Preparation And Microwave Absorption Properties Of Embedded Nickel (iron) Carbon Nano-onions

Carbon nano-onion(CNOs),as one of the allotropes of carbon,is a concentric,multilayer fullerene with sp~2 hybridization on the surface,and the interlayer distance of CNOs is usually 0.334 nm.It has attracted extensive attention because of its unique curved graphite layer structure,which is conducive to the absorption and dissipation of electromagnetic waves.In this paper,Ni-core CNOs(Ni@CNOs),hollow CNOs(HCNOs),Fe-core CNOs(Fe@CNOs)were synthesized by arc discharge method.The graphitization degree of three kinds CNOs was increased by high temperature annealing,and amorphous carbon and graphite flakes were removed by air burning,and excess catalyst was removed by acidification washing.The morphology of carbon nanoonion was observed by SEM and TEM.The nickel core and iron core of carbon nanoonion were both core-shell structure,while the hollow carbon nanoonion was hollow inside.XRD,Raman,TGA and other tests further confirmed its structure.We conduct the test about microwave absorbing properties of the carbon nano onions/paraffin compounds by using the vector network analyzer.The three-dimension porous structure,thick carbon shell and large number of defects endow Ni-cored carbon onions with a lot polarization centers that can stimulate multiple dielectric resonances,leading to wide response frequency bandwidth and multiple strong microwave absorption features.It was evidenced that the bandwidths over-10 d B were from 3.4 to 18.0 GHz when the thickness of samples ranged from 1.5 to 5.0 mm,especially the bandwidth of above-10 d B is 13.5?18 GHz for the thickness of 1.5 mm.Due to the lack of metal atoms inside the hollow carbon nanoonions,the magnetic loss caused by ferromagnetic resonance was reduced,which resulted in the weaker wave absorption performance of the hollow carbon nanoonions than the nickel core carbon nanoonions.The iron-core carbon nanoonion has fewer crystal defects and less polarization center because of the higher graphitization degree,which leads to its poorer wave absorption performance than the nickel-core carbon nanoonion.