Thermochimica Acta 414 (2004) 137–143 Nanocrystallization of anatase in amorphous TiO 2 Daniel Švadlák a , Jana Shánˇ elová a , Jiˇ r´ ı Málek a,∗ , Luis A. Pérez-Maqueda b , José Manuel Criado b , Takefumi Mitsuhashi c a Department of Physical Chemistry, Faculty of Chemical Technology, University of Pardubice, ˇ Cs. Legi´ ı Sq. 565, 532 10 Pardubice, Czech Republic b Instituto de Ciencia de Materiales de Sevilla, CSIC-UNSE, Americo Vespucio s/n, Isla de la Cartuja, Sevilla 41010, Spain c Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba-shi, Ibaraki 305-0044, Japan Received 4 September 2003; received in revised form 12 December 2003; accepted 15 December 2003 Abstract The kinetics of nanocrystallization in amorphous TiO 2 has been studied in non-isothermal conditions by DSC. It was found that this process could be well described by standard Johnson–Mehl–Avrami–Kolmogorov (JMA) model with kinetic exponent m ∼ = 1. The kinetic parameters were calculated by simultaneous analysis of experimental data taken at different heating rates. These parameters were used as a basis for prediction of crystallization kinetics in isothermal conditions. The agreement between the JMA model prediction and experimental data depends on the method of preparation of amorphous TiO 2 . © 2004 Elsevier B.V. All rights reserved. Keywords: Amorphous TiO 2 ; Crystallization; JMA model; Kinetic analysis 1. Introduction Titania (TiO 2 ) is a material widely used in the electronics, ceramics and pigment industries. The high photocatalytic activity of titania has been well-documented [1]. It is also well known that such activity of amorphous titania is negli- gible and that of nanocrystalline anatase is greater rather that the rutile or brookite [2]. Many approaches have been used to obtain a nanocrystalline titania with desired properties. One of the most popular method is a controlled crystalliza- tion of amorphous titania (a-TiO 2 ) prepared by hydrolysis of alkoxide based sol–gel synthesis or precipitation process. Exarhos and Aloi [3] studied isothermally the kinet- ics of the crystallization of a-TiO 2 films using in situ time-resolved Raman spectroscopy. They found that the JMA nucleation-growth model could describe the kinetics of this process. The JMA kinetic exponent extracted from experimental data was found to be 1.4 <m< 2. Very similar behavior was reported also by Stojanovi´ c et al. [4] who found somewhat higher values of the kinetic expo- nent 2.2 <m< 3 for crystallization of a-TiO 2 powder in non-isothermal conditions. Nevertheless, Zhang and Ban- ∗ Corresponding author. Tel.: +420-466-036-554; fax: +420-466-036-361. E-mail address: jiri.malek@upce.cz (J. M´ alek). field [5] have found that the JMA model cannot describe the isothermal experimental data of crystal growth of nanocrys- talline anatase in a-TiO 2 , obtained by X-ray diffraction and transmission electron microscopy. They applied a kinetic model adopting Smoluchowski coagulation approach as a suitable tool to interpret quantitatively the experimental data. From their analysis it seems that the crystallization of amorphous titania is a complex process comprising several steps such as interface nucleation, crystal growth of anatase and oriented attachment of surrounding anatase particles. The aim of this paper is to analyze the applicability of the JMA model for nanocrystallization process in amorphous ti- tania using non-isothermal calorimetric measurements. The kinetic parameters are then calculated by simultaneous anal- ysis of experimental data taken at different heating rates. The prediction capability of the kinetic models is tested by using isothermal crystallization data. The advantage of this approach is a possibility to reveal a complex crystallization behavior frequently found in oxide systems [6,7]. 2. Experimental Amorphous titania was prepared by controlled hydrol- ysis of titanium isopropoxide Ti[OCH(CH 3 ) 2 ] 4 , supplied by WAKO Pure Chemical Industries, Ltd., by using two 0040-6031/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2003.12.009