Effect of pH on Amorphous Calcium Carbonate Structure and Transformation

Journal Article · Wed Jul 13 00:00:00 UTC 2016 · Crystal Growth and Design

DOI:https://doi.org/10.1021/acs.cgd.6b00630· OSTI ID:1329423

Tobler, Dominique J. ^[1]; Rodriguez Blanco, Juan Diego ^[1]; Sørensen, Henning O. ^[1]; Stipp, Susan L. S. ^[1]; Dideriksen, Knud ^[1]

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1. Univ. of Copenhagen (Denmark)

A number of organisms produce crystalline calcium carbonate via a metastable precursor phase termed amorphous calcium carbonate (ACC). ACC also forms during production of CaCO₃ for industrial purposes, e.g., paper manufacturing and synthesis of fillers for polymers. Previous studies suggest that the local structure of ACC controls crystallization kinetics and pathways, i.e., the crystalline polymorph(s) that form(s) in the process. We used pair distribution function (PDF) analysis to provide evidence that the local structure of ACC gradually changes as the pH of the synthesis solutions is increased from 10.6 to 12.7, at ambient conditions. Here, these changes correlate with the mole fraction of incorporated hydroxide ions, which varies gradually from negligible at pH 10.6 to 0.12 at pH 12.7. At lower pH (10.5), vaterite and calcite formed in less than 2 min, but as the pH increased, the lifetime of ACC increased, and it transformed directly to calcite (i.e., no vaterite intermediate). Although higher pH led to a preferable transformation into calcite with decreasing crystal size, variations in ACC local structure cannot be linked to development of a calcite like motif, as has been suggested. On the basis of comparing the measured vaterite PDF to a range of structural models to determine Ca–Ca distances, we found no obvious structural similarity between vaterite and the ACC precursor either, although such analysis is complicated by the ambiguity of the vaterite structure. Presumably, the absence of vaterite and the prolonged ACC stability with increasing synthesis pH could indicate inhibition of crystal nucleation and growth by hydroxide ions.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: Engineering and Physical Sciences Research Council; MIRO; NanoCArB; USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1329423
• Journal Information: Crystal Growth and Design, Journal Name: Crystal Growth and Design Journal Issue: 8 Vol. 16; ISSN 1528-7483
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
calcite
crystal structure
crystallization
crystals
inorganic carbon compounds