Fivefold-coordinated aluminum in tectosilicate glasses observed by triple quantum MAS NMR

Citation
Mj. Toplis et al., Fivefold-coordinated aluminum in tectosilicate glasses observed by triple quantum MAS NMR, AM MINERAL, 85(10), 2000, pp. 1556-1560
Citations number
25
Categorie Soggetti
Earth Sciences
Journal title
AMERICAN MINERALOGIST
ISSN journal
0003004X → ACNP
Volume
85
Issue
10
Year of publication
2000
Pages
1556 - 1560
Database
ISI
SICI code
0003-004X(200010)85:10<1556:FAITGO>2.0.ZU;2-5
Abstract
Eight glasses with molar Mg/2Al approximate to 1 in the system MgO-Al2O3-Si O2 have been studied by magic angle spinning (MAS) NMR spectroscopy. Using triple quantum (3Q) NMR techniques we find evidence for significant concent rations of Al coordinated to five O atoms in all glasses, the proportion in creasing with decreasing Mg/Al and decreasing silica content. In glasses wi th Mg/2Al = 1, up to 6% of the Al is estimated to be coordinated to five ra ther than four O atoms. Calculations of the polymerization state of these l iquids made assuming that all aluminum is in tetrahedral coordination charg e balanced by magnesium are thus seriously in error. Such errors may be of even greater importance at the high temperatures and pressures relevant to the Earth and materials sciences.