51001

Need yellow trivalent chromating [United States] 

January 20, 2009

The company that I am working for has received a request from a customer to begin useing trivalent plating instead of hexavalent, but does not want to loose the yellow color or properties that the hexavalent provides. Is this even possible and if it is where might I look to find some more in depth answers and possibly a recipe for chemical bath?

Thanks,
Riley

Riley Holtz
product designer - United States

Hi, Riley. All of the new generation high performance trivalents chromates are proprietary and trade secret; you won't find a recipe. But, yes, some are naturally yellow and others are dyed yellow. Getting the yellow color is not the hard part . . . getting equivalent performance is the hard part :-)

Hexavalent chromates were simple and robust. Proprietary trivalent chromates can deliver equivalent salt spray hours when done properly, but it can be harder and there are various issues you can encounter like poor adhesion, lack of conductivity, too-easy removal by subsequent treatments, and a yellow color that is not as consistent.

In a word, trivalent chromating is tougher to do properly.

Regards,

Ted Mooney, P.E.  finishing.com Brick, New Jersey

True replacement? In your opinion is trivalent a suitable replacement for hexavalent? With some of the research I have continued to do I have seen some claims that the hardness can be matched but trivalent can also turn into hexavalent if oxidation is introduced. Thanks for all your help.

Riley holtz
product designer - Michigan

Hi, Riley. I assume you are talking about chomate conversion coating rather than chrome plating. I would not call it a true replacement because it does not offer the same robustness, economy, ease of use, and freedom from extraneous problems like loss of conductivity after topcoating, poor adhesion of subsequent paint, and lowered resistance to post treatment chemistry. But I would call it a necessary replacement. In 2009 we cannot continue to ship components for public use that have a thin coating of carcinogenic jelly on them :-)

We have an ongoing thread about inadvertent conversion from trivalent to hexavalent in letter 47049. Good luck.

Regards,

Ted Mooney finishing.com Brick, New Jersey

I will add a few comments to the others already posted here...

In Germany there are essentially zero requests for yellow trivalent passivates. This is because the German Automotive Industry has decided to associate yellow with hexavalent. Therefore... all specifications have changed to clear and maybe a few black (but on ZnNi or ZnFe).

I see other customers in Europe requesting the yellow trivalent passivates. These are never for automotive applications.

I have two general recommendations... but you will need to purchase theses products through established plating additive chemistry suppliers.

1) Thick-Film Passivate + Yellow Dye.

this option will give you excellent results in salt spray testing and adding a sealant to your process will continue to further the salt spray results. You can also obtain a very similar color and typical yellow hexavalent iridescence.

2) "True" Yellow Passivate

these passivates have essentially "just hit the market (my opinion)". Corrosion protection is not as good as the Thick-Film Passivates, but it is also not too bad and you can maybe get 48 - 96 hours to White Rust without the use of a sealant. Addition of sealant continues to give you more protection.

Thomas E. Kidd
- Budapest, Hungary