Thermal Conductivity of Molten Silicate of Al₂O₃-CaO-Na₂O-SiO₂ Measured by Means of a Front Heating-Front Detection Laser Flash Method

Thermal conductivity values have been systematically obtained for molten silicates containing Al₂O₃, CaO, Na₂O, and SiO₂ by means of a front heating-front detection laser flash method. The measurements were made for 13 samples in the temperature range between 1073 K and 1823 K (800 °C and 1550 °C), depending on the composition. Thermal conductivities of the silicate melts are found to be relatively insensitive to the variation of temperature, but they depend on the composition ratio, particularly the ratio of Non-Bridging Oxygen ions per Tetrahedrally coordinated cation—NBO/T. The thermal conductivity values decrease from 2.8 W/mK to 1.5 W/mK with the NBO/T value until it reaches about 1. Thermal conductivity values become constant for silicate melts with a higher value of NBO/T. It is known that the length of the silicate chain decreases with disconnection by the addition of alkaline earth cation or alkaline cation. The strong correlation between thermal conductivity and NBO/T is quite likely to suggest that silicate chain is a preferential path for heat transport in silicate melts.