Paralinear Oxidation of CVD SiC in Simulated Fuel-Rich Combustion

The oxidation kinetics of CVD SiC were measured by thermogravimetric analysis (TGA) in a 4H2·12H2O·10CO·7CO2·67N2 gas mixture flowing at 0.44 cm/s at temperatures between 1300° and 1450°C in fused quartz furnace tubes at 1 atm total pressure. The SiC was oxidized to form solid SiO2. At ≥1350°C, the SiO2 was in turn volatilized. Volatilization kinetics were consistent with the thermodynamic predictions based on SiO formation. These two simultaneous reactions resulted in overall paralinear kinetics. A curve fitting technique was used to determine the linear and parabolic rate constants from the paralinear kinetic data. Volatilization of the protective SiO2 scale resulted in accelerated consumption of SiC. Recession rates under conditions more representative of actual combustors were estimated from the furnace data.