Synthesis And Microwave Absorption Performance Of Magnetic Particles@Nitrogen Doped Carbon Nanotube

Recently,with the rapid development of industrial technology,all kinds of radio communication equipment have been widely used in our daily life,bringing great convenience to our life,meanwhile,the application of electromagnetic wave is also a double-edged sword,bringing convenience but also electromagnetic leakage,electromagnetic radiation,electromagnetic interference and other problems.The application of absorbing materials is an effective means to solve the above negative electromagnetic effects.Therefore,the development of efficient absorbing materials has aroused great attention in the field of functional materials.Carbon nanotubes（CNTS）are considered as one of the most potential wave-absorbing materials due to their chemical stability,adjustable dielectric loss characteristics,and easy load magnetic materials.In this research,melamine with high nitrogen content was selected as the carbon source,and the composite material of carbon nanotubes and magnetic particles was synthesized by catalytic pyrolysis of magnetic metal.While synthesizing carbon nanotubes,N atom doping was realized.The effects of ferromagnetic metal composition,flow rate,heat treatment temperature and other processes on the growth of carbon nanotubes were systematically studied,and then the effects of nitrogen doped carbon nanotubes structure,magnetic metal composition,crystal phase and relative content on the absorption properties of composite materials were investigated.The specific content is as follows:Firstly,Fe/Fe₃C@carbon nanotube composite absorbing material with iron as magnetic component was prepared.During the experiment,it was found that Fe₃C,as an intermediate product in the growth process of carbon nanotubes,finally remained in the composite material.On the basis of the presence of Fe₃C without affecting magnetic loss,more heterogeneous interfaces could be introduced to enhance the dielectric loss of the composite material.In addition,nitrogen doping forms in carbon nanotubes include pyridine-N,pyrrorole-N and graphite-N.According to Debye’s polarization theory,the three doping forms are conducive to improving the dipole polarization ability of carbon nanotubes,and heteroatomic doping will introduce defects of carbon nanotubes,which will affect the electrical conductivity of carbon nanotubes.Thus,the minimum reflection loss(RL_min)of Fe/Fe₃C@NCNTs at 6.4GHz is-65.8 d B due to the synergistic effect of dielectric and magnetic losses of nitrogen doped carbon nanotubes and Fe/Fe₃C composites.In addition to pure metals,ferromagnetic metals also include binary and ternary alloys.The stability of binary and ternary ferromagnetic alloys is enhanced compared with that of pure ferromagnetic metals.Their specific magnetic anisotropy and natural resonance frequency determine their electromagnetic response characteristics.In this paper,Fe Co@NCNTs,FeNi@NCNTs and Fe Co Ni@NCNTs composites are further prepared,and the influence of ferromagnetic alloy composition on the electromagnetic properties of the composites is explored.It is found that Fe Co Ni@NCNTs has a good wave absorption when the filling rate is only 15%.When the minimum reflection loss is-22.3 d B at 4.56 GHz and the thickness is 1-5 mm,the effective bandwidth（RL≤-10 d B）can reach 13.92 GHz（4.08GHz-18 GHz）.