干法纺丝法制备低氧含量SiC纤维

Dry Spinning of SiC Fibers of Low Oxygen Contents

降低SiC纤维中的氧含量是提高其耐温性能的主要途径之一。本文以高分子量聚碳硅烷(PCS)为原料,通过干法纺丝、高温烧成等工艺,制得了氧含量为3.41%(质量分数)的SiC纤维。通过TG-DTA,IR等手段分析了干纺PCS纤维的无机化过程,并通过元素分析、XRD和SEM等手段,对纤维的结构、组成和耐高温性能进行了分析。结果表明:干纺PCS纤维烧成时,存在着二甲苯残留溶剂的挥发、自交联反应和无机化等复杂的过程,制备的SiC纤维在1000℃的空气中灼烧1 h后强度保持率约为91%。

Reducing the oxygen content in SiC fibers is important to enhance the high-temperature resistance of the fibers. For this aim, the low-molecular-weight polycarbosilane（LM-PCS） was recomposed into high-molecular-weight PCS（HM-PCS） which was then dissolved in xylene to form the spinning solutions of different concentration of the precursors. Subsequently, PCS fibers were dry spun from the solutions, and were pyrolyzed into the SiC fibers. The oxygen content in the fibers formed under a special heating procedure without air-curing was 3.41wt%. The tensile strength of the fibers retained 91% after heat treatment for 1 h in air at 1000 ℃. The removal of the residual solvent, the self cross-linking process and the ceramization process during the fiber formation were followed by IR, XRD, SEM, gel content and TG-DTA of green PCS fibers. Four stages of reactions were involved in the pyrolysis process of PCS fibers with the increase of temperature： （1） T 〈250 ℃： the volatilization of the moisture absorbed from atmosphere and the residual amounts of solvent, （2） T = 250～550 ℃： self cross-linking between molecules, （3） T=550～750 ℃： transformation of the polymer to ceramics and （4） T= 750～1250 ℃： transformation of the amorphous phase to crystallization. Self cross-linking was mainly the cross-linking between Si-H bonds and Si-CH3 bonds in the range of 250～550℃. During the self cross-linking, a small amount of oxygen from the atmosphere went into the cross-linking reaction.