Measurements of the melting point of graphite and the properties of liquid carbon (a review for 1963–2003)

Abstract

Scientific literature on the melting temperature of graphite and its properties in melting is reviewed, beginning with the study by Bundy in 1963 and proceeding up to 2003. Data obtained by Pirani in 1930 that has been quoted in some recent publications is also considered. Successive experimental data and theoretical predictions on the melting point of carbon are summarized. The history of carbon studies, starting in 1963, is given, covering both laser and electrical heating of the graphite. The main divergence in the experimental results is in the value of the true melting temperature of graphite in the range of 4000 or 5000 K. The paper first describes laser heating. Pulsed laser heating of graphite usually shows the absence of a melting temperature plateau in the heating of a low-density graphite specimen (only a deflection point is observed on the increasing signal of the pyrometer). Carbon vapour, as a result of graphite sublimation, usually plays a leading role in the temperature measurements near the melting point under slow heating. The volume electrical heating of graphite is then discussed. Several electrical pulse investigations are listed: measurements of different properties; heating of low density graphite; and very slow pulse heating up to steady-state by alternating current. A separate section shows the data on spectral emissivity investigations, which are required in graphite temperature measurements. Reliable experimental data for the graphite melting point are presented: enthalpy of solid state under melting (10.5 kJ/g); enthalpy of liquid state under melting (20.5 kJ/g); heat of graphite melting (10 kJ/g); liquid-carbon resistivity (730 μΩ cm) near the melting point at a density of 1.8 g/cm 3 under high pressures (several GPa); estimation of expansion (70%) during melting at 100 MPa pressure; and melting temperature T m = 4800 ± 100 K at a pressure 10–100 MPa. Most of these data are obtained by electrical fast heating (1–5 μs), that are supported by the data of carefully executed laser-pulse heating.