Manganese-calcium intermixing facilitates heteroepitaxial growth at the (1014) calcite-water interface

Journal Article · Tue Sep 05 00:00:00 EDT 2017 · Chemical Geology

DOI:https://doi.org/10.1016/j.chemgeo.2017.09.001· OSTI ID:1379947

Xu, Man ^[1]; Riechers, Shawn L. ^[1]; Ilton, Eugene S. ^[1]; Du, Yingge ^[1]; Kovarik, Libor ^[2]; Varga, Tamas ^[2]; Arey, Bruce W. ^[3]; Qafoku, Odeta ^[1]; Kerisit, Sebastien  ^[1]

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1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Physical and Computational Sciences Directorate, Physical Sciences Division
2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Earth and Biological Sciences Directorate, Environmental Molecular Sciences Division
3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Energy and Environment Directorate, Nuclear Sciences Division

For this research, in situ atomic force microscopy (AFM) measurements were performed to probe surface precipitates that formed on the (10$$\bar{1}$$4) surface of calcite (CaCO₃) single crystals following reaction with Mn2⁺-bearing aqueous solutions. Three-dimensional epitaxial islands were observed to precipitate and grow on the surfaces. In situ time-sequenced measurements demonstrated that the growth rates were commensurate with those obtained for epitaxial islands formed on calcite crystals reacted with Cd2⁺-bearing aqueous solutions of the same range in supersaturation with respect to the pure metal carbonate phase. This finding was unexpected as rhodochrosite (MnCO₃) and calcite display a 10% lattice mismatch, based on the area of their (10$$\bar{1}$$4) surface unit cells, whereas the lattice mismatch is only 4% for otavite (CdCO₃) and calcite. Coatings of varying thicknesses were therefore synthesized by reacting calcite single crystals in calcite-equilibrated aqueous solutions with up to 250 μM MnCl₂. Ex situ X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray reflectivity (XRR), and AFM measurements of the reacted crystals demonstrated the formation of an epitaxial (Mn,Ca)CO₃ solid solution. The epitaxial solid solution had a spatially complex composition, whereby the first few nanometers were rich in Ca and the Mn content increased with distance from the original calcite surface, culminating in a topmost region of almost pure MnCO₃ for the thickest coatings. The effective lattice mismatch was therefore much smaller than the nominal mismatch thus explaining the measured growth rates. Lastly, these findings highlight the strong influence played by the substrate on the composition of surface precipitates in aqueous conditions.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC05-76RL01830; AC06-76RLO-1830
• OSTI ID: 1379947
• Alternate ID(s): OSTI ID: 1576815
• Report Number(s): PNNL-SA-125533; PII: S0009254117304904
• Journal Information: Chemical Geology, Vol. 470; ISSN 0009-2541
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
58 GEOSCIENCES
Metal carbonates
Epitaxy
Mineral growth
Lattice mismatch
Mineral coatings