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In situ current density mapping, scanning electron microscopy, and energy dispersive spectroscopy were used to study the effects of cerium as a corrosion inhibitor for an aluminum copper alloy (AI 2024-T4) in chloride containing solutions. It was found that cerium inhibits corrosion of this alloy by reducing the rate of the cathodic reaction. This was due to the formation of cerium-rich films over copper containing intermetallics which act as local cathodic sites. Results from tests carried out on an aluminum/copper galvanic couple, which was used to simulate the electrochemical behavior of the copper containing intermetallics, showed that corrosion inhibition was associated with the formation of a Ce-rich film over the copper in agreement with that observed for the alloy.

In situ surface X‐ray diffraction was used to identify the detailed structure of the passive film that forms on (000)− and (110)‐oriented iron single crystals in a borate buffer solution at +0.4 V vs. mercurous sulfate reference electrode, a high passive potential. The passive film is a new phase: a spinel with a fully occupied oxygen lattice, octahedral site occupancy of 80 ± 10%, tetrahedral site occupancy of 66 ± 10%, and an octahedral interstitial site occupancy of 12 ± 4%. The passive film forms with an epitaxial relationship to the substrate iron; for growth on Fe(001), film(001)‖Fe(001) and normalfilmfalse[1true1¯0false]‖normalFefalse[100false] , while for growth on Fe(110), film(111)‖Fe(110) and normalfilmfalse[1true1¯0false]‖normalFefalse[100false] . The in‐plane lattice parameter for the passive film (the LAMM phase) is 8.39 ± 0.01 Å for growth on both faces, and the out‐of‐plane lattice parameter is 8.25 ± 0.1 Å [Fe(001)] and 8.42 ± 0.1 Å [Fe(110)]. The passive film forms a nanocrystalline microstructure with numerous defects. Specifically, the grain size is 50–80 Å in‐plane and about 30 Å out‐of‐plane. There is a small mosaic spread of 2.5 to 4.1° and a high density of antiphase boundaries and stacking faults. The structure of the film determined in situ was found to be identical to that found for an emersed sample, indicating that the high potential film studied here is stable on removal from the electrolyte. Some of the implications of the film structure on passivity are discussed. © 2000 The Electrochemical Society. All rights reserved.

In situ x-ray specular reflectivity and glancing-incident-angle x-ray diffraction measurements have been performed at the Au(001) surface in a 0.01 M HC10 4 solution under potential control in an electrochemical cell. At -0.4 V versus an Ag/AgCl electrode, the gold surface exhibits a hexagonal reconstructed layer with a mass density 21% greater than the underlying bulk layers. The reconstruction disappears above 0.5 V, and the excess atoms form a new atomic layer with a density corresponding to 22% of a bulk layer. The reconstruction fully recovers below -0.3 V.

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