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

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.