The direct losses caused by the corrosion of metal materials are enormous. With the progress of industrialization, the corrosion problem has become more and more serious. The huge harm of corrosion is not only reflected in economic losses, but also brings heavy casualties, environmental pollution, waste of resources, hinders the development of new technologies, and promotes the loss of natural resources.
Salt spray corrosion is the common and most destructive atmospheric corrosion. Its corrosion on the surface of metal materials is caused by the electrochemical reaction between chloride ions penetrating the oxide layer and protective layer of the metal surface and the internal metal. At the same time, chloride ions contain a certain amount of hydration energy and are easily squeezed out by pores and cracks adsorbed on the metal surface, replacing oxygen in the chlorinated layer, converting insoluble oxides into soluble chlorides, and converting passive surfaces into active ones. surface, causing extremely bad adverse reactions to the product. The salt spray test chamber can test the product's resistance to salt spray corrosion by manually creating a salt spray environment within its volume.
Four salt spray test detection methods
1. The neutral salt spray test is a widely used accelerated corrosion test method. Use 5% sodium chloride salt solution, adjust the pH value of the solution in the neutral range (6~7) as a spray solution, the test temperature is 35 °C, and the salt spray sedimentation rate is required to be between 1~2ml/80cm.
2. The acetate spray test is developed on the basis of the neutral salt spray test. Add glacial acetic acid to the 5% sodium chloride solution to reduce the pH of the solution to about 3, so that the solution becomes acidic, and finally forms a salt spray that changes from neutral salt spray to acid, and its corrosion rate is about 3 times that of the NSS test. .
3. The copper salt accelerated acetic acid salt spray test is a rapid salt spray corrosion test developed abroad. The test temperature is 50 ℃, and a small amount of copper salt and copper, copper chloride are added to strongly induce corrosion, and the corrosion rate is about 8 times that of the NSS test.
4. Alternate salt spray test is a comprehensive salt spray test, which is actually a neutral salt spray test plus a constant damp heat test. Mainly used for cavity-type complete machine products. Salt spray corrosion occurs not only on the surface of the product but also inside the product due to the penetration of the humid environment. Replace the products alternately under two environmental conditions of salt spray and damp heat, and finally check whether the electrical and mechanical properties of the whole product have changed.