂O₃-SiO2 system. Both the combustion temperature and wave velocity decreased with an increase in the amount of silica. The reacted product consisted of solid crystalline TiB₂ phase and CaO-Al₂O₃-SiO₂ matrix. No significant reaction between the TiB₂ and the matrix was observed. It was found that the binary calcium aluminate matrix (Ca₁₂Al₇O₃₃ and CaAl₂O₄ compounds) could form amorphous phase (glass) at a high cooling rate. Under a normal cooling rate, significant formation of glass in the matrix was found possible only by adding another glass-former, e.g., silica (SiO₂). The addition of SiO₂ led to the formation of Gehelenite, to the reduction of the other crystal phases and to an increase in the glass phase in the matrix. A pure glass matrix was obtained for all compositions in the composition range from Ca₁₂Al₇O₃₃ to CaAl₂O₄ compounds provided that an adequate amount of SiO₂ was added. The resulting glass matrix can be expressed by the formula Ca₂(Si_xAl_1-x)₃O, where x=0.32-0.58, depending on the composition. Effects of the TiB₂ phase on the combustion synthesis process and on the microstructure are also discussed. TiB₂ increased the reactivity and led to the formation of the molten matrix which was critical for glass formation. However, its effects on the vitrification of the matrix was considered to be minimum. The mechanism of glass formation in the matrix is discussed using the Zachariasen-Warren network theory

Numerical simulation on thermal shock damage behavior of TiB₂-Cu composite via combustion synthesis

Hong-Changqing; Han-Jiecai; Zhang-Xinghong; Xu-Qiang(Harbin Inst. of Technol., China)

Rare-Metal-Materials-and-Engineering. Jan. 2006; 35(1): 47-51

The thermal shock behavior of TiB₂-Cu composite by combustion synthesis was investigated using plasma arc heating and numerical simulation. The transient temperature field and thermal stress fields affected by inhomogeneous boundary conditions of heat transfer in high temperature were simulated and analyzed based on the thermal physical data with ANSYS commercial software. The results reveal that the maximum compression stresses are generated at center of sample and decreased along radius. The compression stresses transform to tensile stresses when the arc beam gets across the heating area, and the largest tensile stress takes place in the edge of the specimen. The crack may initiate in the edge of the sample, and then properly propagates to the position of center in the direction of radius. The experiment of plasma arc heating also favor and approve the rationality of theoretical model

Heat-resistant gradient material of TiC-Mo/W system synthesized in SHS/HP method

Li-Yong; Zhang-Zhimin(Beijing Inst. of Technol., China)

Rare-Metal-Materials-and-Engineering. Jan. 2006; 35(1): 21-4

Such experimental researches as XRD, SEM and TEM were conducted on the synthesized ceramic heat-resistant gradient material of TiC-Mo/W system prepared by combining SHS with the new method of HP. The result of XRD shows that the reaction product is no other than TiC and Mo/W. TEM analysis finds that TiC ceramic particle becomes a ellipsoidal distribution, tiny and relatively even particle, with Mo/W metal phase in-between; SEM indicates that the shape of multi-metal phase appears to be island-like and distributes in continuous gradient clouds. The compacting density, bending strength, fracture toughness and rigidity value of the synthesis can be prepared to be applicable gradient material structure under suitable pressure and temperature. In the course of SHS/HP, Mo/W distributes into ceramics TiC in the manner of gradient clouds along the sample grade direction. According to the research, the characteristics of the material is anisotropic and transversally isotropic along the direction and vertical grade direction respectively

Pyrolysis behavior of paint in car steel sheet recycling process

Cao-Lei; Muhlberger-F; Adam-T; Streibel-T; Zimmermann-R; Kettrup-A; Wang-Hai-zhou(Anal. & Testing Inst., Central Iron & Steel Res. Inst., Beijing, China)

Journal-of-Iron-and-Steel-Research. Jan. 2006; 18(1): 54-8, 43

The pyrolysis behavior of car paint in waste steel recycling process was studied by single photon ionization (SPI)/resonance enhanced multi-photon ionization (REMPI)-time of flight mass spectrometry (TOFMS). It was found that, the phenol compounds are formed during pyrolysis of car paint not only in synthetic air, but also in nitrogen atmosphere. A large amount of PAHs are produced from 300degC to 1190degC and most at 700degC and 800degC. The combustion is completed in the range from 1000degC to 1190degC

Solar home system electrification as a viable technology option for Africa's development

Wamukonya-N(UNEP Collaborating Centre for Energy & Environ., Rose Nat. Lab., Rodkilde, Denmark)

Energy-Policy. Jan. 2007; 35(1): 6-14

This paper is based on a review of the effectiveness of solar home systems (SHS) in Africa in meeting users expectations on a service based analytical approach. Various projects have deployed SHS on the promise that they are cost-effective, can meet end-user demands, have ability to alleviate poverty, can save time and reduce emissions. However, a close review of the actual cost of these systems given the services they provide indicates most of the promises remain unmet and hence questions the wisdom of using public funds to support the system at the expense of more appropriate technologies. [All rights reserved Elsevier]

A change in the propagation velocity during the heterogeneous micropyretic/combustion synthesis

Li-HP(Jin-Wen Inst. of Technol., Taipei, Taiwan)

Modelling-and-Simulation-in-Materials-Science-and-Engineering. Dec. 2006; 14(8): 1293-305

Micropyretic/combustion synthesis is a technique whereby a material is synthesized by the propagation of a combustion front across a powder. Heterogeneous distributions of reactants and a diluent are common during micropyretic synthesis when powders are mixed and the conventional modelling treatments thus far have only considered uniform systems. Heterogeneities in a composition are thought to result in local variations of thermophysical/chemical parameters for the reactant, such as density, heat capacity and thermal conductivity. The result is changes in combustion temperature, propagation velocity and the propagation pattern of a combustion front. This study investigates the impact of heterogeneities during micropyretic synthesis with Ni + Al. Correlations of heterogeneities in the reactants and diluent with propagation velocity and combustion temperature are also investigated. In addition, a map, considering concurrent heterogeneities in the reactants and diluent, has been generated to provide a better understanding of the effect of heterogeneities on propagation velocity during micropyretic synthesis

