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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Sulfur embrittlement of Ni sulfamate platings
Q. I am attempting to reproduce periodic sulfur embrittlement of Ni platings from a Ni sulfamate barrel plating process by using a Hull Cell. The basic Hull Cell set-up is 267 mL with a NON-activated Ni anode, MgCl as a corroding agent, 2 Amps constant current, boric acid and wetting agent. A four decade old article by Greene suggests running the anode in the passivated condition to create reactive azodisulfonate that may codeposit with the Ni. Another suggestion is to use a sulfur activated anode (but literature from the suppliers of these anodes states that the sulfur is bound in a precipitate after dissolution of the anode and is not free to participate the plating process).
Can anyone offer inputs on these methods or suggest other bath variations/chemistries that may force sulfur to be codeposited with the Ni? Thanks
electronics manufacturing - Phoenix, Arizona, USA
2004
A. I very strongly doubt that sulfur depolarized anodes are the cause of the sulfur embrittlement. And while I am not a smart enough chemist to truly understand azodisulfonate and the "magic stress reducers" associated with nickel sulfamate plating, I doubt that they are the cause either. My understanding, inferred from people who are the smart enough chemists, is that these sulfur deposition problems invariably come from brighteners and leveling agents that someone deliberately put into the bath, or from oils of some sort that found their way in.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004
A. I have never heard of sulfur depolarised nickel causing sulfur induced hardening or embrittlement. However, many additives, such as saccharin, have sulfur in their molecular structure and when they are co-deposited , they can cause sulfur embrittlement. This is only usually seen when the nickel is heated to over 160 °C - the higher the temperature the shorter the time needed to see it. At 160 °C it takes about 2 hrs.
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004
A. Sulfur depolarized anodes are definitely not a source for sulfur in the nickel deposition. During running a sulfamate electrolyte there is the possibility to create azodisulfonate, which is a source for sulfur in the deposition. The azodisulfonate is created at polarized anodes (Reasons for high polarization can be: To low chloride content, to high anodic current density, wrong anode material). Sulfur depolarized anodes help to prevent the creation of azodisulfonate even in low-chloride sulfamate bath.
Marcus Hahn- Lucerne, Switzerland
2004
adv.: Supplier of Copper Anodes, Nickel Anodes, Bismuth Metal, & Other Metal Products for Industry & The Arts
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