UV/VIS‐spectroscopy of aluminates in liquid and solid oxide slags

Abstract

Structural information of liquid oxide melts including statements concerning their basicity are important not only for the metallurgy of steelmaking but also for the refractory industry, for ceramic productions and for glass manufacturing. After the introduction of infrared emission spectroscopy of liquid melts up to 1600°C it is now possible to receive UV/VIS‐spectra of these melts in different atmospheres. The comparison to already published spectra is possible by recording spectra of quenched samples at room temperature with the same optical system as the high temperature ones. The suitability of the Fe‐ and Cr‐Ions as test‐ions for the indications of the features of liquid aluminate melts is discussed. A new spectroscopical method for the investigation of melts above 1450°C was developed. Octahedral‐coordinated Fe3+ causes intensive charge‐transfer (CT) absorptions in the melts. These CT‐bands shift towards higher wavelengths and get broader and more intensive at higher temperatures; the results are discussed by the use of the Urbach‐approximation. The CT‐bands of Cr(VI) are attached to various chromate species. The properties of liquid silicates will be the subject of a later investigation.

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

“…(1) agrees with the observed temperature-dependent red shift in CaO-Ah03 slags, especially during the phase transition vitreous/liquid in air [7]. Spectrum (E) shows the extinction of the highly doped slag I with a mass content of 5 % Fez03 at 1500°C in air.…”

“…The experimental set up for the acquisition of UVIVISspectra has already been described in detail previously [7], only the lamp system has been changed. The UVIVIS radiation is now provided by a 1000 W Xenon short arc lamp.…”

“…The extinction includes all attenuations of the incident light beam by scattering and reflection processes from the doped sample. The subtraction of the extinction spectra acquired from the undoped sample results in the absorbance spectrum (A: absorbance), which contains only information about of the doped species Fe(III) or Cr(VI), [7]. The acquired spectra show the extinction E as a function of the wavelength A..…”

“…This spectrometer allows the study of charge-transfer (CT) transitions occurring in the complex between the Fe 3+ and the coordinating 0 2ion of the molten CaO-MgO-Si02 system in the wavelength range between 200 and 800 nm. The experimental set-up and the theory of CT transitions have already been described in a previous work [7].…”

“…The interpretation of these different values will provide information about the structure of the complexes in the oxide matrix [6...9]. In the molten slags at 1500°C, both complexes coexist in an equilibrium [I; 2] according to equation (7). They superpose their absorption characteristics and give rise to a different band structure then at 20°C.…”