Letter 15029

Nickel over nickel [Spain] 

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I am working with a sulfamate bath

600 g/l of sulfamate
40 g/l of boric acid
10 g/l of NiCl2
pH=4 +-0.2
T=44ºC +-0.5
maximum current density 1.5 amps square decimeter
Thickness = 1 mm

I need to plate nickel over nickel. I have no possibilities (by the moment) to make a sulfamate strike or a Woods strike. I have some information about nickel activation with 20% sulfuric acid with this sequence:

5 minutes of reverse current at 10 amps/dm2
2 minutes of reverse current at 20 amps/dm2
2 minutes of direct current at 10 amps/dm2
then rinse with deionized water and plate nickel at 0.6-0.8 amps/dm2.

In all the tests I made in laboratory the adherence was perfect but I have doubts in passing from the laboratory to the plant. Any suggestion in this respect it will be very appreciated.

Angel Vidal
- Spain

I would agree that it may be a problem taking this method to production. If you could keep the sulfuric acid clean by dummying, you may have a better chance. As soon as any copper or other metal builds up in the sulfuric acid, you will start plating a non-adherent smut which will be a problem.

Tom Pullizzi Platronica.com Falls Township, PA

I don't like to use the words direct and reverse, however, what you are doing makes good adhesion, Make the part CATHODIC in the clean electronic grade sulfuric acid using bagged carbon anodes. Be aware that any sulfuric soluble impurities (iron, copper, zinc,) either coming in with the sulfuric acid or dragged in by you, will co-deposit but not adhere over old nickel oxide, and then your deposit will blister off. Also the addition of about 1/2 oz/gal very clean and pure ammonium bifluoride will enhance the adhesion. Any metallic impurities will compromise this process, and it will also compromise a Sulfamate strike or a Woods Strike. Theoretically the only difference in the results from electrolytic plain acid versus a metallic strike is that NOW you must transfer to the plating tank more rapidly.

Robert H Probert Robert H Probert Technical Services Garner, NC, USA Editor's note:        Mr. Probert is the    author of Aluminum How-To

I am aware of the fact that cyanide sounds like a four letter word but in case that you have cyanide in your premises, a cathodic activation in an alkaline cyanide solution is the best way to activate nickel and to enable plating nickel on nickel. If you stick to the sulfuric acid activation, use the previous reply and add fluorides. I recommend to activate in the sulfuric acid only when parts are activated cathodically.(what you call direct).

Sara Michaeli     chemical process supplier Israel

Hi, we run a Pulse Reverse Nickel chloride process. We are able to run reverse for e.g. 5 min. and then start up the electroforming process, without the item leaving the bath. This could solve all your problems.

Lars B. Andersen
- Denmark

Thank you very much Tom, Robert, Sara and Lars for your comments. The part is already plated and everything has gone OK. It was 1 piece, 8 tons, but only 1 piece. The sulfuric was as clean as possible and the dead time was as short as we could.

Thanks again,

Angel Vidal
- Spain

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