本文關(guān)鍵詞： 聚碳硅烷 SiC陶瓷前驅(qū)體 硅雜烯配位聚合 前驅(qū)體改性 SiC_f/SiC-ZrC復(fù)合材料　出處：《中國科學(xué)院大學(xué)(中國科學(xué)院過程工程研究所)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：碳化硅(SiC)陶瓷材料具有抗蠕變、耐腐蝕、高強度以及抗氧化等諸多優(yōu)異性能,廣泛應(yīng)用于化工、核能、國防、航空、航天等重要領(lǐng)域,特別是SiC陶瓷纖維及其復(fù)合材料已成功應(yīng)用于航天載人飛機宇宙艙、航空發(fā)動機高熱部件、導(dǎo)彈燒蝕部件以及核能工業(yè)高溫高劑量輻射部件等構(gòu)件上,是先進陶瓷中的重要一員。有機前驅(qū)體轉(zhuǎn)化技術(shù)在制備SiC陶瓷纖維以及大尺寸復(fù)雜結(jié)構(gòu)SiC陶瓷基復(fù)合材料時,因其具有成分可控,操作多變,低溫裂解等優(yōu)點而備受關(guān)注,而其技術(shù)關(guān)鍵點在于高性能陶瓷前驅(qū)體聚碳硅烷(Polycarbosilanes,PCS)的合成。伴隨著工業(yè)上對SiC陶瓷需求的不斷增加,國內(nèi)外研究人員針對PCS的合成路線展開了廣泛而深入的研究,其突出代表為日本科學(xué)家S.Yajima開發(fā)的"兩步法"工藝路線,美國科學(xué)家L.Interrante等人開發(fā)的開環(huán)聚合工藝路線等。然而PCS的合成至今仍無法像聚烯烴一樣實現(xiàn)大規(guī)模工業(yè)化生產(chǎn),主要原因在于PCS的聚合單體硅雜烯((?))遠不如烯烴((?))穩(wěn)定,硅雜烯化合物的批量合成和應(yīng)用目前仍然是一個世界性難題。本論文基于對硅雜烯中間體的深刻認知,借鑒茂金屬對烯烴聚合的催化過程,提出了一條硅雜烯配位插入聚合反應(yīng)合成PCS的全新工藝路線,并對其反應(yīng)機理和應(yīng)用做了深入研究,主要的研究內(nèi)容和結(jié)論如下:(1)發(fā)現(xiàn)了一步合成聚碳硅烷的新反應(yīng)。以甲基二氯硅烷(SiRMeCl2,R=Me,Ph,Et,H)和茂金屬(MCp2Cl2,M = Ti,Zr,Hf)為原料,通過金屬鈉脫氯和催化重排聚合反應(yīng)一步合成了含有金屬元素的PCS。該全新反應(yīng)避免了 S.Yajima路線中高能耗高危險的熱力學(xué)重排步驟,而且所合成的產(chǎn)物中額外引入了金屬元素,因此產(chǎn)物被稱作聚金屬碳硅烷。金屬元素隨前驅(qū)體一同高溫裂解后可以轉(zhuǎn)化為相應(yīng)金屬碳化物陶瓷相,進一步強化了所制備陶瓷材料的性能。該合成反應(yīng)具有原料轉(zhuǎn)化率高、反應(yīng)條件溫和、操作步驟簡潔以及生產(chǎn)過程安全等優(yōu)點,所得產(chǎn)物有望成為制備低成本、高性能SiC陶瓷纖維和陶瓷基復(fù)合材料的重要化工原料。(2)研究了聚鋯碳硅烷(Polyzirconocenecarbosilane,PZCS)的物理性質(zhì)和化學(xué)結(jié)構(gòu)組成。PZCS呈黑褐色塊體,具有良好的可熔可溶性,塊體置于空氣中比較穩(wěn)定,但溶液對空氣較為敏感。通過 EDS、XPS、FT-IR、29Si-NMR、UV、GPC、MALDI-TOF-MS等多種檢測手段對PZCS的化學(xué)結(jié)構(gòu)和元素組成進行了分析,結(jié)果表明PZCS由Si、Zr、C、H、以及少量O和Cl元素組成,具有線性分子結(jié)構(gòu),分子鏈中含有聚碳硅烷特有的Si-H和Si-CH2-Si等結(jié)構(gòu)單元,其平均分子量Mn在900～1500之間,并且分子量分布非常集中(Mw/Mn=1.3～1.5)。TG、XRD和SEM測試結(jié)果表明,PZCS經(jīng)1000℃高溫處理后陶瓷收率大于58%,陶瓷產(chǎn)物主要由SiC和ZrC兩種陶瓷相組成,其中ZrC晶粒為納米級尺寸并均勻分散于連續(xù)的無定形SiC相當中。(3)研究了聚金屬碳硅烷的合成反應(yīng)機理。