Copper ferrite obtained by two "soft chemistry" routes

Patron-L; Gingasu-D; Mindru-I; Carp-O; Matei-D; Neagoe-C; Balint-I(Inst. of Phys. Chem. "I.G. Murgulescu" Spl. Independentei, Bucharest, Romania)

Journal-of-Alloys-and-Compounds. 30 Nov. 2006; 425(1-2): 357-61

Nanoparticles of copper ferrites with tetragonal structure were obtained by two soft chemical methods: a complexation method and a self-propagating combustion. We demonstrated that in both these methods the precursors of copper ferrites were polynuclear coordination compounds. Three polynuclear coordination compounds with glycine as ligands: [Fe(III)₂Cu(II)(NH₂CH₂COO)₄(OH)₃](NO₃)middotH₂O, [Fe(III)₂Cu(II)(NH₂CH₂COO)₆(NH₂CH₂COOH)₂](NO₃)₂ and [Fe(III)₂Cu(II)(NH₂CH₂COOH)_4.5](NO₃)₈middot4H₂O were synthesized. The complex compounds were characterized by elemental chemical analysis and physico-chemical measurements (IR, UV-vis, magnetic measurements). The copper ferrites were investigated by XRD, IR spectra and magnetic measurements. The crystallite sizes of the copper ferrites were found in the range 18-29nm. [All rights reserved Elsevier]

Phase transformation and catalytic activity of hexaaluminates upon high temperature pretreatment

Chen-Bin-Wang; Tsao-Fa-Yeh; Jia-Lin-Bi; Hsin-Gwo-Lee; Kuang-Shing-Chu(Dept. of Appl. Chem., Nat. Defense Univ., Taoyuan, Taiwan)

Journal-of-Alloys-and-Compounds. 30 Nov. 2006; 425(1-2): 353-6

Both hexaaluminates powder have been synthesized with the co-precipitation method. High temperature pretreatment catalysts are characterized by X-ray diffraction (XRD) and BET method. The catalytic activity in methane combustion also is reported. The hexaaluminate structure is formed and retains the surface area of 20-30m²/g upon calcinations at 1200degC for both SLMA (Sr_0.8La_0.2MnAl₁₁O₁₉) and SBLMA (Sr_0.3Ba_0.5La_0.2MnAl₁₁O₁₉). The surface area of SBLMA is larger than that of SLMA upon temperature higher than 1200degC illustrating the superior thermal stability of the barium hexaaluminate. Partial replacement of Sr²⁺ ion with Ba²⁺ ion improves the thermal stability of the Ba-containing system. Also, the high surface area for SBLMA can be understood from the microstructural change of pore size. The SBLMA possesses larger pore than the SLMA to resist sintering under high temperature aged and shows a good activity in methane combustion. [All rights reserved Elsevier]

Synthesis and characterization of Sr- and Mg-doped LaGaO₃ by using glycine-nitrate combustion method

Min-Shi; Ning-Liu; Yudong-Xu; Yupeng-Yuan; Majewski-P; Aldinger-F(Sch. of Mater. Sci. & Eng., Hefei Univ. of Technol., China)

Journal-of-Alloys-and-Compounds. 30 Nov. 2006; 425(1-2): 348-52

The Sr- and Mg-doped LaGaO₃ powders with the composition of La_0.85Sr_0.15Ga_0.85Mg_0.15O_2.85 were synthesized by using glycine-nitrate combustion method. The results show that unsintered powders prepared by glycine-nitrate combustion method contain the main phase (LaGaO₃). The samples contain less amount of secondary phases than by the sol-gel method and solid-state reaction method at the same sintering temperature. It will help to obtain LSGM materials with high conductivities .The sizes of synthesized powders are greater than those by the sol-gel method and smaller than those by solid-state reaction method. The sintering shrinkage analysis shows that the sintering temperature of LSGM prepared by glycine-nitrate combustion method is about 1432degC, at least 60degC lower than that by solid-state reaction method. The ionic conductivity increases with the increase of testing temperature. The curve of ln(sigmaT) versus 1/T exists two straight lines. This shows that activation energy of oxygen-vacancy motion at lower temperatures is greater than that at higher temperatures. [All rights reserved Elsevier]

Characteristics of nano-sized ZnGa₂O₄ phosphor prepared by solution combustion method and solid state reaction method

Sung-Park; Ju-Hyeon-Lee; Hye-Jung-Park; Kang-Yoo; Byung-Woo-Kim; Jae-Chun-Lee(Dept. of Mater. Sci. & Eng., Myongji Univ., Kyunggi-Do, South Korea)

Journal-of-the-European-Ceramic-Society. 2007; 27(2-3): 965-8

ZnGa₂O₄ phosphors were prepared by both SCM (solution combustion method) and SSRM (solid state reaction method). The properties of the both ZnGa₂O₄ phosphors were investigated by TGA (Thermogravimetric analysis), SEM (scanning electron microscope), BET (Brunauer Emmett Teller), PL (photoluminescence) and XRD (X-ray diffraction). The particle size of SCM phosphor was about one-hundredth of SSRM phosphor. The PL intensity of SCM phosphor was about 1.5-fold higher than that of SSRM phosphor. The SCM phosphor was also tried to be doped with Mn²⁺ ions. The highest PL peak was observed with Mn²⁺ ions of 0.003mol fraction. The peak was shifted from blue (470nm) to green (513nm) color. These results might be very useful for high efficiency phosphors for displays such as field emission displays and plasma display panels. [All rights reserved Elsevier]

Alon-based materials prepared by SHS technique

Zientara-D; Bucko-MM; Lis-J(Fac. of Mater. Sci. & Ceramics, Univ. of Sci. & Technol., Cracow, Poland)

