聚碳硅烷的高温高压生成机理研究Ⅱ蒸馏产物的结构分析

以液态聚硅烷（LPS）在450℃反应得到的聚碳硅烷（PCS）粗产品为原料,经溶解、过滤、热处理后减压蒸馏,收集蒸馏馏分并进行表征,由此推出不同摩尔质量的PCS的典型结构,进而推测出LPS转化为PCS分子的机理是：随着温度的升高,LPS中的Si—Si键发生断裂、重排,转化为Si—C键,生成低分子碳硅烷;随着温度的继续升高,碳硅烷分子间发生脱氢、脱甲烷缩合反应,摩尔质量逐渐长大,生成PCS。     

聚碳硅烷的结构和形态

通过GPC-VPO-[η]测得了聚碳硅烷（PCS）的分子量、分子量分布和分子的形态与尺寸;通过IR-NMR-元素分析联合,定量表征了组成PCS的结构基团及支化程度。结果表明,常压高温裂解法合成的PCS是一种分子量较低,分子量分布较窄的低聚物,分予内以Si—C键为主的六元稠环组成的扁球体状分子,分子的支化程度很高,分子结构很紧密,等效球体半径（Re）在甲苯中约为1nm左右。     

聚碳硅烷应用的研究进展

聚碳硅烷(PCS)作为碳化硅(SiC)陶瓷的先驱体,具有陶瓷产率高、制备连续纤维可改性加工性优异以及自交联性良好等特点,被广泛用于航空航天等高科技领域.本文就聚碳硅烷的性能以及它在SiC陶瓷和其他方面的应用进行了阐述.     

二乙烯基苯/聚二甲基硅烷改良聚碳硅烷合成工艺的研究

在传统的合成体系中加入适量的二乙烯基苯,通过常压高温自由基聚合反应,获得了产率较高、可纺性优良的先驱体聚碳硅烷。采用正交实验设计研究了反应温度、升温速率、二乙烯基苯的质量分数、裂解温度和保温时间五个因素对聚碳硅烷产率的影响。方差分析表明,在反应温度为420℃、二乙烯基苯的质量分数为1·5%、升温速率为6℃/h、裂解温度为530℃、保温时间为5h条件下,可以得到粗产率为50%的黄色透明固态聚碳硅烷;各因素对聚碳硅烷产率影响的显著性依次为:升温速率>反应温度>二乙烯基苯的质量分数>保温时间>裂解温度。     

聚铝碳硅烷的制备及应用进展

介绍了碳化硅（SiC）陶瓷纤维、含铝SiC陶瓷纤维的特点,综述了用聚碳硅烷、聚硅碳硅烷、聚二甲基硅烷与乙酰丙酮铝反应制备聚铝碳硅烷先驱体的合成方法,聚铝碳硅烷的化学结构及在制备耐超高温陶瓷纤维和发光陶瓷薄膜中的应用,评述了各种制备工艺的优缺点,提出了当前工作中需要解决的问题,并展望了今后的发展趋势。     

聚钽碳硅烷陶瓷先驱体的制备与表征

为了提高SiC陶瓷纤维的综合性能,利用聚二甲基硅烷热解制得的产物液态聚硅烷(LPS)与五氯化钽(TaCl5)反应,制得含钽SiC陶瓷纤维的先驱体聚钽碳硅烷(PTCS).研究表明,反应过程中存在LPS的裂解重排反应,Si-H键在反应中显示出很高的活性,PTCS摩尔质量的增加是LPS形成的Si-H键与TaCl5发生交联反应的结果,用LPS与TaCl5为原料不但能够使钽元素成功地引入到先驱体中并分布均匀,而且由于其成本比其它原料相对低廉,便于大批量合成.     

聚碳硅烷—沥青共聚物的性能及应用

提要将聚二甲基硅炕与沥青共热解,合成了不同沥青含量的聚碳硅烷——沥青共聚物,并对其结构和性能进行了研究。这种共聚物经热处理可转变成碳——碳化硅陶瓷。本文用该共聚物为先躯体制得了耐热氧化性优越的碳——碳化硅复合纤维。     

聚碳硅烷化学转化法制备C／Sic复合材料

本文对聚碳硅烷化学转化法制备碳纤维增强碳化硅复合材料的工艺进行了研究,确定了较佳的成型、热处理等工艺条件。     

聚二甲基硅烷合成聚碳硅烷的研究

以聚二甲基硅烷为原料,采用正交设计的方法研究了常压高温裂解重排法中反应温度,裂解温度,保温时间对聚碳硅烷结构的影响,结果发现,该合成方法的最佳工艺条件为：反应温度470－475℃,裂解温度560℃,保温时间6h,3个因素对聚碳硅烷的显著性影响顺序为：反应温度＞保温时间＞裂解温度,从聚二甲基硅烷出发合成的先驱体聚碳硅烷的支化度较低,可纺性好。     

