Application of UV/VIS‐Reflection Spectroscopy for Determination of the Oxidation State of Liquid Slags with High Fe³⁺‐Contents

Abstract

This work considers the reflectivity of liquid oxides (silicates and phosphates) in the ultraviolet and visible spectral range using a reflection angle of 0°. We have developed a spectroscopic reflection method (impulse‐flash‐technique) and have investigated CaO‐FeOn‐SiO2 and CaO‐FeOn‐P2O5 with Fe2O3‐contents above 32 mol‐% (FeO1.5) at a temperature of 1400°C applying oxygen partial pressures of po2 = 0.001 bar up to po2 = 0.21 bar. The increased reflectivity in the ultraviolet spectral range is based on the very intensive electron transfer (charge transfer bands, CT) from the oxide ion (bound to the respective matrix) to the Fe3+‐ion. The increased reflectivities in the visible spectral range are due to d‐d‐transitions in the Fe3+‐ion located in Fe3+‐O2− ‐complexes. This can be proven in the following way. The reflection bands in the visible range are much less pronounced than the CT‐bands in the UV range. In the slag melts, complexes with the coordination number 4, Fe3+(O2−)4, have been found predominantly. The relation between the redox state of liquid slags and their UV‐reflectance has been evaluated quantitatively. The basic investigations for recording the redox state of liquid silicates and phosphates during a running metallurgic process are part of this work. Liquid silicates and phosphates are the most important slag systems in this context.