Abstract
High silica porous glasses were prepared by varying acid treatment of phase-separated soda borosilicate glass and one of them was impregnated by sodium nitrate solutions. The porous glasses were heat treated to form nonporous glasses and the end point of their thermal shrinkage (sintering temperature) was determined. The glass transition temperature was determined for NaNO3-impregnated and sintered glasses. The glass transition temperature was linearly related to the sintering temperature and decreased linearly with increasing logarithm of sodium oxide content. ΔTg/ΔlogC, where Tg is the glass transition temperature and C is the content of water (-0.1wt%) or sodium oxide (0.1-3wt%) of nonporous glasses, was determined. Sodium oxide lowered the glass transition temperature more strongly than water. ΔTg/ΔlogC was calculated for pure silica glass and some silicate glasses from the data available in the literatures and compared with the results of the present work. ΔTg/ΔlogC for water decreased and that for sodium oxide increased with decreasing glass transition temperature.
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