1. Different nature:
1, pickling: The use of acid solution to remove the oxide and rust on the surface of steel, a method of cleaning the metal surface.
2, passivation: The metal is oxidized by a strong oxidizer or electrochemical method, so that the surface becomes inactive or blunt process.
Second, the principle is different:
1, pickling: generally immerse the parts in an aqueous solution such as sulfuric acid to remove the oxide film on the metal surface. It is the pre-treatment or intermediate treatment of electroplating, enamel, rolling and other processes.
2. Passivation: If the corrosion products generated by the metal due to the action of the medium have a dense structure, form a film (often invisible), and are closely covered on the surface of the metal, the surface state of the metal is changed, so that the electrode potential of the metal is greatly changed in the positive direction, and it becomes a blunt state of corrosion resistance.
Third, the process is different:
1, pickling: stainless steel hanging → chemical degreasing (conventional alkaline chemical degreasing or surfactant degreasing)→ hot water washing → water washing → first step pickling → water washing → second step pickling → water washing → Transfer to the next process (such as: chemical coloring → recovery → water washing → hardening treatment → water washing → closed treatment → water washing → drying → finished products).
2, passivation: stainless steel workpiece pickling passivation before the surface dirt, etc., should be mechanically cleaned, and then degreasing. If the pickling solution and passivation solution cannot remove grease, the presence of grease on the surface will affect the quality of pickling passivation, so the oil removal and degreasing can not be omitted, and can be carried out with lye, emulsifier, organic solvent and steam.
Pickling and passivation are two commonly used methods in metal surface treatment.
Pickling is to eliminate particles, oxide and other substances on the surface of the metal by soaking the metal in the acid solution, so as to achieve the effect of cleaning the surface and improving the quality. Passivation is to increase the thickness of the oxide film on the metal surface by soaking the metal in a chemical liquid containing passivating agents to protect the metal surface from corrosion.
Therefore, the main difference between pickling and passivation is the difference in purpose and effect.
The main purpose of pickling is to clean and remove useless substances on the surface of the metal, while the purpose of passivation is to enhance the corrosion resistance and protection of the metal.
Pickling and passivation are both surface treatment processes, but their functions and principles are different.
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Pickling is to dissolve and corrode harmful substances such as oxide, rust or oil on the metal surface through acid to obtain a smooth and clean metal surface. Pickling is mainly used to remove oxides and rust chips from metal surfaces for subsequent processes such as painting, electroplating and welding.
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Passivation extends the service life of the metal by forming a layer of corrosion-resistant oxide film on the metal surface. Passivating agent is a solution that can form a specific chemical reaction to generate passivating film, mainly used to prevent the corrosion of metal materials in acidic, alkaline, corrosive gases and other environments.
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In general, pickling and passivation are necessary surface treatment processes, but the application is different. Pickling is mainly used to remove dirt and oxides from metal surfaces, while passivation is to improve the corrosion resistance of metal materials.