Thermodynamic behaviour of the non-bridging oxygen-free glass system X Ag2O ∙ (2-X) Na2O ∙ 2 Al2O3 ∙ 3 SiO2 ∙ B2O3 in contact with nitrate melts

Abstract

Equilibrium data for the Na+/Ag+ ion exchange at 375 °C between the glass 2 Na2O ∙ 2 Al2O3 ∙ 3 SiO2 ∙ B2O3 (Tg = 560 °C), which is free of non-bridging oxygen, and AgNO3—NaNO3 salt melts are analyzed in two different ways (I and II). With the description of the glass as a regular solution (I) as well as with that as a mixed phase with a ñ-type behaviour (II), the high selectivity of the glass system for the Ag+ ions, having the larger crystalline ionic radius as compared to the Na+ ions, is reflected by model-owned parameters. However, the existence of mechanical compressive stress and its partial reduction by structure relaxation in consequence of the viscosity-lowering effect of a high silver content are considerably differently in the two models.