The complex behaviour of iron making slag systems, in particular phase equilibria and viscosity, remains one of the key issues for successful control and optimisation of industrial BF operations. The present paper reports recent developments of thermodynamic and viscosity models and demonstrates application of these studies to ironmaking. The thermodynamic modelling is carried out using the computer package FactSage. A new structurally-based quasi-chemical viscosity model for fully liquid silicate slags has been developed for the Al_2O_3-CaO-'FeO'-MgO-SiO_2 system at metallic iron saturation. The quasi-chemical viscosity model takes into account the complex internal structures of silicate slags evaluated from the quasi-chemical solution model, and is therefore more robust in its predictive ability than empirically-based viscosity models. The combination of FactSage thermodynamic calculations and the use of the new quasi-chemical model provides a powerful tool with which to predict the viscosities of fully liquid and partly crystallised slags. Examples illustrating application of the thermodynamic and viscosity models to iron making applications are presented.
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