Investigation of propagation modes and temperature/velocity variation on unstable combustion synthesis

2002 ◽  
Vol 17 (12) ◽  
pp. 3213-3221 ◽  
Author(s):  
H. P. Li
Keyword(s):  
Activation Energy ◽  
Combustion Synthesis ◽  
Combustion Front ◽  
Propagation Velocity ◽  
Combustion Temperature ◽  
Front Propagation ◽  
Combustion Reaction ◽  
Velocity Variation ◽  
Material Synthesis ◽  
Unstable Combustion

Combustion synthesis/micropyretic synthesis is a technique in which material synthesis is accomplished by the propagation of a combustion front across the sample. In some cases, the combustion front may propagate in an unstable mode where the propagation velocity and combustion temperature of the combustion front are altered periodically. In this study, the processing conditions leading to unstable combustion reaction were first studied theoretically. The boundary temperatures separating stable and unstable reactions were then determined. The numerical analysis showed that the combustion temperature and the propagation velocity changed periodically during unstable combustion. As the combustion reaction became unstable, the average propagation velocity and the oscillatory frequency of front propagation decreased. The products of unstable combustion synthesis possessed the banded structures, implying the occurrence of the unstable oscillatory propagation, as demonstrated experimentally. In this study, high activation energy combustion (Ti + 2B reaction) and low activation energy combustion (Ni + Al reaction) were both chosen to illustrate the effect of unstable combustion. It is the first time the experimental and numerical results were combined to investigate the temperature and propagation velocity variations during unstable combustion.

Banded structures in unstable combustion synthesis

1995 ◽  
Vol 10 (6) ◽  
pp. 1379-1386 ◽  
Author(s):  
H.P. Li
Keyword(s):  
Combustion Synthesis ◽  
Combustion Front ◽  
Propagation Velocity ◽  
Processing Parameters ◽  
Processing Conditions ◽  
Oscillatory Frequency ◽  
Unstable Combustion ◽  
Band Spacing ◽  
Initial Processing ◽  
Oscillatory Combustion

Banded structures in combustion-synthesized products have been observed during unstable combustion synthesis. The formation of the banded structures is discussed in this article. It is noted that the band spacing was changed when several initial processing conditions were varied. Any change in the processing parameters that correspondingly caused more unstable combustion was observed to decrease the propagation velocity of the combustion front and increase the band spacing. The correlation of the band spacing and oscillatory frequency of the unstable oscillatory combustion with the propagation velocity was also discussed. From the results studied in this work, it is noted that the change of the band spacing can be used to infer the degree of the instability of the combustion front.

Effect of mechanical alloying on combustion synthesis of MoSi2

2001 ◽  
Vol 16 (11) ◽  
pp. 3060-3068 ◽  
Author(s):  
Hyung-Sang Park ◽  
Kwang-Seon Shin ◽  
Yong-Seog Kim
Keyword(s):  
Mechanical Alloying ◽  
Combustion Synthesis ◽  
Ignition Temperature ◽  
Lamellar Structure ◽  
Combustion Temperature ◽  
Low Energy ◽  
Combustion Reaction ◽  
Diffusional Process ◽  
Powder Mixtures ◽  
Energy Ball

Characteristics of the combustion synthesis of MoSi2 using elemental Mo and Si powder mixtures prepared by mechanical alloying were investigated. The mechanical alloying resulted in powders of pseudolamellar structure and a partial conversion of the elemental powders to hexagonal MoSi2 phase. Combustion reaction of the mixture was ignited around 670 °C, which is much lower than that with the powder prepared by low-energy ball milling. A mathematical model was developed to demonstrate the possibility of the ignition of the combustion reaction of the lamellar structure via a solid-state diffusional process. On the basis of model, effects of mechanical alloying time on the ignition temperature and combustion temperature are discussed.

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.

Experimental Study and Modelling of Combustion Front Velocity in Ti-2B and Ti-C Based Reactant Mixtures

2006 ◽  
Vol 45 ◽  
pp. 2656-2663 ◽  
Author(s):  
M. Martinez Pacheco ◽  
R. Bouma ◽  
O. Arias Cuevas ◽  
Laurens Katgerman
Keyword(s):  
Experimental Study ◽  
Particle Size ◽  
Combustion Synthesis ◽  
Combustion Front ◽  
Theoretical Calculations ◽  
Heat Losses ◽  
Front Velocity ◽  
Experimental Results ◽  
Combustion Reaction ◽  
Analytical Expressions

Experiments on combustion synthesis for the Ti-2B and Ti-C systems diluted with an inert metal are presented. The paper shows the influence of geometry, composition, density and particle size of diluent on the combustion front velocity. A Ti-2B reactant mixture diluted with Al and Cu and a Ti-C reactant mixture diluted with Al are studied. The metallic diluent and its concentration are varied. Besides, each experiment is based on a stack of cylinders with decreasing diameter in order to vary the heat losses. In some experiments the eventual quenching of the combustion reaction has been observed. Furthermore these experimental results are compared with theoretical calculations based on analytical expressions derived for such systems.

