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Ab Initio Prediction of Surface Stability of Fluorite Materials and Experimental Verification
Stockholm University, Faculty of Science, Department of Geological Sciences.
2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 13, 6639-6650 p.Article in journal (Refereed) Published
Abstract [en]

Utilizing first-principle simulations [based on density functional theory (DFT) corrected for on-site Coulomb interactions (DFT+U)], we develop a model to explain the experimental stability in solution of materials having the fluorite structure, such as CaF2 and CeO2. It is shown that the stability of a surface is mainly dependent on its atomic structure and the presence of sites where atoms are deficiently bonded. Using as reference planes the surfaces with low surface formation energies, viz., (111), (100), and (110), our results reveal the relation between the surface energy of any Miller-indexed plane and the surface energy of those reference planes, being dependent on the fluorite surface structure only. Therefore, they follow the same trend for CaF2 and CeO2. Comparison with experimental results shows a correlation between the trends of dry surface energies and surface stabilities during dissolution of both CaF2 and CeO2, even though the chemical processes of dissolution of CeO2 and CaF2 are different. A deviation between ab initio predictions and experiments for some surfaces highlights the sensitivity of the developed model to the treatment of surface dipolar moments.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2013. Vol. 117, no 13, 6639-6650 p.
National Category
Nano Technology Physical Chemistry
URN: urn:nbn:se:su:diva-89273DOI: 10.1021/jp312645fISI: 000317317600017OAI: diva2:616741
Available from: 2013-04-18 Created: 2013-04-18 Last updated: 2013-05-22Bibliographically approved
In thesis
1. A surface approach to understanding the dissolution of fluorite type materials: Implications for mineral dissolution kinetic models
Open this publication in new window or tab >>A surface approach to understanding the dissolution of fluorite type materials: Implications for mineral dissolution kinetic models
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Traditional dissolution models are based in the analyses of bulk solution compositions and ignore the fact that different sites of a surface dissolve at different rates. Consequently, the variation of surface area and surface reactivity during dissolution are not considered for the calculation of the overall dissolution rate, which is expected to remain constant with time. The results presented here show the limitations of this approach suggesting that dissolution rates should be calculated as a function of an overall surface reactivity term that accounts for the reactivity of each of the sites that constitute the surface. In contrast to previous studies, here the focus is put on studying the surface at different dissolution times. Significant changes in surface topography of CaF2 were observed during the initial seconds and up to 3200 hours of dissolution. The observed changes include the increase of surface area and progressive exposure of the most stable planes, with consequent decrease in overall reactivity of the surface. The novelty of a proposed dissolution model for fluorite surfaces, when compared with traditional dissolution models, is that it differentiates the reactivity of each characteristic site on a surface, e.g. plane or step edge, and considers the time dynamics. The time dependency of dissolution rates is a major factor of uncertainty when calculating long term dissolution rates using equations derived from dissolution experiments running for short periods of time and using materials with different surface properties. An additional factor of uncertainty is that the initial dissolution times are the most dynamic periods of dissolution, when significant variations of surface area and reactivity occur. The results are expected to have impact in the field of nuclear waste management and to the larger geological and material science community.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2013. 26 p.
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 352
dissolution, topography, fluorite, surface
National Category
Research subject
urn:nbn:se:su:diva-89257 (URN)978-91-7447-701-6 (ISBN)
Public defence
2013-05-29, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 13:00 (English)

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 5: Submitted.

Available from: 2013-05-07 Created: 2013-04-17 Last updated: 2013-08-09Bibliographically approved

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