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.