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Studying the onset of galvanic steel corrosion in situ using thin films: film preparation, characterization and application to pitting

DOI: 10.1088/1361-648X/abd523 DOI Help

Authors: Debi Garai (Diamond Light Source) , Vladyslav Solokha (Diamond Light Source) , Axel Wilson (Diamond Light Source) , Ilaria Carlomagno (Elettra Sincrotrone Trieste SCpA) , Ajay Gupta (Amity University) , Mukul Gupta (UGC-DAE Consortium for Scientific Research - Indore) , V. R. Reddy (UGC DAE Consortium for Scientific Research) , Carlo Meneghini (University Rome) , Francesco Carla (Diamond Light Source) , Christian Morawe (European Synchrotron Radiation Facility) , Jorg Zegenhagen (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Physics: Condensed Matter

State: Published (Approved)
Published: December 2020
Diamond Proposal Number(s): 17145

Open Access Open Access

Abstract: This work reports about a novel approach for investigating surface processes during the early stages of galvanic corrosion of stainless steel in situ by employing ultra-thin films and synchrotron X-radiation. Characterized by X-ray techniques and voltammetry, such films, sputter deposited from austenitic steel, were found representing useful replicas of the target material. Typical for stainless steel, the surface consists of a passivation layer of Fe- and Cr-oxides, a couple of nm thick, that is depleted of Ni. Films of ≈ 4 nm thickness were studied in situ in an electrochemical cell under potential control (-0.6 to +0.8 V vs Ag/AgCl) during exposure to 0.1 M KCl. Material transport was recorded with better than 1/10 monolayer sensitivity by X-ray spectroscopy. Leaching of Fe was observed in the cathodic range and the therefor necessary reduction of Fe-oxide appears to be accelerated by atomic hydrogen. Except for minor leaching, reduction of Ni, while expected from Pourbaix diagram, was not observed until at ≈ +0.8 V Cr-oxide was removed from the film. After couple of minutes exposure at +0.8 V, the current in the electrochemical cell revealed a rapid pitting event that was simultaneously monitored by X-ray spectroscopy. Continuous loss of Cr and Ni was observed during the induction time leading to the pitting, suggesting a causal connection with the event. Finally, a spectroscopic image of a pit was recorded ex situ with 50 nm lateral and 1 nm depth resolution by soft X-ray scanning absorption microscopy at the Fe L2,3-edges by using a 80 nm film on a SiN membrane, which is further demonstrating the usefulness of thin films for corrosion studies.

Journal Keywords: stainless steel; ultra-thin films; corrosion; X-ray spectroscopy; synchrotron radiation

Subject Areas: Materials, Physics

Instruments: B16-Test Beamline , B18-Core EXAFS , I08-Scanning X-ray Microscopy beamline (SXM)

Other Facilities: P64 at PETRA III/DESY; ID03 at ESRF