OXIDATION PROTECTION OF POROUS REACTION-BONDED SILICON-NITRIDE

Oxidation kinetics of both as-fabricated and coated reaction-bonded si licon nitride (RBSN) were studied at 900 and 1000 degrees C with therm ogravimetry. Uncoated RBSN exhibited internal oxidation and parabolic kinetics. An amorphous Si-C-O coating provided the greatest degree of protection to oxygen, with a small linear weight loss observed. Linear weight gains were measured on samples with an amorphous Si-N-C coatin g. Chemically vapour deposited (CVD) Si3N4 coated RBSN exhibited parab olic kinetics, and the coating cracked severely. A continuous-SiC-fibr e-reinforced RBSN composite was also coated with the Si-C-O material, but no substantial oxidation protection was observed.