Si—O Stretching Vibrations

For pure Si-MCM-41. this band has been assigned to the Si-O stretching vibrations and the presence of this band in the pure siliceous is due to the great amount of silanol groups present. A characteristic absorption band at about 970 cm 1 has been observed in all the framework IR spectra of titanium-silicalites. It was also reported that the intensity of 970 cm 1 band increased as a function of titanium in the lattice[17] and this absorption band is attributed to an asymmetric stretching mode of tetrahetral Si-O-Ti linkages [18] in the zeolitic framework. The increase in intensity of this peak with the Ti content has been taken as a proof of incorporation of titanium into the framework. 

The pH at which precipitation is carried out has a major influence on the structure of the products obtained. For example, the amorphous silica obtained by hydrolysis of TEOS under acidic conditions has a surface area of 900 m2/g and is weakly crosslinked, with an asymmetric Si—O stretching vibration at 1030 cm-1, whereas the hydrolysis of TEOS obtained under neutral or basic conditions produces a silica having a surface area of 400 m2/g which is strongly crosslinked, with the asymmetric Si—O stretching vibration at 1100 cm-1 (Schraml-Marth et al., 1992 Miller et al., 1994 Liu et al., 1994). 

The correlation between the midgap interfacial state density Du and the thickness strain in thermally grown Si02 films has been studied [110]. The At decreases with the oxidation temperature and with the oxide film thickness. The frequency of the Si—O stretching vibrations increases with increasing oxidation temperature and film thickness. The peak position v is expressed as a function of the average Si—O—Si bond angle as... 

Maximal changes in the Si-O stretching vibrations over the Vsjo=1000-1250 cm" range are observed for OX-50 after HTT-350°C, as the band becomes more broadened (Figure 1.201a). The Vjio band at 1100 cm" becomes more intensive for all samples after HTT as a result of growth of the silica particle size. 

The Si—OH group absorbs, like the alcohols, at 3700-3200 cm due to monomers (in solution) and hydrogen bonded polymers. A strong band due to Si—O stretching vibration occurs at 910-830 cm " In the condensed... 

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