Glass Transformation Temperature and Viscosity

The effect of water concentration on Tg and isothermal viscosity is most evident for the glass former oxides. Commercial vitreous silica is produced with water contents ranging from 1 to 600 wtppm of H2O. The Tg of these glasses decreases from 1200 °C to only 1060 °C over this range. The Tg of vitreous boric oxide ranges from 200 C for glasses containing as much as 1 wt% H2O, to over 300 °C for the driest 

The Tg of a commercial soda-lime-silicate glass which was melted in an older, air-fuel fired tank, which contains about 350 wtppm of water, is typically 5 to 7 K greater than that of the same glass produced by the same manufacturer in an oxygen-fuel tank. Remelting a commercial 

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