The nature of hydroxyl groups in aluminosilicate glasses: Quantifying Si-OH and Al-OH abundances along the SiO2-NaAlSiO4 join by 1H, 27Al-1H and 29Si-1H NMR spectroscopy

Wim J. Malfait, Xianyu Xue

Research output: Contribution to journalArticle

38 Citations (Scopus)

Abstract

The combined results of 27Al-1H and 1H-29Si-1H cross polarization NMR experiments for hydrous glasses (containing 0.5-2 wt% water) along the SiO2-NaAlSiO4 join confirm that the dissolution mechanism of water in aluminosilicate glasses is fundamentally the same as for Al-free systems, i.e. the dissolved water ruptures oxygen bridges and creates Si-OH and Al-OH groups, in addition to forming molecular water (H2Omol). The fraction of Al-OH increases non-linearly as the Al content increases with up to half of the OH groups as Al-OH for compositions close to NaAlSiO4. The relative abundances of the different species are controlled by the degree of Al-avoidance and the relative tendency of hydrolysis of the different types of oxygen bridges, Si-O-Si, Si-O-Al and Al-O-Al. A set of homogeneous reactions is derived to model the measured Al-OH/Si-OH speciation, and the obtained equilibrium constants are in agreement with literature data on the degree of Al-avoidance. With these equilibrium constants, the abundance of the different oxygen species, i.e. Si-O-Si, Si-O-Al, Al-O-Al, Si-OH, Al-OH and H2Omol, can be predicted for the entire range of water and Al contents.

Original languageEnglish
Pages (from-to)719-737
Number of pages19
JournalGeochimica et Cosmochimica Acta
Volume74
Issue number2
DOIs
Publication statusPublished - Jan 15 2010

ASJC Scopus subject areas

  • Geochemistry and Petrology

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