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Interplay between wet-dry-cycles and corrosion initiation due to chloride accumulation on AA1050 - A simple experimental approach

: Schneider, M.; Ferl, S.; Langklotz, U.

Gesellschaft für Chemische Technik und Biotechnologie -DECHEMA-:
European Corrosion Congress, EUROCORR 2017 and 20th International Corrosion Congress and Process Safety Congress 2017 : Corrosion Control for Safer Living, Prague, Czech Republic, 3 - 7 September 2017
Red Hook/NY: Curran Associates, 2017
ISBN: 978-1-5108-6250-0
S.691 (Vol.2)
European Corrosion Congress (EUROCORR) <2017, Prague>
International Corrosion Congress and Process Safety Congress <20, 2017, Prague>
Fraunhofer IKTS ()

Generally aluminum alloys are susceptible to pitting corrosion in chloride containing environments, e. g. in marine climates. A well-known but not well-documented fact is the increasing of chloride concentration over a number of wet-dry cycles which are the outstanding feature of atmospheric corrosion. Moreover, time and frequency of wet-dry cycles and consequently the adsorption of chlorides are quite randomly under natural weathering, complicating the quantification of results. For example reported accumulation rates of chloride from the atmosphere on indoor aluminum surfaces range between 0.01 and 0.13μgcm-2a-1 [1]. In a simple experimental approach the authors simulated a number of natural wet-dry-cycles on an aluminum alloy AA1050. The chloride concentration was monitored by a Cl- -ion sensitive electrode and the electrode potential of the aluminum sample by measurement of the open circuit potential. The choronovoltametric experiments were complemented by FT-IRRAS-technique to investigate the development of oxide films and corrosion products. The deposition of sodium chloride itself cannot be directly detected by IRRAS because NaCl is infrared inactive. However, the influence of chloride ions can be deduced indirectly due to the formation of characteristic corrosion products and the oxide film composition (e.g. occurrence of cadwaladerite). Additionally, owing to the hygroscopic properties of the sodium chloride salt, the amount of adsorbed water is an indication of the salt deposition on the surface. The use of the IRRAS mode allows the study of very thin layers down to less than 1μm. This implies the possibility to detect alteration of the native surface layer before the corrosion attacks emerge. Post experimental microscopic investigation complete the study.