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Chloride limits for nickel sulfamate bath?
Q. We are doing nickel plating in nickel sulfamate bath.
Last time we make up solution and we have increased concentration of chloride 12,75g/l (operating limit 6-9g/l)and nickel concentration is
75g/l (operating limit 75-90g/l.
Plate we got on test peaces are very good considering the color, no pitting and adhesion. Does any one know do the increased chlorides in this case can interfere with plate quality, or to interfere wit bath work? We did not notice any problem but I just want to check and exchange experience.
Thanks in advance.
plating engineer - Belgrade, Serbia
2007
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A. Chlorides increase the tensile stress in the deposit, therefore you want to use the lowest concentration of chlorides that will still corrode your anodes at the current density that you use. If you are at 20 amps per square foot (2.16 amps per square decimeter) and using INCO's S-Rounds, then you only need 0.5 oz/gal(3.75 gm/Liter) of chloride. But if you are using electrolytic nickel or Rolled Depolarized then it will take 6 or 8 oz/gal. If the metal dissolution from the anodes does not keep up with the plate-out rate, then the pH will go down and the deposit will increase in tensile stress,  Robert H Probert Robert H Probert Technical Services  Garner, North Carolina  2007 A. That concentration is just a little high. Chloride ions promote anode dissolution but also increase stress. If you are not doing electroforming work or your plate is relatively thin, it may be OK. As a matter of fact, adhesion to some difficult to activate alloys might improve. You will have to monitor your Ni++ concentration closer and take the anodes out of the tank when idle. Guillermo MarrufoMonterrey, NL, Mexico 2007 A. The increased chloride concentration will have an influence on your internal stress of the nickel deposition. It will move from compressive to tensile stress, how much will depend on your other bath and working conditions. - Lucerne, Switzerland 2007 |
A. The presence of chloride ions in a nickel sulphamate bath is not required as long as the anodes are either inert (not recommended) or are sulfur nickel (S-nickel). The presence of chloride is primarily to promote anodic dissolution and hence anodic polarisation. This stops the anode from passivating and reduces the rate at which nickel oxides and hydroxides are created at the anode, both of which can adversely affect the quality of the nickel deposit as well as knock the bath's chemical balance out.
In theory, nickel sulphamate does not need chloride, but most users, even electroformers, use some chloride; I have known as much as 10g/l of nickel chloride being used without too many problems. The presence of chloride will switch the stress from compressive to tensile, but in many cases this can be accommodated by increasing the amount of added stress reliever. An alternative to chloride is bromide, which does not seem to affect the stress but does promote some anodic polarisation. Nickel bromide is, however, much more expensive than the corresponding chloride.
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
adv.
"The Sulfamate Nickel How-To Guide"
by David Crotty, PhD
& Robert Probert
published Oct. 2018
$89 plus shipping
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