Redox equilibria and coordination of Fe 2+ and Fe 3+ in silicate glasses from 57Fe mossbauer spectroscopy

Abstract

Summary 1. Mossbauer spectroscopy can be used to determine the Fe 3+ /ΣFe of silicate melts as accurately as colorimetric methods. 2. In silicate melts and glasses, the Fe 3+ /ΣFe governs the number of oxygens ligands around Fe 3+ . In oxidized melts, ferric iron is in tetrahedral coordination, whereas in reduced melts, ferric iron is octahedrally coordinated. Ferrous iron is always in octahedral coordination. 3. Simple linear relations exist, in binary metal oxide — silica and ternary metal oxide — alumina — silica melts, between Fe 3+ /ΣFe and oxygen fugacity, temperature, types of network-modifying cations and Al/(Al + Si). 4. Experimental data from binary, ternary and quaternary systems can be combined to derive a numerical expression for melts with at least eight components that relate redox equilibria of iron oxide to temperature, oxygen fugacity and bulk chemical composition of the melt.