Microwave Absorption Performance Of Composite Nanorattles With Hierarchical Structure

Electromagnetic interference (EMI) has become a great concern due to the rapid increase in the use of electrical instruments. Recently, considerable attentions have been paid to the development of high-efficient microwave absorbers. It goes without saying that the traditional microwave absorbers, such as Fe3O4, fail to defend the EMI, because of their large density, weak absorption characteristics and narrow absorption frequency range. A possible and efficient solution to achieve the goal of light weight, thin thickness, wide absorption frequency range, strong absorption characteristics is the combination of different kinds of materials and the design of hollow structure.On the other hand, reports shows that the shape anisotropy and size have significant impact on the absorption properities. Considering the effects of shape anisotropy, especially the dependence of microwave absorption on aspect ratio and size, many experimental and theoretical efforts have been reported. There were reports about the impact of aspect ratio on the microwave absorption performance of dielectrical loss materials, such as the one-dimensional carbon nanotube polymer composites. Recently, there are corresponding results about magnetic materials. However, the influence of aspect ratio and size on the combined dielectric-magnetic materials has not been investigated till now as far as we know. In this work, we synthesized Fe3O4-based hierarchical nanostructures with unique morphology and combined dielectric-magnetic characteristics, and investigated the influence of aspect ratio to the microwave absorption properties. The primary coverage is summarized as follows:1. Elliptical nanorattles with spinel Fe3O4 cores and coppor silicateshells were synthesized by combining solvothermal reaction and calcination process. Futhermore, the microwave absorption properties of the elliptical nanorattles were investigated in terms of complex permittivity and permeability. The maximum reflection loss value of these nanorattles could reach-28 dB with a thickness of 2 mm, and the absorption bandwidths with the reflection loss lower than-10 dB was up to 5 GHz. This indicated that the core-shell composite nanorattles might be attractive candidate materials for microwave absorption applications. Futhermore, the results of reflection loss shows that the aspect ratio is of great significance to the microwave absorption of the Fe3O4@CuSiO3 system. When the thickness of shell keeps unchanged, the intensity of absorption tends to increase with the rising of aspect ratio. Moreover, the increase of shell thickness is beneficial for the microwave absorption.2. Hierarchical magnetic yolk-shell nanorattles with mixed barium silicate and barium titanium oxide shells were synthesized based on a "hydrothermal-assisted crystallization" route. The yolk-shell nanorattles with different core sizes and shell thicknesses were synthesized by manipulating the synthetic parameters. Moreover, a possible formation mechanism based on the dissolution-precipitation, sacrificial-templating crystallization and in-situ transformation processes was proposed. The as-synthesized yolk-shell nanorattles had high porosity, magnetization, and large specific surface area, which were demonstrated to be attractive candidate materials for microwave absorption enhancement. Significantly, the maximum reflection loss for these nanorattles increased by enlarging the shell thickness, which could reach-37.6 dB at 7 GHz with a thickness of 2 mm, and the absorption bandwidths of these nanorattles with the reflection loss lower than-20 dB was up to 7.5 GHz. This study highlighted the importance of unique yolk-shell structure and opened up a promising strategy to design novel high-efficient absorbers for microwave absorption applications.