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Methods for preventing corrosion of metals


Metal material is the most widely used engineering material in modern society, which plays a very important role in human civilization and development. Metal materials are not only used in industrial and agricultural production, scientific research, but also everywhere in daily life. Metal materials are used all the time. However, metal materials are easy to react with the surrounding medium, resulting in metal corrosion. Once the metal is corroded, its performance will be greatly reduced. If the metal parts on the equipment corrode, the equipment will not work, bringing economic and other losses to people. Therefore, metal corrosion prevention is very important.
There are many ways to prevent metal corrosion, which are divided into the following:
In the process of manufacturing metal parts, add corrosion resistant materials that are not easy to react with the surrounding medium. For example, in chromium, nickel titanium and other in the air is not easy to oxidize, can generate dense printing thin film, can resist acid, alkali, salt and other corrosion, added to iron or copper, can be made into corrosion resistance excellent metal products. It is conducive to metal powder metallurgy to flexibly mix various metal elements and obtain metal parts with excellent corrosion resistance by adding metal powders with different properties. Iron carbon alloy and other metal materials can also be used by heat treatment to prevent corrosion.
Two, the use of coating corrosion prevention. Coating methods include three categories: coating and spraying, coating and chemical conversion film. A protective layer is made on the surface of a metal to separate it from the corrosive medium, thereby reducing corrosion.
Coating is the organic and inorganic compound coating on metal surface, the commonly used method is to paint and plastic coating, spray coating is by spray gun or disc atomizer, with the aid of pressure or centrifugal force, scattered into a uniform and fine droplets, in application of the coated material on the surface of the coating method, mainly for the points: electric arc spraying, plasma spraying, electrostatic spraying, manual spraying, etc.; Metal coating is a process of using metal powder to form a coating on the surface of the workpiece, mainly including: electroplating, hot plating, spray plating, infiltration plating, electroless plating, mechanical plating, vacuum plating, etc. Chemical conversion film is a stable compound film layer formed on the metal surface by chemical or electrochemical methods. According to the medium used in film formation, chemical conversion film can be divided into oxide film, phosphate film, chromate film and so on.
According to the coating method of the protective layer of the material, can be divided into: (1) non-metallic protective layer: such as paint, plastic, glass fiber reinforced plastic, rubber, asphalt, enamel, concrete, enamel, rust oil and so on. (2) Metal protective layer: a metal or alloy is plated on the metal surface as a protective layer to slow down the corrosion rate. The metals used as protective coatings are usually zinc, tin, aluminum, nickel, chromium, copper, cadmium, titanium, lead, gold, silver, palladium, rhodium and various alloys.
Three, deal with corrosive media. Treatment of corrosive medium is to change the nature of corrosive medium, reduce or eliminate the harmful components in the medium to prevent corrosion. This method can only be carried out when the amount of corrosive medium is limited, and of course cannot be handled for the atmosphere filled with space. The treatment of corrosive media is generally divided into the following two categories.
One is to remove harmful components in the medium and improve the properties of the medium. For example, in the heat treatment furnace by protecting gas to prevent oxidation, in the acid soil mixing lime neutralization, to prevent soil corrosion. The other type is to add corrosion inhibitor in the corrosive medium. In the corrosive medium to add a small amount of corrosion inhibitor, can make the speed of metal corrosion greatly reduced, this substance is called corrosion inhibitor or corrosion inhibitor. For example, caustic soda or lime is added to the tap water system to remove excessive carbon monoxide in the water and prevent corrosion of water pipes, and corrosion inhibitors are added to the steel pickling solution to inhibit pickling and hydrogen brittleness.

Four, electrochemical protection: the use of direct current to change the potential of the protected metal, so as to slow or stop corrosion protection is called electrochemical protection. This kind of protection method mainly has the external source cathodic protection law, the protector protection law and the anode protection law.