Diffusivities of polyvalent elements in a 15Na2O · 85SiO2 glass melt

Diffusivities of various polyvalent elements (Sn2+, As3+, As5+, Sb3+, Sb5+, Ti4+, V4+, V5+, Cr3+, Fe3+ and Cu+) were measured in a melt with the basic composition of 15Na2O · 85SiO2. The method used was the square-wave voltammetry. Within the temperature range of 1300–1550°C, a linear correlation between log D and 1/T was observed. At lower temperatures, diffusion coefficients were larger than expected from an Arrhenius temperature dependence. This effect is explained by the crystallization of cristobalite below 1300°C. Under this condition, the residual melt is enriched in Na2O and the decreasing viscosity leads to higher diffusivity. The results are compared with those obtained from a silicate melt richer in soda content.