Preparation Of High Thermal Conductive Carbon Materials And Study Of Their Heat Transport Mechanisms

Carbon materials have already been promising candidates for heat sink, due to its low density, high specific strength, high modulus, low thermal expansion coefficient, high thermal shock resistance, high heat stability, high corrosion resistance and high thermal conductivity. In this paper, micro carbon materials were prepared by using natural graphite flakes, graphite nanoplatelets and graphene sheets as the thermal conductive components, respectively. The relationship between chemical composition, microstructure and thermal conductivity of the resultant materials were researched systemically, and the corresponding heat transfer model was established. The research content of this paper is as following:Graphite flakes/C composites with high thermal conductivity were fabricated from natural graphite flakes and spinning pitch by a hot-pressing technique at 500? and 10 MPa, followed by carbonization and graphitization. The X-ray pole figure measurements show that the orientation degree of graphitized composite is higher than that of hot-pressed and carbonized composite and presents a descending tendency from 74.4% to 71.2% with the content of pitch increasing. An increasing tendency of the average crystallite diameter (La), crystallite stack height (Lc) and degree of graphitization (g) and the apparent density can also be observed. The in-plane thermal conductivity of graphitized composite could achieve a maximum value of 485W/m K with a through-out thermal conductivity of 15±3W/m K.The graphite nanoplatelets/C composites were fabricated from graphite nanoplatelets and spinning pitch by a hot-pressing technique at 600? and 23 MPa, followed by carbonization and graphitization. The orientation degree of (002) plane, La and g of the graphitized composites all show a declined trend with the content of pitch increasing. The sheets have an anisotropic structure, and the in-plane thermal conductivity of graphitized composites can achieve a maximum value of 405W/m K, with a through-out thermal conductivity of 1.0±0.3W/mK.Stable reduced graphene oxide aqueous dispersions were synthesized from graphene oxide suspensions with hydrazine as reducing agent via microwave-hydrothermal process in ammonia solution. The HNGO films were obtained by vacuum filtration of above dispersions. The C/O atomic ratio and orientation degree of (002) plane of HNGO films all increase with the increasing of hydrazine dosage. The in-plane thermal conductivity of the films can achieve a maximum value of 1056W/m K. The HNGO film was further thermally reduced by a hot-pressing technique. The reduction degree, orientation degree and La of the as-obtained film all have a significant increase by hot-pressing. The in-plane thermal conductivity can achieve 1839 W/mK.