Modification Research On The Oxidation Resistance Of Silicon-carbon-oxygen On Carbon Fiber Surface

With the rapid development of aviation and space technology, there are increasing needs for the new super light, high temperature resistance and oxidation resistance composites. However the antioxidant property of carbon fiber is poor, the high temperature composites will result in performance degradation because of the low oxidation resistance, limiting the carbon fiber high-performance play. So there is a need to improve the oxidation resistance of carbon fiber, and anti-oxidation of carbon fiber surface modification has been one focus of the study.In this study, we prepared Si-C-O gel using sol-gel method basing on dimethyl dimethoxy silane and ethyl orthosilicate as precursors, ethyl alcohol and distilled water as solvent. Si-C-O coating was prepared by sintering impregnated carbon fiber Si-C-O gel in argon atmosphere. Precursors hydrolyze in acid(p H=3)of hydrochloric acid as a catalyst, polymerize under alkaline conditions(p H=8)of ammonia as a catalyst to form rigid porous materials; precursors hydrolyze without hydrochloric acid as a catalyst, as well polymerize under alkaline conditions(p H=8)of ammonia as a catalyst to form flexible porous materials. We studied the structure and composition of the two productions, the results show they are amorphous structure before and after heat treatment, and surface coating contains the Si-C and Si-O bonds.Through analytical methods such as XRD, SEM, TEM, we studied the rigid surface coating modified carbon fiber, researched the influence of precursor compound, alcohol-water ratio effects on the film morphology, explored heat treatment temperature, number of precursor composition and coating effects on oxidation resistance of carbon fiber to optimize preparation technology of carbon fiber surface modification, analysis of the modified anti-oxidation behavior of carbon fiber. Precursor compound and alcohol-water ratio effect sol stick degrees, higher stick makes coating easy to crack, lower stick make it difficult to form uniform coating. When ethyl orthosilicate and dimethyl dimethoxy silane compound is lower than 1:4, alcohol-water ratio is 5:1, the prepared gel is suitable for carbon fiber surface modification. In different proportions, when ethyl orthosilicate was not added, dimethyl dimethoxysilane as a precursor, the antioxidant properties of carbon fiber modified with Si-C-O coating is best, oxidation starting temperature has increased by 200 ℃. After heat treatment at different temperatures and found that oxidation-starting temperature after heat treatment rises with the sintering temperature of modified carbon fiber. Using dimethyl silane as precursor, 1200 ℃ heat treatment, we prepared different layers of Si-C-O coating modified carbon fiber. In the study, we found that carbon fiber with two layers of coating has the best antioxidant properties, the initial oxidation of the sample temperature has increased by 500 ℃, and has good thermal shock resistance, 800 ℃ thermal shock five times the weight loss 1.8%. The coating oxidation resistance behave well before 1000 ℃ still oxidation experiments 6h, after 6h significant weight loss, the coating failure after 10 h.