Silica activity and raman spectra of the CaO-SiO2-TiOx system

Abstract

The thermodynamic activity of SiO2 in CaO-SiO2-TiOx slags was measured by the slag-metal-gas equilibrium method. Slags containing up to 43 mol% TiOx, were equilibrated with molten copper in molybdenum crucibles in H2-H2O-Ar gas atmosphere. The oxygen partial pressure and temperature were maintained at ∼10-12 atm and 1873 K, respectively. In the equilibrated slags, the proportion of titanium in the reduced Ti3+ state ranged from 16% to 54% of total Ti by mass. Results showed that at a given CaO/SiO2 ratio, the activity coefficient of SiO2 increases with increasing TiOx concentration. Samples of CaO-SiO2-TiOx slags were also examined by Raman spectroscopy. Raman spectra obtained for oxidised and reduced CaO-SiO2-TiOx slags show that the Ti4+ ion has a tetrahedral coordination, while the coordination of Ti3+ appears to be predominantly octahedral. These findings are consistent with the observed effect of titania on the silica activity in the CaO-SiO2-TiOx slags.