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Passivation on Stainless Steel

Categories: ZCMIM NewsStars: 3StarsVisit: -Release time: 2019-06-20 08:48:00
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General process of stainless steel passivation includes:

1. Alkaline cleaning to remove pollutants (grease, impurities, etc.);

2. Water rinse;

3. Acid soaking to remove iron ions or sulfide, forming a passivation layer;

4. Water rinse;

5. Dry;

6. Test samples.

Stainless steel has natural corrosion resistance, which may mean that passivation is unnecessary. But stainless steel is not completely free from corrosion. Corrosion resistance of stainless steel mainly comes from the composition of chromium. Chromium contacts air (oxygen) and forms a thin film of chromium oxide on stainless steel surface. Corrosion resistance of stainless steel is due to chromium oxide (chromium in stainless steel can be formed by air passivation).

Under ideal conditions, pure and clean stainless steel is exposed to oxygen in the atmosphere, forming a thin layer of chromium oxide that protects the stainless steel from corrosion. In real circumstances, the impurity in manufacturing environment, adding sulfide on stainless steel to improve machining performance, or iron particles may adhesion stainless steel parts surface during process, that all might destroy the formation of chromic oxide on the surface of stainless steel. As a result, these contaminants must be removed. The process of removing contaminants and forming oxide layers are called passivation.

Passivation is a non-electrolytic process in which free iron is removed from the surface, usually using nitric acid or citric acid, to form an inert, protective oxide layer that makes stainless steel more resistant to rust due to the lack of iron reacting with the atmosphere.

Keywords in the article: General process of stainless steel
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