Active‐to‐Passive Transition and Bubble Formation for High‐Temperature Oxidation of Chemically Vapor‐Deposited Silicon Carbide in CO–CO ₂ Atmosphere

Abstract

Oxidation behavior of chemically vapor‐deposited SiC in CO─CO 2 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 CO 2 /CO partial pressure ratio ( P co2 / P co ). The critical P co2 / P co value for the transition was 1O 2 times as large as a theoretical value calculated from the Wagner model. In the passive oxidation above 1873 K, SiO 2 bubbles were grown. The expansion and rupture of bubbles caused cyclic rapid mass gain and mass loss.