THE NATURE OF DISSOLVED WATER IN SODIUM-SILICATE GLASSES AND ITS EFFECT ON VARIOUS PROPERTIES

Sodium trisilicate glasses containing large amounts of water (up to 12 wt%) have been synthesized by use of a hydrothermal technique. When high water concentrations are present in sodium silicate glasses there are primarily two species of water present: molecular water and hydroxyls bonded to the glass network ((TBOND)Si-OH). As water is added to the glass, the concentration of hydroxyls first increases rapidly but at about 4-5 wt% total water it levels off to a constant value. The molecular water concentration first increases slowly with total water content but at (TURN)6 wt% total water it becomes the dominant water species.; Density and refractive index measurements have been performed and analyzed in terms of the concentrations of the different species of water. The density of "wet" glasses decreases monotonically with water content and has been analyzed in terms of the partial molar volumes of "dry" sodium trisilicate, molecular water and hydroxyls. The contributions from molecular water and hydroxyls are the same up to (TURN)5 wt% water, but then deviate for higher water contents. The refractive index of these glasses has a maximum at (TURN)4-5 wt% water. Beyond this point it decreases with total water content. By use of the Lorentz-Lorenz equation the electronic polarization is calculated and analyzed in terms of the "dry" sodium silicate, molecular water and hydroxyls. According to the analysis the hydroxyls are responsible for the maximum in the index of refraction.; In addition, the response of "wet" glasses to ionizing radiation is drastically affected by the presence of dissolved water. The optical and ESR absorption bands induced by radiation are much weaker for "wet" glasses than for the dry counterparts. A mechanism for the radiation-protection effect of water has been postulated. This consists of the decomposition of molecular water into transient species of OH(DEGREES) and H(DEGREES) which combine with the radiation-induced defect centers to form colorless (TBOND)Si-OH.