Structure of Liquid Slags and Ultraviolet/Visible Reflection Spectroscopy of Molten and Glassy Silicates (Fe₂O₃‐CaO‐SiO₂)

Abstract

The first part of this work is a description of the molecular structure of liquid silicates. From the knowledge of the chemical bond, the Me n+···02bond distance and the Me n+/02coordination number, the Me n+ ...Q2-bond polarity (Me=Ca, Mg, AI, Fe...) of liquid oxide slag systems is derived. There exists a connection between this value and the activity coefficient of an oxide component. We illustrate this connection for important slag systems. The second part of this work deals with the reflectivity of liquid silicates in the ultraviolet and visible spectral range using the reflection angle 0°. For these considerations, we have developed a spectroscopic reflection method (impulse-flash-technique). We have investigated the systems CaO-FeO n-Si02 with Fe 203 -contents above 24 % (mass percent) and a CaO-Fe203-flux with an Fe203-content of 60 % in the temperature range from 1400°C to 1500°C applying an oxygen partial pressure of Po 2 = 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 Men+-ion (Me n+=Fe3+, Mn 2+ ..). The increased reflectivities in the visible spectral range are due to dod-transitions in the Men+-ion located in Me n+ _0 2--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 liquid slags complexes with the coordination number 4, Fe 3+{02-)4 were found. In glassy silicates, complexes with the coordination number 6 dominate. The reflection spectra have been analysed quantitatively and related to the molecular structure of the liquid and glassily solidified systems. In the present work, we describe a quantitative correlation between the reflectivity in the UV range and the molar Fe3+-content. The basic investigations for recording the redox state of liquid silicates during a running metallurgical process are part of this work.