Preparation Of Mesophase Pitch-based Complex Carbon Foam And Electromagnetic Shielding Performance

With the rapid development of the electronics industry,the electronic components used in electronic equipment generate a large amount of electromagnetic radiation,which narrows the sensitivity of the electronic equipment and harms human health.For this reason,the use of electromagnetic shielding materials for electromagnetic shielding is a part of the effective ways.Metallic materials are widely used electromagnetic shielding materials.However,metal has the disadvantages of heavyweight and easy corrosion.Therefore,it is vital to seek electromagnetic shielding materials with lightweight,corrosion resistance,low cost and broadband.Carbon foam has the characteristics of lightweight,stable chemical properties,and electrical and thermal conductivity of carbon materials.At the same time,the cell structure of carbon foam has the characteristics of controllable,which gives carbon foam the potential as an electromagnetic shielding material.Therefore,electromagnetic shielding performance of carbon foam has been most valued by researchers at home and abroad in recent years.However,the influence of the pore structure of the carbon foam on the electromagnetic shielding effectiveness of the carbon foam has not meant clearly explained.The improvement of the electromagnetic shielding effectiveness based on the improvement of the electrical conductivity or magnetic permeability of the carbon foam,and the adjustment of the dielectric and magnetic properties is noted in the initial stage.In this thesis,mesophase pitch-based carbon foam(MPCF)is prepared by high-pressure nitriding carbonization method with mesophase pitch as the raw material,and then mesophase pitch and Fe₃O₄,MWCNTs and Fe₃O₄&MWCNTs mixture materials are used as precursors,and the high-pressure nitriding carbonization method is also used to prepare mesophase pitch-based carbon foam(MPCF).Three kinds of composite carbon foams(Fe₃O₄/MPCF,MWCNTs/MPCF,Fe₃O₄/MWCNTs/MPCF),study the electromagnetic shielding performance of the four carbon foams,and analyze their electromagnetic shielding mechanism.Specific research content and the main results are as following:(1)The mesophase pitch-based carbon foam(MPCF)was prepared,and the impact of the pore structure of MPCF on the electromagnetic shielding performance was studied,and the electromagnetic shielding mechanism was discussed.The research results demonstrate that a high cell density provides more interfaces for the reflection of electromagnetic waves,so the electromagnetic shielding effectiveness of carbon foam decreases with the increase in cell density.When the cell density is the highest(6.05×10⁹cell/cm³),the conductivity and total shielding effectiveness of the carbon foam achieve the maximum values(77.5S/m and 17.18d B,respectively).At this time,the absorption loss accounts for 77%of the total loss,indicating that the electromagnetic shielding mechanism of carbon foam is mainly absorption loss.(2)Electromagnetic shielding performance of Fe₃O₄/MPCF composite carbon foam was studied,and the electromagnetic shielding mechanism was analyzed.The results of the study show that with the increase of nano-Fe₃O₄,the number of cells in the carbon foam increases,and the total shielding effectiveness gradually increases.The electromagnetic energy absorption loss accounts for the proportion of the aggregate loss slightly.Mainly loss.When the addition amount of nano-Fe₃O₄is7wt%,the highest shielding efficiency reaches 25.09d B.When the addition amount of nano-Fe₃O₄exceeds 7wt%,the electromagnetic shielding efficiency is not greatly improved significantly,but the cell density and compressive strength are slightly reduced.`(3)Prepared MWCNTs/MPCF composite carbon foam,studied its electromagnetic shielding performance,and analyzed the electromagnetic shielding mechanism.With the increase of MWCNTs addition,the cell density,electrical conductivity and compressive strength of composite carbon foam show a trend of first stepping up and then decreasing.The total electromagnetic shielding effectiveness of composite carbon foam increases with the addition of MWCNTs.When the addition amount of MWCNTs is 2.1wt%,the total electromagnetic shielding effectiveness reaches 31.21d B,and the proportion of electromagnetic energy absorption loss to the total loss also shows a gradually increasing trend,reaching a maximum of 92%.Studies have found that the addition of MWCNTs dramatically reduces the skin depth of electromagnetic waves,which is the main cause for the increase in electromagnetic energy absorption.(4)Study the electromagnetic shielding performance of Fe₃O₄/MWCNTs/MPCF composite carbon foam,and analyses the electromagnetic shielding mechanism.The mass ratio of Fe₃O₄and MWCNTs is 4:1.With the increase of Fe₃O₄/MWCNTs addition,the cell density,compressive strength,electrical conductivity,total shielding efficiency,and wave absorbing efficiency of the composite carbon foam show a trend of first increasing and then decreasing.When the addition of Fe₃O₄/MWCNTs is2.8wt%,the above properties all have an inflection point,the total electromagnetic shielding efficiency is as high as 36.7d B,and the absorption loss accounts for 95%of the total electromagnetic loss.It is shown that the mass ratio of Fe₃O₄and MWCNTs is more appropriate,and the dielectric properties and permeability are better matched.The better matching lead to the minimum skin depth(0.76mm),so the electromagnetic shielding is mainly based on absorption loss.