Preparation Of Graphene Microspheres Supported Magnetic Nanocomposite Particles And Its Microwave Absorbing Properties

With the rapid development of communication technology and radar technology.electromagnetic wave interference and electromagnetic pollution has become more and more serious.Absorbing materials can not only eliminate or reduce electromagnetic interference and reduce electromagnetic leakage,but also effectively reduce target radar reflection,so they play an important role in the development of stealth technology.Graphene has the advantages of excellent conductivity,thermal conductivity,mechanical properties,low density and high specific surface area,ao it is a potential ideal absorbing material.However,two-dimensional graphene has poor impedance matching characteristics and is prone to surface/surface aggregation,which makes it difficult to effectively exert its wave-absorbing potential.Based on this,this paper uses two-dimensional graphene self-assembly to construct a three-dimensional magnetic graphene hollow microsphere absorbing structure,hoping to provide a new idea for the application of two-dimensional graphene.In this paper,three kinds of graphene hollow microspheres（GHMs@FeCo,GHMs@CoNi and GHMs@FeNi3/NiFe2O4）loaded with different magnetic nanocomposite particles were successfully prepared by using water-in-oil emulsification technology and high-temperature calcination.XRD.Raman.XPS,SEM,TEM,EDS,VSM and vector network analyzers were used to in-depth study the phase structure,surface chemical composition,microstructure morphology.element distribution,magnetic response characteristic and electromagnetic parameters of the magnetic graphene hollow microspheres,respectively.The electromagnetic parameters of hollow microspheres were used to calculate the reflection loss value within 1-18 GHz with different matching thicknesses,and their respective absorption mechanisms are analyzed.The research results show that the three prepared graphene hollow microspheres loaded with different magnetic nanocomposite particles have excellent microwave absorbing properties.Among them,GHMs@FeCo has a minimum reflection loss value of-73.47 dB at a frequency of 13.75 GHz with a matching thickness of 2.4 mm,and an effective absorption bandwidth of 7.23 GHz;by adjusting the spherical wall thickness and Fe/Co atomic ratio in GHMs@FexCoy,the best absorbing performance was obtained.GHMs@CoNi has a minimum reflection loss value of-56.16 dB at a frequency of 13.67 GHz with a matching thickness of 2.55 mm;when the matching thickness is 2.4 mm,the widest effective absorption bandwidth reaches 8.65 GHz;and the matching thickness is between 2.1-3.2 mm,its effective absorption bandwidth can reach above 6.0 GHz.GHMs@FeNi3/NiFe2O4 has a minimum reflection loss value of-58.96 dB at a frequency of 14.43 GHz with a matching thickness of 2.25 mm;when the matching thickness is 2.4 mm,the widest effective absorption bandwidth reaches 7.31 GHz;and the matching thickness is between 2.2-2.6 mm,its effective absorption bandwidth can reach above 6.0 GHz.Magnetic graphene hollow microspheres have multiple loss mechanisms for electromagnetic waves,including the interfacial polarization between graphene and magnetic nanocomposite particles and between composite particles and composite particles,and the electronic polarization of magnetic nanocomposite particles;strong dielectric loss composed of Debye dipole relaxation,polarization caused by graphene residual functional groups and defects,Maxwell-Wagner relaxation and other;and the strong magnetic loss caused by natural resonance and exchange resonance.The synergistic effect between the dielectric loss and the magnetic loss is beneficial to enhance the microwave absorbing performance of the magnetic graphene hollow microspheres.