Journal-of-the-European-Ceramic-Society. 2007; 27(2-3): 775-9

The aim of the presented paper was preparation of the highly reactive in the sintering powders in the Al-O-N system by SHS method. Combustion reactions of metallic aluminium and corundum powder mixtures (from 15% Al-85% Al₂O₃ to 50% Al-50% Al₂O₃) were performed in nitrogen atmosphere. The obtained powders were ground and hot-pressed at 1750, 1850 and 1950degC for 1h under 25MPa in nitrogen flow. In contrast to conventional methods, which require 24h of the precursor heat treatment at 1200degC our studies, showed that it is possible to prepare almost pure gamma-alon materials using SHS reaction. Sintering of the powders led to obtained dense materials composed of pure gamma-alon or gamma-alon-AlN composites. The phase composition of the sintered bodies was controlled by the chemical composition of the starting mixture and the sintering temperature. [All rights reserved Elsevier]

New synthesis methods of MgAl₂O₄ spinel

Pcurariu-C; Lazu-I; Ecsedi-Z; Lazu-R; Barvinschi-P; Mrginean-G(Fac. of Ind. Chem. & Environ. Eng., "Politehnica" Univ. of Timisoara, Romania)

Journal-of-the-European-Ceramic-Society. 2007; 27(2-3): 707-10

The paper presents a study concerning the influence of the precursors upon the synthesis temperature, particle size and morphology of the MgAl₂O₄ spinel. With this view there have been used by comparison three synthesis methods: thermal conversion of the heteropolynuclear complex combination resulted from the oxidation reaction of 1,2-ethanediol with Mg and Al nitrates; combustion method based on the exothermal redox reaction of Mg and Al nitrates with an adequate fuel (urea, glycine, beta-alanine) and sol-gel method, starting from aluminium isopropoxide and Mg nitrate. The obtained samples have been characterized by X-Ray diffraction and scanning electron microscopy. [All rights reserved Elsevier]

Precursors for the combustion synthesis of metal oxides from the sol-gel processing of metal complexes

Epifani-M; Melissano-E; Pace-G; Schioppa-M(Consiglio Nazionale delle Ricerche, CNR-IMM, Lecce, Italy)

Journal-of-the-European-Ceramic-Society. 2007; 27(1): 115-23

Sol-gel processing of methanol solutions of Cu(II) acetylacetonates was used for obtaining controlled polymerization of the complex molecules. The resulting sols were evaporated and the resulting precipitate was heated until a self-sustaining combustion reaction took place. The simultaneous presence of nitrate ions and the acetylacetonato ligands resulted in a sharp combustion process, characterized by low activation temperature and intense exothermic feature. The same processing was applied to other metals and other ligands, showing that the sol-gel processing of transition metal complexes can be a simple, convenient, flexible generalization of the citrate-nitrate method for preparing precursors for the combustion synthesis of oxide powders. Moreover, the controlled sol-gel processing of the metal complex can be used as a tool for controlling the precursor structure and, hence, the morphology of the final product. [All rights reserved Elsevier]

Large-scale ECOKATS experiments: Spreading of oxide melt on ceramic and concrete surfaces

Foit-JJ(Forschungszentrum Karlsruhe, Inst. fur Kern-und Energietechnik, Karlsruhe, Germany)

Nuclear-Engineering-and-Design. Dec. 2006; 236(24): 2567-73

Large-scale ECOKATS experiments are performed to study spreading of an oxide melt on ceramic and concrete surfaces. The oxide melt generated by a thermite reaction was composed of 41wt.% Al₂O₃, 24wt.% FeO, 19wt.% CaO and 16wt.% SiO₂. This melt was selected as the most appropriate simulation of a corium melt because of its wide freezing range of approx. 450K. Despite a rather low liquidus temperature, the attempt to measure melt viscosity failed. As spreading of high-temperature oxide melts is nearly isothermal during the early phase of motion, i.e., only thin thermal boundary layers will develop, the melt viscosity can be estimated from a two-dimensional spreading experiment, ECOKATS-V1, on a ceramic substrate by approximate self-similar solutions. To further study the influence of the gas release from the substrate caused by thermal erosion of the underlying concrete by a corium melt on spreading, a large amount of the oxide melt was released into a 2.6m long and 0.29m wide channel leading into a 3mtimes4m rectangular surface. Spreading on a concrete substrate is influenced by the gas release from the decomposed concrete, which changes viscosity. A viscosity increase by a factor of 3.6 was estimated from spreading in the concrete channel. [All rights reserved Elsevier]

Ways to lower transformation temperatures of porous NiTi shape memory alloy fabricated by self-propagating high-temperature synthesis

Rong-LJ; Jiang-HC(Inst. of Metal Res., Chinese Acad. of Sci., Shenyang, China)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 25 Nov. 2006; 438-440: 883-6

Self-propagating high-temperature synthesis (SHS) of porous NiTi alloy for hard tissue implants shows shape memory effect and superelasticity due to the B2harrB19' transformation. In order to decrease the A_F temperature to the human body temperature, 310K, the effects of preheating temperature, thermal cycling and the third element Mo on the transformation temperatures were investigated using differential scanning calorimetry. The experimental results indicate that the preheating temperature has no obvious effect on the transformation temperatures; the transformation temperatures slightly decreased with increasing number of thermal cycles, but the A_F temperature was still above 310K within 10 times; the addition of Mo decreased transformation temperatures considerably, and the R-phase transformation was induced during cooling. Transformation temperatures of porous TiNi(Mo) shape memory alloys with appropriate Mo contents fabricated by SHS meet the demands for human-body implants. [All rights reserved Elsevier]

Shape memory characteristics of TiNi casting alloys made by using self-propagating high-temperature synthesis

Kitamura-K; Kuchida-T; Inaba-T; Tokuda-M; Yoshimi-Y(Dept. of Mech. Eng., Nagano Nat. Coll. of Technol., Nganao, Japan)

Materials-Science-and-Engineering-A-Structural-Materials:-Properties,-Microstructure-and-Processing. 25 Nov. 2006; 438-440: 675-8

