Determination of crystal nucleus size of potassium chloride from ethanol solution caused by ultrasonic irradiation

The solubilities of electrolyte salts, such as sodium chloride (NaCl) and potassium chloride (KCl), are small in alcohol solution. As an application of such dilute solubility, nucleation phenomena were investigated by the dynamic laser scattering (DLS) method at different supersaturation degrees, prepared by different solubilities of KCl in aqueous ethanol solutions. The supersaturated solution of KCl was very stable, and therefore ultrasonic irradiation was utilized as a trigger of nucleation. The time-change of the sizes of fine KCl crystals was measured, and the nucleus size was obtained by extrapolating the size of the fine crystals to zero-time. The nucleus size of KCl was correlated by the modified Gibbs–Thomson equation as a function of supersaturation. It was found that the nucleus size tended to increase when supersaturation decreased, but three different curves for three different temperatures could be obtained. The modified Gibbs–Thomson equation represented the nucleus size at three different temperatures. The correlated “minimum supersaturation energy” parameters were converged to zero at the saturated temperature. The parameter “minimum supersaturation energy” could be interpreted as “ultrasonic effective energy” that could be defined as the received energy in the solution from ultrasonic irradiation.