Thermal conductivity of the CaO-Al2O3-SiO2 system

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 1873 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.