Self-propagating high-temperature synthesis (SHS) is a new method of making an ingot of TiNi. This method shows little gravity segregation. The purpose of this study is to investigate the difference of the shape memory characteristics of the TiNi casting alloys made from a SHS ingot and from a conventional melt cast ingot. The samples used in this study were rods made by centrifugal casting. Differential scanning calorimetry (DSC), X-ray diffraction, and tensile test were used to examine the shape memory characteristics on the samples. The heat treatment conditions were 773K-1.8ks and 1073K-3.6ks, respectively. The DSC samples were both ends (the top and bottom area) of the rod samples. The results of the XRD measurements showed that TiNi phase was obtained in all the samples. In contrast, the result of the DSC test showed that more gravity segregation effect happened in the melt cast sample than in the SHS sample. As the conclusion of this study, gravity segregation had little effect in the SHS ingot sample. [All rights reserved Elsevier]

Nonlinear analysis of concrete-filled steel SHS and RHS columns

Young-B; Ellobody-E(Dept. of Civil Eng., Univ. of Hong Kong, China)

Thin-Walled-Structures. Aug. 2006; 44(8): 919-30

This paper presents an accurate nonlinear finite element model for the behaviour and design of axially loaded concrete-filled square hollow section (SHS) and rectangular hollow section (RHS) steel tube columns. The nonlinear material models for confined concrete and steel tubes were carefully modeled in the finite element analysis. The column strengths and load-axial shortening curves were evaluated. The results obtained from the finite element analysis were verified against experimental results. An extensive parametric study was conducted to investigate the effects of different concrete strengths and cross-section geometries on the strength and behaviour of concrete-filled SHS and RHS steel tube columns. The study was conducted over a wide range of concrete cube strengths ranged from 30 to 110MPa. The overall depth of the steel tube-to-plate thickness ratio ranged from 10 to 40 covering compact SHS and RHS steel tube sections. The column strengths predicted from the finite element analysis were compared with the design strengths calculated using the American, Australian and European specifications. Based on the results obtained from the parametric study, it is found that the design strengths calculated using the American Specifications and Australian Standards are conservative, while the design strengths calculated using the European Code are accurate, except for the concrete-filled RHS compact steel tube columns having the overall depth of the steel tube-to-plate thickness ratio of 40. [All rights reserved Elsevier]

Effect of contamination on the performance of hydrodynamic bearings

Khonsari-MM; Booser-ER(Dept. of Mech. Eng., Louisiana State Univ., Baton Rouge, LA, USA)

Proceedings-of-the-Institution-of-Mechanical-Engineers,-Part-J-Journal-of-Engineering-Tribology. Aug. 2006; 220(J5): 419-28

This paper surveys three areas: experimental evaluations and operating experience relating to contaminant detrimental effects to the particle size and hardness; importance of film thickness; and self-propagating damage with high-chromium steel rotors and chlorine oil additives. Analytical thermal criteria are also presented for a particle size limit to avoid flash temperature scuffing failures from particles embedding in a bearing at a sliding surface contact

Nanoparticle dispersion-strengthened coatings and electrode materials for electrospark deposition

Levashov-EA; Vakaev-PV; Zamulaeva-EI; Kudryashov-AE; Pogozhev-YuS; Shtansky-DV; Voevodin-AA; Sanz-A(Moscow State Inst. of Steel & Alloys, Technol. Univ., Moscow, Russia)

Thin-Solid-Films. 23 Nov. 2006; 515(3): 1161-5

Advanced electrode compositions were developed using self-propagating high-temperature synthesis (SHS). Electrospark deposition (ESD) was applied to produce tribological coatings which were disperse-strengthened by incorporation of nanosized particles. Nanostructured electrodes of cemented carbides were produced using powder metallurgy technologies. They allow increasing the coatings density, thickness, hardness, Young's modulus and wear resistance. Positive effects of the nanostructure of electrodes on the deposition process and structure and properties of the coatings are discussed. In that case the tungsten carbide phases become predominant in the coatings. A mechanism of the dissolution reaction of WC with Ni at the contact surface of electrode was proposed. It was shown that the formation of the coating structure starts on the electrode and is accomplished on the substrate. [All rights reserved Elsevier]

Synthesis process dependent photoluminescent properties of Zn₂SiO₄:Mn²⁺ upon VUV region

Yuhua-Wang; Yan-Hao; Lihui-Yuwen(Dept. of Mater. Sci., Lanzhou Univ., China)

Journal-of-Alloys-and-Compounds. 30 Nov. 2006; 425(1-2): 339-42

The influence of the synthesis method on VUV luminescence properties of Zn₂SiO₄:Mn²⁺ green phosphor was investigated by comparing the properties of samples prepared by four routes: solid-state reaction (SR), sol-gel processing (SG), hydrothermal process (HP) and solution combustion process (SC). On the basis of X-ray powder diffraction, SEM micrographs and photoluminescence measurements, the samples prepared through SC process have spherical-like morphology, higher luminescence intensity and shorter decay time, which is because the samples have higher crystallinity and regular, uniform spherical-like morphology. It can be concluded that SC process is the most efficient method to prepare high quality compounds for practical applications among the four methods. [All rights reserved Elsevier]

Hydriding and dehydriding properties of nanostructured Mg₂Ni alloy prepared by the process of hydriding combustion synthesis and subsequent mechanical grinding

Liquan-Li; Xiaofeng-Liu; Yunfeng-Zhu(Coll. of Mater. Sci. & Eng., Nanjing Univ. of Technol., China)

Journal-of-Alloys-and-Compounds. 30 Nov. 2006; 425(1-2): 235-8

In this study, we synthesized a nanostructured Mg₂Ni alloy by means of hydriding combustion synthesis and subsequent mechanical grinding. Results on the structural change with mechanical grinding and the hydriding/dehydriding properties are presented. It was found that the nanostructured Mg₂Ni showed great improvement in hydriding rates at 313 and 373K, and the reaction of dehydriding began at around 370K, which is 190K lower than that of the HCS product. Several factors were considered accounting for the enhancement in hydriding and dehydriding properties. [All rights reserved Elsevier]

