Modeling viscosity of SiO2-Al2O3-CaO based slags using Arrhenius and VFT models as well as the CALPHAD method

The first step of modeling the viscosity of slags is to choose a temperature-related viscosity model which plays a significant role in determining the framework of the entire model. In the present work, two temperature-related viscosity models, the Arrhenius and the VFT (Vogel-Fulcher-Tammann) models are compared for calculating the viscosity of slag systems taking the experimental data for the SiO2-Al2O3-CaO system as basis. The results show that the VFT model shows a better performance in describing experimental data for the temperature dependence of dynamic viscosity among all the investigated systems compared to the Arrhenius model. Such a good performance by the VFT model is explained by the actual network structure of liquid oxide systems described well by this model. Moreover, a linear relationship between the two semi-empirical parameters of the VFT model (ln A and T0) is found for the first time, which can decrease the number of independent parameters when modeling the viscosity of slags by this model. In addition, the viscosities of the CaO-Al2O3 and SiO2-CaO systems are modelled by the combined VFT-CALPHAD (CALculation of PHAse Diagrams) model over wide temperature and composition ranges.