Thermal conductivity of CaO–SiO2–Al2O3 glassy slags: Its dependence on molar ratios of Al2O3/CaO and SiO2/Al2O3

Abstract

Thermal conductivities of CaO–SiO2–Al2O3 glassy slags have been determined using the nonstationary hot wire method as functions of (mol.-%Al2O3)/(mol.-%CaO) and (mol.-%SiO2)/(mol-%Al2O3) ratios over a temperature range 300–1270 K. The thermal conductivities of the samples investigated were in the range between 1·0 and 1·6 W m−1 K−1. The thermal conductivities of samples having a constant concentration of SiO2 increased with increasing the (mol.-%Al2O3)/(mol.-%CaO) ratio as long as the constant pressure heat capacity per unit volume was kept constant. This increase in thermal conductivities would be due to increases in the speed of sound and/or the phonon mean free path by re-polymerisation of the network structure of silicate glasses by Al2O3. On the other hand, the thermal conductivities of samples having a constant value of NBO/T (the ratio of the number of non-bridging oxygen ions per tetrahedrally coordinated cation) decreased with increasing the (mol.-%SiO2)/(mol.-%Al2O3) ratio. This decrease in thermal conductivities would be dominated by the constant pressure heat capacities per unit volume of the samples.