Deintercalation process of fluorinated carbon fibres—II. Kinetic study and reaction mechanisms Original Research Article

The deintercalation process of fluorine species from fluorine-graphite intercalation compounds (F-GICs) has been investigated by evolved gas analysis. The controlled transformation rate thermal analysis method was used. In this way, the rate of production of the gaseous phase is permanently controlled at low pressure, so that both temperature and pressure gradients can be lowered at will, avoiding the overlap of the successive steps of the reaction. These experiments have been carried out on stage-1 F-GICs with CF ratios ranging from 3 to 4, which were obtained from high-temperature treated carbon fibres (ex-pitch) fluorinated at room temperature with PF2 < 10 bar in the presence of gaseous HF. The thermal analysis exhibits three parts: the first two parts correspond to the deintercalation of fluorine and HF; and the third part (> 460 °C) to the degradation of the carbonaceous skeleton. The activation energies associated with the different parts have been determined by the rate-jump method. A kinetic study of the deintercalation/decomposition processes has been proposed. The first (deintercalation) part is apparently accompanied by a post-deintercalation reaction of evolving fluorine with carbon atoms of defects leading to the formation of covalent CF bonds. The deintercalation is achieved during the second part which can be described by a two-dimensional interfacial advancement process. The apparent activation energy of this deintercalation part has been evaluated to be 144 kJ mol−1. The degradation part, with 240 kJ mol−1 activation energy, can be ascribed to a two-dimensional nucleation and growth of nuclei mechanism.