Study of Anatase-to-Rutile Phase Transformation in Milled and Unmilled Samples

Anatase-to-rutile phase transformation was studied in milled and unmilled samples. Ball milling was carried out in two types of ball mills, planetary and tumbler, with a ball-to-powder ratio of 40:1 over 2-48 hours. First, the unmilled samples were heated in the furnace at various temperatures for different periods of time. The results revealed that the anatase-to-rutile transformation completed at 980 after 48 hours. The rate of transformation in milled samples was greatly higher than that of unmilled ones. Activation energy in unmilled samples was about 440 kj/mol. The rate of transformation in the planetary ball mill was higher than that in tumbler mill. In the former, transformation almost finished after 16 hours of milling while in the lattar, it did not finish even after 48 hours. XRD results revealed that the transformation proceeds through an intermediate srilankite phase in all milled samples. However, srilankite was not observed in the unmilled samples.