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-1 at 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.