Thermodynamics of iron redox equilibria and viscosity-structure relationship of CaO-Al2O3-FetO melts

Abstract

The effects of composition on the iron redox equilibria and structural changes in the CaO-Al2O3-FetO melts have been investigated at 1823 K. The ferric to ferrous (Fe3+/Fe2+) ratio increases with increasing basicity and total iron oxide content when the activity of CaO (a(CaO)) is greater than 0.3. However, the Fe3+/Fe2+ ratios decrease with increasing iron oxide content in the case of the existence of octahedrally coordinated Fe3+ ions in a(CaO) = 0.2 composition range. From Raman spectroscopic analysis, it was observed that the addition of iron oxide (up to 10 wt% T.Fe) to calcium aluminate melts modifies the aluminate networks. Furthermore, the non-bridging oxygen per tetrahedron (NBO/T) ratio in the CaO-Al2O3-FetO melts increases with increasing content of iron oxide because the [FeO4]-tetrahedron ferrite networks substitutes for the [AlO4]-tetrahedron aluminate networks. The activation energy for the viscous flow of the CaO-Al2O3-FetO melts has a good linear relationship with the relative concentration of polymerized [AlO4] unit, i.e., ln Q(Al)(4).