A comparative study on combustion synthesis of Nb-Si compounds

Yeh-CL; Chen-WH(Dept. of Mech. & Autom. Eng., Da-Yeh Univ., Changhua, Taiwan)

Journal-of-Alloys-and-Compounds. 30 Nov. 2006; 425(1-2): 216-22

A comparative study on the preparation of niobium silicides (such as Nb₃Si, Nb₅Si₃, and NbSi₂) in the Nb-Si system was conducted by self-propagating high-temperature synthesis (SHS) from elemental powder compacts of different stoichiometries. Effects of the sample green density, preheating temperature, and starting stoichiometry on combustion characteristics, as well as on product composition were studied. Test specimens with five different compositions including Nb:Si=3:1, 5:3, 3:2, 1:1, and 1:2 were employed in this study. Experimental observations indicated that except for the sample of Nb:Si=3:1, upon ignition self-sustained combustion was well established and proceeded throughout the entire sample. Measured results showed that the reactant compact of Nb:Si=5:3 had the highest flame-front propagation velocity, followed sequentially by the powder compacts with Nb:Si=3:2, 1:1, and 1:2. Variation of the combustion temperature with sample initial stoichiometry is in a manner consistent with that of the flame-front velocity. On account of the close atomic ratios, the test specimens made up of either Nb:Si=5:3 or 3:2 yielded a single-phase silicide Nb₅Si₃ in both alpha and beta forms. As identified by the XRD analysis, it was found that alpha-Nb₅Si₃ was dominant in the final product from the Nb:Si=5:3 compact, but beta-Nb₅Si₃ was the major composition formed by the Nb:Si=3:2 compact. Because of the nonexistence of a silicide phase with the atomic ratio Nb/Si=1, a multiphase product consisting of alpha-Nb₅Si₃ and NbSi₂ was synthesized from the reactant compact of Nb:Si=1:1. For the samples with Nb:Si=1:2, the disilicide NbSi₂ was monolithically produced along with trivial amounts of unreacted Nb and Si. Based upon the temperature dependence of combustion wave velocity, the activation energies associated with combustion synthesis of Nb₅Si₃ and NbSi₂ were determined to be 259.2 and 160.9kJ/mol, respectively. [All rights reserved Elsevier]

Microwave sintering of AlN powder synthesized by a SHS method

Shyan-Lung-Chung; Cheng-Yu-Hsieh; Lin-C-N; Jiping-Cheng; Agrawal-DK(Dept. of Chem. & Mater. Eng., Nat. Univ. of Kaohsiung, Taiwan)

Journal-of-the-European-Ceramic-Society. 2007; 27(1): 343-50

Sintering of the AlN powder synthesized by a combustion synthesis method, which was developed recently by the present authors, was studied by using a microwave sintering technique. A single mode microwave cavity was used and an insulation package with a simple configuration was developed. A high sintering temperature (1900degC or higher) and a stable and uniform heating were readily achieved. A temperature measurement technique using a thermocouple with extrapolation was established to obtain the sintering temperature. A percent theoretical density of 99.5% and a thermal conductivity of 186W/mK were obtained for a specimen which was sintered at 1900degC with a soaking time of 30min and 3wt.% of Y₂O₃ added. The effects of sintering aid (i.e., Y₂O₃) and sintering temperature on densification, microstructure and thermal conductivity of the sintered specimens were investigated. [All rights reserved Elsevier]

Hot pressed titanium nitride obtained from SHS starting powders: Influence of a pre-sintering heat-treatment of the starting powders on the densification process

Cardinal-S; Russias-J; Esnouf-C; Fantozzi-G; Bienvenu-K(GEMPPM, INSA, Villeurbanne, France)

Journal-of-the-European-Ceramic-Society. 2007; 27(1): 327-35

Synthesis of titanium nitride (TiN) powders by the self propagating high temperature synthesis (SHS) process is economically appealing. This chemical reaction allows producing fine grains powders with a high specific surface area (12m²/g). After a thermal treatment above 1000degC under argon atmosphere, the physical and microstructural characteristics of the powders are drastically modified: density increases and specific surface decreases. Powders morphology and heat treatment influence are investigated by transmission electron microscopy. Observations reveal a regular nanocrystalline layer, surrounding the particles. After heat treatment, this layer disappears from grains surface and powders undergo important morphological changes. The behavior of these special ceramic powders during the sintering stage by the hot press process is investigated. Bulk specimens obtained are characterized from a physical, microstructural and mechanical point of view and the beneficial effect of the heat treatment on starting powder is explained. Bulk specimens processed in the optimum conditions reach a relative density superior to 98%, a microhardness of 1790Hv and a Young modulus of 430MPa. [All rights reserved Elsevier]

Rapid synthesis of mesoporous ceria-zirconia solid solutions via a novel salt-assisted combustion process

Chen-W; Fengsheng-Li; Jiyi-Yu; Leili-Liu; Gao-H(Nat. Special Superfine Powder Eng. Res. Center, Nanjing Univ. of Sci. & Technol., Jiangsu, China)

Materials-Research-Bulletin. 14 Dec. 2006; 41(12): 2318-24

Mesoporous ceria-zirconia solid solutions were prepared by a novel salt-assisted combustion process using ethylene glycol as a fuel and nitrate as an oxidant. The effects of various operating conditions such as the fuel-to-oxidant ratio and the nature and amount of added salt on the characteristics of the products were investigated by X-ray diffraction (XRD) and nitrogen adsorption analysis. Results from transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) showed that the introduction of leachable inert inorganic salt as a hard agglomeration inhibitor into the redox mixture precursor led to the breakup of fractal nanocrystallite agglomerates and the mesoporous structure formed by the loose agglomeration of monodispersed nanoparticles, which was also confirmed by small-angle XRD and nitrogen adsorption analysis. The presence of salt was found to result in a more than 10-fold increase in the specific surface area of the products from 17.34 to 208.17m²/g at a given molar ratio of ethylene glycol-nitrate. A mechanism scheme was proposed to illustrate the possible formation processes and discuss the role of the salt additives. [All rights reserved Elsevier]

Phase composition and magnetism of combustion products in Ba-Fe-O compounds synthesized under applied DC electric field

