Modeling of wave configuration during electrically ignited combustion synthesis

2001 ◽  
Vol 16 (1) ◽  
pp. 93-100 ◽  
Author(s):  
O. A. Graeve ◽  
E. M. Carrillo-Heian ◽  
A. Feng ◽  
Z. A. Munir
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
High Temperature ◽  
Combustion Synthesis ◽  
Small Samples ◽  
Combustion Mode ◽  
Temperature Synthesis ◽  
Ignition Point ◽  
High Temperature Synthesis ◽  
Material Systems

A model was developed to study the process of current-ignited combustion synthesis. In this process, Joule heating raises the temperature to the ignition point, at which the sample reacts to form a product. Two material systems were modeled: the synthesis of SiC and MoSi2. It was found that the mode of combustion is a function of the size (radius) of the sample. The anticipated volume combustion mode was only evident in small samples. At higher values of the radius, the mode becomes wavelike (selfpropagating high-temperature synthesis) in nature. The transition from volume to wave combustion mode also depended on the properties of the material. The results are interpreted in terms of thermal conductivity and heat-transfer conditions.

Preparation of (Mo,Nb)Si2 Ternary Alloys by Self−Propagating High−Temperature Synthesis

2011 ◽  
Vol 266 ◽  
pp. 219-222
Author(s):  
Pei Zhong Feng ◽  
Shuai Zhang ◽  
Xiao Hong Wang ◽  
Wei Sheng Liu ◽  
Jie Wu
Keyword(s):  
High Temperature ◽  
Flame Front ◽  
Propagation Velocity ◽  
Combustion Temperature ◽  
Front Propagation ◽  
Ternary Alloys ◽  
Combustion Mode ◽  
Temperature Synthesis ◽  
High Temperature Synthesis ◽  
Front Propagation Velocity

An experimental study on the preparation of (Mo,Nb)Si2 ternary alloys was conducted by self-propagating high-temperature synthesis method from elemental powder compacts of different stoichiometries. And the combustion mode, combustion temperature, flame-front propagation velocity and product structure were discussed. The results show that (Mo,Nb)Si2 ternary alloys are characterized by an unsteady state combustion mode with a spiral−trajectory reaction front from top to bottom. The combustion temperature and flame−front propagation velocity decrease with the addition of coarse niobium powder. The combustion temperature and flame-front propagation velocity of MoSi2 are 1629K and 3.13mm/s respectively. However, those of (Mo0.8Nb0.2)Si2 alloy are 1460K and 1.97mm/s. The solid solubility of niobium in MoSi2 is less than 2.5at.%, and the combustion synthesis produce still remains Cllb single-phase structure in (Mo1-x,Nbx)Si2(x<0.075) sample. The C40-type structure appears in (Mo0.925,Nb0.075)Si2 compact and the intensity of diffraction peaks of C40-type phase gradually reinforces with the increase of niobium content. Combustion synthesis is an effective technology for producing (Mo,Nb)Si2 ternary alloys.

Enhanced Thermoelectric Properties of BiCuSeO Ceramics by Bi Vacancies

2018 ◽  
Vol 913 ◽  
pp. 803-810 ◽  
Author(s):  
Wen Qiang Ma ◽  
Cheng Jie Deng ◽  
Jin Le Lan ◽  
Xiao Ping Yang ◽  
Yuan Hua Lin
Keyword(s):  
Thermal Conductivity ◽  
High Temperature ◽  
Power Factor ◽  
Slight Reduction ◽  
Temperature Synthesis ◽  
Pristine Sample ◽  
Plasma Sintering ◽  
High Temperature Synthesis ◽  
Spark Plasma ◽  
Sintering Method

Polycrystalline Bi1-xCuSeO (0 ≤ x ≤ 0.05) ceramics were prepared by self-propagating high-temperature synthesis followed by spark plasma sintering method. All the samples correspond with single BiCuSeO phase and high vacancies sample had higher density. The highest power factor of 4.71×10-4 W.m-1.K-2 was obtained by 5% Bi vacancies at 873K, which is about 32% higher than that of the pristine sample. Along with slight reduction of thermal conductivity, the maximum ZT reached 0.68. The results show that vacancy engineering is a promising method for thermoelectric applications of BiCuSeO and related ceramics.

