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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2018: 2.631

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
Source Normalized Impact per Paper (SNIP) 2018: 1.103

Online
ISSN
1945-3027
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Volume 100, Issue 5-6

Issues

Influence of hydration on 23Na, 27Al, and 29Si MAS-NMR spectra of sodium saponites and sodium micas

Jesus Sanz / Isabel Sobrados / Jean-Louis Robert
  • IMPMC, UMR 7590, CNRS-Université Pierre et Marie Curie, Case courrier 115, 4 place Jussieu, 75252 Paris Cedex 05, France
  • Other articles by this author:
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Published Online: 2015-05-12 | DOI: https://doi.org/10.2138/am-2015-4832

Abstract

Synthetic sodium saponites, NaxMg3(Si4-xAlx)O10(OH)2·nH2O, with 0.33 ≤ x ≤ 1, and trioctahedral sodium micas series, Na(Mg3-yAly)(Si3-yAl1+y)O10(OH)2·nH2O, with 0 ≤ y ≤ 1, have been investigated by MAS-NMR spectroscopy. The presence of anhydrous, one-layer and two-layer hydrates, deduced by X‑ray diffraction, has been associated with specific lines detected in 23Na MAS-NMR spectra. In these phyllosilicates, the location of tetra- and octahedral charge has been analyzed by 27Al MAS-NMR spectroscopy. The salient result is the major effect of the interlayer charge on 29Si chemical shift of the four NMR components ascribed to Si3, Si2Al, SiAl2, and Al3 environments. This effect is much more important than the most commonly accepted contribution of the ditrigonal distortion of tetrahedral sheets. In saponites, 29Si MAS-NMR spectra change considerably with the sodium hydration. In dehydrated samples, where Na cations are engaged in two pseudo-hexagonal cavities, 29Si MAS-NMR components split as a consequence of the partial sodium occupancy of three neighboring hexagonal rings that surrounds a particular tetrahedron. In hydrated samples, where Na+ cations interact with water, chemical shifts of resolved components are averaged as a consequence of interlayer water and cation mobilities.

Keywords: 2:1 phyllosilicates; 29Si; 27Al; and 23Na MAS-NMR spectroscopy; Si-Al distribution; charge location; hydration state

About the article

Received: 2013-12-05

Accepted: 2014-11-30

Published Online: 2015-05-12

Published in Print: 2015-05-01


Citation Information: American Mineralogist, Volume 100, Issue 5-6, Pages 1076–1083, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2015-4832.

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© 2015 by Walter de Gruyter Berlin/Boston.

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