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Page 8 of 27 Liu et al. Microstructures 2023;3:2023020 https://dx.doi.org/10.20517/microstructures.2023.02

Figure 4. The effect of environmental variables on the passive film. (A) The passive film in the open air is constituted by a two-layer
structure, specifically, the Cr-rich inner layer and the Fe-rich outer layer. (B) When immersion in the solutioncontaining chlorides, the
[28] [35]
CrOOH disappears . (C) When the temperature increases, the passive film thickens and becomes more enriched in Cr . (D) When
[37]
the hydrostatic pressure increases, less Cr O is detected . (E) Removing oxygen decreases the point defects in the passive film and
2 3
[35]
lowers the film/solution potential drop . (F) Hydrogen sulfide accelerates the film dissolution process and local acidification
[38] [36]
processes . (G) Increasing the anodic potential transforms the passive film from p-type to n-type . (H) Hydrogen charging makes
- 2- [39,40]
the passive film more conductive and imparts it with a larger OH /O ratio . (I) Stress creates more point defects and more soluble
[41,42]
CrO in the passive film .
3
Point Defect Model (PDM) and proposed that reducing the oxygen content in the solution can reduce the
potential difference of the field/substrate interface and decreases the point defect diffusivity [Figure 4E] .
[35]
Hydrogen sulfide generates hydrogen ions via the reacidification effect [Figure 4F] . Adding hydrogen
[38]
[38]
sulfide does not change the semiconductor type of the passive film, but thins the film [Figure 4F] . A
higher anodic current indicates that it accelerates the dissolution of the passive film. When the
concentration was increased, the number of oxygen vacancies increased and Fe in the passive film was
2+
consumed.