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。其工艺流程为熔融纺丝、固化、热处理。纤维为无定形连续细纤维，具有耐热性和高抗拉强度。该纤维有望作为陶瓷基复合材料的增强材料。氧化固化的纤维加工过程中含有大量的氧（大于10wt%），但近年来通过辐射交联固化的方法开发出了低氧型纤维（小于1wt%）。本研究利用中国科学研究资助项目(C)研制的高温炉，在1300 ~ 1800℃的惰性氧化气氛下，对前驱体纤维的力学性能、氧化机理和高温热解机理进行了研究。氧含量较低的前驱体陶瓷纤维在Ar气氛中加热时，热解速度较慢，高温热解过程中SiO和CO气体的析出受到抑制，与高氧纤维相比，明显保持了原有的高强度。在低于1500°C的氮气气氛下热处理的纤维具有更高的强度和杨氏模量，这是由于在纤维表面形成了氮化层。另一方面，纤维的氧化速率遵循收缩盘公式来控制扩散。氧化被认为是由气体通过硅膜微孔的扩散所控制的。在纤维表面形成的氧化膜抑制了高温热解，提供了相当的高温强度。当低氧型纤维包覆较薄的氧化层时，纤维的水解受到明显抑制。纤维芯部的晶体结构由无定形变为- sic微晶。涂层薄氧化层可显著提高材料的抗拉强度和杨氏模量。上述研究成果对前驱体陶瓷纤维和纤维增强陶瓷基复合材料的开发具有重要的指导意义。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