Synthesis And Microwave Absorbing Properties Of Magnetic Metal/Dielectric Nanoparticles

Absorbing materials have a wide range of applications in military and civilian. But thetraditional microwave absorbing materials have many shortcomings, for example, short of hightemperature resistant, bad of acidproof alkalescence, absorbing band is narrow, the big density, etc.It is difficult to satisfy people for "thin, wide, light, strong" demand of absorbing material. Therefore,it is an urgent need to develop a new absorbing material. The core-shell structure composite nano-absorbing material is a new absorbing material, which can achieve the superposition of core-shelladvantage without influencing each other. Wave impedance matching between core and shell can berealized by rational designing, thus the electromagnetic waves can access to the material interior toachieve maximum absorption of electromagnetic waves. Therefore, the study of our nano-materialshas a very important theoretical and application significance.In this paper, nano-sized Fe has been synthesized by chemical reduction method and differentnano-sized Fe samples can be obtained by control the experiment parameter or annealed at differenttemperature. The best sample was choosed to be the core, which was coated with a dielectric layer（Al₂O₃, SiO₂） by chemical deposition or microemulsion method. The microstructure, magnetic,electromagnetic characteristics and absorbing properties were studied.Firstly, different nano-sized Fe samples were prepared by chemical reduction, within threedispersants and were annealed at different temperature under Ar atmosphere. It was found that thedispersion effect of Fe nanoparticles dispersed by PAA was not satisfied. The Fe nanoparticleswhich was dispersed by PEG200had a better dispersion, and the particle size is about40-60nm.The magnetism of Fe nanoparticles is moderate, which is conducive to the dispersion and coatingoperation.Then, the Fe nanoparticles were coated with a Al₂O₃layer using chemical deposition method.The morphology of the coating was roughly spherical with a core-shell structure, and the thicknessof the layer was about3-5nm. The magnetic characteristic of the coated and uncoated samples wereferromagnetic. The cut-off frequency of the sample moved to a higher frequency. However, the peakof the reflection loss had a little reduction. The bandwidth of the coated sample did not reduce. Themicroemulsion method was used to synthesis Fe-Al₂O₃nanoparticles. The core-shell structure of theparticles was clear and the thickness of the shell was about8-10nm. After the coating operation, thesamples were remain ferromagnetic state. There were two reflection loss peaks in the reflection losscurve, and the maximum peak was about-30dB.Finally, Fe nanoparticles were coated with a SiO₂layer by hydrolysis of TEOS. The effect of the coating was well when2ml TEOS was added in the solution. The coating were elliptical, andthe thickness of the shell was about8-10nm. All the coated samples showed ferromagnetism. Thecoated samples had two reflection loss peaks, and the reflection loss reached-30.4dB at13.6GHz.The core-shell nanoparticles were synthesized by chemical methods successfully. The nano-structural of the particles were distinct and the size were moderate. All the samples wereferromagnetism at room temperature. It can achieve a larger electromagnetic wave absorption at Kwavebond.