The High Temperature Heat Treatment To Prepare The Domestic Pan Based High Modulus Carbon Fiber

High modulus carbon fibers are an important variety of carbon fibers. Their high specific modulus combined with low density, low expansion coefficient, good dimensional stability, heat resistance and other excellent performance, make these fibers attractive for high volume applications such as satellite, building up of national defense and national economy. There are less studies on the domestic high modulus polyacrylonitrile (PAN) based carbon fibers. It is great significance of fabricating domestic high modulus PAN-based carbon fibers.In this paper, domestic polyacrylonitrile (PAN) precursor was carbonized in industrial production carbonization lines and converted to PAN-based carbon fibers. The experiments were carried out by two different methods. The two kinds of carbon fibers, one of which were soaked boric acid solution and the other of which were not soaked boric acid solution, were high-temperature treated in two different graphite furnaces under different high temperatures. The Mechanical Properties and structures change of these carbon fibers during graphitization were investigated by means of X-ray diffraction, laser-Raman spectrum, and Surface scanning electron microscopy and so on. And the catalytic graphitization by doping boron was discussed.The results indicated that the Young's modulus of the domestic PAN-based carbon fibers increases through simple high-temperature graphitizing in two different furnaces under different high temperature, yet the strength of the carbon fibers decreases gradually. The Yong's modulus of carbon fibers graphitizing in a closed graphite furnace at 2500℃was up to 413GPa, and the strength deceased to 1.49GPa.The Young's modulus of Soaked in boric acid solution domestic PAN-based carbon fibers also increased during the graphitization temperature increasing, yet the strength of the carbon fibers decreased gradually too. The Young's modulus of Soaked in boric acid solution PAN-based carbon fibers graphitizing in a closed graphite furnace at 2500℃raised to 460GPa, and the strength reduced to 1.60GPa. Comparing to simple high-temperature treatment in a closed graphite furnace, the modulus of doping boron carbon fibers was much larger than that of non-doping boron carbon fibers, and the strength of doping boron reduced more slowly than that of non-doping boron carbon fibers.Through structure analysis of these carbon fibers, the degree of graphitizing carbon fibers increased gradually with heat treatment temperature increasing. The value of d002 decreased, and values of Lc and La increased gradually, which characterized the microstructure of carbon fibers. The structure of doping boron carbon fibers changed more apparently than non-doping boron carbon fibers, which demonstrated that boron element can accelerate the process of graphitizing of PAN-based carbon fibers, and enhances the modulus of PAN-based carbon fibers significantly.