Combustion Synthesis of Ni/Al Base Composites

2012 ◽  
Vol 545 ◽  
pp. 50-55
Author(s):  
X. Zhu ◽  
T. Zhang ◽  
D. Marchant ◽  
V. Morris
Keyword(s):  
High Resolution ◽  
Combustion Synthesis ◽  
Induction Heating ◽  
Thermal Imaging ◽  
High Frequency ◽  
Combustion Temperature ◽  
Combustion Reaction ◽  
Temperature Profiles ◽  
Imaging Camera ◽  
High Frequency Induction

This paper presents a new ignition technique to synthesize NiAl based composites using high frequency induction heating to ignite the combustion reaction. A high resolution thermal imaging camera and two infrared thermometers were used to monitor the complete temperature profiles during synthesis. Thermodynamic calculations were performed to predict the combustion temperature and the effect of preheating temperatures. The results show that the combustion reaction for Ni/Al based composites can be ignited using a high frequency induction heater. High density, multi layer TiC-NiAl composites can be produced using this method, but to ignite the combustion reaction by induction heating for the Ni/Al+Ti/C system, there is a limit for the content of Ti/C, above which the ignition will not start. Ultra fine TiC was synthesized using this technique.

MATHEMATICAL MODELING OF FLAME PROPAGATION IN THE AEROSUSPENSION OF NANOSIZED ALUMINUM POWDER

2020 ◽  
Author(s):  
A. Yu. Krainov ◽  
◽  
V. A. Poryazov ◽  
K. M. Moiseeva ◽  
◽  
...  
Keyword(s):  
Combustion Front ◽  
Propagation Velocity ◽  
Mass Concentration ◽  
Initial Temperature ◽  
Large Diameter ◽  
Front Propagation ◽  
System Of Equations ◽  
Conservation Equations ◽  
Gas Dispersion ◽  
Al Powder

This paper provides a mathematical model of combustion of a nanodispersed aluminum-air suspension (NAAS). The main feature of the model is the local approach for oxidant diffusion which implies the diffusion of oxidizer through alumina layer on the particle surface and its reaction with aluminum. The oxidation rate of aluminum particles and the rate of heat release for the whole assembly of particles are determined from the solution of local combustion problems for each Al nanoparticle. The parameters of the NAAS are determined from the solution of the system of equations which include the energy conservation equations for gas and particles and the mass conservation equations for the components of the gas-dispersion mixture. The developed model does not require setting the ignition temperature of Al nanoparticles. The system of equations is solved numerically. The problem of combustion front propagation is solved with the following formulation: NAAS is placed in a tube of large diameter and length with a closed left end and open right end. The initial mass concentration of Al powder in the air is uniform and less than the stoichiometric value. Since a high-temperature ignition source on the left end of the tube ignites the NAAS, a combustion wave occurs and starts propagating along the tube. In the present study, the dependences of the combustion-front propagation velocity on the Al mass concentration and initial temperature of the NAAS have been determined. With increasing the initial temperature and mass concentration of Al powder, the propagation velocity of the combustion front increases.

Effect of iron and cobalt addition on TiC combustion synthesis

1993 ◽  
Vol 8 (12) ◽  
pp. 3202-3209 ◽  
Author(s):  
Yoon Choi ◽  
Shi-Woo Rhee
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Reaction Mechanism ◽  
Combustion Synthesis ◽  
Combustion Temperature ◽  
Grain Shape ◽  
Arrhenius Plot ◽  
Molar Ratio ◽  
Velocity Measurements ◽  
Cobalt Addition

Fe and Co metals were incorporated into a Ti and C mixture with a molar ratio of 1.0 over the range of 0 to 40 wt. % to study their effect on TiC combustion synthesis. The addition brought about the grain size decrease, change of grain shape (angular to spherical), and different distribution (agglomerated to isolated) of TiC grains. Both Fe and Co additives were distributed around TiC grains and served as a binder. It was observed that reaction between Ti and C was kinetically more favorable than any other reactions in the Ti–C–Fe or Ti–C–Co system. Based on the activation energy from an Arrhenius plot of In[(1−w)1/2u/Tc] vs 1/Tc, which was obtained by combustion temperature and wave velocity measurements, the reaction mechanism in combustion synthesis of TiC with the addition of 20 wt. % Fe and Co was suggested.

scholarly journals Effect of CaO on catalytic combustion of semi-coke

2021 ◽  
Vol 10 (1) ◽  
pp. 011-020
Author(s):  
Luyao Kou ◽  
Junjing Tang ◽  
Tu Hu ◽  
Baocheng Zhou ◽  
Li Yang
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Combustion Rate ◽  
Activation Energies ◽  
Combustion Reaction ◽  
Tg Analysis ◽  
Conversion Rates ◽  
Apparent Activation Energies ◽  
Ozawa Integral Method ◽  
Addition Amount

Abstract Generally, adding a certain amount of an additive to pulverized coal can promote its combustion performance. In this paper, the effect of CaO on the combustion characteristics and kinetic behavior of semi-coke was studied by thermogravimetric (TG) analysis. The results show that adding proper amount of CaO can reduce the ignition temperature of semi-coke and increase the combustion rate of semi-coke; with the increase in CaO content, the combustion rate of semi-coke increases first and then decreases, and the results of TG analysis showed that optimal addition amount of CaO is 2 wt%. The apparent activation energy of CaO with different addition amounts of CaO was calculated by Coats–Redfern integration method. The apparent activation energy of semi-coke in the combustion reaction increases first and then decreases with the increase in CaO addition. The apparent activation energies of different samples at different conversion rates were calculated by Flynn–Wall–Ozawa integral method. It was found that the apparent activation energies of semi-coke during combustion reaction decreased with the increase in conversion.

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