Synthesis And Electromagnetic Wave Absorption Properties Of Urchin-like Carbon-Coated Cobalt-Nickel Alloy

Rapid development of information communication equipment and sophisticated electronics leads to ubiquitous electromagnetic wave radiation problem,which increasingly brings serious harm to human heaths.Therefore,it is particularly important to explore high-performance absorbers to convert the electromagnetic wave energy into other form energy with little harm to human.Due to the high saturation magnetization and the high Snoek limit in the GHz range,metallic soft magnetic materials such as iron,cobalt,nickel and their alloy particles exhibited much desirable EMW absorption capacities than other non-magnetic metallic materials.On the other hand,carbon materials,especially graphene,have become a research hotspot in the field of electromagnetic wave absorption due to their advantages such as low density,high chemical stability,high electrical conductivity,and adjustable dielectric constant.In this paper,urchin-like carbon-coated cobalt-nickel alloy materials(CoNi@NC) and related materials were obtained by simple solvothermal method,wet chemical method,and subsequent annealing treatment.The absorbing performance of this material as an electromagnetic wave absorber and the mechanism of electromagnetic wave loss are studied in detail.The research contents are as follows:1.A simple preparation method was used to coat the nitrogen-containing carbon source on the urchin-like cobalt-nickel precursor,the Nitrogen-doped-carbon-coated cobalt-nickel alloy material was then formed by annealing at 700?.The prepared CoNi@NC material inherited the urchin-like microstructure intact.Co@NC and CoNi materials were also prepared as a control group,and the corresponding structural characterization and phase analysis were performed.Through microscopic characterization,it is known that the length of the nano-needles on the surface of the urchin-like structure is about 2.5?m and the diameter is about 60-70 nm.The particle diameter of the inner cobalt-nickel alloy particles ranges from 12 to 38 nm,and the coated graphene is about 7 layer,forming the core-shell structure.2.CoNi@NC,Co@NC and CoNi materials were made into absorbing performance test samples.Their electromagnetic parameters were measured in the frequency range of 2-18GHz,and their reflections loss(R_L)values under different thicknesses were calculated.The results show that the electromagnetic wave absorption performance of the CoNi@NC sample is better than other samples.Compared with the magnetic metal/carbon composite materials in other literatures,the electromagnetic wave absorption performance of the CoNi@NC sample prepared in this paper is more competitive,shows potential application prospects in the field of electromagnetic wave absorption.3.The electromagnetic wave absorption and loss mechanism of CoNi@NC samples were studied by exploring reflection loss(two-dimensional and three-dimensional),impedance matching,complex permittivity,complex permeability,Cole-Cole semicircle,eddy current loss and attenuation coefficient.The analysis shows that the CoNi@NC sample has more dielectric loss mechanisms,and its magnetic loss mechanism is dominated by exchange resonance In addition,the sample's"antenna-like"nanoneedle array on the surface of the unique urchin-like structure can effectively capture incident electromagnetic waves,greatly improving the multiple reflection and scattering times of electromagnetic waves inside the material,and enhancing the electromagnetic wave attenuation ability.