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Effect of salt spray corrosion on stainless steel passivation film caused
Salt spray corrosion will destroy the passive film of stainless steel, making it lose decorative, lower mechanical strength; some electronic components and electrical lines, power lines due to corrosion caused by the interruption, particularly in vibration environments, particularly serious; when salt fog landing surface of the insulator, the surface resistance will decrease; after absorption of saline solution insulator, it will reduce the volume resistivity of four orders of magnitude; moving parts or mechanical parts moving parts due to the corrosive substance, as well as causing increased friction moving parts are stuck.
Salt spray corrosion mechanism
Of salt spray corrosion of a metal material such as stainless steel, the main conductive metal salt solution penetrate internal electrochemical reaction, with "low electric potential metal - electrolyte solution - high potential impurity" micro-cell system, electron transfer, appears as an anode metal dissolution, i.e. the formation of new compounds corrosion. Metal protective layer and an organic material protective layer also, when used as an electrolyte salt solution into the unit, will form a metal electrode and the metal protective layer or organic material is another micro-electrode cell.
Salt spray corrosion damage process played a major role in chloride ions. It has a strong penetrating power, easily penetrate into the metal interior stainless steel passivation layer, destruction of metal passivation. At the same time, chlorine ions having a small hydration can easily be adsorbed on the metal surface, the metal oxide layer is protected by a substituted oxygen, metal such as stainless steel surface damage.
In addition to chloride ions, but also by the salt spray corrosion mechanism was dissolved in saline solution in (essentially dissolved salts in the liquid film surface of the sample) the effects of oxygen. Oxygen can cause depolarization of the surface of a metal such as stainless steel, accelerate the dissolution of the anode metal, since the salt spray test continuously during spraying, on the surface of the specimen continuously settling salt film, so that the oxygen content is always maintained at near saturation. The formation of corrosion products that penetrate metal defect volume expansion in the salt solution, thereby increasing the internal stress of the metal, causing stress corrosion, resulting in the stainless steel passivation layer muster.