Deviation from Wiedemann-Franz Law for the Thermal Conductivity of Liquid Tin and Lead at Elevated Temperature

The thermal conductivities of tin and lead in solid and liquid states have been determined using a nonstationary hot wire method. Measurements on tin and lead were carried out over temperature ranges of 293 to 1473 K and 293 to 1373 K, respectively. The thermal conductivity of solid tin is 63.9 ± 1.3 W · m^-1 · K^-1 at 293 K and decreases with an increase in temperature, with a value of 56.6 ± 0.9 W · m ^-1 · K^-1 at 473 K. For solid lead, the thermal conductivity is 36.1 ± 0.6 W · m^-1 · K ^-1 at 293 K, decreases with an increase in temperature, and has a value of 29.1 ± 1.1 W · m^-1 · K^-1 at 573 K. The temperature dependences for solid tin and lead are in good agreement with those estimated from the Wiedemann-Franz law using electrical conductivity values. The thermal conductivities of liquid tin displayed a value of 25.7 ± 1.0 W · m^-1 · K^-1 at 573 K, and then increased, showing a maximum value of about 30.1 W · m^-1 · K^-1 at 673 K. Subsequently, the thermal conductivities gradually decreased with increasing temperature and the thermal conductivity was 10.1 ± 1.0 W · m^-1 · K^-1at 1473 K. In the case of liquid lead, the same tendency, as was the case of tin, was observed. The thermal conductivities of liquid lead displayed a value of 15.4 ± 1.2 W · m^-1 · K^-1 at 673 K, with a maximum value of about 15.6 W · m^-1 · K^-1 at 773 K and a minimum value of about 11.4 ± 0.6 W · m ^-1 · K^-1 at 1373 K. The temperature dependence of thermal conductivity values in both liquids is discussed from the viewpoint of the Wiedemann-Franz law. The thermal conductivities for Group 14 elements at each temperature were compared.