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Effect of citric acid on a electroless nickel plated surface

Dear sirs,

Does citric acid ⇦this on eBay or Amazon [affil links] has any complexation/ corrosion power on electroless nickel plated steel surfaces?
a customer is using citric acid as a kind of leaching agent together with a blowing agent, under 4 bar pressure. After a certain number of injected parts we clearly see a pitting phenomenon on the coating (the same happened with the raw steel and that was the reason for us to coat the tools).

Thank you for your comments.

Best regards,
Paulo

Paulo Vilaça
Plating shop - Portugal
November 6, 2008

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First of two simultaneous responses --

Citric aicd will complex and dissolve nickel oxide. if there are any imperfections, or alloying constituent metals in the surface, pitting will occur under the conditions you describe.

I suggest: a use a very high Phosphorus EN alloy. even then there may be corrosion if trace stabilizers are present in the surface.

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])
November 10, 2008

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Second of two simultaneous responses --

Paulo,
You failed to mention the strength or concentration of the citric acid . Electroless nickel, if properly deposited, is very resistant to citric acid solutions. Are you sure the thickness of the EN is adequate? I would increase the thickness, have your customer determine what the acid concentration is, and review the current pressure that they are using in this leaching process. Both of these could be too strong and don't have to be.

Mark Baker
Process Engineer - Syracuse, New York
November 10, 2008

During immersion tests diluted citric acid has been found to have a negligible effect on a high Phos EN (10-12% Phos). Aeration introduces complex variables that end up in accelerated corrosion. But most surely your EN is not thick enough or is of inferior quality. G. Marrufo-Mexico

Guillermo Marrufo
Monterrey, NL, Mexico
November 11, 2008