An X-ray absorption near-edge spectroscopy study of the oxidation state ofchromium in electrodeposited oxide films

The oxidation state of chromium incorporated into simulated corrosion films of nickel has been investigated using the technique of 'in situ' X-ray Abs orption Near-Edge Spectroscopy (XANES). The films were prepared by electroc hemical deposition of the appropriate oxide (hydroxide) onto a graphite sub strate. Cathodic deposition from a 0.01 M Cr(NO3)(3) solution at constant c urrent results in a Cr3+ oxide (hydroxide) film. deposition from a 0.01 M K 2CrO4 solution produces a film which is predominantly Cr3+ but With some Cr 6+. This material is air-sensitive and the ratio of Cr6+ to Cr3+ increases with time of exposure to ambient. Cathodic rcodeposition of Cr3+ with nicke l hydroxide from Cr(NO3)(3) solution results in a film with chromium in the 3; oxidation state. On the other hand, cathodic codeposition from a Cr6+ s olution of K2CrO4 with nickel hydroxide leads to a film containing Cr6+. (C ) 1999 Elsevier Science Ltd. All rights reserved.