4 years ago

Uncovering the Atomistic Mechanism for Calcite Step Growth

Uncovering the Atomistic Mechanism for Calcite Step Growth
Marco De La Pierre, Julian D. Gale, Paolo Raiteri, Andrew G. Stack
Determining a complete atomic-level picture of how minerals grow from aqueous solution remains a challenge as macroscopic rates can be a convolution of many reactions. For the case of calcite (CaCO3) in water, computer simulations have been used to map the complex thermodynamic landscape leading to growth of the two distinct steps, acute and obtuse, on the basal surface. The carbonate ion is found to preferentially adsorb at the upper edge of acute steps while Ca2+ only adsorbs after CO32−. In contrast to the conventional picture, ion pairs prefer to bind at the upper edge of the step with only one ion, at most, coordinated to the step and lower terrace. Migration of the first carbonate ion to a growth site is found to be rate-limiting for kink nucleation, with this process having a lower activation energy on the obtuse step. Computer simulations have been used to map the initial thermodynamics for the growth of steps on a calcite surface from aqueous solution, leading to the identification of the competing atomic pathways. This revealed that growth is limited by the rearrangement of adsorbed ion pairs from the exposed corner of the step edge to kink nucleation sites.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/anie.201701701

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