Self-propagating high-temperature synthesis of the SiC
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Yoshinari Miyamoto and Mitsue Koizumi Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567, Japan (Received 29 October 1985; accepted 26 February 1986) Self-propagating high-temperature synthesis (SHS), also called combustion synthesis, is useful for fabricating numerous ceramics. In the case of SiC, heat released from the exothermic reaction is not sufficient to completely convert the mixed reactants of constituent elements into SiC in the usual nonadiabatic experimental system. This disadvantage could be overcome by a new ignition process called, the "direct passing method of electric current." By using this method, stoichiometric fine SiC powder could be obtained rapidly and efficiently with low electric power. This paper also involves the effect of particle size of Si and C initial reactant powders on conversion efficiency into SiC and also on particle size of SiC powder fabricated by this method.
I. INTRODUCTION It has been revealed that self-propagating high-temperature synthesis, developed by Merzhanov et al.,1 is simple, efficient, and useful for fabricating many refractory materials and other compounds. The basic study of the solid-solid reaction system in the SHS process and its application has begun in recent years.2^1 The SHS process is based on the fact that a strong exothermic reaction, which occurs during the formation of a compound, can rapidly propagate spontaneously through a cold-pressed reactant in a few seconds. A chain reaction of synthesis is initiated normally by ignition on one end of the pellet. There is the possibility that self-sustaining combustion is basically dependent on the magnitude of heat of formation (Aff). J. B. Holt and Z. A. Munir5 have indicated that the adiabatic temperature calculated from enthalpy and heat capacity of each product may determine whether or not the combustion will take place. In the case of SiC, the heat of formation is relatively low and not sufficient for converting the mixed reactants of Si and C powder completely in the usual system.6 Experimentally, preheating the mixed reactants in a furnace prior to ignition is suggested for improving the ignitability and conversion efficiency into SiC.5 However, heating the reactants for a relatively long time in comparison with the combustion time allows the formation of compound even in a small amount by a solidstate reaction, which will act to inhibit the ignition. This disadvantage could be overcome by a new ignition process, which is called the direct passing method of electric current. By using this method, the SHS of SiC can take place and stoichiometric /?-SiC powder can be obtained efficiently with low electric power. In addition, the effect of the particle size of Si and C reactant powders on J. Mater. Res. 1 (2), Mar/Apr 1986 http://journals.cambridge.org
conversion efficiency into SiC and on the particle size of SiC powder is studied.
II. EXPERIMENTAL PROCEDURE A. Ignition method The quantity of heat released on the formation of SiC from the constituent elements is rep
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