Swelling of pitch-based carbon fibres during activation in carbon dioxide

Isotropic pitch-based carbon fibres are activated by carbon dioxide and by steam at a temperature ranging from 850 to 1000 degrees C. In both cases, a significant increase in micropore volume, as measured by physical adsorption of N(2) and CO(2), is found. Fibre diameter steadily decreases during gasification by steam. In contrast, an intermediate diameter increase is observed during activation by CO(2). The interval of burn-off corresponding to fibre swelling depends on the gasification temperature. Phenolic resin-based fibres do not show swelling which indicates that it is specific to pitch-based fibres activated by CO(2). Oxygen is taken up during swelling on the incompletely stabilized part of the isotropic pitch-based carbon fibres. The origin of swelling and its effect on microporosity are discussed in relationship to fibre stabilization during activation. (C) 1997 Elsevier Science Ltd.