Iron Contaminated Cobalt Hardened Gold Plating Bath

A. I know with the case of Rhodium plating, you can utilize potassium ferrocyanide [affil links] 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 [affil links] 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.

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,

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.