DEINTERCALATION PROCESS OF FLUORINATED CARBON-FIBERS - II - KINETIC-STUDY AND REACTION-MECHANISMS

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 p ressure 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 C/F ratios ranging from 3 to 4, which were obtained from high-temperature treated carbon fibres (ex-pitch) fluori nated at room temperature with P-F2 <10 bar in the presence of gaseous HF. The thermal analysis exhibits three parts: the first two parts co rrespond to the deintercalation of fluorine and HF; and the third part (>460 degrees C) to the degradation of the carbonaceous skeleton. The activation energies associated with the different parts have been det ermined by the rate-jump method. A kinetic study of the deintercalatio n/decomposition processes has been proposed. The first (deintercalatio n) part is apparently accompanied by a post-deintercalation reaction o f evolving fluorine with carbon atoms of defects leading to the format ion of covalent C-F bonds. The deintercalation is achieved during the second part which can be described by a two-dimensional interfacial ad vancement process. The apparent activation energy of this deintercalat ion 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-dime nsional nucleation and growth of nuclei mechanism. (C) 1998 Elsevier S cience Ltd. All rights reserved.