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Nickel Sulphate differences and Nickel Plating

I have a question on Nickel sulphate. We have a Nickel Plating bath here in our shop and have recently run out of Nickel sulphate. We had a hard time finding replacement for it but finally did. The solution we received in is different from the solution we had just recently run out of. The first thing I noticed was the name "Electroless Grade" Nickel sulphate. Our bath is not an electroless system. Also the CAS #'s are different. The solution we had been using had a CAS# of 7786-81-4 and the solution we just received has a CAS# of 10101-97-0. I understand some of the differences between the two, but my question is whether or not I can use new solution with my existing bath or will there be incompatibilities? Any help or insight would be greatly appreciated.

Sam Snead
- Buffalo, New York
2003

Besides the concentration which might be different and has to be carefully observed in any calculations or additions, your new electroless grade Ni sulphate is purer and hence it will not harm your bath (it normally is a little more expensive).

Guillermo Marrufo
Monterrey, NL, Mexico
2003

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Sam,

Thanks for raising this issue. I think it is potentially a very important point because both CAS numbers refer to what is essentially the same chemical. 7786-81-4 refers to nickel sulphate, whilst 1010-97-0 refers to nickel sulphate hexahydrate. This difference can affect the concentration of nickel in a solution, as the hexahydrate will also include the "weight" of the water in the molecule. It is therefore important to check that any nickel sulphate solutions are bought and specified in terms of molarity, not g/litre or ozs/ gallon. This in turn can affect the colour of the solution if the nickel is bought in terms of concentration nickel sulphate, the weaker hexahydrate will appear paler and I bet it isn't any cheaper! I would suggest that anyone buying nickel sulphate solutions should check for themselves how much nickel is actually in solution. As far as using "electroless nickel grade" is concerned, all it means is that it is purer than conventional nickel sulphate and doesn't contain so much other metal impurities. It will also be correspondingly more expensive, so your supplier may be quite keen to sell it to you as their only type! I have checked and found that it is not just nickel sulphate that can have two CAS numbers for essentially the same material (the only difference being the water of crystallisation), so when anyone buys plating salts that may have this type of problem, they should check the real cost of their metal salts it can be an expensive way to buy water!

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2003

You have to be careful in buying salts. A few years ago we had a purchasing agent who bought anahydrous salts rather than paying for all that water. The material absorbed water from the air and got extremely hard and of course the weight changed, making it difficult to determine how much to add. At least with fully hydrated salts you can calculate the mole addition rate for desired elements.

Don Piett
- Thompson, Manitoba, Canada
2003