Investigation of Crystal Nucleation of Highly Supersaturated Aqueous KNO3 Solution from Single Levitated Droplet Experiments

In this work, we use an electrodynamic balance (EDB) to study primary crystal nucleation from single levitated aqueous potassium nitrate (KNO3) solution droplets under isothermal conditions. We investigate crystallization in droplets with volumes less than one nanoliter. From induction time distributions we derive nucleation rates of KNO3. Nucleation processes were found to occur at different mechanisms. Results are interpreted based on the classical nucleation theory (CNT) to gain more information about the prevailing nucleation mechanism. We also investigate the shape and morphology of crystals using scanning electron microscopy. Two typical morphology types of crystallized particles could be identified, depending on whether nucleation occurred during the evaporation phase or at constant supersaturation of solute.