Paralinear oxidation of silicon nitride in a water vapor oxygen environment

Two silicon nitride materials were exposed to a 50% H2O/50% O-2 gas mixture flowing at 4.4 cm/s for 100 hours at temperatures between 1200 degrees and 1400 degrees C. Reaction kinetics were monitored with a continuously recording microbalance. Both materials exhibited paralinear kinetics. This is due to the simultaneous oxidation of Si3N4 by H2O to form SiO2 and volatilization of the silica by H2O. At long times, recession of the Si3N4 can be approximated by the linear loss rate due to silica volatility.