CVD mullite coatings in high-temperature, high-pressure air-H sub 2 O

Crystalline mullite was deposited by chemical vapor deposition (CVD) onto SiC/SiC composites overload with CVD SiC. Specimens were exposed to isothermal oxidation tests in high-pressure air+H sub 2 O at 1200 deg C. Unprotected CVD SiC formed silica scales with a dense amorphous inner layer and a thi...

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Bibliographic Details
Published in:Journal of the American Ceramic Society 2000-03, Vol.83 (3), p.657-659
Main Authors: Haynes, J A, Lance, M J, Cooley, K M, Ferber, M K, Lowden, R A, Stinton, D P
Format: Article
Language:English
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Summary:Crystalline mullite was deposited by chemical vapor deposition (CVD) onto SiC/SiC composites overload with CVD SiC. Specimens were exposed to isothermal oxidation tests in high-pressure air+H sub 2 O at 1200 deg C. Unprotected CVD SiC formed silica scales with a dense amorphous inner layer and a thick, porous, outer layer of critobalite. Thin coatings (approx2 mu m) of dense CVD mullite effectively suppressed the rapid oxidation of CVD SiC. No microstructural evidence of mullite volatility was observed under these temperature, pressure, and low-flow-rate conditions. Results of this preliminary study indicate that dense, crystalline, high-purity CVD mullite is stable and protective in low-velocity, high-pressure, moisture-containing environments.
ISSN:0002-7820