title: Al coordination and water speciation in hydrous aluminosilicate glasses: direct evidence from high-resolution heteronuclear 1H-27Al correlation NMR.
abstract: In order to shed light on the dissolution mechanisms of water in depolymerized aluminosilicate melts/glasses, a comprehensive one- (1D) and two-dimensional (2D) NMR study has been carried out on hydrous Ca- and Mg-aluminosilicate glasses of a haplobasaltic composition. The applied techniques include 1D 1H MAS NMR and 27Al-->1H cross-polarization (CP) MAS NMR, and 2D 1H NOESY and double-quantum (DQ) MAS NMR, 27Al triple-quantum (3Q) MAS NMR and 27Al-->1H heteronuclear correlation (HETCOR) and 3QMAS/HETCOR NMR. Ab initio calculations were also performed to place additional constraints on the 1H NMR characteristics of AlOH and Si(OH)Al groups. This study has revealed, for the first time, the presence of free OH (i.e. (Ca, Mg)OH), SiOH and AlOH species, in addition to molecular H2O, in hydrous glasses of a depolymerized aluminosilicate composition. The AlOH groups are mostly associated with four-coordinate Al, but some are associated with five- and six-coordinate Al.
authors.affiliation: Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori 682-0193 Japan. xianyu@misasa.okayama-u.ac.jp
authors.forename: Xianyu
authors.initials: X
authors.lastname: Xue
authors.forename: Masami
authors.initials: M
authors.lastname: Kanzaki
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D000538:Aluminum Silicates / Q000737:chemistry*; D003198:Computer Simulation; D005898:Glass / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011522:Protons; D014867:Water / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D011522:Protons; D014867:Water; C049037:aluminosilicate; D000535:Aluminum