Influence of water on the structure and kinetics of structural relaxation in sodium borate glasses

Abstract

The influence of the water content on the microinhomogeneous structure of sodium borate glasses containing 2.5 and 5.0 mol % Na2O and on the kinetics of structural relaxation in vitreous boron oxide and sodium borate glasses is studied by the small-angle X-ray scattering (SAXS) technique. It is demonstrated that an increase in the water content brings about an increase in the size of the inhomogeneity regions and a decrease in the mean square of the difference between the electron densities 〈(Δρ)2〉 for the microinhomogeneous structure. The inference is made that water has a catalytic effect on the aggregation of alkali borate structural units. The kinetic dependence of the intensity of small-angle X-ray scattering by thermal density fluctuations is described by the Kohlrausch equation. The exponent β in the Kohlrausch equation is close to 1.0 for “dry” glasses and decreases to 0.5 for glasses containing 0.7–1.0 mol % H2O.