AN ELECTROCHEMICAL IMPEDANCE STUDY ON ATMOSPHERIC CORROSION OF STEELSIN A CYCLIC WET-DRY CONDITION

Citation
A. Nishikata et al., AN ELECTROCHEMICAL IMPEDANCE STUDY ON ATMOSPHERIC CORROSION OF STEELSIN A CYCLIC WET-DRY CONDITION, Corrosion science, 37(12), 1995, pp. 2059-2069
Citations number
16
Categorie Soggetti
Metallurgy & Metallurigical Engineering
Journal title
ISSN journal
0010938X
Volume
37
Issue
12
Year of publication
1995
Pages
2059 - 2069
Database
ISI
SICI code
0010-938X(1995)37:12<2059:AEISOA>2.0.ZU;2-W
Abstract
The corrosion rates of steels with different nickel contents (0, 2.5, 10 and 20 wt%) were monitored by the AC impedance method under a cycli c wet-dry condition, which was conducted by exposure to alternate cond itions of 1 h immersion in a 0.05 M NaCl solution and 7 h drying at 60 %RH and 25 degrees C. The corrosion rates of the ordinary carbon steel and the 2.5% Ni containing steel were greatly accelerated by the wet- dry cycles, while those of steels containing at least 5% Ni were only slightly affected. AC impedance tests indicated that the addition of 5 % Ni greatly reduced the corrosion rates of the steel exposed to the c yclic wet-dry environments containing chloride ions, in good agreement with one year exposure tests in the atmospheric marine environments. Within the wet-dry cycle for the carbon steel, a gradual increase in t he corrosion rate and a shift of the corrosion potential to negative v alues were observed at the initial stage of the drying period. These i ndicated that the anodic metal dissolution rate was accelerated by a s light increase in the chloride ion concentration. At the intermediate stage of drying, the corrosion rate rapidly increased and the corrosio n potential remained constant. This can be attributed to the accelerat ion of both the anodic metal dissolution process and the cathodic oxyg en reduction process which is usually controlled by the rates of O-2 t ransport through the thin electrolyte film. At the final stage, just b efore the surface dried out, the corrosion rate rapidly decreased, shi fting the corrosion potential to the noble direction. At this stage, t he anodic process was greatly inhibited. The corrosion testing system employed in this study is very useful for the rapid evaluation of the corrosion performance of metals in atmospheric marine environments and for mechanistic study.