Self-diffusivity of iron in alkali–lime–alumosilicate glass melts

Self-diffusion coefficients of iron were measured in glass melts with the basic mol% composition of 16 R₂O, 10 CaO, x Al₂O₃ and (74 − x) SiO₂ with x=0, 5, 10, 15 and R=Li, Na, K and Cs in the temperature range of 900–1300°C using square-wave voltammetry. All diffusion coefficients had an Arrhenian dependence which depended on the type of alkali present and the Al₂O₃-concentration. Larger alkali cations, e.g. Cs⁺, as well as an increase in the Al₂O₃-content led to a decrease in the diffusion coefficients and also to an increase in viscosity. Within one glass composition, the Stokes–Einstein equation is fulfilled with respect to the dependence of the diffusivity upon viscosity. At constant viscosity, however, increasing size of the alkali cation and increasing Al₂O₃-content led to larger iron diffusion coefficients.