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) SiO 2 with x = 0, 5, 10, 15 and R = Li, Na, K and Cs in the temperature ra nge of 900-1300 degrees C using square-wave voltammetry. All diffusion coefficients had an Arrhenian dependence which depended on the type o f 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. W ithin 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. (C ) 1998 Elsevier Science B.V. All rights reserved.