Melting of Graphite at Very High Pressure

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Abstract
A method of flash‐heating small rods of graphite inside a superpressure cell has been developed. The heating energy was inserted in less than 7 msec from a bank of electrolytic capacitors. This quick heating and cooling allowed fusion and freezing of the graphite to occur without serious melting or reaction of the surrounding wall material. Electrical data were recorded with oscillographs and cameras. The start of melting was found to be indicated by an abrupt downward trend of resistance. Polished cross sections of the samples showed clearly the part which melted. Melting temperatures increased from about 4100°K at 9 kbar to a maximum of about 4600°K in the region of 70 kbar, then decreased to about 4100°K at 125 kbar. A value of 25 kcal/mole for the heat of fusion at 48 kbar was determined. The graphite/diamond/liquid triple point is shown to be at about 4000 to 4200°K and 125 to 130 kbar.