Abstract
Sn4+-Sn2+ redox in binary alkali silicate melts was studied by means of differential pulse voltammetry. The half-wave potential, E1/2, of the reduction of Sn4+ to Sn2+ shifts toward the negative with changing the alkali metal ions from Li+ through Na+, K+ and Cs+, at a fixed concentration for each alkali metal oxide. Conversely, E1/2 shifts to the positive with an increase in the content of each of the alkali oxide. This tendency for Sn4+-Sn2+ redox was different from those of Sb5+-Sb3+ and Cr6+-Cr3+ redox. The presence of Sb5+ and Cr6+ result in a strong acid, which leads to E1/2 shift to the negative with an increase in basicity. These results for Sn ions can be interpreted in terms of complex formations of Sn4+ and Sn2+, in which the coordination numbers of the oxide ion for both ions do not differ significantly and their equilibrium constants for complex formation depend largely on the alkali species.
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