Chemical durability of sodium disilicate glasses in different corrosion media at neutral to basic pH values

Abstract

The chemical corrosion of sodium disilicate glasses in neutral to basic media was investigated. H2O, 1 mol/l NaOH, 1 mol/l LiOH, and a dilution series of sodium silicate solutions with a molar SiO2:Na2O ratio of 2.18 were used as corrosion media in static corrosion tests at temperatures of 30 °C and corrosion times up to 180 d. The corrosion process was characterized gravimetrically and in some cases by chemical analysis. Additionally, the temperature dependence of the corrosion in H2O at temperatures up to 70 °C was investigated. The nature of the corrosion process depends on the character of the corrosion media: The corrosion in 1 mol/l NaOH and 1 mol/l LiOH follows predominantly a square root time law, whereas corrosion in H2O or in sodium silicate solutions can be described by a linear time law. An additional result is that the corrosion rates increase in all cases with pH: in the case descnbed here corrosion in H2O and in alkaline silicate solutions proceeds faster than corrosion in sodium or lithium hydroxide solutions with higher pH values. The dilution series of sodium silicate solutions was used to check the dependence of the corrosion process on the concentration of glass dissolution products in the leachate. The results indicate the importance of surface adsorption processes.