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Pitting problem in nickel sulfamate bath
2004
Q. I am have a pitting problem with my bath ( nickel Sulfamate) the pitt's are down low near the agitation of the solution. The pitt's seems to clean and slanted upwards however the surface tension is being kept down around 25 dynes/cm. There is 15 ppm of Pb in the solution and 326 ppm of mg in it. Here is the other level's of the bath
nickel sulfamate ---- 10.7 oz/gal
Add a MgCl --------- .45 oz/gal
Boric acid ----------- 5.10 oz/gal
pH ----------------- 3.9-4.0
Temp---------------- 136 F
I ran hull Cell's of 1amp no air 2 amp air, 3 amp air, 5 amp air. and there was no problem with the hull Cell's. Where can I look next.
David MorrisonQC chemist - Titusville, Pennsylvania, USA
A. What sort of agitation are you using and what is your operating cathodic current density? If you are using an air sparge, your problem could be too much air causing impingement pitting. If it is agitation by pumping, you may be getting air (or some other gas) into the electrolyte and this is coming out as bubbles. Your description suggests pitting caused by air bubbles. Your bath composition, operating pH and temperature are all OK. The lead doesn't seem to be a problem as it doesn't show up in the Hull cell tests. Out of interest, why are you using magnesium chloride and not nickel chloride, surely the nickel salt is more usual, but perhaps more expensive?
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004
Q. Also I just got back the results for a test that was ran on two tanks. It found 497 mg/L of Nitrogen ammonia [on eBay or Amazon] in one tank and 288 mg/L of Nitrogen ammonia in the other tank. The method Source for the test was EPA 350.2 Could some one please enlighten me on these results.
Thank you,
David Morrison [returning]- Titusville, Pennsylvania, USA
2004
A. Sounds like the sulphamate is breaking down into ammonia and sulphate. This is well known with sulphamate but normally only occurs at over 70C. I wonder if inert anodes could also cause this to occur? It would still be useful to know the answers to the previous questions.
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2004
2004
A. Ref.documentation
impurity limit ppm
fe 200
cu 10
zn 10
pb 2
al 6
cr 2
- Paris, France
A. David, ammonia is the result of the sulfamic radical breaking down. IT IS A COMMON IMPURITY IN CHEAP SULFAMIC ACID. I left you the procedure for qc-ing incoming sulfamic acid. Other causes of high ammonia are: too hot, like above 140 F, time, high anode current density (so be sure you have enough anode area and be sure to flush out the sludge from the anode bags frequently - after every run in your case). ammonia does not cause pits.
Ammonia causes brittleness. You do not have high ammonia, yours is actually very low right now. Brittleness starts at about 4000 to 5000 mg/L.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
2004
adv.
"The Sulfamate Nickel How-To Guide"
by David Crotty, PhD
& Robert Probert
published Oct. 2018
$89 plus shipping
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