Effects of Aggregation of Reactant Powder Particles on the Kinetics and Mechanism of Solid State Reaction between BaCO₃ and TiO₂

Abstract

Mechanism and kinetics of the solid state reaction have. been studied with special emphasis on the effects of aggregation of reactant powder particles. Equimolar mixtures of BaCO₃ and TiO₂ were prepared by partial precipitation and ball milling methods using two kinds of TiO₂ powders with approximately the same ele-mentary particle size in different states of aggregation.
It is shown that BaTiO₃ is the only product when fine TiO₂ was used but that aggregated TiO₂ yielded additional products Ba₂TiO₄ and BaTi₄O₉. Disintegration of large TiO₂ aggregates by ball-milling decreased the amounts of additional products, and prolonged ball-milling led to substantially the same reaction products and kinetics as those observed with fine TiO₂. No single rate equation has been successfully applied to reaction isotherms obtained with different mixtures. Kinetic behavior has been interpreted in terms of the relative amounts of the reaction products as influenced by the state of aggregation of reactant powder particles.