Hydrous sodium silicate glasses obtained by drying sodium silicate solutions

Abstract

Concentrated sodium silicate solutions with a SiO2:Na2O molar ratio of 3.3 and a SiO2 content of 27 wt% were dried at temperatures between 30 and 100 °C to residual water contents between 11 and 45 wt%. The materials are brittle, transparent and X-ray amorphous. Their structure is discussed, with the conclusion that it is vitreous. The materials were investigated by thermal analysis techniques (e.g. differential scanning calorimetry in open and closed crucibles, thermogravimetry, hot stage microscopy), optical and electron microscopy, and X-ray diffraction. Up to six thermal events detected by thermal analysis are discussed. Two of these thermal events were analysed with respect to their heat rate dependence and are discussed with respect to structural transitions (glass to gel and gel to sol). Other events are also discussed, such as the temperatures of foam formation during heating and the boiling temperatures of the investigated samples.