OXIDATION PROTECTION OF CARBON-CARBON COMPOSITES USING CHEMICAL-VAPOR-DEPOSITION AND GLAZE TECHNOLOGY

Low pressure chemical vapour deposition (LPCVD) has been used to apply silicon carbide coatings to a carbon-carbon (C/C) composite using methyl-trichloro-silane as the precursor. When cooled from the deposition temperature, the SiC coatings develop cracks due to thermal expansion mismatches between the coating and substrate. The cracks require sealing at temperatures between 600 and 1100-degrees-C to prevent oxidation of the underlying carbon. Two compositions of a borosilicate glass have been tested as crack sealants, being applied either as an outer glaze or between two layers of the CVD SiC. Compositional variations near the surface of the glass have been investigated using laser microprobe mass spectroscopy. Devitrification of the silica-rich surface of the glass has been studied using X-rav diffraction and scanning electron microscopy.