Preparation And Absorbing Properties Of One-dimensional Magnetic Absorbing Materials

With the tremendous advancement of science and information technology,the rapid development of national defense military stealth technology,whether civilian or military,has increasingly requirements for electromagnetic wave absorbing materials.In recent years,new types of absorbing materials have become the research hotspots for scientists.In addition to the principle of impedance matching and attenuation,they also need to meet the requirements of "thin thickness","wide frequency bandwidth","lightweight" and " powerful absorption".Moreover,they are required to have good physical and chemical properties to adapt to complex and varied environments.Recent advances in microwave absorbing materials have shown that rational design of the microstructure of the material helps to increase its absorption efficiency.Among them,one-dimensional microwave absorbing materials with high aspect ratio,shape anisotropy and geometric effects,because of their one-dimensional structure,induce electrons/phonons to vibrate in the axial direction to dissipate electromagnetic waves.Therefore,designing and synthesizing one-dimensional nanochains with magnetic loss and dielectric loss as microwave absorbing materials has become a new research hotspotIn this paper,Fe₃O₄ and ZnFe₂O₄ with high saturation magnetization,which were easy to recycle and environmentally friendly,were used as magnetic cores.One-dimensional Fe₃O₄@SiO₂ and ZnFe₂O₄@SiO₂ nanochains were formed with the aid of external magnets,which are combined with dielectric materials including MnO₂,graphene,NiO,carbon layer and NiCo₂O₄ to obtain three different composite structures?flower,aerogel and hollow structure?.These composite structures make the microwave absorbing materials have higher dielectric loss and magnetic loss in the 2-18 GHz band,while improving material impedance matching and reducing material density.In addition,the basic properties such as microstructure,phase composition and magnetic properties of the composites were analyzed The main contents are as follows?1?The hydrothermal/in situ growth method was used to grow flower-like MnO₂ on the one-dimensional Fe₃O₄@SiO₂ nanochains,and then the one-dimensional flower-like Fe₃O₄@SiO₂@MnO₂ nanochains and the graphene aqueous solution prepared by the Hummers method were mixed for a hydrothermal reaction.During the reaction,the one-dimensional flower-like Fe₃O₄@SiO₂@MnO₂ nanochains induced the self-crimping of graphene to form a porous aerogel with enough strength,which meets the light weight requirements of the absorbing material.It can be known from the electromagnetic parameters that the addition of graphene enhanced the dielectric loss of the absorbing material,and the large specific surface area of the MnO₂ nanoflower and a large number of voids between the layered graphene aerogels generated more interface polarization.When the mass ratio of sample to paraffin is 3:7,the minimum reflection loss?RLmin?at 7.78 GHz is-55.01 dB,and the effective absorption bandwidth is 4.26 GHz with a matching thickness of 3.2 mm.The improvement of absorbing performance is due to the synergistic effect between graphene and one-dimensional flower-like Fe₃O₄@SiO₂@MnO₂ nanochains,which improves the impedance matching of absorbing materials.At the same time,electromagnetic waves can be reflected multiple times in the flower-like structure and the layered graphene structure,thereby enhancing the absorption of electromagnetic waves?2?One-dimensional flower-like yolk-shell structure of Fe₃O₄@SiO₂@NiO nanochains were prepared by a simple one-step hydrothermal method.It was observed from SEM that the ends of the flower-shaped nanochains were broken,revealing the Fe₃O₄ magnetic cores in the nanochains.Due to its unique hollow structure,the density of the material was greatly reduced,which is in line with the light weight of the absorbing material The comparison of test results with doping samples of 10wt%and 30wt%shows that when 30wt%is doped,the interlaced complex one-dimensional nanochains are more likely to form a three-dimensional conductive network,enhancing the anisotropy of the surface,and making the natural formant move to high frequency.Increasing the doping amount also regulates the dielectric constant and dielectric loss.Its minimum reflection loss can reach-54.28 dB at 12.9 GHz and the effective absorbing band reaches 4.0 GHz?11.05-15.05 GHz??3?One-dimensional flower-like ZnFe₂O₄@SiO₂@C@NiCo₂O₄ nanochains with multi-layered core-shell structure were prepared by solvothermal/hydrothermal/annealing method.SEM test showed that the particle size of ZnFe₂O₄ nanospheres were about 100-160 nm.The combination of one-dimensional ZnFe₂O₄@SiO₂ nanochains and carbon material contributes to free electrons conduction,thereby improving the energy dissipation,and the one-dimensional ZnFe₂O₄@SiO₂@C material exhibited an ultra-wide effective absorption band of 6.22 GHz.After being compounded with NiCo₂O₄ nanoflowers,the high porosity and large void space existing in the flower-like crease structure not only provide many active sites,but also cause multiple reflections and diffraction of incident electromagnetic waves,thereby enhancing microwave absorption performance.The minimum reflection loss of the sample can reach-54.29 dB at 11.14 GHz.The effective absorbing band can reach a maximum of 5.66 GHz?11.94-17.60 GHz?,when the thickness is 3.2 mm,covering almost the entire Ku band,which means that the sample is a promising material for Ku-band electromagnetic wave absorptionIn summary,by studying the absorbing properties of one-dimensional magnetic absorbing materials,it is shown that the prepared absorbing materials have a good application prospect.This work provides more reference for the development of absorbing materials and a theoretical basis for relevant problems in practical applications.