Effect of Coordination Structure of Iron Ions on Absorption of Light in Slags Containing Iron Oxides

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The absorption edge shift for the charge transfer band in slags containing iron oxides has been investigated from the viewpoints of (1) the scattering of light due to crystallisation of slags, (2) the change of the coordination number for Fe^<3+> ions and (3) the electron donor power of oxygen ions. Absorption coefficient measurements were made on Fe_2O_3-CaO-SiO_2, Fe_2O_3-CaO-SiO_2-Al_2O_3 and Fe_2O_3-Na_2O-SiO_2 slags in the 0.3-3mum wavelength range.1. The absorption edge was found to move slightly to higher wavelengths with increasing Fe_2O_3 content, but shifted markedly to higher wavelengths with increasing basicity i.e. (%CaO) / (%SiO_2) and (%Na_2O) / (%SiO_2) ratios and Al_2O_3 content.2. X-ray diffraction revealed no traces of crystalline phases forany of the samples. Thus, it has been concluded that the absorption edge shift for the charge transfer band is not due to crystallisation of slags.3. If Fe^<3+> ions occupy tetrahedral coordination sites rather than octahedral coordination sites, interaction between the iron and oxygen electrons will become smaller, resulting in a shift of the absorption edge to higher wavelengths. However, the results have shown that the absorption edge shifts to higher wavelengths as the ratio of (Fe^<2+> ions in tetrahedral symmetry/the total Fe^<3+> ions) decreases. Thus, it has been considered that the absorption edge shift to higher wavelengths is not associated with the change of the coordination number for Fe^<3+> ions.4. The absorption edge was observed to shift to higher wavelengths with increasing the ion refractivity of oxygen in the slags. Consequently, it has been proposed that the absorption edge shift is relevant to the electron donor power of oxygen ions.