Quantitative determination of water speciation in aluminosilicate glasses:a comparative NMR and IR spectroscopic study

Water speciation in hydrous aluminosilicate glasses (with NaAlSi3O8, KAlSi3 O8, LiAlSi3O8 and LiAlSi4O10 composi tions) was studied with infrared (IR) and static H-1 nuclear magnetic resonance (NMR) spectroscopy. Using IR spec troscopy, the water speciation was determined from the peak intensities (li near absorbance as well as integrated intensity) of the near-infrared (NIR) absorption bands at 4500 and 5200 cm(-1) assigned to structurally bonded h ydroxyl groups and molecular H2O, respectively. For LiAlSi4O10 glasses, a n ew calibration of the linear and integral molar absorption coefficients of the IR absorption bands at 4500 and 5200 cm-' is presented. Using NMR spect roscopy, the water speciation was determined from the static 1H NMR spectra acquired at temperatures between 170 and 130 K, where the H-1 NMR signal c onsists of a well-defined Fake doubler due to rigid water molecules and an overlapping, but narrower, central peak due to structurally bonded OH group s. The distinct nature of these two signals (doublet and Gaussian) enables a reliable deconvolution of the 1H NMR spectra and quantitative determinati on of water speciation in the glasses. For a series of hydrous NaAlSi3O8 gl asses containing 1.5-10 wt.% water, we found a very good agreement of water speciation determined by NMR and IR spectroscopy (about 4% standard deviat ion in OH concentration), demonstrating the reliability of both methods. To tal water contents determined with H-1 NMR spectroscopy are in excellent ag reement with results from Karl-Fischer titration (KFT, < 2% standard deviat ion). Depending on whether peak heights or peak areas are used for the evaluation of MR spectra, relatively large deviations in water speciation (12-24% in OH content) are observed for KAlSi3O8, LiAlSi3O8 and LiAlSi4O10 glasses. St atic H-1 NMR spectroscopy on KAlSi3O8 and LiAlSi4O10 glasses containing 2.8 0-4.25 wt.% water tends to support the use of peak areas instead of peak he ights for calculation of water speciation from NIR spectra. However, in the case of the LiAlSi3O8 glass (4.04 wt.% water), no clear conclusion can be drawn from the NMR data and other effects such as the choice of the baselin e for the NIR peaks or water-dependent molar absorption coefficients may ha ve to be taken into account. In order to resolve these questions, more syst ematic NMR and IR spectroscopic studies on glass series covering a large ra nge of water concentrations are required. (C) 2001 Elsevier Science B.V. Al l rights reserved.