Thermal conductivity of CaO–SiO 2 –Al 2 O 3 glassy slags: Its dependence on molar ratios of Al 2 O 3 /CaO and SiO 2 /Al 2 O 3

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.