Structural transformation of nanocrystalline titania grown by sol-gel technique and the growth kinetics of crystallites

Structural transformation of nanocrystalline titania prepared by sol-gel method with hydrolysis precursor titanium isopropoxide was investigated. At the same time, the growth kinetics of titania powders was also studied. It was found that the grain size of the powders increased slowly with autoclave heating temperature up to 503K, when hydrolysis pH value was 0.9, but grew rapidly when heating temperature was higher than 503K. The activation energies for growth of anatase crystallites in two temperature regions were calculated to be 18.5kJ/mol and 59.7kJ/mol respectively. The x-ray diffraction results show that the transformation from anatase phase to rutile phase starts at 503K and structural transformation finished when temperature raises to 543K, which is a temperature much lower than that of the transformation reported in the literature.