Abstract
The evolution of the surface topography of a calcite crystal subject to dissolution is documented through in situ real-time imaging obtained via atomic force microscopy (AFM). The dissolution process takes place by exposing the crystal surface to deionized water. AFM data allow detection of nucleation and expansion of mono- and multilayer rhombic etch pits and are employed to estimate the spreading rate of these structures. Spatially heterogeneous distributions of local dissolution rate are evaluated from the difference between topographic measurements taken at prescribed time intervals. We rest on a stochastic framework of analysis viewing the dissolution rate as a generalized sub-Gaussian (GSG) spatially correlated random process. Our analysis yields: (i) a quantitative assessment of the temporal evolution of the statistics of the dissolution rates as well as their spatial increments; (ii) a characterization of the degree of spatial correlation of dissolution rates and of the way this is linked to the various mechanisms involved in the dissolution process and highlighted through the experimental evidences. Our results indicate that the parameters driving the statistics of the GSG distribution and the spreading rate of the multilayer pits display a similar trend in time, thus suggesting that the evolution of these structures imprints the statistical features of local dissolution rates.Article HighlightsWe investigate dynamics of dissolution patterns on a calcite crystal in contact with deionized water via AFM imagingTemporal behavior of parameters of our statistical model is consistent with surface pattern evolutionA nested model for the spatial correlation of rates embeds multiple mechanisms driving dissolution rate.
Highlights
Proper assessment of reactive processes at solid–liquid interfaces is of critical importance for the characterization of flow and transport in porous media, as these drive possible alterations of key physical attributes of the hosting formation, such as porosity, permeability, or storage (Hommel et al 2018)
We note that the generalized extreme value (GEV) model does not include information about the statistical behavior of incremental values, a feature which is naturally embedded in the generalized sub-Gaussian (GSG) framework
We monitor the evolution of the surface topography of a calcite crystal subjected to dissolution through in situ real-time atomic force microscopy (AFM) measurements
Summary
Proper assessment of reactive processes at solid–liquid interfaces is of critical importance for the characterization of flow and transport in porous media, as these drive possible alterations of key physical attributes of the hosting formation, such as porosity, permeability, or storage (Hommel et al 2018). A bulk powder experiment is typically considered a pillar for the estimation of dissolution rates (Luttge et al 2013), which are inferred by monitoring changes in dissolved solute concentrations. While these experiments are simple and characterized by a remarkable level of reproducibility, an intrinsic difficulty is related to the observation that measured changes in mass must be normalized by the powder surface area to obtain proper units of rate, i.e., mass per unit area per unit time. Large discrepancies between dissolution rates evaluated under identical laboratory conditions are documented (Arvidson et al 2003) and are attributed to the way the powder surface area is computed and to the actual portion of the mineral surface that is available for the reaction (Luttge et al 2013; Luttge 2005)
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