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Holistic approach to dissolution kinetics : linking direction-specific microscopic fluxes, local mass transport effects and global macroscopic rates from gypsum etch pit analysis
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Peruffo, Massimo, Mbogoro, Michael M., Edwards, Martin A. and Unwin, Patrick R. (2013) Holistic approach to dissolution kinetics : linking direction-specific microscopic fluxes, local mass transport effects and global macroscopic rates from gypsum etch pit analysis. Physical Chemistry Chemical Physics, Volume 15 (Number 6). pp. 1956-1965. doi:10.1039/c2cp43555a ISSN 1463-9076.
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WRAP_Peruffo, PCCP, 2013.pdf - Accepted Version Download (1079Kb) | Preview |
Official URL: http://dx.doi.org/10.1039/C2CP43555A
Abstract
Dissolution processes at single crystal surfaces often involve the initial formation and expansion of localized, characteristic (faceted) etch-pits at defects, in an otherwise comparatively unreactive surface. Using natural gypsum single crystal as an example, a simple but powerful morphological analysis of these characteristic etch pit features is proposed that allows important questions concerning dissolution kinetics to be addressed. Significantly, quantitative mass transport associated with reactive microscale interfaces in quiescent solution (well known in the field of electrochemistry at ultramicroelectrodes) allows the relative importance of diffusion compared to surface kinetics to be assessed. Furthermore, because such mass transport rates are high, much faster surface kinetics can be determined than with existing dissolution methods. For the case of gypsum, surface processes are found to dominate the kinetics at early stages of the dissolution process (small etch pits) on the cleaved (010) surface. However, the contribution from mass transport becomes more important with time due to the increased area of the reactive zones and associated decrease in mass transport rate. Significantly, spatial heterogeneities in both surface kinetics and mass transport effects are identified, and the morphology of the characteristic etch features reveal direction-dependent dissolution kinetics that can be quantified. Effective dissolution velocities normal to the main basal (010) face are determined, along with velocities for the movement of [001] and [100] oriented steps. Inert electrolyte enhances dissolution velocities in all directions (salting in), but a striking new observation is that the effect is direction-dependent. Studies of common ion effects reveal that Ca2+ has a much greater impact in reducing dissolution rates compared to SO42−. With this approach, the new microscopic observations can be further analysed to obtain macroscopic dissolution rates, which are found to be wholly consistent with previous bulk measurements. The studies are thus important in bridging the gap between microscopic phenomena and macroscopic measurements.
Item Type: | Journal Article | ||||
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Subjects: | Q Science > QD Chemistry | ||||
Divisions: | Faculty of Science, Engineering and Medicine > Science > Chemistry | ||||
Library of Congress Subject Headings (LCSH): | Electrochemistry, Chemical kinetics, Chemical microscopy, Crystals, Gypsum | ||||
Journal or Publication Title: | Physical Chemistry Chemical Physics | ||||
Publisher: | Royal Society of Chemistry | ||||
ISSN: | 1463-9076 | ||||
Official Date: | 14 February 2013 | ||||
Dates: |
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Volume: | Volume 15 | ||||
Number: | Number 6 | ||||
Page Range: | pp. 1956-1965 | ||||
DOI: | 10.1039/c2cp43555a | ||||
Status: | Peer Reviewed | ||||
Publication Status: | Published | ||||
Access rights to Published version: | Restricted or Subscription Access | ||||
Date of first compliant deposit: | 24 December 2015 | ||||
Date of first compliant Open Access: | 24 December 2015 | ||||
Funder: | European Research Council (ERC), Saint-Gobain Gyproc, University of Warwick. Molecular Organisation and Assembly in Cells, Birmingham Science City, Advantage West Midlands (AWM), European Regional Development Fund (ERDF) |
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