Parkin-IP; Kuznetsov-MV; Morozov-YG; Busurin-SM; Chernega-ML(Dept. of Chem., Univ. Coll. London, UK)

Journal-of-Magnetism-and-Magnetic-Materials. Feb. 2007; 309(2): 202-6

The effect of non-contact electric fields applied directly during combustion synthesis of barium ferrites is presented. The microstructure, phase composition and magnetic characteristics of the combustion products were obtained by scanning electronic microscopy (SEM), X-ray diffraction and vibrating sample magnetometry (VSM). A correlation was found between the observed magnetic properties of the product and the magnitude of the applied electric field. The role of oxygen exchange activated by the electric field during the combustion synthesis is discussed. [All rights reserved Elsevier]

Crystal structure and magnetic properties of BaFe_12-xDy_xO₁₉ powders prepared using gel self-propagating combustion

JIanxun-Qiu; Le-Liang; Mingyuan-Gu(State Key Lab. of Metal Matrix Composites, Shanghai Jiao Tong Univ., China)

Journal-of-Composite-Materials. Aug. 2006; 40(15): 1385-92

The hexagonal BaFe_12-xDy_xO₁₉ (x = 0.1-0.5) powders are synthesized by the gel self-propagating combustion technique, which is combined with the sol-gel method and self-propagating combustion synthesis. The changes in heat and weight of dry gel during self-propagating combustion are investigated with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The effects of the molar ratio of citric acid on nitrates (C/N), calcination temperature, and substitution amount of Dy³⁺ on crystal structure and magnetic properties are studied by means of X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). In gel self-propagating combustion, the formation temperature of barium ferrite is decreased to 850degC. The changes in crystal structure during calcination are tracked. There is no Cr-Fe₂O₃ appearing in the powders when C/N is not less than 1.0. After some Fe³⁺ has been substituted with Dy³⁺, the magnetic properties are improved. The specific saturation magnetization reaches a maximum of 58.05 Am²/kg, and coercivity reaches a minimum of 420.33 kA/m with the substitution amount x = 0.2. This substituted barium ferrite can be used as a magnetic recording material

Thermally induced vibrations due to rub in real rotors

Pennacchi-P; Bachschmid-N; Vania-A(Dipt. di Meccanica, Politecnico di Milano, Italy)

Journal-of-Sound-and-Vibration. 6 Feb. 2007; 299(4-5): 683-719

The analysis of the effects of the rotor-to-stator rub in the rotor dynamics field has produced many models, often nonlinear or with particular attention to chaotic behaviour, but with scarce correspondence with real rotors since Jeffcott-like rotors are mainly used without thermal transients, or sometimes real rotors are used but with very simple thermal modelling. One of the most remarkable aspects of the rotor-to-stator rub at operating speed is the possibility of observing spiral vibration phenomena in the synchronous vibration, i.e. the vibration vector changes its amplitude and rotates even at the rated speed. This is due to the combined effect of the contact forces which introduce heat and of the resulting thermal bow. The phenomenon is also called vector turning or thermally induced vibrations. It is interesting to analyse the dynamical behaviour of the machine: the spirals can have a self-propagating trend or conversely a self-correcting trend. The model presented in the paper for the analysis of the spiral vibration has a unique characteristic in that it allows real machines to be analysed, since it uses a fully assembled machine model (rotor, bearings and foundation) and implements a rather sophisticated thermal and contact model. The experimental validation of the proposed model is performed on data coming from a real machine: the generator of a 50MW combined cycle power plant, in which unstable spiral vibrations were observed at the operating speed during a power increase. [All rights reserved Elsevier]

Synthesis of AlON refractory raw materials from aluminum dross using thermite reaction process

Joo-H; Yun-J; Hwang-K; Jun-B(Mater. Sci. & Eng., Kyungnam Univ., Masan, South Korea)

Materials-Science-Forum. 2006; 510-511: 866-9

Aluminum dross is presented as a potential material to form AlON using thermite reaction. The commercial MgAl powder, active carbon, and titania were prepared to make a chemical furnace (self-propagation combustion). The preheating temperature of 300degC is enough to imitate ignition of the mixture as fuel and oxidizer. The addition of Y₂O₃ (1wt. %) is effective to enhance solid solution products between Al₂O₃ and AlN in the aluminum dross. The level of contamination like an alkali metal oxide in the aluminum dross was reduced highly by the heat from chemical furnace

Synthesis and characterization of uncapped gamma-Fe₂O₃ nanoparticles prepared by flame pyrolysis of ferrocene in ethanol

Inamdar-SN; Haram-SK(Dept. of Chem., Pune Univ., India)

Journal-of-Nanoscience-and-Nanotechnology. July 2006; 6(7): 2155-8

Nanoparticles of iron(III) oxide were synthesized by spontaneous combustion of ferrocene in ethanol solution using a simple spirit lamp. X-ray powder diffraction and electron diffraction analysis of the powder suggested the formation of gamma-Fe₂O₃ (maghemite phase) having lattice constant 8.3539 plusmn 0.0209 Aring. Transmission electron micrograph suggested the formation of spherical particles with an average diameter of 24.7 plusmn 1.6 nm. A sextet with an isomeric shift of 0.328 mm s^-1 seen in the Mossbauer spectrum recorded at room temperature, further supports the formation of gamma-Fe₂O₃. The particles were dispersed freely in the polar solvents like ethanol, dimethyl sulfoxide, and water. Infra red spectrum gave bands at 400, 432, 565, and 638 cm^-1, which confirms the presence of gamma-Fe₂O₃ phase

Study on preparation of nanocrystalline ferrites using spent alkaline Zn-Mn batteries

Guoxi-Xi; Li-Yang; Maixi-Lu(Key Lab. for Environ. Pollution Control of Henan, Chem. & Environ. Sci. Coll. of Henan Normal Univ., China)

