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Calcite Dissolution Rate Spectra Measured by In Situ Digital Holographic Microscopy

Published

Author(s)

Alexander Brand, Pan Feng, Jeffrey W. Bullard

Abstract

Digital holographic microscopy in reflection mode is used to track in situ, real-time nanoscale evolution of topography of calcite surfaces exposed to showing or static deionized water. The method utilizes conventional immersion objective lenses and is able to capture full-field holograms of the surface at rates of up to 12.5 frame s^-1. Numerical reconstruction of the hologram provides 3D surface topography with vertical resolution of a few nanometers. The method is applied to measure the time-dependent dissolution rate of cleaved (104) Iceland spar calcite surfaces, in terms of either surface normal height changes or absolute volume changes. A statistical distribution, or spectrum, of dissolution rates is generated by sampling multiple area domains on multiple crystals. The data show that dissolution is not described well by a single or average rate value, although the maximum probability dissolution rate agrees well with published mean dissolution rates (e.g., 0.1 µmol m^-2 s^-1 to 0.3 µmol m^-2 s^-1). Etch pits and other sources of rapidly dissolving material appear at different times and have a heterogeneous spatial distribution across the surface. This makes the distribution in rates measured on a single crystal dependent both on the length scale of observation and on time, even under conditions of nominally constant undersaturation. Statistical analysis of the inherent noise in the measurements indicates that the methods for obtaining them are robust, and that the rate spectra reflect fundamental variability of the material instead of measurement artifacts. The same method can be applied to study other dissolution or growth processes at other mineral surfaces to develop a better understanding of the kinetics in terms of rate spectra.
Citation
Geochimica Et Cosmochimica Acta
Volume
213

Keywords

calcite, digital holographic microscopy, dissolution kinetics

Citation

Brand, A. , Feng, P. and Bullard, J. (2017), Calcite Dissolution Rate Spectra Measured by In Situ Digital Holographic Microscopy, Geochimica Et Cosmochimica Acta, [online], https://doi.org/10.1016/j.gca.2017.07.001 (Accessed July 23, 2024)

Issues

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Created July 24, 2017, Updated November 10, 2018