Design And Electromagnetic Properties Of Core-Shell Porous Structure And Periodic Structure Coating Based On WC Powder

With the development of modern science and technology,the problem of electromagnetic radiation and electromagnetic environmental pollution has become increasingly serious.The application of absorbing materials is useful to solve the problem.Absorbing material refers to a class of materials that can absorb the energy of electromagnetic waves,and convert the electromagnetic wave energy into thermal energy,mechanical energy or other forms of energy through the dielectric loss of the material.Although ceramic absorbing materials have the ability to absorb microwaves at high frequencies.But its poor low frequency absorption ability and narrow absorption band have limited its performance.In this paper,the electromagnetic properties and microwave absorption properties of tungsten carbide（WC）were studied.In order to enhance the electromagnetic absorbing ability of WC,the core-shell structure and frequency selective surface are combined for the design of WC materials at the micro-scale and macro-scale,respectively,to improve its microwave absorption performance.In terms of microstructure,a core-shell porous structure of WO₃@WC was designed and synthesized.In terms of macrostructure,WC was used as the raw material to prepare the coating by atmospheric plasma spraying（APS）.Combined with High Frequency Structure Simulator（HFSS）software,a periodic structure surface is designed.The experimental results show that the original WC powder has poor microwave absorbing performance.In this paper,the WC porous powder was prepared by spray granulation.When the thickness is 2.8mm,the absorbing property of the powder is strongest at 13.3GHz,which reaches-15.45d B.The specific surface area of the WC porous powder after the spray granulation process is greatly increased compared to the WC powder.The adsorption-desorption isotherms of N₂ shows that the prepared material has a porous structure.The porous structure can make the electromagnetic wave enter the material and generate multiple reflections,which increases the reflection loss of the powder.In order to further improve the microwave-absorbing performance,the WC porous powder was heated and oxidized to form a WO₃@WC core-shell porous material.The study found that the WO₃@WC powder which was heated to 410°C without heat preservation had the strongest microwave-absorbing ability,and the optimal matching thickness was reduced to 2.1mm.The uneven interface between tungsten oxide on the surface and tungsten carbide on the inner layer of the core-shell structure can enhance the polarization.On the other hand,the high resistance of tungsten trioxide on the surface reduces the conduction loss.The two mechanisms compete,causing the absorption ability of powder to decrease,then increase,and then decrease with the increase of tungsten oxide.In terms of macroscopic structure,the coating was prepared by atmospheric plasma spraying.The surface of the coating prepared by WC powder spraying shows the typical surface morphology of thermal spraying ceramics.There are many holes in the cross section of the coating,which are mainly caused by incomplete melting and accumulation of powder.The porosity of the coating is 16.7%.The phases of the coating at different depths were characterized.The overall composition of the coating is uniform,and the coating is composed of W₂C,W and W₂（C,O）.The hardness of the coating is uniform and the average micro Vickers hardness is 602.5 HV.The absorption ability of the coating is poor,and the maximum reflection loss is-2.95 d B at 8.29 GHz when the thickness is 0.6 mm.When the period length（p）of the square periodic structure is 16.45 mm,the side length of the square periodic patch（a）is 2.79 mm,and the coating thickness（t）is 0.85 mm,the reflection loss of the composite coating reaches-44.09 d B at 11.8 GHz.Compared with the spray coating,the absorbing ability of the composite coating has been greatly improved.