【作者】 李文华；

【导师】 王军；

【作者基本信息】 国防科学技术大学 ， 材料科学与工程， 2012， 博士

【摘要】 连续透波纤维增强陶瓷基复合材料已成为耐高温透波材料的重点研究方向。硅硼氮(SiBN)纤维具有强度高、耐高温、抗氧化和介电性能好等优点，是陶瓷基透波复合材料理想的增强体。本文开展了先驱体转化法制备连续SiBN陶瓷纤维的基础研究。针对聚硼硅氮烷(PBSZ)合成过程易交联、软化点低及组成难以调节等不足，重点研究BCl3、HMeSiCl2和HMDZ合成PBSZ的反应机理，合成出具有不同组成和高软化点的PBSZ，研究不同组成PBSZ的理化性能，由不同组成的PBSZ出发制备了SiBN陶瓷纤维，找到了适合制备连续SiBN陶瓷纤维的PBSZ，并探索了连续SiBN陶瓷纤维的制备工艺。在采用GC-MS对BCl3和HMDZ的反应过程及HMeSiCl2和HMDZ的反应过程进行分析的基础上，对BCl3、HMeSiCl2和HMDZ合成PBSZ的反应过程进行研究，发现BCl3、HMeSiCl2和HMDZ合成PBSZ的反应过程分为两个阶段：反应温度在室温到150℃为第一阶段，BCl3和HMeSiCl2分别与HMDZ发生胺解反应，反应产物主要是BCl3和HMDZ及HMeSiCl2和HMDZ150℃反应产物的混合物，以及少量含BNSi结构的产物。反应温度在150℃到240℃为第二阶段，BCl3的胺解产物通过脱除HMDZ或Me3SiNH2进行缩合，使得分子链长大或生成BN六元环结构，HMeSiCl2的胺解产物通过脱除HMDZ或Me3SiNH2进行缩合，使得链增长或生成SiN六元环结构，BNSi链亦通过脱除HMDZ或Me3SiNH2进行缩合，使得链增长或缩合成BNSi杂环结构，形成的BN六元环、SiN六元环及BNSi杂环通过脱除HMDZ或Me3SiNH2进一步聚合。BCl3、HMeSiCl2和HMDZ合成PBSZ的反应为缩聚合反应。基于缩聚合反应凝胶点的理论，建立BCl3、HMeSiCl2和HMDZ的摩尔比与其凝胶点的关系，找到BCl3、HMeSiCl2和HMDZ反应交联的原因，提出合成高软化点PBSZ的方法，即控制BCl3、HMeSiCl2和HMDZ平均官能度小于2，并适度提高反应体系的温度。研究表明，在摩尔比为1:0:6、1:0.5:6、1:1:6和0.5:2:6，提高反应温度至300℃，保温10h的条件下，BCl3、HMeSiCl2和HMDZ反应得到PBSZ的软化点均在100℃以上的，反应产物不交联。采用EA、FT-IR、1H-NMR、11B-NMR和29Si-NMR对PBSZ-1:0:6、PBSZ-1:0.5:6、PBSZ-1:1:6及PBSZ-0.5:2:6的组成结构进行分析，结果表明：随着MeHSiCl2摩尔比的增加，PBSZ的B元素含量逐渐降低，N元素含量逐渐升高，Si元素含量也逐渐升高；当MeHSiCl2摩尔比小于1时，随着MeHSiCl2摩尔比的减少，PBSZ结构中BN环状结构逐渐增多，SiN环状结构和BNSi结构逐渐减少；当MeHSiCl2摩尔比大于1时，PBSZ以SiN环状结构为主，BN环状结构和BNSi结构较少。对不同组成PBSZ的流变性能、水解稳定性、热分解及热解产物的高温结晶性进行研究，发现：(1) PBSZ-1:0.5:6和PBSZ-1:1:6的可纺性优于PBSZ-1:0:6，PBSZ-0.5:2:6的可纺性最差。对PBSZ-1:0:6、 PBSZ-1:0.5:6、 PBSZ-1:1:6及PBSZ-0.5:2:6的熔融纺丝工艺进行优化，制备了四种PBSZ纤维。(2)四种PBSZ纤维在室温和相对湿度为75%条件下，放置18h后水解率分别为0.6%、1.9%、3.0%及5.2%，PBSZ纤维表现出较好的抗水解特性。PBSZ中Si-NH-Si结构较BN环状结构易水解，随着PBSZ中Si-NH-Si结构含量的增加，在室温和相对湿度为75%条件下，PBSZ水解速率逐渐增大。(3) PBSZ-1:0:6、PBSZ-1:0.5:6及PBSZ-1:1:6在1000℃氮气气氛下的质量保留率分别为35wt%、47wt%及60wt%，Si-NH-Si的引入提高了PBSZ在1000℃氮气气氛下的质量保留率。(4) PBSZ-1:0:6在1400℃氩气气氛下的热解产物开始形成h-BN相，PBSZ-0.5:2:6在1600℃氩气气氛下的热解产物开始形成SiC和Si3N4微晶，而PBSZ-1:0.5:6和PBSZ-1:1:6在1600℃氩气气氛下的热解产物仍不结晶。PBSZ-1:0:6、PBSZ-1:0.5:6和PBSZ-1:1:6纤维以MeHSiCl2为不熔化气氛，经不熔化工艺优化，在典型脱碳热解条件下制备了三种不同组成的定长SiBN陶瓷纤维。由PBSZ-1:0:6纤维制备的定长SiBN陶瓷纤维是中空纤维，其组成为Si0.3BN1.4，强度为1.0GPa，模量为103GPa；PBSZ-1:0.5:6纤维制备的定长SiBN陶瓷纤维是实心纤维，其组成为Si0.55BN1.8，强度为1.2GPa，模量为125GPa；PBSZ-1:1:6纤维制备的定长SiBN陶瓷纤维也是实心纤维，其组成为Si0.95BN2.2，强度为1.5GPa，模量为150GPa。随着PBSZ原纤维中Si-N-Si结构含量的增加，PBSZ-1:0:6、PBSZ-1:0.5:6和PBSZ-1:1:6纤维制备的定长SiBN陶瓷纤维从中空到密实，纤维强度逐渐提高，表明PBSZ中Si-N-Si含量的增加对提高SiBN陶瓷纤维的性能有促进作用。采用Materials Studio模拟计算PBSZ-1:1:6的Hildebrand溶解度参数为9.0-9.8(cal0.5/cm1.5)。与75种常用溶剂比较发现，PBSZ-1:1:6的不良溶剂主要是极性大的水、醇、腈及酰胺等。采用HSPiP软件计算PBSZ-1:1:6的Hansen溶解度参数为δD=19.09MPa1/2、δP=19.47MPa1/2、δH=0.69MPa1/2，溶解度球半径R为19.9MPa1/2。与1258种溶剂相比较发现，沸点在25-100℃之间的PBSZ-1:1:6的不良溶剂主要包括醇、氟代烷烃、水及乙腈等，这与基于Hildebrand溶度公式筛选的不良溶剂类别基本一致。经PBSZ-1:1:6纤维与乙腈的溶解性实验和集束实验，验证了乙腈能够实现PBSZ-1:1:6纤维的集束。以乙腈为集束剂，在纺丝温度为210℃、纺丝压力为0.4MPa、收丝筒转速为300m min-1的工艺条件下，实现了PBSZ-1:1:6的多孔连续熔融纺丝，纤维的连续长度大于1000m。以MeHSiCl2为不熔化反应气氛，不熔化温度为95℃，保温时间为4h的条件下进行不熔化，在NH3浓度为50%，10℃/min升至1000℃，并在600℃保温2h的热解条件下，初步制备了连续SiBN陶瓷纤维，其组成为Si0.91BN2.1，纤维直径约为10μm，强度为0.6GPa。更多还原

