CVD mullite and mullite-alumina corrosion protection coatings for silicon based ceramics

Application of silicon-based ceramics (SiC, Si3N4) and SiC/SiC composites a s high-temperature structural materials requires the development of environ mentally resistant coatings due to rapid degradation of the protective sili ca scale in high temperature water vapor. The CVD method of fabricating den se, high-purity, crystalline mullite (3Al(2)O(3)x2SiO(2)) and mullite-alumi na coatings was utilized in this study. The textured mullite coatings were generally comprised of crystalline grains (0.3-0.5 mum) with a columnar str ucture. Coatings with thickness of less than 2 mum, provided excellent corr osion protection for Si3N4 and SiC/SiC exposed to low-velocity, high pressu re (1 MPa) steam at 1200 degreesC.