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

The reaction between SiC powder and H₂O has been studied at 400°–800 °C under 10 and 100 MPa. Silicon carbide reacted with H₂O to yield amorphous SiO₂ and CH₄ by the reaction SiC + 2H₂O→SiO₂ + CH₄ above 500 °C. Cristobalite and tridymite crystallized from amorphous silica after the almost complete oxidation of SiC above 700 °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.