Materials-Letters. Dec. 2006; 60(29-30): 3582-5

The nanocrystalline ferrites were synthesized by sol-gel and self-propagating combustion methods using spent alkaline Zn-Mn batteries dissolved in nitric acid. The thermal decomposition process of dried gels, the essence of auto-combustion and the morphological structure of nanocrystalline ferrites were investigated by using DTA, TG, IR, XRD and SEM. The precise metal ion stoichiometry of the nanocrystalline ferrites was analyzed by ICP. The results demonstrated that the essence of auto-combustion of the dried gels was oxidation-reduction reaction induced by heat and the nanocrystalline Mn-Zn ferrites with a diameter of 20 nm could be prepared directly by auto-combustion reaction. [All rights reserved Elsevier]

Formation of Y-junction carbon nanotubes by catalytic CVD of methane

Mohamed-AR; Siang-Piao-Chai; Zein-SHS(Sch. of Chem. Eng., Univ. Sains Malaysia, Pulau Pinang, Malaysia)

Solid-State-Communications. Nov. 2006; 140(5): 248-50

Y-junction carbon nanotubes were grown by catalytic CVD of methane at 700degC on NiO-CuO-MoO(7:2:1) (w/w/w)/SiO₂ catalyst. For comparison, NiO-CuO(8:2) (w/w)/SiO₂ and NiO-MoO(8:2) (w/w)/SiO₂ catalysts were tested for carbon nanotube formation. TEM analysis indicates that no Y-junction structures were formed with the latter two catalysts. This finding elucidates why the addition of a small amount of MoO to NiO-CuO/SiO₂ catalyst is crucial for enhancing the formation of Y-junction carbon nanotubes. [All rights reserved Elsevier]

Formation of beta-SiAlON micropalings consisting of nanorods during combustion synthesis

Kexin-Chen; Guanghua-Liu; Heping-Zhou; Kegang-Ren; Jiangtao-Li; Pereira-C; Ferreira-JMF(Dept. of Mater. Sci. & Eng., Tsinghua Univ., Beijing, China)

Scripta-Materialia. Nov. 2006; 55(10): 935-8

Novel beta-SiAlON micropalings consisting of nanorods have been prepared by combustion synthesis with proper additives. According to TEM images associated with SAD pattern, the preferred growth direction of the nanorods is proved to be [001]. An epitaxial nucleation and anisotropic growth mechanism is proposed to explain the formation of those micropalings. By this mechanism, new fine crystals are formed on the side faces of coarse crystals and each coarse prismatic beta-SiAlON crystal is surrounded by parallel nanorods. [All rights reserved Elsevier]

Microwave-induced combustion synthesis and electrical conductivity of Ce_1-xGd_xO_2-1/2x ceramics

Yen-Pei-Fu; Yen-Shao-Chang; Shaw-Bing-Wen(Dept. of Mater. Sci. & Eng., Nat. Dong-Hwa Univ., Hualien, Taiwan)

Materials-Research-Bulletin. 14 Dec. 2006; 41(12): 2260-7

Ce_1-xGd_xO_2-1/2x nanopowder were successfully synthesized by microwave-induced combustion process. For the preparation, cerium nitrate, gadolinium nitrate hexahydrate, and urea were used for the microwave-induced combustion process. The process took only 30min to obtain Ce_1-xGd_xO_2-1/2x powders. The exo-endo temperature, phase identification, and morphology of resultant powders were investigated by TG/DTA, XRD, and SEM. The as-received Ce_1-xGd_xO_2-1/2x powders showed that the average particle size ranged from 18 to 50nm, crystallite dimension varied from 11 to 20nm, and the specific surface area was distribution from 16 to 46m²/g. As for Ce_1-xGd_xO_2-1/2x ceramics sintered at 1450degC for 3h, the bulk density of Ce_1-xGd_xO_2-1/2x ceramics were over 91% of the theoretical density, the maximum electrical conductivity, sigma_700degC=0.017S/cm with minimum activation energy, E_a=0.869eV was found at Ce_0.80Gd_0.20O_1.90 ceramic. [All rights reserved Elsevier]

A study on the formation of strontium hexaferrite nanopowder by a sol-gel auto-combustion method in the presence of surfactant

Ebrahimi-SAS; Alamolhoda-S; Badiei-A(Center of Excellence in Magnetic Mater., Univ. of Tehran, Iran)

Journal-of-Magnetism-and-Magnetic-Materials. Aug. 2006; 303(1): 69-72

Strontium hexaferrite is a hard magnetic material and has been extensively used as a permanent magnet. In this work, a novel sol-gel auto-combustion method was used to synthesize ultra-fine strontium hexaferrite, and the effect of the surfactant on the crystallite size of the final product was investigated for the first time. The DTA/TGA plot exhibited the formation temperature of hexaferrite. The XRD results show that adding surfactant to the sol does not change the composition of the combustion product and the surfactant burns completely during the combustion process. The average crystallite size of hexaferrite powders was also measured by the X-ray line broadening technique employing the Scherrer formula. The results show that adding surfactant to the gel makes the particle size of the final product much smaller. [All rights reserved Elsevier]

Synthesis of nanocrystalline lanthanum strontium manganite powder by the urea-formaldehyde polymer gel combustion route

Prabhakaran-K; Joseph-J; Nitin-Madhusudan-Gokhale; Suresh-Chandra-Sharma; Lal-Ramji(Naval Mater. Res. Lab., Thane, India)

Journal-of-the-American-Ceramic-Society. July 2006; 89(7): 2335-7

Nanocrystalline lanthanum strontium manganite (LSM) powder has been synthesized by combustion of a transparent gel obtained by the polymerization of methylol urea and urea in a solution containing La³⁺, Sr²⁺, and Mn²⁺(LSM ions). Chemistry of the transparent urea-formaldehyde (UF) polymer gel formation and structure of the gel have been proposed such that the LSM ions act in between the growing UF polymer chains by interacting through NH, OH, and CO groups by co-ordination and prevent polymer self-assembly through inter-chain hydrogen bonding as evidenced from infrared spectrum. Thermally stable structures formed by the decomposition of UF polymer below 300degC undergo combustion in the presence of nitrate oxidant in a temperature range from 350degC-450degC. A perovskite LSM phase has been formed by self-sustained combustion of the dried gel initiated with little kerosene. The powder obtained after de-agglomeration and calcination at 600degC for 2 h has D₅₀ value of 0.19 mum, and the particles are aggregates of crystallites 10-25 nm in size

