The Evolvement Rule Of Cross Structure Of PAN-Based Carbon Fiber Treated By High Temperature

The skin-core structure difference in strength carbon fiber was small, but large in high strength and high modulus carbon fiber. It was very important to research the evolution rule of the chemical structure in the radial and the mechanism under high-temperature treatment, especially the time effect and tension effect. It would provide profound guidance for preparing high modulus carbon fiber and the structure changes at high temperature.In this thesis, the main research objects were the T300 and GCF1 carbon fiber which were treated at 1500-2500℃. The evolvement rule of the cross-structure of PAN-based carbon fiber was studied from the evolvement of the composition, aggregation structure, chemical structure and microstructure of the fiber during high temperature treatment process. It was to reveal the evolution mechanism and the relationship between the evolvement rule of cross-structure and the initial composition and structure of carbon fiber.The results showed that:in the heat treatment process, due to uneven heat transfer and diffusion, the chemical structure, aggregate structure and microstructure of carbon fiber existed skin-core difference. With the heat treatment temperature increased, the skin-core structure difference was enlarged. The structure was gradient distributed along the radial. In the heat treatment process, the growth of the graphite crystallite size in the carbon fiber exhibited a temperature-driven self-assembly process. When the HTT below 1900℃, because of the removal of N elements consumed energy, the structure changed complex, the difference changed slightly. After it reached 1900℃, due to the rapid removal of N atoms of the core caused some defects, which would obstruct graphite C growing, the core R value decreased slowly, the radial difference gradually increased.Extended treatment time at 1500℃, the degree of graphitization of the radial difference was decreased, at 2100℃, the radial difference was increased. With the tension increasing at 2500℃, the fiber diameter and the graphitization degree of fiber increased. When the tension increased, the fiber skin-core difference in the degree of graphitization decreased, the radial difference was reduced.The initial difference in the radial structure of GCF1 carbon fiber was larger than T300. When the treatment temperature was below 1900 ℃, radial structure difference of GCF1 was larger than T300; when the treat temperature was above 1900℃, and the radial structure of both T300 and GCF1 were similar. Because of the radial graphitization degree difference of GCF1 was greater than T300, when treated at 1500℃, the radial graphitization degree difference was rapidly shrinking extended heat treatment time. But when treated at 2100℃, the cross-structure difference in T300 was larger because of the larger N content.Radial structure of carbon fiber and the mechanical properties were closely linked. When the radial graphitization degree difference was slight, we will get fibers with high Young's modulus and low tension strength. But when the structure difference was aggravated, the tension strength decreased rapidly and Young's modulus increased quickly.