Characterization of natural chromite ((Mg,FeII)(Al,FeIIICr)2O4) samples from the Bushveld Complex, South Africa
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Fe3+/Fe2+ ratios were determined for a suite of chromite samples from the Bushveld Complex, South Africa, using57Fe Mössbauer spectroscopy and a ceric sulphate titration method. Two distinctly different types of chromite were identified. Type I chromites have low Fe3+/Fe2+ ratios (between 0.2 and 0.4), and contain 3 cations for every 4 oxygen ions in the chemical formula unit. Type II chromites, on the other hand, have Fe3+/Fe2+ ratios between 0.7 and 1.3, and contain considerably less than 3 cations per 4 oxygen ions in the formula unit. Type II chromites result from the oxidation of type I chromites and can be reduced back to the latter by heating in a gas mixture containing 1% CO and 99% CO2 at 1000 °C.
KeywordsOxidation Oxygen Sulphate Spectroscopy Thin Film
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