STUDIES ON SOLUTION-DERIVED CERAMIC COATINGS FOR OXIDATION PROTECTIONOF CARBON-CARBON COMPOSITES

Carbon-carbon composites have been coated with silica and zircon prepa red by sol-gel technique and with methylsilsesquioxane, a preceramic p olymer. The effect of processing parameters for preparation of the sol s and coating procedure on coating morphology has been studied. Oxidat ion behaviour of uncoated and coated carbon-carbon composites has been studied. Coatings with continuous and uniform structure, obtained by controlled processing, have been found to give effective oxidation pro tection. Zircon coatings are found to have better oxidation resistance than silica coatings. Coating of the composites with methylsilsesquio xane and subsequent pyrolysis results in the formation of silicon-oxy- carbide coatings. These coatings are found to provide very effective o xidation resistance at high temperature up to 1200 degrees C.