EFFECTS OF WATER-CONTENT ON THE PROPERTIES OF SODIUM ALUMINOSILICATE GLASSES

Sodium aluminosilicate glasses of the general formula 25Na2O.xAl2O3.(75 - x)SiO2 were prepared with a range of hydroxyl contents. Both the glass transformation and isokom temperatures decrease as the hydroxyl content increases. The magnitude of the decrease in each property is a function of the alumina content of the glass, with the largest effects occurring for the glass containing 25 mol% Al2O3. The magnitude of the effect of water as a function of alumina content reflects the decrease in the concentration of nonbridging oxygens in the glass with increasing Al2O3 content, since the effect of the terminal hydroxyl species on the connectivity of the glass is enhanced by the elimination of nonbridging oxygens. The results indicate that the large effect of water content on the properties of these glasses must be considered when discussing the role of alumina in glasses.