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Galvanic corrosion in marine environments: Effects associated with the inversion of polarity of Zn/carbon steel couples
Author(s) -
Refait Philippe,
Jeannin Marc,
François Emilie,
Sabot René,
Grolleau AnneMarie
Publication year - 2019
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.201810568
Subject(s) - materials science , galvanization , corrosion , cathodic protection , galvanic cell , anode , metallurgy , cathode , passivation , galvanic corrosion , galvanic anode , carbon steel , zinc , composite material , electrode , layer (electronics) , chemistry
This article focuses on the corrosion processes resulting from the galvanic coupling between an unprotected carbon steel coupon and a “passivated” Zn‐coated carbon steel coupon. Monitoring of the galvanic current showed that the galvanized steel coupon acted as cathode, which confirmed the inversion of polarity due to Zn passivation. However, it remained cathode for only 6 months and behave as anode for the rest of the experiment (i.e., 5 years). At the end of the experiment, both coupons presented localized degradation. The local corrosion rates were estimated by residual thickness measurements. The highest (200 μm/year) was measured on the more corroded parts of the galvanized steel coupon, while the lowest (13 μm/year) corresponded to the cathodic zones of the same coupon, covered by passivated zinc. The phenomena could be interpreted via the thorough analysis of the corrosion product layers by X‐ray diffraction and μ‐Raman spectroscopy as the composition of these layers depended on the anodic/cathodic character and intensity of the metal surface underneath.