OXIDATION BEHAVIOR OF SI-SIC AT HIGH-TEMPERATURE

Oxidation behavior of high-purity Si-SiC composite (molar ratio 40/60) was studied during reactions at 1600 K for 15h in Ar-O-2 (P-o2: 0.02- 97 kPa) atmospheres to evaluate the oxidation-resistant property. The oxidation rate was determined by measuring CO and CO2 concentrations d uring the oxidation using a quadrupole mass spectrometer. The oxidatio n kinetics obeyed the linear-parabolic law at high oxygen partial pres sures (97 kPa) and obeyed the linear law at low oxygen partial pressur es (0.02 kPa). The former case accompanied the weight gain, while the latter the weight loss. The oxygen partial pressure causing the transi tion from passive to active oxidation was estimated to lie between 0.1 kPa and 0.02 kPa. In passive oxidation, apparent low oxidizability of Si as compared with that of SiC was considered to result from the con version of Si in the surface layer of the sample into SiC caused by it s reaction with C released from SiC. Cooperative actions between Si an d SiC were discussed in connection with the oxidation resistance of Si -SiC composite.