Improvement of chemical durability of high expansion glasses by ion exchange

Abstract

In order to prepare a high expansion glass with good chemical durability, Na2O · 2SiO2 glass was ion-exchanged in molten LiNO3 at 460 to 520° C. A Li2O rich layer, of 100 to 200 μm thickness, was produced on the glass surface. Corrosion rate in hot water (98° C) and thermal expansion coefficient were measured. The thin layer on the surface had a much lower corrosion rate in hot water and a lower expansion coefficient than the bulk glass. Because the ion-exchanged layer was thin with respect to the bulk glass, an overall high expansion was maintained. However, it acted as a protective layer giving rise to improved chemical durability.