Letter 19077

Nickel and cobalt anodes

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Our shop has a Ni-Co electroforming process and we are interested in using electrolytic cobalt like anodes. And we have one question: Is it possible maintain the cobalt in solution using electrolytic cobalt anodes connected to the same power supply alongside the nickel anodes?.

Thanks for you attention,

Henry Rodriguez
- Guarne, Colombia

You probably need to hire a literature search. Nickel and cobalt are so very very near identical that you might be able to use the same power supply and vary the number of anodes of each metal to keep the alloy deposition within a reasonable range. Problems, I doubt if you can buy sulfur depolarized cobalt chips, thus electrolytic.NOT great for electroforming. Iwould guess that you can not use SD nickel and electrolytic in the same tank and maintain the alloy balance within range even with two power supplies.

James Watts
- Navarre, Florida

James has hit one problem on the head - I too do not know where to get sulphur depolarised cobalt from, so you will have to take account of that in the bath formulation. This could affect the properties of the electroforming deposit. Secondly, cobalt is consumed from the electrolyte much faster than nickel is, so you will need to dissolve more cobalt than nickel. To do this, you will need to have each type of anode controlled by a separate rectifier and they will have to operate at different current densities, but with a common cathode. It is therefore theoretically possible to do what you weant, but in practise it will be much more complicated and will need a lot of setting up and checking.

Trevor Crichton R&D practical scientist - UK

James,

Your right. Using SD(sulphur depolarized)nickel and regular electronickel in the same basket is not good practice. The SD will dissolve preferentially and could cause uneven current distribution.

A few years ago I did a test using electrolytic cobalt as an anode in a bath of cobalt sulphate with no chlorides and the cobalt anode corroded fine so there would be no need for SD cobalt. That said, I think it would be difficult to get the anode ratio between nickel and cobalt right to get the desired alloy composition. I don't know that this could be calculated, it may require plain old trial and error.

Don Piett
- Canada

I ran a cobalt line with chloride and electrolytic cobalt chips and plated 0.005 with no adhesion problem. But, electroforming is usually done from a sulfamate bath. Normally you are looking for an extremely low internal stress. Henry has not given us enough to really give him an answer. He may find an answer in literature. I do remember an article or two about 15 years ago. Alloy deposition is no piece of cake.

James Watts
- Navarre, Florida

Cobalt will ALWAYS plate out faster than nickel. Cobalt plates out faster at lower current densities. Establishing a "balance" is probably impossible and definitely a life long R&D; program. Best advice, first question the accuracy of the interpretation of your instrument analysis that separates cobalt and nickel, then always be prepared to add Cobalt as concentrated Cobalt Sulfamate (and have it reliably analysed to separate nickel from cobalt).

Robert H Probert Robert H Probert Technical Services Garner, North Carolina Editor's note:        Mr. Probert is the    author of Aluminum How-To / Aluminio El Como

Answer or follow-up on this subject (in non-commercial fashion).

 

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