OXIDATION BEHAVIOR OF POROUS SIC AT HIGH- TEMPERATURES

The oxidation behavior of porous high-purity SiC was studied at 1600 a nd 1700 K for 15h in Ar-O-2(Po-2: 0.02-97 kPa) by measuring the oxidat ion rate, In oxidation at 1600 K, only the weight gain of the SiC was observed after the oxidation, and the amount of cristobalite on the ox idized surface increased with increasing Po-2. In oxidation at 1700 K, the weight loss was observed at the oxygen partial pressure of 0.02 k Pa while the weight gains were observed at an oxygen partial pressures of 2 and 97 kPa. The oxidation rate was determined by measuring the e volved gases throughout the oxidation reaction using a mass spectromet er. The oxidation kinetics obeyed the parabolic law under 0.02-97 kPa at 1600 Ii and under 2-97 kPa at 1700 K, indicating that the passive o xidation occurred, The transition oxygen partial pressure below which the oxidation mechanism changes from passive to the active one, is pre sumed to be approximately 0.1 kPa in the case of the oxidation at 1700 K.