On the kinetics of diffusion-limited layer growth in solid-solid systems

Abstract

The diffusion-limited growth of an intermediate layer between two saturated solid solutions is investigated theoretically. It is shown that conventional approaches based on Fick’s law alone can give rise to significant errors if the partial molar volumes of the diffusing species are not constant, because the contribution of bulk flow to the species fluxes is not accounted for. New expressions for layer growth rates in spherical and planar geometries are derived, subject to the condition that the mass or molar density of the new phase is uniform. These results are seen to reduce formally to the standard expressions under appropriate limiting conditions. It is concluded that the old and new approaches are complementary, each being valid under a particular set of circumstances.