Thermal Treatment of Chromium(III) Oxide with Carbonates Analyzed by Far-Infrared Spectroscopy

Abstract

The chemical state of thermochemically treated chromium(III) oxide (Cr₂O₃) with various carbonates was analyzed by far-infrared (far-IR) spectroscopy (spectral region 700–25 cm⁻¹). Non-toxic Cr₂O₃ was oxidized with potassium, sodium, and calcium carbonate, respectively, to toxic Cr(VI) and Cr(V) compounds during thermal treatment at 1000 °C. In reverse, thermochemical treatment of Cr₂O₃ with magnesium carbonate lead to the formation of the Cr(III) compound MgCr₂O₄. Higher temperatures (>1200 °C) or reducing atmospheric conditions prevent the formation of Cr(VI)/Cr(V) compounds, too. Additionally, it was found that polyethylene powder with a low particle size (<70 μm) is favorable for the collection of good far-IR spectra of inorganic powders.