Preparation Of Carbon-based Thermal Conductive Fillers Doped 1D C/C Composites With High Thermal Conductivity

With the rapid development of the aviation and space industry,more urgent requirements for heat dispersing materials are suggested to overcome the bottleneck of thermal issue,Owing to its high thermal conductivity,low density,low heat expansion coefficient and chemical stability etc,1-dimension(1D)carbon/carbon(C/C)composites has attracted great attention in recent years.However,the highly anisotropy and lower mechanical properties the 1D C/C composites with high thermal conductivity limits their applications.Therefore,it is of great value and significancein improving the thermal conductivity perpendicular to the longitudinal direction of fiber of the 1D C/C composites.Using mesophase pitch-based carbon fibers(MPCF)with lager diameter of40?50?m as conductive phase and mesophase pitch added with a certain sized fillers(short graphite fiber,natural flake graphite,multi-walled carbon nanotubes)as a binder,1D C/C composites were prepared by a hot-pressing method at 500 ~oC,subsequent carbonization and graphitization treatments.The morphology and microstructure of the samples were characterized.The influence of adding fillers on the thermal conductivity of the composites in various directions was investigated.The results show as follows:1.With the increase of the heat treatment temperature,the thermal diffusivity and the thermal conductivity of the 1D C/C composites along the longitudinal direction of carbon fiber continuously increases.After graphitized at 3000 ~oC,the thermal diffusivity and the thermal conductivity along the fiber's longitudinal direction of the 1D C/C composites reach 650.5 mm~2/s and 800.1 W/(m·K)respectively.The thermal conductivity perpendicular to side plane and main surface direction are 25.4 W/(m·K)and 27.6 W/(m·K).And the flexural strength of that composites perpendicular to the longitudinal direction of fiber reaches 72.9 MPa.2.The pores of material increase with addition of short graphite fiber,With the adding amount increasing of short graphite fiber,the density,the flexural strength and the thermal conductivity of the 1D C/C composites along the longitudinal direction of carbon fiber decrease.and the thermal conductivity of the composites perpendicular to the longitudinal direction of fiber increases and then deceases.In comparison with 1D C/C composites without addition,the thermal diffusivity of the 1D C/C composite doped with 6vol.%short carbon fiber perpendicular to side plane and main surface direction reaches to 52.2 mm~2/s and 49.7 mm~2/s.and its flexural strength and thermal diffusivity along longitudinal direction drop to 61.0 MPa and 430.7 mm~2/s respectively.3.The bulk density of C/C composites doped with natural flake graphite does not show obvious difference.However,the doping of natural flake graphite obvious changes the thermal conductivity of the composites in different directions.With the increase of the doping content and the particle size of natural flake graphite,the thermal diffusivity of the 1D C/C composites along the longitudinal direction of carbon fiber decreases,on the contrary,their thermal diffusivity perpendicular to fiber's longitudinal direction shows an upward trend.In comparison with 650.5 mm~2/s of thermal diffusivity along the axial direction of carbon fiber of undoped 1D C/C composite,the C/C composite doped with 16vol.%natural flake graphite with a particle size of 60?m,decreases about 21%to 510.9 mm~2/s,And its thermal diffusivity perpendicular to side plane and main surface direction increase about 98%and 118%to 41.1 mm~2/s and 48.9mm~2/s,respectively.The doping of natural flake graphite in 1D C/C composite significantly increases the flexural strength perpendicular to fiber's longitudinal direction of the composites to 94.0 MPa.4.A certain content of multi-walled carbon nanotubes were also added into the mesophase pitch binder to improve the physical properties of 1D C/C composites.The results indicate that both the room-temperature thermal diffusivity and the flexural strength of the composites perpendicular to the longitudinal direction of fiber firstly increass and then decease.For the 1D C/C composites filled with 3vol.%carbon nanotubes,its thermal diffusivity perpendicular to side plane and main surface direction increases about 92%and 66%to 36.7 mm~2/s and 40.1 mm~2/s,respectively,and its flexural strength increases 56%to 113.4 MPa.