Dependence of the Melting Temperature on Pressure up to 2000 Bar in Uranium Dioxide, Tungsten, and Graphite

The melting points of uranium dioxide, tungsten, and graphite were measured as a function of the isostatic pressure up to 2000 bar (200 MPa), in a laserheated autoclave filled with inert gas. The measured melting curves and their slopes were compared with predictions obtained from the Clausius-Clapeyron equation and existing thermochemical data of these substances. While for tungsten and graphite the results show reasonable agreement with the equilibrium thermodynamic calculations, the melting point of UO2 increases with pressure with a slope more than three times larger than expected.