Sodium Redistribution Between Oxide Phases

Alkali transport between a glass substrate and an oxide overlayer occurs by a mechanism of ion exchange between the alkali and protons. Thermodynamics requires that the difference in chemical potential of the alkali and the proton be the same in both phases at equilibrium. The influence of chemical composition of the glass on the chemical potential of alkali ions is discussed. Good agreement between predictions of the direction of alkali transport and observed transport is obtained.