Brookite → rutile phase transformation of TiO2 studied with monodispersed particles

TiO2 is a polymorphic material (anatase, brookite, and rutile) of current interest for a variety of technological applications. Though the anatase --> rutile transformation has been studied extensively, the brookite transition has rarely been addressed up to date due to the difficulties encountered in obtaining phase-pure brookite. The brookite --> rutile transformation has been studied in this work using monodispersed quasi-spherical particles (similar to154 nm, composed of phase-pure brookite nanocrystals of similar to25 nm) as a starting material. The transition mainly proceeds within the individual particles in the temperature range 500-600degreesC, without the positive detection of the anatase polymorph. The transformation kinetics are best expressed by the "contracting spherical interface" model in the studied temperature range, from which an apparent activation energy of 143.4 +/- 1.2 kJ/mol was derived. The rate parameter for the phase transition may be expressed as k = 1.28 x 10(4) exp(-17248 +/- 144/T) s(-1). (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.