ANTIOXIDATION OF CARBON-CARBON COMPOSITES BY SIC CONCENTRATION GRADIENT AND ZIRCON OVERCOATING

After the formation of a concentration gradient of SiC within a carbon-carbon composite, a zircon (ZrSiO4) thin film was coated on the surface. Oxidation-resistance tests of the treated C-C composites were then carried out. A concentration gradient of SiC was produced by heating the C-C composite in silicon powder at 1450 degrees C for 3 hours. The concentration of SiC along the direction of the carbon fiber sheets decreased rapidly up to 0.25 mm and, in the perpendicular direction, decreased steeply in a range of 0.4-0.6 mm. By the overcoating of zircon with the thickness of 1.5 mu m, a remarkable improvement in the oxidation resistance was observed; the weight loss was almost negligible al 1000 degrees C and one hundredth of the original composite at 1400 degrees C.