What is passivation?
Passivation is the process of placing a metal in nitrite, nitrate, minate or diminate solution to form a minate passivation film on the metal surface. It is often used as a post-treatment of zinc and cadmium coatings to improve the corrosion resistance of the coatings. Protection of non-ferrous metals; Improve the adhesion of the paint film. Common passivating agent: nitrate, nitrite Salt, chromate, dimethylate, etc. The surface passivation process is a process that covers the protective dielectric film on the surface of the semiconductor device to prevent surface contamination. Passivation treatment is usually carried out using acidic or alkaline solutions, by placing the metal in these solutions, a series of chemical reactions occur on the surface of the metal to form a protective oxide film.
Such as the boiler after pickling, water washing, rinsing, the metal surface is very clean, very active, easy to suffer corrosion, so it must be immediately passivation treatment, so that the cleaned metal surface to generate protective film, slow down corrosion.
The process principle
After the metal is treated with oxidizing media, the corrosion rate decreases significantly compared with the original untreated phenomenon called metal passivation. The passivation mechanism can be mainly explained by the film theory, that is, it is believed that the bell is due to the interaction between the metal and the oxidizing medium, which generates a very thin, dense,Love cover good performance, can be firmly attached to the metal surface of the bell film, this film into an independent phase exists, usually oxygen and metal compounds, it plays the role of metal and corrosive medium completely separated, prevent metal and corrosive medium direct contact, so that the metal basically stop dissolving to form a bell state to prevent corrosion effect.
Main Functions
- Improve corrosion resistance: The dense oxide film formed can effectively block the erosion of external corrosive media and improve the corrosion resistance of metal products.
- Improve appearance: Passivation treatment can make the metal surface show uniform, consistent color and luster, beautiful and generous.
- Improve lubrication performance: the metal surface after passivation is smoother and more uniform, with better lubrication performance, suitable for some occasions that require sliding friction.
- Increase the antioxidant capacity: the formed oxide film has certain antioxidant properties, which can slow down the oxidation rate of the metal surface and extend the service life of metal products.
In general, passivation treatment is an important metal surface treatment process, which can significantly improve the performance and quality of metal products, and is widely used in aerospace, automobile manufacturing, electronics and other fields.
Basic characteristics
It is simple to operate, convenient to use, economical and practical. At the same time, high efficiency corrosion inhibitor and fogging agent are added to prevent metal from excessive corrosion and hydrogen embrittlement, and inhibit the production of acid fog. Especially suitable for small complex workpieces, not suitable for coating, better than similar products in the market.
Process flow
Cleaning: First of all, clean the metal products to remove the grease, dirt and other impurities on the surface to ensure that the metal surface is clean.
Pickling or alkali washing: After cleaning, metal products usually need to be pickling or alkali washing treatment. Pickling or alkali washing can remove the oxide layer and rust on the metal surface to provide good surface conditions for subsequent passivation treatment.
Passivation treatment: After cleaning and pretreatment, the metal products are soaked in acidic or alkaline solutions containing passivating agents for passivation treatment. Passivating agents are usually compounds containing metal ions such as chromium, iron, and zinc, which can chemically react with the metal surface to form a dense oxide film.
Neutralization and cleaning: After the bell treatment is completed, the metal products need to be removed from the bell solution for neutralization and cleaning. Neutralization treatment can neutralize the passivating agent remaining on the metal surface to prevent adverse effects on the metal surface, and then, use water or alkaline solution to thoroughly clean the metal surface to remove the residual passivating agent and other impurities.
Drying: Finally, the metal products after passivation are dried to ensure that the surface is completely dry to prevent secondary pollution or oxidation caused by moisture residues.
Passivation principle
The mechanism of passivation can be explained by the film theory, that is, passivation is due to the interaction between metal and oxidizing substances, which generates a very thin, dense, good covering performance, and firmly adsorbed passivation film on the metal surface. This film exists as an independent phase, usually a compound of oxidized metals.
It plays the role of completely separating the metal from the corrosive medium, preventing the metal from contacting the corrosive medium, so that the metal basically stops dissolving and forming a blunt state to achieve the role of anti-corrosion.
