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Formation of calcium sulfate through the aggregation of sub-3 nanometre primary species

DOI: 10.1038/ncomms11177 DOI Help

Authors: Tomasz Stawski (Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences) , Alexander E. S. Van Driessche (CSIC - U.Granada) , Mercedes Ossorio (LEC, IACT, CSIC-UGR) , Juan Diego Rodriguez-blanco (University of Copenhagen) , Rogier Besselink (German Research Centre for Geosciences) , Liane G Benning (University of Leeds)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Nature Communications , VOL 7

State: Published (Approved)
Published: April 2016

Open Access Open Access

Abstract: The formation pathways of gypsum remain uncertain. Here, using truly in situ and fast time-resolved small-angle X-ray scattering, we quantify the four-stage solution-based nucleation and growth of gypsum (CaSO4·2H2O), an important mineral phase on Earth and Mars. The reaction starts through the fast formation of well-defined, primary species of <3 nm in length (stage I), followed in stage II by their arrangement into domains. The variations in volume fractions and electron densities suggest that these fast forming primary species contain Ca–SO4-cores that self-assemble in stage III into large aggregates. Within the aggregates these well-defined primary species start to grow (stage IV), and fully crystalize into gypsum through a structural rearrangement. Our results allow for a quantitative understanding of how natural calcium sulfate deposits may form on Earth and how a terrestrially unstable phase-like bassanite can persist at low-water activities currently dominating the surface of Mars.

Subject Areas: Earth Science, Chemistry

Instruments: I22-Small angle scattering & Diffraction

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