Solute clustering and crystallization from solution

Three experimental studies, consisting of a laser Raman spectroscopic study, a vertical column experiment, and a microscopic observation, were carried out to evaluate the structures and characteristics of solute clustering in NaNO;The results of these experimental studies suggest that solute clustering occurs in NaNO;For a given solution concentration, as the solution becomes supersaturated, a dynamic rearrangement occurs between lower-ordered ionic species and clusters. The present study explains this rearrangement process in terms of the coalescence of some of the clusters at the expense of other clusters and the dilution of the lower-ordered species.;Thermodynamic considerations and analyses of this solute clustering are described in terms of relationship of free energy versus the solute mole fraction. Models for the nucleation and the crystal growth mechanisms are proposed. These models are based on the fluctuations and changes in structures and properties of solvated solute clusters.;The proposed nucleation models consider two types of mechanisms: the mechanism that occurs under metastable conditions, and the mechanism that occurs under unstable conditions. The latter mechanism is associated with the spinodal-type decomposition. The proposed crystal growth model suggests a dynamic arrangement between the lower-ordered species and the clusters at and near the crystal-solution interface of a growing crystal. The model also suggests a depletion of the clusters as the solution concentration decreases during the growth process.