In 2021, about 100 million tons of metal will be scrapped by corrosion, accounting for 20% to 40% of annual production. In addition, with the process of industrialization, corrosion problems become increasingly serious. U.S. corrosion consumption (material consumption and corrosion) in 1949 for 5 billion U.S. dollars, in 1975 for 70 billion U.S. dollars, in 1985 for 168 billion U.S. dollars, more than 80 times more than in 1949. It is estimated that the annual scrapping of steel equipment due to corrosion is equivalent to 30% of annual production. Obviously, the value of damage to metal components is much greater than metal materials. The annual economic loss caused by corrosion in developed countries accounts for about 2% ~ 4% of GDP; the United States each year because of corrosion consumes 3.4% more energy; China's annual economic loss caused by corrosion of at least 20 billion. The great harm of corrosion is not only reflected in the economic loss, but also brings significant casualties, environmental pollution, waste of resources, impede the development of new technologies and promote the loss of natural resources.
The background and mechanism of salt spray corrosion.
It is caused by the environment of corrosive substances or the destruction or degradation of their properties. Most corrosion occurs in the atmospheric environment, which contains corrosive components and oxygen, humidity, temperature changes, pollutants and other factors.
Salt spray corrosion is a common and destructive atmospheric corrosion. Salt spray refers to the chloride atmosphere, and its main corrosive component is sodium chloride. Salt spray corrosion on the surface of metal materials is caused by the electrochemical reaction of chloride ions through the oxidation layer and protective layer on the metal surface and inside the metal. At the same time, chloride ions contain a certain amount of hydration energy, easily adsorbed in the metal surface pores and cracks extrusion and replace the oxygen in the chloride layer, so that insoluble oxides into soluble chloride, so that the passivated surface into an active surface, the product has an extremely bad adverse reaction.
Anode:The metal loses electrons and becomes a metal cation, which enters the solution as a hydrated ion while leaving a considerable number of electrons in the metal.
Cathode:The remaining electrons left in the cathode metal are depolarized by oxygen, reduced and absorbed into hydroxide ions.
Electrolyte:Sodium chloride dissociates to produce sodium ions and chloride ions, and some chloride ions, metal ions and hydroxide ions react to produce metal corrosive.
Salt spray corrosion hazards.
1) salt spray corrosion will damage the protective layer of metal, so that it loses its decorative properties and reduce its mechanical strength.
2) certain electronic components and circuits are interrupted by corrosion, especially in the vibration environment.
3)when salt spray falls on the surface of insulators, the surface resistance will drop; after the insulator absorbs the salt solution, its volume resistance will drop by four orders of magnitude.
4)The moving parts of mechanical parts or moving parts increase friction due to corrosion, causing moving parts to get stuck.
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