Preparation Of Magnetic Metal/Dielectric Core-Shell Materials And Their Microwave Absorption Properties

With the rapid development of information technology,the electromagnetic radiation caused by high frequency electronic equipment is becoming more and more serious.Electromagnetic radiation poses a serious threat to the normal operation of electronic equipment and human health.Therefore,the key to solving electromagnetic radiation problem is to develop efficient microwave absorbent materials.In addition,microwave absorption materials have important applications in military stealth and other fields.Although magnetic metallic materials have excellent absorbent properties,their high metal density and poor antioxidant capacity severely limit their practical application.For applications,the development of microwave absorption materials with"thin thickness,""wide bandwidth,""light mass"and"strong absorption"has become the main direction.Magnetic/dielectric composites have become a promising class of microwave absorbent materials due to their excellent resistance-matching and multiple attenuation mechanisms.In this paper CIP@SiO₂and Ni@C magnetic metal and dielectric composite microwave absorbent materials were designed and prepared by using carbonyl iron Powder（CIP）and nickel metal.Through the material microstructure control,the resistance matching is optimized,the absorption bandwidth is broadened,the absorption strength is increased,and the microwave absorption mechanism of the material is analyzed.The specific study is as follows:（1）The porous carbonyl iron microspheres were prepared by annealing and corrosion,and the porous CIP@SiO₂ composites with core-shell structure were prepared by hydrolyzing ethyl n-silicate onto the surface of the porous carbonyl iron microspheres loaded with silica sols.The reasons for the formation of porous carbonyl iron were analyzed,and the influence of corrosion time on the surface pore size of carbonyl iron microspheres and the microwave absorption performance of composite materials was studied.Resistance matching is effectively regulated by surface loading of SiO₂ dielectric materials and the microwave absorption performance of the materials is optimized.Based on transmission line theory,the dielectric constant and magnetic conductivity of the material were tested and the absorptivity of the material was calculated.In the microwave frequency band（2-18 GHz）,the effective absorption bandwidth of the composites was 8.37 GHz,with a minimum reflection loss of-34.89 d B.（2）Hollow porous Ni@C composites with core-shell structure were synthesized by hydrothermal method and in situ pyrolysis of nickel-based trimeric acid framework at high temperature.The effects of annealing temperature on the microstructure,dielectric constant and magnetic conductivity of composites were investigated.The dielectric loss and magnetic loss mechanism of composites were investigated.The composite showed good microwave absorption,effective absorption bandwidth of 5.78 GHz and minimum reflection loss of-39.6d B.In this paper,based on the design of magnetic/dielectric composite microwave absorption materials,CIP@SiO₂ and Ni@C composite materials with core-shell structure were prepared respectively.Through microstructure control,both composites show excellent microwave absorption performance,which provides reference for the development of high performance microwave absorption materials.