Oxidation behaviour of carbon/carbon composites impregnated with silica and silicon oxycarbide

Carbon/Carbon Composites made with high strength carbon fibers as reinforce ment and pitch as matrix precursor have been impregnated with silica sol an d silicon oxycarbide precursor (in sol form). On subsequent heat treatment to 1000 degrees C and 1600 degrees C, these composites have been found to e xhibit slag and glassy coatings. Apparent density of the composites at diff erent stages has been measured by water penetration while pore volume and p ore size distribution have been measured by mercury porosimeter. The porosi ty of composites made with surface cleaned fibers and impregnated with sili ca has been found to increase while of those impregnated with silicon oxyca rbide to decrease on heat treatment from 1000 degrees C to 1600 degrees C. Oxidation behavior and inhibition of oxidation of the impregnated composite s has been studied using TGA in the temperature range 40-800 degrees C (up to 20% burn off). The effect of impregnation towards oxidation inhibition h as been studied through SEM investigation on partially oxidized samples. It has been found that silicon oxycarbide is better oxidation inhibitor than silica. (C) 2000 Elsevier Science Ltd. All lights reserved.