Self-diffusion of iron in alkali-magnesia-silica glass melts

Alkali-magnesia-silica glass melts with lithium (74 SiO2, 16 Li2O, 10 MgO), sodium ((90 - x) SiO2, x Na2O, 10 MgO (x- = 10, 15, 20, 25)), potassium ((90 - x) SiO2, x K2O, 10 MgO (x = 10, 15, 20, 25)) and caesium (74 SiO2, 16 Cs2O, 10 MgO) tall compositions given in mol%) doped with 0.2 mol% Fe2O3 were studied by means of square-wave voltammetry. Decreasing Na2O- and K2O-contents lead to a decrease in the self-diffusion coefficients of iron and an increase in the viscosities of the liquids. A comparison of diffusivities of different alkali ions shows that at constant temperature, the self-diffusion coefficients decrease from lithium to caesium. Within the error limits, in most of the glasses studied. the Stokes-Einstein equation is fulfilled with respect to the dependence of the diffusivity on the viscosity. At constant viscosity, i,e., mobility of the glass network, the self-diffusion coefficients decrease with increasing alkali concentrations and decreasing size of the alkali cation. These effects are discussed using a structural model for the incorporation of iron into alkali containing glasses. (C) 1998 Elsevier Science B.V. All rights reserved.