Microstructure and properties of PAN-based carbon fiber with different graphitization temperature (up to 3000 °C)

Understanding and regulating the graphitization process are critical to high-modulus carbon fiber production technologies. In this work, a series of high modulus polyacrylonitrile (PAN)-based carbon fibers (CFs) were prepared via the graphitization process at different temperatures up to 3000 degrees C in a continuous production line, and the evolution mechanism of the microstructures was investigated. The results showed that the primary reaction at the temperature of 2300-2600 degrees C is the condensation between graphite molecules, and over 2700 degrees C is mainly the growth and accumulating of crystallite. Moreover, due to the difference in graphitization difficulty between the skin and core layer of the CFs, the degree of graphitization at the surface is higher than that in the core. SAXS analysis suggests that the transition of amorphous carbon may begin near the micropores due to the sufficient space to rearrangement, and the amorphous carbon can more easily convert to graphite carbon above 2700 degrees C. Additionally, the optimization of CF microstructures leads to an increase in both tensile strength and elastic modulus with rising graphitization temperatures above 2700 degrees C.