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Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

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Best Corrosion Protective Coating for Mild Steel Plate

I am designing some explosion proof boxes to be used in coal mines. I am looking for a electro-plated coating that will offer superior corrosion protection and that can be painted afterwards with an epoxy powder coat. Straight nickel has been suggested by one vendor but all the threads seem to indicate that this is a poor choice. Zinc, Zinc-Nickel, Tin-Zinc and several other combinations are recommended by others. It's hard to choose. Any advice?

Michael Marr
Product Designer - Thornhill, Ontario, Canada
May 21, 2008

Hi, Michael. Zinc and zinc alloys offer cathodic protection whereas nickel offers only barrier layer protection. This means the zinc will cathodically protect the steel in the event of a scratch whereas the nickel will cathodically accelerate corrosion in the event of a scratch.

Although zinc alloys are more corrosion resistant than plain zinc when left uncoated (because the galvanic potential of the alloy is closer to steel), I'm not sure that they afford additional real-world protection when the component is epoxy coated. I'd probably go with plain zinc plating and chromate conversion coating under the epoxy.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 21, 2008

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