Evolution de l'arrangement et des dimensions des couches d'un carbone graphitable entre 1700 et 2500°C

The use of radial distribution functions of interatomic distances, P(r), in case of a pitch coke treated at temperatures between 1700° and 2500°C allows to follow tridimensional organisation and the growth of the carbon layers as a function of temperature. These results are obtained by comparing the experimental radial distribution functions of a sample treated at temperatures of 1700, 2050, 2100 and 250°C with synthetic functions calculated for a graphitic model with C-C distances less than 10 Å; the agreement of the two types of curves allows essentially:On one hand to evaluate the importance of the distorsions between the layers and to follow their evolution with temperature.On the other hand to determine the size of the diffusing domains, the measurements being confirmed by another method based on the analysis of diffusion band profiles. We have found a sudden enlargement of the average diameter of layers at a temperature of about 2000°C, on the average they change from 80 Å at 1900°C to 300 Å at 2000°C. We have shown[1] that it is in this range of temperature that the interstitial carbon atoms rearrange and are eliminated from between the layers and that the defects affecting the hexagonal rings disappear.The results obtained show that the organisation and growth of graphitic layers are related directly to the evolution of the interstitial carbon atoms: the rearrangement and the elimination of these interstitial atoms at 2000°C sweeps away defects which, up to there, hinder the tridimensional growth of the pitch coke.