碳纤维表面化学修饰及其与SiBCN陶瓷基体的界面结合特性

发布时间：2018-05-07 18:01

本文选题：碳纤维 + 氧化石墨烯　；参考：《哈尔滨工业大学》2017年博士论文

【摘要】：随着现代航空航天技术的进步,具有高马赫数的新型高超声速航天飞行器已经成为世界军事大国研究重点,X系列空天飞行器成为其中的代表。而热防护系统作为其重要子系统之一,它成为制约高超飞行器服役能力的关键技术。针对服役环境,对系统所采用的材料提出了具有轻质、耐高温、抗氧化烧蚀及高可靠性的基本特征,以满足热防护系统的需求。而连续碳纤维增强陶瓷基复合材料所制备的多孔材料,由于其较高的孔隙率,较低的密度,良好的高温稳定性使其成为重要的候选材料之一,此外做为新型的刚性多孔陶瓷基隔热材料,SiBCN陶瓷的引入相较于传统的SiOC陶瓷能进一步提高其耐热性。连续碳纤维增强复合材料具有高强度、高硬度、低比重和耐化学腐蚀等优点,在过去几十年一直是材料学科研究的热点,由于其杰出的力学性能在航空航天、汽车及国防等领域有着广泛的应用。相较于传统的金属或者合金材料,碳纤维复合材料还具有更好的面内拉伸性能以及密度更低的优势。由于碳纤维与基体之间存在弱界面限制了碳纤维复合材料性能的发挥。本论文主要研究了氧化石墨烯接枝改性碳纤维(CF-g-GO)三维织物和纳米二氧化硅改性碳纤维(CF-g-nanosilica)三维织物两种复合增强体;并以此为基础结合原位聚合法和先驱体浸渍裂解法,经过浸渍和高温热解等工艺,合成了两种新型的CF-g-GO/SiBCN-Ⅰ和CF-gnanosilica/SiBCN-Ⅱ陶瓷基复合材料,并研究了两种复合材料的制备工艺方法,探讨了两种复合材料的化学基团组成、元素分布及含量等变化规律,并对其机械性能及热物理性能进行了研究。采用3-氨丙基三乙氧基硅烷和3-缩水甘油醚氧基丙基三甲氧基硅烷两种硅烷偶联剂分别修饰氧化石墨烯和碳纤维,通过开环反应制备了氧化石墨烯接枝改性碳纤维复合增强体。研究了碳纤维/氧化石墨烯杂化结构的合成工艺及接枝氧化石墨烯前后碳纤维界面化学组成及微观组织的变化。FTIR、XPS及SEM等分析测试结果表明了氧化石墨烯被高效的接枝到碳纤维表面。单丝拉伸测试表明接枝氧化石墨烯能一定程度上弥合碳纤维表面由于氧化作用而产生的缺陷,使改性碳纤维自身的拉伸强度和断裂功能得到提高,同时起到增加纤维表面的粗糙度和增强界面机械咬合的作用。以1,4-对苯二异氰酸酯为单体合成了大分子偶联剂聚异氰酸酯(PPDI),采用二氧化硅纳米颗粒为增强相,结合异氰酸酯与羟基的亲核加成反应制备了二氧化硅纳米颗粒改性碳纤维复合材料,研究了碳纤维/纳米二氧化硅杂化结构的合成机理及接枝前后碳纤维界面化学组成及微观组织演变规律。通过测试分析结果表明纳米二氧化硅被均匀有序的包覆在碳纤维表面,并且通过改变反应条件可实现对纤维表面二氧化硅纳米颗粒的接枝率及接枝密度的有效调控。纳米二氧化硅改性碳纤维力学测试结果表明,不同纳米二氧化硅接枝量会影响碳纤维的拉伸性能,其中当碳纤维和纳米二氧化硅质量比5:1时,改性碳纤维力学性能最好,其拉伸强度和断裂功分别提高至3.74GPa和34.25J/m3,与碳纤维原丝相比,其拉伸强度和断裂功分别提高了45%和132%。结合AFM测试结果表明,二氧化硅纳米颗粒接枝到碳纤维表面,不仅极大地增加了碳纤维的表面粗糙度及比表面积,还有效地改善了碳纤维的机械性能。以氧化石墨烯接枝改性连续碳纤维为增强体,以甲基三氯硅烷、三氯化硼和六甲基二硅氮烷三种小分子为单体,在改性碳纤维三维织物表面经过原位聚合、热解等工艺制备了CF-g-GO/Si BCN-Ⅰ陶瓷基复合材料。经测试分析表明复合材料主要由Si、B、C和N四种元素构成,其键接方式主要有B-N键、Si-N键和Si-C键三种共价键。采用热重分析法测试了CF-g-GO/SiBCN-Ⅰ陶瓷基复合材料在空气气氛下的抗氧化性能。结果表明在1400°C时其失重率为26%,这是由于在温度700~836°C范围SiBCN中BN及部分纤维发生了氧化,并生成了氧化硅玻璃相和氧化硼玻璃相,玻璃相的生成阻止了复合材料的进一步氧化。通过对不同密度复合材料的压缩测试表明,复合材料的压缩模量和压缩强度随着密度的增加而增加,经过四次浸渍裂解循环后,复合材料的压缩性能达到最好,其x/y方向压缩强度和压缩模量分别为5.56±0.52MPa和87.92±8.13MPa,z方向压缩强度和压缩模量分别为0.91±0.32MPa和35.10±5.07MPa。以纳米二氧化硅改性连续碳纤维三维织物为增强体,采用三氯硅烷、三氯化硼和六甲基二硅氮烷三种单体,制备了另外一种CF-g-nanosilica/SiBCN-Ⅱ陶瓷基复合材料。研究结果表明,采用SiBCN-Ⅱ型先驱体所制备的复合材料有更好的力学性能,同样经过四次浸渍裂解循环后,所得复合材料的x/y方向压缩强度和压缩模量分别为7.36±0.67MPa和223.53±16.15MPa,z方向压缩强度和压缩模量分别为0.92±0.25MPa和46.4±9.31MPa,明显高于采用SiBCN-Ⅰ所合成的复合材料,这主要是由于SiBCN-Ⅱ在1400°C热解后拥有更高的陶瓷产率及高温稳定性所致。采用热失重测试方法研究了CF-g-nanosilica/SiBCN-Ⅱ陶瓷基复合材料的在空气中的动态氧化行为。结果表明,该复合材料的氧化行为主要分为三个阶段:第一阶段,当温度在28~826°C时,复合材料未发生明显氧化;第二阶段为826~900°C时,样品失重速率骤升,主要是因为碳纤维表面包覆的SiBCN多元陶瓷中BN发生了氧化反应,生成B2O3和NO2气体,气体挥发,导致陶瓷中出现孔隙,从而引起纤维氧化而导致失重;第三阶段为900~1200°C,随着温度升高,SiBCN中Si和B分别发生氧化生成了玻璃态的氧化硅及氧化硼弥合了氧化过程中产生的缺陷,有效地保护了纤维在高温氧化环境中不受损伤。因此通过接枝二氧化硅纳米颗粒和表面包覆SiBCN陶瓷先驱体均能有效地提高碳纤维在高温环境中的抗氧化性能。
[Abstract]:With the progress of modern aerospace technology, a new type of hypersonic spacecraft with high Maher number has become the focus of the world's military power research. The X series airspace vehicle has become one of the representative. As one of its important subsystems, thermal protection system has become the key technology to restrict the service ability of the hypervehicle. The basic features of the materials used in the system are light, high temperature resistant, antioxidation and high reliability, to meet the requirements of the thermal protection system. The porous material prepared by continuous carbon fiber reinforced ceramic matrix composites is made by its high porosity, low density and good high temperature stability. One of the important candidates, in addition to a new type of rigid porous ceramic based insulation, the introduction of SiBCN ceramics is more heat-resistant than traditional SiOC ceramics. Continuous carbon fiber reinforced composites have the advantages of high strength, high hardness, low