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Mesophase pitch-based large-diameter fibers were used to prepare unidirectional carbon/carbon (C/C) composite blocks, and mesophase pitch incorporated by various carbonaceous fillers was selected as a modified binder. The C/C composites were produced through a hot-pressing method, followed by carbonization and graphitization treatments. The influence of the carbonaceous fillers on the microstructure and physical properties of the C/C composites in different directions was investigated. The results show that both filler type and volume fraction have an important effect on the directional thermal conductivity of resulting composites. The through-thickness thermal conductivity of composites is significantly improved to be as high as 40–60 W/m K due to the incorporation of some carbonaceous dopants, which can tune their thermal conduction performance in different directions and thus solve the limitation of one-directional high thermal conduction. A three-dimensional carbon-based conductive network is diagramed to illustrate the thermal conduction mechanism of various carbon materials. The reinforcing effect on the directional thermal conductivity depends on the geometrical and physical characteristics, volume fractions and spatially distributed status of carbonaceous fillers. The flexural strengths of the composites are obviously improved owing to the decrease in porosity in the composites and the enhanced interfacial interaction between the carbon fibers and pitch-derived carbon matrix by doping with natural graphite flakes or carbon nanotubes. [ABSTRACT FROM AUTHOR]

One-dimensional (1-D) and two-dimensional (2-D) mesophase pitch-based graphite fiber (MPGF)/acrylonitrile butadiene styrene (ABS) resin composites were prepared from unidirectionally arranged MPGF/ABS resin laminae by a hot-press method. The morphologies, optical texture and crystal structure of the MPGFs and their ABS resin composites were investigated. The influence of the volume fraction, diameter and graphitization temperature of the MPGFs and the composite architecture on the thermal properties of the composites was discussed. The thermal diffusivity and thermal conductivity of the resultant composites parallel to the longitudinal fiber direction increase markedly with the volume fraction, diameter and graphitization temperature of the fibers. The 1-D composite with a fiber volume fraction of 62% possesses a bulk density of 1.64 g/cm 3 and shows a high thermal diffusivity of 372 mm 2 /s and a high thermal conductivity of 518 W/m K parallel to the longitudinal fiber direction at room temperature. The corresponding axial thermal conductivity of the fibers, graphitized at 2900 °C with a diameter of 50–55 μm, is estimated to be 825 W/m K. The 2-D composite filled with a high (54%) volume fraction of MPGFs also exhibits a high thermal conductivity in two directions (parallel to the longitudinal directions of the incorporated fibers). [ABSTRACT FROM AUTHOR]

Ribbon-shaped carbon fibers have been prepared from mesophase pitch by melt-spinning, oxidative stabilization and further heat treatment. The internal graphitic layers of ribbon-shaped carbon fibers graphitized at 2800°C show a highly preferred orientation along the longitudinal direction. Parallel stretched and unidirectional arranged ribbon-shaped carbon fibers treated at about 450°C were sprayed with a mesophase pitch powder grout, and then hot-pressed at 500°C and subsequently carbonized and graphitized at various temperatures to produce one-dimensional carbon/carbon (C/C) composite blocks. The shape and microstructural orientation of ribbon fibers have been maintained in the process of hot-pressing and subsequent heat treatments and the main planes of the ribbon fibers are orderly accumulated along the hot-pressing direction. Microstructural analyses indicate that the C/C composite blocks have a typical structural anisotropy derived from the unidirectional arrangement of the highly oriented wide ribbon-shaped fibers in the composite block. The thermal conductivities of the C/C composites along the longitudinal direction of ribbon fibers increase with heat-treatment temperatures. The longitudinal thermal conductivity and thermal diffusivity at room temperature of the C/C composite blocks graphitized at 3100°C are 896W/mK and 642mm2/s, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Graphite blocks were prepared from natural graphite (NG) flake and mesophase pitch powder by a hot-pressing technique at a relatively low temperature (500°C). The effect of pitch binder content and heat-treatment temperature on the physical properties of the graphite blocks was investigated. X-ray analyses indicate that the graphite block has a highly preferred structural orientation, and field emission scanning electron microscopy and polarized light microscopy observations further prove that the graphitic layers of the graphite flakes are clearly oriented perpendicular to the hot-pressing direction. Graphitized blocks prepared from 86wt.% NG and 14wt.% mesophase pitch have a low electrical resistivity of 1.45μΩm and a high thermal conductivity of 522W/mK, as well as a high thermal diffusivity of 396mm2/s in the direction perpendicular to the hot-pressing direction at room temperature. [Copyright &y& Elsevier]