Apple And Fluid Coke Derived Porous Carbon Based Materials And Their Electromagnetic Absorption Performance

By affecting the life of large-scale equipment,accurate operation of precision instruments,etc.,electromagnetic interference problems have been seen everywhere in the industrial and commercial fields.Electromagnetic radiation can weaken the biological immune system,break DNA strands and promote cancers,representing severe threats to human health.In order to solve the above electromagnetic problems,it is necessary to develop and apply high-performance EM wave absorbing materials.The porous material derived from natural products have been widely used as their unique structure and performance.Porous materials also have great research potential for the preparation of lightweight absorbers.At present,only a few studies have been reported.The apple fruit was taken as the research object,and the porous Si C material resembling the porous structure of apple was prepared by chemical vapor deposition.By selecting a biomass material with a porous structure,and adjusting the process in order to acquire the right material and component,a new high-performance EM wave-absorbing material with a natural porous structure of the biomass material and artificially imparted characteristics was prepared.The prepared porous Si C maintained the same cellular,interconnected porous structure of the apple.The formation process and influencing factors of Si C were studied,and the in-situ growth of secondary Si C in the system was analyzed by controlling the chemical environment.Using thermodynamic and kinetic simulations and theoretical calculations,the mass transfer process at the atomic scale was studied and the correctness of the proposed growth mechanism was verified.The binary Si C material with stacking fault structure prepared at a mass ratio of Si: C of 6: 1 has a significantly better wave-absorbing performance than other Si C materials.The maximum reflection loss value of porous Si C(Si: C=6: 1)is 48.8 d B,and the effective absorption band(RL>10 d B)is 14-18 GHz.This is because Si C absorbs electromagnetic waves through intrinsic dipole-orientation polarization,and the stacking structure of binary Si C produces electron loss and interfacial polarization that can dissipate electromagnetic waves under the influence of an applied electromagnetic field,thereby enhancing the wave-absorbing performance.Comparing the wave-absorbing properties of the waveguide and coaxial samples,it was found that the open-cell structure in which the remains of the apple are connected can reflect and scatter the incident electromagnetic waves multiple times,making it difficult for the electromagnetic wave to “escape the system” and enhance impedance matching.At the same time,in the process of multiple reflections and scattering,the electromagnetic wave can be better absorbed by the Si C component of the porous skeleton,further enhancing the wave absorbing performance.After conclusion was drawn that the porous structure can effectively enhance the microwave absorbing properties,in order to further study the effect of the porous structure on the microwave absorbing properties,a fluidized coke with a particle size of 150-212 ?m was selected as the research object,and the chemical activation method was used in situ.Porous coke materials were made with different pore structures and the products have onion-like layered structures.The influence of different pore structure on electromagnetic parameters and absorbing properties of materials was studied.By adjusting the pore structure of the porous material,the complex permittivity(increase and decrease)can be effectively adjusted,the impedance matching degree and attenuation performance of the material can be improved,and the wave absorbing performance can be enhanced.When the alkali to coke ratio is 3.5:1,the maximum reflection loss of the porous carbon material derived from fluid coke is 20 d B,and the effective absorption frequency band is 4.8-18 GHz.Using the porous carbon material made from the fluid coke with controllable porous structure as the porous skeleton,and a C/Ni composite that is a composite of a dielectric material and a magnetic material as the skeleton material,the coupling of a dielectric material and a magnetic material was achieved.The effects of porous carbon sources with different pore structures and different additions of Ni on the microwave absorption properties were investigated.The intrinsic relationship of component content and microstructure with dielectric and magnetic properties was established.The effect of structure and composition on the microwave absorbing properties was investigated and the mechanism of microwave absorption was revealed.Uniform loads can be achieved in both AFC-2.5 and AFC-3.5 when the amount of Ni introduced is appropriate.In the AFC-2.5 and AFC-3.5,the amount of Ni introduced is 5% and 10%,respectively,the morphology is the best,and there is a uniform Ni load on the surface of the carbon sphere and inside the pore structure.When the amount of Ni introduction is too much,clusters of Ni would appear and detach from the carbon matrix.Under the condition of ensuring the load morphology,the more the amount of Ni introduced,the higher the interface content of carbon and nickel.Under the effect of external electromagnetic field,the electric dipole moment relaxation phenomenon and effect in the composite made the real part and the imaginary part of the dielectric constant increase,and enhanced material's ability to store and dissipate electromagnetic waves,and it ultimately acts to enhance the electromagnetic wave absorption performance.Our results have revealed a coupling effect between dielectric materials and magnetic materials,a synergistic effect of dielectric loss and magnetic loss,relaxation of electric dipole moment polarization of C/Ni composite layers,multiple reflections of porous structures to regulate electromagnetic parameters,and increase of specific surface area.Under the joint action of these mechanisms,the maximum reflection loss of AFC-3.5-10 % Ni is 47 d B,the absorption performance in the 3.5-18 GHz band is greater than 10 d B,and the effective absorption band width is 14.5 GHz.