Under an SGER award the feasibility of growing thin coatings of mullite (3 Al2O3 . 2 SiO2) on ceramic substrates will be studied. The deposition method will be chemical vapor deposition of ultra- thin layers of the constituent compounds, followed by post- deposition heat treatment to form the mullite by inter diffusion. Process characteristics for development of optimal properties of oxidation resistance, resistance to sodium attack, spall resistance during thermal cycling, and hardness will be developed for substrates of silicon carbide and silicon nitride ceramics. The possibility of depositing functionally graded coatings by this technique on these substrates will also be evaluated.
