Abstract
Nanometer-thick passive films on metals usually impart remarkable resistance to general corrosion but are susceptible to localized attack in certain aggressive media, leading to material failure with pronounced adverse economic and safety consequences. Over the past decades, several classic theories have been proposed and accepted, based on hypotheses and theoretical models, and oftentimes, not sufficiently nor directly corroborated by experimental evidence. Here we show experimental results on the structure of the passive film formed on a FeCr15Ni15 single crystal in chloride-free and chloride-containing media. We use aberration-corrected transmission electron microscopy to directly capture the chloride ion accumulation at the metal/film interface, lattice expansion on the metal side, undulations at the interface, and structural inhomogeneity on the film side, most of which had previously been rejected by existing models. This work unmasks, at the atomic scale, the mechanism of chloride-induced passivity breakdown that is known to occur in various metallic materials.
Highlights
Nanometer-thick passive films on metals usually impart remarkable resistance to general corrosion but are susceptible to localized attack in certain aggressive media, leading to material failure with pronounced adverse economic and safety consequences
To the best of our knowledge, the experimental advances, including transmission electron microscopic (TEM) characterization[28,29,30,31], promote powerful evidence on the structure and chemistry of the passive film[20,28,29,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45] as well as the evolution imparted by chloride[36,39,43,46], no technique has succeeded in directly following the evolution of the passive film, in chloride-containing media, across the entire film ranging from the surface to the metal/film interface
In order to monitor the transport and effect of chloride ions, passive films were formed under three designated conditions: passivation in H2SO4 electrolyte, passivation in H2SO4 + NaCl electrolyte, and initial passivation in H2SO4 electrolyte and subsequent addition of NaCl into the H2SO4 electrolyte (Supplementary Note 3, Supplementary Figs 5 and 6)
Summary
Nanometer-thick passive films on metals usually impart remarkable resistance to general corrosion but are susceptible to localized attack in certain aggressive media, leading to material failure with pronounced adverse economic and safety consequences. It is worthy of note that these issues were extensively studied by X-ray photoelectron spectroscopy (XPS)[7,14,15,16,17,18,19,20,21], Auger electron spectroscopy (AES)[7,14,16,19,22,23,24,25,26,27], secondary ion mass spectrometry[7,8,16,19,25], and radiotracer techniques[11] It is still very difficult and challenging to guarantee the precision and accuracy of observed locations and concentrations of a very small amount of chloride in an extremely thin passive film with a thickness of only a few nanometers. The present findings allow for the atomic-scale mechanism of passivity breakdown to be revisited on the basis of real-space imaging in multidimensions
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
