UV/VIS-spectroscopy of molten and solid CaO-MgO-SiO2 - slags

The previously developed high temperature set-up has been used to monitor the redox state of molten slags at 1500°C directly by UV/VIS spectroscopy. Slags of the CaO-MgO-SiO₂-system were doped with Fe₂O₃ mass contents of 0.80 and 5%. Spectroscopical results at different oxygen partial pressures of the investigated Fe³⁺ charge-transfer (CT) transitions in the wavelength range between 200 and 800 nm were found to be representative for the redox state of the slag. The peak positions and shifts give further information about the optical basicity and the structure of molten slags. The time dependence of the oxidation/reduction equilibrium process was measured and evaluated concerning diffusion mechanisms. In Cr₂O₃-doped silicate-slags in the liquid state CrO₃ - and Cr³⁺- species occur. The different CrO₃-species (CrO₄^2- and Cr₂O₇^2-) in silicate slags have been indicated spectroscopically and registed quantitatively. Further investigations on Cr₂O₃-doped slags uncovered the well known evaporation of chromium out of molten slags as a decrease in the CrO₃ concentration in time. In the molten slag the CrO₃ slowly evaporates, which can be seen spectroscopically as a decrease in the CT-band intensity. The results obtained on numerous optical parameters of molten slags will establish the application of reflection spectroscopy at high temperatures.