The absence of a mixed-alkali effect in the leaching of corrosion-resistant glasses

Abstract

Alkali depth profiles in water-leached glasses with molar composition 16A₂O·8CaO· 2MgO·1Al₂O₃·73SiO₂ (A=Na, K and Na+K) were determined using secondary ion mass spectroscopy (SIMS). In the glass containing only sodium an apparent correlation exists between the alkali diffusion coefficient derived from the leaching kinetics, assuming this process is governed by ion exchange, and that determined via electrical conductivity measurements in the dry glass. In the other two glasses the diffusion coefficients derived on the basis of ion exchange are much higher than the ones found in the dry glasses. These data can be interpreted in terms of a model for the leaching of glass where the rate-determining step is the diffusion of molecular water.