Melting curve of graphite and thermophysical properties of graphite and liquid carbon in the vicinity of this curve
Phys. Rev. B 113, 014117 – Published 26 January, 2026
DOI: https://doi.org/10.1103/d8sv-tnt5
Abstract
Using a pulse electric heating technique, measurements of temperature, specific volume, pressure, specific enthalpy, and electrical resistivity of highly oriented pyrolytic graphite samples in quasistatic processes were carried out. In these processes the samples were subjected to controlled thermal expansion along the hexagonal axis of graphite and melting occurred at pressures of 0.2–2.5 GPa. The melting line of graphite was determined directly from the Clapeyron-Clausius equation by measuring the pressure dependence of the jumps in specific volume and enthalpy of the graphite samples on melting. It was found that the melting temperature of graphite in the specified pressure range increases with increasing pressure from approximately 6000 to 6200 K. Extrapolation of this dependence to higher pressures shows that the melting temperature reaches its maximum at a pressure of about 4 GPa. Based on the measurement results, the values of specific heat capacity, speed of sound, and isochoric temperature coefficient of resistivity of graphite and liquid carbon near the melting line were determined. It is shown that liquid carbon in the studied ranges of density and pressure is a metal for which the isochoric temperature coefficient of resistivity is negative. The obtained results are compared with literature data, and a detailed discussion of the discrepancies between the results is given. It is argued that the currently used phase diagram of carbon requires significant improvement.
