Preparation And Structural Properties Of C/C Composites Reinforced By High Thermal Conductivity Graphite Films

With the increase in many high power densityc omponents in the fields of aerospace,electronics and so on,a large amount of heat was accumulated,seriously restricting the miniaturization,integration and high-performance of these devices.The use of materials with high thermal conductivity(TC)have become a solution to these limitations.The high thermal conductivity C/C composites(HTC-C/Cs)not only possess low density,high specific strength,high specific modulus,but also have excellent thermal and electrical conductivity.It is the preferred material of communications satellite,aircraft brake pads,nozzle throat lining and other high heat production,but in urgent need of heat conduction components.The high thermal conductivity mesophase pitch-based carbon fiber,which has been mainly used to improve the thermal conductivity of HTC-C/Cs,has excellent thermal conductivity.However,there are disadvantages of mesophase pitch-based carbon fiber such as complicated preparation process,difficult weaving and high cost,which greatly limits the further development and application of HTC-C/Cs.In response to the above problems,this study use a new type of high thermal conductivity graphite material-artificial high thermal conductivity graphite films,which has appeared and developed rapidly in recent years,as a thermal conductivity reinforcement to prepare HTC-C/Cs.It is not only has a higher thermal conductivity than high thermal conductivity mesophase pitch-based carbon fibers,but also has a relatively lower cost and other advantages.Therefore,It undoubtedly plays an important role in improving the thermal conductivity and cost saving of C/C composites with HTC graphite films as the reinforcement.A liquid-phase impregnation-carbonization method of preparing C/C composites(HTC-C/Cs)with HTC graphite films as the reinforcement and impregnated pitch as the matrix is introduced in this study.Firstly,The effect of graphite films volume fraction on the properties of the prepared materials was discussed.The results show that:1)The volume fraction of graphite film also has a great influence on the thermal conductivity of C/C composites.As the volume fraction of graphite films increases,the TG of the material increases gradually,and the flexural strength gradually decreases;2)The resistivity of the prepared material gradually decreases with the increase of the volume fraction of the graphite film,which is in inverse relationship with the increase of the TG of the materials;3)The TG of C/C composites reinforced by graphite fills has anisotropy,and its TG along the graphite films is 8 times than that of vertical to the graphite films;.4)The high thermal conductivity graphite films reinforced C/C composites with the 48%volume fraction of graphite films,CPI of six times and graphitized at 2800°C has the highest TG along the graphite films which is up to 371.2 W · m-1 · K-1.Next,the effects of carbonization/precursor impregnation(CPI)times and high-temperature graphitization on the microstructure,thermal conductivity and bending strength of C/C composites with 50%volume fraction of graphite films were also studied.The results show that:1)The carbonization/precursor impregnation(CPI)times has a great influence on the thermal conductivity?resistivity and bending strength of C/C composites.The TC along the graphite films and bending strength of HTC-C/Cs gradually increased with the increase of CPI times,but there is a tendency of a rapid increase in the initial period and a slow increase in the latter;2)The pitch matrix carbon filled between the graphite films present tropism structures along the surface of the graphite film in the prepared C/C composites,owing to the induction orientation of precursor pitch by graphite films;3)The crystallite size,graphitization degree and thermal conductivity of the graphitized C/C composite are greatly improved.The density,flexural strength and TC of the C/C composite with CPI of six times and treated at 2800 ? are 1.46 g·cm-3,15.19 Mpa and 367.3 W · m-1 · K-1,respectively.The C/C composites with CPI of six times and graphitized at 2800? have higher density and thermal conductivity(TC),which are 1.46 g cm-3 and 367.3 W · m-1· K-1,respectively.At the same time,its flexural strength is 15.19 MPa.In addition,chemical vapor deposition of the prepared C/C composites was also performed in this study.It was found that some of the pores in the C/C composites were well filled,the density and bending strength of the materials were increased,and the surface of the prepared material was more smooth after the deposition of SiC.