A NOVEL TECHNIQUE FOR MEASURING THE THERMAL-CONDUCTIVITY OF METALLIC MATERIALS DURING MELTING AND SOLIDIFICATION

A new technique for measuring the thermal conductivity of metallic materials during liquid/solid phase transformation is proposed and applied to the determination of the thermal diffusivity and thermal conductivity of Wood's metal (Bi, 48%; Pb, 26%; Cd, 13%; Sn, 13%) at the melting point. The technique incorporates measurements in two sequences: (1) during a one-dimensional propagation of the phase transition interface, and (2) during a quasi-equilibrium state where the interface is stationary. The position of the interface is determined from measurement of the electrical resistance over the specimen including the interface. The resistance over time obtained during the melting/freezing processes enables the determination of the speed of the solid-liquid interface. The thermal diffusivity and conductivity at the interface can be evaluated from the speed of the interface, temperature gradients normal to the interface, and thermal properties. The mean value of the thermal conductivity at the transition temperature, was found to be 32.9 W m(-1)degrees C-1 and 22.4 W m(-1)degrees C-1 for the solid and the liquid phases respectively. Independent measurements of the electrical resistance gave the ratio of the resistivity of the solid and the melt equal to 1.51. A Lorenz number is evaluated to be about twice the theoretical value for a metal. A brief discussion of a tentative separation of the electronic and the lattice component of the thermal conductivity is made.