Influence of emulsion types on nucleation kinetics and growth habit in the cooling crystallization

Experiments on unseeded batch cooling crystallization were made to investigate the influence of emulsion [solution in non-solvent (S/NS) emulsion and non-solvent in solution (NS/S) emulsion] on crystal size and growth habit of various materials such as hexahydro-1,3,5-trinitro-1,3,5-triazine, ammonium sulfate, potassium dihydrogen phosphate (KDP), and -glycine. Size of crystals obtained from the S/NS emulsions was found to be significantly larger than that obtained from the NS/S emulsions. Those results were explained by broad induction time distribution of nucleation in the isolated solution droplets and subsequent seeding effect by free movement of early-induced crystals by vigorous agitation. As a result, the population density of crystals was shown to be smaller in the S/NS emulsions than that in the NS/S emulsions. In the S/NS emulsions, desupersaturation rate should be slow and high supersaturation is subsequently generated during crystal growth stage. Therefore, it may be concluded that crystal morphology of the materials with supersaturation dependent growth habit, such as ammonium sulfate, KDP and -glycine, can be controlled by selection of emulsion type.