Studies On Catalytic Graphitization Of Carbon Materials

Carbon materials have attracted tremendous attention due to their high strength, high modulus, resistance of heat and chemical corrosion, anti-friction, low-electronic resistivity, anti-radiation, thermal conductivity, shock absorption and noise reduction, etc. They are widely used in different fields, such as aerospace, defense industry and other advanced fields, also used in high-level sports recreation supplies, medical equipments, machinery, transportation and other civilian industry. In generally, the graphitization of carbon materials is one of the most important factors to their properties. However, the graphitization of carbon need high temperature treated. In order to decrease energy waste and accelerate the degree of graphitization of non-graphitizable carbon, some organic or inorganic chemical additives are used to accelerate the graphitization of carbon, which called catalytic graphitization. Therefore, the catalyzed graphitization is the key point of carbon material research. In this dissertation, the effects of some new catalysts and dispersion method of catalysts in carbon materials on the catalytic graphitization of phenolic resin carbon and PAN-based carbon fibers have been studied. The details are summarized as follows:(1) The catalytic graphitization of PAN-based carbon fibers by Mo-B catalysts:a sol-gel synthesis method was used to modify Mo-B catalysts on the surface of PAN-based carbon fibers, which can instead of electroless/electronic plating due to its simplicity for operator, uniform dispersion, control of ingredient and good catalytic effect. The effects of the Mo, B and Mo-B on the graphitization of PAN-based carbon fibers were investigated. The as-treated carbon fibers were then graphitized at 2400℃for 2h. The structural changes were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM) and high-resolution transmission electronic microscope (HRTEM). The research showed that the catalytic effect of Mo-B was better than single Mo or B. The results indicated that much better graphitization could be achieved in the presence of 9.31wt.% Mo-4.64wt.% B, with an interlayer spacing (doo2) of 0.3358 nm and a crystalline size (Lc) of 28 nm.(2) The catalytic graphitization of phenolic resin by Fe-Ni catalysts in an externally magnetic field:the mechanical and electrical properties of carbon materials are determined not only the degree of the graphitization of the carbon materials but also orientation of hexagonal carbon layers. The Fe and Ni doped phenolic resin was first carbonized and then graphitized at different temperatures. Both the carbonization and graphitization were carried out in an externally magnetic field. The externally applied magnetic field was found to promote the graphitization and to improve the orientation of the hexagonal carbon layers. In the presence of Fe-Ni, a high degree of graphitization could be achieved by applying a magnetic field. This resulted in a d002 of 0.3355 nm and full-width at half maximum (FWHM) value of 0.103°after a 1200℃heat treatment. In comparison, the absence of a magnetic field resulted in a d002 of 0.3358 nm and FWHM of 0.305°.(3) The catalytic graphitization and performances of PAN/phenolic resin-based C/C composites by Fe-Ni catalysts in an externally magnetic field: previous studies (2) have shown that an externally applied magnetic field can not only promote the graphitization but also improve the orientation of the hexagonal carbon layers. Polyacrylonitrile (PAN)/phenolic resin-based C/C composites were carbonized and then graphitized in an externally magnetic field with Fe/Ni as catalysts. By using the PAN-based carbon fibers as reinforcements, we can therefore investigate the effect of the direction of the external applied magnetic field on the properties of the graphitized C/C composites. The results indicated that the electrical resistivity evidently decreased with increase of the graphitization of C/C composites. And then, the electrical resistivity of C/C composites had obviously differences in the different magnetic field directions, the graphitized C/C composites had a lower electrical resistivity in the parallel direction than the perpendicular direction of magnetic field. However, it was found that the higher graphitization was unfavorable to the compression strength of the C/C composites.