Growth of Ionic Crystals from Concentrated Aqueous Solutions-Hypothesis of Cation Dehydration and Insertion to Growing Interfaces

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Abstract
The growth of ionic crystals from aqueous solution has been studied by in-situ observation using a microscope. The concentration distributions around the growing crystals, NaClO3 whiskers and NH4Cl dendrites, were measured by multiple-beam interferometry (MBI). In-situ observation of the growth of twelve kinds of alkali salts was carried out under a microscope. It was found that the characteristic growth features, such as growth forms, growth rates and the stability of facets, of those crystals can be arranged in order according to the radii of the cations of each salt. In order to explain the experimental results, a hypothesis of the difficulty of the dehydration of cations was proposed. The difficulty of inserting a cation into various types of kink sites are compared. The characteristic features of the growth form among CsCl, KCl, and NaCl, and characteristics of growth rates among the directions of growing interfaces can be explained by the variation of the difficulty of dehydration.