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

The effects of MgO and Al₂O₃ on the redox state of chromium in CaO-SiO₂-CrO _x system have been investigated at 1873 K (1600 °C) under Ar-CO-CO₂ atmosphere and analyzed by means of X-ray photoelectron spectroscopy. From the analysis of the Cr 2p core level spectra, it was found that both Cr(II) and Cr(III) exist simultaneously in CaO-MgO/Al₂O₃-SiO₂-CrO _x , and the quantitative ratio Cr(II)/Cr(III) has been obtained by deducing from the area under the computer-resolved peaks. Substitutions of CaO by MgO, SiO₂ by Al₂O₃ favored the Cr(II) state existing in the system in the composition ranges of 3 to 10 wt pct MgO and 5 to 20 pct Al₂O₃. Meanwhile, from the analysis of the O1s spectra in CaO-MgO-SiO₂-CrO _x , it was found that the ratio of the non-bridging oxygen content increased first due to the CrO contribution to the electron distribution uniformly as O⁻ at MgO low content. Afterward, it went to decreasing with continuing addition of MgO because ionic contribution of MgO is less than that of CaO and the influence of the CrO clustering on the non-Bridging oxygen is limited due to only 5 wt pct CrO _x . In CaO-Al₂O₃-SiO₂-CrO _x system, Cr(II) acts as a network modifier to compensate Al³⁺ charge balance to make the structure stable, so the non-bridge oxygen in this system continues decreasing.