SiC陶瓷纤维先驱体——聚铝碳硅烷的合成与表征

在高温常压下,以聚二甲基硅烷(Polydimethylsilane,PDMS)和乙酰丙酮铝(Al(AcAc)3)为原料,合成了碳化硅(SiC)陶瓷纤维先驱体———聚铝碳硅烷(Polyaluminocarbosilane,PACS)。采用红外光谱法和凝胶渗透色谱法对制备的PACS进行了结构和分子量表征;通过正交实验设计,研究了反应温度、裂解温度、反应时间和原料配比4种因素对PACS的Si-H键含量、支化度和数均分子量Mn的影响,并用极差分析法进行了主次因素分析,结果表明反应温度是上述三指标的主要影响因素。综合分析各指标对PACS后续纺丝性能和高温碳化过程的影响,确定制备PACS较优的实验条件为:反应温度390℃、裂解温度490℃、反应时间10h及原料Al(AcAc)3与PDMS配比4%(质量分数)。     

先驱体转化法制备耐高温Si-Al-C-O纤维

以聚硅碳硅烷(PSCS)与乙酰丙酮铝为原料,在常压高温条件下反应制备出聚铝碳硅烷(PACS),经过熔融纺丝、空气预氧化、烧成等工艺,制备出性能优异的耐高温Si-Al-C-O(KD-A)纤维.研究了PACS纤维组成,预氧化过程中的质量增加、Si-H反应程度、凝胶含量,探讨了氧对KD-A纤维性能的影响;通过元素分析、AES和SEM等一系列分析,研究了KD-A纤维的结构组成以及耐高温性能.研究表明,PACS纤维空气预氧化过程中,主要是Si-H键与氧发生反应生成Si-O-Si交联结构;KD-A纤维的组成SiC1.51O0.31Al0.013耐高温性能明显优于普通SiC纤维,在空气中1000℃下加热100h后,强度保留率达到60%左右.     

具有优异纺丝性的陶瓷先驱体含铝聚碳硅烷的合成及表征

选择适当分子量的低分子量聚碳硅烷与Al(AcAc)3在自制常压高温合成装置中合成了含铝碳化硅纤维的先驱体--聚铝碳硅烷(polyaluminocarbosilane,PACS).并对PACS进行了软化点测试、傅立叶红外光谱(FT-IR)分析、凝胶渗透色谱(GPC)测试、元素分析以及可纺性研究.由中等分子量聚碳硅烷为原料合成出的软化点为194.8～220.1,Si-H键含量为0.857,数均分子量为2353,分子量分布呈"双峰"分布的PACS,经熔融纺丝得到了直径为5μm、表面光滑、直径均匀的原丝,表现出了优异的纺丝性能.     

添加填料合成SiC（Al）纤维的先驱体聚铝碳硅烷

以聚硅碳硅烷和乙酰丙酮铝为原料,在反应装置的裂解柱中加入填料,在常压下合成了聚铝碳硅烷.结果表明:添加填料使合成聚铝碳硅烷的时间缩短46%,聚铝碳硅烷的从1008增大到2436,分子量的分布变窄,—Si—Si—键的含量低;在N_2气氛中,在400℃以下失重减少,在1200℃陶瓷的产率从65%提高到69%;加入填料可促进—Si—Si—链转化为—Si—C—Si—链,制备出的聚铝碳硅烷纤维在预氧化过程中氧的增重少,预氧化烧成后得到的Si—Al—C—O连续纤维强度为2.1 GPa,在Ar中1800℃烧结可得到致密的SiC(Al)纤维.纤维的结晶行为与不加填料时的类似.     

聚二甲基硅烷高温高压合成聚碳硅烷工艺研究

以聚二甲基硅烷(PDMS)为原料,在高压釜内高温高压反应制备了聚碳硅烷(PCS)先驱体,研究了合成条件对反应终压、Si-H键含量、产物产率、软化点、分子量及其分布及可纺性的影响.研究表明,随着反应温度的提高,反应时间的延长,反应终压逐渐增大,产物的分子量与软化点增高,但同时分子量的分散性增大使可纺性变差.当PDMS在高压釜内460℃下反应4～6h,或450℃下反应6～7h时,可以制得软化点约为200～220℃的PCS,其高分子部分含量约 5%～10 %(质量分数),Si-H键含量大于0.9,可纺性较好,适合于制备SiC纤维.     

聚碳硅烷纤维的不熔化与SiC纤维制备研究

以聚二甲基硅烷(PDMS)为原料,在高压釜内高温高压反应制备了聚碳硅烷(PCS)先驱体,经熔融纺丝制备了PCS纤维,研究了在190 C下不同不熔化时间对PCS纤维氧化增重、Si-H键反应程度、凝胶含量、氧含量及最终SiC纤维氧含量与性能的影响.研究表明,在不熔化过程中,PCS结构中的Si-H键与氧反应,在PCS分子间形成Si-O-Si交联结构.随着不熔化时间的延长,PCS纤维发生氧化增重、Si-H键反应程度提高、凝胶含量增加,SiC纤维中氧含量也逐渐增加.在不熔化保温3h,制备的SiC纤维强度可达2.52GPa.随着不熔化时间的进一步延长,SiC纤维氧含量增加,其强度逐渐降低.     

