The role of pH and Mg on the stability and crystallization of amorphous calcium carbonate

► We studied the effect of pH and Mg in the crystallization of amorphous CaCO3 (ACC). ► The study combined synchrotron-based scattering with electron microscopy. ► The pH-dependent C speciation and hydration strength of Mg2+ control ACC structure. ► This ACC structure governs the ACC dissolution rat...

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Bibliographic Details
Published in:Journal of alloys and compounds 2012-09, Vol.536 (SUPPL.1), p.S477-S479
Main Authors: Rodriguez-Blanco, J.D., Shaw, S., Bots, P., Roncal-Herrero, T., Benning, L.G.
Format: Article
Language:English
Subjects:
Amorphous materials
Calcite
Calcium carbonate
Cross-disciplinary physics: materials science
rheology
Crystal growth
Crystallization
Dissolution
Exact sciences and technology
Growth from solutions
Magnesium
Materials science
Methods of crystal growth
physics of crystal growth
Nanostructured materials
Physics
Stability
Synchrotron radiation
Transformations
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Summary:► We studied the effect of pH and Mg in the crystallization of amorphous CaCO3 (ACC). ► The study combined synchrotron-based scattering with electron microscopy. ► The pH-dependent C speciation and hydration strength of Mg2+ control ACC structure. ► This ACC structure governs the ACC dissolution rate and crystallization pathway. The effects of pH and Mg on the crystallization of amorphous calcium carbonate (ACC) to vaterite and/or calcite were studied using a combination of in situ time resolved synchrotron-based techniques and electron microscopy. The experiments showed that Mg increased the stability of ACC and favoured the formation of calcite over vaterite. A neutral (∼7) starting pH during mixing promoted the transformation of ACC into calcite via a dissolution/reprecipitation mechanism. Conversely, when ACC formed in a solution that started with a high initial pH (∼11.5), the transformation to calcite occurred via metastable vaterite, which formed via a spherulitic growth mechanism. In a second stage this vaterite transformed to calcite via a surface-controlled dissolution and recrystallization mechanism. These crystallization pathways can be explained as a consequence of the pH-dependent composition, local structure, stability and dissolution rates of ACC.
ISSN:0925-8388
1873-4669
DOI:10.1016/j.jallcom.2011.11.057