Oxidation Protective Film of SiC Prepared by Using Si-polymer and CVD Method on 3D-C/C Composites, and Oxidation Protection in H2O and CO2 Gas Phases at High Temperature

Abstract

The influence of H2O and CO2 gases on the high temperature oxidation of CVD-SiC was investigated under a condition of active oxidation for SiC. The SiO gas produced by the active oxidation of SiC was further oxidized to form SiO2 protective scale against oxidation on the SiC surface at 1700°C. The SiO2 scale growth rate was controlled by the diffusion rate of the oxidant gases in the SiO2 scale. The oxidation protection ability of the CVD-SiC on the 3D-C/C surface was also improved by using a newly developed Si-polymer process. Poly-vinyl alcohol was more effective as the binder to obtain a dense SiC layer than phenolic resin. Although the CVD-SiC film was successfully formed on the side of the yarn exposed in the 3D-C/C surface, cracks were observedto form on the cross section of the yarn. The crack formation was attributable to the difference in the CTE between longitudinal and transverse direction of carbon fiber.