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OD bands in the IR spectra of a deuterated soda-lime-silica glass
IR spectra of a deuterated glass of the composition (in mol%) 16 Na2O · 10 CaO · 74 SiO2 complete earlier spectroscopic studies on water-poor soda-lime-silica glasses. The approved IR spectroscopic method of the deuterium exchange allows a reliable assignment of the hydroxyl bands also in the case of glasses. By spectra comparison the assignment of the IR bands at 3500 and 2800 cm-1 to hydroxyl groups with different hydrogen bonding is verified. The IR band at about 4500 cm-1 is interpreted as both a combination of the stretching vibrations vO-H and vSi-OH and a combination of the stretching vibration vO-H and the deformation vibration δSiOH. The bands at 1763 and 1602 cm-1 are attributed to combination vibrations of the glass network.
Determination of the water content of alkali lime silica glasses by IR spectroscopy using nuclear reaction analysis for calibration
Systematic IR and NRA investigations were performed for two series of glasses with very different water contents. The glasses had the composition (in mol%): 16 R₂O · 10 CaO · 74 SiO₂ (R = sodium, potassium). The IR absorption coefTicients of the OH bands were found to be linearly correlated with the total hydrogen content obtained by the NRA measurements. Using the hydrogen concentration values from NRA, the total water contents were calculated and so-called practical IR extinction coefTicients were deduced. The values found for the soda-lime-silica glasses are 381 · mol¯¹ · cm¯¹ for the band at 3550cm¯¹ and 561 · mol¯¹ · cm¯¹ for the band at 2800cm¯¹. The values for the potassium-lime-silica glasses are 231 · mol¯¹ · cm¯¹ for the band at 3550 cm¯¹ and 78 l · mol¯¹ · cm¯¹ for the band at 2800 cm¯¹ Also, Scholze's two-band method was applied, resulting in good agreement between the water contents of the glasses derived from the IR and the NRA measurements.
Water concentration and diffusivity in Silicates obtained by vacuum extraction
Water concentration, Cw, and the mean effective diffusion coefficient of water, Dw, were measured by vacuum hot extraction coupled with mass spectrometer evolved gas analysis (VHE). The study includes silica, soda- and potassium-lime-silica, cordierite, and lamp bulb glasses of water concentrations between 0.017 and 0.17 mol H2O/l (122 and 1159 wt. ppm) as well as cordierite single crystals. Cw was obtained by integration of the VHE water degassing rate dQw/dt. For powdered samples (≈ 50 to 150 mg) of silica, soda-lime-silica and cordierite glass with water concentrations between 0.033 and 0.15 mol/1, VHE results well confirm IR spectroscopy within 5 to 15 % accuracy. Dw could be obtained by two methods: dQw/dt of powdered samples was measured during isothermal VHE experiments and dQw/dt fitted versus time with the appropriate diffusion models. Alternatively, powdered samples were pre-annealed in vacuum before measuring their residual water concentradon by VHE as described above. Cw was then analogously fitted versus the vacuum pre-annealing time. The applied methods and samples allowed the measuring of Dw within 10-9 and 10-13 cm2 s-1. Calculated values of Dw for soda-lime-silica glasses agree with literature data and values obtained by IR spectroscopy within a factor of 2 to 4.
Water release behaviour of soda-lime-silica glass melts
Glass with the composiüon (in mol%) 16Na₂O * 10CaO * 74SiO₂ and a water content of 0.12 to 0.005 mol/1 has been investigated by IR spectroscopy. It has been found that at a water content of < 0.01 mol/l the rado of the extincdons of the absorpdon bands at 3550 and 2800 cm⁻¹ is not constant. Through the vacuum hot extraction method it could be shown that the release of bonded water from glass melt does not occur continuously, and is not determined by the kinetics of formadon of molecular water. At concentrations > 0.01 mol/l the largest part of bonded water is released at temperatures < 1000°C. Small amounts of water can be detected at temperatures > 1250°C as well. This high-temperature release of strongly bonded water is caused by changes in the structure of glass melt or by the simultaneous release of other volatile species.