Thermal Conductivities of Molten Na2O–SiO2 Slags from the Perspective of Depolymerization of the Silicate Network

The thermal conductivities of molten KNO₃, molten NaCl, and molten xNa₂O–(100−x)SiO₂ (x = 20, 33, and 40) (mol%) are measured over the temperature ranges between 623–723 K, 1173–1473 K, 1173–1573 K, respectively, by nonstationary hot-wire method to elucidate the relationship between thermal conductivities of molten Na₂O–SiO₂ slags and silicate network structures. 1) The thermal conductivity measurements of molten KNO₃ reveal that the measurements are successfully made without the influence of electrical leakage from the bare metallic wire to the melt as the present data are in good agreement with the reported data measured by the nonstationary hot-wire method with ceramic-coated hot-wires. 2) The thermal conductivity measurements of molten NaCl measured at 1173 and 1273 K agree well with the recommended data. However, the data at 1373 and 1473 K are much smaller than the recommended data due to some electrical noise affecting the voltage changes ΔV between the potential leads. 3) The thermal resistivities of molten Na₂O–SiO₂ at liquidus temperatures ρ_LT increase with an increase in the number of nonbridging oxygens (NBO) per tetrahedrally coordinated atoms (e.g., Si, Al), i.e., NBO/T, and have a linear relationship between ρ_LT and NBO/T.