具有“双负”性能的纳米金属/SiCN/Si3N4多孔陶瓷复合材料的研究

Double negative materials have some unique electromagnetic properties such as negative equivalent permittivity (ε) and permeability (μ). Nature double negative materials are commonly made of metal particles and insulating dielectric host materials. Their double negative properties can be realized by tailoring the composites and microstructure of composites, which is different form the artificial electromagnetic materials with periodic resonant structure. However, some problems are still prominent, for instance, only one item of the permittivity and permeability shows negative, the frequency bands are different or frequency band is narrow at which double negative properties present, and the mechanism of double negative materials is not well defined. In this proposal, a novel composite of nano-metal particles/SiCN/Si3N4 porous ceramic composites with “double negative” properties will be studied. The composites are made up of Si3N4 porous ceramic as matrix, SiCN precursor ceramic coated on the surface of porous of Si3N4 ceramic and in-situ reduced nano-metal particles and nano-carbon domains embedded in the SiCN ceramic coating. The “double negative” properties of the composites would be tailored by designing porous microstructure, controlling the coating layer thickness of precursor ceramic and adjusting the precipitation of nano-metal particles and nano-carbon domains. The “double negative” properties mechanism, including the microstructure evolution in the composites and the relationship between magnetic and dielectric properties and microstructure would be investigated by using advanced characterization methods. The results are supposed to be significant scientifically foundation in the areas of highly directive antenna, highly effective microwave absorber and cloaking materials.

双负材料具有等效介电常数(ε)和等效磁导率(μ)同时为负的独特电磁性能。本征双负材料通常由金属颗粒和绝缘介质基体组成，不同于具有周期性谐振结构的人工电磁双负材料，该材料可通过调节材料组成和微观结构实现材料的“双负”特性。针对目前本征双负材料存在的介电常数和磁导率出现负值频段较窄或频段不同，以及材料“双负”机理不明确等问题，本项目拟以Si3N4多孔陶瓷为骨架，负载SiCN前驱体陶瓷膜层，并在SiCN层中原位析出纳米金属磁性颗粒和纳米碳，研究一种具有“双负”性能的纳米金属/SiCN/Si3N4多孔陶瓷复合材料。通过对复合材料孔微结构设计、前驱体陶瓷膜厚度及原位纳米金属粒子和纳米碳析出控制等，实现复合材料的可控“双负”性能。借助先进的材料表征手段，研究复合材料的微观结构演变及其电磁性能的关系，探索其“双负”性能机理，为该材料在高指向天线、高吸波材料、全隐身材料等方面的应用提供重要科学理论依据。

双负材料最初由Veselago理论提出。以往有关双负材料的研究大都集中在周期性结构阵列的构造方面，通过调整介质板上印刷金属谐振单元的结构形状和介质板厚度等参数实现双负性质，但该方法存在无限长周期结构与器件小型化的矛盾。最近研究发现，从材料自身性质出发由金属磁性颗粒与绝缘电介质基体复合也可以得到本证双负性能。Tsutaoka给出了可能的微观机制结构模型，材料负介电常数源于金属颗粒团簇极化的介电共振及在逾渗阈值附近金属团簇等效电子在微波段的等离子体震荡，其负磁导率源于磁性金属颗粒的旋磁共振。.本研究以多孔Si3N4陶瓷为基体，以Fe、Co、Ni等金属颗粒为磁性相，以负载在多孔陶瓷上SiCN前驱体陶瓷膜层中原位析出的纳米碳和金属相共为导电相，开发研究了一种新型的纳米金属/SiCN/多孔Si3N4陶瓷材料。本项目开展了五个方面的研究工作：SiCN陶瓷制备工艺研究；纳米金属/SiCN复合陶瓷制备工艺及性能研究；Si3N4多孔陶瓷制备工艺研究；SiCN/Si3N4多孔复合陶瓷制备工艺及性能研究；纳米金属/SiCN/Si3N4多孔复合陶瓷制备工艺及性能研究。研究表明：Si3N4陶瓷具有低介电常数及良好的透波性，其多孔结构可使负载的纳米磁性金属颗粒和纳米碳在孔内部形成三维网络结构，降低逾渗阈值，提高等效电子浓度。SiCN陶瓷前驱体聚硅氮烷在低温流动阶段有利于纳米金属颗粒的分散，高温下可有效保护纳米金属颗粒的抗氧化性，经热处理后其内部可逐渐析出纳米自由碳，可调整复合材料的逾渗阈值。通过系统调整材料的结构与成分，获得了具有良好性能的复合材料体系，借助于X射线光电子能谱、拉曼光谱、核磁共振、电子探针微区分析、SEM、TEM等先进测试研究手段，探索了复合材料微观结构演变特征和电磁性能机理。取得的成果为这类材料在高性能电磁吸波材料的研制及电磁隐身系统的开发应用提供科学理论依据。