新型聚金属碳硅烷的合成反应与应用研究

发布时间：2018-01-20 13:36

本文关键词： 聚碳硅烷 SiC陶瓷前驱体硅杂烯配位聚合前驱体改性 SiC_f/SiC-ZrC复合材料　出处：《中国科学院大学(中国科学院过程工程研究所)》2017年博士论文　论文类型：学位论文

【摘要】：碳化硅(SiC)陶瓷材料具有抗蠕变、耐腐蚀、高强度以及抗氧化等诸多优异性能,广泛应用于化工、核能、国防、航空、航天等重要领域,特别是SiC陶瓷纤维及其复合材料已成功应用于航天载人飞机宇宙舱、航空发动机高热部件、导弹烧蚀部件以及核能工业高温高剂量辐射部件等构件上,是先进陶瓷中的重要一员。有机前驱体转化技术在制备SiC陶瓷纤维以及大尺寸复杂结构SiC陶瓷基复合材料时,因其具有成分可控,操作多变,低温裂解等优点而备受关注,而其技术关键点在于高性能陶瓷前驱体聚碳硅烷(Polycarbosilanes,PCS)的合成。伴随着工业上对SiC陶瓷需求的不断增加,国内外研究人员针对PCS的合成路线展开了广泛而深入的研究,其突出代表为日本科学家S.Yajima开发的"两步法"工艺路线,美国科学家L.Interrante等人开发的开环聚合工艺路线等。然而PCS的合成至今仍无法像聚烯烃一样实现大规模工业化生产,主要原因在于PCS的聚合单体硅杂烯((?))远不如烯烃((?))稳定,硅杂烯化合物的批量合成和应用目前仍然是一个世界性难题。本论文基于对硅杂烯中间体的深刻认知,借鉴茂金属对烯烃聚合的催化过程,提出了一条硅杂烯配位插入聚合反应合成PCS的全新工艺路线,并对其反应机理和应用做了深入研究,主要的研究内容和结论如下:(1)发现了一步合成聚碳硅烷的新反应。以甲基二氯硅烷(SiRMeCl2,R=Me,Ph,Et,H)和茂金属(MCp2Cl2,M = Ti,Zr,Hf)为原料,通过金属钠脱氯和催化重排聚合反应一步合成了含有金属元素的PCS。该全新反应避免了 S.Yajima路线中高能耗高危险的热力学重排步骤,而且所合成的产物中额外引入了金属元素,因此产物被称作聚金属碳硅烷。金属元素随前驱体一同高温裂解后可以转化为相应金属碳化物陶瓷相,进一步强化了所制备陶瓷材料的性能。该合成反应具有原料转化率高、反应条件温和、操作步骤简洁以及生产过程安全等优点,所得产物有望成为制备低成本、高性能SiC陶瓷纤维和陶瓷基复合材料的重要化工原料。(2)研究了聚锆碳硅烷(Polyzirconocenecarbosilane,PZCS)的物理性质和化学结构组成。PZCS呈黑褐色块体,具有良好的可熔可溶性,块体置于空气中比较稳定,但溶液对空气较为敏感。通过 EDS、XPS、FT-IR、29Si-NMR、UV、GPC、MALDI-TOF-MS等多种检测手段对PZCS的化学结构和元素组成进行了分析,结果表明PZCS由Si、Zr、C、H、以及少量O和Cl元素组成,具有线性分子结构,分子链中含有聚碳硅烷特有的Si-H和Si-CH2-Si等结构单元,其平均分子量Mn在900～1500之间,并且分子量分布非常集中(Mw/Mn=1.3～1.5)。TG、XRD和SEM测试结果表明,PZCS经1000℃高温处理后陶瓷收率大于58%,陶瓷产物主要由SiC和ZrC两种陶瓷相组成,其中ZrC晶粒为纳米级尺寸并均匀分散于连续的无定形SiC相当中。(3)研究了聚金属碳硅烷的合成反应机理。通过对实验数据、表征结果以及DFT模拟计算等的综合分析,提出了扩散控制与高反应活性协同作用的催化重排聚合反应机理,其要点如下:ⅰ)甲基二氯硅烷在金属钠作用下脱氯所产生的甲基硅双自由基与硅杂烯为互变异构体,二者可以通过共振实时互相转换。茂金属快速捕捉硅杂烯结构,并通过配位插入聚合反应生成最终产物。ⅱ)茂金属与氯化钠组成的质密层包覆于金属钠表面,阻止了甲基氯硅烷与金属钠的直接接触,保证了层内原料的低浓度,通过原料的耗尽效应,有效地抑制了副反应热聚合的发生。(4)研究了对聚锆碳硅烷的优化与改性工艺。ⅰ)研究了二氯二甲基硅烷与二氯一甲基硅烷的催化共聚合反应。结果表明,通过改变二氯二甲基硅烷与二氯一甲基硅烷的共聚合比例,产物经热解后所得陶瓷材料中自由碳含量从23%下降到6%,实现了对产物中碳元素含量的可控性调节。ⅱ)研究了 LiAlH4和NH3两种脱氯剂对PZCS的脱氯效果。实验证实,经两种脱氯剂处理后,PZCS中的Cl元素含量均有所下降,产品的稳定性得到提高。其中,LiAlH4可以使PZCS中C1元素含量下降35%～50%,但其脱氯产物AlCl3会使PZCS分子链断裂,聚合物分子量大幅下降,严重影响前驱体性能;NH3的脱氯能力相对较弱,但N元素的引入使最终制备的陶瓷材料中含有Si-C-N相陶瓷,有利于提高陶瓷材料性能。ⅲ)研究了 PZCS前期热处理过程。经过200～260℃前期热处理,PZCS的陶瓷收率由58%提高到67%,平均分子量也从930升至2300,其主要原因在于热处理过程发生了以Si-H键为核心的热交联反应。(5)研究了 SiC_f/SiC-ZrC复合材料的制备工艺并对其结构和性能进行分析表征。以化学气相渗透技术(Chemical Vapor Infiltration,CVI)制备的SiC纤维预制体为增强体,PZCS的二甲苯浓溶液(浓度为55%)为浸渍液,通过前驱体浸渍裂解技术(Precursor Infiltration Pyrolysis,PIP)制备了 SiC_f/SiC-ZrC 复合材料。SEM、TEM 和XRD分析结果表明,SiC纤维表面被一层由热解碳(Pyrolytic Carbon,PyC)和SiC所组成的界面层所覆盖,界面层外部连接着连续致密的SiC-ZrC复相陶瓷基体,基体中ZrC晶粒尺寸极小(10～50 nm)并均匀分布于连续的SiC陶瓷相中。经实测,SiC_f/SiC-ZrC复合材料具有较高的弯曲强度和断裂韧性,分别达到了 495.2±71.6MPa和16.9±2.05MPa·m1/2,材料断裂模式为典型的非脆性断裂,分析其原因在于PyC-SiC界面层以适当的强度连接着基体和纤维,在有载荷作用时,界面层既能很好地在基体与纤维之间传递载荷,也能通过界面断裂吸能来有效分散过大的应力,引导裂纹沿纤维轴向扩展,造成纤维拔出,从而达到吸能增韧的作用。通过考察SiC_f/SiC-ZrC复合材料在不同温度下的氧化行为可知,在较高温度下(1000℃以上),复合材料具有良好的抗氧化性能,这是由于SiC的氧化产物在高温时能形成质密的玻璃态氧化膜,有效阻止空气向基体内部扩散,从而达到保护材料的效果;在较低的温度下(800℃以下),SiC的氧化产物无法形成质密氧化膜,材料基体被空气大量氧化,导致材料力学性能严重下降。
[Abstract]:Silicon carbide (SiC) ceramic material has creep resistance, corrosion resistance, high strength and oxidation resistance and other excellent properties, is widely used in chemical industry, nuclear power, defense, aviation, aerospace and other fields, especially SiC ceramic fibers and composites have been successfully applied to manned aircraft cabin aircraft engine high temperature part of the universe, and missile components ablation and the nuclear power industry in high temperature and high dose radiation components and other components, is an important member of advanced ceramics. The organic precursor conversion technology in the preparation of SiC ceramic fibers and the complex structure of large size SiC ceramic matrix composites, because of its controllable components, the operation is changeable, low-temperature cracking has attracted attention, and the the key point is that the technology of high performance ceramic precursor polycarbosilane (Polycarbosilanes, PCS) synthesis. With the increasing demand of SiC ceramic industry, the researchers