The oxidation behaviour of carbon fibres has been studied in air at di
fferent temperatures from 550 to 860-degrees-C. A linear relationship
has been observed between the carbon fibre size and oxidation time. Ex
perimental results show that the oxidation process is in a mixed contr
ol zone, i.e. controlled both by diffusion of the gaseous reactant and
product within the boundary layer and by the chemical reaction. The a
ctivation energy of carbon burn-off is 140 +/- 5 kJ mol-1. The uniform
nature of the surface oxidation makes it possible to re-size the carb
on fibres to smaller diameters.