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Cadmium plating and trivalent chromate

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Q. After many, many years of receiving terrific cadmium plated parts per AMSQQP416 [affil link], TY I, CL I (w/Hexavalent Chromate sealant).

However, around the beginning of 2021, the Hexavalent Chromate sealant was no longer "available" and a less-effective Trivalent Chromate product was introduced as a post-plate sealant.

This product has proven itself to be FAR less effective. Now, since that time to present, we've battling non-stop dark spotty issues on the plated parts.

We are desperate to find the cause of the dark spots.

We ship product around the US and internationally in cardboard boxes with desiccant.

Jason Lawrence
- East Haddam, Connecticut
July 24, 2022

A. Hi Jason. Years ago Gene Packman told us that there were no trivalent chromates for cadmium plating for economic reasons. I'm not sure whether that is still the case but it may be. If there are no trivalent chromates designed for cadmium, your problem may not be solvable with trivalent chromates.

As you may realize, cadmium plating is decreasingly available because of regulations, toxicity, and perceived toxicity. The best answer for you may be to re-examine whether cadmium plating is the only possible finish for your components because the trend will continue. If you are convinced that cadmium plating is essential, you may have to find another plating shop which is willing to continue applying proven hexavalent chromates rather than these trivalent chromates which are not working.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

A. The dark spotty issues may very likely be due to leaving the cyanide film on. Normally, ahead of ANY chromate a 1/4% by vol, fresh, nitric acid dip is used to kill the un-rinsable cyanide film ahead of the chromate. Ask your chromate supplier what is best to neutralize the cyanide ahead of HIS chromate.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
July 26, 2022

July 27, 2022

A. IMHO any chromate (i.e., a hexavalent passivate) that works on zinc will work approximately as well on cadmium. A lot of suppliers have dropped them out of their lines, but they are still available. A lot of platers have decided to go with just trivalent passivates. If you are having articles plated with cadmium, then you are already ROHS non-compliant so putting a traditional hexavalent chromate on the article - in my opinion - doesn't make it any more or less non-compliant.

Tom Rochester
CTO - Jackson, Michigan, USA
Plating Systems & Technologies, Inc.
supporting advertiser
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⇩ Closely related postings, oldest first ⇩

Q. We have recently introduced Trivalent Chromium passivation on zinc plating in our shop.

We also wanted to use this on Cadmium plating . But with this we are getting very dull finish on cadmium plating.

With Hexavalent Chromium passivation on Cadmium plating we were getting good results.

Can anybody explain why this is happening & what could be the done to get good finish on cadmium plating using trivalent passivation.

Paresh Lele
- Delhi, India

A. The reason for the poor results on cadmium deposits is that the chemistry you are using was designed for use with zinc deposits and works differently on cadmium. Trivalent conversion coatings for cadmium are basically of two kinds: a modified hexavalent product for clear with minimal protection or a trivalent product formulated for aluminum which will give a dull grey/clear finish on cadmium. The market for cadmium plating processes is very limited due to the supposed toxicity of metal (really the dust, but that is another story). Cadmium plate is not RoHS or ELV compliant so why should anyone develop a chromate that is?

Gene Packman
process supplier - Great Neck, New York

thumbs up sign Thanks Gene, I think you've explained the reason very well.


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)

A. Trivalent chromate on cad? I am yet to hear of such a product. I have had several people asking about one but know of none. Part of the reason is economics, a small market.

That being said, make sure the plater is actually plating the cadmium you have specified and not substituting zinc. There are not too many platers who still plate cadmium due to lessened demand and the toxicity of the bath components.

Gene Packman
process supplier - Great Neck, New York

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