Otavite-calcite solid-solution formation at the calcite-water interface studied in situ by synchrotron X-ray scattering

Journal Article · Tue Apr 01 04:00:00 EST 1997 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/S0016-7037(97)00010-0· OSTI ID:543162

Chiarello, R P; Sturchio, N C; Xu, Songtao ^[1]

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1. Argonne National Lab., IL (United States); and others

Synchrotron X-ray scattering measurements were performed in situ during the formation of thin (50-600 {Angstrom}) overgrowths of otavite-calcite solid-solutions at the (1014) cleavage surface of single- crystal calcite. These solid-solutions were precipitated from EDTA-bearing aqueous solutions having varied initial saturation states of otavite and calcite. From repetitive X-ray diffraction scans, the Cd/(Ca + Cd) ratios and the effective thicknesses (average domain size perpendicular to the calcite cleavage surface) of the solid-solutions were determined as a function of time. Additional in-plane X-ray diffraction scans were done to further characterize the relationship between the solid-solutions and the calcite cleavage surface. The solid-solution phase grew epitaxially with a (1014) growth plane oriented parallel to the calcite (1014) cleavage surface. The compositions of the solid-solutions evolved with time, while their growth rates (increases in effective thickness) remained fairly constant (10-54 {Angstrom}/hr). In each experiment, the coverage of the initial surface by the solid-solution (calculated from the difference between the initial and final Cd concentrations in the aqueous solution) was about 20%. Glancing-incidence X-ray reflectivity scans were also monitored as a function of time. From these scans, we determined that the solid-water interface did not become significantly rougher during the nucleation and growth of the solid-solution phase. These observations indicate that the solid-solution grew by layer spreading and that most growth may have occurred preferentially at macrostep faces produced during cleavage. 30 refs., 6 figs., 2 tabs.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 543162
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 7 Vol. 61; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
58 GEOSCIENCES
CALCITE
MICROSTRUCTURE
SOLID SOLUTIONS
X-RAY DIFFRACTION