Studies On Catalytic Graphitization Of Carbon Materials

Carbon fibers have a series of comprehensive performances, such as high strength, high modulus, resistance of heat and chemical corrosion, anti-friction, electronics conductivity, thermal conductivity, anti-radiation, a good damper, shock absorption, noise reduction, also are the ideal resistant ablation, the structural and functional composite material element; phenolic resin is easy for raw materials, low cost, heat-resistant, resistant to erosion, good technology, and is commonly used in composite material as a matrix resin. So they are widely used in aerospace, defense and military and other cutting-edge fields, also used in high-level sports recreation supplies, medical equipment, machinery, transportation and other civilian sectors. The performances of carbon material have great relations with crystal degree, microstructure, macrostructure and surface characteristics. Carbon can develop from disorder to order structure by heat treatment, but it needs high temperature. Appropriate adding some elements can effectively reduce the transition temperature(called catalytic graphitization). Catalytic graphitization can simplify the equipment and reduce energy requirements, so it has important practical significance and value. In this paper, catalytic graphitization of non-graphitizing carbon-PAN-based carbon fibers and phenolic resin and modifing carbon fibers by electroless plating methods have been studied. The details are as follows:(1) Catalytic graphitization of PAN-based carbon fibers in the presence of copper and boride: PAN-based carbon fibers, copper and boride were mixed by grinding method, then treated in graphitizing furnace at high temperature treatment (HTT). The changes of copper and boride and the influence of the content of catalyst and heat treatment temperature on graphitization degree were investigated by X-ray diffraction (XRD), Raman spectroscopy and SEM. The results show that the graphitization degree improve from 25.6% to 95.6% which imply binary catalyst system copper and boride can be more obviously increasing the graphitization degree of PAN-based carbon fibers power than copper or boride alone. Boron help improve the carbon fiber graphite crystal, reducing defects. After the formation of boron carbide, it help the copper to participate in catalytic role of graphitization. The main catalytic graphitization mechanism of copper and boron is the dissolution- precipitation mechanism, and the boron of carbide formation - decomposition mechanism at higher temperature. (2) Catalytic graphitization of phenolic resin by addition of copper and boride: Comparing the impact of adding catalysts way on graphitization, it was found that the grinding way of copper and boride had a better catalytic graphitization effect than the solution disperse way of catalysts into phenolic resin. The former, the graphitization degree reached up to 93%, and the interlayer spacing d002 reduced to 0.3360 nm, comparable of the graphite d002 of 0.3354 nm. While the latter, the graphitization degrees was only 66.6%, d002 was 0.3385 nm, and peaks of diffraction had poor symmetry. The former method is simple, the catalyst content and proportion can be precise control, and the most importance, has significant catalytic effect. Graphitization temperature plays a decisive role.Copper can change the orientation of the carbon arrangement in phenolic resin, boron can break the cross-linked carbon bond and eliminate carbon structural defects.So they improve the phenolic resin carbon development structure from random orientation to the order orientation of layers of graphite very well during the heat treatment process.(3) Catalytic graphitization of PAN-based carbon fiber by electroless plating Fe-Ni alloy: After removing filler, roughening, sensitization, activation and other pretreatments on the surface of carbon fibers, Fe-Ni alloy can be better deposition on the surface of carbon fibers and the effects of Fe-Ni alloy on the graphitization of PAN-based cabon fibers were investigated. Fe-Ni alloy has a good catalytic role on graphitization of PAN-based carbon fiber by the analysis of XRD and Raman. At the conditions of 1h electroless plating and 2400℃treatment, the ratio of I_D/I_G is 0.322, graphitization degree is 83.7% and the interlayer spacing d002 is 0.3368 nm.