Thermal Behavior and Phase Transformation of TiO₂ Nanocrystallites Prepared by a Coprecipitation Route

TiO₂ freeze-dried precursor powders were synthesized using a coprecipitation route that includes titanium tetrachloride (TiCl₄) as initial material prepared at 348 K (75 °C) and pH 7. Differential scanning calorimetry/thermogravimetry (DSC/TG), X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) and high resolution TEM were utilized to characterize the thermal behavior and phase transformation of the TiO₂ freeze-dried precursor powders after calcination. The main compound of the TiO₂ freeze-dried precursor powders was TiO₂·H₂O based on a TG analysis conducted at a heating rate of 20 K (20 °C)/min. The anatase TiO₂ (a-TiO₂) first appeared at 473 K (200 °C), then from a-TiO₂ transformed to rutile TiO₂ (r-TiO₂) at 773 K (500 °C). The activation energy of a-TiO₂ formation from TiO₂ freeze-dried precursor powders was 242.4 ± 33.9 kJ/mol, whereas, the activation energy of phase transformation from a-TiO₂ to r-TiO₂ was 267.5 ± 19.1 kJ/mol. The crystallite size of a-TiO₂ grew from 3.5 to 23.2 nm when raising the calcination temperature from 473 K to 873 K (200 °C to 600 °C). In addition, the crystallite size of r-TiO₂ increased from 17.4 to 48.1 nm when calcination temperature increased from 773 K to 1073 K (500 °C to 800 °C).