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The nature of crevice corrosion of aluminum in chloride solutions
Author(s) -
Baumgärtner Marianne,
Kaesche H.
Publication year - 1988
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19880390304
Subject(s) - crevice corrosion , corrosion , dissolution , aluminium , materials science , pitting corrosion , chloride , metallurgy , electrolyte , metal , foil method , scanning electron microscope , alloy , composite material , chemistry , electrode
To study crevice corrosion of pure aluminum, polished specimens partly covered with a glass foil were polarized potentiostatically in 1 N NaCl‐solution at potentials negative to the critical potential for stable pitting (pitting potential). For comparison, non‐crevice experiments were performed on polycrystalline and singlecrystalline material in neutral as well as acidified 1 N NaCl‐solution and in AlCl 3 ‐solutions. Corrosion morphology was examined by scanning electron microscopy. In current‐time plots recorded during experiments on crevice corrosion, both an incubation and a propagation stage are discernible. If experiments were interrupted during the induction period, micropits were found inside the crevice. This unstable micropitting is detectable down to 0.30 V below the pitting potential. In contrast, during crevice corrosion propagation, the aluminum surface undergoes general attack. In a range of 0.2 V below the pitting potential, dimpled surfaces are produced. At more negative potentials, metal dissolution occurs crystallographically oriented. An identical behaviour was detected on unshielded samples polarized in the same potential range in both 1 N AlCl 3 ‐ and acidified 1 N NaCl‐solution. Hence, the build‐up of an acidic electrolyte is considered the sufficient requirement for crevice corrosion initiation.