EFFECT OF THE ACTIVATING GAS ON TENSILE-STRENGTH AND PORE STRUCTURE OF PITCH-BASED CARBON-FIBERS

Petroleum pitch-based activated carbon fibres have been prepared by CO 2 and steam activation. The effects of the activating gas on porosity and mechanical properties of the activated carbon fibres have been ana lyzed. The original carbon fibre contains a narrow porosity that is we ll developed upon activation in both CO2 and steam (an apparent surfac e area of about 1700 m(2)/g is obtained after a 50% burn-off). The act ivated carbon fibres obtained exhibit different porous texture evoluti on with burn-off depending on the activating gas used. CO2 essentially develops microporosity and causes a steady decrease in the tensile st rength with burn-off, while the fibre diameter does not change signifi cantly. Contrarily, steam produces a wider porous texture and, after t he initial stages of the activation process, the tensile strength rema ins nearly constant and the fibre diameter decreases. The results have been interpreted considering the different behaviour of the two molec ules (CO2 and steam) involved in the reaction in the narrow microporos ity. In this sense, CO2 seems to react to a larger extent than steam i nside the narrow microporosity due to its larger coefficient diffusion .