碳纤维表面Si-C-O抗氧化性改性研究

发布时间：2018-02-27 05:01

  本文关键词： 碳纤维 聚合物前驱体 Si-O-C气凝胶 抗氧化性能　出处：《哈尔滨工业大学》2016年硕士论文　论文类型：学位论文

【摘要】：随着航天航空技术的快速发展,对新型超轻质、耐高温、抗氧化复合材料需求越来越迫切。但是碳纤维的抗氧化性能较低,在高温条件复合材料会因为低抗氧化性而导致综合性能下降,限制了碳纤维高性能的发挥,因而有必要对碳纤维的抗氧化性进行改善,碳纤维的表面抗氧化改性研究一直是研究的重点之一。本文以二甲基二甲氧基硅烷、正硅酸乙酯作为前驱体,乙醇和蒸馏水为溶剂,采用溶胶凝胶法制备Si-C-O凝胶,浸渍碳纤维,氩气保护气氛下烧结制备Si-C-O结构涂层。前驱体在盐酸作为催化剂的酸性环境下(p H=3)发生水解反应,然后在氨水作为催化剂的碱性环境下(p H=8)发生聚合反应改性刚性碳纤维多孔材料;前驱体在不加入盐酸下水解,在氨水作为催化剂的碱性环境下(p H=8)发生聚合反应改性柔性碳纤维多孔材料,并研究二者的结构和成分,在热处理前后都为无定型结构,表面涂层含有Si-C键、Si-O键。重点研究刚性碳纤维多孔材料改性,通过XRD,SEM,TEM等分析测试方法,研究前驱体配比、醇/水比对涂层形貌结构的影响;探究热处理温度、前驱体配比、涂覆次数对碳纤维抗氧化性能的影响,优化碳纤维表面改性的制备工艺,分析改性后碳纤维的抗氧化行为。前驱体配比、醇/水比影响溶胶粘度,粘度过大涂层过后易开裂,粘度过小不利于形成均匀的涂层,正硅酸乙酯/二甲基二甲氧基硅烷质量比小于1:4、醇/水比为5:1,制备的凝胶适合应用于碳纤维表面改性;不同配比中,以不加入正硅酸乙酯,以二甲基二甲氧基硅烷作为前驱体制备Si-C-O结构涂层改性碳纤维的抗氧化性能最好,氧化起始温度提高了200℃;在不同温度热处理后,发现改性后碳纤维的氧化起始温度随着热处理烧结温度的升高而升高。以二甲基二甲氧基硅烷为前驱体,1200℃热处理,在碳纤维表面制备不同层数Si-C-O结构涂层,研究发现涂覆二层的碳纤维抗氧化性能最好,样品氧化初始温度提高了500℃,且热震性能良好,800℃热震5次后,失重1.8%;1000℃静态氧化实验6h前涂层抗氧化性能良好,6h后失重明显,10h后涂层失效。
[Abstract]:With the rapid development of aerospace technology, the demand for new super lightweight, high temperature and oxidation resistant composite materials is becoming more and more urgent, but the oxidation resistance of carbon fiber is relatively low. Under high temperature conditions, the composite materials will have lower comprehensive properties due to low oxidation resistance, which limits the high performance of carbon fiber, so it is necessary to improve the oxidation resistance of carbon fiber. In this paper, Si-C-O gel was prepared by sol-gel method with dimethyl dimethoxy silane, ethyl orthosilicate as precursor, ethanol and distilled water as solvent. The Si-C-O coating was sintered in argon atmosphere. The precursor was hydrolyzed in acidic environment with hydrochloric acid as catalyst. Then the rigid carbon fiber porous material was modified by polymerization in alkaline environment with ammonia water as catalyst, and the precursor was hydrolyzed without hydrochloric acid. The flexible carbon fiber porous material was modified by polymerization in alkaline environment with ammonia water as catalyst. The structure and composition of the two materials were studied, and the structure was amorphous before and after heat treatment. The surface coating contains Si-C bond and Si-O bond. The modification of rigid carbon fiber porous material is studied. The influence of precursor ratio and alcohol / water ratio on the morphology and structure of the coating is studied by means of XRDX SEMTEM, and the heat treatment temperature and precursor ratio are investigated. The influence of coating times on the oxidation resistance of carbon fiber, the preparation process of carbon fiber surface modification was optimized, the oxidation resistance behavior of modified carbon fiber was analyzed. The precursor ratio and the ratio of alcohol to water affected the sol viscosity, and the coating was easy to crack after the viscosity was too large. The viscosity is too small to form a uniform coating. The mass ratio of ethyl orthosilicate to dimethyl dimethoxy silane is less than 1: 4 and the ratio of alcohol to water is 5: 1.The gel prepared is suitable for the surface modification of carbon fiber. The oxidation resistance of carbon fiber modified by Si-C-O structure coating prepared by dimethyl dimethoxy silane as precursor is the best, and the initial oxidation temperature of carbon fiber is increased by 200 鈩，

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