高温宽频吸波SiC纤维的设计/制备与结构/性能演变

The radar stealth technique of high-temperature components such as the exhaust nozzle has become one of the bottleneck problems in developing advanced aerospace vehicles. Radar-stealth SiC fibers reinforced ceramic matrix composites have been applied to advanced fighters by the USA and Europe. Import of these techniques to China is strictly blocked. Electromagnetic modification of SiC fibers is the foundation of making radar-stealth composites. Studies show that dielectric and magnetic losses can be effectively improved with magnetic metal elements added into SiC fibers, making it possible to prepare SiC fibers with high temperature resistance, oxidation resistance and broadband absorption. Preliminary studies showed that it was effective to modify the electromagnetic property with Cobalt of high Curie temperature. However, traditional chemical and physical doping method only resulted in low concentration of Cobalt and weak electromagnetic properties. Our group has developed a new technique of preparing nanosized Cobalt colloid. Highly dispersed nanosized Cobalt can be introduced into the precursor polycarbosilane (PCS), which show bad spinnability. In this project, we'll employ dry spinning technology, self crosslinking and pyrolysis to processed high-temperature broadband-absorbing SiC fibers..This application plans to systematically study the rule of dry spinning performance of preceramic polymer solution, the influence of the amount of Cobalt introduced on the microstructure, mechanical property and electromagnetic properties of SiC fibers, evolvement rules of phase composition, microstructure, mechanical property and electromagnetic property of SiC fibers under long-time high temperature and oxidation circumstances and provide theoretical and technical bases for Cobalt-containing SiC fibers as reinforcement in high temperature wave-absorbing ceramic matrix composites.

尾喷管等高温部件的雷达隐身问题是我国先进航空航天器发展的技术瓶颈之一。美欧等国已将雷达隐身碳化硅纤维增强陶瓷基复合材料用于先进战机，对中国严密技术封锁。对SiC纤维进行电磁性能改性是该复合材料具有雷达隐身性能的基础。研究表明，通过对SiC纤维掺杂磁性金属元素可有效提高其介电/磁损耗，有望制备出耐高温、抗氧化、宽频吸波的SiC纤维。传统化学和物理掺杂法引入磁性金属量低，电磁性能弱，我团队发展了一种新型金属溶胶制备技术，可在纤维先驱体聚碳硅烷中引入大量高度分散的金属纳米粒子，但熔融纺丝性能差。本项目拟使用干法纺丝、原丝自交联和高温热解技术，制备耐高温宽频吸波SiC纤维。拟系统研究先驱体溶液的干法纺丝性能和规律；金属加入量和高温、长时、氧化环境对含磁性金属SiC纤维微结构与力学/电磁性能的影响规律；为含磁性金属SiC纤维作为吸波型陶瓷基复合材料增强体提供理论/技术依据。

本基金目标是制备耐高温、抗氧化和耐化学腐蚀的吸波碳化硅纤维。该纤维可以作为结构功能一体化的复合材料的增强纤维，对解决尾喷管等高温部件的雷达隐身问题是一次积极的探索。利用一种新型的溶胶粒子，可在纤维聚碳硅烷中引入大量高度分散的钴纳米粒子。使用干法纺丝、交联和热解等技术，制备不同钴含量的碳化硅纤维。系统研究了制备过程中关键技术和科学问题。还以钴溶胶粒子为原料，以沥青为隔离剂，经热解和除碳等步骤，开发出一种核壳结构的多功能陶瓷纳米粒子。系统研究了含钴碳化硅纤维和含钴陶瓷纳米粒子结构演变规律、组成和结构，并获得其结构演变规律和对吸波和电池性能的影响规律，获得的主要结果如下：.1）含钴陶瓷纳米粒子的结构是以Co2Si为核、以介孔C（混杂着Co3O4\SiO2\SiOC\SiC）为壳。通过控制除碳程度，可以调控核壳陶瓷纳米粒子的组成、结构和性能。其优异的吸波性能来源于：.（1）陶瓷纳米颗粒中的硅钴化合物与四氧化三钴赋予纳米粒子介电损耗和磁损耗（涡流损耗及自然与交换共振）；.（2）碳基质和碳化硅则有效增强了材料的导电性，从而进一步提高其电导损耗；.（3）在热解和除碳过程中，大量介孔的形成有效延长电磁波的传播路径，从而提升对电磁波的吸收/反射比率；.（4）在外电场作用下，多孔核壳结构相界面处的界面极化和偶极极化，大幅度地提高了材料的微波吸收性能。.上述原因赋予含钴陶瓷纳米颗粒在较薄的涂层厚度下，在X波段具有优异的微波吸收能力和有效吸收带宽，在轻薄的高性能微波吸收材料方面存在巨大的应用潜力。.2）钴溶胶的引入，降低了原丝的氧化活性，需要升高交联温度使原丝交联固化.在热解的过程中，钴促进SiCxOy相分解，催化晶粒生长，提高初始结晶温度，1100℃热解的纤维力学性能最优，钴元素的加入还提高了纤维的介电损耗和吸波性能。