液态聚硅烷高压合成聚碳硅烷先驱体的组成与结构表征

以液态聚硅烷(LPS)为原料,首次在高温高压条件下制备了聚碳硅烷(PCS)先驱体,对其组成及结构进行了表征.研究表明,LPS高压合成的PCS是以Si-C为主链的聚合物.其重均分子量为2861,分子量分布系数为1.92,实验式为SiC1.89H481O0.05,主要含有由Si-CH3,Si-CH2-Si,Si-H组成的SiC4,SiC3H等结构单元,C H/Si-H值约为9.83,SiC3H/SiC4值约为0.48,是支化度较高的分子.高压合成的PCS比常压PCS有高的分子量及Si H键含量,比常压合成体现出了PCS先驱体的优异性.     

耐高温的SiC(Al)纤维

聚硅碳硅烷 (PSCS)与乙酰丙酮铝(Al(AcAc)₃)在一定条件反应制备了耐高温SiC(Al)纤维先驱体聚铝碳硅烷( PACS)。PACS通过熔融纺丝、预氧化处理、低温烧成、高温烧结等一系列工艺过程制备了耐高温SiC (Al)纤维 。SiC (Al) 纤维的化学组成为Si₁C_1.15O_0.026Al_0.013,主要结构是平均晶粒为95 nm的β-SiC,O和游离C含量均大大低于Nicalon纤维 ( O>10wt%,游离C>10wt%),同时含有微量的Al和少量的 α -SiC。纤维表层O含量和Si含量略高于纤维内部,表面光滑平坦,没有明显表面缺陷。 SiC (Al) 纤维的平均直径为13 μm,平均强度为2.3 GPa,1400℃氩气中处理1 h,强度保留率95%以上;1800℃氩气中处理1 h,强度保留率为71%。纤维的高温稳定性高于Nicalon纤维,低于Tyranno SA纤维。      

含铍碳化硅陶瓷先驱体聚铍碳硅烷的合成

以氢氧化铍、硫酸和乙酰丙酮为原料合成了乙酰丙酮铍(Be(acac)2).用乙酰丙酮铍和聚碳硅烷在加热的条件下反应一定时间,生成了树脂状的产物.反应中乙酰丙酮铍被消耗,生成产物熔点相对起始聚碳硅烷熔点升高.元素分析表明产物中含有铍元素,凝胶渗透色谱分析表明产物分子量相对起始聚碳硅烷向增大的方向发生变化.傅立叶红外光谱分析表明产物中主要存在如下结构:Si(CH3)2—CH2—,—Si(CH3)·(H)—CH2—.核磁共振1H-NMR分析表明反应物中Si—H键被消耗.根据分析结果推测了反应机理,Si—H键的消耗在产物的形成中起了重要作用.实验与理论分析表明先驱体产物是一种含铍聚碳硅烷,可以命名为聚铍碳硅烷(PBeCS).在1200℃的高温处理下产物作为先驱体可以转化为碳化硅陶瓷,元素分析表明碳化硅陶瓷中含有铍,是含铍碳化硅陶瓷.     

聚碳硅烷的合成与特性研究

研究了由聚二甲基硅烷热解制备聚碳硅烷的过程，探讨了合成条件笃产物特性的影响。提高反应温度、产物的分子量与熔点随之增高，但同时分子量的分散性增大使可纺性劣化。采用适当的制备方法已获得了具有所需特性的聚碳硅烷。     

Production mechanism of polyzirconocarbo- silane using zirconium(IV)acetylacetonate and its conversion of the polymer into inorganic materials

The reaction of polycarbosilane with zirconium(IV)acetylacetonate proceeded at 573 K in nitrogen atmosphere by the condensation reaction of the Si–H bonds in polycarbosilane and the ligands of zirconium(IV)acetylacetonate accompanied by the evolution of acetylacetone, and then the molecular weight increased by the cross-linking reaction with a formation of Si–Zr bond. The obtained polyzirconocarbosilane showed higher ceramic yield than the polycarbosilane. Zirconium contained in the pyrolysed polyzirconocarbosilane was furthermore found to have the effect of inhibiting crystalline grain growth of -type SiC up to high temperature, so Si–Zr–C–O fibre, which was obtained by the use of polyzirconocarbosilane as precursor, showed high tensile strength up to high temperature.     

Dry sol-gel condensation of p-X-C6H4SiH3 (X = H, CH3, CH3O, F, Cl) to organosilica p-X-C6H4SiO3 using nickelocene

The dry sol-gel reaction at toluene in ambient air atmosphere of p-X-C6H4SiH3 (X = H, CH3, CH3O, F, Cl) to p-C6H4SiO3 in high yield, catalyzed by nickelocene, is reported. The highest yield, molecular weight, polydispersity index, and TGA residue yield were obtained for p-Cl-C6H4SiH3. Some degree of unreacted Si-H bonds still remained in the gel because of steric reason. All the insoluble gels adopt an amorphous structure with a smooth surface. A plausible mechanism for the dry sol-gel reaction was suggested.     

