Kinetics of hydration of calcium sulphate hemihydrate

Abstract

The kinetics of hydration of α-CaSO₄·0.5H₂O has been studied by calorimetry, analysis of the liquid phase, measurement of the combined water, and electron microscopic observations. Hemihydrate particles dissolve immediately after mixing with water and subsequently form hydrated layers on their surfaces by intrusion of water molecules, which grow to a thickness of ca. 0.09 µm according to a parabolic law and then undergo destruction, when the dihydrate nuclei are generated for the first time. At this point in time, the induction period terminates, and subsequent hydration of hemihydrate proceeds in accordance with the previously proposed rate equation based on the dissolution–crystallization mechanism.