Thermal conductivity of liquid metals and alloys obtained by subsecond ohmic pulse heating experiments

Wire samples are resistively pulse heated. Time resolved the current through the specimen and the voltage drop across the specimen is measured. Radiance temperature of the sample was measured with a pyrometer and volume expansion with a fast acting CCD-camera. These measurements allow the calculation of specific heat and the mutual dependencies between enthalpy, electrical resistivity, temperature, and density of the metal in the solid and liquid phase. Thermal conductivity is close related to electrical conductivity. Based on the free electron model for metals, theory found that the ratio of thermal conductivity and electrical conductivity for metals is directly proportional to temperature, called Wiedemann-Franz-Lorenz (WFL) relation. To examine the validity of the WFL relation, values of the ratio of the experimental to theoretical values for the Lorenz function (L/L0), for temperatures close to the melting point, were compared and showed that L/L0 is close to unity for most metals and that small deviations may be due to measurement uncertainties. At lower temperatures and for some metals significant deviations from the theoretical Lorenz number were found and attempts to counteract by modification of the WFL were made. Even larger discrepancies occurred when using WFL for alloys, as electron-electron interactions, electron-phonon interactions, as well as lattice contributions need to be considered. These limiting effects vanish at melting as the crystal structure vanishes and WFL becomes a reasonable tool to determine thermal conductivities for liquid metals. Work partially funded by the Austrian Science Fund (FWF) Project P 23838-N20.