Summary for nickel in gold plating Discussion
Nickel present in top layer of gold is usually explained by porosity, diffusion, or the way the surface was analyzed rather than by nickel truly being part of the gold finish. Dave Dixon asked how up to 6% nickel could appear in a gold-over-nickel system plated to ASTM B488 Type 2, Code C, 50 microinches minimum, especially since the plater uses cobalt hardener. One answer said pores in the gold can expose nickel, and heating can drive nickel to the surface; it advised better cleaning/activation of the nickel and increasing gold thickness, noting that about 100 millionths of gold may be needed to be pore-free in many cases. Another answer warned that 50 microinches of gold is very thin and likely porous, so nickel may soon be exposed anyway. It also noted that EDAX can read several microns deep, so the nickel signal may come from below the surface, and reminded that ASTM allows cobalt, iron, or nickel hardeners, so the supplier should be using pure cobalt.
Q. Due to concerns over nickel dermatitis, my company has decided to plate gold over nickel, per ASTM B488 type 2, code C, 50 micro inches min. Surface analysis of our parts shows up to 6% nickel in the top gold layer. The plater uses cobalt as a hardener. I am trying to figure out how the nickel could be present in the top layer. Is this normal? Any ideas on where it is coming from?
Thanks,
Dave Dixon
Consumer electronics mfgr. – Santa Cruz, California, USA
2003
A. Pores in the gold deposit can result in nickel at the surface. If the object is heated nickel will diffuse to the surface. To assure no pores, be sure the nickel is properly cleaned and activated. And the thickness should be increased. I have found that it takes about 100 millionths of gold to be pore free in many cases.
Don Baudrand
Consultant – Poulsbo, Washington
(Don is co-author of “Plating on Plastics”
and “Plating ABS Plastics” eBay
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AbeBooks
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A. Just a few points about your concerns regarding nickel allergies. Firstly, the only real way of avoiding it is to have a system that does not wear away or release nickel (i.e., use a nickel alloy). Plating 50 microinches (which I reckon is just about 1.2 microns) of gold onto jewellery will not last long, so the customer will soon be exposed to nickel again. Secondly, such thin layers of gold will be porous and leave nickel exposed. Thirdly, how did you do your analysis? If you used EDAX, the electron beam will penetrate a good few microns (depending on the voltage) into the “surface”, so the emitted X-rays will show nickel. The ASTM spec you refer to allows gold to be hardened by either iron, cobalt or nickel, so make sure your supplier is using pure cobalt. I would recommend you either put a lot more gold down or avoid using nickel as an interlayer.
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2003