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Trapping Amorphous Intermediates of Carbonates – A Combined Total Scattering and NMR Study
journal contribution
posted on 2018-10-10, 00:00 authored by Sebastian Leukel, Martin Panthöfer, Mihail Mondeshki, Gregor Kieslich, Yue Wu, Nina Krautwurst, Wolfgang TremelCrystallization via
metastable phases plays an important role in
chemical manufacturing, biomineralization, and protein crystallization,
but the kinetic pathways leading from metastable phases to the stable
crystalline modifications are not well understood. In particular,
the fast crystallization of amorphous intermediates makes a detailed
characterization challenging. To circumvent this problem, we devised
a system that allows trapping and stabilizing the amorphous intermediates
of representative carbonates (calcium, strontium, barium, manganese,
and cadmium). The long-term stabilization of these transient species
enabled a detailed investigation of their composition, structure,
and morphology. Total scattering experiments with high-energy synchrotron
radiation revealed a short-range order of several angstroms in all
amorphous intermediates. From the synchrotron data, a structural model
of amorphous calcium carbonate was derived that indicates a lower
coordination number of calcium compared to the crystalline polymorphs.
Our study shows that a multistep crystallization pathway via amorphous
intermediates is open to many carbonates. We could isolate and characterize
these transient species, thereby providing new insights into their
crystallization mechanism.