In situ observation of epitaxial growth during evaporative simultaneous crystallization from aqueous electrolytes in droplets

Abstract

In this study, crystallization phenomena were investigated by real-time in situ observation of seeded droplets under evaporation using a self-developed hot-stage platform. Ternary solutions at eutonic conditions at 25◦C were investigated for the following systems: NaCl–KCl–H2O, NaCl–CaSO4– H2O, and NaCl–Na2SO4–H2O. Evidence of epitaxial growth was found for aqueous NaCl–KCl and aqueous NaCl–Na2SO4. Sodium chloride nucleated and grew epitaxially upon the other substrates in a larger proportion compared with the inverse. This observation could be related to the higher solubility, and consequently higher residual supersaturation of NaCl regarding the other components. Hopper-like NaCl crystals developed in almost all systems. The results may help devise strategies to control particle morphologies and purity in industrial crystallization from complex systems.