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What harm does salt spray corrosion cause to passivation film on the surface of stainless steel plate?

DataTime:[11/7/2018]
Salt spray corrosion will destroy the passivation film on the surface of the stainless steel plate, so that the decorative nature of the plate will be lost, and the mechanical strength of the material will be reduced. Some electronic components and electrical wiring will cause the power line to be interrupted due to corrosion, especially in vibration. In the environment, it is particularly serious; whenever the salt spray falls onto the surface of the insulator, the surface resistance of the stainless steel plate will be reduced; after the insulator absorbs the salt solution, the volume resistance will also be reduced by four orders of magnitude; the movement of mechanical parts or moving parts Due to the formation of corrosive substances, the friction of the material is increased so that the moving parts are jammed.
Let's look at the mechanism of salt spray corrosion. Salt spray corrosion of stainless steel and other metal materials, mainly conductive salt solution infiltrated into the stainless steel plate to generate electrochemical reactions, generate low-potential metal - electrolyte solution - high potential impurity micro-battery system, resulting in electron transfer, metal as the anode Dissolution occurs and new compounds, ie corrosion products, form. The same applies to the metal protective layer and the organic material protective layer. After the salt solution as an electrolyte penetrates into the interior, a micro-battery with a metal as an electrode and a metal protective layer or an organic material as another electrode is formed.
Chloride ions play a major role in the salt fog corrosion damage process. It has a very strong penetrating power and easily penetrates the passivation layer on the surface of the stainless steel plate and enters the interior of the stainless steel plate while destroying the passivation state of the metal. And chloride ion has a very small hydration energy and is easily adsorbed on the surface of the stainless steel plate, thereby replacing the oxygen in the oxide layer on the surface of the stainless steel plate, so that the metal surface such as stainless steel is damaged.
In addition to chloride ions, the salt spray corrosion mechanism is also affected by oxygen dissolved in the salt solution (essentially the salt solution that dissolves on the surface of the sample). Oxygen can lead to the depolarization process of stainless steel and other metal surfaces, speed up the dissolution of the anode metal, because the salt spray process continues to spray, the salt liquid film continuously settles on the surface of the sample, so that the oxygen content will always remain near saturation . The formation of corrosion products, so that the volume of the salt solution infiltrated into the metal defect expansion, so it also increases the internal stress of the stainless steel plate, the formation of stress corrosion, resulting in the surface of the passive layer of the stainless steel plate bulging.
Source: China Stainless Steel Plates Manufacturer - Yaang Pipe Industry Co., Limited (www.yaang.com)

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