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Mechanochemical access to defect-stabilized amorphous calcium carbonate

DOI: 10.1021/acs.chemmater.8b02339 DOI Help

Authors: Sebastian Leukel (Johannes Gutenberg-Universität Mainz; Graduate School Materials Science in Mainz) , Martin Panthöfer (Johannes Gutenberg-Universität Mainz) , Mihail Mondeshki (Johannes Gutenberg-Universität Mainz) , Gregor Kieslich (University of Cambridge) , Yue Wu (National University of Singapore) , Nina Krautwurst (Johannes Gutenberg-Universität Mainz) , Wolfgang Tremel (Johannes Gutenberg-Universität Mainz)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemistry Of Materials

State: Published (Approved)
Published: August 2018
Diamond Proposal Number(s): 13843

Abstract: Amorphous calcium carbonate (ACC) is an important precursor in the biomineralization of crystal-line CaCO3. The lifetime of transient ACC in nature is regulated by an organic matrix, in order to use it as an intermediate storage buffer or as a permanent structural element. The relevance of ACC in material science is related to our understanding of CaCO3 crystallization pathways. ACC can be obtained by liquid-liquid phase separation, and it is typically stabilized with of the help of macro-molecules. We have prepared ACC by milling calcite in a planetary ball mill. The ball-milled amor-phous calcium carbonate (BM-ACC) was stabilized with small amounts of Na2CO3. The addition of foreign ions in form of Na2CO3 is crucial to achieve complete amorphization. Their incorporation generates defects that hinder recrystallization kinetically. In contrast to wet-chemically prepared ACC, the solvent-free approach makes BM-ACC an anhydrous modification. The amorphization process was monitored by quantitative Fourier transform infrared (FTIR) spectroscopy and solid state 23Na magic angle spinning nuclear magnetic resonance (23Na MAS-NMR) spectroscopy, which is highly sensitive to changes in the symmetry of the local sodium environment. The struc-ture of BM-ACC was probed by vibrational spectroscopy (FTIR, Raman) and solid state MAS NMR (23Na, 13C) spectroscopy. A structural model revealing the partly unsaturated coordination sphere for the Ca2+ ions was derived from the analysis of total scattering data with high-energy synchrotron radiation. Our findings aid in the understanding of mechanochemical amorphization of calcium carbonate and emphasize the effect of impurities on the stabilization of the amorphous phase, which allowed the synthesis of a so far unknown defect variant of ACC with new proper-ties. This may also represent a general approach to obtain new amorphous phases in a variety of different systems.

Subject Areas: Chemistry, Materials


Instruments: I15-Extreme Conditions