纳米SiC@BNC核壳结构的原位构建及高热导AlN-Si/B/C/N微波衰减体系的介电性能调控

Microwave tube is the key element in radar, microwave communication and navigation, space remote sensing etc. system, while the microwave attenuating materials play a key role in the microwave tube. With the development of microwave tube toward high frequency, high power and small size, a microwave attenuating materials with high thermal conductivity, well controlled dielectric properties is required. There are two basic elements in the microwave attenuating materials, matrix and the microwave absorber. Usually AlN with high thermal conductivity and specific electrical properties, is an ideal matrix material, while SiC is a relatively good candidate for microwave absorbing material. However, AlN and SiC could form solid solution easily at high temperature, which lead to the significant decrease in thermal conductivity. Up to now, it is a problem to keep high thermal conductivity together with to manipulate the dielectric properties..Nano sized Si/B/C/N possess superior stability at high temperature, is usually used as thermal barrier material. Recently, it was found that Si/B/C/N also showed higher microwave attenuating properties than SiC. In addition, Si/B/C/N could form SiC@BNC core-shell structure at high temperature. In this paper, nano-sized Si/B/C/N amorphous powder was used as the effective microwave absorbing elements, and AlN was used as the matrix material. AlN-Si/B/C/N composite was developed with both high thermal conductivity and well-tailored dielectric properties thorough the in situ formed SiC@BNC core-shell structure at high temperature, which could effectively avoid the formation of solid solution between AlN and SiC. Based on the microstructure characterization, thermal properties and dielectric properties etc. testing, a dielectric properties calculation model can be developed with the aid of computer aided simulation. This study could not only help to provide the theory and experimental reference for the development of the dielectric properties calculation model for ceramics, but also could provide the idea and experimental method for the design of microstructure for simutaneous thermal and dielectric properties control.

微波管是雷达、微波通讯及导航、空间遥感系统等的关键部件，而微波衰减材料是微波管中的关键材料。随着微波管向高频、大功率、小型化方向发展，迫切需要高热导、介电性能可调的微波衰减材料。衰减材料包括基体和衰减剂两部分。AlN是理想的基体材料，而SiC是较理想的衰减剂。但是，SiC和AlN极易固溶，导致热导率严重下降，热性能和介电性能无法兼顾。.Si/B/C/N不仅具有优异的高温性能，而且衰减性能比SiC更优，晶化后可原位形成SiC@BNC核壳结构。本研究以AlN为基体，以纳米Si/B/C/N为衰减剂，通过原位构建纳米SiC@BNC核壳结构，避免SiC和AlN的固溶，制备热性能、介电性能兼顾的氮化铝基衰减体系。综合表征材料的微结构、电学、热学等性能，结合计算机数值模拟，建立体系的介电常数计算模型。本项目的实施不仅为材料计算提供理论和实验基础，而且对于热、介电性能兼顾的体系的微结构设计提供新的思路。

微波管是雷达、微波通讯及导航、空间遥感系统等的关键部件，而微波衰减材料是微波管中的关键材料。随着微波管向高频、大功率、小型化方向发展，迫切需要高热导、介电性能可调的微波衰减材料。衰减材料包括基体和衰减剂两部分。AlN是理想的基体材料，而SiC是较理想的衰减剂。但是，SiC和AlN极易固溶，导致热导率严重下降，热性能和介电性能无法兼顾。Si/B/C/N不仅具有优异的高温性能，而且衰减性能比SiC更优，晶化后可原位形成SiC@BNC核壳结构。本研究以AlN为基体，以纳米Si/B/C/N为衰减剂，通过原位构建纳米SiC@B NC核壳结构，避免SiC和AlN的固溶，制备热性能、介电性能兼顾的氮化铝基衰减体系。本工作进一步研究了氮化铝基其他衰减材料体系，包括碳、硅等的掺杂对于氮化铝基体系介电性能和热导率的影响，开发了新型氮化铝-纳米碳体系，材料表现出高导热、大衰减和介电性能易调节的突出优势。同时，也研究了氮化硅基衰减材料体系，初步制备了高热导率氮化硅-TiN材料。该体系的热导率和力学性能优异，在8-12GHz波段介电常数达17-18，介电损耗0.35-0.5，表现出理想的衰减性能，是大功率微波器件潜在的候选材料之一。

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