Internal stress control of nickel electroforming in sulfamate bath

A. Before you decide to add other chemicals, first make sure your impurities, sulphate and ammonium ions are low. Then lower your chloride concentration and current a little bit. Also increase temperature a little.

A. Please give us your operating parameters.

A. Sulphamate nickel is about the easiest nickel bath to achieve a zero stress deposit. However, the correct conditions must be used and you do not give any details. To get zero stress, you can add up to about 1 g/l of saccharin (sodium salt), but the resulting stress level will depend on the operating temperature and cathodic current density. However, one word of caution about using saccharin, it contains sulfur and this can cause embrittlement in nickel, especially if the deposit is used above 160 °C. You may want to consider using a cobalt additive as this will increase the hardness of the nickel and can be used under zero stress conditions. The exact degree of "zero stress" will also be important, as the bath tolerance to additives will diminish as the "zero stress" range becomes narrower.

Alternatively, you may want to talk to your supplier, who will be able to advise on suitable additives for your needs.

A. Saccharin drives the stress downward from tensile toward compressive, however, at 300 °C it will break down and cause separation (loss of adhesion). It cannot be used in heated applications.

Low current density is good.

pH close to 4.0 is good.

Chlorides cause increase in tensile. Less than 1/2 oz/gal chloride is enough if used with S-round anodes, all other anodes require higher chloride - hence higher tensile stress.

Nickel Bromide instead of chloride causes compressive stress, but be sure IT is clean.

Dirty carbon which contains organic sulfur will cause stress.

You need to buy the best nickel sulfamate, then carbon treat it with sulfur free powdered activated carbon, then "dummy" overnight at 2 amps per square foot on a zig-zag cathode, then plate at 20 ASF, 100-120 °F, with only moderate and uniform agitation

Thank you all for your answers. They are helpful.

The conditions I used in the tank is 15 ASF, T=130 °F, pH 4.15. The tank is older and I was just in the position to be in charge.

I still have slightly tensile tension by using those condition. Maybe, I need to do some carbon treatment of the solution.

A. Carbon treatment should be done preferably on a small sample of bath before treating all of it. Some treated carbons contain chlorides (tensile stress riser).

A. It depends on the purity of the carbon. Bad carbon will add impurities. Ideally, you should use sulfur free powdered activated carbon. You may have to treat two times, the first will take out the surfactant, then the second will take out the organics that you want to remove. You should try a small batch in the Hull Cell to determine what will happen to the main solution. If you do no have a Hull Cell, then try a 4 liter beaker test. Either way, predict what will happen with the carbon treatment in a small batch first, then, if it improves, treat the production solution. Come back for more info and to let us know what happened.

A. Hello Wesley,
I would use a granulated activated carbon. There are also carbon filter tubes you can use in your filter housing. The filter tubes work well for smaller baths (10-50 gal) I don't think the carbon supplied for fish tanks is as effective due to the lower purity. I like to pull bath samples in glass beakers at different stages of the treatment. One sample before carbon polish, one after 2hrs, one after 4 hrs and so on. You will see the solution color go to a light emerald green color when successful. If you do use carbon filters only run each filter or filter sets for 2 hrs, then replace with new ones. If you plan to do a full blown batch carbon treatment, the granulated type carbon is easier to work with than powdered.

Thanks for the help! Think I will try the high grade granules and let them precipitate in the treatment tank. I only have to treat a very small batch. Thanks again.