J. Acocella

The nature of dissolved water in sodium silicate glasses and its effect on various properties

Abstract Sodium silicate glasses with a wide range of water contents were prepared. For water contents up to twelve wt% the specimens were prepared by melting Na 2 O·3 SiO 2 glass and varied amounts of water in hydrothermal pressure vessels. A few higher water content samples were synthesized by hydrating glasses in an autoclave under a steam atmosphere. The concentration of different species of water was analyzed by infrared spectroscopy. Density refractive index and the induced absorption due to γ-irradiation were analyzed in terms of the different water species present in the glasses. It has been observed that the effect of water on all these properties can be explained in terms of the different contributions of hydroxyls and molecular water.

Thermal properties of Na2O·3SiO2 glasses with high water content

Abstract Na 2 O·3SiO 2 glasses with various water contents (up to ∼8wt%) were prepared under high pressure, hydrothermal conditions and their thermal properties, were analyzed by DTA and dilatometry. The glass transition temperature (Tg) determined by the two methods agreed reasonably well. Exsolution of dissolved water occurs at temperature above Tg and is accompanied by foaming. Both the glass transition temperature and the foaming temperature decrease with increasing water content, while the thermal expansion coefficient increases with increasing water content. The change of the glass transition temperature with water content was compared with equations applicable to polymer plasticizers, and was found to be best described by an equation which takes the different contribution of hydroxyl ions and molecular water into account. It was concluded that the hydroxyl ions lower Tg drastically while the molecular water lowers it only slightly by merely diluting the glasses.

Radiation-induced defects in glasses with high water content

Abstract Na 2 O3SiO 2 glasses containing up to 17 wt. % H 2 O have been x-irradiated at 77K and studied by ESR and optical techniques as a function of anneal temperature. It is shown that the radiation-protected characteristic of hydrosilicate glasses containing > 2 wt. % water is related to the postirradiation reaction of H 2 O molecules with HC 1 and HC 2 hole centers to form free OH° radicals, observed for the first time in glasses.