Kinetics of the Reaction between BaCO₃ and TiO₂

Abstract

The reaction between BaCO₃ and TiO₂ has been studied in air and in CO₂ at 700-1020°C. Several products (Ba₂TiO ₄, BaTiO₃, BaTi₃O₇, and BaTi₄O₉) were obtained when the mixtures of BaCO₃ and TiO₂ were heated in air, but, under the CO₂ atmosphere of 300-700mm Hg, BaTiO₃ with very small amounts of BaTi₃O₇ was observed.
The kinetics of the reaction between BaCO₃ and TiO₂ under the CO₂ atmosphere of 500mm Hg were studied. The process of the reaction is composed of two steps, i.e. a phase boundary reaction followed by a subsequent diffusion process. The kinetic data can be expressed reasonably by the first-order equation for the earlier stage, and by Tamman's equation for the later one. The activation energy for the earlier stage of rutile is about 43Kcal/mol. There is a discontinuity at about 830°C in the plotting of log k against l/T for the earlier stage of anatase. The activation energies are about 34 and l6Kcal/mol above and below 830°C respectively. The activation energy for the later stage is about 34Kcal/mol for both anatase and rutile.