Oxidation mechanism of metallic chromium at room temperature

A quantitative study of the surface composition of clean metallic and oxidized chromium exposed to atmospheric conditions was carried out employing X-ray photoelectron spectroscopy (XPS). Advanced tools were used for the fitting process and surface composition analysis. We found that, in contrast with most metals, the oxidation does not come about through the formation of an oxide layer. State of the art analysis showed that, even at long exposures, a fraction of the chromium surface retains its metallic nature even at the top layers. Depth profile of XPS spectra shows no shape modulation from angle to angle which strongly suggest both Cr3+ and Cr6+ species coexist with the metallic species throughout the probing depth of XPS. The oxidation mechanism of metallic chromium exposed to ambient is through the partial oxidation of surface regions.