通過對實驗數(shù)據(jù)、表征結(jié)果以及DFT模擬計算等的綜合分析,提出了擴散控制與高反應(yīng)活性協(xié)同作用的催化重排聚合反應(yīng)機理,其要點如下:ⅰ)甲基二氯硅烷在金屬鈉作用下脫氯所產(chǎn)生的甲基硅雙自由基與硅雜烯為互變異構(gòu)體,二者可以通過共振實時互相轉(zhuǎn)換。茂金屬快速捕捉硅雜烯結(jié)構(gòu),并通過配位插入聚合反應(yīng)生成最終產(chǎn)物。ⅱ)茂金屬與氯化鈉組成的質(zhì)密層包覆于金屬鈉表面,阻止了甲基氯硅烷與金屬鈉的直接接觸,保證了層內(nèi)原料的低濃度,通過原料的耗盡效應(yīng),有效地抑制了副反應(yīng)熱聚合的發(fā)生。(4)研究了對聚鋯碳硅烷的優(yōu)化與改性工藝。ⅰ)研究了二氯二甲基硅烷與二氯一甲基硅烷的催化共聚合反應(yīng)。結(jié)果表明,通過改變二氯二甲基硅烷與二氯一甲基硅烷的共聚合比例,產(chǎn)物經(jīng)熱解后所得陶瓷材料中自由碳含量從23%下降到6%,實現(xiàn)了對產(chǎn)物中碳元素含量的可控性調(diào)節(jié)。ⅱ)研究了 LiAlH4和NH3兩種脫氯劑對PZCS的脫氯效果。實驗證實,經(jīng)兩種脫氯劑處理后,PZCS中的Cl元素含量均有所下降,產(chǎn)品的穩(wěn)定性得到提高。其中,LiAlH4可以使PZCS中C1元素含量下降35%～50%,但其脫氯產(chǎn)物AlCl3會使PZCS分子鏈斷裂,聚合物分子量大幅下降,嚴重影響前驅(qū)體性能;NH3的脫氯能力相對較弱,但N元素的引入使最終制備的陶瓷材料中含有Si-C-N相陶瓷,有利于提高陶瓷材料性能。ⅲ)研究了 PZCS前期熱處理過程。經(jīng)過200～260℃前期熱處理,PZCS的陶瓷收率由58%提高到67%,平均分子量也從930升至2300,其主要原因在于熱處理過程發(fā)生了以Si-H鍵為核心的熱交聯(lián)反應(yīng)。(5)研究了 SiC_f/SiC-ZrC復(fù)合材料的制備工藝并對其結(jié)構(gòu)和性能進行分析表征。以化學(xué)氣相滲透技術(shù)(Chemical Vapor Infiltration,CVI)制備的SiC纖維預(yù)制體為增強體,PZCS的二甲苯濃溶液(濃度為55%)為浸漬液,通過前驅(qū)體浸漬裂解技術(shù)(Precursor Infiltration Pyrolysis,PIP)制備了 SiC_f/SiC-ZrC 復(fù)合材料。SEM、TEM 和XRD分析結(jié)果表明,SiC纖維表面被一層由熱解碳(Pyrolytic Carbon,PyC)和SiC所組成的界面層所覆蓋,界面層外部連接著連續(xù)致密的SiC-ZrC復(fù)相陶瓷基體,基體中ZrC晶粒尺寸極小(10～50 nm)并均勻分布于連續(xù)的SiC陶瓷相中。經(jīng)實測,SiC_f/SiC-ZrC復(fù)合材料具有較高的彎曲強度和斷裂韌性,分別達到了 495.2±71.6MPa和16.9±2.05MPa·m1/2,材料斷裂模式為典型的非脆性斷裂,分析其原因在于PyC-SiC界面層以適當?shù)膹姸冗B接著基體和纖維,在有載荷作用時,界面層既能很好地在基體與纖維之間傳遞載荷,也能通過界面斷裂吸能來有效分散過大的應(yīng)力,引導(dǎo)裂紋沿纖維軸向擴展,造成纖維拔出,從而達到吸能增韌的作用。通過考察SiC_f/SiC-ZrC復(fù)合材料在不同溫度下的氧化行為可知,在較高溫度下(1000℃以上),復(fù)合材料具有良好的抗氧化性能,這是由于SiC的氧化產(chǎn)物在高溫時能形成質(zhì)密的玻璃態(tài)氧化膜,有效阻止空氣向基體內(nèi)部擴散,從而達到保護材料的效果;在較低的溫度下(800℃以下),SiC的氧化產(chǎn)物無法形成質(zhì)密氧化膜,材料基體被空氣大量氧化,導(dǎo)致材料力學(xué)性能嚴重下降。
[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

【學(xué)位授予單位】：中國科學(xué)院大學(xué)(中國科學(xué)院過程工程研究所)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：O634;TQ174.1

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