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The Effect of Nitrate on Salt Layers in Pitting Corrosion of 304L Stainless Steel

DOI: 10.1149/2.0421509jes DOI Help

Authors: Steven Street (University of Birmingham) , W. Xu (University of Birmingham) , M. Amri (Diamond Light Source) , Liya Guo (University of Birmingham) , Sarah Glanvill (University of Birmingham) , Paul Quinn (Diamond Light Source) , Fred Mosselmans (Diamond Light Source) , Joan Vila-comamala (Diamond Light Source) , Christoph Rau (Diamond Light Source) , Trevor Rayment (Diamond Light Source) , Alison Davenport (University of Birmingham)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The Electrochemical Society , VOL 162 (9) , PAGES C457 - C464

State: Published (Approved)
Published: June 2015
Diamond Proposal Number(s): 7414 , 8810

Open Access Open Access

Abstract: Current oscillations were observed during one-dimensional pitting corrosion of 304 L stainless steel in neutral 1 M NaCl solutions with varying NaNO3 concentrations. Synchrotron X-ray diffraction was used to identify the salt layer at the corrosion front. It was found that, although current oscillations were induced in solutions with higher concentrations of NaNO3, the salt species in the pit did not change and a nitrate-free salt was present in all solutions. At higher NaNO3 concentrations, a change of salt crystal morphology was detected. Electrochemical oscillations were seen to coincide with secondary pitting on the pit surface indicating that two corrosion regimes were operating in parallel. Synchrotron radiography was used on artificial pits to measure the change in corrosion front and material loss in situ. Before nitrate was added, the corrosion front showed non-uniform material loss across the interface when beneath the salt layer. Nitrate addition induced a local region of passivation that propagated across the pit surface. Surface roughness was quantified using R-values and seen to vary without a clear trend until passivation, after which it stayed constant. A mechanism is suggested in which partial passivation occurs in these systems, where passivated areas are undercut as the corrosion front moves, generating surges in current.

Subject Areas: Chemistry, Materials

Instruments: I13-2-Diamond Manchester Imaging , I18-Microfocus Spectroscopy