Abstract: Kinetic study was conducted by X-ray broadening and TEM characterization on the growth of anatase and rutile nanocrystallits in TiO₂ nanoparticles during
isothermic heating at different tempretures. Results indicate that the growth of the heat-treated titania nanocrystallites becomes significant as the temperature
increases to higher than 823K, where anatase growth conforms to the fifth order kinetic equation with exponent 1.15 for time t, its apparent activity energy
correlated is (38.67±6.37)kJ/mol at the temperatures lower than 823K, and (201.55±5.62)kJ/mol at the higher temperatures, owing to the effects of
nanometer scale and phase-transformation. The rutile growth closely fits the second order kinetic equation with exponent 1.03 for time t,
its apparent activity energy calculated is (108.72±5.06)kJ/mol from Arrhenius plots.

Key words: titania nanocrystallites, heat-treatment, kinetics, anatase, rutile, apparent activity energy