Holistic approach to dissolution kinetics: linking direction-specific microscopic fluxes, local mass transport effects and global macroscopic rates from gypsum etch pit analysis

Abstract

(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. 1956pp. -1965pp. . ISSN 1463 Permanent WRAP url: http://wrap.warwick.ac.uk/54301/ Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes the work of researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-forprofit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Publisher's statement: None A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP url' above for details on accessing the published version and note that access may require a subscription. 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 10 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 15 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 20 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 s...

In situ nanoscale observations of gypsum dissolution by digital holographic microscopy

“…However, (101) steps are less stable (Weijnen et al, 1987), and etch pits bounded by (001) and (100) are typically observed in the present study, based on the angles between the intersecting walls. Similar etch pit morphologies in gypsum have been reported by Fan and Teng (2007) and Peruffo et al (2013).…”

“…5, are (21 ± 2) pmol m −2 s −1 and (7.1 ± 4) µmol m −2 s −1 . These values are somewhat lower than, yet still basically consistent with, the surface normal rates of (40 ± 5) µmol m −2 s −1 , (50 ± 20) µmol m −2 s −1 , and (57 ± 14) µmol m −2 s −1 reported by Peruffo et al (2013), Colombani (2008), and Mbogoro et al (2011), respectively. Both ROI 1 and ROI 2 return to a lower rate of dissolution after the brief acceleration.…”

“…These etch pits are highly anisometric, being much longer than they are wide and appearing as narrow slits when viewed from above. Similar morphologies for etch pits in gypsum have been reported by Peruffo et al (2013).…”

“…Shindo et al (1996) reported AFM observations of layer-by-layer dissolution of (010) anhydrite by the nucleation, growth, and coalescence of rectangular terraces. Peruffo et al (2013) used AFM to link direction-specific microscopic fluxes, local mass transport effects and global macroscopic rates from analysis of etch pits formed in gypsum surfaces within the first 100 s of contact with water. Fan and Teng (2007) reported in situ AFM observations, using a fluid cell, of anisotropy in step velocity and an absence of deep etch pits.…”

Combinatorial localized dissolution analysis: Application to acid-induced dissolution of dental enamel and the effect of surface treatments

“…[6][7][8][9][10][11][12] Studies of the mechanism and kinetics of dissolution processes are important for both fundamental understanding and for various technical applications. This area requires methodologies that can probe dissolution under conditions of high and well-defined mass transport, 13 so that surface kinetics can be extracted free from convolution from mass transport.…”