Effect of Pressure on Graphitization of Carbon. VII. Effect of Pre-Heat-Treatment on Graphitization of Carbon under High Pressure

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Abstract
The soft carbon samples PV-15, -17 and -20, and the hard carbon samples PH-15 and -20, which were prepared by pre-heat-treatment of a polyvinylchloride coke PV-7 at 1500, 1700 and 2000°C and a phenolformaldehyde resine char PH-7, at 1500 and 2000°C, respectively, under reduced pressure, were re-heat-treated under quasi-hydrostatic pressure of 5 kbar. The strctural changes in these carbons by the re-heat-treatment under pressure were studied by X-ray diffraction analysis. On the soft carbons, the rate of development of graphitic compenent was found to become small with the increase in temperature pre-heat-treatment. On these samples, especially on PV-20, the normal homogeneous graphitization of turbostratic component was observed above about 1700°C besides the heterogeneous graphitization. However, the hard carbon samples PH-15 and PH-20 showed the same abrupt heterogeneous graphitization at around 1500°C as the original PH-7. These results suggest that the structure of carbon sample is related to the heterogeneous graphitization under high pressure. One can deduce a conclusion from results of this series of experiments that the heterogeneous graphitization is more dominant in a carbon sample having a lower degree of graphitization, for example, a larger c0-spacing and a smaller crystallite size.