Many studies have indicated that the reactivity of reactants in chemical reactions can be increased by mechanical activation through high-energy ball milling. Ball milling is also a way of inducing phase transformation. In this research the polymorphous transformation of TiO_2 (anatase type) during planetary ball milling was investigated. Ball milling was performed in a various powder to ball weight ratios and different times. SEM and XRD were used to evaluate the characteristics of samples. While the anatase to rutile transformation was not completed when heating the samples at 950℃ for 24 hrs, a complete phase transformation could be achieved by ball milling. XRD results showed that rutile is the only phase after prolonged ball milling. Any increase in the powder to ball weight ratio resulted in an increase in the phase transformation time. The XRD analysis of the samples being milled at different times reviled that the transformation of anatase to rutile proceeds through srilankite as an intermediate phase. Considering the temperature rise and high pressure at the collision sites during the ball milling, it was proposed that the polymorphous transformation of TiO_2 could be explained in term of a temperature - pressure phase diagram.
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