Chemical Vapor Reaction Fabrication And Oxidation Behavior Of Ceramic Coatings On Carbon Fibers

The poor high-temperature oxidation resistance of carbon fibers have limited the development and applications at high temperature of carbon fiber reinforced composites.Therefore,much interest has been shown in protecting coatings on carbon fiber in recent years.In this paper,we prepared SiC coating,SiC/PyC coatings,and SiO₂/SiOC coating on carbon fibers by low-temperature chemical vapor reaction,and explored the influence of experimental conditions to as-prepared coatings.The structure,morphology,and oxidation resistant of the coating were characterized by scanning electron microscopy?SEM?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,and thermo-gravimetric analysis?TGA?.Silicon carbide coating on carbon fibers was realized based on low temperature gassolid reaction,in which carbon fibers reacted with Si vapor which produced by the mixture of Si and Cu powders at 1200-1300 ?.In this system,the existence of copper led to the formation of Si liquid phase,which could produce enough Si vapor at lower temperatures.The oxidation resistant properties of the SiC coated carbon fibers were significantly improved.The initial oxidation temperature of the SiC coated carbon fibers was about 150-200 ? higher than that of the raw carbon fibers.The SiC-coating carbon fibers treated at 1250 ? possessed higher anti-oxidant property than that treated at 1300 ?.To protect carbon fibers during the SiC coating preparation,we deposited a PyC layer on carbon fibers by CVD with dimethylbenzene as the precursor.The influence of deposition time on the structure and thickness of PyC coating was studied.The SiC/PyC coating on carbon fibers was prepared by the reaction of Si with a PyC layer deposited on the fibers.The oxidation resistance of the SiC/PyC double-layer coated carbon fibers was improved.SiO₂/SiOC coating was prepared in a “trace-oxygen system” by the reaction of SiO,O2 and carbon at the temperature of 1150-1300 ?.The SiO vapor was produced by Si oxidation.The structure and composition of coating were influenced by reaction temperature and oxygen partial pressure.