Views: 347 Author: Site Editor Publish Time: 2020-05-09 Origin: Site
In the process of product use, you will encounter the problems of product aging and corrosion. Then, it is very important to determine the effects of corrosion and aging, and salt spray corrosion is a common and most destructive atmospheric corrosion. This is an environmental test that mainly uses artificially simulated salt spray environmental conditions created by salt spray test equipment to evaluate the corrosion resistance of products or metal materials.
Salt spray corrosion will damage the metal protective layer, make it lose its decorativeness, and reduce its mechanical strength; some electronic components and electrical circuits, due to corrosion, cause power line interruptions, especially in vibrating environments, especially when salt spray When landing on the surface of the insulator, the surface resistance will be reduced; after the insulator absorbs the salt solution, its volume resistance will be reduced by four orders of magnitude; the moving parts of the mechanical parts or moving parts due to the generation of corrosive substances, increase the friction and cause movement Parts are stuck.
Neutral salt spray test
This is the most widely used accelerated corrosion test method in the earliest application field. Under normal circumstances, it uses 5% sodium chloride aqueous solution, the solution PH value is adjusted to a neutral range (6.5 ~ 7.2) as a spray solution. The test temperature is 35 ℃, the sedimentation rate of salt spray is required to be between 1 ~ 3ml / 80cm2.h, and the sedimentation rate is generally between 1 ~ 2ml / 80cm2.h. Every 24h is equivalent to one year in the natural environment.
Acetate spray test
It was developed on the basis of neutral salt spray test. It is to add some glacial acetic acid to the 5% sodium chloride solution, so that the pH value of the solution is reduced to about 3, the solution becomes acidic, and the salt mist formed finally becomes acidic from the neutral salt mist. Its corrosion rate is about 3 times faster than the neutral salt spray test. Every 24h is equivalent to 3 years in the natural environment.
Copper salt accelerated acetate spray test
It is a kind of rapid salt spray corrosion test recently developed abroad. The test temperature is 50 ℃. A small amount of copper salt-copper chloride is added to the salt solution, which strongly induces corrosion. Its corrosion rate is about 8 times that of the neutral salt spray test. Every 24h is equivalent to 8 years in the natural environment.
The corrosion of metal materials by salt mist is mainly caused by the conductive salt solution infiltrating into the metal to undergo an electrochemical reaction, forming a "low potential metal-electrolyte solution-high potential impurity" microbattery system, electron transfer occurs, and the metal as the anode appears to be dissolved The formation of new compounds or corrosion products. The metal protective layer and the organic material protective layer are also the same. When the salt solution as the electrolyte penetrates into the inside, a micro battery with a metal as an electrode and a metal protective layer or an organic material as another electrode is formed.
The main role in the process of salt spray corrosion damage is chloride ion. It has a strong penetrating power, easily penetrates the metal oxide layer into the metal, and destroys the passive state of the metal. At the same time, chloride ions have very little hydration energy and are easily adsorbed on the surface of the metal, replacing the oxygen in the oxide layer that protects the metal, causing damage to the metal.
In addition to chloride ions, the salt spray corrosion mechanism is also affected by the oxygen dissolved in the salt solution (essentially the salt liquid film dissolved on the surface of the sample). Oxygen can cause the depolarization process of the metal surface and accelerate the dissolution of the anode metal. Due to the continuous spraying during the salt spray test, the salt liquid film that has continuously settled on the surface of the sample keeps the oxygen content near saturation. The formation of corrosion products expands the volume of the salt solution that has penetrated into the metal defects, thus increasing the internal stress of the metal, causing stress corrosion and causing the protective layer to bulge.
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