The effect of alumina on the Sn2+/Sn4+ redox equilibrium and the incorporation of tin in Na2O/Al2O3/SiO2 melts

Abstract Glasses with the basic compositions 10Na 2 O · 10CaO · x Al 2 O 3 · (80 − x )SiO 2 ( x =0, 5, 15, 25) and 16Na 2 O · 10CaO · x Al 2 O 3 · (74 − x )SiO 2 ( x =0, 5, 10, 15, 20) doped with 0.25–0.5 mol% SnO 2 were studied using square-wave-voltammetry at temperatures in the range from 1000 to 1600 °C. The voltammograms exhibit a maximum which increases linearly with increasing temperature. With increasing alumina concentration and decreasing Na 2 O concentration the peak potentials get more negative. Mossbauer spectra showed two signals attributed to Sn 2+ and Sn 4+ . Increasing alumina concentrations did not affect the isomer shift of Sn 2+ ; however, they led to increasing quadrupole splitting, while in the case of Sn 4+ both isomer shift and quadrupole splitting increased. A structural model is proposed which explains the effect of the composition on both the peak potentials and the Mossbauer parameters.