(754f) A Mechanistic Model for Crystal Growth of Calcite

Calcite (CaCO₃) is one of the most abundant simple salts in the geological environment. It is also used in paints, paper making and the cement industry. Crystal growth of calcite and the effect of impurities, both inorganic (e.g., Mg, Sr¹) and organic (e.g., aspartate, citrate²), on the growth spirals has been extensively studied via experiments in the biomineralization literature.  We present a high-fidelity growth model that starts from the crystal structure data and is able to calculate the relative growth rates on all the faces of the crystal and can thus predict the morphology. The model accounts for the long-range solid-solid interactions; it also captures the effect of the solvent on the crystal growth of calcite surfaces. The intermolecular interactions in the solid have been modeled using the Periodic Bond Chain (PBC) theory³. The concept of a building unit of the PBC has been applied to account for the stoichiometry and dipole moment properties of the PBCs. The model also allows for the presence of multiple growth units along the step edges by using the kink rate model developed by Kuvadia & Doherty⁴. Our model correctly predicts the shape of the growth spirals on the (10-14) surface of calcite grown from aqueous solution, including the presence of an asymmetric spiral, as reported in the literature from AFM experiments⁵. The effect of Ca²⁺ to CO₃^2- ion ratio in the solution on the growth process, specifically on the step velocities of the asymmetric edges of the growth spiral, has been captured by this model. The model also explains the effect of inorganic impurities such as Mg²⁺ ions on the growth spirals of calcite.

This high-fidelity crystal growth model is capable of being generalized to a wide class of ionic crystals, including such important materials as titanium dioxide, potassium dihydrogen phosphate (KDP), etc. Ultimately, the model will provide a tool for predicting crystal morphology so that suitable growth media can be designed (e.g., solvent(s), additives, supersaturation) to deliver inorganic crystals of desired shapes depending on their applications.

References:

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3. Hartman, P. and Perdok, W. G. Acta Crystallogr. 8(1), 49–52 Jan (1955).

4. Kuvadia, Z. B. and Doherty, M. F. Cryst. Growth Des. 11, 2780–2802 (2011).

5. Larsen, K., Bechgaard, K., and Stipp, S. L. S. Geochom. Cosmochim. Acta 74, 2099–2109 (2010).