Preparation And Electromagnetic Properties Of Resin Based Magnetic Carbon Materials

With the widespread application of electronic products and electrical equipment,electromagnetic radiation pollution has increased,resulting in severe consequences.In addition to water and air pollution,electromagnetic radiation pollution has become a new type of environmental pollution.Society demands effective electromagnetic wave(EMW)absorbers that are lightweight,with a broad absorption band and strong absorption,to solve excessive electromagnetic radiation.In this paper,phenolic resin and melamine resin are used as carbon-based precursors,which are combined with magnetic materials.Three magnetic carbon foam EMW absorbing materials are obtained by in-situ carbonization.(1)Phenolic resin based magnetic carbon foamPhenolic resin and iron acetylacetonate-N-N dimethylacetamide(Fe(acac)₃-DMF)solution are polymerized in situ,then foamed,and then carbonized in situ to obtain phenolic resin-based magnetic carbon foams(MCFs).The effects of Fe(acac)₃-DMF addition and foaming pressure on the EMW absorption capacity of the MCFs were studied.The results show that the MCF-3obtained with 0.12 g/m L Fe(acac)₃ and under a controlled pressure of 0.4 MPa possesses has the strongest EMW absorption capacity.The minimum reflection loss(RL_min)value of MCF-3 is-54.02 d B and the ef effective absorbing bandwidth is 14.04 GHz when the matching frequency is 8.92 GHz and the matching thickness is 3.05 mm.In addition,MCF-3 can effectively absorbing EMWs from C-band to Ku-band by simply adjusting the thickness of the absorbers.The superior absorption behavior is proved to be attributed to the MWS polarization between the different multiphases along with the residual loss.Besides,the multiple reflections and scatterings inside the macroporous structures of MCFs increase the path of EMW propagation,being beneficial to the attenuation of EMW.(2)Nitrogen doped phenolic resin based magnetic carbon foamRhodamine B(Rh B)is adsorbed on the phenolic resin-based magnetic adsorption carbon foam,and then carbonized in situ to obtain nitrogen-doped phenolic resin-based magnetic carbon foams(N-MCFs).The results shows that N-MCF-2 with Rh B adsorption time of 2 min has the strongest EMW absorption capacity.N-MCF-2 possesses a lowest RL_minvalue of-60.46 d B with a matching thickness is only 1.70 mm,and the corresponding effective bandwidth is 14.29 GHz and 13.79 GHz for-10 d B and-20 d B,respectively.Nitrogen doping causes defect polarization and dipole polarization effects,leading to increased dielectric loss.N-doping induces both defect polarization and dipole polarization effects,resulting in the enhancement of dielectric loss Additionally,the distorted skeletons caused by N-doping induce distortion of the graphite lattice and change of local density of the carbon atomic state,increasing the magnetic moment of the material.(3)Melamine based magnetic carbon foamHerein,melamine resin based magnetic carbon foam(MCMF)was fabricated via impregnating polymerized melamine formaldehyde(MF)foams in Fe₃O₄nanoparticle solution,followed by in situ pyrolysis.The results shows that MCMF was proved to possess a solid 3D-foam architecture consisting of interconnected cells and smooth skeletons,with graphitic C₃N₄/carbon and CFe_15.1.?-Fe,Fe₃O₄and Fe₃C formed on the skeleton surface.The EMW absorption capacity of MCMF is better than the that of carbonized MF foam without Fe₃O₄(CMF),possessing excellent absorption behavior,with a minimum RL value of-47.38 d B and a matching thickness as thin as 3.90 mm.The corresponding effective absorbing bandwidth is as broad as13.32 GHz.MWS polarization and residual loss are beneficial to EMW absorption.MWS polarization and the residual loss were proved to be beneficial for EMW absorption capacity.Besides,graphitic/C₃N₄enriches the interface polarization effect and the electromagnetic matching effect.The microporous structures are beneficial for increasing EMW propagation,resulting in internal multiple reflections and scatterings,which are also beneficial for EMW attenuation.