Nano-deterioration of steel passivation film: chloride attack in material defects

MH Wang and SR Wu and P Wang and BQ Dong and ML Ma and Z Wang and J Zhong and HS Li and DS Hou, MATERIALS AND STRUCTURES, 56, 35 (2023).

DOI: 10.1617/s11527-023-02121-z

A chloride attack is one of the culprits for the structural deterioration of steel passivation film in the coastal environment, which greatly limits the sustainability of the materials in infrastructure. Since the passivation film is usually only a few nanometers to tens of nanometers, it is necessary to study methods at appropriate scales. To effectively assess the hazards of chloride ions, the nanoscale process of gamma-FeOOH deterioration is revealed by reactive molecular dynamics and electronic structures. It is found that the perfect gamma-FeOOH can not deteriorate and the defects can facilitate chloride attack. The Cl- is first adsorbed on the defects of gamma-FeOOH, and then induces the Na+ to form Cl-Na pairs. The vibration of Cl-Na pairs will weaken the interaction between the layers of gamma- FeOOH and thus break the gamma-FeOOH structure. The electronic structural analyses prove that the Cl ions have strong bonding with the hydroxyls of gamma-FeOOH, but Na ions are the opposite. Therefore, the Cl and Na ions play the role of anchoring the gamma-FeOOH surface and breaking the gamma-FeOOH structure by vibration, respectively. The detail of nanoscale static and dynamic properties are also revealed. This phenomenon can be recognized as the first step in the structural deterioration of steel passivation films.

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