Decomposition/Plate-out of Electroless Nickel Bath

A. Hi Matewos.
1. It is very difficult to assume anything without a detailed information about the type of bath, and what exactly was a problem (photos?).
2. If this is a proprietary EN solution - contact your supplier, they will be the best source of information.
3. Very common problem for EN - bath is out of balance. It has to be proper concentration of Nickel and reducer, correct ratio between them, temperature, pH, proper concentration of additives (stabilizers, complexers). Sometimes, if the additives are out of balance, there is no way to recover the bath, you have to make a new bath.
4. If the problem with plate-out - discard the old bath, clean the tank from Nickel, make a new bath.

A. There are many things that can decompose an EN bath/
Do you filter the solution regulary?
Do you take out the solution and disolve the Nickel at the bottom of the tank?
Do you analyse the solution twise a shift ?
Do you replenish every hour?
Do you keep PH and temperature at the recommended levels?

There is more but this is good for starting.

A. In the early days of electroless nickel plating, the tanks were made of stainless, and had the difficulty you mention. So platers switched to polypropylene tanks, which were fine until plateout began, then it became uncontrollable. More recently (the last 5-10 years), platers have switched back to stainless tanks but with an impressed current to stop the unwanted catalytic action. You can buy these cathodic protection units commercially from plating equipment suppliers and distributors like Palm International.

Or maybe they're 'anodic protection units'. Drives me crazy trying to remember which one you call them :-)

A. Robert,

I don't know if I understood your question , but what you are describing is the formation of metallic salts. If this is the case its not an electroless reaction. For a reaction to be considered plating, (either electrolytic or electroless) you must reduce the salts to the "0" valence state or metallic state. Please give more details to better help you.

A. Hi Bomook. Sounds to me like spontaneous plate-out. Electroless nickel plating isn't easy :-(

What is your tank made of? What brand and type of electroless nickel are you using? Thanks.

Q. Thanks for your answers.

Tanks made of PVC.

EL-Ni is alkaline ammonium-citrate type bath.

Thank you.

A. There are surely many things that I haven't seen that may still be fine, but I've personally never seen a PVC electroless nickel tank; I think polypropylene or cathodically protected stainless steel would be better. The baths I'm familiar with run about 185-190 °F. -- is your bath operating cooler than that?

EN will, of course, spontaneously deposit on any catalytic material. If the tank was not cleaned properly or was improperly filtered, that could be the problem. It could also be a chemical imbalance with insufficient stabilizer, but I'm not an EN chemistry expert. Is this home-brew or a commercial solution? If a commercial solution, the supplier's tech service people should be helping you start up this line. Good luck.

A. Some alkaline EN's, especially ammonia [on eBay or Amazon] based ones operate at a much lower temp. They are also more prone to self destruction if the stabilizer is not maintained in a perfect range.
How is the tank passivated? How often? A critical step, particularly as the tank surface get some wear or roughness.

A. The EN bath is alkaline and therefore working at R.T.
I think PVC is not bad for Tanks.
I found some clue for spontaneous deposition.
I observed cross-sectioned deposits with SEM and EDS.
As a result, Na, S, Cl, Ca, Pb, etc. is analyzed. Of course, Ni and P were measured. I think these are one of materials of rack coating. What do think of this? Does it make sense?

A. Alkaline EN baths for plating on plastics are designed to plate at room temperature, and may continue to plate at summer time ambient temperatures, especially if the filter pump is left running. May than likely the inside of the filter began plating, which consumed all of the stabilizers (the Pb and S in the EDS), which then allowed plating to continue in the tank.

In future, turn off the pump, cool the bath if possible, and replenish the bath to its normal range, before shutting down.

From a strength viewpoint, PVC is adequate for the tank for an alkaline EN bath. However, it is more prone to plateout than polyethylene or polypropylene, which are preferred tank materials.

A. I see some good advice in the other answers. However, carbon pack filters cannot be used for this electroless nickel, Carbon will remove a portion of the stabilizers and make the bath unstable.

A. Your employer needs to send someone to school on EN. If a tank needs to operate at pH 5, it should never be allowed to get to pH4. pH needs to be controlled to ±0.1 and no more than ±0.2 pH units.
Your problem was adding concentrated ammonium hydroxide in a large amount. You need to make several small diluted additions. What happened was in the area that you added it, the tank went supercritical and tried to plate out the nickel on everything. You artificially aged the solution, so instead of getting 6 - 10 tank turnovers you will get 4 -6.
A plater or the person that controls the tank chemistry, really needs to go to the vendors school. Typically 2-4 days.

A. James is right. EN is not chicken feed to control. You need to get more training. Something else, never raise pH when the bath is at its higher level of activity (a very large load just came in, you've just made other additions, some masking just failed and those surfaces are pulling metal like hell, etc.).

A. The standard for electroless nickel is bleaching the equipment with concentrated nitric acid. Have you tried it?