【Abstract】 Silicon boronitride (SiBN) ceramic fibers, with high mechanical strength, excellenthigh-temperature resistance, good stability against oxidation, and good dielectricproperties, are promising candidates as reinforcements in ceramic matrix composites forhigh temperature microwave-transparent applications. Hence, present work focuses onthe basic research of continuous SiBN ceramic fibers via the polymer-derived ceramics(PDCs) method.The synthesis of polyborosilazane (PBSZ) usually gives preceramic polymers withlow softening point and single composition, which are not suitable to be used asprecursors for continuous SiBN ceramic fibers as they can readily get crosslinked.Therefore, the mechanism of the synthesis of PBSZ using BCl3, HMeSiCl2and HMDZwas investigated, and polyborosilazanes of high softening point and variouscompositions were prepared. The properties of PBSZ with various compositions werestudied so as to synthesize the most suitable precursor for continuous SiBN ceramicfibers. The preparation process of continuous SiBN ceramic fibers was also studied.The reaction of BCl3, HMeSiCl2and HMDZ was investigated by GC-MS based onthe analysis of the reactions between BCl3and HMDZ, HMeSiCl2and HMDZ,respectively. The results suggested that the process of the condensation polymerizationof BCl3, HMeSiCl2and HMDZ could be divided into two stages. At the first stage(RT-150℃), the main reaction was the condensation reaction of Si-Cl and B-Cl withHMDZ, and the products were composed of the products of reaction between BCl3andHMDZ at150℃, the products of reaction of HMeSiCl2and HMDZ at150℃,and someBNSi structures. At the second stage (150-240℃), the mixture formed at the first stagewas condensed to form ring structures with loss of HMDZ or SiMe3Cl.Based on the understanding of the reaction of BCl3, HMeSiCl2and HMDZ, therelationship between the molar ratio of BCl3, HMeSiCl2and HMDZ and the gelationpoint was conformed. The reason why the crosslinking of PBSZ happened was studied.The softening point of PBSZ could be enhanced by increasing the reaction temperatureon the condition that the suitable molar ratio of BCl3, HMeSiCl2and HMDZ was used tomake the average function number of the reactants less than two. The results showedthat the softening point of PBSZ was enhanced to above100℃by increasing thereaction temperature to300℃with the molar ratio of BCl3, HMeSiCl2and HMDZ as1:0:6,1:0.5:6,1:1:6and0.5:2:6, respectively.The composites and structures of preceramic polymer PBSZ-1:0:6, PBSZ-1:0.5:6,PBSZ-1:1:6and PBSZ-0.5:2:6were studied by EA, FT-IR,1H-NMR,11B-NMR and29Si-NMR. The results showed that with the increase of the HMeSiCl2molar ratio, thecontent of B decreased and the contents of Si and N increased. When the HMeSiCl2 molar ratio was less than1, with the decrease of the HMeSiCl2molar ratio, the BN ringswere the main structure in PBSZ and the content of SiN and BNSi structures decreased.While the HMeSiCl2molar ratio was more than1, the SiN rings were the main structureand the content of BN and BNSi structures decreased.The properties of PBSZ precursors with various compositions were studied.