specific gravity and chemical corrosion resistance. In the past few decades it has been a material subject. Because of its outstanding mechanical properties, it has a wide range of applications in aerospace, automotive and national defense fields. Compared to traditional metal or alloy materials, carbon fiber composites have better tensile properties and lower density. The weak interface between carbon fiber and matrix restricts carbon fiber. In this paper, two kinds of composites reinforced with graphene oxide graft modified carbon fiber (CF-g-GO) and nano silica modified carbon fiber (CF-g-nanosilica) fabric are mainly studied in this paper. On this basis, the technology of in-situ polymerization and precursor impregnation cracking, impregnation and high temperature pyrolysis are used as the basis. Two new types of CF-g-GO/SiBCN- I and CF-gnanosilica/SiBCN- II ceramic matrix composites were synthesized, and the preparation methods of two kinds of composites were studied. The chemical group composition, the distribution and content of the two kinds of composite materials were discussed. The mechanical properties and the thermal physical properties of the two composites were studied. Graphene oxide and carbon fibers were modified by two silane coupling agents, which were two kinds of silane coupling agents, such as triethoxy silane and glycidyl triethyl trimethoxy silane, respectively. The carbon fiber reinforced carbon fiber reinforced polymer was prepared by the ring opening reaction. The synthesis process of carbon fiber / graphene oxide hybrid structure and the grafted graphene oxide were studied. The chemical composition and microstructure change of the carbon fiber interface.FTIR, XPS and SEM show that the graphene oxide is efficiently grafted onto the surface of carbon fiber. The tensile test of monofilament shows that the graft copolymer can partly bridge the defects of the carbon fiber surface due to oxidation, and make the modified carbon fiber itself. The tensile strength and fracture function are improved, at the same time, the roughness of the fiber surface and the mechanical occlusal of the interface are increased. The macromolecule coupling agent (PPDI) is synthesized by 1,4-, and the silica nanoparticles are used as the enhanced phase, and the nucleophilic addition reaction of isocyanate and hydroxyl group is made. Silica nanoparticles modified carbon fiber composites were prepared. The synthesis mechanism of carbon fiber / nano silica hybrid structure and the chemical composition and microstructure evolution of carbon fibers before and after grafting were studied. The results showed that the nano silica was coated on the surface of carbon fiber uniformly and orderly. The change of reaction conditions can effectively control the grafting ratio and the grafting density of silica nanoparticles on the fiber surface. The mechanical test results of nano silica modified carbon fiber show that the grafting amount of different nano silica will affect the tensile properties of carbon fibers, of which carbon fiber and nano silica are modified when the mass ratio is 5:1. The tensile strength and fracture work of its tensile strength and fracture work were improved to 3.74GPa and 34.25J/m3 respectively. The tensile strength and fracture work of the carbon fiber were increased by 45% and 132%. respectively compared with the carbon fiber precursor. The results showed that the grafting of silica nanoparticles onto the surface of carbon fibers not only greatly increased the surface roughness and specific surface of carbon