OXIDATION OF Si//3N//4 AND SiC BY HIGH TEMPERATURE - HIGH PRESSURE WATER VAPOR.

Silicon nitride and silicon carbide have attracted great attention in recent years because of their potential application as high-temperature structural ceramics. Oxidation resistance is one of the most important properties in these applications. A certain numbers of reports argued that the oxidation rate was accelerated when water vapor coexisted with oxygen. However, the reaction of Si//3N//4 or SiC by H//2O only has not been studied yet. The authors have studied the oxidation of Si//3N//4 and SiC powders by H//2O under hydrothermal conditions where almost only high-temperature high-pressure H//2O exist. The reactions are quite different from the reactions in oxidative atmosphere without H//2O. The present paper discusses the effects of H//2O on high-temperature degradation of Si//3N//4 and SiC powders and ceramics based on the experimental results.