Redox behavior and diffusion of copper in soda-lime-silica melts

Glasses with the base mol% composition xNa2O · 10CaO · (90 − x)SiO2 with x = 10, 16, 20 and 26 were investigated at high temperatures using square-wave voltammetry. The recorded voltammograms exhibit two peaks. That at less negative or (depending on temperature and glass composition) even positive potential is attributed to the reduction of Cu2+ to Cu+, while that observed at more negative potential is caused by the reduction of Cu+ to metallic copper. For both redox steps, the peak potentials decrease linearly with temperature. Those of the composition with 10 mol% Na2O show the most negative values. The diffusion coefficients can be fitted to Arrhenius equation. If referenced to the same viscosity, the diffusion coefficients decrease with increasing Na2O-concentration. The effect of composition on the thermodynamics as well as on diffusivities is explained by the incorporation of the copper ions into the melt structure.