MECHANISM OF COMBUSTION SYNTHESIS OF SILICON-CARBIDE

The mechanism of self-propagating high-temperature synthesis (SHS) or combustion synthesis of SiC has been investigated using pellets consisting of silicon and carbon powders. The combustion reaction was initiated by rapidly heating the pellet on a graphite strip. The reaction products were analyzed using scanning and transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. The results show that it is possible to produce beta-SiC without any residual silicon and carbon. Occasionally, a very small number density of alpha-SiC precipitates embedded in the beta-SiC matrix was observed. Based upon the microstructural features, it is proposed that the formation of SiC involves the dissolution of carbon into liquid silicon, diffusion of C into liquid silicon, and subsequent precipitation of SiC. The size of the SiC crystallites is determined by the diffusion coefficient of carbon in liquid silicon and the time available for SiC precipitation. The activation enthalpy for the SHS process is estimated to be 59+/-3 kcal/mol.