fig4

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 CrOOH disappears^[28]. (C) When the temperature increases, the passive film thickens and becomes more enriched in Cr^[35]. (D) When the hydrostatic pressure increases, less Cr₂O₃ is detected^[37]. (E) Removing oxygen decreases the point defects in the passive film and lowers the film/solution potential drop^[35]. (F) Hydrogen sulfide accelerates the film dissolution process and local acidification processes^[38]. (G) Increasing the anodic potential transforms the passive film from p-type to n-type^[36]. (H) Hydrogen charging makes the passive film more conductive and imparts it with a larger OH^-/O^2- ratio^[39,40]. (I) Stress creates more point defects and more soluble CrO₃ in the passive film^[41,42].