Improvement of oxidation resistance of unidirectional Cf/SiO2 composites by the addition of SiCp

Unidirectional carbon fiber reinforced fused silica composites (uni-Cf/SiO2) with addition of different contents of SiC particle (SiCp) were prepared by slurry infiltrating and hot-pressing. The model of oxygen infiltrating into the composite was supposed according to the characterization of fiber/matrix interface observed by transmission electronic microscope (TEM). The oxidation process of the composite was analyzed by thermo-gravimetry and differential scanning calorimeter (TG-DSC) method and the oxidation resistance was evaluated by the residual flexural strength and the fracture surface of the composite after heat treatment at elevated temperatures method. The results showed that the oxidation of carbon fiber started at 480 °C and ended at 800 °C and the oxidation of SiCp started at above 1000 °C in the composite. The addition of 20 wt.% SiCp had a better oxidation resistance. According to the characterization of fiber/matrix interface observed by TEM, gaps existed at the fiber/matrix interface which resulted from the CTE mismatch of carbon fiber and SiO2 matrix. While the CTE mismatch between SiCp and SiO2 matrix could also result in the pre-existing gaps in the matrix. The oxygen penetrated along the gaps and simultaneously reacted with carbon fiber ends and SiCp, which filled the gaps at the fiber/matrix interface and the pre-existing gaps in the matrix and subsequently prevented oxygen from infiltrating inward.