Abstract
The discolouration of vitreous silica by sodium was viewed as a surface phenomenon, hence techniques such as electron spectroscopy for chemical analysis (ESCA) and infra-red reflection spectroscopy (IRRS) along with a variety of other analytical tools were used to investigate the interaction. When vitreous silica was exposed to sodium vapour at about 300‡ C, the formation of Si-O− bonds were observed. In addition sodium which had diffused into the glass was found to be in an ionic state. At a higher temperature of exposure to sodium, about 450‡ C, crystalline sodium metasilicate (and possibly silicon) was formed. Using the experimental results presented here and elsewhere, a model has been developed based on the formation of sodium metasilicate and non-stoichiometric silicon oxide when vitreous silica is exposed to sodium vapour. The discolouration phenomenon is attributed solely to the formation of non-stoichiometric silicon oxide.
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