The effects of magnesium and aluminium ions’ additions on the kinetics of titanium dioxide structural transformation

Abstract

Knowledge of kinetics structural transformation of titanium dioxide is very important for the calcination process in titanium white production. Some impurities of titanium raw could have the influence in the crystalline structure of products and the kinetics of transitions. Sulphate salts of aluminium or magnesium were added into samples of TiO2 suspension. After drying, the samples were studied by thermogravimetry at a heating rate of 10 K min−1 to temperature at 1,000 °C. Results of thermogravimetric investigations of dry titanium dioxide suspension show two-stage decreases of sample mass: the first stage is associated with the removal of water, and the second stage is related to the emission of sulphur oxides. A method of X-ray diffraction (XRD) was used in the investigation of the kinetics of anatase–rutile transformation. The samples after drying were heated at 750, 800, 850 or 900 °C in a muffle furnace for 70 min, and then the phase composition was analysed using the XRD method. The results of XRD measurements show that at a temperature of 800 °C after 60 min, the complete transformation of titanium dioxide into rutile occurs. The addition of Al ions to the suspension of TiO2 has a negative influence on (increases) the time it takes for the complete transformation of the anatase into rutile. Analysis of these phase-transformation diffractograms led to an activation energy in the Avrami–Erofeev model with n = 8/3 of 178 kJ mol−1. The influence of the Mg ion’s addition on the kinetics of the phase transformation is negligible.