Redox equilibrium of Fe3+/Fe2+ and diffusivity of iron in alkali-alkaline earth-silicate glass melts

The redox behavior and diffusivity of iron were studied in alkali-alkaline earth silicates glass melts by means of square wave voltammetry (SWV). According to voltammograms, the potential of the peak due to Fe3+/Fe2+ moved towards the negative direction with a temperature decrease and the peak current showed a strong dependence on frequency at constant temperature. The standard enthalpy and entropy determined were 75 kJ/mol and 23 J/molK, respectively. The activation energy for the diffusion of iron was 148 kJ/mol. The redox ratio, [Fe2+]/[Fe3+] calculated under the assumption that the melt is in equilibrium with air lay in the range 0.02 similar to 0.11. By comparison of the thermodynamic properties and the diffusion coefficient of the present melt with those of other silicate melts cited in the literature, the dependence of the peak potential on alkali concentration and, the relation between the self-diffusion coefficient and viscosity are discussed.