Controllable Preparation,Electromagnetic Wave Absorption Mechanism And Performance Of Magnetic Cu-based Composites

With the upgrading of electronic information technology,electromagnetic（EM）wave technology has been widely used in all fields,such as our production,life,agriculture,industry,and military.It not only threatens human health,but also affects the normal operation of electronic equipment.So,it is necessary to synthesize excellent EM wave absorbing materials.Cu fibers belong to the dielectric loss-type EM wave absorbers with the advantages of low percolation threshold,high conductivity,high abundance,and low cost,but the disadvantages of high reflection and poor environmental resistance limits its practical applications.Hence,combining it with magnetic metal（Co,Ni）can endow the material with good conductivity,high saturation magnetization,and strong magnetic anisotropy.The enhancement of oriented polarization,interfacial polarization,and dipole/defect polarization can be achieved by designing one-dimensional core-shell nanotubes and hollow nano-flowers/spheres heterostructures as absorbers,which can easily form local conductive network and large specific surface area（multiple scattering effect）.Eventually,the superior EM wave absorbing materials were synthesized.The specific studies are as follows:1.Controllable preparation of Cux Ni1-x/Ni core-shell composites with broadband and strong microwave absorptionUsing hydrazine hydrate as reducing agent,Na OH as alkali,ethylenediamine（EDA）as the crystal surface selective promoter in the system,a one-step liquid phase reduction-oxidation method is adopted to synthesize the hollow Cu_xNi_1-x/Ni microspheres and nanotubes with adjustable composition and structure.By changing the reaction temperature,time,stirring speed,gas flow rate,reactant concentration,and Cu²⁺/Ni²⁺molar ratio to control the content of Cu and Ni,morphology,and structure of the magnetic hollow micro/nanomaterials,the diameter of the nanotubes is 0.1～2μm,the length is 2～12μm,and the wall thickness is 10～140 nm;the diameter of the microsphere is 0.2～5μm,and the wall thickness is 10～180 nm.Among them,Cu_xNi_1-x/Ni nanotubes and hybrid hollow structures reach the maximum RL values of-64.69 and-38.46 d B,respectively,and the wide band（RL（?）-20 d B）is 7.0 and 10.58 GHz,respectively,corresponding to 2.1～3.3 and 1.7～4.4mm thickness value.Its superior electromagnetic wave absorption performance is due to the one-dimensional,hollow and core-shell structures,which produce the multi-polarization,natural resonance,exchange resonance,high attenuation,and proper impedance matching.2.Controllable preparation of Co1-x Cux hollow microspheres and broadband microwave absorptionThe Co1-x Cu_x hollow microspheres were prepared by a simple one-pot hydrothermal reduction method,with a diameter ranging from 5～10μm.The reaction temperature,time,surfactant ratio,and the feeding ratio of copper salt to cobalt salt were used to control the content of Cu and Co in the product,morphology,and structure of the magnetic hollow microspheres.With the increase of reaction temperature,the product subsequently was assembled into urchin-like Co_1-xCu_xsuperstructures（0.5～1.0μm in diameter）and further into hollow microspheres driven by the minimization surface free energy;as the reaction time increases,due to the deposition of Co on the surface of the Cu core,the peak intensity of the Co in the product is gradually increasing.The saturation magnetization of the product also shows a decreasing trend with the increase of Cu²⁺in the feed ratio.When the molar content of Cu is 1.2%,the maximum absorption bandwidth of the hollow microspheres is 9.68 GHz（RL≤-10 d B）,its maximum reflectivity at 15.87 GHz is-37.94 d B,and the sample matching thickness is only 1.3 mm.The synthesized hollow nanospheres have excellent microwave absorption properties,and this experiment provide a simple,controllable,and low-cost method for preparing heterogeneous hollow nanospheres.3.Controllable preparation of two-dimensional C/Cu Ni composites and microwave absorption propertiesUsing oleic acid as the carbon source and sodium sulfate as the sacrificial template,a two-dimensional C/Cu Ni composites was synthesized through a one-step self-assembly.The composition,structure,and properties of the products were adjusted by changing Cu²⁺/Ni²⁺ratios and the calcination temperature.The products were characterized by XRD,EDX,XPS,SEM and Raman spectroscopy.As the calcination temperature increases,the contents of Ni and Cu increase and the carbon content gradually decrease in the two-dimensional C/Cu Ni nanocrystalline structure.shows an increasing trend because high temperature helps carbonization.As the Cu²⁺/Ni²⁺ratio increases,the size of the nanocrystals gradually increases.C/Cu Ni composites formed at 600℃with Cu²⁺/Ni²⁺=1:3 ehxibit the superior EM wave absorption properties.The absorption bandwidth is 9.68 GHz（RL≤-10 d B）at a sample thickness of 2.1 mm and a filling ratio of 25%corresponding to the maximal RL value of-49.99 d B at 6.08 GHz.