Study On Catalytic Graphitization Of Carbon Materials

Carbon materials have a series of comprehensive performances, such as low density, resistance to heat and chemical corrosion, good electronic conductivity and thermal conductivity, high strength, high modulus, good anti-friction and anti-radiation and so on. The graphitization of carbon materials is one of the most important factors to their properties. The thermodynamically unstable carbon is transformed into graphite structure by graphitizing. However, the graphitization of carbon needs high temperature treatment. In order to accelerate the degree of graphitization and reduce the temperature of graphitization, some organic or inorganic chemical additives were used to enhance the graphitization of carbon materials. This phenomenon is called catalytic graphitization. In this thesis, the effects of some new catalysts and dispersion methods of catalysts in carbon materials on the catalytic graphitization of PAN-based carbon fibers and C/C composites, and the change of the properties of carbon materials after high temperature treatment have been studied. The main points are summarized as follows:(1) A facile alternate electrolysis in B(OH)3 and NiCl2 aqueous solution was used to improve catalytic graphitization of PAN-based carbon fibers. On the one hand, the boric acid used as electrolyte brings a mild experimental condition. On the other hand, the alternate electrolysis has been employed to destroy the texture of the PAN-based carbon fibers and to impregnate synchronously catalysts into the matrix of carbon fibers. The changes of morphology and structure of fibers were characterized by scanning electron microscopy (SEM) and x-ray diffraction (XRD). The results indicate that the graphitization of the fibers is improved obviously after the fibers were treated in above electrolyte solution and heat treated at 2400℃for lh. The graphitization degree of the PAN-based carbon fibers is about 85% and Lc is about 150 A.(2) The influence of the graphitization degree and residual catalysts on the properties of C/C composites:PAN-based C/C composites were prepared by hot pressing method with the raw materials of furan resin containing 4 wt.% yttrium catalyst and PAN-based carbon fibers treated by nitric acid. The properties of C/C composites at different heat treatment temperatures were investigated. The degree of graphitization of C/C composites was characterized by XRD, and the mechanical and electrical properties of C/C composites were investigated by Electronic Universal Testing Machine and the Four-Point Probes, respectively. The results show that yttrium plays a significant role in promoting the graphitization degree of C/C composites. With the increase of heat treatment temperature, the resistivity of C/C composites decreases gradually and the conductivity is proportional to the graphitization degree. However, the compressive strength reduces, and the residual catalysts have a obviously adverse effect on the mechanical properties of C/C composites.(3) Study on the preparation and properties of G/C composites:Graphene/carbon (G/C) composites were prepared in 1.5cm diameter tube with the raw materials of graphite oxide and furan resin. The influence of graphite oxide on the graphitization degree, the mechanical and electrical properties of G/C composites were investigated. The structure change of G/C composites was characterized by XRD, and the mechanical and electrical properties of G/C composites were evaluated by Electronic Universal Testing Machine and the Four-Point Probes, respectively. The results indicate that the graphitization of G/C composites is effectively accelerated by the graphene. Because of the excellent mechanical and electrical properties of grahene, the electronic conductivity and compressive strength of G/C composites are improved obviously, which is favorable for the further application of G/C composites followed heat treatment.