Active-to-Passive Transition and Bubble Formation for High-Temperature Oxidation of Chemically Vapor-Deposited Silicon Carbide in CO–CO2 Atmosphere

Oxidation behavior of chemically vapor-deposited SiC in CO─CO₂ atmospheres (0.1 MPa) was investigated using a thermogravimetric technique at temperatures from 1823 to 1923 K. Active or passive oxidation was observed depending on temperature and CO₂/CO partial pressure ratio ( P _co2/ P _co). The critical P _co2/ P _co value for the transition was 1O² times as large as a theoretical value calculated from the Wagner model. In the passive oxidation above 1873 K, SiO₂ bubbles were grown. The expansion and rupture of bubbles caused cyclic rapid mass gain and mass loss.