Preparation And Electromagnetic Wave Absorbing Performance Of Porous Carbon Materials

In recent years,with the rapid development of electronics industries,electronic and electrical equipment has been widely used in the daily life,which facilitate our life as well as bring us problems,such as electromagnetic radiation and interference.At the same time,in the military field,it is urgently necessary to develop electromagnetic?EM?wave stealth technology as the development of radar detection technology.In face of increasingly harsh environmental conditions,the existing materials can't meet the demand.However,the design of porous carbon?PC?materials become a new idea to fabricate the EM wave absorber materials,as their advantages of lightweight and high efficiency to EM wave absorption.Therefore,it is very significance to develop porous carbon materials as a new kind of “lightweight,thin thickness,broadband absorption,strong loss” EM wave absorber materials.As for porous carbon materials,the microstructure of carbon can affect its absorbing performance.Carbon generally exist in form of amorphous and crystalline structure in carbon materials.The crystalline carbon with graphite structure has good conductivity,and the content of graphite in carbon-based material has great influence on its absorbing properties.Fristly,graphite nanosheets?GNS?was incorperated into the PI?ODA/PMDA type?by in-situ polymerization,and FeCl₃ was added as a magnetic particle source and an agent to regulate the pore size,and a series of porous carbon/GNS/ferromagnetic nanoparticles composite absorbent?PC/GNS/Fe?was obtained.The morphology of the porous structure was adjusted through the additive amount of FeCl₃,and the pore size decreases with the increase of additive amount.The degree of graphitization of the materialswas adjusted by the additive amount of GNS.At the low GNS loading,GNS was well dispersion in the matrix,and the dielectric loss of the materials improved significantly as the addition of GNS.With the increase of the additive amount,GNS tended to reunion in the matrix.Due to the skin effect,the dielectric loss of the material can't improve steadily.At 0.2 wt.% FeCl₃ and 0.5 wt.% GNS loading,the material showedthe best EM wave absorption performance.At a thickness of 2.6 mm,an optimal RL of-36.5 dB?>99.9% attenuation?is observed at 8 GHz,which indicated its strong absorption characteristics.Moreover,at a thickness of 1.4 mm,the effective absorption bandwidth?RL?-10 dB?was up to 3.6 GHz?14.4¹8 GHz?,which shown broadband absorption characteristics.Thus,the increase of the crystallinity of the carbon can improve the dielectric loss of the material.And by regulating the pore size and the crystallinity of the carbon,the EM wave absorbing properties of the material can be optimized.To prepare porous carbon materials,polymer materials are a kind of ideal carbon sources to made controllable porous carbon materials.However,the key is to protect the porous structure of the polymer materials from collapse during the carbonation process.A diamine monomer containing thiazole structure was designed and synthesized.And benzothiazole moieties were incorporated into the polyimide?PI?backbone by polymerization.The benzothiazole moieties in the main chain enhance the rigidity of the polymer chain,and the electron-withdrawing effect of the thiazole groups reduce the stability of imide structure in the PI.Therefore,the glass transition temperature?Tg,404 ?,DMA?of the PI was higher than its initial thermal decomposition temperature?390 ?,DTG?.By a facile and handy liquid-liquid phase separation method,the porous polyimide membrane with “honeycomb-like” porous structure was prepared.After carbonization,the morphology of the pores was kept,and the pore size averages 280 nm.Furthermore,the porous carbon was modified by Fe₃O₄ nanoparticles by a chemical coprecipitation method.And a porous carbon/Fe₃O₄ nanoparticles composite absorbent?PC/Fe₃O₄?was obtained.With a thickness of 5.5 mm,an optimal RL of-20.1 dB?>99% attenuation?is observed at 12.7 GHz.Moreover,with the thickness from 1.3 to 5.5 mm,the minimum RL curves in Ku band are all lower than-10 dB?>90% attenuation?.Therefore,it is a promising carbon source to make the porous carbon materials facilely and controllably.