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Electropolishing or Passivation

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Is there a difference between Electropolishing and Passivation? If so which is better? Do you use citric acid in passivation and not in electropolishing?

Thanks,

Robert Hart
- Abbott Part, Illinois, USA

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Passivation is a non-electrolytic process which removes iron from the surface, rendering stainless steel more rust-proof. Electropolishing is an electrolytic process which dissolves the asperities to leave an ultra smooth surface for such reasons as cleanliness and to prevent materials from sticking. Both are traditionally done with very strong and concentrated acids.

It so happens that electropolishing is a very effective passivation method, though, traditionally rated as better than nitric acid passivation, so that if a part is electropolished it needs no supplemental passivation.

There are changes these days though, including citric acid passivation, and environmentally friendly electropolishing solutions.

Ted Mooney, P.E. RET finishing.com Brick, New Jersey

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There are many differences between electropolishing and passivation. Ted has eluded to some of these. Which method you use depends on your desired end result. If aesthetics (shiny surface) is important you need to electropolish, which also improves corrosion resistance dramatically because of the removal of the electrically active asperites, etc. There is a higher cost to electropolishing.

If just corrosion resistance is important, you can passivate with citric acid systems to get excellent results.

The Ultimate in corrosion resistance is attained by the combination of the two. Electropolishing followed by passivation with citric products on the market give you outstanding appearance AND corrosion resistance due to the VERY high chrome/nickel surface. Corrosion resistance is better than either one alone.

Lee Kremer Stellar Solutions, Inc. McHenry, Illinois