finishing.com -- The Home Page of the Finishing Industry
A website for Serious Education, promoting Aloha,
& the most FUN smiley you can have in metal finishing

HomeFAQsSuggested
Books
Help
Wanteds
Advertise
on this site
FORUM
(current
topics)
topic 7051

Iron Contaminated Cobalt Hardened Gold Plating Bath


(2001)

Q. I am trying to remove Iron from a potassium cyanide gold citrate based plating solution. The bath has a gold content of 4 g/l with a pH of 4.2 - 4.6 and a cobalt content of 300 - 500 mg/L. The bath has a Iron content of 200 mg/L and it is causing a problem as to meeting a purity of deposit spec. The Iron is being plating out in a matter of 0.298% in deposit. I have tried a variety of resins but to no success.

The Iron has to be possibly lowered to 25 - 35 mg/L to pass our purity of deposit spec.

Is there a chemical treatment process which will not remove all of the Gold and most of the iron. Dummy plating is not an option.

Doug Duda
- Southington, Connecticut


March 8, 2011

A. I know with the case of Rhodium plating, you can utilize Potassium Ferrocyanide to precipitate out Iron impurities. We have utilized this method very efficiently, however, the affect on Gold and/or Cobalt concentration is unknown to me.

I would take a small sample size ~ 100 mL of solution and try to add Potassium Ferrocyanide to this. I would try a 1:1 stoichiometry ratio. The solution may need to sit for a couple of days and try to be very careful with siphoning out the solution, as these complexes are very fluffy and will go back into solution easily.

Try to run the analysis on the solution, following the precipitation method and see how much of the iron has been depleted.

James Danford
- Temecula, California


April 2, 2013

Q. Is 200 PPM of Iron contamination in a cobalt hardened gold tank enough to cause galling and why? The gold concentration is at .3 tr oz/gal.

Bert Barrett
- Riverside, California


April 3, 2013

A. Hi Bert. Are we on the same wavelength regarding the meaning of "galling"? To me it means something similar to "cold welding", where material is pulled from one the surface when rubbed against another surface. Is that what you are referring to, cold welding of contacts or something like that? Thanks.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


April 9, 2013

A. Hello Bert,
I can tell you that the iron concentration in your bath is too high and can cause the problems you are experiencing. This is especially true operating the bath at 0.30 tr. oz/gal. When acid gold baths were in the formulation stage, Fe was considered as a hardening agent. The problem that was discovered is that the Au deposit was too brittle using Fe at the same level as lets say nickel and cobalt. In moving contacts there is a transfer of the deposit from one part to the other. This is also true when other alloys are used as a hardening agent and the concentration is too high.

Mark Baker
Process Engineer - Mesa, Arizona, USA



This public forum has 60,000 threads. If you have a question in mind which seems off topic to this thread, you might prefer to Search the Site

ADD a Q or A to THIS thread START a NEW THREADView CURRENT TOPICS

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices


©1995-2017 finishing.com     -    Privacy Policy
How Google uses data when you visit this site.