ON THE KINETICS OF SOLID-LIQUID-SOLID PHASE-TRANSFORMATION

Solid-solid phase transformation of different hydrates or polymorphs i n suspension proceeds in such a way that the metastable phase dissolve s and the stable phase precipitates from the solution. If the starting point lies within the metastable zone of the stable phase, the transf ormation starts only after elapse of the corresponding induction perio d. In the case when the starting point is situated outside the metasta ble zone of the stable solute, the transformation proceeds without any delay. These theoretical considerations are illustrated by an example with recrystallization of calcium sulphate in presence of phosphoric acid; a small concentration change of the acid changes the kinetics si gnificantly.