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SS2.08 - Two-Step Phase Transformation of Anatase to Rutile in Aqueous Suspension 
April 22, 2014   4:30pm - 4:45pm

The kinetics of the anatase to rutile phase transformation have been quantified for hydrothermally treated nanocrystalline anatase (TiO). Kinetic models based on interface-nucleation or dissolution-precipitation were used to fit the experimental data. Results show that at highly acidic conditions, anatase phase transforms to rutile predominantly by a dissolution-precipitation mechanism, presumably due to the comparatively high solubility of TiO at 250 °C and pH 1.0. In contrast, the data were fit well to the interface-nucleation model for experiments performed at pH 3.0. However, the kinetic data for the phase transformation at pH 2.2 were not fit well using either model. A new kinetic model was derived, which combines the interface-nucleation and dissolution-precipitation models into a two-step transformation mechanism: interface-nucleation followed by dissolution precipitation. The experimental data, which include both particle size and phase composition versus time, are fit well by this new model. Thus, new insight into the mechanism of the anatase to rutile phase transformation under hydrothermal conditions are gained, demonstrating the importance of oriented aggregation induced interface-nucleation mechanism even under conditions of high titania solubility.

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