The kinetics of solvent-mediated phase transformations

Abstract

A number of mineralogical and synthetic precipitates undergo solid to solid phase changes via a solution phase. A review of the literature reveals a lack of both experimental data and a framework for its interpretation. A model is developed, for the case of a polymorphic phase transformation, which involves the dissolution of the metastable phase and growth of nuclei of the stable phase. The concepts of dissolution and growth time scales have been introduced and it is shown that their sum is the time required for the disappearance of the metastable phase. Mechanistic insight is best obtained by measure­ment of the supersaturation profile rather than conversion data. It is shown that such profiles are dominated by the plateau supersaturation, which is the point at which dissolution and growth are balanced. Its value is determined by the relative surface areas of the phases and their kinetic constants. The model has been successfully used to simulate available kinetic data for the α → β polymorphic transformation in copper phthalocyanine.