Experimental Studies on the Oxidation States of Chromium Oxides in Slag Systems

Abstract

In view of the importance of the thermodynamic behavior of chromium in the slag phase as well as the serious discrepancies in the earlier reports on the valence state of chromium in slag melts, the oxidation state of chromium oxides in CaO-SiO 2 -CrO x and CaO-MgO-(FeO-) Al 2 O 3 -SiO 2 -CrO x were investigated experimentally in the present study using two different experimental techniques. The gas-slag equilibrium technique was adopted to study the CaO-SiO 2 -CrO x system between 1823 K (1550°C) and 1923 K (1650°C) and equilibrated with mixtures of CO-CO 2 -Ar gases corresponding to three different oxygen partial pressures (between 10 À4 and 10 À5 Pa). After equilibrating, the samples were quenched and subjected to analysis using the X-ray absorption near edge structure method to determine the distribution ratio of Cr 2+ /Cr 3+ in the slags. The second technique examined the applicability of the high-temperature mass spectrometric method combined with the Knuden effusion cell for quantifying the valence states of Cr in the multicomponent system CaO-MgO-(FeO-) Al 2 O 3 -SiO 2 -CrO x up to a maximum temperature of 2000 K (1727°C). The results showed that the Knudsen cell-mass spectrometric method could be used successfully to estimate the valence ratio for Cr in silicate melts. According to the present study, the Cr 2+ /Cr 3+ ratio increased with increasing temperature and a decreasing slag basicity as well as the oxygen partial pressure prevailing in the system. A mathematical correlation of X CrO /X CrO1.5 as a function of temperature, oxygen partial pressure, and basicity was developed in the present work based on the present results as well as on those assessed from earlier data.

Viscosity Measurements of CaO–SiO₂–CrO Slag

“…The compositions selected for viscosity measurements were projected into this phase diagram, all of which were in the complete liquid phase zone. The basicity (R) of slags was very close to 0.5, which promotes the existence of Cr 2 + based on the X CrO /X CrO1.5 ratio prediction equation obtained by Wang et al 16) Furthermore, the ratio of divalent to trivalent chromium ((%Cr 2 + )/(%Cr 3 + )) in the slag with a basicity of 0.5 was predicted by the software under different CrO contents and temperatures. As shown in Figs.…”

Effects of MgO and Al2O3 Addition on Redox State of Chromium in CaO-SiO2-CrO x Slag System by XPS Method

“…The data deduced from XPS Cr2p spectrum show a reasonable agreement with literature values. [1,5,10,11] B. Structure of Slag Comparing Figures 6 and 7, O1s spectra in MgO series and Al 2 O 3 series present different shapes.…”

“…Some values showed a tendency of increase of the divalent chromium in the slag with increasing basicity, which was different from the results of the earlier study. In view of this, the present authors [11] adopted two techniques to determine the relationship between the ratio of Cr 2+ to Cr 3+ with respect to temperature, oxygen partial pressure as well as the slag chemistry; one is classical gas/slag equilibrium with XANES analysis, and the other one is high-temperature mass spectrometry. As reported by Irmann, Cr(III) would exist as [CrO 2 ] À in basic slag phase.…”

Analysis of Cr with Various Valence States in Industrial EAF Slag for Making Stainless Steel

“…But some amorphous phase in slag may cause large error. X-ray photoelectron spectroscopy (XPS), [11][12][13][14] x-ray fluorescence (XRF), 15) x-ray absorption near edge structure (XANES) 11,14,16,17) and high temperature mass spectrometric (MS) method combined with Knuden effusion cell 14,16) were reported to distinguish the Cr 2 + and Cr 3 + in slag. These instrumental analysis methods may work well in Lab, but may face some barriers in plant.…”