Design And Preparation Of GNs/Magnetic Particle Composites And Microwave Absorbing Performance

With the rapid development of science and technology,various electronic and electrical equipment play a huge role in social production and daily life.However,the electromagnetic（EM）interference and pollution problems generated during the working process are becoming more and more serious,which has an adverse impact on the performance of electronic equipment,as well as the ecological environment and human health.Therefore,it is necessary to find high-performance EM absorption materials.Excellent EM absorbing materials should meet the"thin,strong,light and wide"goals of new absorbing materials.Aiming at the above goals,this work has carried out the research of carbon-based composite absorbing materials.On the basis of the dielectric loss of Graphene nanosheets（GNs）,the magnetic loss mechanism is added,and the composites obtains excellent wave absorbing performance.The magnetic Co-Ni alloy is grown on the surface of GNs,and the GNs/Co-Ni composites is obtained.In addition to effectively reducing the accumulation of GNs,it also improves the impedance matching ability of the composites through magnetic loss,and further optimizes the electromagnetic wave absorption performance.Since the electrode potential of Ni is higher than that of Co,Ni is easier to reduce than Co.In the process of depositing Co-Ni alloys,Ni preferentially nucleates,and Co particles are beneficial to the growth of alloy particles.Through the study of EM wave absorption performance,it is found that adjusting the composition of the alloy will affect the dielectric loss,magnetic loss and impedance matching of the composites.When the molar ratio of Co to Ni is 3:2,when the thickness is 2.6 mm,the excellent reflection loss（RL）value is-47.26 d B,and the effective absorption bandwidth（EAB）is 1.7 mm and the width is 3.71 GHz.On the basis of the dielectric loss of GNs,the dielectric and magnetic loss mechanisms are added,and the composites obtains excellent absorbing performance.The core shell structure is introduced to enhance the interface polarization dielectric loss.Through multiple loss mechanisms,a core shell GNs/Co@Co₃O₄ composites with excellent EM absorption performance under ultra-thin thickness is prepared,the shell thickness is about 25 nm,and the nucleus is about 100 nm.The core shell structure enhances the EM wave scattering of the composites,the dipole polarization at the defect site and the interface polarization at the core-shell interface,which further optimizes impedance matching.When the core shell structure is 1.6 mm ultra-thin,the excellent absorption performance is obtained,RL=-55.16 d B,and when the thickness is 1.2 mm,the EAB is 3.84 GHz.This ultra-thin thickness and excellent EM absorbing performance of the composites can meet the requirements of coating a variety of invisible materials on invisible aircraft.On the basis of the dielectric loss of GNs,the dielectric and magnetic loss mechanisms are added,and the composites obtains excellent absorbing performance.Introducing a petal structure with multiple pores and a large specific surface area,and through multiple loss mechanisms,the GNs/Co₃O₄ composites obtained is a light-weight absorbing material with a wide range of frequency bands.The GNs/ZIF-67 derivatives were prepared by the ZIF-67 template method.Then,the GNs/Co₃O₄ composites with hexagonal multi-layer flower-like structure is obtained through pyrolysis process.With the increase of pyrolysis temperature and time,the interlayer spacing of GNs/Co₃O₄composites become larger,and obtained the pore structure which can enhance the multiple scattering of EM wave.The unique microstructure helps to improve dielectric loss,magnetic loss,and optimize the impedance matching characteristics.When the pyrolysis temperature is 350℃,the time is 30 min,and the thickness is 3.4 mm,the excellent RL value-52.46 d B,corresponding to different thicknesses in different bands（S,C,X,Ku band）have EAB.The obtained GNs/Co₃O₄ composites has the advantages of light weight,wider absorption frequency band,and simple preparation process.On the basis of GNs dielectric loss,increase the dielectric and magnetic loss mechanism to obtain excellent absorbing performance.Introduce multi-layer,flower-like structure of Fe₃O₄-Mo S₂,introduce multiple loss mechanisms,improve impedance matching,and obtain GNs/Fe₃O₄-Mo S₂ composites with excellent EM absorption properties.The influence of Fe₃O₄ particle size and Mo S₂ flower-like structure on the EM wave absorbing performance of the composites was explored.The microstructure can achieve the purpose of controlling the wave absorbing performance of the composites.First,increase the EM wave absorption strength;second,broaden the EAB.When GNs/Fe₃O₄-2-Mo S₂ is 2.1 mm,when the frequency is at 10.8 GHz,the excellent absorption performance is obtained,RL=-55.96 d B,and the thickness is 1.5 mm,the EAB is 4.00 GHz.In the frequency range of 8.0-12.0 GHz,it has the potential to solve the short-range fire control radar stealth of warships.Based on the above analysis,it can be seen that GNs,as a dielectric material,introduces multiple loss mechanisms,which can effectively improve the dielectric loss,magnetic loss and impedance matching of composites.GNs/Co-Ni composites mainly absorb electromagnetic wave by adding magnetic loss;Shell GNs/Co@Co₃O₄ composites mainly absorbs EM wave by adding dielectric and magnetic loss;multi-petal GNs/Co₃O₄composites mainly absorbs EM wave by adding dielectric and magnetic loss;flower-shaped GNs/Fe₃O₄-Mo S₂ composites Adding dielectric and magnetic loss mainly absorbs EM wave.