Computational Modelling of Oxide Surface Tensions in Secondary Metallurgy and Continuous Casting

Two computational models were used to estimate the surface tensions of oxide systems containing SiO(2), CaO, Na(2)O and Al(2)O(3) as a function of temperature and composition. The compositions of the oxide melts were chosen to correspond to those of ladle slags in secondary metallurgy and to casting powders in continuous casting of steel. The first model uses Butler's equation to calculate the surface tensions of the multicomponent melts and is based on Tanaka et al.'s consideration of the ionic radii of the components as well as surface tensions and molar volumes of pure components. In the second model the same ionic radii dependent contribution is applied as activity coefficients to a constrained free energy model where the surface layer is considered as a separate phase in the system. In the model, the constrained interfacial area is analogous with a component mass balance in a traditional computation of a multiphase chemical equilibrium and surface energy with the corresponding chemical potential. Based on the results it is concluded that the effect of temperature on the surface tensions of the considered oxide melts is insignificant when compared to the effect of chemical composition. According to the validation the results agree well with published surface tension data. The multi-component surface tension approach provides a practical method for evaluation of e.g. functioning of various casting powders in industrial steel casting practice.