Phase evolution on heat treatment of sodium silicate water glass

Heat treatment of sodium silicate water glass of the nominal composition Na2O/SiO2 = 1:3 was carried out from 100 °C up to 800 °C and the advancement of the resulting phases was followed up by powder X-ray diffraction, scanning electron microscopy and thermogravimetry along with differential thermal analysis. The water glass, initially being an amorphous solid, starts to form crystals of β-Na2Si2O5 at about 400 °C and crystallizes the SiO2 modification cristobalite at about 600 °C that coexists along with β-Na2Si2O5 up to 700 °C. At 750 °C Na6Si8O19 appears as a separate phase and beyond 800 °C, the system turns into a liquid.