Review of the Factors Affecting the Thermophysical Properties of Silicate Slags

This paper is dedicated to the memory of the of Prof. Masanori Iwase and his life and work. The factors which affect the thermo-physical properties of silicate and aluminno-silicate slags are reviewed. These include (i) the polymerisation of the silicate network (ii) various cation effects and (iii) temperature. Of these, the degree of polymerisation of the silicate network (expressed here through the parameter Q (= 4-NBO/T)) is the most important and the viscosity (eta), electrical resistivity and thermal conductivity all increase as Q increases. Various ways in which different cations affect the properties are considered for each individual property viz. the -M-O bond strength affects (i) liquidus temperature (ii) activity coefficient of SiO2 and (iii) thermal expansion coefficient and whereas both the size and number of available cations affect the electrical conductivity and resistivity. The following observations were made: i. There is less scatter in property data for liquid slags at a specific temperature than that for the liquidus temperature. ii. The relation between Arrhenius parameters, ln A and B for viscosity and electrical resistivity is non-linear. iii. The magnitude of the thermal conductivity (k) in solid slags is related to the rigidity of silicate network and the rapid decrease in k with increasing temperature occurs at a temperature where the viscosity reaches eta = 10(6) dPas. iv. The introduction of Al2O3 into the silicate chain results in significant changes to the properties The ways in which the various properties can be calculated from chemical composition are outlined.