Factors which affect the morphology of AlN particles made by self-propagating high-temperature synthesis (SHS)

Agathopoulos-S; Fu-R; Chen-K; Ferreira-JMF(Dept. of Mater. Sci. & Eng., Univ. of Ioannina, Greece)

Journal-of-Crystal-Growth. 15 Oct. 2006; 296(1): 97-103

AlN was produced from Al powder via self-propagating high-temperature synthesis (SHS) at 8 and 12MPa N₂ pressure. In the light of earlier studies, the discussion of the experimental results points out that AlN diluents, the endothermic nature of NH₄F decomposition, and the reducing capability of carbon black are features that can be considered for controlling the combustion temperature as well as the temperature and the prolongation of the after-burning period, which are all determinants of the morphology of the produced AlN particles. The presence of iron as mineralizer resulted in a complex microstructure, probably reflecting a complicate reaction mechanism. [All rights reserved Elsevier]

Synthesis of LiNiO₂ cathode by the combustion method

Myoungyoup-Song; Ikhyun-Kwon; Hunuk-Kim; Shim-S; Mumm-DR(Eng. Res. Inst., Chonbuk Nat. Univ., Jeonju, South Korea)

Journal-of-Applied-Electrochemistry. July 2006; 36(7): 801-5

To determine optimum conditions for the synthesis of LiNiO₂ by the combustion method, syntheses were carried out in air and under oxygen at various calcination temperatures and for different times. The electrochemical properties of the prepared samples were then investigated. The optimum conditions are preheating at 400 degC for 30 min in air in the mole ratio of urea to nitrate 3.6 and calcination at 750 degC for 36 h under O₂. The LiNiO₂ synthesized under these conditions had a first discharge capacity of 189 mAh g^-1 at 0.1 C-rate and relatively good cycling performance. This sample has a larger value of I₀₀₃/I₁₀₄ (smaller cation mixing) and a smaller R-factor (larger hexagonal ordering). Cycling performance was investigated in various voltage ranges. The first discharge capacity increased as the upper limit of the voltage range rose. The first discharge capacity was small but cycling performance was good when the sample was cycled in the voltage range with the lowest upper limit

Preparation of Al-Ti-C master alloy by SHS

Wang-Hongtao; Xia-Tiandong; Zhao-Wenjun; Liu-Tianzuo(Lanzhou Univ. of Technol., China)

Rare-Metal-Materials-and-Engineering. Dec. 2005; 34(12): 2009-12

Al-Ti-C master alloys used as grain refiners of the aluminum and its alloys have been prepared by self-propagating high-temperature synthesis (SHS) technology. The influence of pressure, diameter and preheating temperature of green-pellet on combustion temperature (T_c) during preparing Al-Ti-C master alloy and the microstructure of synthesized product has been investigated. The results show that synthesized master alloy consist of Al, Al₃Ti and TiC, and green-pellet pressure and preheating temperature have remarkable influence on combustion temperature (T_c) and microstructure of synthesized product. However, in this study, the influence of green-pellet diameter is unapparent

Synthesis and hydrogenation properties of Mg-3mol%LaNi₃ composite prepared under an external magnetic field

Qian-Li; Kuang-Di-Xu; Chou-K-C; Xiong-Gang-Lu; Jie-Yu-Zhang; Lin-G-W(Sch. of Mater. Sci. & Eng., Shanghai Univ., China)

Intermetallics-. Jan. 2007; 15(1): 61-8

The Mg-3mol%LaNi₃ composition was successfully prepared by different techniques, namely, the composite was synthesized by hydrogen combustion synthesis (HCS) with and without an external high magnetic field. The hydrogen storage capacities and hydriding/dehydriding (H/D) rates of the two composites at different temperatures were evaluated and their structures and morphologies were examined. Our main goal in this study is how to control the process of HCS by the external high magnetic field and to investigate its effect on the hydrogenation properties of the composite and analyze these changes from the relationship between the microstructure and crystalline state and the energy injected into the composite from the external high magnetic field. [All rights reserved Elsevier]

Enhancement of the physical properties of rare-earth-substituted Mn-Zn ferrites prepared by flash method

Ahmed-MA; Okasha-N; El-Sayed-MM(Phys. Dept., Cairo Univ., Giza, Egypt)

Ceramics-International. Jan. 2007; 33(1): 49-58

The effect of rare-earth ions on the structural, magnetic and electrical properties of rare-earth-doped manganese-zinc ferrite is reported. The compounds with the formula Mn_0.5Zn_0.5R_0.05Fe_1.95O₄ where R=Tb, La, Ce and Th, were prepared by the flash combustion technique. The prepared samples reveal that by introducing a relatively small amount of R(NO₃)₃ or R(Cl₃) instead of Fe₂O₃, an important modification of both structure and physical properties was obtained. Curie temperature, effective magnetic moment, electrical resistivity, density, thermoelectric and lattice constant were directly affected by these substitutions either by their partial diffusion in the spinel lattice or the formation of the crystalline secondary phases (orthoferrite and/or garnet) on the grain boundaries which suppress the abnormal grain growth. Correlation between the ionic radii and the measured physical properties were studied. [All rights reserved Elsevier]

The scientific basis of calculations of highly efficient compact heat-transfer apparatuses with judicious heat-transfer intensifiers

Gortyshov-YuF; Popov-IA(Kazan State Tech. Univ., Russia)

Thermal-Engineering. April 2006; 53(4): 249-61; Original: Teploenergetika-. April 2006; 53(4)

Results of classification of the existing data on hydrodynamics and heat transfer under forced convection in channels with spherical holes (SHs) are presented. The energy efficiency of the use of SHs under laminar and turbulent flow of a coolant is shown. The effects of regime and design parameters on heat transfer in such channels are studied. A flow-regime chart is developed

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