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Ted Mooney, P.E. RET

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Thread 332/53

What is Trivalent Plating

Dear sirs/madam,

I am a new person engaging in metal industry. I wonder who can tell me what is a "Trivalent plating finish"?

Alex Wen
zhangyu metal products co. ltd. - Suzhou, Jiangsu province, China
2004
publicly reply to Alex Wen

The traditional way to chromium plate is from a plating bath containing chromic acid. The chrome in chromic acid is in the hexavalent state because the formula for chromic acid is H2CrO4. It is also possible, although more difficult, to plate chromium from a proprietary plating bath where the chromium is in the Cr+3 state instead of Cr+6; this is called trivalent chrome plating. One of the advantages is that trivalent chromium is considered much less toxic than hexavalent chromium.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004
publicly reply to Ted Mooney

I currently have a customer requirement for the following plating:

"Zinc Plate per ASTM B633, SCI, Type III with Clear Trivalent Chromate Conversion Coating.Finish must withstand Min. 100 hr salt spray test per ASTM ASTM B117. No additional topical dips or coatings to be applied to the finish."

My understanding is that Hexavalent plating is superior to Trivalent in passing the salt spray test but is typically rated at 11 hrs.

My question, is the above spec achievable?

Ron Zea
Artesyn technologies - Milpitas, California, USA
2005
publicly reply to Ron Zea

That's actually a different topic, Ron. Chrome plating and chromate conversion coatings are very different things. All trivalent chromate conversion coatings are highly proprietary, but yes, I believe there are trivalent chromate conversion coatings that can achieve 100 hours without supplementary treatment.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2006
publicly reply to Ted Mooney

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