可控径向分支钴颗粒的制备及电磁性能研究

Cobalt microparticles with tunable radial branches:preparation&electromagnetic property control

微纳米级铁磁性金属颗粒的外形调控会导致各向异性和表面原子比例变化,并对其电磁性能有很大影响。工作利用一步水热还原法制备了具有发散分支结构的微米级钴颗粒。通过对反应体系组成的设计实现了分支结构尺寸的调控,根据分支的长径比不同,分别得到了剑麻状,花状以及类球状颗粒。采用SEM、TEM和XRD对所得材料进行了形貌及结构表征,用VSM以及矢量网络分析仪对材料的室温磁性能和电磁参数进行了测试。研究了材料在2~18 GHz频段的微波电磁特性。结果表明,基于形状各向异性带来的表面原子比例和矫顽力提升,以及多尺度的花瓣结构对入射电磁波的多重散射效应,适度的分支结构(花状)的钴颗粒具有最好的电磁波损耗能力。研究还发现,一方面分级结构可通过更丰富的界面和多尺度协同促进电磁波的多重反射和散射,进而延长传输路径并增强微波耗散;而另一方面,过高的分支化结构会导致吸波复合材料的电导率和介电损耗提高,不利于吸收剂添加量的提升和阻抗匹配设计。

The shape control of micro-nano-scale ferromagnetic metal particles leads to anisotropy and surface atomic ratio change,and has a great influence on its electromagnetic properties.In this work,micron-sized metallic cobalt particles with divergent branching structure were prepared by one-step hydrothermal reduction.Through the design of the composition of the reaction system,the size of the branch structure was controlled.According to the difference of the aspect ratio of the branches,sisal-like,flower-like and spheroidal particles were obtained.The morphology and structure of the materials were characterized by SEM,TEM and XRD.The room temperature magnetic properties and electromagnetic parameters of the materials were tested by VSM and vector network analyzer.The microwave electromagnetic properties of the material in the 2-18 GHz band were studied.The results show that cobalt particles with moderate branching structure(flower shape)had the best loss capacity of electromagnetic wave,based on the increase of surface atomic ratio and coercivity caused by shape anisotropy,as well as the multiple scattering effect of multi-scale petal structure on incident electromagnetic wave.The study also found that,on the one hand,the hierarchical structure could promote multiple reflection and scattering of electromagnetic waves through a richer interface and multi-scale synergy,thereby prolonging the transmission path and enhancing microwave dissipation.On the other hand,excessively branched structures could lead toimproving the conductivity and dielectric loss of the absorbing composite,which was not conducive to the increase of the amount of absorbent added and the impedance matching design.