The Fe2+/Fe3+-redox equilibrium in 5Na2O·15CaO·xAl2O3·(80−x)SiO2 (x=5–25) liquids

Liquids with the basic compositions of 5Na2O·15CaO·xAl2O3·(80−x)SiO2 (x=5,10,15,20,25) doped with 0.25 mol% Fe2O3 were studied by means of square-wave voltammetry in the temperature range 1200–1600°C. With increasing temperature, redox equilibria were shifted to the reduced state. Increasing the alumina concentration from 5 to 10 mol% resulted in an increase in the standard potentials, i.e., in a shift to the reduced state. If the alumina concentration is further increased, the standard potentials decrease again. The latter is caused by the incorporation of alumina in sixfold coordination.