Influence of redox equilibrium on the properties of glasses with a high iron concentration

Abstract

In glasses of the System Na2O-CaO-SiO2-Fe2O3, Fe2+ and Fe3+ ions were found by Mössbauer spectroscopy. In samples melted in oxidizing atmosphere, both ions occurred in tetrahedral coordination, whereas they occurred in coordination number 6 in samples with high iron content and melted under reducing conditions. It is shown that a total iron concentration has a stronger influence on the glass properties than the redox state. Differences in the properties of glasses melted in oxidizing and reducing atmosphere, respectively, were observed at lower temperatures, while at higher temperatures they are very small (however, the tendency is still maintained). Density, microhardness, transition temperature and thermal expansion coefficient of the glasses studied are affected by the changes in redox equilibrium. One can conclude that after reducing treatment iron ions present in the glass structure play a similar role as a network modifier. At higher temperatures, this kind of activity is very weak, according to viscosity and liquidus temperature measurements.