THE EFFECT OF WATER ON PHASE-SEPARATION OF SODIUM-SILICATE GLASSES

The effect of water on the thermodynamics and kinetics of phase separation in Na2O-SiO2 glasses was studied. Glasses were prepared and remelted under varying water vapor partial pressures to obtain glasses containing approximately 0.05 and 0.1 mol% H2O. Wet glasses were found to have lost Na2O compared with dry glasses of the same original composition during remelting. Wet and dry glasses of the same nominal composition had identical clearing temperatures to within +/-5-degrees-C, but by taking into account the different Na2O contents of the glasses the immiscibility boundary of the wet compositions was found to be shifted to higher SiO2 contents compared with that of the dry glasses. Coarsening rates determined by small angle X-ray scattering measurements increased with increasing water content as expected but the activation energy was independent of water content.