posted on 2002-10-01, 00:00authored byHengzhong Zhang, Jillian F. Banfield
The kinetics of crystallization and crystal growth of nanocrystalline anatase in amorphous
titania (2.5−3 nm) samples in the temperature range 300−400 °C was studied by X-ray
powder diffraction (XRD) and transmission electron microscopy (TEM). A kinetic model
adopting the Smoluchowski coagulation formulation, combined with our phenomenologically
derived model kernels, was used to quantitatively interpret the observed kinetic data. It
was revealed that the transformation in the amorphous titania comprises four steps:
interface nucleation of anatase on contact areas of amorphous particles, with an activation
energy of 147 kJ/mol; crystal growth of anatase by redistribution of atoms from either
amorphous particles or smaller anatase crystals onto nanocrystal surfaces, both with an
activation energy of 78 kJ/mol; and oriented attachment of adjacent anatase particles that
are in appropriate orientations, which is less temperature dependent.