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Redox Equilibria of Chromium in Calcium Silicate Base Melts

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Abstract

The oxidation state of chromium has been determined at 1600 °C in CaO-SiO2-CrO x melts with CaO/SiO2 ratios (mass pct) of 0.66, 0.93, and 1.10, and 0.15 to 3.00 pct Cr2O3 (initial). A few experiments were also carried out with CaO-SiO2-Al2O3-CrO x melts at 1430 °C. The slag samples were equilibrated with gas phases of controlled oxygen pressure. Two techniques were applied to determine the oxidation state: thermogravimetry and quenching of the samples with subsequent wet chemical analysis. In the low-oxygen pressure range, the chromium is mainly divalent. In the high-oxygen pressure range, it is trivalent and hexavalent. It was found that the Cr3+/Cr2+ and Cr6+/Cr3+ ratios depend on oxygen pressure at a constant CaO/SiO2 ratio and a constant content of total chromium, according to the ideal law of mass action. According to the respective chemical reactions, these ratios change proportional to \( p_{{{\text{O}}_{2} }}{}^{1/4} \) or \( p_{{{\text{O}}_{ 2} }}{}^{3/4}, \) respectively. They also increase with increasing basicity. The data are used to compute the fractions of the different ions in the melt. There is a certain range of oxygen pressure in which all three valence states, Cr2+, Cr3+, and Cr6+, coexist. The color of the solidified slag samples is described and is explained with the help of transmission spectra.

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Authors and Affiliations

  1. Institut für Metallurgie, Technische Universität Clausthal, 38678, Clausthal-Zellerfeld, Germany

    A.-M. Mirzayousef-Jadid (Scientist) & Klaus Schwerdtfeger (University Professor Emeritus)

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  1. A.-M. Mirzayousef-Jadid
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  2. Klaus Schwerdtfeger
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Correspondence to Klaus Schwerdtfeger.

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Manuscript submitted July 29, 2008.

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Mirzayousef-Jadid, AM., Schwerdtfeger, K. Redox Equilibria of Chromium in Calcium Silicate Base Melts. Metall Mater Trans B 40, 533–543 (2009). https://doi.org/10.1007/s11663-009-9225-3

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  • DOI: https://doi.org/10.1007/s11663-009-9225-3

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