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首页> 外文学位 >Preparation of silicon carbide fibers from polysilanes: (I) Role of polyvinylsilazane as a spinning aid for polycarbosilane. (II) Synthesis and characterization of polymethylsilane.
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Preparation of silicon carbide fibers from polysilanes: (I) Role of polyvinylsilazane as a spinning aid for polycarbosilane. (II) Synthesis and characterization of polymethylsilane.

机译：由聚硅烷制备碳化硅纤维：（I）聚乙烯基硅氮烷作为聚碳硅烷的纺丝助剂的作用。 （II）聚甲基硅烷的合成与表征。

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摘要

The effect of the addition of polyvinylsilazane (PSZ) on the characteristics (i.e., spinnability, rheological behavior, wetting behavior, evaporation behavior, etc.) of polycarbosilane (PCS) solutions was investigated. Spinnability of PCS solution was characterized by number of breaks occurring during spinning and amount of fibers formed after spinning. PCS and PCS+PSZ solutions were characterized by measuring surface tension, contact angles and rate of solvent evaporation. Effect of PSZ on mechanical properties of SiC fibers prepared from PCS and PCS+PSZ solutions was also investigated. Chemical changes taking place in PCS and PCS+PSZ fibers during heat treatment from 40-600{dollar}spcirc{dollar}C in nitrogen were studied by Fourier transform infrared spectroscopy (FTIR).; Addition of PSZ to PCS greatly improved spinnability of PCS solutions. Significant differences in wetting characteristics were observed for PCS solutions and PCS+PSZ solutions deposited on stainless steel and teflon substrates, as well as on PCS-coated and PCS+PSZ-coated stainless steel substrates. The rate of evaporation of solvent was higher for PCS solution than for PCS+PSZ solution at identical polymer concentrations. As-spun PCS and PCS+PSZ fibers developed similar tensile strengths and rupture strains. After heat treatment at 400{dollar}spcirc{dollar}C in nitrogen, PCS+PSZ fibers showed higher tensile strength and rupture strain compared to PCS fibers. Based on FTIR spectra of PCS and PCS+PSZ fibers during heat treatment from 40-600{dollar}spcirc{dollar}C, it is suggested that PSZ acts as a cross-linking aid for PCS. PCS+PSZ fibers developed higher tensile strengths than PCS fibers at all heat treatment temperatures between 200-1150{dollar}spcirc{dollar}C.; SiC fibers were fabricated from polymethylsilane (PMS) and PMS/PCS polymer blends. PMS polymers were synthesized by a Wurtz-coupling polymerization of methyldichlorosilane (MDCS) and methyltrichlorosilane (MTCS) in 70:30 wt% proportion with sodium in refluxing toluene. The addition of polar solvents (i.e., THF and 1,4-dioxane) to toluene improved yields and increased the molecular weight of PMS polymers. As-prepared PMS polymers with additives were heat-treated to increase molecular weight to permit fiber spinning. As-prepared PMS polymers were also fractionally-precipitated to isolate higher molecular weight fractions suitable for fiber spinning. The heat treatment approach was ineffective in obtaining molecular weight increases reproducibly. Fractionally- precipitated PMS polymers were useful in preparation of high strength pyrolyzed SiC fibers. These fibers, however, exhibited poor thermal stability at high temperatures. More investigations will be needed to address this problem.
机译：研究了添加聚乙烯基硅氮烷（PSZ）对聚碳硅烷（PCS）溶液的特性（即，可纺性，流变行为，润湿行为，蒸发行为等）的影响。 PCS溶液的可纺性由纺丝过程中发生的断裂数和纺丝后形成的纤维量表征。通过测量表面张力，接触角和溶剂蒸发速率来表征PCS和PCS + PSZ溶液。还研究了PSZ对PCS和PCS + PSZ溶液制备的SiC纤维力学性能的影响。通过傅里叶变换红外光谱（FTIR）研究了在氮气中从40-600 {spcirc {dollar} C进行热处理期间，PCS和PCS + PSZ纤维发生的化学变化。在PCS中添加PSZ极大地改善了PCS解决方案的可纺性。对于沉积在不锈钢和聚四氟乙烯基材上以及PCS涂层和PCS + PSZ涂层不锈钢基材上的PCS溶液和PCS + PSZ溶液，观察到润湿特性的显着差异。在相同的聚合物浓度下，PCS溶液的溶剂蒸发速率高于PCS + PSZ溶液。初纺PCS和PCS + PSZ纤维表现出相似的拉伸强度和断裂应变。与氮气相比，PCS + PSZ纤维在氮气中在400℃进行热处理后，显示出更高的拉伸强度和断裂应变。基于PCS和PCS + PSZ纤维在40-600 {C的热处理过程中的FTIR光谱，建议PSZ用作PCS的交联助剂。在200-1150℃至40℃之间的所有热处理温度下，PCS + PSZ纤维的拉伸强度都比PCS纤维高。 SiC纤维由聚甲基硅烷（PMS）和PMS / PCS聚合物共混物制成。通过与钠在回流甲苯中的重量比为70:30的甲基二氯硅烷（MDCS）和甲基三氯硅烷（MTCS）进行Wurtz偶联聚合，可以合成PMS聚合物。向甲苯中加入极性溶剂（即THF和1，4-二恶烷）可提高产率并增加PMS聚合物的分子量。将带有添加剂的预制备PMS聚合物进行热处理，以增加分子量，使纤维纺丝。制备好的PMS聚合物也要进行部分沉淀，以分离出适合纤维纺丝的更高分子量的馏分。热处理方法不能有效地获得分子量增加。部分沉淀的PMS聚合物可用于制备高强度热解SiC纤维。然而，这些纤维在高温下表现出差的热稳定性。为了解决这个问题，将需要进行更多的调查。

著录项

  • 作者

    Saleem, Mohamed.;

  • 作者单位

    University of Florida.;

  • 授予单位 University of Florida.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 1998
  • 页码 437 p.
  • 总页数 437
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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