Abstract
The interplay between polymorphism and facet-specific surface energy on the dissolution of crystals is examined in this work. It is shown that, using cationic additives, it is possible to produce star-shaped calcite crystals at very high supersaturations. In crystallization processes following the Ostwald rule of stages these star-shaped crystals appear to have higher solubility than both their rhombohedral counterparts and needle-shaped aragonite crystals. The vapour pressures of vaterite, aragonite, star-shaped calcite and rhombohedral calcite crystals are measured using thermogravimetric analysis and the corresponding enthalpies of melting are obtained. Using inverse gas chromatography, the surface energy of the aforementioned crystals is measured as well and the surface energy of the main crystal facets is calculated. Combining the effect of facet-specific surface energies and the enthalpies of melting on a modified version of the classical solubility equation for regular solutions, it is proved that the star-shaped calcite crystals can indeed have higher apparent solubility than aragonitecrystals.
Highlights
In his work ‘On the equilibrium of heterogeneous substances’ [1], Prof
The results show that the star-shaped calcite crystals have much higher surface energy (γ total) than their rhombohedral counterparts and aragonite
Analysis of scanning electron microscope (SEM) images suggests that the material obtained for experiments run for less than 24 h contains star-shaped calcite crystals, such as those reported previously in the literature
Summary
In his work ‘On the equilibrium of heterogeneous substances’ [1], Prof. J. The vapour pressures of vaterite, aragonite and both the rhombohedral and star-shaped calcite were measured using thermogravimetric analysis (TGA). The results show that the star-shaped calcite crystals have much higher surface energy (γ total) than their rhombohedral counterparts and aragonite. The vapour pressure data for all three polymorphs of CaCO3 are measured for the first time, as well as the corresponding surface energies. Surface energy measurements were conducted on aragonite, rhombohedral calcite and starshaped calcite samples. The surface energy plot obtained by an IGC measurement is determined by the adsorption of the different solvent probes on the different crystal facets. Of each poloymorph, carries a different surface energy that appears in different proportions depending on the crystal habit This in silico methodology simulates the adsorption process taking place during an IGC measurement. It uses an optimization algorithm to identify the best combination of these parameters to fit the experimentally obtained IGC plot
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