Preparation And Microwave Absorption Performance Of Magnetic Composites Based On Mesoporous Carbon Microspheres

Microwave absorbing materials have been applied extensively in both military stealthy and electromagnetic wave shielding fields with the development of electronic technology.Therefore,it is imperative to develop microwave absorbing material with strong absorption,wide bandwidth and low density.In this paper,a series of microwave absorbing materials based on mesoporous carbon microspheres?MCMSs?were prepared and the related microwave loss mechanism were discussed.?1?MCMSs with fine particle size distribution between 1-10 ?m were prepared by spray-drying method.The BET area and total pore volume of MCMSs can reach 1218 m2/g and 2.5 cm3/g,respevtively.A maximum reflection loss of-12 dB is obtained at the matching thickness of 2 mm for MCMSs.The performance is limited for its weak impedance matching.?2?Fe₃O₄/MCMSs composites were prepared by a facile wet-impregnation method using MCMSs as carbon substrates to enhance the magnetic loss ability.The composites show good fluidity and low bulk density of 0.2-0.39 g/m3.The Fe₃O₄ nanoparticles with sizes between 9-14 nm are homogeneously confined in the mesoporous channels.The Fe₃O₄/MCMSs composites also have high BET surface areas of 266-735 m2/g.The composites exhibits a maximum reflection loss of-25 dB at 12.6 GHz and a broad bandwidth over 4.7 GHz.Such good microwave electromagnetic performances can be attributed to the synergistic effects of highly dispersed Fe₃O₄ nanoparticles and mesoporous channels.?3?To improve the absorbing properties at low frequency,NiFe2O4/MCMSs composites were prepared by co-precipitate method.A maximum reflection loss of-21 dB at 5.9 GHz and an absorption band of 2.1 GHz are obtained at the matching thickness of 5 mm.The absorption performance at low frequency is better than that of Fe₃O₄/MCMSs composites for its soft magnetic property and extremely low resonant frequency,which can lead to several resonant peaks at low frequency.?4?The optimum technical conditions of the pretreatment process and chemical nickel plating were explored.A homogenous nickel coating forms on the surface of MCMSs.The complex permittivity holds a high value before and after the chemical nickel plating process,while the magnetic loss increases significantly.The reflection losses at the thickness of 2-5 mm are all lower than-10 dB.A maximum reflection loss of-20 dB at 7.4 GHz and an absorption width of 2.0 GHz for the chemical nickel plating MCMSs are obtained at the matching thickness of 3 mm.The results indicate that the microwave absorbing performance can be improved significantly by chemical nickel plating.