Epitaxial Calcite Morphology Modified in the Presence of Magnesium and Sulfate Ions

Abstract

Magnesium and sulfate are a determinant key in CaCO₃ mineralization. However, the works of the literature have failed to provide a clear understanding of how these ions influence the nucleation-growth of CaCO₃ precipitation. Our study uses an electrochemical method, having for principle to impose a dissolved oxygen reduction potential on gold (111) films. This technique that allows the exclusive and controlled crystallization of epitaxial calcite established an ideal system for the study of foreign ions influence. The polymorph, composition and morphology of crystals are characterized using scanning electron microscopy (SEM) coupled with X-ray energy dispersive spectroscopy (EDS) and Raman spectroscopy. The results demonstrate that the increase of calcium concentration in calcocarbonic pure solution enhances the nucleation and then the growth of calcite crystals without affecting their morphology and their orientation. However, the magnesium directly modifies the surface morphology of calcite as a consequence of Mg substitution to calcium ions and the inhibitive effect of magnesium is assured by an incorporation mechanism. In the matter of sulfate ions influence, the experimental results indicate that SO₄²⁻ slows down the epitaxial calcite nucleation by substituting itself to carbonate ions preferentially in the center of the crystals facets causing an enlargement of the lattice parameter.