Thermodynamics of the Cu+/Cu2+-redox equilibrium in soda-silicate and soda-lime-silicate melts

Abstract The thermodynamics of the redox equilibrium of Cu + /Cu 2+ were determined by square-wave voltammetry in glass melts with the base mol% compositions x Na 2 O · (100 − x ) SiO 2 ( x = 15, 20, 26 and 33) and (26 − x ) Na 2 O · x CaO · 74 SiO 2 ( x = 0, 5, 10 and 15) doped with 1 mol% CuO in the temperature range from 850 to 1150 °C. All recorded voltammograms showed two maxima attributed to the reductions of Cu 2+ to Cu + and Cu + to metallic copper. Both peaks are shifted to smaller potentials with decreasing temperature. With increasing melt basicity, the [Cu + ]/[Cu 2+ ]-ratio first increases, and remains constant for optical basicities >0.56. The effect of composition on the redox equilibrium is explained by the incorporation of both Cu + and Cu 2+ in octahedral coordination into the melt structure.