Kinetics and Mechanism of the Reaction Between TiO2 and SrCO3

Abstract

The kinetics of the reaction between strontium carbonate and titanium dioxide were studied in the temperature range 800° to 975°K in order to test the validity of existing solid-state reaction models and to determine the effect of deviations from stoichiometry on solid-state reactions. Anatase, rutile, and nonstoichiometric rutile were isothermally reacted with strontium carbonate, and reaction rate data were obtained using thermogravimetric analysis. The kinetics of reaction between strontium carbonate and stoichiometric anatase were found to be described by the Ginstling-Brounshtein equation. The activation energy for this reaction is 66.6 kcal/mole and the frequency factor is 4.5 × 109 min-1. The kinetics of the reaction between strontium carbonate and both stoichiometric and nonstoichiometric rutile were found to be described by a nuclei growth rate equation based on the transport-controlled growth of spheroids of any shape (plates, spheres, etc.) from a constant number of nuclei in a matrix of composition different from that of the product. The activation energy for the reaction between strontium carbonate and stoichiometric rutile is 97.8 kcal/more and the frequency factor is 3.2 × 1015 min-1. The fact that the solid-state reaction model applicable to the reaction between strontium carbonate and titania is dependent on the structure of titania is explained by considering the process of epitaxial growth. Defects were introduced into the rutile lattice by heating under vacuum and in a carbon monoxide atmosphere. As the O : Ti ratio of rutile decreased from 2.00 to 1.97, a decrease in the activation energy and frequency factor was observed. Both methods of defect preparation resulted in an equivalent effect on the kinetics of the reaction.