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Removing chrome oxide passivation layer from stainless nano particles

August 12, 2012

Q. I want to etch off the Cr oxide passivation on stainless steel nano particles using HCl. Is this a clean and controlled process? After the etch, I want to keep the particles from repassivation. Any suggestions?

Sudarsan U
- Portland, Oregon, USA

August 13, 2012

A. Sudarsan,
I've never had any experience in nano-scale applications, but I suspect that an HCl etch, especially on that scale, would not be considered clean or controlled. You might want to search this forum for previous questions and the responses concerning treatments to activate the surface of stainless for electroplating.

Preventing repassivation should be as simple as not exposing your particles to citric acid, nitric acid, or air.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
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McHenry, Illinois
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September 11, 2012

A. We agree with Ray. Etching in HCl is a harsh process for nano-particles. If passive layer is removed, the particle will immediately dissolved in the acid. In order to replace the initial passive film by the new one, it is necessary to apply the process of slow passive dissolution. During such process the initial passive film will slowly dissolve in the solution, and the new passive film of required thickness and composition will grow.

Anna Berkovich
Russamer Lab
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Pittsburgh, Pennsylvania
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