Corrosion Science, ( ISI ), No (48), Year (2006-2) , Pages (1004-1018)

Title : Evaluation of Current Transients and Morphology of Metastable and Stable Pitting on Stainless Steel Above Pitting Potential ( Evolution of current transients and morphology of metastable and stable pitting on stainless steel near the critical pitting temperature )

Authors: Mohammad Hadi Moayed , R.C. Newman ,

Citation: BibTeX | EndNote

Type 904L austenitic stainless steel with a critical pitting temperature (CPT) of 56 C was polarized at 750 mV (Ag/AgCl) in 1 M NaCl at 45, 49 and 54 C. Current transients due to metastable pitting were recorded at these three temperatures, and a smaller number of stable pit current transients were recorded at 62 C. The metastable pit current, I, followed a power law relationship I  tn during initial growth prior to repassivation. The exponent n increased with temperature, from 0.5 to 1.5. To grow at the lower temperatures, the pits need to be more occluded (lower value of n; lower pit current density). The repassivated metastable pits showed two morphologies: small occluded cavities associated with the small transients, and open ones with polished surfaces for large transients recorded close to the CPT. A new type of deterministic repassivation was identified for the latter type of pit. The stable pit currents rose in proportion to t3/2, just like the faster-growing metastable pits, but only for a few seconds; then there was a drop in current and a further noisy increase occurred with a lower exponent. These pits undercut the metal surface, producing a lacy metal cover. The results are broadly consistent with a model that attributes the CPT to the onset of passivation in the saturated pit solution. A new feature requiring explanation is that, very close to the CPT, pits can precipitate a salt film but fail to undercut the surface. It is hypothesized that since a higher anodic current density is required at the undercutting site than at the pit base, there will be a range of temperatures where the former but not the latter would exceed the critical current density for passivation and is thus disallowed.

Keywords

Pitting corrosion; Stainless
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@article{paperid:102351,
author = {Moayed, Mohammad Hadi and R.C. Newman},
title = {Evaluation of Current Transients and Morphology of Metastable and Stable Pitting on Stainless Steel Above Pitting Potential},
journal = {Corrosion Science},
year = {2006},
number = {48},
month = {February},
issn = {0010-938X},
pages = {1004--1018},
numpages = {14},
keywords = {Pitting corrosion; Stainless steel},
}

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%0 Journal Article
%T Evaluation of Current Transients and Morphology of Metastable and Stable Pitting on Stainless Steel Above Pitting Potential
%A Moayed, Mohammad Hadi
%A R.C. Newman
%J Corrosion Science
%@ 0010-938X
%D 2006

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