Studies in the system calcium sulphate/water. Part 4.—Rehydration of hexagonal CaSO4

Abstract

The rehydration of hexagonal CaSO₄ has been studied in the temperature range 298–393 K and at water vapour pressures of 3 × 10³-8.2 × 10³ N m^–2. The reaction is controlled by diffusion of water, following the parabolic law. The rate of rehydration is strongly affected by the external water vapour pressure, probably through an adsorbed multilayer of water. This effect has been corrected for in terms of the B.E.T. relationship and an activation energy of 46 kJ mol^–1 has been calculated for the rehydration.