Effect of Coexisting Minerals on Graphitization of Carbon. I. Heat Treatments of Carbon under 3 kbar in the Presence of Limestone

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Abstract
The effect of the presence of limestone on the graphitization of carbon was investigated by the heat treatments of the carbon sample under the quasi-hydrostatic pressure of 3.2 kbar. The carbon sample used was a coke (PV-7) prepared by carbonization of polyvinylchloride up to 680°C. It was placed between two disks of limestone so as to make a sandwich-type specimen. The heat treatments were performed in a simple piston-cylinder type vessel at various temperatures of 800–1300°C for 20–240 min. Above 1000°C, the carbon specimens were obtained as caked tablets. The profiles of (002) diffraction line of these carbon tablets were found to be composite, consisting of a sharp component profile at 26.5° and a broad one at lower angle than 26.2°. The component GM corresponding to the sharp component profile seemed to have the graphite structure. The content of the component GM increased very rapidly with the increase in heat treatment temperatures above 1000°C. Phenomenally, the developement of the graphite structure seemed to be closely related to the recrystallization and the melting of coexisting limestone, but some chemical effects should not be excluded.

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