CHARACTERISTICS OF PRECURSOR CERAMIC FIBER UNDER SEVERE ENVIRONMENTS

以无机聚合物为前驱体制备了前驱体陶瓷纤维。其工艺是先驱体聚合物熔融纺丝、固化和热处理。纤维为无定形、连续的细小纤维，具有耐热性和较高的拉伸强度。该纤维有望作为陶瓷基复合材料的增强材料。纤维中含有大量的氧(10wt%以上)，这些氧来自于氧化固化过程中的纤维，但最近开发的低氧型纤维(1wt%以下)是通过辐射交联法固化的。本研究利用GRANT-IN-AID研制的高温炉，在1300ﾟ-1800ﾟC的惰性和氧化气氛的恶劣环境下，研究了原丝纤维的力学性能、氧化机理和高温热解机理(C)。氧含量较低的前驱体陶瓷纤维在h…下的热解速度较慢在Ar气氛下，纤维中SiO和CO气体的析出受到抑制，与高含氧纤维相比，显著保持了纤维原有的高强度。在低于1 500ﾟC的氮气气氛中热处理的纤维，由于在纤维表面形成了氮化物层，因此具有更高的强度和杨氏模数。另一方面，纤维的氧化速率遵循收缩圆盘公式以控制扩散。氧化被认为是由气体通过二氧化硅薄膜中的微孔扩散控制的。纤维表面形成的氧化膜抑制了高温热解，并提供了相当高的高温强度。当低氧纤维表面覆盖较薄的氧化物层时，纤维的热分解受到明显的抑制。纤维芯部的结晶结构由非晶态转变为β-碳化硅微晶。通过在陶瓷纤维表面涂覆一层氧化膜，可以显著提高纤维的抗拉强度和杨氏弹性模量，为陶瓷纤维及其增强陶瓷基复合材料的发展提供了有益的参考。较少

Precursor ceramic fibers have been produced from inorganic polymers as the precursor. Its process is melt-spinning of precursor polymer, curing and heat treatment. The fibers are amorphous and continuous fine fibers, and they have heat resistance and high tensile strength. The fibers have been expected as the reinforcement of ceramic matrix composites. The fibers contain large quantities of oxygen (more than 10wt%) coming from fiber-precessing of the oxidation-curing, but low-oxygen-type fibers (less than 1wt%) have been recently developed by curing with radiation crosslink. In this research work, mechanical properties, oxidation mechanism and high-temperature pyrolytic mechanism of the precursor fibers have been studied under the severe invironments of inert and oxidation atmosphere at temperatures of 1300ﾟ-1800ﾟC,using high-temperature furnace prepared by the GRANT-IN-AID FOR SCIENTIFIC RESEARCH (C).Precursor ceramic fibers with lower oxygen contents were pyrolyzed more slowly when h … More eated in an Ar atmosphere, and SiO and CO gases evolution of the fibers due to the high temperature pyrolysis were suppressed, significantly retaining their original high strength in the comparison with that of high oxygen-contained fibers. The fibers heat-treated in a N_2 atmosphere at temperatures below 1500ﾟC have higher strength and Young's modulus than that treated in an Ar, because of a formation of the nitride layr on fiber surface.On the other hand, the oxidation rate of the fibers followed the contracting-disc formula for diffusion control. The oxidation is considered to be controlled by the gaseous diffusion through the micropores in the silica film. The oxide film formed on the fiber surface suppressed high-temperature pyrolysis and provide considerable high-temperature strength. When the low-oxygen-types fibers were coated with more thin oxide layr in thickness, the hyrolysis of the fibers was suppressed significantly. The crystl structure in the core of the fibers changed from amorphous to beta-SiC microcrystallines. The tensile strength and Young's modulus were fairly improved by coating thin oxide layrs.These above research results are considered to be very effective for the development of precursor ceramic fibers and the the fibers reinforced ceramic matrix composites. Less