The electrochemical series of elements in the Na 2O·2SiO 2 glass melt

Abstract

The thermodynamics of redox equilibria were studied by square-wave voltammetry in a glass melt with the basic composition of Na 2O · 2SiO 2 in the temperature range of 850–1600°C. The melts were doped with oxides of As, Sb, Sn, Cu, V, Fe, Cr and Ti. While iron and titanium-doped glass melts exhibit only one reduction step, all other polyvalent compounds studied are reduced in two electron steps. In the case of As-, Sb-, Sn- and Cu-doped melts, the metallic state is formed during the second reduction step. Standard potentials measured depend linearly upon the temperature. In all cases studied, the reduced states are favored at higher temperatures. The electrochemical series of elements is nearly the same as those previously reported for soda–lime–silicate and borosilicate glass melts. However, in comparison to these glass melt compositions, the standard potentials in the Na 2O · 2SiO 2 melt are shifted to lower potentials. This cathodic shift can be explained as an effect of the higher basicity of the Na 2O · 2SiO 2 melt.