A micromechanistic model of the combustion synthesis process: Part II. Numerical simulation
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A series of computer experiments was conducted for the self-propagating combustion synthesis process in the N b - C system, based on the general theoretical model that was developed previously.1 A detailed and quantitative description was given for the various physical and chemical processes that take place during the combustion synthesis process. The results are presented at various length scales in order to provide an insight into understanding the mechanisms that are responsible for the self-propagating behavior. It was shown that a fundamental understanding and precise control of the process require a strong emphasis on the joint contributions of the rates of the various mass and energy redistribution processes that occur during the combustion synthesis process. A proper balance of each of the elementary process rates must be achieved to give rise to self-propagating behavior. This paper illustrates some of the capabilities of the general theoretical model in quantitatively describing the self-propagating combustion synthesis process.
I. INTRODUCTION The combustion synthesis [or self-propagating hightemperature synthesis (SHS)] process has been widely studied recently, particularly as a means to prepare a large number of advanced ceramic, intermetallic, and composite materials.2"15 The process generally starts by preparing a pellet that consists of powdered solid reactants. One end of the pellet is then raised to an elevated temperature by rapidly exposing it to a high-temperature heat source. The reaction will be ignited and proceed in a self-sustaining manner under the conditions that favor self-propagation. Precise control of the reaction conditions is essential for conducting a reliable process and for ensuring microstructural reproducibility. Development of a fundamental understanding of the combustion synthesis process has been attempted both experimentally16"22 and theoretically.23"38 A more complete, quantitative theoretical model has been developed recently1 for selfpropagating combustion synthesis processes. The model, in its more general form, incorporates the appropriate conservation equations to account for the heat, mass, and momentum transport processes that have been observed or suggested to take place during the combustion synthesis process. Microstructural parameters are accounted for, and derived from percolation concepts as applied to disordered porous granular media. In this work, the general theoretical model that was developed previously1 was applied to the selfpropagating combustion synthesis process in the N b - C system. A series of computer experiments was conJ. Mater. Res., Vol. 9, No. 10, Oct 1994
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ducted. The results are presented here at various length scales, in order to develop an understanding of the mechanisms that are responsible for the self-propagating behavior. The purpose of the present work is primarily to illustrate some of the capabilities of the theoretical model. The model also provides a more complete, quantit
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