The Catalysed and Uncatalysed Nucleation of Gypsum Crystals from Aqueous Solution

Gypsum (Calcium Sulphate Dihydrate) has been precipitated by mixing aqueous solutions of calcium chloride, sodium sulphate and sodium chloride at 25°C. In the absence of solid gypsum, classical nucleation theory predicts rates reasonably well only at the expense of some adjustable parameters like surface energy term. This has been attributed to the difficulties associated with the application of equilibrium thermodynamics to a process of kinetic origin. The presence of solid matter acts as a catalyst and decreases the induction period. In this case, the habit as well as the quantity of gypsum added greatly influences the induction period. Possible reasons for this have been given.