Formation and Failure of γ‐NiOOH During Nickel Corrosion in Oxygen‐Pressured Concentrated Alkali at 270°C

The corrosion behavior of pure nickel in oxidizing concentrated alkaline environments was systematically studied. Weight‐loss measurements and surface/phase characterization show that nickel deviates from conventional passivation, in which a continuous, adherent NiO/Ni(OH) 2 film suppresses further dissolution. In 75 wt% NaOH at 270°C under 4.2 MPa oxygen pressure, nickel undergoes rapid and persistent dissolution, with a weight‐loss‐derived corrosion rate reaching 6.088 ± 0.16 mm y −1 at 168 h (mean ± SD, n = 3). SEM, XRD, Raman, and XPS identify only a thin, poorly crystalline Ni(OH) 2 ‐like layer on the specimen surface, with no thick, continuous, adherent protective film. In contrast, the flake‐like solids collected from the autoclave are identified as γ‐NiOOH by XRD and Raman. This spatial separation suggests that Ni(OH) 2 is further oxidized to γ‐NiOOH under high O 2 pressure and detaches as loosely flakes, continuously exposing fresh metallic nickel surface. The inability to establish a stable, protective scale explains the sustained high corrosion rate and highlights the limitations of γ‐NiOOH as a corrosion product under strongly oxidizing, concentrated alkaline conditions.