Study of the mixed alkali effect in glasses and its relation to glass structure and alkali earth ion content

Abstract

The mixed alkali effect in borosilicate glasses has been studied by diffusion and interpreted in terms of the glass structure parameters. Sodium and potassium diffusion couples were prepared and the interdiffusion zone studied. The glass structure influences the alkali ion diffusion; a mixed alkali effect is present. The smaller alkali ion, sodium, has a greater influence on the diffusion than the larger, potassium ion. The influences of the alkali earth ions on the superimposed existing mixed alkali effect have been studied. The presence of magnesium, calcium and barium further decrease sodium and potassium diffusion coefficients by one or two orders of magnitude, in the interdiffusion zone. An explanation of these results lies in Dietzel's field strength theory of the mixed oxide effect in glasses. © 1989.