Stable silicate glasses containing up to 10 weight percent of water

Abstract

Alkali silicate glasses containing other metal oxides such as PbO, ZnO, Al 2O 3, BaO, MgO, P 2O 5, B 2O 3, and ZrO 2 in amounts of 0–20 mol% total are hydrated in a steam atmosphere at elevated temperatures resulting in a water content of 3–30% by weight. Various species of water are shown to exist in the hydrated glasses. They consist of the free silanol groups, hydrogen-bonded silanol groups, monomeric molecular water and polymeric species of molecular water up to hexamer. These species of water are in true solution in the homogeneously hydrated silicate glasses. Four types of hydration kinetics are distinguished among the silicate glasses of various compositions. The properties of the resulting products are compared and the origin of the differences is discussed. The properties of hydrated glasses are studied with measurements of infrared absorption spectra, thermogravimetric analysis, durability, viscosity and stress-strain behavior. The relative polarizing power of cations in silicate glasses are calculable from infrared spectra. The overall polarizing power of all the cations in a silicate glass is proportional to the fraction of free silanol groups in the glass and is a function of the glass composition. If reflects the extent of the chemical reaction and chemical binding of the various species of water in the glass, and offers a clue in synthesizing hydrated glasses with no loosely bonded molecular water. Theories are proposed to explain various observed phenomena and properties of the hydrated glasses. The structure cohesion of hydrated glasses is distinguished from those of the anhydrous glasses, invert glasses and organic polymers. A flow mechanism is proposed to explain the lowering of viscosity due to the presence of water in glass. A dynamic structure of the bonding of water in glass is deduced from the combined data (infrared and others) of the present study. With this model, the unusual combination of properties may be understood.