Ultraviolet/visible spectroscopy of molten slags and glasses (up to 1600 degrees C)

The aim of this research project is to obtain information about the molecul ar structure of liquid oxides (silicates and aluminates) by application of spectroscopic methods. The chemical structure is correlated with the proper ties of the oxide melts (e.g. basicity, redox state, equilibria). Spectrosc opic methods are also suitable for the control of melts Juring smelting. Fo r these investigations, spectroscopic methods have been developed (waveleng th range 220 up to 780 nm) for research studies of temperatures up to 1600 degreesC at different oxygen partial pressures. Measurements of slags with and without 3d cation dopings have been investigated. The eigenabsorption ( electron transition valence band/conduction band in the silicates) in the u ltraviolet-range in undoped liquid silicates is connected with the dissocia tion of these silicates. Slag systems of samples from CaO-SiO2; CaO-MgO-SiO 2; CaO-Al2O3-SiO2 and CaF2-CaO-Al2O3 have been doped with oxides of 3d cati ons: Fe2O3 [Fe2+/Fe3+]; Cr2O3 [Cr6+-species] and CoO [Co2+] With mass conte nts 0.80% up to 50% and samples without dopings have been prepared. With an increase of basicity, a red-shift of the charge transfer bands has been me asured, which has been quantitatively evaluated. The height and the long-wa ve decrease (Urbach-range) of the Fe3+-bands depend on the redox state of t he slag. In liquid slags, the Cr6+-species is spectroscopically detectable as Cr2O7--anion, whilst in the glassy slags at room temperature the CrO42-- anion exists. The Cr2O72--anion is not stable in liquid slags and in a diff usion-controlled thermal dissociation, gaseous CrO3 is evaporated. Within t he visible range, the d-d-absorption bands of the tetrahedral Co2+ (O-2(-)) (4)-complex decrease with an increase of temperature. By quantitative evalu ation of the spectra, the dissociation degree and the dissociation enthalpy have been determined as a function of temperature up to a temperature abov e the liquidus temperature. (C) 2001 Elsevier Science B.V. All rights reser ved.