Effect of Coexisting Minerals on the Graphitization of Carbon under Pressure. IV. Accelerating Effect of Calcium Oxide

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Abstract
Heat treatments of polyvinylchloride coke in the presence of three kinds of calcium oxide calcined at different temperatures were carried out in order to study the effect of the reactivity of calcium oxide on the acceleration of graphitization of carbon under the quasihydrostatic pressure of 3.2 kbar. A remarkable difference in the accelerating effect on graphitization was confirmed. In the presence of the most reactive calcium oxide calcined at 920°C, the graphitization of the carbon began at about 1100°C and the content of the graphitic component became 100% by heat treatment at 1500°C for 60 min. While in the presence of the least reactive calcium oxide calcined at 1470°C, the graphitic component, an even hump on the corresponding diffraction angle, could not be detected in specimens heat-treated below 1500°C. The content of graphitic component and the distribution of calcium in heat-treated specimens were measured by an electron microprobe analyzer. It was found that the part having a larger content of calcium had a larger content of the graphitic component. A possible mechanism of the accelerating effect of calcium compound on graphitization is considered to be chemical concerning the intermediate formation of carbide or metal. The formation of the graphitic component seems to proceed by the reaction: