Examples of preventing passivation???? Passivation process

The principle of passivation can be explained by the thin film theory, that is, the passivation is due to the interaction between the metal and the oxidation properties, and a very thin, dense, well-covering film is generated on the metal surface during the action, and the passivation film is firmly adsorbed on the metal surface. This film exists in separate phases, usually oxygen and metal compounds. It plays the role of completely separating the metal from the corrosive medium and preventing the metal from coming into contact with the corrosive medium.

So that the metal basically stops dissolving, forming a passivated state, to achieve the effect of anti-corrosion.

It is widely used in food machinery, medical equipment, furniture, hardware parts, pressure vessels and communication equipment and other fields.

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Passivation is the last process step in chemical cleaning and is a critical step in the protection of the material from corrosion. For example, after pickling, water flushing and rinsing, the metal surface of the boiler is very clean and very activated, and it is easy to suffer from corrosion, so it must be passivated immediately to form a protective film on the cleaned metal surface and slow down corrosion.

In the field of automatic control, there is also a special name "channel passivation". In a fail-safe system (F-System), if a fault is detected by ->F-IO, the affected channel or all channels are switched to the -> safe state.

Note: After the metal is treated with oxidizing medium, its corrosion rate is significantly lower than that before the original treatment, which is called metal passivation. The passivation mechanism can be explained mainly by the thin film theory, that is, the passivation is due to the interaction between the metal and the oxidizing medium, and a very thin, dense, well-covering passivation film can be firmly attached to the metal surface during the action.

This film exists in separate phases, usually compounds of oxygen and metals. It plays the role of completely separating the metal from the corrosive medium, preventing the metal from being in direct contact with the corrosive medium, so that the metal basically stops dissolving and forms a blunt state to prevent corrosion.

Passivation refers to the passage of metals with strong oxidizing agents.

Or electrochemical oxidation treatment, so that the surface into an inactive state, that is, passivation process, is to transform the metal surface into a state that is not easy to be oxidized, and delay the corrosion rate of the metal. In addition, an active metal or alloy, in which the chemical activity is greatly reduced, and becomes a state, is also called passivation.

Basic meaning. Passivation, if the corrosion products generated by the metal due to the action of the medium have a dense structure, forming a thin film (often invisible), which is tightly covered on the surface of the metal, it changes the surface state of the metal, so that the electrode potential of the metal jumps greatly in the positive direction, and becomes a corrosion-resistant blunt state. For example, when Fe Fe2+, the standard potential is , and it jumps to + after passivation, and shows the best corrosion resistance, this film is called passivation film.

Passivation of metals can also be spontaneous (e.g., the formation of a layer of insoluble compounds, known as oxide films, on the surface of metals). In industry, the metal is passivated with passivating agent (mainly oxidant) to form a protective film.

Common example: cold concentrated sulfuric acid.

Cold concentrated nitric acid. Passivation can occur with iron and aluminum.

Corrosion definition. Corrosion is an electrochemical process in which a small amount of ionized ions are present on the surface of an untreated metal that move from the high-potential region (cathode) to the low-potential region (anode), thus generating an electric current. Under the action of this current, it will accelerate the destructive attack on the metal and cause corrosion in the parts where the metal potential is weak, which is commonly known as rust.

Passivation principle. The mechanism of passivation can be explained by the thin film theory, that is, the passivation is due to the interaction between the metal and the oxidizing substance, and a very thin, dense, well-covering passivation film is generated on the metal surface during the action, and it is firmly adsorbed on the metal surface. This film exists in separate phases, usually compounds of oxidized metals.

It plays the role of completely separating the metal from the corrosive medium, preventing the metal from coming into contact with the corrosive medium, so that the metal basically stops dissolving and forms a blunt state to achieve the effect of anti-corrosion.

with anti-rust oil. The main difference between passivation and antirust oil is that the product is different; Anti-rust oil is the use of oil film to seal the pores on the metal surface to isolate contact with oxygen and effectively prevent rust, in fact, there is no reaction. The oil film is relatively easy to be removed and destroyed with the progress of production; Passivation is the use of oxidizing substances in the passivation solution to produce redox reactions with metals, so as to promote the formation of a layer of metal oxides on the surface of the metal to achieve the purpose of effectively protecting the metal.

This process is a chemical reaction.

The resulting passivation film is dense, intact and not easy to be destroyed.

Iron, aluminum and other active metals can be quickly dissolved in dilute nitric acid or dilute sulfuric acid, but the dissolution phenomenon in concentrated nitric acid or concentrated sulfuric acid is almost completely stopped, carbon steel is usually easy to rust, if an appropriate amount of nickel and chromium is added to the steel, it will become stainless steel.

The essence of metal passivation is that the metal is oxidized by concentrated sulfuric acid, concentrated nitric acid, etc., and a dense oxide film is formed on the surface, and this oxidation mask film is insoluble in concentrated sulfuric acid and concentrated nitric acid, because the hydrogen ions ionized by concentrated sulfuric acid and concentrated nitric acid are relatively small. Oxidants such as hypochlorous acid and potassium permanganate can also passivate metals or alloys.

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Some metals are anodized or treated with chemical methods (such as reaction with strong oxidants) to change from an active state to an inactive state (passivation), which is called passivation. After the metal is passivated, a strong, tight oxide protective film forms on its surface, preventing the metal inside from continuing to corrode. Aluminum, iron, chromium, nickel and other metals will be passivated when placed in concentrated sulfuric acid and concentrated nitric acid at room temperature.

Therefore, concentrated nitric acid can be shipped in aluminium containers, and concentrated sulphuric acid can be stored in iron or aluminium containers.

Passivation is the process of placing a metal in a nitrite, nitrate, chromate or dichromate solution to form a chromate passivation film on the surface of the metal. It is often used as a post-treatment of zinc and cadmium coatings to improve the corrosion resistance of the coating; protection of non-ferrous metals; Improving the adhesion of paint film, etc.

Iron and aluminum can be quickly dissolved in dilute nitric acid or dilute sulfuric acid, but the dissolution phenomenon in concentrated nitric acid or concentrated sulfuric acid has almost completely stopped, carbon steel is usually easy to rust, if an appropriate amount of Ni and Cr is added to the steel, it will become stainless steel. The phenomenon that the chemical stability of a metal or alloy is significantly enhanced due to some factors is called passivation.