The purpose of passivation treatment is to prevent corrosion of materials. After the boiler is pickled, washed with water, and rinsed, the metal surface is very clean, very activated, and susceptible to corrosion. Therefore, it must be passivated immediately to form a protective film on the cleaned metal surface to slow down corrosion.
Passivation treatment places some relatively active metals in a specific environment and will change from the original active state to an inactive state. That is to say, these metals have passivation behavior, which can improve the corrosion resistance of metals, such as chromium, Nickel, cobalt, titanium, zinc, iron, etc. all have passivation properties. The oxidants that produce passivation include concentrated nitric acid, potassium nitrate, potassium dichromate, potassium permanganate, potassium chlorate, acetic acid, boric acid, phosphoric acid and citric acid.
The formation of a passivation film during the passivation treatment greatly reduces the corrosion rate. The maximum thickness of the passivation film on carbon steel is 10um, the thickness of the passivation film on aluminum is 3um, and the thickness of the passivation film on stainless steel is only 1um. The passivation film is often a compound of oxygen and metal. The passivation phenomenon is caused by the chemical oxidation of the metal and the passivator, which is called chemical passivation. The method of applying an external anode current to change the metal from an active state to a passive state is called anode passivation. change.
Anodic oxidation of aluminum and aluminum alloys (i.e., anode passivation) refers to placing aluminum and aluminum alloys in an appropriate electrolyte and conducting anode electrification treatment. The surface can generate an oxide film with a thickness of 10~200um. This oxide film has excellent corrosion resistance. The performance, wear resistance, and decorative properties are greatly improved.
