Study On Preparation And Electromagnetic Properties Of Porous Alumina-based Absorption Materials

With the wide application of radar detection technology and wireless communication technology in military field,electromagnetic wave absorption materials play an important role in the stealth of military equipment.Traditional electromagnetic wave absorption materials have many problems,such as high density,narrow frequency band and weak absorption capability.The development of new porous materials is an effective way to solve above problems.Therefore,in this paper,porous Al₂O₃ is used as the matrix and different absorbent are introduced into the porous Al₂O₃ by hydrothermal method to construct the microwave absorption composite with unique microstructure.The following section describe the research contents of this paper.CoP supported on porous Al₂O₃ nanostructures(CoP@Al₂O₃)were prepared by hydrothermal method and low-temperature phosphating.Thanks to the through-hole of the matrix and the vacuum impregnation,the pore wall of porous Al₂O₃ matrix can be uniformly covered by CoP.When the concentration of CoCl₂·6H₂O and NH₄F in the precursor solution gradually increases,needle-like CoP structure will turn into needle-flake heterostructure,and the deposition amount of CoP increases.The complex permittivity of CoP@Al₂O₃ increases with the increasing CoCl₂·6H₂O and NH₄F concentration in the precursor solution,which is mainly due to the increasing absorbent content,the enhancement of interfacial polarization and dipole polarization,and the formation of three-dimensional conductive network.When the concentration of CoCl₂·6H₂O and NH₄F in the precursor solution are 0.04 mol/L,and the sample thickness is 4.0 mm,the CoP@Al₂O₃ has the positive absorption performance.Its minimum reflection loss is-64.57 dB at 9.57 GHz,and its effective absorption bandwidth(RL<-10 dB)is 3.21 GHz.Fe³⁺and Co²⁺were introduced into porous Al₂O₃ matrix by one-step hydrothermal method to prepare Fe_xCo_yP supported on porous Al₂O₃ nanostructures(Fe_xCo_yP@Al₂O₃).When the FeCl₃·6H₂O concentration increases and the CoCl₂·6H₂O concentration decreases,the deposition amount of the Fe_xCo_yP will become more uniform and the needle-like structure will gradually become the flake-like structure,and the absorbent deposition amount will increase first and then decrease.Fe₂Co₂P@Al₂O₃ have the highest complex permittivity,the real and imaginary part are 6.56-6.16 and 5.84-3.42,respectively.Fe₃Co₁P@Al₂O₃ have the minimum complex permeability,the mean values of the real and imaginary parts are 1.05 and 0.008,respectively.When the sample thickness is 2.6 mm,the Fe₁Co₃P@Al₂O₃ has the positive microwave absorption performance.Its minimum reflection loss is-26.19 dB at 12.4 GHz,and its effective absorption bandwidth is 2.77 GHz at 9.63-12.4 GHz.FeP/CoP supported on porous Al₂O₃ nanostructures(FeP/CoP@Al₂O₃)prepared by two-step hydrothermal method consists of needle-like CoP and flake-like FeP.The deposition amount of FeP increases with the increase of FeCl₃·6H₂O concentration,but the FeP has the same morphology.The complex permittivity of FeP/CoP@Al₂O₃ increases with the increasing FeCl₃·6H₂O concentration in the precursor solution.When the concentration of CoCl₂·6H₂O and FeCl₃·6H₂O in the precursor solution are 0.04 mol/L and 0.03 mol/L,respectively,the FeP/CoP@Al₂O₃ has the best absorption performance.Its minimum reflection loss is-55.21 dB at 11.69 GHz,and its effective absorption bandwidth is 2.41 GHz at 9.99-12.4 GHz.CoP/PCNSs supported on porous Al₂O₃ nanostructures(CoP/PCNSs@Al₂O₃)were prepared by using glucose as porous carbon nanosheets(PCNSs)source and CoCl₂·6H₂O as Co²⁺source.When the concentration of CoCl₂·6H₂O in the precursor solution gradually increases,the deposition amount of CoP in CoP/PCNSs@Al₂O₃ gradually increases,and the heterostructures of porous carbon nanosheets/CoP increase.In addition,the morphology of CoP changes from needle-like to needle-flake heterostructures.The complex permittivity and the imaginary part of complex permeability of CoP/PCNSs@Al₂O₃ increase with the increase of CoCl₂·6H₂O concentration in precursor solution,but the real part of complex permeability shows an opposite trend.When the sample thickness is 3.2 mm,the concentrations of glucose and CoCl₂·6H₂O in the precursor solution are 0.03 mol/L and 0.04 mol/L,respectively,the effective absorption bandwidth of CoP/PCNSs@Al₂O₃ is 3.15 GHz at 8.94-12.19 GHz.