DIFFUSION OF SODIUM IN MIXED GLASS FORMER OXIDE GLASSES

The mixed glass former effect (MGFE) is a non-linear variation of transport properties as a function of the glass former composition when one glass network former is replaced by another one. In order to better understand the MGFE, the effect of the variation of the glass former composition on the transport of a selected ion was studied. The composition and temperature dependencies of sodium tracer diffusion coefficients, D*Na, were determined for different mixed glass former oxide glasses, which are two types of sodium borosilicate glasses, sodium boroaluminosilicate glasses and a commercial, ion-exchangeable alkali aluminosilicate glass. In the case of sodium borosilicate glasses of the type (Na2O)0.2[(BO1.5)x(SiO2)1!x]0.8, the tracer diffusion coefficient of sodium as a function of the glass composition at constant temperatures between 208 and 503 °C shows a shallow minimum at values of the composition parameter x of around 0.7. Values determined for the Haven-ratio, HR, are all smaller than one and show as a function of x a shallow minimum at x. 0.7. Some structural information wa