Effect of Mg on the Synthesis of TiB2 Powder by a Self-Propagating High-Temperature Synthesis Technique

2013 ◽  
Vol 347-350 ◽  
pp. 1144-1147
Author(s):  
Su Li ◽  
Jun Shou Li ◽  
Fang Zhao ◽  
Ming Hui Ye
Keyword(s):  
High Temperature ◽  
Combustion Synthesis ◽  
Formation Mechanism ◽  
Molar Ratio ◽  
Synthesis Reaction ◽  
Hexagonal Crystal ◽  
Temperature Synthesis ◽  
High Temperature Synthesis ◽  
Higher Temperature ◽  
Combustion Synthesis Reaction

Micro-nanoTiB2 ceramic was prepared through increasing the molar ratio of Mg and leaching with suitable acid by the combustion synthesis reaction of Mg, TiO2 and B2O3, which could get higher temperature and purer product. The Samples were investigated by XRD and SEM, and the results showed the diameter of the TiB2 was 200 nm ~ 300 nm and the shape of the TiB2 was irregular hexagonal crystal. The diameter of the TiB2 was decreased with the increase of Mg powder. The formation mechanism of TiB2 has been studied.

Reverse burning phenomenon in self-propagating high-temperature synthesis

1998 ◽  
Vol 13 (6) ◽  
pp. 1626-1630 ◽  
Author(s):  
Jou-Hong Lee ◽  
Ai-Yi Lee ◽  
Chien-Chong Chen
Keyword(s):  
High Temperature ◽  
Combustion Synthesis ◽  
External Heat ◽  
The Other ◽  
Green Density ◽  
Temperature Synthesis ◽  
Green Pellet ◽  
High Temperature Synthesis

An interesting reverse burning phenomenon was observed during the combustion synthesis of zirconium-based materials. When an external heat was applied to one end of a green pellet, the ignition was initiated at the other end. Also, the ignition position, measured from the heated end, was proportional to the apparent green density of the compact. The possible explanations for this reverse burning phenomenon are discussed.

scholarly journals Self-Propagating High-Temperature Synthesis of Silicon Carbide and Silicon Nitride Nanopowders Composition using Sodium Azide and Halides

2013 ◽  
Vol 16 (1) ◽  
pp. 41 ◽  
Author(s):  
Yu.V. Titova ◽  
A.P. Amosov ◽  
G.V. Bichurov ◽  
D.A. Maidan
Keyword(s):  
Silicon Carbide ◽  
High Temperature ◽  
Silicon Nitride ◽  
Combustion Synthesis ◽  
Sodium Azide ◽  
Average Particle Size ◽  
Average Particle ◽  
Temperature Synthesis ◽  
High Temperature Synthesis ◽  
Working Volume

<p>Regularities of self-propagating high-temperature synthesis (SHS) or combustion synthesis (CS) by using “silicon – sodium azide – ammonium hexafluorosilicate – carbon – aluminum” powder mixture in the nitrogen atmosphere were investigated. The thermodynamic analysis of the combustion synthesis was performed. Experimental investigation of the combustion process: the measurement of linear rates of the combustion front propagation and the maximum combustion temperatures was conducted in a laboratory reactor with working volume 4.5 liters. The influence of the components ratio in the initial mixture on the combustion temperature, combustion rate and composition of reaction product was studied. The phase composition of the product synthesized was determined with an X-ray  diffractometer. It was disclosed that the SHS product consists of the composition (mixture) of silicon carbide nanopowder with silicon nitride whiskers and a final halide. Investigation of surface topography and morphology of the product particles was carried out with a scanning electron microscope. Optimal mixture for the synthesis of nanoscale composition based on silicon carbide was determined: “14Si+6NaN<sub>3</sub>+(NH<sub>4</sub>)<sub>2</sub>SiF<sub>6</sub>+15C+Al”. In this case, the SHS product consists of four phases: silicon carbide (β-SiC) – 48.57 wt.%, α-silicon nitride (<em>α</em>-Si<sub>3</sub>N<sub>4</sub>) – 27.04 wt.%, β-silicon nitride (β-Si<sub>3</sub>N<sub>4</sub>) – 5.83 wt.%, and sodium hexafluoroaluminate (Na<sub>3</sub>AlF<sub>6</sub>) – 18.56 wt.%. The average particle size of the composition was in the range of 70–130 nm. It was shown that the composition of the silicon carbide with silicon nitride and the final halide Na<sub>3</sub>AlF<sub>6</sub> playing a role a flux can be used as a modifier of castable aluminum alloys and as a reinforcing phase of aluminomatrix composites.</p>

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