The dissolution and growth of sparingly soluble inorganic salts: A kinetics and surface energy approach

Abstract

This paper examines the role of interfacial free energy, especially the electron acceptor/donor or Lewis acid-base (AB) terms, in regulating not only the rates of these reactions but also in determining the solubility behavior of the crystal, S∞. For a considerable number of compounds, the solubilities show a general increase as the solid/liquid interfacial tensions (γSL) decrease, but despite suggestions to the contrary, the relationship between γSL and logS∞ should not necessarily be linear. Interfacial tensions between water and the solid surfaces of a number of sparingly soluble electrolytes have been determined by contact angle measurements by using surface tension component theory to yield the Lifshitz-van der Waals (LW) and Lewis acid-base components. The systems to be discussed will include dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP), hydroxyapatite (HAP), and fluorapatite (FAP). The interfacial tension values, -4.2, 4.3, 10.0, and 18.5 mJ m-2, respectively, were of the same order of magnitude as those calculated from crystallization and dissolution kinetics data.