Corrosion protection of metal

Corrosion protection of metal

1, the type of metal corrosion: 1, chemical corrosion (metal and external medium caused by chemical action only surface damage. If the metal surface is in contact with air, the production of oxides is a kind of chemical corrosion.)2, electrochemical corrosion (refers to the damage caused by electrochemical action when the metal surface has electrolyte solution in existence.)

Two, measures to prevent corrosion:

1. Reasonable material selection and design is to choose the appropriate materials according to the requirements of the use environment, such as alloy steel containing nickel, chromium, aluminum, silicon, titanium and other elements, or as far as possible to choose nylon, plastic, ceramic and other materials when conditions permit.

2. Reasonable design should be paid attention to avoid contact between metal materials with great potential difference. When two metals with different electrode potentials must be assembled together, they should be separated by insulating materials. If two materials with different electrode potentials cannot avoid contact, the area as far as possible as the cathode part should not be too large, and the anode part should not be too small.

3. Cover the protective layer

1) the metal covering method of small activity with high corrosion resistance of metals such as: lead, tin, chromium, etc., using a variety of thermal spraying and plating technology to cover these metals on the surface of the protected metal, can achieve the purpose of corrosion prevention.

2) Non-metallic material covering method refers to covering the surface of jinshan with organic or inorganic substances to achieve the purpose of anti-corrosion. The commonly used covering materials are coating, plastic, rubber, asphalt, etc

3) Chemical protection law a layer of oxide or phosphate compound film is generated on the metal surface by chemical or electrochemical methods to prevent the corrosion of the metal.

4) By surface alloying, the corrosion resistant metal is diffused to a certain depth on the surface of the steel at high temperature to obtain the corrosion resistant alloy coating.

3, electrochemical protection

1) Anodic protection includes two methods to prevent electrochemical corrosion. When a metal is immersed in an electrolyte solution, a potential will be established between the metal surface and the solution. In corrosion electrochemistry, this potential is called natural corrosion potential. Different metals have different potentials in a given solution. The potential of the same metal, due to the electrochemical heterogeneity between its parts, causes a certain potential difference between different parts. It is this potential difference that leads to the electrochemical corrosion of the metal in the electrolyte solution. Applying a direct current to a metal immersed in an electrolyte solution causes a change in the metal's natural corrosion potential, a phenomenon known as polarization. When the current is positive. The process of metal anode potential changing in the positive direction is called anodic polarization. On the contrary, when the current through the negative current, the metal anode as its potential to the negative direction of the process is called cathodic polarization. The curve drawn between potential and current density is called the polarization curve. When the metal with blunt tendency is anodized, if the current reaches enough value, a passivation film with high corrosion resistance can be formed on the surface of the metal to reduce the current and make the metal surface appear blunt. The passivation state can be maintained by applying a small current, and the amount of dissolution on the surface of the metal in the passivation state is very small, thus preventing the corrosion of the metal. This is the basic principle of anodic protection.

2) Cathodic protection ① Impressed current cathodic protection ② Sacrificial anode cathodic protection.