Preparation Of Coal-based Carbon Foam And Its Electromagnetic Shielding Properties

With the popularization of communication equipment,more and more attention has been paid to save electromagnetic interference?EMI?.Researchers are competing to develop new EMI materials for easy corrosion and high specific weight of traditional metal materials.At present,carbon foam with light weight,high conductivity and adjustable pore structure is the preferred material to replace metal EMI materials.The electromagnetic interference shielding effectiveness?EMI SE?of graphene foams have been widely studied,and SE of pitch-based carbon foams has also been little investigated.However,EMI SE of coal-based carbon foam has not been presented up to now.Therefore,EMI SE of coal-based carbon foams and modified were tudied,which provides a data basis for promoting the application of coal-based carbon foam.In this work,we used vitrinite enrichment of the coal of Hongshan second mine as raw material to prepare coal-based carbon foam by high pressure permeability nitrogen.Carbon foams were modified with the nano-Fe₃O₄,conductive graphite and PAN carbon fiber as additives.The effect of pore cell structure of coal-based carbon foam and the amount of three additives on the total electromagnetic interference shielding effectiveness?SEtotal?were studied.The morphology of the pores of the carbon foam was observed by SEM,and the diameter and number of pores in the SEM photos were counted by the software Nano measurer 1.2 to obtain the average pore size,pore size distribution,and pore cell density.The electrical conductivity was tested by MS8050 multimeter,and the EMI SE was measured by N5234 A agilent vector network analyzer.The main results are summeried as follows:?1?As the foaming pressure increased,the cell density of carbon foam increases,the average pore diameter decreases,the pore size distribution becomes narrower and SE shows an increasing trend.When the foaming pressure is 8MPa,the1.48×1010cell/cm³ of the largest pore density,the 88.95?m of the smallest average pore sizes,and the narrowest pore size distribution are achieved,respectively.Moreover,SEtotal of the carbon foam up to 19 d B.And the electromagnetic absorption loss?SEA?of carbon foam accounts for 87.06% of SEtotal,which shows that coal based carbon foams are an EMI material with high SEA characteristics.?2?With the mass fraction of additive nano-Fe₃O₄ increased,the cell density first increased and then decreased,and the average pore diameter first decreased and then increased.Meanwhile,SE of coal-based carbon foam increases also.When the amount of nano-Fe₃O₄ is 2wt%,the minimum average pore size of 101.56?m,thenarrower pore size distribution and the pore density of 8.77×10⁹cell/cm³ are obtained.When the mass fraction of nano-Fe₃O₄ is 10wt%,EMI SE achieves 25.7d B,of which the SEA accounts for 81.04% of the SEtotal.?3?With the mass fraction of conductive graphite increased,the cell density of the carbon foams increases first and then decreases,and EMI SE increases gradually,too.When the amount of conductive graphite is 1wt%,the average cell diameter with the narrowest distribution and pore cell condensity reach to 121.68?m and 8.13×10⁹cell/cm³.When the amount of conductive graphite is 9wt%,the maximum SE is26.5d B,and SEA accounts for 86.86% of the SEtotal.?4?As the mass fraction of PAN-based carbon fiber increased,the cell density first increases and then decreases,the average pore diameter first to reduces and increase,and the SEtotal of coal-based carbon foams increase gradually.When the mass fraction is 1.5wt%,the pore cell density and average pore diameter achieve9.77×10⁹cell/cm³ and 100.22?m,respectively.When the mass fraction is 2.5wt%,the SE is optimally 30.5d B,and the SEA account is for 96.62% of the SEtotal.?5?In contrast,the SE of carbon foams modified by PAN-based carbon fiber is higher than that of modified carbon foams by nano-Fe₃O₄ and conductive graphite.Compared with green carbon foam?before carbonization?,the SE of carbon foam?after carbonization?increased significantly.