Abstract
The transpassive corrosion of highly alloyed austenitic
stainless steels UNS N08904, UNS S31254 and UNS S32654
was investigated at 20 and 70 °C in a range of simulated
bleaching solutions with conventional and rotating
ring-disc electrode voltammetry, as well as
electrochemical impedance spectroscopy. The overall
transpassive oxidation rate of UNS S32654 was found to be
much higher than that of the other two alloys. The
general features of the impedance spectra demonstrate
that transpassive dissolution is favoured for UNS S32654
and secondary passivation predominates for the two other
steels. The addition of oxalic acid resulted in a
significant increase of the transpassive oxidation rate
at both temperatures. At room temperature, the addition
of diethylenetriaminopentaacetic acid (DTPA) led to a
decrease of the transpassive oxidation rate, especially
at pH 3. Conversely, the addition of DTPA to the pH 3
solution at 70 °C has been found to increase the
transpassive oxidation rate. A kinetic model of the
process is proposed, featuring a two-step transpassive
dissolution of Cr via a Cr(VI) intermediate species and
taking into account the dissolution of Fe(III) through
the anodic film. The model has been found to be in
quantitative agreement with the steady-state current
versus potential curves and the impedance spectra. The
kinetic parameters of transpassive dissolution have been
determined and the relevance of their values is
discussed.
| Original language | English |
|---|---|
| Pages (from-to) | 3335-3349 |
| Journal | Electrochimica Acta |
| Volume | 47 |
| Issue number | 20 |
| DOIs | |
| Publication status | Published - 2002 |
| MoE publication type | A1 Journal article-refereed |
Keywords
- stainless steel
- transpassivity
- simulated bleaching solution
- electrochemical impedance spectroscopy
- rotating ring-disc voltammetry
- kinetic model