OXIDATION OF Y-ALPHA'-SIALON AND ALPHA-SI3N4 POWDERS IN THE TEMPERATURE-RANGE 800 TO 1000-DEGREES-C

The oxidation of Y-alpha'-SiAlON and alpha-Si3N4 powders was investiga ted in air in the temperature range 800 to 1000 degrees C. The oxidati on rate was evaluated by determining the change in oxygen content of t he powders during oxidation. It Nas found that Y-alpha'-SiAlON powder was more easily oxidized than the alpha-Si3N4 powder and the oxidation law of these powders was of a parabolic type. Diffusion of oxygen thr ough the oxide layer formed on the specimen surface was thought to be the rate controlling step. The apparent activation energies for the ox idation process were similar to 126 kJ/mol and 147 kJ/mol for Y-alpha' -SiAlON powder and alpha-Si3N4 powder, respectively.