Sodium-Caesium Electric Field Assisted ion Exchange in a Mixed-Alkali (Na, K) Lime Silicate Glass

In this study, sodium exchange for caesium in a mixed alkali lime silicate glass was carried out using electric field-assisted ion exchange (EF-IE). Na/Cs exchange was realised by applying electric fields up to 2000 V cm−1 for 5 min on glass tubes immersed in molten CsNO3 at 460 °C. The chemical concentration profiles measured near the glass surface showed a bilayer concentration profile which comprises caesium and potassium-rich layers, the formation of the potassium-rich layer being associated with the different mobility of alkali ions. Nanoindentation analysis outlined that surface layer produced by Na/Cs ion-exchange is characterised by poorer mechanical properties than Na/K ion-exchanged layer. Raman spectroscopy investigation revealed that the Na/ Cs ion-exchanged layer has a denser structure with respect to raw glass, this being responsible for the different mechanical properties.