Viscosity of TiO₂-FeO-Ti₂O₃-SiO₂-MgO-CaO-Al₂O₃ for High-Titania Slag Smelting Process

The present study demonstrates the dependence of viscosity on chemical composition and temperature of high-titania slag, a very important raw material for producing titanium dioxide. The results indicated that completely molten high-titania slag exhibits a viscosity of less than 1 dPa s with negligible dependence on temperature. However, it increases dramatically with decreasing temperature slightly below the critical temperature, i.e., the solidus temperature of the slag. Above the critical temperature, the slag samples displayed the same order of viscosity at 0.6 dPa s, regardless of their compositional variation. However, the FeO, CaO, and MgO were confirmed to decrease viscosity, while SiO₂ and Ti₂O₃ increase it. The apparent activation energy for viscosity-temperature relation and liquidus temperature based on experiments and thermodynamic calculations are also presented. Conclusively, the critical temperatures of the slags are on average 15 K below their corresponding calculated liquidus temperatures. The increase in FeO content was found to considerably lower the critical temperature, while the increase in both Ti₂O₃ and TiO₂ contents increases it. The main phases of the slag in solid state, as indicated by X-ray diffraction, are (Fe, Mg)_xTi_yO₅ (x + y = 3, pseudobrookite) and rutile.