Diffusion of copper in soda–silicate and soda–lime–silicate melts

Copper diffusion coefficients were measured in glass melts with the base compositions xNa2O·(100 − x)SiO2, x = 15, 20, 26 and 33 mol% and (26 − x)Na2O·xCaO·74SiO2, x = 0, 5, 10 and 15 mol% doped with 1 mol% CuO in the temperature range from 900 to 1150 °C by square-wave voltammetry. The current–potential curves recorded exhibit two distinct maxima which are attributed to the reduction of Cu2+ to Cu+ and Cu+ to metallic copper. The peak currents decrease with decreasing temperature. The mean diffusion coefficients for the Cu+/Cu2+-species are calculated from the peak currents and fitted to Arrhenius equation. The activation energies of the copper diffusion are in the range from 126 to 170 kJ mol− 1. Diffusion coefficients related to the same viscosity decrease with increasing Na2O-concentration. The incorporation of copper into the melt structure is discussed.