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Black sludge in nickel anode baskets
We have a nickel sulphamate bath to make 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 the leak in 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
^- Privately contact this inquirer -^
July 24, 2010
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
July 28, 2010
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 (appr. 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.
Best regards
- WARSAW, POLAND
August 9, 2010
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 chlorides 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
- Italy
August 10, 2010
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
August 26, 2010
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
August 30, 2010
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.
- Italy
August 31, 2010
Have the parts mechanically rotated at a slow pace as they are plating.
Jim Schwartzmyer- North Tonawanda, New York, USA
September 15, 2010
How can I rotate the tubes while they are into the bath? I work with racks and it's very difficult to have rotation and the electrical contact together.
Daniele Santin- Italy
December 31, 2011 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. Hi sir
we are doing Nickel chrome plating for automotive parts.
My question is what is the reasons for sludge forming
is there any methods to clean that sludge?
what is the frequency of cleaning would be appropriate for 3000 litre capacity baths of bright and semibright nickel.
What are the problem we will face,if sludge is not cleaned.
I am new to industry.. please help with that...
Thank you...
- CHENNAI, TAMILNADU, INDIA
January 9, 2012
Marxe,
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.
Kishore Phadnis
- Mumbai, Maha. India
January 12, 2012
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- Hendersonville, Tennessee, USA