The effect of the pre-heat-treatment on the kinetics of graphitization of carbon has been investigated. The starting material was a coke prepared from polyvinylchloride by heating it to 680°C in flowing nitrogen (PV-7). Four samples having different pre-heat-treatment conditions were selected; the original coke PV-7, the second one prepared from PV-7 by the heat treatment at 1500°C for 60 min (PV-15), the third also from PV-7 by the treatment at 2060°C for 60 min (PV-7-20), and the fourth by the heat treatment of PV-15 at 2060°C for 60 min (PV-15-20). Each sample was heat-treated in a high purity graphite crucible at temperatures ranging from 1800°C to 2400°C for a variety of residence time under reduced pressure of 0.01-0.02 Torr. In this heat treatment, the temperature of the graphite crucible was raised up to 1700°-2100°C in the first 30 sec, and then increased gradually so as to reach the designed temperature within 2 min. The temperature variation after the set-up was detected by an optical pyrometer not to exceed ±20°C. The c₀-spacing of the heat-treated samples was determined from the (004) X-ray diffraction line by referring to the inner standard of silicon.
For the all samples examined, the c₀-spacing has been found to decrease with increasing the residence time. The relationship between c₀-spacing and residence time was analyzed in the same way as employed by Fischbach for the analysis of the kinetics of graphitization (Nature, 200, 1281 (1963)); The method consists of shifting the curves of c₀-spacing vs. logarithm of residence-time at any heat treatment temperature (T) so as to form a master curve. The effective activation energy can be evaluated by plotting the amount of such shifts against 1/T. Because of the scatter of the experimental data and of some ambiguity in forming the master curve, the effective activation energy has roughly been determined with inevitable uncertainty of 20-50kcal/mol. It has been found, however, that the carbon sample pre-heat-treated at the higher temperature has the higher effective activation energy. In addition, the repeated heat treatments of one specimen have been found to produce the same effect on the change of the c₀-spacing as the continuous heat treatment, if the total residence time equals with each other.