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 las er-heated autoclave filled with inert gas. The measured melting curves and their elopes were compared with predictions obtained from the Clausius-Clap eyron equation and existing thermochemical data of these substances. While for tungsten and graphite the results show reasonable agreement with the eq uilibrium thermodynamic calculations, the melting point of UO2 increases wi th pressure with a slope more than three times larger than expected.