(1)The melt-spinning ability of PBSZ-1:0.5:6and PBSZ-1:1:6was better than PBSZ-1:0:6.The melt-spinning ability of PBSZ-0.5:2:6was the worst among the four kinds of PBSZprecursors. Four kinds of PBSZ fibers were fabricated by melt-spinning of PBSZ-1:0:6,PBSZ-1:0.5:6, PBSZ-1:1:6and PBSZ-0.5:2:6.(2) Precursor fibers of PBSZ-1:0:6,PBSZ-1:0.5:6, PBSZ-1:1:6and PBSZ-0.5:2:6hydrolyzed0.6%,1.9%,3.0%and5.2%respectively after being exposed for18h under ambient conditions with the relativehumidity of75%. The hydrolytic experiments of PBSZ-1:0:6, PBSZ-1:0.5:6,PBSZ-1:1:6and PBSZ-0.5:2:6fibers indicated that the PBSZ polymers only with BNrings had better hydrolytic stability than that of preceramic polymers with the mixtureof BN and Si-N-Si groups as the Si-N-Si groups hydrolyzed faster than the BN groupsin polyborosilazane.(3) The ceramic yield of PBSZ-1:0:6, PBSZ-1:0.5:6andPBSZ-1:1:6in N2atmospheres under1000℃is35wt%,47wt%and60wt%,respectively. The ceramic yield of PBSZ was enhanced by increasing Si-N-Si structuresin the PBSZ polymers.(4) The pyrolysis of PBSZ-1:0:6started to form BN crystals at1400℃and that of PBSZ-0.5:2:6started to produce SiC/Si3N4crystals at1600℃,while there had no crystals appeared during the pyrolysis of PBSZ-1:0.5:6andPBSZ-1:1:6at1600℃because of the BNSi structures in the PBSZ.The tensile strength and Young’s modulus of Si0.3BN1.4hollow fiber derived fromPBSZ-1:0:6is1.0GPa and103GPa, respectively. The tensile strength and Young’smodulus of Si0.55BN1.8dense fiber derived from PBSZ-1:0.5:6is1.2GPa and125GPa,respectively. The tensile strength and Young’s modulus of Si0.95BN2.2dense fiberderived from PBSZ-1:1:6is1.5GPa and150GPa, respectively. The results indicated thatthe increase of Si-N-Si structures in the PBSZ was beneficial to enhance the mechanicalstrength of the obtained SiBN ceramic fibers.The Hildebrand solubility parameter of PBSZ-1:1:6was9.0-9.8cal0.5/cm1.5, whichwas calculated by Materials Studio. Based on the Hildebrand solubility parameter, theselected bad solvents for PBSZ-1:1:6were polar solvents such as water, alcohols,imides and cyanides. The Hansen solubility parameter (HSP) of PBSZ-1:1:6wasδD=19.09MPa1/2, δP=19.47MPa1/2, δH=0.69MPa1/2and the radius of HSP sphere is19.9MPa1/2. Based on the Hansen solubility parameter, the selected bad solvents with boilingpoint between25℃and100℃for PBSZ-1:1:6were water, alcohols, alkyl fluoridesand cyanides. Especially, the acetonitrile didn’t dissolve the PBSZ-1:1:6fibers, whichcould be used as sizing finishes for PBSZ-1:1:6fibers.The multifilamental continuous melt-spinning of PBSZ-1:1:6was realized at210 ℃with pressure of0.4MPa, and the continuous PBSZ-1:1:6fibers were sized byacetonitrile and stretched by the spool at a rotation rate of ca.400m min-1to produceflexible endless fibres with lengh of>1000m. The continuous PBSZ-1:1:6fibers werecured at95℃for4h under HMeSiCl2. The continuous cured PBSZ-1:1:6fibers werepyrolyzed to1000℃(10℃min-1, at600℃holding for2h) under NH3atmospheres.Continuous SiBN ceramic fibers with a near-stoichiometric composition of Si0.91BN2.1were obtained with ca.0.6GPa in tensile strength and ca.10μm in diameter.更多还原