The mechanism of reequilibration of solids in the presence of a fluid phase

The preservation of morphology (pseudomorphism) and crystal structure during the transformation of one solid phase to another is regularly used as a criterion for a solid-state mechanism, even when there is a fluid phase present. However, a coupled dissolution–reprecipitation mechanism also preserves the morphology and transfers crystallographic information from parent to product by epitaxial nucleation. The generation of porosity in the product phase is a necessary condition for such a mechanism as it allows fluid to maintain contact with a reaction interface which moves through the parent phase from the original surface. We propose that interface-coupled dissolution–reprecipitation is a general mechanism for reequilibration of solids in the presence of a fluid phase.

A single crystal of KBr is transformed to a porous single crystal of KCl by immersion in saturated KCl solution. The image shows partial transformation of a crystal of KBr (core) to KCl (porous, milky rim) by an interface coupled dissolution–reprecipitation mechanism. The external dimensions and crystallographic orientation of the original crystal are preserved, while a reaction interface moves through the crystal.Figure optionsDownload as PowerPoint slide