Diffusivity Of Copper In Aluminosilicate Melts, Studied By Square Wave Voltammetry

Copper diffusion coefficients were measured in glass melts with the base mol% compositions 26Na2O.xAl2O3.(74-x)SiO2(x=5,10,15 and 20); xNa2O.10CaO.10Al2O3.(80-x)SiO2 (x=10,15,20 and 25) and xNa2O.20Al2O3.(80-x)SiO2(x=10,15 and 20) doped with 1 mol% CuO, by means of square wave voltammetry. The voltammograms were recorded in the temperature range from 900 to 1150 degrees C. Each voltammogram exhibited two maxima, attributed to the reduction of Cu+ to metallic copper and Cu2+ to Cu+. The calculated Cu+/Cu2+ diffusion coefficients were fitted to the Arrhenius equation and the activation energies of the copper diffusivities were determined. If Na2O and CaO are predominantly incorporated in the network to compensate the charge of [AlO4] tetrahedra, the diffusion coefficients are larger than in melts in which they are mainly coordinated with nonbridging oxygens.