Preparation of an anti-oxidative SiC/SiO₂ coating on carbon fibers by a sol-gel method

A SiC/SiO₂ ceramic coating on carbon fibers was prepared by a sol-gel method followed by heat treatment at high temperature. The structure and the morphology of the SiC/SiO₂ coating were characterized by X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. The oxidation resistant properties of the carbon fibers with and without the coating were compared by thermogravimetric analysis. Results indicate that a uniform and continuous coating can improve the oxidation resistance of carbon fibers. The oxidation resistance of the coated carbon fibers increased with increases in the sol concentration and heat treatment temperature. A coating of thickness 300 nm increased the onset oxidation temperature by about 200℃ and the single fiber tensile strength was decreased by 37.7% compared with the pristine carbon fibers. After isothermal oxidation at 700℃ for 90 min, the single fiber tensile strength of the coated carbon fibers was decreased to 1.37 GPa. The oxidation resistance of the fibers was decreased when the coating thickness exceeded 400 nm due to the spallation of the coating.