Commonly used methods are:
Change the internal structure of the metal. Such as making various corrosion-resistant alloys, such as adding chromium and nickel to ordinary steel to make stainless steel.
[Protective layer method]
Cover the metal surface with a protective layer to isolate the metal product from the surrounding corrosive medium and prevent corrosion.
1. Coat the steel surface with oil, gelatin, paint or enamel, plastic and other corrosion-resistant non-metallic materials.
2. Use electroplating, hot-plating, spraying and other methods to coat the surface of the steel with a layer of metals that are not easily corroded, such as zinc, tin, chromium, nickel, etc. These metals often form a dense oxide film due to oxidation, thereby preventing steel from being corroded by water and air.
3. Form a fine and stable oxide film on the surface of steel by chemical methods. For example, a thin black iron oxide film forms on the surface of steel parts such as machine parts and firearms.
[Electrochemical protection method]
Use the principle of primary battery to protect the metal, and try to eliminate the primary battery corrosion of the primary battery reaction. Electrochemical protection methods are divided into two categories: anodic protection and cathodic protection. The most common method is cathodic protection.
[Treatment of corrosive media]
Eliminate corrosive media, such as frequent cleaning of metal equipment, placing desiccants in precision instruments, and adding a small amount of corrosion inhibitors to corrosive media to reduce corrosion rates.
[Electrochemical protection]
The metal to be protected is used as the cathode to corrode the battery so that it will not be corroded, so it is also called cathodic protection. There are two main methods of this method:
[Sacrificial anode protection method]
This method combines active metals (such as zinc or zinc alloys) with the metal to be protected. When electrochemical corrosion occurs, this active metal acts as a negative oxidation reaction of the electrode, thereby reducing or preventing the corrosion of the protected metal. This method is often used to protect steel piles and seagoing hulls in water, such as protecting steel gates in water. Usually, several zinc blocks are welded below the waterline of the hull or on the rudder near the propeller to prevent corrosion of the hull.
[Applied current protection method]
Connect the metal to be protected to the negative pole of the power supply, and another inert conductive material to connect to the positive pole of the power supply. After electrification, negative charges (electrons) accumulate on the metal surface, thereby inhibiting the metal from losing electrons and obtaining protection. This method is mainly used to prevent the corrosion of metal equipment in soil, sea water and river water. Another electrochemical protection method is called anodic protection, which is the process of passing the anode within a certain potential range by applying a voltage. It can effectively block or prevent the corrosion of metal equipment in acid, alkali and salt.
