The infrared transmission spectra of four silicate glasses before and after exposure to water
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(Received 8 March 1990; accepted 19 June 1990) The infrared transmission spectra of four silicate glasses were investigated. By using blown glass films, 1-2 jinn thick, detailed infrared transmission spectra were generated over the 4000-180 cm"1 range, both before and after the films were exposed to water. The water had little effect on the spectra of the 70SiO2-20Na2O-10Al2O3 (mol %) and Pyrex compositions, but had a large effect on the spectra of the 70SiO2-30Na2O (mol %) and Corning 015 compositions. The Si-O nonbridged stretching band at —950 cm"1 and a largely overlooked bending band at —600 cm"1 were the bands most sensitive to hydration in the 70/30 and 015 compositions. Changes were also seen in the Si-O-Si bridged stretching bands at —1050 cnT1 and —770 cm"1. The water, however, had no effect on the dominant Si-O-Si bending band at 460 cm"1. It was also discovered that the 70/30 and 015 films reacted with the atmosphere to form a carbonate layer on their surface. This carbonate accounted for the 1450 cm"1 and 230 cm"1 bands seen in their infrared transmission spectra. I. INTRODUCTION
Infrared spectroscopy is a valuable tool for studying the structure and the aqueous corrosion of glass. Studies of glass and water are typically performed using thin slices of glass, having thicknesses of approximately 0.5-1 mm.1"3 With such samples, infrared transmission spectroscopy is effective down to about 2000 wave numbers. As a result, studies of this type tend to focus on the main water bands in the 3800-2500 cm"1 range, but miss the structural vibrations of the glass in the 1200-200 cm"1 range. Bartholomew et al.4 summarize the infrared absorption bands associated with water in glass. Hench et al.5'8 have shown how infrared reflection spectroscopy (IRRS) can be used to see the effect of water on the structural bands of glass. IRRS, however, is not effective much above 1200 cm"1 and therefore does not pick up the water bands at the higher wave numbers. A reflectance spectrum can be extended to higher wave numbers only by a mathematical deconvolution (Kramers-Kronig analysis) in which the reflectance spectrum is converted to an absorption spectrum.910 Other drawbacks of IRRS are that it is limited to surface depths of about 0.5 jam and that it is affected by any surface roughening which may occur during corrosion. Thin glass films, between 1 and 2 ^im thick, can be formed by blowing molten glass. With such samples, transmission spectroscopy can be extended into the far-infrared region, down to 50 cm"1. In previous studies, thin blown films have been used to study the structure of a variety of silicate glasses.11"15 The KBr pellet technique has also been used to study the strucJ. Mater. Res., Vol. 5, No. 10, Oct 1990
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ture of silicate glasses in the infrared region.16 18 The KBr technique, however, does not lend itself to hydration studies since the glass samples must be ground into a powder and since potassium bromide is quite hydrophilic. In this investigation, t
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