Oxidation of SiC powder by high-temperature, high-pressure H2O

The reaction between SiC powder and H2O has been studied at 400 degrees-800 degrees C under 10 and 100 MPa. Silicon carbide reacted with H2O to yield amorphous SiO2 and CH4 by the reaction SiC + 2H(2)O -> SiO2 + CH4 above 500 degrees C. Cristobalite and tridymite crystallized from amorphous silica after the almost complete oxidation of SiC above 700 degrees C. The oxidation rate, as calculated from the weight gain, increased with temperature and pressure. The Arrhenius plotting of the reaction rate based on a Jander-type model gave apparent activation energies of 167-194 kJ/mol. Contrasted with oxidation in oxidative atmosphere, oxidation in H2O is characterized by the diffusion of H2O and CH4 in an amorphous silica layer where the diffusion seemed to be rate determining. Present results suggest that the oxidation of SiC includes the diffusion process of H2O in silica layers when atmospheres contain water vapor.