Preparation And Properties Of Carbon Microspheres/Iron-Cobalt Alloy/Cobalt Ferrite @ Hollow Microspheres Microwave Absorbing Materials

As the international situation is complex,it is urgent to enhance national defense and military strength.Environmental problems brought by electromagnetic technology are also increasingly prominent.Therefore,special materials,such as microwave absorbing materials,which can effectively reduce the harm of electromagnetic waves,have been paid attention by various countries,and it is of great significance to develop high-performance absorbing materials that can meet the requirements of current social development.Cobalt ferrite(CoFe₂O₄)is a kind of common absorbing material with low price and mature technology,but it has the disadvantages of high density and high resistivity.In this paper,considering the electromagnetic properties of hollow glass microspheres(HGMs),carbon microspheres(CMs)and Fe-Coalloy(Fe-Co),a series of appropriate methods were adopted to composite the above materials to achieve complementary advantages,and CMs/Fe-Co/CoFe₂O₄@HGMs composites were obtained.The phase,morphology,composition,thermal properties and microwave absorption properties of the composite powders were analyzed and characterized by XRD,SEM,Raman,DSC and vector network analyzer respectively.The main results are as follows:Firstly,a series of CoFe₂O₄@HGMs composite powders were prepared,and the influence of the mass ratio of CoFe₂O₄ and HGMs on the wave absorption performance of the composite powders was investigated.The results show that when the mass ratio of the two in the composite powder is appropriate,CoFe₂O₄ can be well coated on the surface of HGMs,and the dielectric loss of the material increases.When the mass ratio of the two is 2:1,the composite powder obtained has the best wave absorption performance.When the coating thickness is 2 mm,the reflectivity to electromagnetic wave is-3.78 dB near the frequency of 15.40 GHz.Its wave absorption performance is better than that of pure CoFe₂O₄ and powders obtained by simple mechanical mixing of the two.Secondly,CMs was introduced into CoFe₂O₄@HGMs composite powder by hydrothermal method to obtain CMs/CoFe₂O₄@HGMs composite material,and the influence of different hydrothermal temperature and glucose concentration on the wave absorption performance of composite powder was investigated.The results show that carbon microspheres cannot be obtained when the temperature or concentration is too low,and the electrical properties of the materials improve more obviously when the temperature or concentration is too high,but the impedance matching becomes worse.When the hydrothermal temperature is 160? and the glucose concentration is 0.2 mol/L,the composite powder has the best wave absorption performance.When the coating thickness is 2 mm,the reflectivity of the composite powder to the electromagnetic wave near the frequency of 18GHz is-4.25 dB.Finally,heat treatment of CMs/CoFe₂O₄@HGMs was carried out in nitrogen atmosphere,and the effects of different heat treatment processes on the phase and wave absorption properties of the composite powder were investigated.The results show that increasing the heat treatment temperature and prolonging the heat treatment time is beneficial to improving the dielectric properties of the materials,but only under the appropriate treatment conditions can we get good performance of the absorbing materials.When the heat treatment time is 2 h and the temperature is 600?,the CMs/Fe-Co/CoFe₂O₄@HGMs composite powder can be obtained.It has good electromagnetic properties and impedance matching,and has the strongest absorption ability to electromagnetic waves.When the coating thickness is 2mm,the reflectivity is-50.94 dB near the frequency of 10.96 GHz,less than-10 dB in the frequency range of 9.04 GHz to 13.68 GHz,and the bandwidth reaches 4.64 GHz.