Infrared spectroscopy of hydrous silicic glasses at temperatures up to 600°C and implications for the incorporation and dynamics of water in glasses
Behrens, Harald; Schmidt, Michael O.
published: May 1, 1998
ArtNo. ESP154017202005, Price: 29.00 €
Mid-infrared absorption spectra (1400-4000 cm-1) of aluminosilicate and silica glasses (0.87- 2.80 wt. % total water) containing both OH groups and molecular H2O were measured at temperatures up to 600 °C using a heating stage attached to an IR microscope. Spectral features of OH stretching and H2O bending modes were separated from network vibrations by subtracting spectra of dry glasses measured at the same temperatures. A new type of OH stretching vibration at low frequency ( 1750 cm-1), previously undocumented for hydrous glasses, was identified for a peralkaline aluminosilicate composition (NBO/T = 1/122 and NBO/SigmaO = 1/24 on an anhydrous basis, total water contents: 0.87 and 1.85 wt. %). Preliminary extinction coefficients of the OH stretching and H2O bending bands were determined using total water contents determined by Karl-Fischer titration and molecular H2O contents determined by near infrared spectroscopy. Loss of water from the samples (thicknesses 51-9211m) was negligible during heating for 1 min at 300 °C (except for KAlSi,O8 glass with 2.80 wt. % water), varied between 6 and 15 % relative during heating for 1 min at 600 °C and became more important during heating for longer durations above 400 °C. Temperature-induced changes of the OH stretching bands are similar to those observed earlier for glasses free of molecular H2O (SCHOLZE 1959 a, KEPPLER & BAGDASSAROV 1993). With rising temperature, the intensities of OH stretching vibrations strongly decrease below 3500 cm-1 but slightly increase above 3500 cm-1 for all glasses studied. The shape of the band becomes more symmetric at its maximum and the integrated intensity strongly diminishes. The integrated intensities of the H2O bending band are reduced by 15-28 % for the aluminosilicate glasses and by 55 % for the silica glass at 600 °C compared to measurements at 20 °C after heating. The decrease in integrated intensity is mainly attributed to the variation of the extinction coefficients with temperature due to decreasing hydrogen bonding. Extrapolating low temperature data we infer that in the polymerized silicate glasses at most 10 % of the molecular H20 reacts with network oxygen forming OH after heating to 600 °C. Evidence for a rapid interconversion of hydrous species is given only for a peralkaline glass containing 1.84 wt. % water at temperatures above 350 °C by comparison to near-infrared spectroscopic measurements.