Abstract

We have applied one-dimensional (1D) 1H MAS NMR, 27Al → 1H CP MAS NMR, as well as 2D 27Al triple-quantum (3Q) MAS NMR, 27Al → 1H heteronuclear correlation (HETCOR) and high-resolution 3QMAS/HETCOR NMR techniques to KAlSi3O8 (Or), NaAlSi3O8 (Ab) and NaAlSiO4 (Ne) glasses containing 0~2 wt% H2O to shed light on the dissolution mechanisms of water in aluminosilicate melts (glasses). An Al Q3-OH group, characterized by 1H chemical shifts of 1.3–1.9 ppm, was identified for all hydrous glasses. Its abundance increases with bulk Al/Si ratio. The 27Al chemical shifts (δiAl) of this species are 64–68 ppm, larger than those of Al Q4 by 3–6 ppm. Despite this difference, it is only through 27Al → 1H HETCOR and 3QMAS/HETCOR, but not 27Al MAS or 3QMAS NMR that the peaks are resolved. This study has demonstrated that depolymerization and formation of AlOH/SiOH is a general water dissolution mechanism for polymerized aluminosilicate melts (glasses), and HETCOR NMR experiments involving 1H are the key to its revelation.

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