Research On Graphene-based Nanocomposites For Electromagnetic Microwave Absorption Applications

Electromagnetic wave absorbing material not only has special strategic position in the military application,but also has increasingly used in the civil application.The application of conventional absorbing materials by adding to coatings results in a high mass fraction,up to 50-80%,which can not meet the requirements of absorbing coating in terms of thin,light,wide and strong.Graphene is characterized by its special two-dimensional sheet structure,high conductivity and thermal conductivity,high specific surface area,light weight,conducive to the absorption and attenuation of electromagnetic waves;these characteristics make it to be an important absorbing material.In particular,the surface of reduced graphene has oxygen-containing groups such as hydroxyl and carboxyl,and can generate defect polarization and electron dipole relaxation and the like.When used as an absorbing material,it contributes to dielectric loss and a small amount of magnetic loss.However,it is difficult for a single component absorber to meet both impedance matching and loss characteristics at the same time.Therefore,the preparation of graphene-based composite nanometer material absorber and its absorbing performance become an important direction of developing high performance absorbing materials.In this paper,CoFe₂O₄@RGO,Co3O₄,RGO,LSMO@RGO and MoS₂@RGO nanocomposites were prepared as absorbers respectively with RGO as matrix nanocomposite absorbing materials.The optimal composition and optimal preparation process of each system were determined.To obtain excellent absorbing properties the influence of ratio in the nanocomposites and the amount of nonacomposites addition on the absorption performance of coatings were studied.Moreover,,the loss mechanism of each graphene-based nanocomposite system was revealed,and the application prospect of each system was analyzed.CoFe₂O₄ nanoparticles were prepared by hydrothermal method.The effect of Co addition on the morphology of cobalt oxide was studied.CoFe₂O₄@RGO nanocomposite absorbing materials were prepared by blending and dispersing method.The effects of the addition amount on the absorption properties of electromagnetic waves were studied,and the best absorbing properties were obtained.In the CoFe₂O₄ and RGO mass ratio of one to one,the composite material is only 5%,the minimum reflectivity of-25.66 dB,the widest effective frequency band width of up to 7.17 GHz.The impedance matching and electromagnetic wave absorption mechanism of CoFe₂O₄@RGO composites were studied.The main loss mechanism was dielectric loss.Co3O₄ nanosheets were prepared by hydrothermal synthesis,and the preparation process was optimized.Co3O₄@RGO nanocomposite absorbing materials were prepared by blending and dispersing method.The influences of the ratio and the amount of addition on the absorbing properties of the system were studied.With the mass ratio of Co3O₄ and RGO was 1:1 and the addition of composite material was only 5%,the minimum reflectivity of-45.15 dB was achieved and the widest effective frequency band width was up to 7.14 GHz.The main loss mechanism was dielectric loss.La_0.7Sr_0.3MnO₃ powder was prepared by sol-gel self-combustion method,and the preparation process was optimized.LSMO@RGO nanocomposites were prepared by blending and dispersing method.The influence of the ratio and the amount of addition on the absorbing properties of the composites and the absorbing mechanism were studied.The impedance matching between the two materials was solved.The magnetic loss of La_0.7Sr_0.3MnO₃ is complementary to that of RGO dielectric loss.When the ratio of these two was 1:1 and the addition of LSMO@RGO nanocomposites was only 10%,the composites obtained the minimum reflectivity,-45.7 dB and the best effective absorption frequency band,7.31 GHz.MoS₂@RGO nanocomposites were prepared by blending and dispersing method.The influence of the electromagnetic property of MoS₂ as well as ratio and the amount of addition on the absorbing property of MoS₂@RGO nanocomposites system was studied.When the addition amount of RGO was 5%and MoS₂ was 10%,the minimum reflectivity of-26.7 dB and the widest bandwidth of 5.05 GHz were obtained.The main loss mechanism of MoS₂@RGO nanocomposites was dielectric loss.Finally,the electromagnetic properties and absorbing properties of each material system were compared and analyzed.The matching effect of graphene in the composites and the contribution to the loss mechanism were studied.The large size graphene-based nanometer composite absorbing coating was prepared and its absorbing performance was studied.