The effect of heating conditions on micropore formation during the carbonization of polyimide films

Abstract

Carbon films were prepared by the heat-treatment of polyimide (PI) films at different temperatures between 400 °C and 900 °C. Heat-treatment was carried out by two methods (one-step and step-wise methods). In the one-step method, the temperature was increased directly to the pyrolysis temperature. In the step-wise method, the temperature was increased to the pyrolysis temperature in steps of 100 °C. The micropore surface area of the carbon films obtained was estimated from the α_s-plots of the nitrogen-adsorption isotherms at -196 °C. In the one-step method, the micropore surface areas of the carbon films heat-treated at 800 °C and 900 °C were 400 m² g^-1 and 600 m² g^-1, respectively. Micropores were not formed for the carbon films heat-treated at 700 °C in the one-step method. On the other hand, in the step-wise method, the micropore surface areas of the carbon films heat-treated at 700 °C, 800 °C and 900 °C were 340 m² g^-1, 440 m² g^-1 and 230 m² g^-1, respectively. These results suggested that heat treatment method largely affects the micropore structure of the carbon films derived from PI.