at home and abroad for PCS The synthetic route carried out extensive and in-depth study, the outstanding representative of Japanese scientists S.Yajima development of the "two step" process, American scientist L.Interrante et al developed ring opening polymerization process route. However, the synthesis of PCS is still not the same as the polyolefin large-scale industrial production, the main reason is that the polymerization of monomer heterosilicon en PCS ((?)) than the olefin ((?)), heterosilicon batch synthesis and application of the compounds is still a worldwide problem. In this paper, a deep understanding of heterosilicon ene intermediates based on the reference of metallocene olefin polymerization catalysis process, put forward a heterosilicon a new process of graphene coordination insertion polymerization reaction for the synthesis of PCS, and the reaction mechanism and application of the in-depth study, the main research contents and conclusions are as follows: (1) found a step into a new reaction to a Polycarbosilane. Two chlorosilane (SiRMeCl2, R=Me, Ph, Et, H) and metallocene (MCp2Cl2, M = Ti, Zr, Hf) as raw material, the polymerization step containing metallic elements PCS. the synthesis of the new reaction to avoid the rearrangement step S.Yajima in thermodynamic route of high energy consumption and high risk by sodium chloride removal and catalytic rearrangement, and the synthesized product additional metal elements, so the product is called polysilane. Metal elements with metal carbon precursor with high temperature cracking after can be transformed into the corresponding metal carbide ceramic phase, and further strengthen the performance of the prepared ceramic material. The reaction has high conversion rate of the raw materials. The advantages of mild reaction conditions, concise operating steps and production process safety, the product is expected to become the preparation of low cost, an important chemical raw material for high performance SiC ceramic fiber and ceramic matrix composites. (2) studied poly zirconium carbon silane (Polyzircon Ocenecarbosilane, PZCS) the physical properties and chemical structure of.PZCS was dark brown color, good fusible soluble and relatively stable block in the air, but the solution is sensitive to the air. By EDS, XPS, FT-IR, 29Si-NMR, UV, GPC, MALDI-TOF-MS and other means of detection of the chemical structure of PZCS and the elements are analyzed, the results show that the PZCS by Si, Zr, C, H, and a small amount of O and Cl elements, with a linear molecular structure, molecular chain containing Polycarbosilane specific Si-H and Si-CH2-Si structural units, the average molecular weight of Mn in 900 ~ 1500, and the molecular weight distribution concentration (Mw/Mn=1.3 ~ 1.5).TG, XRD and SEM test results show that the PZCS is 1000 DEG C after high temperature treatment, the ceramic yield is more than 58%, ceramic products are mainly composed of SiC and ZrC two kinds of ceramic phase, the ZrC nano grain size and uniformly dispersed in the amorphous continuous SiC quite. (3) studied the reaction mechanism of synthesis of polysilane metal carbon. Based on the experimental data, a comprehensive analysis of the characterization results and the DFT simulation of the proposed reaction mechanism catalyzed rearrangement diffusion control and high reaction activity of the synergetic effect of polymerization, the main points are as follows: I) two methyl chlorosilane in metal the effect of sodium removal of methyl silicon chlorine generated tautomers biradicals and heterosilicon graphene, two can be converted to each other by resonance. Real time rapid capture heterosilicon metallocene olefin structure, and through the coordination insertion polymerization reaction of the final product. II) metallocene and sodium chloride is composed of dense layer sodium metal is coated