Ultraviolet/visible reflection spectroscopy of molten and glassy silicates (MeOn–CaO–SiO2) and phosphates (MeOn–CaO–P2O5), Men+ = Fe3+, Mn2+

Abstract

This work deals with the reflectivity of liquid oxides (silicates and phosphates) in the ultraviolet and visible spectral range using a reflection angle of 0°. For these considerations, we have developed a spectroscopic reflection method (impulse-flash-technique). By use of this method, we can also record kinetic processes, such as crystallization processes of a supercooled glassy matrix to a crystalline equilibrium phase at high temperatures (transition from specular reflection to diffuse reflection). We have investigated the systems CaO–MeOn–SiO2 and CaO–MeOn–P2O5 (Men+=Fe3+, Mn2+) with Fe2O3- and MnO-contents above 24% (mass-%) in the temperature range from 1400°C to 1550°C applying an oxygen partial pressure of pO2=0.21bar. The spectra are compared with a CaO–Fe2O3-flux with an Fe2O3-content of 60%. 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. The increased reflectivity in the visible spectral range is due to d–d-transitions in the Men+-ion located in Men+–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 fluxes, complexes with the coordination number 4, Men+(O2−)4 with Men+=Fe3+ or Mn2+, were found. In glassy silicates and phosphates, complexes with a coordination number of six dominate. During the quenching process of a silicate to a temperature in the solidus range (up to 900°C) the complexes with a coordination number of six are formed with low order in the glassy matrix. This takes place within a rapid reaction. Subsequently, the crystallization process of the silicates into equilibrium phases starts. The reflection spectra were analyzed quantitatively and related to the molecular structure of the liquid and glassy solidified systems. In the present work, we describe a quantitative correlation between the reflectivity in the UV range and the molar Men+-content. 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.