Oxidation states and coordinalion structures of iron ions in silicate melts during relaxation process and at equilibrium

Changes of oxidation states and local structural environments of iron ions in calcium silicate melts have been determined during the equilibration pro cess by Mossbauer spectroscopy to investigate the equilibrium states of iro n ions from the viewpoint of the effects of basicity! iron oxide and basic oxide concentrations The fraction of Fe3+ ions to the total iron ions becam e constant within 2 h after the equilibration operation was started. On the other hand, it took about 20 and 6 h for the coordination structures of Fe 3+ ions to settle down bq, sharing between tetrahedral and octahedral sites when the samples were melted at 1608 and 1678 K, respectively. From these results it has been considered that the structural coordination of the melt s is determined by rearrangement of oxygen ions rather than diffusion of ir on ions in the silicate melts. With respect to the equilibrium state of iro n ions it was found that Fe3+ ions tend to be in octahedral symmetry, at la rger ratios of the number of Fe3+ ions to that of nonbridging oxygen ions, and to be in tetrahedral symmetry when the glass matrix is basic.