抄録
Structure and air-oxidation behavior of the isotropic pitch-based carbon fiber were investigated. The carbon fiber was heat-treated with various temperatures in the range from 1000 to 2500℃ under argon gas atmosphere. Lattice constant d002 of the carbon fiber obtained by powder X-ray diffraction analysis was significantly reduced by the heat-treatment from 1500 to 2000℃. The crystallite sizes of the carbon fiber Lc (002) and La (110) were only 3nm even after heat-treatment with 2000~2500℃. While the carbon fibers heat-treated with 1000 and 1500℃ showed broad peaks of D- and G-bands in Raman spectra, those peaks became sharp after heat-treatment with more than 2000℃. It was observed by thermogravimetry (TG) that both air-oxidation starting temperature of the carbon fiber and activation energy of the oxidation reaction became higher as the increase of heat-treatment temperature of the carbon fiber. In the air-oxidation test which was carried out at 550℃ under stagnant air, the carbon fiber heat-treated with 1000℃ lost its weight by 35% for 1 hour since starting the test. On the other hand, the carbon fibers heat-treated with 2000 and 2500℃ only lost their weights less than 0.1% for 1 hour since starting the test. After 3 hours from the start of the test, the rates of weight loss of the carbon fibers heat-treated with 2000 and 2500℃ increased about 5 times compared with that of initial 1 hour. It may be noticed that new active points in the carbon fiber were created by air-oxidation and these newly created points accelerated the air-oxidation reaction. For the carbon fibers heat-treated with 2000 and 2500℃, much higher peaks of D-band in Raman spectra were observed after 10% weight loss than those of before air-oxidation, and these findings are probably due to the newly created active points.
