Diffusivity and incorporation of tin in Na2O/CaO/Al2O3/SiO2 melts

Diffusion coefficients of tin were measured in melts with the basic compositions 10Na2O · 10CaO · yAl2O3 · (80 − y)SiO2 (y = 0, 5 and 15) and 16Na2O · 10CaO · yAl2O3 · (74 − y)SiO2 (y = 0, 5, 10, 15 and 20) doped with 0.25 and 0.5 mol% SnO2. Each voltammograms exhibits a maximum due to the Sn2+/Sn4+ redox pair. From the peak currents, the diffusion coefficient was calculated. The diffusion coefficients could be fitted to Arrhenius equation. Diffusion coefficients related to the same viscosity, i.e. not the same temperature decreased with increasing Na2O-concentration. With increasing Al2O3-concentrations, the viscosity corrected diffusion coefficients increased until [Na2O] = [Al2O3]. At further increasing Al2O3-concentrations, they decreased again. These effects were explained by a structural model for the incorporation of Sn4+.