Cycle for Electroless Nickel Plating on Molybdenum?

"Chemical (Electroless) Nickel Plating"
by G. G. Gawrilov

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A. Gawrilov's book, Gawrilov's Chemical (Electroless) Nickel Plating ⇦[this on on Amazon, ... on AbeBooks affil links], says that Mo pretreatment "can take place in alkaline solutions containing potassium ferricyanide; HCl, HF and mixtures of nitric and sulfuric acid". Also, you need contact of aluminum or magnesium for Ni-P plating. He gives german and russian references, and a patent DOS 2046521.

A. The trick here is to lay down a strike (cap-off) layer of "anything" at a rate sufficient to out-pace the rate of oxidation of the Mo substrate. As far as I know, there are no E-less processes capable of it and I've tried them all on high aspect-ratio Mo surfaces. Adhesion of the cap-off layer always suffers unless it it applied RAPIDLY, and I mean in just a few seconds on Mo.

Unfortunately, this means you must push the rates with DC current, and you must introduce reactant along the surface at even higher rates to support this high current. There is a trick you may be able to get by with if adhesion is not of great concern. There are "Immersion" Gold treatments available Technic, Inc. Oromerse) which deposit approx. 5 microinches of Au, sufficient to get an E-less Ni process started. Your long aspect ratio may provide mechanical adhesion of the interior deposits once the Nickel is applied. You experiment (play around) with that bath a bit and you may be able to find parameters that yield sufficient adhesion, assuming that Gold is allowed directly on the Mo by your Materials Engineers.

Good Luck,
Dave,
SUNNYvale, CA

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Ed. note: We've appended your inquiry to an earlier thread where Dave Kinghorn has offered some insightful advice.

A. Mr. MacKenzie: We nickel plate tungsten wires using a potassium hydroxide cleaning and a nickel sulfamate strike and plate. This should work well for molybdenum also. -Kirk

"Electroplating Engineering Handbook"
by Larry Durney

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A. I have plated Nickel on molybdenum using the sequence given in handbook edited by A.K.Graham. It worked fine.

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Ed. note: the current edition of Graham's Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon affil links] is edited by Durney.

ASM Metals Handbook Vol. 5: "Surface Engineering"

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A. Molybdenum has a very tenacious oxide layer that is very difficult to remove. Its structure is extremely complex and varied. However, a description on how to electroplate onto molybdenum is given in Graham's Electroplating Engineering Handbook (most recently edited by Durney) and in ⇦[this on eBay, AbeBooks, Amazon affil links] . I would have concerns about depositing electroless nickel onto molybdenum because of the slow rate of metal deposition, the lack of polarization and the rapid formation of molybdenum oxides. You may be better off trying to put down a protective electrolytic metal and then electroless nickel

A. Earl Groshart stated in the 1991 Metal Finishing Guidebook that molybdenum could be plated by the following procedure:

1. Degrease in steel soak and electrocleaners
2. Anodic treatment in 885 g/L sulfuric acid plus 720 g/L phosphoric acid at 7-8 A/dm2 for 2-3 min
3. Etch in 300 g/L potassium ferricyanide plus 100 g/L potassium hydroxide at 85 °C for 1/2-1 minute
4. Strike in a standard chromium plating bath
5. Strike in chloride nickel strike The part should be rinsed between steps.

I have never tried this myself. Good luck.

A. I suspect your problem is not the ruthenium, but the molybdenum. There are many electroplating baths that will deposit ruthenium (e.g., see patents WO1992/17625 and US Patent 4375392). The trick is to make sure the molybdenum is free of oxides and other substances that will stop the ruthenium from depositing.

A. An earlier response to a similar question has highlighted the existence of details of electroplating onto molybdenum in a chapter on surface engineering in Vol. 5 of the ASM International Metals Handbook. There are also a couple of patents on plating onto molybdenum (e.g., US Pat 3,386,896); this particular one uses gold as the coating agent and stresses that since molybdenum has a strong propensity to form a wide range of oxides, after the gold strike has been put down, the coated molybdenum sheet should be heat treated to reduce the oxides.
Having dabbled a bit with molybdenum in the distant past, I too found it was a strong oxide producer and was a real problem to get an adherent coating onto it. Giving it better consideration and with the benefit of hindsight, I can see the sense in using a sinter or reduced atmosphere heat treatment.
One thing that has occurred to me is that it may be possible to directly electroplate molybdenum by using jet plating. I know I was successful in directly jet plating nickel onto a piece of dirty aluminium that I didn't even bother to clean, so I could see that the technique could perhaps eliminate the need for specialised heat treatments with molybdenum. Maybe it is worth a go?

A. Hello Kay,
The bond strength of the Ni plated Moly would only be as good as the pre-plate and Ni plating process employed. I have seen that Ni sulfamate baths have a better success rate than standard watts baths in brazing applications. I would have to say that the bond strength would be greater on the brazed part itself. The Ni plating should hold up to the brazing temps you described. I think the biggest hurdle you are going to have is to nail down a process for the plating on Moly. Hope this helps.