Voltammetric studies of Fe2+/Fe3+-redox equilibria in some Na2O · CaO · Al2O3· SiO2 liquids

Abstract Thermodynamics of the Fe 2+ /Fe 3+ -equilibrium were studied in liquids with the basic mol% compositions of 10Na 2 O · 10CaO · x Al 2 O 3 · (80 − x )SiO 2 ( x =0, 5, 10, 15, 20, 25 mol%) and 16Na 2 O · 10CaO · x Al 2 O 3 · (74 − x )SiO 2 ( x =0, 5, 10, 15). The method used was the square-wave voltammetry. The temperatures applied were 1000–1600°C. With increasing temperatures, in all liquids the equilibrium was shifted to the reduced state. In the peralkaline range (([Na 2 O] + [CaO])/[Al 2 O 3 ] > 1), with increasing alumina concentration, the equilibrium was also shifted to the reduced state. By contrast, in the peraluminous range, with further increasing the Al 2 O 3 content, the equilibrium constant remains the same (at 1000°C) or was shifted to the oxidized state again. A structural explanation for this behavior is given.