Synthesis-dependant structural variations in amorphous calcium carbonate

Abstract

Amorphous calcium carbonate (ACC) was synthesised in the presence of the additives magnesium and poly(aspartic acid) (pAsp) and the structure and crystallisation of these ACC samples was investigated using a range of techniques including X-Ray Absorption Spectroscopy (XAS), X-Ray Diffraction (XRD) and Infra-Red Spectroscopy (IR). The experiments demonstrated that synthetic ACC can be produced with different short-range structures, according to the solution additives used. While the first Mg–ACC precipitates showed short-range structures most similar to aragonite, with monohydrocalcite short-range structures developing with incubation in solution, the initial pAsp–ACC precipitates possessed short-range structures resembling vaterite. The results show that the influence of these additives on the crystallisation of calcium carbonate is apparent even in the precipitation of the first amorphous precursor phase, and that the first stages of recrystallisation involve the expulsion of water from the structure rather than significant changes in the short-range structure around the calcium ions.