Thermodynamics of Titanium Oxide in CaO–SiO₂–Al₂O₃–MgO_satd–CaF₂ Slag Equilibrated with Fe–11mass%Cr Melt

Abstract

Thermodynamic equilibrium between the CaO–SiO₂–Al₂O₃–MgO_satd–CaF₂(–TiO_x) slags and the Fe–11mass%Cr melt was investigated at 1873 K in order to understand the thermodynamic behavior of titanium oxide in the refining slags. The equilibrium between silicon and titanium in steel melts and their oxides in the slags are theoretically expected and experimentally proved well. The activity coefficient of TiO₂ increases by increasing the basicity in logarithmic scale. By combining this with the previous results, in multi component calcium(–magnesium) silicate slags containing Al₂O₃ and TiO₂, TiO₂ could be considered as a basic oxide in silicate base melts, while it could be the relatively acidic oxide in the aluminate (very low silica) base melts. The activity coefficient of TiO₂ gradually decreases by substituting silica for alumina, indicating that the attraction between TiO₂ and SiO₂ is greater than that between TiO₂ and Al₂O₃ in the present slag system. This could be explained from the electronegativity difference between each cation involved. The activity of TiO₂ in the 10%MgO slag system shows a negative deviation from an ideality, while that in the CaO–SiO₂–Al₂O₃–MgO_satd(–CaF₂) system is relatively close to the ideal behavior up to about 10 mol% TiO₂. This is mainly due to the relatively basic characteristic of TiO₂.