J. Phys. Chem. B 1998, 102, 7523-7529
Water in Silicate Glass:
17O
7523
NMR of Hydrous Silica, Albite, and Na2Si4O9 Glasses
Hideki Maekawa,* Takeshi Saito,† and Toshio Yokokawa DiVision of Chemistry, Graduate School of Science, Hokkaido UniVersity, Sapporo, 060-0810, Japan ReceiVed: January 6, 1998; In Final Form: July 8, 1998
The mechanism of incorporation of water in silica (SiO2), albite (NaAlSi3O8), and Na2Si4O9 composition glass has been studied by 1H, 17O, 23Na, 27Al, and 29Si NMR spectroscopy. Hydrated samples were prepared by quenching the melt from high pressure and high temperature with use of solid-media apparatus with a 17O-enriched starting material. Water content of the hydrated glasses was estimated from 1H NMR peak intensities compared with reference materials. For SiO2 glass, the 17O NMR spectrum has a sharp resonance line at the position corresponding to the chemical shift of molecular water. 17O NMR of both dry and hydrous (50 mol % H2O) albite glasses shows two environments with peaks for Si-O-Si and Si-O-Al. No significant difference was seen between dry and hydrated glasses. For the Na2Si4O9 glass, 1H and 29Si NMR results are consistent with each other and suggest the formation of Si-OH and molecular water in this glass. 17O NMR of this glass shows significant differences between dry and hydrated glass. The intensity of the nonbridging oxygen peak for the hydrated sample decreased considerably with added water. The intensity change of the nonbridging oxygen peak could be quantitatively explained by a formation of a complex with equal molar amounts of Na+ and H2O.
Introduction The mechanism of incorporation of hydrous species in molten and glassy silicates have long been of interest in both geochemistry and glass science.1,2 Water is the most important magmatic volatile, both in terms of its abundance and in its influence on melt properties and crystal-liquid phase relations. It is wellestablished that water dissolves in silicate glasses in at least two distinguishable forms: hydroxyl groups and H2O molecules. The physicochemical properties of water-containing silicate melts, such as viscosity,3-5 melting points,6 and diffusivity of the cations,7 have been reported. Properties of water-containing silicate glasses, for example, decrease of the glass transition temperature,8 decrease of dc conductivity,9 and lowering of the chemical durabilities,10 have also been reported. The solubility of water in silicate melts of various compositions has been investigated and its dependence on pressure has been interpreted in terms of possible hydrous species in silicate melts.11-19 The influence of water on the macroscopic properties of silicate melts has been studied extensively. However, direct structural information about the nature of hydrogenbearing species and their bonding environments cannot be obtained readily from such measurements. Rather, investigation of glasses quenched from melts is often used to answer these questions. Stolper and Silver20-24 extensively studied the dissolution of water in silicate melts by means of near-IR spectroscopy and demonstrated the presence of molecular water species at high water contents. At water contents
