Effect of Na ₂ O/K ₂ O Ratio on Chemical Durability of Alkali‐Lime‐Silica Glasses

Abstract

The chemical resistance of mixed‐alkali glasses to water was measured by determining the sodium, potassium, calcium, and silicon ions extracted instead of evaluating it from the alkalinity of the mixed‐alkali extracts. In glasses of the composition K 2 O and Na 2 O 18, CaO 10, and SiO 2 72% the minimum extraction of alkali (maximum durability) occurred for a K 2 O/‐Na 2 O ratio of 2.6/1.0 (by weight). Based on an ionic‐composition analysis of the results, an empirical index is suggested for determining the relative degree of ion‐exchange and network‐breakdown modes of reactions that occur when such mixed‐alkali glasses are attacked by water.