Formation of SiC in the Isotropic Pitch-Based Carbon Fiber and Its C/C Composites

Formation of SiC in the isotropic pitch-based carbon fiber and its C/C composites was investigated. The carbon fiber heat-treated at 2000°C and the glass-like carbon derived from a resol type phenolic resin which was heat-treated at 2000°C were reacted with SiO gas at 1700°C for 5 hours. It was found that SiC crystal formed on the surface of the carbon fiber, and the part of the carbon fiber was broken. The D-band peak of raman spectrum of the carbon fiber became higher after the reaction, which may indicate the increase of defects on the surface of carbon fiber. The surface of glass-like carbon showed less damage than that of the carbon fiber, and the D-band peak decreased after the reaction. The C/C composites were also prepared from the same carbon fiber and phenolic resin, and heat-treated at 2000°C. The C/C composites were reacted with SiO gas in the same way, and it was found that the damage on the carbon fiber was low. It is considered that the carbon matrix derived from resin may protect the carbon fiber. SiC formation test was conducted for a commercially available rigid insulation, DON-1000-H, under SiO gas atmosphere at 1600 ∼ 2000°C for 5 hours. SiC was formed in both of the carbon fiber and the carbon matrix in DON-1000-H after the SiC formation test, and the weight of DON-1000-H increased by 1.9 ∼ 2.9%. The compressive stress at 5% displacement of DON-1000-H decreased by 33.3 ∼ 48.7 % after the SiC formation test. The higher the temperature of SiC formation atmosphere, the more changes of the weight and the compressive stress of DON-1000-H. High temperatures probably accelerate the formation of SiC which caused the damage on rigid insulations.