Voltammetric study of Fe ions in M2O-M′ O-SiO2 (M: Alkali metal, M′: Alkaline-earth metal) glass melts

Abstract

The half-wave potentials of the reduction of Fe3+ in 16M2O (M: Li, Na, K and Cs) · 10M′O (M′: Mg, Ca, Sr and Ba) · 74SiO2 glass melts were examined by differential pulse voltammetry. In all melts, the half-wave potential shifted to the positive side with increasing temperature. The equilibrium of Fe3+/Fe2+ moved toward the reduced side with increasing temperature. The replacement of Li+ ions by larger alkali ions resulted in a positive shift of the half-wave potentials. On the other hand, the smaller the ionic radius of the alkaline-earth metal ion, the larger the half-wave potential. The Fe3+/Fe2+ equilibrium was mainly affected by the stability of the Fe3+-complex and the basicity of the melts. Variations in the kinds of alkali and alkaline-earth metal ions influenced the stability of the complex and the basicity of the melts, respectively. The half-wave potential moved toward the positive side (45 mV at 1473 K) when the atmosphere over the melts was changed from pure oxygen gas to air; thus, the reversibility of Pt: O2 reference electrode was confirmed.