Thermodynamic Properties of Fe_tO-Na₂O, Fe_tO-SiO₂-Na₂O, Fe_tO-P₂O₅-Na₂O and Fe_tO-P₂O₅-SiO₂-Na₂O Slags

Abstract

The chemical equilibria of gas-slag reactions have been studied to clarify the effect of soda on the thermodynamic properties of slags in the hot metal treatment. The slags studied are the Fe_tO-Na₂O system (1610°C) equilibrated with P_CO2=1atm by using a Pt-crucible, the Fe_tO-SiO₂-Na₂O system (1400°C), the Fe_tO-P₂O₅-Na₂O system (1200°C) and the Fe_tO-P₂O₅-SiO₂-Na₂O system (1200°C) equilibrated with H₂O/H₂ gas mixture by using a solid iron crucible. The influence of slag composition on the activity of iron oxide and the Fe³⁺/Fe²⁺ ratio has been determined. It has been clarified that the results can be expressed in terms of the Lumsden's regular solution model over a wide range of composition in the systems of Fe_tO-Na₂O and Fe_tO-SiO₂-Na₂O. However, the model is not applicable to phosphate slags containing Na₂O. The iso-activity line for each component, iso-Fe³⁺/Fe²⁺ ratio lines and iso-P_O2 lines for the Fe_tO-SiO₂-Na₂O slag in equilibrium with liquid iron at 1400°C have been calculated using the regular solution model.