Two types of carbon fiber based high modulus- and isotropic-pitch were exposed to isothermal oxidation in air and CO2 gas and the weight change was measured by TGA apparatus. The kinetic equation was introduced f=1--(-atb) and the constant b was obtained in the range of 1.02~1.68 for the isotropic fiber and obtained 0.91~1.93 for the high modulus fiber respectively. In considering the effect of the atmosphere for isothermal oxidation, the value of the constant b obtained in the carbon dioxide was higher than that obtained in the air. Therefore, it was found that the pitch based carbon fiber shows sigmoidal characteristic when it is oxidized in the carbon dioxide. In addition, it was also found that kf = 0.5, which was reaction constant at f = 0.5, was a very useful parameter for evaluation of the oxidation reactivity of pitch based carbon fibers. According to the consideration, it is suggested that the conversion-time curves of the pitch based carbon fibers are correlated by normalized equation f=1--(-AτB), where τ=t/tf= 0.5.

• Jae-Seung Roh(Department of Materials Engineering, Chungnam National University)