【作者】 赵星辰；

【导师】 王敦辉；

【作者基本信息】 南京大学 ， 凝聚态物理， 2013， 硕士

【摘要】 微波吸收材料在日常生活和军事技术方面都有重要的应用前景,开发轻质、高稳定性和高吸收性能的微波吸收材料是当前的研究热点之一。磁性金属是一类常用的微波吸收材料,其对微波的吸收主要由磁损耗来承担,吸收性能有限。如果能同时引入介电损耗,将进一步提高其吸收性能。本文分别研究了Fe@石墨烯核壳结构和FeNi3-石墨烯纳米复合物的微波吸收性能,其主要内容如下：1.Fe-石墨烯核壳结构的微波吸收性能我们采用水热反应和氢气还原相结合的方法制备出Fe@Graphene纳米核壳结构。测量结果表明该核壳结构的介电性质与纯Fe或机械混合Fe-石墨烯复合物的完全不同。在这种核壳结构中,由于Fe和石墨烯功函数的差异以及界面处二者的化学相互作用,Fe中的部分电荷将注入到石墨烯中并在微波的作用下振动且产生极化,从而导致该核壳结构介电常数的实部增大；此外,由于极化驰豫,介电常数的实部随频率的增大而减小,产生介电频散。同时,载流子的运动导致了对微波能量的吸收,故核壳结构的介电损耗也得到提高。增大的介电常数和介电频散更有利于材料满足阻抗匹配条件,而介电损耗的提高则更有利于微波能量的耗散,这两个因素的共同作用导致了Fe@Graphene核壳结构具有优异的微波吸收性能。此外,Fe@Graphene核壳结构界面处轨道的强烈杂化也会导致电荷转移,从而影响其微波吸收性能。这项工作为探索高性能微波吸收材料提供了新的研究思路,同时也进一步拓宽了石墨烯基材料的应用领域。2.FeNi3-石墨烯纳米复合物的微波吸收性能研究了不同比分的FeNi3-石墨烯纳米复合物的微波吸收性能。相对于纯FeNi3,共生长的FeNi3-石墨烯表现出完全不同的微波介电响应并表现出优异的微波吸收性能,而且复合物中石墨烯的含量对微波吸收性能也有影响。这项工作表明,让FeNi3和石墨烯共生长,可以有效地改变FeNi3-石墨烯纳米复合物的介电性质,从而得到微波吸收性能优异的FeNi3-石墨烯纳米复合物。但是,该复合物微波吸收性能提升的物理机制尚待进一步证实。更多还原

【Abstract】 Microwave absorption material (MAM) is of great importance in both civil and military applications. Considerable attention has been paid to the development of MAM with low density, high stability and excellent absorption performance.Magnetic metal is usually to be utilized as MAM. However, its absorption propery is limited since magnetic loss is the only mechanism for dissipating microwave energy. If dielectric loss is involved in, the absorption performance of magnetic metal would be further improved. In this dissertation, we investigated the dielectric, magnetic and microwave absorption properties of Fe@Graphene core-shell structure and FeNi3-Graphene nanocomposite. The main results are as follows:1. Microwave absorption performance of Fe-Graphene core-shell structure.We synthesized Fe@Graphene core-shell structure by hydrothermal reaction and following reduction in H2. The experimental results show that the dielectric property of the core-shell structure is totally different from that of pure Fe and mechanically-mixed Fe-Graphene composite. In the core-shell structure, the difference of work function and the chemical interaction at the interface of Fe-graphene introduce free charges to graphene. The charges vibrate with the stimuli of the microwave and bring about polarization, increasing the value of the real part of permittivity (ε’). Furthermore, the relaxation of polarization results in the decrease ofwith the increase of frequency, i.e., dielectric dispersion. Meanwhile, the motion of free charges would lead to the absorption of microwave energy. Thus, the dielectric loss is also enhanced. The increased ε’ and dielectric dispersion give rise to a good impedance matching and the enhanced dielectric loss is more favorable for the dissipation of microwave energy. The aforementioned factors would account for the excellent microwave absorption performance of the core-shell structure. In addition, the strong hybridization between the graphene π and Ni3d valence-band states at interface leads to the transfer of partial charge, which would give rise to the change of microwave absorption performance. This work provides a novel idea for exploring high-performance microwave absorption material as well as expands the application field of graphene-based materials.2. Microwave absorption performance of FeNi3-Graphene nanocomposite.The microwave absorption performance of FeNi3-Graphene nanocomposite with different concentration of graphene was studied. Compared with pure FeNi3, FeNi3-Graphene compositie shows quite different microwave dielectric response and exhibits excellent microwave absorption property. Moreover, the absorption performance is influenced by the concentration of graphene. This work indicates that the co-growth of FeNi3and graphene can intrinsically change the dielectric property of FeNi3-Graphene nanocomposite and lead to a high-performance microwave absorption nanocomposite. Moreover, the physical mechanism of the improved absorption performance needs to be further investigated.更多还原