STRUCTURAL CONVERSIONS IN MESOPHASE PITCHES AND METAL CLUSTER FORMATION IN THE MATRIX OF PITCH DURING HEAT-TREATMENT

Quantitative X-ray phase analysis and Raman spectroscopy have been use d to study the influence of transition metals and the temperature-time factor on processes of carbonization and graphitization of mesogenic pitches. With an increase in temperature to 1100 degrees C there is a gradual increase in the concentration of graphite-like phase (G(ph)) a nd in the size of the regions of coherent scattering of this component , with a simultaneous reduction in the content of other hydrocarbon co mponents, Above 1100 degrees C there remains only one G(ph) and with a n increase in temperature there is an increase in its degree of crysta llinity. The introduction into the pitch matrix of a transition metal in a quantity of 1% catalyses both processes: the content of G(ph) in cluster pitch heat-treated at 700 degrees C corresponds to its content for initial pitch heat-treated at 900 degrees C, An increase in the i ron content to 5% leads at 250 degrees C to the appearance of an entir ely amorphous phase, which is due to amorphization of part of the G(ph ). A similar effect is observed in specimens where, along with 1% Fe, there is 1% Mn or 1 . 5% Co. Copyright (C) 1996 Elsevier Science Ltd.