CATHODIC REDUCTION OF PASSIVE FILMS ON IRON IN BORATE AND PHOSPHATE BUFFER PH 8.4: DIFFERENT MECHANISMS REVEALED BY IN SITU TECHNIQUES.

Conference · Sun Mar 25 04:00:00 EST 2001

OSTI ID:780779

SCHMUKI, P ^[1]; VIRTANEN, S; ISAACS, H S

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1. BROOKHAVEN NATIONAL LABORATORY

The electrochemical behavior of passive Fe and thin, sputter-deposited films of Fe{sub 2}O{sub 3} was studied in borate and phosphate buffer pH 8.4 solutions. Cyclic voltammograms and in situ light absorption measurements--which enable the monitoring of the oxide film thickness--indicate a similar behavior of the Fe electrode in both pH 8.4 solution, especially a presence of a oxide-free surface at low cathodic potentials. However, X-ray absorption near edge structure (XANES) studies--which allow a simultaneous monitoring of changes in the samples' average valency and thickness - reveal that the reactions taking place during reduction of the passive film on iron are completely different for the two electrolytes. In borate buffer (pH 8.4), reduction leads to a complete dissolution of the passive film and the end product of reduction is soluble Fe(2+). In phosphate buffer (pH 8.4), there is no dissolution in a direct step to low cathodic potentials, but the resulting reduction product is metallic iron. Hence, the formation of the bare oxide-free metal surface at cathodic potentials takes place by different mechanisms in the two pH 8.4 solutions, depending on the type of anion present in the solution.

• Research Organization: Brookhaven National Lab., Upton, NY (US)
• Sponsoring Organization: USDOE Office of Energy Research (ER) (US)
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 780779
• Report Number(s): BNL--68216; KC0201020; KC0201020
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BORATES
CATHODIC PROTECTION
DISSOLUTION
ELECTROCHEMICAL CORROSION
IRON
IRON OXIDES
PASSIVATION
PHOSPHATES
PROTECTIVE COATINGS
REDUCTION