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Hard nickel using cobalt

I am currently working on a hard nickel bath using cobalt I have managed to hit my goal in hard by turning up the temperature how ever the filters and pumps did not seem to like it. So I was forced to back the temperature off. My question is what level of Cobalt are people using and where else can I find hardness.

David Morrison
QC chemist - Titusville, Pennsylvania, USA
2004

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First of two simultaneous responses --

You don't mention what chemistry you are using, so the correct answer would be: it depends. But assuming all-sulphate chemistry, adding the ammonium ion will increase hardness. It will produce other effects such as brittleness as well. Other options would be to use sulfamate chemistry, lower temp, lower ASF or use pulsing currents.

Guillermo Marrufo
Monterrey, NL, Mexico
2004

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Second of two simultaneous responses --

700 ppm should satisfy your needs and you already know what favors its plating out rate and that it is difficult to hold 700 ppm. Do not forget that higher temperature breaks down the SN and makes ammonia ⇦ this on eBay or Amazon [affil links] which causes brittleness.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2004

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Details of your chemistry are too sparse to make any comments on it, but I don't like the idea of heating the electrolyte to get the required hardness. This can cause all sorts of problems, depending on the system. You also don't give any details of your requirements, so we are shooting in the dark. However, NiDI have a report written by S. Alec Watson on "Additives to sulphamate nickel solutions" and this describes the effects of cobalt on the hardness of nickel. Basically, the greatest hardness (about 520Hv) is achieved with the addition of 6g/l Co ion. This will correspond to a deposit of about 33-35% Co when plated at 5-6A/dm2. This, of course all relates to sulphamate chemistry and all it's nuances, but it should, in principal, be true of other systems, with the caveat that sulphamate systems generally have lower stress. The reason for the variation in bath and deposit compositions is that cobalt is preferentially deposited when in conjunction with nickel.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004