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 °C. In both cases, a significant increase in micropore volume, as measured by physical adsorption of N₂ and CO₂, is found. Fibre diameter steadily decreases during gasification by steam. In contrast, an intermediate diameter increase is observed during activation by CO₂. 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 CO₂. 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.