| With the continuous development of electronic technology and communication industry,various communication and electronic equipment have spread to millions of households,and the 5G era is coming.Although it enriches our daily lives,it also brings a worsening electromagnetic environment.This not only affects the normal operation of the device,but also causes harm to our body,and is the main cause of diseases such as cardiovascular disease and cancer mutation.Therefore,more and more attention has been paid to efficient electromagnetic wave absorbing materials.So far,many excellent absorbing materials have played an important role in many fields such as aviation,communication and electronic technology.Among many absorbing materials,nano-materials have better comprehensive properties due to their light weight,unique nano-effects and structure.After a lot of research,ferromagnetic metal materials(Fe,Co,Ni)and their alloys as traditional magnetic microwave absorbing materials have the advantages of low cost,good flexibility and easy processing,but they also often have poor impedance matching performance and density.Defects such as large absorption band,narrow absorption band,thick matching thickness and poor weather resistance make it increasingly difficult to meet the requirements of "lightweight,strong absorption,wide absorption band,thin matching thickness,excellent weather resistance" emphasized by modern absorbing materials,so Multicomponent composites have attracted much attention.According to research,the embedding of dielectric materials to form a core-shell structure can effectively improve many disadvantages of traditional magnetic materials.This thesis focuses on the preparation of core-shell wave-absorbing materials coated with carbon material coated nickel submicron spheres and cobalt-nickel submicron spheres.The preparation process,structure design and mechanism of wave absorbing are discussed.The main research work and conclusions obtained in this thesis are as follows:(1)First,a simple solvothermal method was used to synthesize nickel submicron spheres.The nickel submicron spheres were coated with phenolic resin,and then calcined in a tube furnace to obtain core-shell Ni@C submicron spheres.Flexible composite materials are obtained by compounding Ni,Ni@C submicron spheres and PVDF.The dielectric constant and magnetic permeability at various filling amounts in the range of 2-18 GHz were measured by the coaxial method,thereby obtaining relevant reflection loss values.We explore the influence of the unique core-shell structure after carbon coating on the absorption performance;explore the effect of adjusting the different coating and sintering conditions on the material’s dielectric parameters and absorbing properties..After adjustment,when the carbonization condition is 850 ℃,for 3 h,the thickness of the carbon shell is 64.3 nm and the filling amount is only 20 wt%,the minimum reflection loss of Ni@C/PVDF composite material can reach-71.32 at 14.04 GHz dB,effective bandwidth(RL≤-10 dB)reaches 5.62 GHz with a thickness of 1.95 mm.(2)Ni/RGO composite absorbing material was obtained by one-step solvothermal method through reduction of nickel salt and graphene oxide by sodium hypophosphite,and performance testing was performed by compounding it with PVDF.After a lot of research,reduced graphene oxide(RGO)prepared by the redox method has a large number of defects and residual functional groups that reduce the conductivity of graphene.At the same time,the appearance of these defects and functional groups can be used as the center of polarization,which is conducive to electromagnetic waves.Absorption and attenuation.In addition,the RGO-based composite has a threedimensional layered structure,is easy to realize electron transmission,and has strong polarization loss.In this experiment,RGO was coated on magnetic nickel submicron spheres to form a unique core-shell structure.It was conducted by conductance loss,dipole polarization,interface polarization,eddy current loss,and interference cancellation caused by multiple reflections.Excellent electromagnetic absorption performance in coordination with various electromagnetic wave absorption mechanisms.(3)In order to verify that the carbon-coated core-shell structure improves the absorbing performance of ferromagnetic metals,in this experiment,CoNi alloy spheres were prepared by a solvothermal method,and CoNi submicron spheres were coated with a phenolic resin.Shell CoNi@C submicron sphere.CoNi@C submicron spheres were compounded with PVDF by thermal volatilization and hot-pressing method,and the dielectric constant and permeability at various filling amounts in the range of 2-18 GHz were measured by the coaxial method,thereby obtaining relevant reflection loss values.By comparison,the carbon-coated core-shell structure enhances the absorption intensity,widens the absorption width,and optimizes the absorption performance. |
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