Thermal Conductivity of the CaO–Al₂O₃–SiO₂ System

Abstract

Thermal conductivity of the CaO–Al₂O₃–SiO₂ system, which is one of the most important silicate melts in iron- and steelmaking processes, was measured using non-stationary hot wire method in the range from liquidus temperature to 1 873 K. Measurements were carried out at various compositions, and iso-thermal conductivity line of the CaO–Al₂O₃–SiO₂ system was drawn in iso-thermal sections at 1 673 K, 1 773 K, and 1 873 K. Thermal conductivity decreased with basicity increase, when CaO/SiO₂ ratio is smaller than unity, whereas it showed constant value when CaO/SiO₂ ratio is larger. In case Al₂O₃ content was varied at constant CaO/SiO₂ ratio of 0.39 and 0.90, thermal conductivity showed maximum at 15–20 mass% Al₂O₃, suggesting that Al₂O₃ behaves as an amphoteric oxide. In the temperature range of interest, the thermal conductivity of each composition decreased as temperature rises. Temperature dependence showed deviation from linearity with the reciprocal of absolute temperature, which was considered to be due to the thermally-induced depolymerisation of the silicate structure at higher temperature. Also, thermal conductivity was found to conform to an exponential function of 1/T during deploymerization with the apparent activation energy.