fibers. The mechanical properties of carbon fibers were effectively improved. CF-g-GO/Si BCN- I ceramics were prepared on the surface of modified carbon fiber three-dimensional fabric by in-situ polymerization, pyrolysis and other processes by using methyl three chlorosilane, three boron chloride and six methyl two silanane as monomers. Based on the test and analysis, the composite material is mainly composed of four elements, Si, B, C and N. The bonding mode is mainly composed of B-N, Si-N and Si-C bonds. The thermogravimetric analysis is used to test the anti oxygen properties of CF-g-GO/SiBCN- I ceramic matrix composites in air atmosphere. The results show that the weight loss rate is 26% at 1400 degree C. This is due to the oxidation of BN and some fibers in the range SiBCN of temperature 700~836 C, and the formation of the silica glass phase and the boron oxide glass phase. The formation of the glass phase prevents the further oxidation of the composites. The compression modulus and compressive strength of the composite materials are determined by the compression test of different density composites. The compression strength and modulus of x/y direction are 5.56 + 0.52MPa and 87.92 + 8.13MPa, respectively, and the compressive strength and compression modulus of the Z direction are 0.91 + 0.32MPa and 35.10 + 5.07MPa. respectively, and the nano silica modified continuous carbon fibers are woven in three dimensional fabric. Another kind of CF-g-nanosilica/SiBCN- II ceramic matrix composite was prepared by using three chlorosilane, three boron chloride and six methyl two silicanitane. The results showed that the composites prepared by the SiBCN- type II precursor had better mechanical properties, and the composite after four cycles of lysis was also obtained. The compressive strength and compression modulus of the material in x/y direction are 7.36 + 0.67MPa and 223.53 + 16.15MPa respectively. The compressive strength and compression modulus of the Z direction are 0.92 + 0.25MPa and 46.4 + 9.31MPa respectively, which are obviously higher than those synthesized by SiBCN- I. This is mainly due to the higher ceramic yield and high temperature stability of SiBCN- II after the pyrolysis of 1400 degrees. The dynamic oxidation behavior of CF-g-nanosilica/SiBCN- II ceramic matrix composites in the air was studied by the method of thermal weight loss test. The results showed that the oxidation behavior of the composite was mainly divided into three stages: the first stage, when the temperature was 28~826 C, the composite material had no obvious oxidation; the second stage was 826~900 degree C. When the weight loss rate of the sample rises suddenly, it is mainly because the oxidation reaction of BN in the SiBCN multicomponent ceramic coated on the carbon fiber surface generates B2O3 and NO2 gas, and the gas volatilization leads to the appearance of pores in the ceramics, which causes the fiber oxidation to cause weightlessness. The third stage is 900~1200 C, with the increase of temperature, Si and B occur respectively in SiBCN. The glass state of silicon oxide and boron oxide bridge the defects produced in the oxidation process and effectively protect the fibers from being damaged in the high temperature oxidation environment. Therefore, the oxidation resistance of carbon fibers in high temperature environment can be effectively improved by grafting silica nanoparticles and coating SiBCN ceramic precursors on the surface.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB332

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