1. Surface oxidation: In the passivation process, too high acidity of passivation solution and too long passivation time will lead to nickel surface oxidation and form a white oxide film.
2. Deposition and adhesion: In the passivation process, there are insoluble impurities and suspended substances in the passivation solution, which will adhere to the nickel surface to form a white precipitate.
3. Solution pollution: The passivation solution will be polluted by other metal ions such as iron and aluminum, resulting in white precipitation on the surface of passivated nickel.