Tank material for electroless nickel plating: polypro vs. stainless

A. Hi Arif. Electroless nickel would immediately plate out onto a metal tank. It can be difficult to clean a lined metal tank to prevent seed-out, but some platers like to use disposable drop-in liners. Polypropylene is a widely-used material for tank construction. A more complex approach is a stainless steel tank with an electrolytic protection system which prevents the nickel from plating out on the tank walls. Good luck.

A. One of my first jobs in the plating industry, 35 years ago, was as the production chemist for a Kanigen electroless nickel licensee.

All plating was done in passivated stainless tanks. The 4200 gallons of solution was kept unheated, at night, in large plastic holding tanks. These tanks were piped (using pyrex glass tubing and fittings) to a large number of empty SS tanks of different shapes and sizes. In the morning, only those tanks were filled that accommodated the particular size and shape of the parts that we were running that day. The solution was steam heated and operated at about 200 °F. At the end of the day, the solution was returned to the holding tanks and allowed to cool. Next, 20-25% nitric acid was pumped into the SS tanks that were used during the day. The nitric both passivated the stainless and dissolved the small amounts of nickel that had deposited on the tank. When finished, the nitric was returned to its holding tanks and the SS tanks were well cleaned and rinsed and made ready for another day's work.

The electroless nickel solution life was about 30 days. Things usually went well, with little or no plating on the tanks. If a part was dropped, it could break the passive coating and localized plating would occur. Suspended particles, usually due to filtering problems, could make the tank plate. Sometimes the brittle nickel would flake off of the hanging wires and cause the tank to plate in local areas. When the bath got old, it got more critical and, if not properly controlled, a pH slightly out of adjustment could make the bath totally decompose, spontaneously.

Some of the more modern baths may not work using the above system.

A. The biggest negative of stainless is heat transfer and if the solution ever starts seeding out, it will rapidly self destruct the tank.
The biggest drawback of polypro is the physical damage to the interior by racks and parts which will cause the tank to require longer and more frequent nitric acid strip vs a really nice polished interior. A poly pro tank will last a long time, but as it ages the welds tend to crack and bear close inspection. They also will not take the exterior abuse that stainless will.

All of that said, my vote goes for a very well constructed PP tank.

A. Stainless tanks are stronger. In theory, they can be passivated so EN will not plate on them. In practice, theory doesn't always work, and you may have some baths plate out on the walls.

EN temperatures are at the high end for polypro, and tanks may warp or leak unless carefully designed and constructed. EN can sometimes plate out on poly too.

The best idea, IMO, is a stainless tank with drop in disposable liners. They are cheap compared to losing an entire bath due to plate out, and they can be turned inside out and used twice.

A. Thanks James; thanks Jeffrey. One more alternative is an electronic cathodic protection system where an electric potential is impressed on the stainless steel tank to prevent plate-out.

Regards,

A. Hello, Mike. Like James, I prefer a well-made polypro tank overall, but it's not by a very big margin. A stainless tank with a well-designed cathodic protection system or a stainless tank with a disposable liner are also valid. More often than not, the choice comes down to what you are accustomed to and shops tend to stick with the method that they start with.

A. I use S/Steel tanks with a lab rectifier, I make the tank anodic and I had a rod to the tank making it cathodic. then I pass 1- 3 amps to it, where this prevents the tank from plating, and saves chemicals

A. Hi.
If you prefer to have stainless steel, though your tank is protected by making it anodic, it is better to have another tank as a spare with transfer facility. In practice if tank starts getting plated, then you can't just stop it, except reducing the temp / transferring the chemicals so you may lose the costly chemicals ... Also please consider the temperature while using the transfer mechanism.

Regards,

A. Hello, Ty.

Sorry, I don't know the details of designing those electrolytic protection systems, but I do know that they are commercially available from suppliers, such as Palm International. Good luck.

Regards,

A. Although there are many things that could have happened, like what you mentioned, here's a few of my thoughts. (I'm not the greatest expert in electroless nickel chemistry.)

Are you home-brewing your own Ni-P bath, or are you buying an over the counter product? If over-the-counter bath, make sure you are making it up in the proportion specified by the manufacturer and not too strong in nickel or hypo. Ensure you are using the components specified for the make-up and not the hypo solution for additions. Usually the stabilizers are primarily included in the make-up chemistries, and not the additions so the bath doesn't become over-stabilized (which is obviously not your problem.)

When you plated out the bath the first time, did you make-up a new bath? or did you just add hypo and nickel. If so, you may have lost your stabilizers the first time and if you didn't make them back up, you were doomed to plate out again.

Lastly, are you cooling off the solution when there are no parts in the tank?

Best wishes.

Art

A. Hi Chandrashekhar. When you say the solution collapsed, are you saying that you suffered spontaneous plate-out? If so, it may not be a problem with the process solution, but with the tank or some operation. As you know, once electroless nickel starts plating out it keeps going. What is the construction of your tank? Is it possible a part dropped? Was any specific employee involved in all three incidences; does the fault correlate to a specific time of day where some particular operation is involved like a filter startup?

Regards,