AFM observations and simulations of jarosite growth at the molecular scale: probing the basis for the incorporation of foreign ions into jarosite as a storage mineral |
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Authors: | U Becker B Gasharova |
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Institution: | Universit?t Münster, Institut für Mineralogie, Corrensstr. 24, 48149 Münster, Germany Fax: +49 251 83-38397 e-mail: ubecker@uni-muenster.de, DE Forschungszentrum Karlsruhe GmbH, Institute for Technical Chemistry, Section Water Technology and Geotechnology, Division of Technical Mineralogy, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany, DE
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Abstract: | The growth of K-jarosite was evaluated using scanning electron microscopy (SEM), atomic force microscopy (AFM), and molecular
simulations. SEM micrographs show crystals with almost quadratic and, to a minor extent, triangular faces. These were identified
to be {0 1 2} and (0 0 1) faces, respectively, using an X-ray single-crystal diffractometer. These results are in agreement
with molecular simulations that show that the dipole-free {0 1 2} face is the most stable surface, followed by the (0 0 1)
surface, that can lower its dipole moment perpendicular to the surface during relaxation. On the {0 1 2} face, the most stable
step directions were identified. From these, an idealized equilibrium growth island can be constructed when the corner energies
are minimized by the successive removal of corner ions until a stoichiometric growth island is obtained. Such an equilibrium
growth island is the basis for developing a spiral growth model that explains the mechanism of spiral formation as observed
using AFM. Furthermore, reactive sites that are potential candidates for the incorporation of foreign ions can be located.
Received: 2 January 2001 / Accepted: 30 April 2001 |
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Keywords: | AFM XRD measurements Molecular simulations Crystal growth Jarosite |
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