Influence of the composition of a molten salt on the field-assisted diffusion of potassium ions in the 20Na2O · 80SiO2 glass

Abstract

The kinetics of interaction between the sodium silicate glass 20Na2O · 80SiO2 and molten salts in a dc electric field is investigated using the electron-probe X-ray microanalysis and radioactive-tracer technique. The influence of the electric field strength, the temperature, the interaction time, and the composition of a molten salt on the concentration distribution of alkali cations in the 20Na2O · 80SiO2 glass in the course of field-assisted diffusion is elucidated. The effective electric mobilities of potassium ions are calculated, and the parameters of the temperature dependence of the electric mobility are determined. It is revealed that the application of an electric field does not affect the ion-exchange equilibrium in the system. The correlation factor for diffusion of impurity ions is determined for the first time. The obtained value of the correlation factor indicates that the processes of self-diffusion and heterodiffusion of alkali cations in binary silicate glasses occur through the same (relay-race) mechanism. It is established that the Nernst-Einstein equation, which relates the electric mobility to the diffusion coefficient and provides the basis for the description of the field-assisted diffusion, holds only for the processes bearing no relation to variations in the composition of the glass.