Controlled Synthesis And Electromagnetic Wave Absorption Performance Of Magnetic Metal-Based Composites

Due to the increasing demand for military and commercial applications,tremendous effort has been focus on novel high-efficient electromagnetic wave(EMW)absorption materials with light weight,thin thickness,wide absorption frequency,high stability,strong absorption and good weather fastness characteristics.Among the candidates for EMW absorbers,magnetic metals(eg.Fe,Co,Ni and their alloys)have high high saturation magnetization values,and show obviours advantages in EMW strong absorption performance.However,magmetic metals have strong for its high conductivity,making high frequency permeability decreased distinctly,the absorption band of sole magnetic metal is narrow.The poor corrosion resistance and high density of magnetic metals restric its application in EMW absorption materials.To overcome these problems,such as alloying,or fabricating Yolk-Shell structure or heterostructure composites can be adopted.Herein,we prepared submicron ternary alloy and magnetic metal/carbon composites,then explore the role of composition,morphology,and structure in the EMW absorption performance.(1)U-channelled spherical Fex(CoyNii-y)100-x Janus colloidal particles have been prepared by confined liquid-solid redox reaction strategy.We investgate the effect of composition and morphology for their EMW absorption properties.The results indicate that all of noncentrosymmetric channelled spheres show excellent EMW absorption performances.In particular,the effective absorption(RL<-10 dB)bandwidth of Fei5(Co0.2Ni0.8)85 Janus particles can be reach 9.2 GHz with a thickness of 2 mm,and the strongest RL value is up to-36.9 dB with a thickness of 2.5 mm.Such performances are much better than that of centrosymmetric particles with a similar size and chemical composition.Due to the synergy effect of chemical compositions,the polycrystalline structure and their specific morphology,the loss capacity of EMW and impedance match are enhanced effectively.(2)The Yolk-Shell structured CoFe@C composites are successfully synthesized by high-temperature carbonization from the precursor of CoxFe3-xO4@PR,and study EMW absorber performance are depended on carbon shelles thicknesses,saturation magnetization and cavity structure.The results indictate that the low crystalline carbon shells possess high resistivity,suppress the skin effect,and the electromagnetic parameters can be adjusted by the change of carbon shell thickness.Furthermore,the cavity structure enhances the multiple scattering of EMW,and the impedance match of absorbers can be improved effectively.Fianally,the effective absorption(RL<-10 dB)bandwidth of obtained absorber can reach 8.4 GHz with the thickness of 1.5 mm,and the strongest RL value is up to-35.3 dB with a thickness of 2 mm.(3)We have prepared a series of Co,Co/RGO and Co/Co3O4/RGO samples through high temperature calcination of Co(CO3)0.5(OH)·0.11H20 and Co(Co3)0.5(OH)·0.11H2O/GO predecessors prepared by hydrothermal method,and study the effect of composition and heterostructure for EMW absorption properties.The results show that Co/RGO exhibit excellent EMW absorption properties.The effective absorption(RL<-10 dB)bandwidth of obtained absorber can reach 6.1 GHz with the thickness of 1.5 mm,and the strongest RL value is up to-40.5 dB with the same thickness.Due to the synergy effect of chemical compositions,the impedance match and loss capacity of absorbers are enhanced effectively.