Passivity breakdown, pit initiation and propagation of pits in metallic materials – Review

Nanometer-thick passive films on metals usually impart remarkable resistance to general corrosion but are susceptible to localized attack in certain aggressive media, leading to material failure with pronounced adverse economic and safety consequences. Over the past decades, several classic theories have been proposed and accepted, based on hypotheses and theoretical models, and oftentimes, not sufficiently nor directly corroborated by experimental evidence. Here we show experimental results on the structure of the passive film formed on a FeCr15Ni15 single crystal in chloride-free and chloride-containing media. We use aberration-corrected transmission electron microscopy to directly capture the chloride ion accumulation at the metal/film interface, lattice expansion on the metal side, undulations at the interface, and structural inhomogeneity on the film side, most of which had previously been rejected by existing models. This work unmasks, at the atomic scale, the mechanism of chloride-induced passivity breakdown that is known to occur in various metallic materials.

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Unmasking chloride attack on the passive film of metals

http://www.khdesign.co.uk/acrobat/paper2.pdf

The measurement of corrosion using electrochemical noise

Electrochemical testing to assess corrosion protective coatings

The passivity of metals is reviewed from the perspective of materials science rather than with the usual electrochemical emphasis. Iron and ferrous alloys are used to illustrate the essentials of t...

U. Bertocci

Papers

Studies of passive film breakdown by detection and analysis of electrochemical noise