Structure relaxation of silicate melts containing iron oxide

The changes of oxidation states and coordination structures of iron ions in the liquid state of calcium–silicate (40 mol% CaO–40 mol% SiO2–20 mol% Fe2O3) during the equilibration process have been determined by Mössbauer spectroscopy. The fraction of Fe3+ ions to the total iron ions became constant within 2 h after the equilibration operation was started at 1773 K. Samples were then melted at 1608, 1678, 1773, and 1858 K for soak times ranging from 2 to 72 h in Pt crucibles in air and then quenched in water. On the other hand, it took 20 and 6 h for the coordination structures of Fe3+ ions to settle down by sharing between tetrahedral and octahedral sites when the samples were melted at 1608 and 1678 K, respectively. It was assumed that the coordination in the liquid is determined by rearrangement of oxygen ions. The fraction of Fe3+ ions in tetrahedral symmetry to the total Fe3+ ions at equilibrium decreased with increasing temperature. The standard enthalpy change for the reaction of the change of Fe3+ ions in the coordination structure was calculated as 68.6±17.3 K/mol−1.