聚碳硅烷粘结法低温制备碳化硅多孔陶瓷

分别以平均粒径为10μm和20μm的两种规格碳化硅(SiC)粉末为原料、聚碳硅烷(PCS)为粘结剂,通过包混、过筛、模压成型、1000℃热解等工序制备了SiC多孔陶瓷,研究了PCS含量对SiC多孔陶瓷微观形貌、线收缩率、孔隙率与抗弯强度的影响,并对两种规格粉末制备的SiC多孔陶瓷性能进行了对比。结果表明:随着PCS含量的增加,两种规格粉末制备的SiC多孔陶瓷微观形貌都逐渐变得致密,当PCS含量为13%时,两种规格粉末制备的多孔陶瓷都出现了微观裂纹。随着PCS含量的增加,两种规格粉末制备的SiC多孔陶瓷孔隙率都逐渐降低,线收缩率都逐渐增大,抗弯强度先增大后降低,在PCS含量为10%时,平均粒径为10μm与20μm的SiC粉末制备的多孔陶瓷抗弯强度取得最大值,分别为31.6MPa与29.0MPa。     

Structure and properties of polycarbosilane synthesized from polydimethylsilane under high pressure

The polycarbosilane (PCS), which is the precursor of SiC fiber, was synthesized under high pressure by thermal decomposition of polydimethylsilane. The composition, structure, and properties of the PCS were characterized by the measurements of softening point, elemental analysis, IR, GPC, NMR, TG‐DTG‐DTA, XRD, and oxidative reaction activity, respectively. Structure model of the PCS was therefore inferred. The results showed that the PCS was the polymer with a Si? C backbone with M_n about 1587. IR and NMR showed the presence of SiC₄ and SiC₃H structure units containing Si? CH₃, Si? CH₂? Si, and Si? H groups. The ratio between H in C? H bond and H in Si? H bond was about 8.84 with SiC₃H/SiC₄ and about 0.51 from ¹H NMR and ²⁹Si NMR, respectively. Elemental analysis gave an empirical formula of SiC_1.87H_7.13O_0.03. TG analysis showed that the ceramic yield of the PCS at 1200°C in a N₂ flow was about 78.9%. β‐SiC microcrystal could be obtained when PCS was pyrolyzed at 1250°C with the crystal size about 37.5 Å. Compared with the PCS with similar softening point synthesized under normal pressure, the PCS synthesized under high pressure had approximate elemental composition, higher Si? H bond content and reaction activity, higher molecular weight, and higher ceramic yield, but lower ratio of SiC₃H and SiC₄. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1188–1194, 2006     

液态超支化聚碳硅烷的合成及应用进展

液态超支化聚碳硅烷（LHBPCS）作为一种SiC陶瓷前体,因具有流动性好、可自交联、陶瓷产率高及热解产物接近SiC化学计量比等优点而备受关注。本文在介绍液态超支化聚碳硅烷特点的基础上,重点综述了它的合成方法,包括开环聚合法、Grignard偶合聚合法、Wurtz偶合聚合法、硅氢加成法等,并总结了液态超支化聚碳硅烷在碳化硅基复合材料、碳化硅纤维、碳化硅薄膜等领域的应用,最后指出液态超支化聚碳硅烷今后的研究重点是规模化合成及改性研究等。     

干法纺丝制备聚碳硅烷纤维中残留溶剂含量的影响因素

研究了聚碳硅烷纤维纺丝线上残留溶剂含量的影响因素.结果表明:在纺丝线上距离喷丝孔约0.3 m之内,溶剂的挥发主要由对流和闪蒸过程控制,残留溶剂含量呈指数速率减小,且溶剂挥发量约为纺丝线上溶剂挥发总质量的80%～90%;纺丝原液浓度的增大、纺丝甬道温度的升高和纺程的增加有利于残留溶剂含量的降低,而纤维直径的增大则会提高残留溶剂含量.较佳的纺丝条件为:纺丝原液中聚碳硅烷的质量分数为65%～68%,纺程0.3～1.5 m,纺丝甬道温度为室温.     

