Kinetic Model for $TiO_2$ Polymorphic Transformation from Anatase to Rutile

Madras, Giridhar and McCoy, Benjamin J and Navrotsky, Alexandra (2007) Kinetic Model for $TiO_2$ Polymorphic Transformation from Anatase to Rutile. In: Journal of the American Ceramic Society, 90 (1). pp. 250-255.

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Abstract

We propose a distribution kinetics model for the polymorphic transformation (anatase to rutile) and coarsening of $TiO_2$. Based on population balance equations for the size distributions of the dimorphs, the simplified model applies a first-order rate expression for transformation combined with Smoluchowski coalescence for coarsening of anatase and rutile particles. Two moments of the size distributions (number and mass of particles) lead to dynamic expressions for extent of reaction and average particle diameter. The model describes the time-dependent data of Banfield and coworkers [Am. Mineralogist 84, 528-535 (1999); J. Mater. Res. 15, 437-448 (2000)] fairly accurately, and provides activation energies for anatase coalescence and transformation. The equilibrium constant for the microscopically reversible transformation, occurring without coarsening, yields a small endothermic enthalpy change per mole of $TiO_2$. This probably reflects contributions of the transformation enthalpy of the anhydrous phases at the given particle size, which is very close to zero, and the enthalpy associated with a small amount of dehydration (endothermic water evaporation) during transformation.

Item Type:	Journal Article
Publication:	Journal of the American Ceramic Society
Publisher:	Blackwell
Additional Information:	Copyright of this article belongs to Blackwell.
Keywords:	Solid-solid transformations;Polymorph;Titania;Rutile;Anatase
Department/Centre:	Division of Mechanical Sciences > Chemical Engineering
Date Deposited:	25 Aug 2008
Last Modified:	19 Sep 2010 04:34
URI:	http://eprints.iisc.ac.in/id/eprint/9440

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