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topic 7157

What is Black Oxide on Stainless Steel About?


1) What is the nature of the black oxide on stainless steel?

2) Is there any method, such as plasma or electrochemical methods, to increase the amount of chromium oxide - hydroxide content on the surface?


Diane Dang
- Menlo Park, California



I am not sure what you mean by the black oxide on stainless steel. Are you talking about a black oxide treatment, or are you talking about a "blackening" of the surface (dull gray) that can occur with the wrong procedure. It is not uncommon for this to happen with some grades of stainless with nitric acid passivation. If you contact us we can determine the answer to your question.

You can significantly increase the Chromium oxide amount on the surface of stainless steel by correct passivation. We have seen chrome oxide: iron oxide ratios as high as 13:1 on some tests using CitriSurf passivation of 316L. Normal ratios are not that high, but higher than you can get with nitric acid.

Electropolishing before passivation will help to produce the optimum results. There are many systems available from vendors to the trade.


lee kremer
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Lee Kremer
Stellar Solutions, Inc.
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McHenry, Illinois
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