on the surface, prevents direct contact of methylchlorosilane with sodium metal, the low concentration layer of raw materials, the raw material depletion effect, effectively suppress the side reaction heat polymerization. (4) research on poly zirconium carbon silane Optimization of process and change. I) copolymerization Catalytic Study of two chloro two methyl silane and two chloro methyl silane. The results show that by changing the two chloro two methyl silane and two chlorine methyl silane polymerization ratio, free carbon content of product was obtained after pyrolysis in ceramic materials decreased from 23% to 6% and adjust the controllability of the carbon content in the product. II) on LiAlH4 and NH3 two kinds of dechlorination agent on PZCS dechlorination. Experiments show that two kinds of dechlorination agent after the treatment, Cl content in PZCS decreased, the stability of the products were improved. Among them, LiAlH4 can make the content of C1 in PZCS decreased by 35% ~ 50%, but the dechlorination products of AlCl3 molecular chains of PZCS will be broken, the molecular weight of the polymer decreased sharply, serious influence on the performance of the precursor; dechlorination ability of NH3 is relatively weak, but the ceramic material is introduced into the N element in the preparation of the final Si-C-N containing ceramics, is conducive to improve the properties of ceramics. III) on PZCS pre heat treatment process. After 200 ~ 260 degrees of pre heat treatment, PZCS ceramic yield increased from 58% to 67%, the average molecular weight from 930 to 2300, the main reason is that the thermal crosslinking reaction of Si-H bond as the core the heat treatment process. (5) study of the SiC_f/SiC-ZrC composite preparation and characterization of its structure and performance. By chemical vapor infiltration technology (Chemical Vapor Infiltration, CVI) SiC fiber preform preparation as reinforcement, xylene concentrated solution of PZCS (concentration 55%) for impregnating solution and by precursor impregnation and pyrolysis technology (Precursor Infiltration Pyrolysis, PIP) SiC_f/SiC-ZrC composite was prepared by.SEM, TEM and XRD analysis showed that the SiC fiber surface is a layer made of pyrolytic carbon (Pyrolytic Carbon, PyC and SiC). Covered the interface layer, interface layer is connected with the external continuous dense SiC-ZrC ceramic matrix, minimum size of ZrC grains in the matrix (10 ~ 50 nm) and evenly distributed in the continuous phase. SiC ceramics was measured, the flexural strength and fracture toughness of SiC_f/SiC-ZrC composites is higher, respectively 495.2 and 71.6MPa. 16.9 + 2.05MPa m1/2, fracture mode of materials for non typical brittle fracture, the reason is that the PyC-SiC interface layer due to the strength of connection matrix and fiber, the load, the interface layer can well transfer loads between the matrix and fiber, which can also effectively disperse excessive stress the suction through the interface fracture to propagate along the fiber axis, resulting in fiber pull-out, so as to achieve the energy absorption effect. The toughening effects of SiC_f/SiC-ZrC composites oxidation behavior at different temperatures can be known, at a high temperature (of more than 1000 DEG C), composite material has excellent oxidation resistance, which is due to the oxidation product of SiC can form a dense oxide film glass in high temperature, effectively prevent air diffusion within the matrix, thus protect the material effect; at low temperature (800 DEG C), oxidation products SiC cannot form a dense oxide film, a large number of material matrix by air oxidation, resulting in serious decline. The mechanical properties of materials

【学位授予单位】：中国科学院大学(中国科学院过程工程研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O634;TQ174.1

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