• Topic #49000 "Nickel Anode Bag Problem (stiffness, covered with crystals)"

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.

A. There is insufficient information to make a judged comment, but I would suggest two things. Firstly the nickel contains sulfur and the blackness is due to that. The usual amount of sulfur in sulfur 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.

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.

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.

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.
Best regards,

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.

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.

A. Have the parts mechanically rotated at a slow pace as they are plating.

? 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.

A. 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.

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.