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• Topic #3604 "Nickel plating anode bags: Cleaning, leaching, replacing, double-bagging, etc."
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Nickel anodes turning black, black sludge in anode bags
Q. We received a new batch of nickel anodes from our supplier and they are turning black in our strip plating bath. The supplier said that the only thing that would make them turn black is if they contain sulfur and we have not been able to find any sulfur. The other odd thing is that we have tested both the new anodes and the old anodes to determine if there are any differences and we have not found any. Any help you can give us on this matter would be greatly appreciated.
Littelfuse - Des Plaines, IL, USA
A. All sulfurized anodes turn black with inorganic sulfur matter. The blackness forms faster at lower pH, higher halogen content, higher anode current density, and as a function of the sulfur contained. That is why we use anode bags. Tell us what kind of nickel anodes you are using, the electrolyte, the pH, the halogen.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
A. There is insufficient information to make a judged comment, but I would suggest two things. Firstly the nickel contains sulphur and the blackness is due to that. The usual amount of sulphur in sulphur depolarised nickel (aka S nickel) is well below 1% ( I believe it is as low as 0.2% but I would seek a second opinion on that!); they are usually supplied as rounds. If the nickel is not as rounds, it may well not be "S nickel". Alternatively, the nickel has passivated and the blackness is the nickel oxide. A lot more information is needed, such as what are the bath composition and operating conditions. With this information, perhaps a more helpful comment can be made.
R&D practical scientist
Chesham, Bucks, UK
A. I also agree that the information is a little insufficient, but we have this problem also, in our Ni plating bath. We use 60 inch titanium anode baskets then have them covered with triple flocked bags to keep the fines out of the bath. Anyway, we always use electrolytic "R" rounds for our bath and we got sent "S" rounds by mistake; we did use them but all the "S" rounds have turned black and all the "R" rounds are still the grey color they normally are. We run a ph of 2.00 and the temp is 140 °F.Brian Gaylets
- Scranton, Pennsylvania, U.S.A.
Black sludge in nickel anode baskets/bags
Q. We have a nickel sulphamate bath to do nickel plating over steel tubes. We have a consumption of 100 kg/day of nickel and we charge the nickel twice a week. I observed a lot of black sludge in the bottom of the baskets. This sludge seems to be nickel that didn't dissolve in the right way. It is very porous and light and forms a black powder. Obviously we use meraclon bags to prevent leakage into the bath. We use nickel S-rounds in titanium baskets and the chloride concentration is 2 g/l. Is the black sludge due to the bad dissolution of the nickel? How can I prevent it?
Thank you for your help
Technician - Treviso, Italia
July 20, 2010
A. This black product is what makes an S round an S round. It is the non nickel portion of the anode. The bags are generally sized longer than the baskets to allow room for this sludge to accumulate and not coat the anodes.Gene Packman
- Great Neck, New York
A. Hello Daniele,
Don't worry about it. You needn't prevent it. That's the typical sludge that remains after the dissolution of activated (depolarized) nickel. That sort of nickel contains small amount (approx. 20 ppm.) of sulfur added in order to improve dissolution. The sludge consists of nickel sulfide. Chloride concentration seems to be right for that application.
- WARSAW, POLAND
Q. Due to the high nickel consumption, we have a lot of this sludge in the bottom and this causes problems with the thickness uniformity. In the lower part of the rack (corresponding to the anode area containing the black sludge) we have lower thickness than in the upper part, where we fill up with fresh nickel. I think it is a problem of conductivity and current density due to this anode inhomogeneity. If we increase the chloride concentration, could we solve this problem and dissolve the sludge, keeping the anodes clean?
To avoid the thickness problem, I think also to mask the upper part of the anodes with PP shields while increasing the current to reach more thickness uniformity in the nickel deposit.
Thanks for your help
August 9, 2010
A. If you have high nickel consumption, you need to change your anode bags more frequently. Some people double bag the anodes, one is normally a Dacron and the outer one is normally napped polyPro.
Activate your nickel round additions with a short dip in HCl solution.
I did not have a high consumption and I would empty the anode baskets about twice a year,; pressure wash the chips and put them back in. I changed bags quarterly.
- Navarre, Florida
A. There are a couple other possibilities here.
1) Do the anode baskets go lower in the solution than the racks of tubes? If this is the case, the lowest anodes may have a low anode current density (ACD). They will film over, but not corrode properly, causing excess sludge; you may also see what look like flakes, rather than just a fine silt. That also represents nickel you pay for, but does not end up on the work!
If this is the case, raise the bottom of the anode baskets by fabricating a "floor" from non-corroding plastic. Do NOT shield the anodes at the top.
2) What is the pH of the solution? If the pH rises during production, this also indicates low ACD, which will cause excess sludge. Reduce the number of anode baskets, which will increase the ACD.
ACD is very important in nickel plating, yet it is often overlooked.
- Chicago, Illinois, USA
Q. Thanks for your suggestion. I'll try to reduce the number of anode baskets to increase the ADC. We always find, in fact, black sludge, but also black nickel flakes. They are very light and porous and occupy the bottom of the basket. Is the formation of these flakes due to the low ACD?
Another problem we have is the thickness uniformity. We have a low penetration of the nickel and we cannot use organic additives because after the piece is subject to annealing. How can we increase the nickel deposition in low current density areas? The pieces are tubes and they are arranged in a row. The face of the tube in front of the anode has very high nickel thickness, while we have low thickness where the tubes are close to each other. We cannot increase the distance between the tubes. The bath is well agitated and we do weekly the chemical analysis.
August 30, 2010
A. Have the parts mechanically rotated at a slow pace as they are plating.Jim Schwartzmyer
- North Tonawanda, New York, USA
? How can I rotate the tubes while they are in the bath? I work with racks and it's very difficult to have rotation and electrical contact together.Daniele Santin
Q. Hi sir,
We are doing Nickel chrome plating for automotive parts.
My question is what is the reason for sludge forming?
Is there any methods to clean that sludge?
What frequency of cleaning would be appropriate for 3000 litre capacity baths of bright and semi-bright nickel?
What are the problems we will face if sludge is not cleaned?
I am new to industry, please help with that.
- CHENNAI, TAMILNADU, INDIA
December 31, 2011
Your information is very vague. You have not mentioned what kind of sludge you are talking about.
There are a number of literatures that talk how to remove sludge from the bath. Please contact your supplier who would help you with your specific problem.
- Mumbai, Maha., India
A. The black sludge you are seeing is nickel sulfide which is formed by the dissolution of nickel anodes. It is the primary reason that nickel anodes are bagged: so the nickel sulfide doesn't cause roughness in the solution. It is a naturally occurring sludge but care must be given to proper anode bag maintenance which includes regular inspection of holes in the bags. This can occur when parts are dropped in tanks and tear the bags when they fall against the anode baskets. Even a small tear near the bottom of the basket can allow large amounts of the nickel sulfide sludge to be released to the tank causing a never ending source of particulate roughness.
Daryl Spindler, CEF
decorative nickel-chrome plating - Greenbrier, Tennessee
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