SYNTHESIS OF MULLITE COATINGS BY CHEMICAL-VAPOR-DEPOSITION

Formation of mullite on ceramic substrates via chemical vapor depositi on was investigated. Mullite is a solid solution of Al2O3 and SiO2 wit h a composition of 3Al(2)O(3) . 2SiO(2). Thermodynamic calculations pe rformed on the AlCl3-SiCl4-CO2-H-2 system were used to construct equil ibrium chemical vapor deposition (CVD) phase diagrams. With the aid of these diagrams and consideration of kinetic rate limiting factors, in itial process parameters were determined. Through process optimization , crystalline CVD mullite coatings have been successfully grown on SiC and Si3N4 substrates. Results from the thermodynamic analysis, proces s optimization, and effect of various process parameters on deposition rate and coating morphology are discussed.