Salt spray test chamber expert classroom: the influence of external factors on metal corrosion
The salt spray test chamber is widely used for the salt spray corrosion test on the plating and coating of metal materials and products. The corrosion conditions mainly include relative humidity, temperature, oxygen, salt solution and other external factors that produce chemical reactions on the metal materials. The following explains the impact of different media on corrosion in the environment one by one.
Effect of relative humidity: The higher the relative humidity in the air, the thicker the water film on the metal surface, and the oxygen in the air permeates the film to the metal surface. When the relative humidity reaches a certain value, the corrosion rate increases significantly. This value is called the critical relative humidity.
The influence of temperature: the ambient temperature is related to the relative humidity. In a dry environment, the metal is not easy to rust even at high temperatures. When the relative humidity reaches a critical value, the influence of temperature is significantly intensified. Each time the temperature increases by 10 ° C, the corrosion rate increases twice. Therefore, in the wet tropical or rainy season, the higher the temperature, the more serious the corrosion.
Effect of oxygen: The following reaction formula shows the rusting process. It can be seen that without water and oxygen, the metal will not rust. 20% of the volume in the air is oxygen.
Fe + H2O → Fe (OH) 2
Fe (OH) 2+ H2O + O2 → Fe (OH) 3
Fe + H2O + O2 → Fe （OH） 3
The influence of other substances in the atmosphere: When the atmosphere contains salt spray (the main substance of the salt spray test chamber), sulfur dioxide, hydrogen sulfide and dust, it will accelerate corrosion. Therefore, the difference in the size of corrosion in different environments is obvious, and the city is higher than the rural area. ; Industrial area is higher than living area; coastal area is higher than inland area; high dust is higher than low dust.
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