聚硅氧烷热解SiCf/Si-O-C吸波材料介电温频响应调控机理

The continuous SiC ceramic reinforced ceramic matrix composite high temperature stuctural radar wave absorbing materials, which have intergrated functions of microwave absorbing, thermostability and load bearing, play a key role in novel radar stealth equipments. However, both the the effective control methods of content and order of free carbon in matrix and the regulating methods of dielectric teperature/frequence response of composites are the key issuse of high temperature stuctural radar wave absorbing materials. In our application, in view of its controllable content and order of free carbon and complex permittivity, the polysiloxane derived Si-O-C ceramics would be originally used as matrtix, and the SiCf/Si-O-C high temperature radar wave absorbing composites would be fabricated to avoid the problem of too high complex permittvity, impedance mismatching bewteen air and strong reflection of radar wave caused by too much free carbon in SiC marixs fabricated by both chemical vapor infiltration and polycarbosilane impreganation pyrosis. The control methods of content and order of free carbon in Si-O-C matrix would be found through investigating the effects of polysiloxane architecture, pyrolysis process, and annealing on the content and order of free carbon in Si-O-C matrix. The influencing mechanism of content/order of free carbon on dielectric teperature/frequence response characteristics of composites would be elaborated. Then, the regulating ways of dielectric teperature/frequence response characteristics of SiCf/SiOC composites would be known well. The implement of this project would provide new routes and theroretical guidances for the design of broadband and strong absorption of high temperature structural radar wave absorbing materials.

连续SiC纤维增强陶瓷基高温结构吸波材料集吸波、防热、承载与一体，其发展对新型装备雷达隐身意义重大，但基体自由碳含量/有序度及复合材料介电温频响应特性的有效调控机理仍是高温结构吸波材料亟需解决的关键问题。本申请创造性提出将自由碳含量、有序度及介电常数可调途径较多的聚硅氧烷热解Si-O-C陶瓷作为基体，制备SiCf/Si-O-C高温吸波材料，进行聚硅氧烷分子结构及热解、高温退火工艺条件对自由碳含量与有序度的影响规律研究，建立自由碳含量/有序度的有效控制方法，可避免目前采用化学气相渗透、聚碳硅烷浸渍裂解法制备的SiC基体自由碳含量及有序度过高导致复合材料复介电常数过高、与空气阻抗失配、对雷达波反射明显的问题。阐述自由碳含量、有序度与复合材料不同温度复介电常数频率响应特性的关系，获得SiCf/Si-O-C复合材料介电温频响应特性的调控方法，为高温结构吸波材料强吸收、宽频化设计提供理论基础。

为满足新型装备雷达隐身对集吸波、防热、承载于一体的高温结构吸波材料的的重要需求，本项目以聚硅氧烷为原料，经热解制备SiCf/Si-O-C复合材料。研究了先驱体分子结构、热解温度等工艺参数以及过渡金属催化剂对聚硅氧烷热解Si-O-C块体陶瓷纳米结构与介电性能的影响，发现具有笼状分子结构的RSN-6018有机硅树脂陶瓷产率明显高于线性分子结构硅油，能够制备致密块体Si-O-C陶瓷，随热解温度的升高，Si-O-C陶瓷自由碳含量增加，且有序化程度提高，复介电常数实部与虚部明显增加，吸波性能得到改善。研究了FeCl3催化剂掺量对聚硅氧烷催化热解Si-O-C块体陶瓷碳纳米管生成量、介电频响效应、吸波性能的影响，发现掺FeCl3催化剂0.75 wt%的块体Si-O-C陶瓷原位生成CNTs量最多，CNTs直径约50 nm，壁厚约10 nm，建立CNTs生成量的调控方法。研究了催化热解Si-O-C陶瓷微纳结构与电磁性能随退火温度的变化规律，发现厚度为3.0 mm的1500℃陶瓷试样介电频响明显加强，反射损耗低于-20 dB（吸收99%）的有效吸波频段为3.8 GHz；阐明Si-O-C陶瓷宽频、强吸收的介电物理机制，高温退火使原位生成CNTs转化为微球、针状以及纳米线等SiC微纳结构，与Si-O-C基质形成复杂纳米界面，多重界面极化加强了Si-O-C陶瓷的介电弛豫。分别研究了短切SiC纤维和CNTs增强Si-O-C复合材料，发现CNTs表明官能团能够与聚硅氧烷反应，形成界面结合，有利于CNTs的分散，建立了高体积分数短切SiC纤维（CNTs）在陶瓷基体分散方法。以活性碳纤维、硅粉为原料，通过硅蒸发渗透反应法制备SiC纳米纤维/活性碳纤维（SiCnf/ACF）混杂纤维毡，研究了蒸发温度、Fe催化剂对活性碳纤维毡中SiC纳米纤维生成量、纤维直径以及电磁屏蔽性能的影响规律，建立了SiCnf/ACF混杂纤维毡电磁性能的调控方法，为发展轻质、柔性、耐高温、防氧化电磁功能材料探索了新途径。