高温高压下的绝缘胶接体系研究

叙述了在温度155~175℃,14 MPa压力下使用的绝缘胶接体系研究情况,实物电子线圈8中线与线间绝缘电阻值、线与屏蔽层间绝缘电阻值都大于10Ω,该体系已应用在石油测井仪。     

Combustion of silicon powders containing organic additives in nitrogen gas under pressure: 2. Composition of combustion products

Combustion of silicon powders containing organic dopants in nitrogen gas under pressure was found to yield a mixture of α-Si₃N₄, β-Si₃N₄, SiC, and Si₂N₂O. Relative amount of these compounds in combustion product was found to depend on the pressure of nitrogen gas, type and concentration of dopants, combustion geometry, and cooling rate. The formation of α-Si₃N₄ was found to occur in the presence of oxygen-containing dopants. The type of dopant was also found to affect the morphology of product particles.      

SiC(Nb)陶瓷纤维先驱体聚铌碳硅烷的合成与表征

为了提高SiC陶瓷纤维的综合性能,利用聚二甲基硅烷热解制得的产物液态聚硅烷(liquid polysilane,LPS)与五氯化铌(NbCl5)反应,制各了含铌SiC陶瓷纤维的先驱体聚铌碳硅烷(polyniobiumcarbosilane,PNCS).研究表明:反应过程中存在LPS裂解重排反应,Si-H键在反应中显示出很高的活性,FNCS分子量的增加是LPS形成的Si-H键与NbCl5发生交联反应的结果,用LPS与NbCl5为原料不但能使铌元素成功地引入到先驱体中并且分布均匀,而且由于其成本比其他原料相对低廉便于大批量合成.利用PNCS制备的Si-Nb-C-O陶瓷纤维平均强度为1.8GPa,平均直径为12 μm,耐高温性能优异.     

Suppression of Active Oxidation of Polycarbosilane-Derived Silicon Carbide Fibers by Preoxidation at High Oxygen Pressure

Three types of polycarbosilane-derived SiC fibers (Nicalon, Hi-Nicalon, and Hi-Nicalon S) with different SiO₂ film thicknesses ( b ) were subjected to exposure tests at 1773 K in an argon-oxygen gas mixture with an oxygen partial pressure of 1 Pa. The suppression effect of a SiO₂ coating on active oxidation was examined through TG, XRD analysis, SEM observation, and tensile tests. All the as-received fibers were oxidized in the active-oxidation regime. The mass gain and the SiO₂ film development showed a suppression of active oxidation at b values of ≧0.070 μm for Nicalon, ≧0.013 μm for Hi-Nicalon, and ≧0.010 μm for Hi-Nicalon S fibers. Considerable strength was retained in the SiO₂-coated fibers. For Hi-Nicalon fibers, the retained strength was 71%–90% of the strength in the as-received state (2.14–2.69 GPa).     

Full densification of zirconium carbide ceramics sintered under high pressure at low temperature

Zirconium carbide (ZrC) ceramic is one of the most important and promising materials with a high melting point. However, its low diffusion coefficient affects its densification behavior, which dramatically limits its engineering application. For polycrystal ceramic materials, sintering by thermal diffusion is the most widely used method for consolidation. But in view of the difficult densification behavior of ZrC, it is necessary to develop new sintering methods together with another driving force. In the study, we reported an ultra-high-pressure sintering strategy to fully densify ZrC ceramic under 1.7 GPa at 1600℃. The sintered sample exhibited high density, fine grain size, excellent mechanical properties, and a large number of crystal defects, including dislocation networks and walls, which were similar to those in deformed metals. Its hardness increased to 2057.44 HV0.1 because of its unique microstructure.     

Measurements and correlations for gas liquid surface tension at high pressure and high temperature

Surface tension of water/nitrogen and water–phenol/nitrogen systems was successfully measured by the hanging drop method in a wide domain of temperature (from 100 to 300°C) and pressure (from 4 to 30MPa), conditions little explored in litterature. Results show that surface tension of water–phenol mixtures decreases as phenol mass fraction increases. This decrease is observed under saturated and unsaturated conditions and is more pronounced at low temperatures and does not seem to depend on pressure. The effect of saturation on surface tension in the water/nitrogen system has been correlated with water vapor pressure by using experimental points with a great accuracy. For the water–phenol/nitrogen system, experimental data obtained with different mass fraction of phenol were correlated using Macleod‐Sugden equation for mixtures. © 2018 American Institute of Chemical Engineers © 2018 American Institute of Chemical Engineers AIChE J, 64: 4110–4117, 2018