Fe3O4/ZnO复合网络结构的构筑及磁-电阻抗匹配特性研究

With the rapid development of the information technology, electromagnetic wave has been widely used in military, civilian and other areas. To develop new type of radar absorption material with high electromagnetic wave absorption performance has attracted extensive attention not only because of the crucial importance in military field, but also the significant influence in civilian area. However, for the traditional ferrite based microwave absorption material, the high surface density, narrow effective absorption bandwidth and thick coating thickness restrict their applications in military purpose. In order to overcome these shortcomings for spinel ferrites and satisfy the new requirement on radar absorption material including the strong absorption, wide absorption bandwidth, thin thickness and lightweight, it is required to improve the microwave absorption capacity, impedance matching characteristics and reduce the density of ferrite materials. But it is quite difficult to realize the good impedance matching and strong absorption by only controlling the structure and properties on a single magnetic component and it has become one of the research focuses in this field. In this project, a new type of magneto-dielectric microwave absorption material with constructing dielectric network structure of ZnO nanorods on the surface of the plate-like spinel ferrite particles will be synthesized through a simple chemical process. By tuning up the weight ratio between magnetic and dielectric parts in the composites, the morphology of the hierarchical structure and the annealing parameters, the strong magnetic and dielectric loss and good impedance matching characteristics can be achieved. In that way, the composites with good microwave absorption properties can be obtained. The relationship between electromagnetic absorption properties and impedance matching characteristics of these magneto-dielectric composites will also be deeply discussed and all these investigations will provide theoretical and experimental basis for the design of new broadband and high loss absorption materials.

信息技术的不断发展使电磁波在军事和民用等领域的应用日益广泛。研制高性能吸波材料对军事目标隐身和民用屏蔽均具有重要的战略意义。传统的铁氧体吸波材料面密度大、吸收频带窄、涂层厚度大，严重制约了其在武器隐身技术中的实际应用。为实现吸收强、频带宽、厚度薄、质量轻等新的隐身特性要求，需要降低铁氧体使用密度并提高其衰减能力和阻抗匹配。但仅通过调节铁氧体自身的结构和物性很难实现良好的阻抗匹配和吸收强度，已成为铁氧体吸波材料应用中急需解决的关键问题之一。本项目拟采用化学方法在片状铁氧体颗粒上构筑具有高介电损耗的棒状ZnO网络结构，通过调控磁和电材料之间的比例、异质结构形貌、热处理工艺等，来提高磁和电材料自身的磁损耗和电损耗以及磁电之间的阻抗匹配，实现优异的吸波性能，从理论上揭示磁电复合型吸波材料中磁材料与介电材料之间阻抗匹配的物理规律，为我国宽频、强损耗电磁波吸收材料的发展提供理论和实验依据。

传统的铁氧体材料存在密度大，涂层厚度大、吸收频带窄等缺点，无法满足“薄、强、轻、宽”的要求，其在吸波领域的发展受到了限制。为了解决这些关键问题，一种最有效的途径就是将电损耗型与磁损耗型吸波材料结合，增加磁损耗型吸波材料本身较低的电损耗，提升材料的整体电磁波衰减能力。与此同时，还减薄了涂层厚度，也解决了材料本身的质量重的关键问题。本课题一方面通过设计与制备具有代表性的铁氧体磁性材料Fe3O4纳米微粒的微观形貌以及复合结构来提高吸收能力和降低密度，另一方面通过复合特殊形貌的介电损耗型材料来改善其吸波性能。.(1)首先, 合成出包覆片状MnO2得到卵黄-壳结构的Fe3O4@C@MnO2纳米复合材料。基于此特殊的微观卵黄-壳空心球结构以及碳和MnO2介电材料的引入，Fe3O4@C@MnO2纳米复合材料具有优异的吸波性能，反射损耗可达-58.25db，吸收带宽可达5.44GHz。该部分研究工作对多层介电损耗型材料在电磁吸波中的应用具有重要的指导价值。.(2)其次，由于球形纳米粒子受到Snoek极限和较大退磁因子的影响，难以进一步提高性能。因此, 制备得到Fe3O4@SnO2@MnO2纳米复合材料。基于此特殊的微观核壳结构以及SnO2和MnO2介电材料的引入，Fe3O4@SnO2@MnO2纳米复合材料实现较为优异的吸波性能，反射损耗可达-50.4 dB，吸收带宽可达到9.18 GHz。该部分研究工作对于提高铁氧体材料吸波频段提供了一条有效途径。.(3)最后，具有各向异性的磁性材料的磁化强度会受到外部磁场方向的影响，片状材料的易磁化方向为平行于平面的方向。因此，通过水热法制备出正六边形片状Fe2O3纳米粒子，热处理得到六边形片状Fe3O4纳米粒子，对片状Fe3O4进行面内取向，使得微片堆叠排布。由于片状结构的存在以及对片状纳米粒子实施的取向分布，面内取向Fe3O4纳米粒子的反射损耗可以达到-47.67 dB，相比于无规分布的Fe3O4纳米粒子，反射损耗增加了258%。之后再合成出具有不同形貌的ZnO颗粒，厚度为1.65mm的ZnO纳米花状结构的最小RL值为-66.5dB。该部分研究工作为进一步铁氧体与ZnO介电材料复合提供了理论和实验依据。