Preparation Of Mesophase Pitch-based Carbon Foam And Its Properties

Carbon foams derived from mesophase pitch(CFDFMP)were firstly prepared by the researchers from the US Air Force Materials Laboratory in America.They developed a production process by applying a 'blowing' technique to mesophase pitches to form a carbon foam which had excellent mechanical property.Several years later,Klett et al.from Oak Ridge National Laboratory(ORNL)applied a method of self-foaming to prepare CFDFMP which had high thermal conductivety.The CFDFMP have many excellent properties such as low density,high thermal conductivity,good mechanical strength,resistance of thermal stress and shock.So they are supposed to be used in thermal conduction,porous electrodes,catalyst support,metal and gas filtration,frame materials and so on.Nowadays the CFDFMP have been widely researched as a focus in carbon materials.In this article,the author prepared carbon foams derived from AR mesophase pitch by self-foaming method.The microstructures were observed by scanning electron microscopy(SEM)and optical microscopy(OM).The properties such as bulk density,compressive strength and thermal conductivity and so on were measured.The influences of foaming process and high temperature treatment(HTT)were thoroughly investigated and the author applied chemical vapor deposition PyC and added B₄C grains in order to reinforce the carbon foams.The main research contents and results are as follows.(1)The properties of carbon foams increase with the increasing of foaming pressure.And the carbon foams with symmetrical pores and better properties are prepared by applying invariable pressure.(2)During the research,the carbon foams with better thermal property are prepared at the foaming temperature range from 410℃to 430℃or two hours.(3)The bulk density and compressive strength of carbon foams increase firstly and then fall but the thermal conductivity increase all along as the carbon foams experience the HTT from 850℃to 2500℃.(4)The compressive strength of carbon foams increase markedly after CVD PyC process:when the carbon foams of 0.149g·cm^-3bulk density and 0.66MPa compressive strength are treated by 10h and 70h CVD PyC process, two carbon foams with 0.196g·cm^-3bulk density,1.89MPa compressive strength,0.314W·m^-1·K^-1thermal conductivity and 0.461g·cm^-3bulk density, 11.93MPa compressive strength,1.581 W·m^-1·K^-1thermal conductivity respectively are got.(5)The ligaments of carbon foams widen and the cracks are healed up after CVD PyC process,so the compressive strength of carbon foams increase.There are no obvious interface between pitch carbon and pyrolysis carbon.But the orientation degree of carbon atoms' array in the two carbons is different.(6)The properties of carbon foams with 5～15%B₄C grains decrease due to more cracks appearing in the pore walls.