Preparation,Structures And Properties Of Hierarchical Carbon Foam Material

Carbon foam is a kind of interconnect three-dimensional porous carbon material with excellent properties such as light weight,corrosion resistance,high temperature resistance and low coefficient of thermal expansion,which makes carbon foams have a wide range of applications in aerospace,electronic device,catalyst carrier,electromagnetic shielding,structural engineering and other fields.Aiming at the problems generated from the production of carbon foam such as poor mechanical strength,high cost,complex technology,difficult moulding and other issues,epoxy-modified cyanate ester resins were used as precursor,nano-magnesia as pore-forming agent,then the hierarchical carbon foams were obtained by a series of heat treatment processes such as casting molding,atmospheric carbonization and so on.Furthermore,the structure and properties of the carbon foams were studied.The mechanism of hierarchical pore formation of nano-magnesia/epoxy modified cyanate ester resin mixture was studied by means of SEM,XRD,BET,electronic universal testing machine and four-probe resistivity tester.The results show that the formation of hierarchical structure of the porous carbon foam includes two stages:the epoxy modified cyanate ester resin firstly undergoes self-foaming at 300?700? to form a first-order pores under normal pressure,then nano-MgO reacts with matrix carbon to form secondary pores at the temperature of 1000-1800?.The structures and properties of hierarchical carbon foams with different nano-magnesia contents were investigated by SEM,XRD,electronic universal testing machine and four-probe resistivity tester.Results show that with the increase of nano-MgO content,the degree of graphitization of hierarchical carbon foam and the porosity increase,the volume density,electrical conductivity and compressive strength decrease,wheras the open porosity increases initially and then decrease.When the adding amount of nano-magnesia is 5%,the open porosity arrives at a maxium value of 77.6%.When the adding amount of nano-magnesia is 25%,the opening ratio is 70.3%and the porosity reaches 95.5%.When the addition amount of nano-MgO is 25%,the electrical conductivity and compressive strength reach the minmum values of 14.0S/cm and 0.81MPa,respectively.The effects of the structure and properties of surface-graphitized hierarchical carbon foam and its adsorption properties were investigated.The results show that the graphitization degree of the hierarchical carbon foam is obviously improved,as indicated by that its highest degree of graphitization reaches 23.2%.The mechanical properties and electrical properties of the surface-graphitized hierarchical carbon foams remain the same trend as hierarchical carbon foams,but the mechanical properties and electrical conductivity decrease.When the adding amount of nano-magnesia is 25%,the electrical conductivity and compressive strength of the surface-graphitized hierarchical carbon foam prepared reach the minimum values of 8.62S/cm and 0.51MPa,respectively.The results of adsorption tests show that surface-graphitized hierarchical carbon foams have superior hydrophobicity and excellent oil absorption with adsorption capacity of 7.0?12g/g,and therefore can be used for selective adsorption of oil from oil-water mixed solution.