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A Contribution to the Study of the Critical Pitting Potential of Oxide Covered Aluminum in aqueous chloride solutions

✍ Scribed by Z. A. Foroulis; M. J. Thubrikar


Publisher
John Wiley and Sons
Year
1975
Tongue
German
Weight
762 KB
Volume
26
Category
Article
ISSN
0947-5117

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✦ Synopsis


Abstract

The critical pitting potential of oxide covered aluminum electrodes in aqueous chloride solutions has been investigated as a function of chloride ion concentration, temperature, solution pH and oxide film thickness. The steady state critical pitting potential decreases with chloride ion concentration and increasing solution temperature. Solution pH in the range 5 to 9 has no effect on the breakdown potential. The role of the oxide film thickness is to slightly increase the critical potential for passivity breakdown and intiation of pitting. It is postulated that at the critical pitting potential, passivity breakdown occurs by a process of field assisted Cl adsorption on the hydrated oxide surface and formation of a soluble basic chloride salt with a lattice cation which readily goes in solution. This process of localized dissolution of the hydrated oxide film via formation of a soluble basic aluminum chloride salt, once initiated, is likely to continue in an β€œautocatalytic” fashion until the oxide is locally β€œpenetrated” and dissolution of the substrate metal begins.


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