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Dove PM, Han N, Wallace AF, et al. Kinetics of amorphous silica dissolution and the paradox of the silica polymorphs. Proc Natl Acad Sci U S A. 2008;105(29):9903-8doi: 10.1073/pnas.0803798105.
Dove, P. M., Han, N., Wallace, A. F., & De Yoreo, J. J. (2008). Kinetics of amorphous silica dissolution and the paradox of the silica polymorphs. Proceedings of the National Academy of Sciences of the United States of America, 105(29), 9903-8. https://doi.org/10.1073/pnas.0803798105
Dove, Patricia M, et al. "Kinetics of amorphous silica dissolution and the paradox of the silica polymorphs." Proceedings of the National Academy of Sciences of the United States of America vol. 105,29 (2008): 9903-8. doi: https://doi.org/10.1073/pnas.0803798105
Dove PM, Han N, Wallace AF, De Yoreo JJ. Kinetics of amorphous silica dissolution and the paradox of the silica polymorphs. Proc Natl Acad Sci U S A. 2008 Jul 22;105(29):9903-8. doi: 10.1073/pnas.0803798105. Epub 2008 Jul 15. PMID: 18632576; PMCID: PMC2481359.
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Proc Natl Acad Sci U S A. 2008 Jul 22;105(29):9903-8. doi: 10.1073/pnas.0803798105. Epub 2008 Jul 15.

Kinetics of amorphous silica dissolution and the paradox of the silica polymorphs.

Proceedings of the National Academy of Sciences of the United States of America

Patricia M Dove, Nizhou Han, Adam F Wallace, James J De Yoreo

Affiliations

  1. Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA. [email protected]

PMID: 18632576 PMCID: PMC2481359 DOI: 10.1073/pnas.0803798105

Abstract

The mechanisms by which amorphous silica dissolves have proven elusive because noncrystalline materials lack the structural order that allows them to be studied by the classical terrace, ledge, kink-based models applied to crystals. This would seem to imply amorphous phases have surfaces that are disordered at an atomic scale so that the transfer of SiO(4) tetrahedra to solution always leaves the surface free energy of the solid unchanged. As a consequence, dissolution rates of amorphous phases should simply scale linearly with increasing driving force (undersaturation) through the higher probability of detaching silica tetrahedra. By examining rate measurements for two amorphous SiO(2) glasses we find, instead, a paradox. In electrolyte solutions, these silicas show the same exponential dependence on driving force as their crystalline counterpart, quartz. We analyze this enigma by considering that amorphous silicas present two predominant types of surface-coordinated silica tetrahedra to solution. Electrolytes overcome the energy barrier to nucleated detachment of higher coordinated species to create a periphery of reactive, lesser coordinated groups that increase surface energy. The result is a plausible mechanism-based model that is formally identical with the classical polynuclear theory developed for crystal growth. The model also accounts for reported demineralization rates of natural biogenic and synthetic colloidal silicas. In principle, these insights should be applicable to materials with a wide variety of compositions and structural order when the reacting units are defined by the energies of their constituent species.

References

  1. Proc Natl Acad Sci U S A. 2005 Oct 25;102(43):15357-62 - PubMed
  2. Science. 1991 Mar 15;251(4999):1343-6 - PubMed

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