Surface enhanced Raman spectroelectrochemical studies of the corrosion films on iron and chromium in aqueous solution environments

✍ Scribed by C.A. Melendres; M. Pankuch; Y.S. Li; R.L. Knight

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 739 KB
• Volume: 37
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(92)85202-v

✦ Synopsis

In

situ" laser Raman spectra of the corrosion films on iron have been observed in aerated 5 M KOH and 0.15 M NaCl solutions via surface enhancement by the electrodeposition of a silver overlayer. Essentially the same spectra are observed in the two solutions as a function of applied potential in spite of a breakdown of passivity on iron in the chloride solution. FeJOH), and Fe,O, are found in the prepassive potential region while FeOOH is present in the passive region. A film which is very diilicult to reduce appears to be always present on the electrode surface even at hydrogen evolution potentials; this film is believed to be a-FeOOH. Surface enhanced Raman spectra of the corrosion films on chromium have also been obtained in NaCl solution for the first time. The passive film has a composition that corresponds most closely to an amorphous form of Cr,O, , with some Cr(OH), also present. The film is converted in the transpassive region to a higher oxide form, presumably CrO:-. Reversible reduction of this species to Cr,O, is indicated.