In situ AFM study of the dissolution and recrystallization behaviour of polished and stressed calcite surfaces |
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| Authors: | J Bisschop DK Dysthe B Jamtveit |
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| Institution: | a Physics of Geological Processes, University of Oslo, PO Box 1048 Blindern, 0316 Oslo, Norway
b Institut für Mineralogie, Universität Münster, Corrensstrasse 24, D-48149 Münster, Germany |
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| Abstract: | We investigated the dissolution behaviour of polished calcite surfaces in situ using a fluid-cell atomic force microscope. Polished calcite surfaces enabled us to study the effects of applied surface stress and crystallographic orientation on calcite dissolution pattern formation. Thin-sections of Iceland spar single-crystals polished either parallel or with a 5° miscut angle to  cleavage planes were studied. Compressive surface stresses of up to 50 MPa were applied to some of the thin-section samples by means of elastic concave bending. Experiments were carried out in semi-stagnant deionized water under mainly transport limited dissolution conditions. Samples polished parallel to  cleavage planes dissolved by the formation of etch-pits originating from polishing defects. The dissolution behaviour of 5° miscut surfaces was relatively unaffected by polishing defects, since no etch-pits developed in these samples. Dissolution of the miscut samples led to stepped or rippled surface patterns on the nanometer scale that coarsened during the first 30-40 min of the experiments. Possible reasons for the pattern-coarsening were: (i) progressive bunching of retreating dissolution steps and (ii) surface energy driven recrystallization (Ostwald ripening) under transport limited dissolution conditions. A flat polished miscut surface in calcite may recrystallize into a hill-and-valley structure in a (near-)saturated solution so as to lower its total surface free energy in spite of a larger surface area. No clear effect of applied stress on dissolution pattern formation has been observed. |
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