CVD石墨烯-SiBCN层状复合电磁吸波结构的构筑与吸波机制

SiC fiber reinforced ceramic matrix composites, with excellent high temperature resistance and electromagnetic (EM) wave absorption capacity, are regarded as the radar stealth base of the hot end components in aeroengine, which are developed in many countries as the strategic materials. SiCf/SiC composite possesses excellent high-temperature mechanical properties, though it exhibits high dielectric constant (ε) and low dielectric loss (tanδ), leading to a poor EM wave absorbing property. If SiC matrix is replaced by the SiBCN with low ε and high tanδ, the as-received composites will have both excellent mechanical properties and EM absorbing properties. However, there are still some problems in the application of SiBCN with low ε and high tanδ, such as difficult to fabricate and to stabilize its electromagnetic performance. Therefore, this project proposes that using graphene and SiBCN with low ε and low tanδ that is easy to prepare by chemical vapor deposition (CVD) to construct a laminated composite with low ε, high tanδ, and excellent EM wave absorbing properties under the instructions of the classical absorbing model. The project will explore the effects of theoretical calculation, CVD process, and high temperature atmosphere environment annealing on the EM wave absorbing properties of the laminated graphene-SiBCN composites. We aim to resolve the basic scientific issues, including the formation mechanism and characteristic of graphene/SiBCN interface and the integrated EM wave absorbing mechanism between the laminated construction and the crystallization phases induced by graphene/SiBCN interface, establish a basic method for the design and preparation of the laminated EM wave absorbing structures, and lay a foundation for developing SiBCN based materials with a high EM wave absorbing efficiency and a steady performance.

耐高温、吸波型SiCf增韧陶瓷基复合材料是航空发动机热端部件隐身的基础，是各大国竞相发展的关键材料。常用SiCf/SiC复合材料具有优异的高温力学性能，但电磁吸波效能不足。采用低介电常数、高介电损耗的SiBCN陶瓷替代SiC基体可有效提高复合材料吸波能力，但仍存在“低介高损”型SiBCN制备难度大、性能可控度差等问题。为此，本项目提出采用化学气相沉积（CVD），将石墨烯和易于制备的“低介低损”型SiBCN进行层状复合，在两组元结构和介电性能调控基础上，利用理论模型计算优化复合材料的叠层组成，构筑“低介高损”结构。系统研究理论计算、CVD制备、高温有氧环境退火等对复合材料吸波性能影响，解决石墨烯/SiBCN界面特性与形成、叠层结构与界面诱导相二者间的协同吸波机制等科学问题，建立层状吸波结构设计和构筑的基本方法，实现SiBCN材料吸波性能的高效、稳定化，为吸波型陶瓷基体研发奠定一定基础。

耐高温、吸波型SiCf增韧陶瓷基复合材料是航空发动机热端部件隐身的基础，是各大国竞相发展的关键材料。常用SiCf/SiC复合材料具有优异的高温力学性能，但电磁吸波效能不足。采用低介电常数、高介电损耗的SiBCN陶瓷替代SiC基体可有效提高复合材料吸波能力，但存在“低介高损”型SiBCN制备难度大、性能可控度差等问题。本项目提出采用化学气相沉积（CVD），将石墨烯和易于制备的“低介低损”型SiBCN进行层状复合，解决石墨烯/SiBCN界面特性与形成、叠层结构与界面诱导相二者间的协同吸波机制等科学问题，建立层状吸波结构设计和构筑的基本方法，实现SiBCN材料吸波性能的高效、稳定化。研究发现：CVD过程中等离子功率、乙醇流量、温度和时间均会影响石墨烯的结构与形貌，等离子体处理可以在石墨烯内部构筑开放边界结构，CO2活化可以调控石墨烯层数，KOH活化可以增加石墨烯的缺陷和孔隙数量；通过CVD制备的Si3N4陶瓷其本征介电损耗极低，是良好的透波材料，能与空气实现较优的阻抗匹配；在多孔Si3N4陶瓷内部生长石墨烯制备的Si3N4-ERG/ Si3N4复相陶瓷具有优异的电磁波吸收性能，随着沉积时间的增加，材料的复介电常数实部呈先降低后升高的趋势，复介电常数虚部则逐渐降低，且降低速度随沉积量的增加而减少；利用CVI在石墨烯泡沫内引入非晶Si3N4后制备的复相陶瓷具有出色的独立于温度变化的电磁波吸收能力；Si3N4-ERG/Si3N4在1100℃、1200℃以及1300℃温度下，表现出优异的抗氧化性能，Si3N4-ERG/Si3N4复相陶瓷的复介电常数的变化均不超过1.5。而在1000℃时，由于SiO2涂层的生成速度较慢，使材料内部的ERG先被氧化，即Si3N4-ERG/Si3N4复相陶瓷丧失了电磁波吸收能力。