Salt spray corrosion principle:
Most of the corrosion of metal materials occurs in the atmospheric environment, which contains corrosion components and corrosion factors such as oxygen, humidity, temperature change and pollutants. Salt spray corrosion is one of the most common and destructive atmospheric corrosion.
The corrosion of metal materials by salt spray is mainly due to the penetration of conductive salt solution into the metal to produce electrochemical reaction, forming a "low potential metal electrolyte solution high potential impurity" micro battery system, electron transfer, dissolution of metal as anode and formation of new compounds, namely corrosives. Chloride ion plays a major role in the process of salt spray corrosion damage. It has a strong penetration ability. It is easy to penetrate the metal oxide layer into the metal and destroy the passive state of the metal; At the same time, chloride ions have very small hydration energy and are easy to be adsorbed on the metal surface to replace the oxygen in the oxide layer protecting the metal, so that the metal is damaged.
Salt spray corrosion test method and classification:
Salt spray test is an accelerated corrosion resistance evaluation method of artificial atmosphere. It atomizes a certain concentration of brine; Then spray it into a closed constant temperature box to reflect the corrosion resistance of the tested sample by observing the change of the tested sample after being placed in the box for a period of time. It is an accelerated test method. The salt concentration of chloride in the salt fog environment is several or dozens of times that in the general natural environment, which greatly improves the corrosion rate. Carry out the salt fog test on the product, The time to get the results is also greatly reduced.
When a product sample is tested in natural environment, the corrosion time may take one or even several years, while when tested in artificial salt spray environment, similar results can be obtained as long as a few days or even hours.
Salt spray test is mainly divided into 4 types:
Neutral salt spray test (NSS);
Acetic acid salt spray test (AASs);
Copper accelerated acetic acid salt spray test (CASS);
Alternating salt spray test.
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