Crystal Growth and Dissolution of Calcite in the Presence of Fluoride Ions: An Atomic Force Microscopy Study

Abstract

Growth and dissolution of calcite {1014} surfaces in aqueous solutions in the presence of fluoride ions have been studied by in situ atomic force microscopy (AFM). Supersaturated and undersaturated solutions with respect to calcite were prepared for the growth and dissolution experiments, respectively. The concentration range of solutions containing fluoride ions varied between 0.025 and 50 mM. The crystal growth rates were measured from the step growth of closing of etch pits along the [010] direction as well as the spreading of two-dimensional growth nuclei in the same direction. Dissolution rates were measured from the time-dependent development of the rhombohedral etch pits along both [010] and [421] directions. Low fluoride concentrations (≤0.33 mM) in the supersaturated solutions did not significantly affect the crystal growth rates of calcite. At higher concentrations (up to 5 mM), the growth rate decreased substantially, reaching 50% of the respective rate in the absence of fluoride for the same...