Effect of the activating gas on tensile strength and pore structure of pitch-based carbon fibres

Petroleum pitch-based activated carbon fibres have been prepared by CO2 and steam activation. The effects of the activating gas on porosity and mechanical properties of the activated carbon fibres have been analyzed. The original carbon fibre contains a narrow porosity that is well developed upon activation in both CO2 and steam (an apparent surface area of about 1700 m2g is obtained after a 50% burn-off). The activated carbon fibres obtained exhibit different porous texture evolution with burn-off depending on the activating gas used. CO2 essentially develops microporosity and causes a steady decrease in the tensile strength with burn-off, while the fibre diameter does not change significantly. Contrarily, steam produces a wider porous texture and, after the initial stages of the activation process, the tensile strength remains nearly constant and the fibre diameter decreases. The results have been interpreted considering the different behaviour of the two molecules (CO2 and steam) involved in the reaction in the narrow microporosity. In this sense, CO2 seems to react to a larger extent than steam inside the narrow microporosity due to its larger coefficient diffusion.