Depolymerization effect of water in aluminosilicate glasses: Direct evidence from 1H-27Al heteronuclear correlation NMR

Abstract

We have applied one-dimensional (1D) 1 H MAS NMR, 27 Al → 1 H CP MAS NMR, as well as 2D 27 Al triple-quantum (3Q) MAS NMR, 27 Al → 1 H heteronuclear correlation (HETCOR) and high-resolution 3QMAS/HETCOR NMR techniques to KAlSi 3 O 8 (Or), NaAlSi 3 O 8 (Ab) and NaAlSiO 4 (Ne) glasses containing 0~2 wt% H 2 O to shed light on the dissolution mechanisms of water in aluminosilicate melts (glasses). An Al Q 3 -OH group, characterized by 1 H chemical shifts of 1.3-1.9 ppm, was identified for all hydrous glasses. Its abundance increases with bulk Al/Si ratio. The 27 Al chemical shifts (δ i Al ) of this species are 64-68 ppm, larger than those of Al Q 4 by 3-6 ppm. Despite this difference, it is only through 27 Al → 1 H HETCOR and 3QMAS/HETCOR, but not 27 Al 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 1 H are the key to its revelation.