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Rust formation on etched 304 stainless

1998

Hi,

Recently we have encountered rust on both parylene and noncoated 304 stainless electrode parts.

These parts are etched from a sheet with ferric chloride ⇦ on eBay or Amazon [affil link] after which alkaline neutralizing and multiple DI water baths are used to rinse residual ferric chloride ⇦ on eBay or Amazon [affil link] from the parts. The parts are then sent for parylene C coating.

Additionally, passivation has been tried but did not cure the problem.

We have done an exhaustive test matrix in order to determine the root cause.

So far the only clue are SEM scans which indicate trapped CL ions in the grain of the material. If these ions are trapped in the grain, what processing will dislodge them? There are already numerous rinse steps employed as well as passing DC through one of the final baths.

Any suggestions?

Thanks,

Art Zikorus

Dear Art ,

What passivation did you try , I would bet blind it was not Electropolish , try it I feel sure it will meet your needs , if you need more info please e-mail me direct

Regards

John Tenison - Woods
- Victoria Australia
1998

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1998

I wonder what you mean by Cl trapped in the grains. Chloride ions will not propagate along the grain boundaries of the stainless steel. Chlorides can cause pitting that will undercut the surface such that subsequent cleaning will not remove the chemical. Under some circumstances chlorides can also crack stainless steel - the chemical would not be removed from the cracks by cleaning and/or passivation.

Perhaps more description of the etching process (what temp?) and more description of the test results would help to get you a better answer.

Larry Hanke
Minneapolis, Minnesota

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