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Alfred Larsson. Portrait.

Alfred Larsson

Postdoctoral fellow

Alfred Larsson. Portrait.

The Formation and Breakdown of Passive Film on Ni Alloys : in situ synchrotron studies

Author

  • Alfred Larsson

Summary, in English

Corrosion results in huge annual costs and a large environmental footprint. The corrosion rate of some alloys can be made negligible by the presence of a spontaneously forming oxide film on the surface, a so-called passive film. Famous examples of alloys exhibiting passivity are stainless steels. However, in some demanding applications, stainless steel does not provide significant corrosion resistance. Instead, Ni alloys are used, which are known for their excellent corrosion resistance. The nature, formation, and mechanism of breakdown of the passive films that form on Ni alloys is, however, not well understood.
In this thesis, a combination of in situ synchrotron-based methods has been used to elucidate the chemistry and structure of the thin oxide films that dictate the corrosion resistance, as well as the chemistry of the electrolyte above the sample surface to probe the concentration of dissolved ions and their chemical state. This was also coupled with the use of optical microscopy to provide a full-field view of the surface in situ.
It was found that the passive film on the studied Ni-Cr-Mo alloys mainly contains Cr oxides and Mo oxides, while Ni does not participate in the oxide film. The film is only one nanometer thick and forms rapidly upon exposure to oxygen. It was shown that even if the initial oxidation kinetics are rapid, it takes time for a true steady-state composition to be reached, and aging of the sample surface in air affects the oxide thickness and composition. It was also found that Ni-Cr-Mo alloys exhibit a transpassive breakdown mechanism that is different from that of typical Cr-containing alloys. This mechanism was also found to be connected to the catalytic activity towards the oxygen evolution reaction, which takes place at increased anodic potentials. Lastly, this thesis also covers some method development of both X-ray-based and optical surface-sensitive methods that were used to study the thin oxide films at the solid-liquid interface in situ.

Department/s

  • Synchrotron Radiation Research
  • NanoLund: Centre for Nanoscience
  • LTH Profile Area: Nanoscience and Semiconductor Technology
  • LU Profile Area: Light and Materials

Publishing year

2023

Language

English

Document type

Dissertation

Publisher

Lund University

Topic

  • Subatomic Physics
  • Condensed Matter Physics (including Material Physics, Nano Physics)
  • Physical Chemistry (including Surface- and Colloid Chemistry)
  • Materials Chemistry

Keywords

  • Passivity
  • Corrosion
  • Degradation
  • Nickel alloys
  • synchrotron
  • in situ
  • Fysicumarkivet A:2023:Larsson

Status

Published

Supervisor

  • Edvin Lundgren

ISBN/ISSN/Other

  • ISBN: 978-91-8039-845-9
  • ISBN: 978-91-8039-846-6

Defence date

15 December 2023

Defence time

13:15

Defence place

Rydbergssalen. Join via Zoom: https://lu-se.zoom.us/j/69511786657?pwd=Ym94cVJOWjFoMEZmUlVpaEsrVnZ0QT09

Opponent

  • Arjan Mol (Professor)