Determination of metastable zone width and the primary nucleation kinetics of sodium sulfate

The saturation curve, metastable zone width (MSZW) and primary nucleation kinetics were measured and estimated during sodium sulfate cooling crystallization process. The MSZW is commonly used to characterize crystal nucleation and determine the operation window for crystallization process. The MSZW is the difference between the saturation temperature and the temperature at which crystals are formed at different temperatures, cooling rates and agitating rates. The approach to interpret the MSZW obtained by polythermal method using the classical nucleation theory by Nyvlt was extended. Interfacial energy was determined for the growth of sodium sulfate crystals. Nucleation parameters such as surface entropy factor, radius of critical nucleus, Gibbs free energy, and critical energy barrier were investigated. The nucleation order was established based on the measurements of MSZW dependence on cooling rate and agitating rate. It was experimentally observed that there is rise of solubility with increase of temperature. When the temperature becomes higher, solubility gradually declines. In this investigation, MSZW was observed to enhance with increase of cooling rate and decrease with increase of agitating rate.