The salt spray settling rate in a salt spray test chamber refers to the amount of salt solution that settles on a surface per unit area over a given time. This parameter is crucial in salt spray testing as it influences the density and uniformity of the salt mist, directly affecting the test's reliability and repeatability. In addition to the corrosive effect of chloride ions, oxygen diffusion within the liquid film on metal surfaces also plays a significant role in the corrosion process.
Smaller salt particles have a larger surface area, which enhances oxygen adsorption, thereby increasing the corrosivity of the environment. Naturally, over 90% of salt spray particles have a diameter of 1 µm or less. Research has shown that for particles of this size, the amount of oxygen adsorbed on their surface is balanced with the dissolved oxygen inside them. Beyond this point, further reduction in particle size does not significantly increase oxygen adsorption.
When the liquid film on a metal surface is stagnant, oxygen quickly reaches the cathode, causing rapid corrosion. However, as oxygen is consumed, the reaction slows down. If the liquid film is continuously refreshed, the corrosion process can continue. The renewal rate of the liquid film depends on the salt spray settling rate: a higher settling rate leads to more frequent updates of the liquid film.
If the settling rate is too low—below 0.3 mL/80 cm²·h—the liquid film becomes thinner, allowing oxygen to reach the cathode surface quickly, which initially increases the corrosion rate. However, as the rate stabilizes, the corrosion rate gradually levels off. When the settling rate exceeds 1.2 mL/80 cm²·h, the liquid film thickens, and oxygen diffusion becomes limited due to the increased distance. This results in a slower corrosion rate, even though more salt is being deposited.
Therefore, maintaining a moderate salt spray settling rate ensures stable corrosion rates and consistent, reproducible test results. It is generally recommended to control the settling rate between 1 and 2 mL/80 cm²·h to achieve accurate and reliable outcomes in salt spray testing.
Shopping Bag,Telfar Bag,Black Handbag,Trolley Bag
Ningbo Fineweather International Trade Co., Ltd. , https://www.fwsbag.com