The passivation principle of concentrated sulfuric acid is mainly due to its strong oxidation. When concentrated sulfuric acid is in contact with metals (such as iron, aluminum, etc.), REDOX reaction will occur with the metal surface to form a dense oxide film. This oxide film prevents concentrated sulfuric acid from continuing to react with the metal, thus passivating the metal surface.
Specifically, the strong oxidation of concentrated sulfuric acid is demonstrated by sulfuric acid molecules, rather than sulfate ions. In concentrated sulfuric acid, sulfuric acid molecules do not ionize, but exist in molecular form, and therefore exhibit strong oxidation. When concentrated sulfuric acid reacts with metal (or metal oxides), hydrogen ions in the sulfuric acid molecules react with the metal to form metal oxides or sulfides that are insoluble in concentrated sulfuric acid. These oxides or sulfides form a dense oxide film on the surface of the metal, preventing the concentrated sulfuric acid from continuing to react with the metal.
It should be noted that the passivation of concentrated sulfuric acid is not absolute. If there are cracks or damage on the surface of the passivated metal, concentrated sulfuric acid may still continue to react with the metal. In addition, if dilute sulfuric acid is used or concentrated sulfuric acid is heated, passivation may be destroyed. Therefore, when using concentrated sulfuric acid, it is necessary to take appropriate safety measures, such as wearing protective clothing, wearing gloves and goggles.
Concentrated sulfuric acid passivation is a surface treatment technology that can form a stable oxide protective layer on the surface of the metal, thereby improving the corrosion resistance of the metal.
The passivation principle of the method is to use sulfuric acid to produce a strong high-temperature reaction, and the generated oxide can be covered on the surface of the metal, isolating the contact between the metal and the external environment, and preventing the metal from being oxidized and eroded.
At the same time, in the passivation process, due to the strong acidity of sulfuric acid, the metal surface will produce microscopic convex parts, which further increases the thickness and adhesion of the passivation layer, and increases the chemical stability and corrosion resistance of the metal.