The conversion process from polydimethylsilane to polycarbosilane in the presence of polyborodiphenylsiloxane

The pyrolytic reaction of polydimethylsilane to polycarbosilane in the presence of polyborodiphenylsiloxane have been studied by the use of organosilicon intermediates obtained during the initial pyrolytic stage of polydimethylsilane. In this reaction, the cleavage of the framework of Si-Si bonds occurred. Si-CH₂-Si and Si-H bonds were subsequently formed by the rearrangement reaction between radicals formed and Si-CH₃ bonds. The formation of Si-Si bonds by dehydrogenation between Si-H bonds then proceeded simultaneously or stepwise. It is assumed that polyborodiphenylsilane plays a role in accelerating the polycondensation reaction, that is, the propagation reaction occurred by dehydrogenation between the Si-H bonds, but takes no part in the radical rearrangement reaction from Si-Si bonds to Si-CH₂-Si bonds.     

氢氧化铝-聚丙烯酰胺杂化复合絮凝剂的合成与表征

用氧化一还原引发体系((NH42S2O8-NaHSO3)合成了氢氧化铝-聚丙烯酰胺杂化复合絮凝剂。电导和热失重研究的结果表明,杂化物聚丙烯酰胺链的端基(-SO4^2-)与带正电荷的氢氧化铝胶体粒子以离子键性质键合。实验考察了反应温度,引发剂用量,氢氧化铝粒径和用量等因素对杂化聚丙烯酰胺合成的影响,发现氢氧化铝的存在可使杂化聚合物分子量显著提高。透射电镜结果显示原位聚合过程能使团聚的氢氧化铝胶体微粒纳米化。     

聚碳硅烷制备SiC纤维的热化学交联研究

以异丙醇锆(ZIP)为交联剂、聚碳硅烷(PCS)为先驱体,在Ar气氛的保护下通过干法纺丝、热化学交联工艺使PCS从热塑性转变热固性结构.研究了该工艺对PCS纤维质量变化、Si-H反应程度、溶解性及氧含量等性能的影响.实验结果表明:在不熔化过程中,PCS结构中的Si-H键与ZIP反应,在PCS分子间形成Si-O-Zr交联结构,随着交联温度和保温时间的升高,Si-H反应程度和纤维失重率相应提高;在测试范围内最大Si-H反应程度为73.06%,失重率2.678%,氧含量低于2.0%.     

Synthesis of HMDS Radical Terminated Perhydropolysilazane

The chemical stability of perhydropolysilazane is improved by the introduction of HMDS (1, 1, 1, 3, 3, 3-hexamethyldisilazane) radical. The increase rate of the number average molecular weight of HMDS radical-introduced perhydropolysilazane was ten times slower than that of raw perhydropolysilazane. 1H-NMR analysis revealed that HMDS molecules mainly reacted with terminal Si-H3 groups of perhydropolysilazane.     

Dry sol-gel polycondensation of hydrosilanes to organosilicas catalyzed by colloidal nickel nanoparticles

The dry sol-gel polycondensation at toluene in ambient air atmosphere of p-X-C6H4SiH3 (X = H, CH3, CH3O, F, Cl) to silica p-X-C6H4SiO15 in high yield, catalyzed by colloidal nickel nanoparticles in-situ generated from nickelocene(II), nickel(II) acetate, and bis(1,5-cyclooctadiene)nickel(0), is described. Similar catalytic activities were observed for the catalysts. Similarly, the dry sol-gel polyco-condensation p-X-C6H4SiH3 (X = CH3, CH3O, F, Cl):C6H4SiH3 (9:1 mole ratio) at toluene in ambient air atmosphere of was performed to yield co-silicas (p-X-C6H4SiO1.5)9(p-X-C6H4SiO1.5)1 in high yield using nickelocene. The co-gels with higher molecular weights and TGA residue yield were obtained when compared to the homogels. The highest yield, molecular weight, polydispersity index, and TGA residue yield were obtained for p-Cl-C6H4SiH3. Some degree of unreacted Si-H bonds still remained in the gel matrix because of steric bulkiness. All the insoluble gels adopt an amorphous structure with a smooth surface. A plausible mechanism for the dry sol-gel reaction was suggested.     

Formation of Nickel Silicide Films from Nickel Acetylacetonate and Organosilicon Compounds

Nickel films were deposited from nickel acetylacetonate vapor on silicon, gallium arsenide, and germanium wafers and SiO₂/Si structures, and their composition and properties were studied. Annealing in dimethyldichlorosilane or hexamethyldisilazane vapor exerts a considerable effect on the composition and properties of Ni/Si structures. Films deposited from the gas phase containing nickel acetylacetonate and an organosilicon compound (OSC) were examined. As found by Auger electron spectroscopy with Ar⁺ion profiling of the surface, nickel silicide films can be obtained by Ni(AcAc)₂vapor deposition followed by annealing the resulting nickel film in OSC vapor and by OSC + Ni(AcAc)₂vapor deposition.