Oxidation behaviour of silicon carbide under cyclic and static conditions

Abstract

A silicon carbide sintered in a vacuum, with alumina as the sintering additive, was oxidized under cyclic conditions at 1200 C in flowing dry air, for up to 3000 h. Oxidation under static conditions was carried out for comparison. The cyclic oxidation seemed to proceed in four stages, with different reaction rates; all reactions following an almost parabolic rate law. The difference in the reaction rates may well be related to the accompanying change of the oxide layer properties formed during the oxidation. No considerable degradation of the flexural strength, by oxidation, was observed and the oxidation hardly influenced the room-temperature strength. There were no definitive differences in the microstructure and composition of the oxide layer between the cyclic and static oxidation; strengths of comparable values were obtained in both cases. However, the static oxidation resulted in a higher weight gain and a lower value of surface roughness compared with the cyclic oxidation.