A study of evolved gas control and its effect on carbon yield during the activation of carbon fibres by controlled rate methods

The rate of evolution of CO₂ or CO was used to control the low temperature activation of carbon fibres in O₂ mixtures via a feedback loop operated by a PC and in-house software. The CO₂ or CO concentration was monitored by a mass spectrometer and its level kept constant by varying the O₂ concentration using mass flow controllers. Experiments were carried out at the same evolution rates for identical times at temperatures of 500-800 °C. It was found that the rate of carbon burn off was not constant and varied with the temperature, especially where the rate of CO₂ evolution was controlled. The proposed reason for this was the high temperature gas phase oxidation of CO. However, surface areas of up to 1500 m² g^-1 were produced by these methods and thermal runaway was avoided.