Study Of Preparation And Thermal Property Of Three Dimensional Graphene Based Nanocomposites

Electronic devices keep rapid development toward miniaturization and intelligent direction.Its working power density is increasing thus the temperature goes up rapidly due to the thermal energy generation.The temperature rising,of cause,results in lowering reliablity of electronic devices.How to decrease the device temperature effectively is critical in order to ensure that the electric devices are working in good oder.However,the traditional thermal spreading materials could not meet this demand.Graphene,as a newly found material with two dimensional structrue,has the thermal conductivity of 5300W/(m.K),the highest value amongh the materials found so far.Although graphene possesses such excellent thermal properties,it is difficult to use it in real application because the graphene size is too small(the thickness is only 0.34 nm and the in-plane size is at mirometer level)to manipulate.Assembling the graphenes into macroscopic architectures is an effective and feasible route to commercialize graphene in industry.In recent years,macroscopic graphene film is a milestone during the graphene macroscopic architecture assembling process.The in-plane thermal conductivity of graphene film has reached above 2000/(m?K)at room temperature,which is very useful to spread the thermal energy of low powe W r chips.However,the graphene film could not meet the requirement of high power denstiy chips because the heat flux is too limited when the film thickness is only around 5-10 micrometer.In order to address this problem,the graphene architechure must be dramatically thickened,e.g.centimeter level.Here,we propose a new approach to fabricate graphene nanocomposite bulk with milimeter or centimeter in thickness by introducing copper nanowire and silver particle seperately.Morever,the thermal conductivity is still remaining high.That is to stay,the thermal conductivity is independent of thicnkness,quite different from reported graphene film.Our graphene bulk must be great potential in electric devices fields.We introduce copper nanowire into graphene matrix to form copper-graphene nanocomposite by hot pressing nanocomposite sponges which were fabricated by liquid mixing and rapid freezing technique.The copper nanowire in nanocomposite act as adhesive and filler in order to ensure high density.The density of threedimensional nanocomposite reach about 90% of theoretical density.X-ray diffraction patterns indicate that graphene and copper are well crystallized.The raman spectroscopy show that the graphene structure in nanocomposite does not change any more in comparison with original graphene powder.At the same time,the graphenes are orderly alligned along in-plane direction.The bending strength of nanocomposite is around 80 MPa.The electrical conductivity of composites gradually increases as the copper wire fraction increases,which is up to 3.9×105S/m.The in-plane thermal conductivity at room temperature of nanocomposite is as high as 688 W/(m?K),much higher than reported result(80W/m?K).The silver-graphene nanocomposites were fabricated by the same route as copper-graphene nanocomposite where the silver particles in nanocomposite act as adhesive and filler in order to ensure high density.The density of composite can reach more than 90% of the theoretical density because of bonding and filling of silver particles.X-ray diffraction patterns indicate that graphene and silver are well crystallized.Microstructure results show that the graphene still keeps few-layered structure and silver is randomly distributed in graphene matrix.At the same time,the graphenes are orderly alligned along in-plane direction.The thermal analysis confirms that the threee-dimensional nanocomposites has excellent thermal stability.The bending strength of nanocomposite is around 46 MPa.The electrical conductivity of nanocomposites increases as silver particle content increases,and it is up to 2.1×105S/m when the silver content is 20% in mass.The in-plane thermal conductivity at room temperature of nanocomposite is as high as 820W/(m?K),one order higher than reported result(80W/m?K).This is attributed to the graphene orderly allignment and high density.