Stainless steel pickling passivation principle

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I believe that anyone who knows about pickling will know that pickling relies on a protective film to prevent rust. Let’s look at the detailed principle below: Principle of pickling and passivation of stainless steel
The corrosion resistance of stainless steel is mainly due to the surface being covered with an extremely thin (approximately) dense passivation film. This film corrodes the medium. Isolation is the basic barrier for stainless steel protection. The dynamic characteristics of stainless steel passivation should not be regarded as a complete stop of corrosion but the formation of a diffusion barrier layer that greatly reduces the anodic reaction speed. Generally, membranes tend to be damaged in the presence of reducing agents (such as chloride ions) but can maintain or repair the membrane in the presence of oxidizing agents (such as air).
Stainless steel workpieces will form an oxide film when placed in the air, but the protection of this film is not perfect enough. Usually, thorough cleaning including alkali cleaning and pickling is required first, and then passivation with an oxidant to ensure the integrity and stability of the passivation film. One of the purposes of pickling is to create favorable conditions for passivation treatment to ensure the formation of a high-quality passivation film. Because the average stainless steel surface has a thicker layer through pickling, the surface is corroded and the chemical activity of the acid makes the dissolution rate of defective parts higher than other parts on the surface. Therefore, pickling can make the entire surface even and balanced. Some of the original hidden dangers that easily caused corrosion have been eliminated. But more importantly, through pickling and passivation, iron and iron oxides are dissolved preferentially than chromium and chromium oxides, and the chromium-poor layer is removed, causing chromium to be enriched on the surface of stainless steel. The potential of this chromium-rich passivation film can reach + ． () The potential close to noble metals improves the stability against corrosion. Different passivation treatments will also affect the composition and structure of the film, thereby affecting the rust resistance. For example, electrochemical modification treatment can make the passivation film have a multi-layer structure, form a barrier layer, or form a glassy oxide film to make stainless steel. Can exert maximum corrosion resistance.
The above is the more detailed principle of pickling and passivation of stainless steel compiled by Zhijian editor. If you have any other questions, please feel free to call us! !
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