Effect of hydrolysis conditions on hydrous TiO₂ polymorphs precipitated from a titanyl sulfate and sulfuric acid solution

The relationship between hydrolysis conditions and hydrous titania polymorphs obtained in a titanyl sulfate and sulfuric acid solution was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The results revealed that the feeding rate of the titanyl sulfate stock solution, the concentration of sulfuric acid, and the seed dosage of rutile crystal could significantly affect the hydrolysis rate, thus influencing the titania crystal phase. Hydrous TiO₂ in the form of rutile, anatase, or the mixture of both could be obtained in solutions of low titanium concentrations and 2.5wt% to 15wt% sulfuric acid at 100℃. When the hydrolysis rate of titanium expressed by TiO₂ was more than or equal to 0.04 g/(L·min), the hydrolysate was almost phase-pure anatase, while the main phase state was rutile when the hydrolysis rate was less than or equal to 0.01 g/(L·min). With the hydrolysis rate between 0.02 and 0.03 g/(L·min), the hydrolysate contained almost equal magnitude of rutile and anatase. It seems that although rutile phase is thermodynamically stable in very acidic solutions, anatase is a kinetically stable phase.