Letter 41022

Brittle Nickel Plate

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I am running a high speed sulfamate nickel process plating 18 gauge wire. 350-450 ASF, 16 oz/gal Ni, 140F bath temp. S-rounds for anodes, 1.5 oz/gal NiCl and boric acid to saturation in anode bags. When plating the wire to 27% Ni by weight, I only get about 6 weeks life out of the bath before the plate becomes so brittle the wire won't draw. I have analyzed for ammonia and have found as much as 600 ppm. Anybody have any ideas on the cause and/or the solution?

Kurt Sammons
- Inman, South Carolina

The facility you are working at was plating 27% nickel with indefinite bath life 20 years ago. I know because I ran the operation then. Apparently personnel changes have caused the procedure to be lost. Make sure you have enough anode area and keep the operating temperature down. The problem isn't ammonia, it is sulfate from sulfamate decomposition.

Jeffrey Holmes, CEF - Spartanburg, SC, USA

You do not say what your pH is or how hard it is to control. My guess is that you do not have enough anode area or it is passivating. High speed requires extreme agitation, how is yours?

James Watts
- Navarre, Florida

Hi Kurt,
You share a problem that many high speed Ni Sulfamate platers have in common. The secret I have found is to reach the proper halogen level (chloride). It's really a catch 22 because too much chloride can raise tensile stress, and too little polarizes the anode, causing ammonia to form. The formation of ammonia in the bath will make the deposit brittle. You are using sulfurized anodes, so the low concentration of Ni chloride seems to be the norm. I know of a few high speed plating customers that went to magnesium chloride for a halogen. It is less likely to increase tensile stress, and it can be maintained at a slightly higher level than Ni chloride helping with anode corrosion. You could check with your supplier to see if they concur on using magnesium chloride, or maybe they would suggest raising the Ni chloride a little bit in the bath. Also consider the use of a stress reducer. Good Luck!

Mark Baker
Process Engineer - Syracuse, New York

I'll bet you have more than 600 ppm ammonia. Ammonia causes brittleness and is caused by, high anode current density, low pH, high current density, high temperature and 140 is worse 5than 120 F, and sulfamic acid that contains ammonia to start with. Do a distillation on the incoming sulfamic acid. It is very difficult to find ammponia free sulfamic acid on the open commercial market. Also, your chloride is too high.

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

The decomposition product of sulfamic acid are sulfuric acid and ammonia.

How is your anode efficiency? It should be same as your cathode efficiency. If it is less, then you are probably generating sulfamic acid from Nickel sulfamate and electrolytic decomposing it.

You are probably using anode basket?

Try depolarized Nickel anode bars,use good anode bags, this might help prolong the life of your bath.

2005 Metal Finishing Guidebook & Directory pp.209 & pp. 224
has a good write-up on Nickel anode efficiency.

Hamilton Solidum
- Mays Landing, New Jersey

I thank everyone for their responses. All my research has indicated that ammonia causes stress in the plate, is this correct? Unless I have my chemistry wrong, the sulfamate breaks down into nickel sulfate and ammonium sulfate. Would not high sulfate be an indicator of high ammonia?

I am concerned about our pH levels, currently 2.9-3.4., not too difficult to control. We measure twice a shift and add sulfamic acid about once a day.

I have tried using no NiCl since we are using S-rounds, it was a disaster. Will discuss MgCl with my vendor. My inclination now is to lower the temperature and raise the pH some. What is a good level for the pH?

Kurt Sammons
- Inman, South Carolina

pH 3.6 - 4.0, Temperature 105F, 1.5 oz/gal nickel bromide, no chloride.

Jeffrey Holmes, CEF - Spartanburg, South Carolina

S-Rounds are far better for sulfamate than rolled depolarized because they dissolve with less current and hence make less ammonia. Your pH is too low, low pH makes ammonia,let it rise to 4.0 and hold 3.9 to 4.2. High temp also makes ammonia, try to run at 120 F. High anode current density makes ammonia.

Robert H Probert Robert H Probert Technical Services Garner, North Carolina

I have studied it but never ran a high speed sulfamate bath, only conventional and brush. Also, you already have too good and educated answers. But in my opinion you should have your defective plated wire analyzed by a well equiped and professional lab, not just the bath. There are too many things that can go wrong and raise the stress, from operating conditions to draged-in or by-product substances. Fortunately, most will leave a track to follow in the plate. Good luck.

Guillermo Marrufo
Monterrey, NL, Mexico

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