When iron is placed in water, it gradually rusts, but depending on the conditions, a black rust film may form on the surface and rust may not progress any further.
How the formation of such "rust that protects iron" progresses has not been clarified so far, especially in the process earlier than 1 second because there is no measuring means.
This time, the group of Assistant Professor Hiroshi Wakabayashi of the Graduate School of Science, Tohoku University succeeded in clarifying the process of forming black rust that stops red rust by using high-speed X-ray reflectance measurement.Normal X-ray reflectance measurement takes several minutes to several tens of minutes, but the experimental results obtained are analyzed by the Bayesian estimation method using the surface X-ray diffraction beamline of the large radiation facility SPring-8. By doing so, we speeded this up to 20 milliseconds and realized real-time observation of the film formation process.
The initial process of observed iron passivation occurs in the order that increasing the thickness of the film is prioritized, forming a thick film with many defects, and then rearranging the atomic arrangement inside the film. Was there.Two seconds after the start of film formation, it could be explained by the theory that had been proposed in the past, but the behavior deviated from this theory for the first two seconds.It was also found that the factors that determine the rate of membrane growth differ between the first second and the later times.
This study experimentally observed the formation process of the passivation film that protects the surface of iron and many metallic materials, and elucidated the growth process at the atomic level.This finding deepens the understanding of chemical reactions at solid-liquid interfaces from a different angle than before, and will add new information to research on chemical reactions at solid-liquid interfaces, which is said to be difficult to understand physically in the future. Be expected.
Paper information:[Physical Review Materials] Early stages of iron anodic oxidation: defective growth and density increase of oxide layer
