Passivating electroless nickel tanks; anodic protection

A. Are you using a passivation system in conjunction with the tanks? If you do - When was the last time the connections were checked?

Also, how old is the nitric tank strip? An overload of nickel can hinder its passivation ability.

There is a long list of items to check, including your heating (electric, steam), where the tank seems to be plating out from (sides of tank, heating coil), what is your pH operating range? Have you checked to see if you have an overabundance of hypophosphite?

Also if you have inexperienced platers and they have parts touching the sides of the tank, that will overpower the anodic passivation system and cause the tank to plate out.

A. Hi M. It looks like you already know this, but I'll say it so that newbie readers don't get lost ...

Electroless nickel plating is "auto-catalytic", which means the solution will plate out onto any nickel it sees. So the purpose of the nitric acid is not only to passivate the tank, but to dissolve & remove any nickel which has deposited on it. To the best of my knowledge citric acid will not dissolve the nickel and therefore cannot be substituted for the nitric acid.

Luck & Regards,

A. Hi Paul. Apparently there are actually two explanations and two approaches.

• The first and older approach is called 'reverse plating' where sufficient current is impressed to simply prevent plate-out. But this reputedly can etch the stainless steel and contaminate the solution.
• The second approach is to use equipment to apply just enough current to keep the stainless steel properly passivated, i.e., to keep it permanently in the state that nitric acid passivation puts it in, not enough current to actually function in a reverse plating mode.

I am not knowledgable enough in electrochemistry to say whether the difference is real & significant or whether it is just sales pap & bamboozlement, but we don't like to praise or slam brands & sources anyway ( huh? why?). Instead, I suggest that interested parties read this article by Ron Duncan (dec.) and decide for themselves :-)
https://nanopdf.com/download/anodic-passivation-of-electroless-nickel-plating-tanks_pdf
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. The purpose of the anodic protection unit is to prevent plate-out onto the tank, and it should have detailed instructions for how to set the current to do so.

Such units are, I believe, available from Atotech and Palm International, and probably others.

The usual idea behind leaching is to expose the tank material to a solution which has the same capability for absorbing contaminants as the working solution will have, but for the leaching solution to not introduce any new contaminants to the working solution. So room temp or slightly warmer nitric acid sounds good to me--but why not just go ahead and follow a QQ-P-35C [link is to free spec at Defense Logistics Agency, dla.mil] nitric acid passivation procedure on the tank itself.

Regards,
and good luck.

? Paul, Have some of your answers and many of the same questions? Your note is one year old. Do you still need a response? Am in the disc drive industry. 316 SS anodically protected tanks. Using Kikusuis, Daisy chained to walls, spargers, intakes, heaters, etc. Need defect correlation to anodic (mA) readouts. You still there?

Dan

? Paul,

I have just read your message dated, and I have the very same questions. Did you receive any responses to your queries. If so would you care to share them with me.

Regards,

A. Hi, Paul. For many years polypropylene was considered the best material of construction for electroless nickel tanks. But more recently most people think stainless steel is better because you can prevent spontaneous plate-out by applying a charge that is sufficient to stop the autocatalytic reaction. You probably could build such a system yourself, but specialists like Palm International and Atotech offer systems tailored to the purpose.

If you search the site you'll find a number of threads about stainless tanks for electroless nickel plating. Good luck.

Regards,

A. Jim,

That's a rather weird question of yours (pardon me, I should have said 'strange' as the previous appellation sometimes upsets people).

If your stainless is starting to corrode, join the club!

Perhaps the only thing to do, and I can't swear that it will work, is to scrub it with nitric. That might bring back the sheen or some of it. After all, stainless is not supposed to be attacked by nitric.

But I have a question ... why in the heck did you use stainless steel when there are so many GOOD plastics and even some GOOD fabricators of them, too?

Cheers !

A. Hello, Mr. Wyrough:

I assume you are using an anodic passivation system. You probably should contact the supplier of that system as there certainly could be a relationship between etching of the stainless and the operation of the anodic passivation system.

Freeman:

Electroless nickel can spontaneously "plate-out" onto plastic vessels. It is true that polypropylene tanks were very widely used for electroless nickel, but there has been movement in the direction of using stainless tanks with anodic passivation instead, because it purportedly reduces the likelihood of this spontaneous plate-out. If even a minuscule amount of nickel inadvertently plates out onto the walls or bottom of a polypropylene tank, that nickel acts as a catalyst for further deposition, and you have a chain reaction that spontaneously wastes the tanks contents.

A. An iron buildup in your EN is very probably more from the part rather than the tank. If the tank is pitted, it is nearly impossible to passivate and polishing it out will be nearly impossible. Brush electropolishing it would work, but it is not practical on large tanks. You can buy a new tank for what it would cost to set up to electropolish it via normal methods. If it is already pitted, I have some serious doubts as to how well it would work.

Several companies make thin poly liners for standard size tanks. They are not cheap, but are a lot cheaper than a new tank and eliminate nitric passivation and subsequent waste disposal, so are not a bad economic choice.

Last choice, consider putting in a fabricated 1/4" polypropylene liner using your tank for support. Remember to use a sloppy fit as poly expands roughly ten times more than most metals and 70 to 195 °F is quite a large temp difference, especially since the SS tank will never get that high with a liner in it.

A. Have you tried ammonium citrate passivation at pH 3-3.1 10% W/v citric acid solution adjusting the pH to 3-3.1 with ammonia [on eBay or Amazon] water stronger using only deionized water for the solution. Heat the solution to 80 °C and circulate in the tank for 6 hours then rinse well. Clean the tank first with hot solution of 5% W/V TSP [trisodium phosphate [on eBay or Amazon]] for 1 hour at 80 °C rinse well.

Do you see any discolouration of the Stainless with this Ferrous/Ferric solution? You could also try a HF/HNO3 solution on a section of the tank to see if this most rigorous method of passivation will have the desired effect.

If this works I would then try the milder method mentioned above first.

A. PASSIVATION IS A TERM APPLIED TO SURFACES WHICH ON THE CONTRARY COULD BE ACTIVE, LIKE METALS. IF YOUR TANKS ARE MADE OF THE SUITABLE PLASTICS (E.G. POLYPROPYLENE, KYNAR, ETC.) YOU WILL STRIP THEM, NOT PASSIVATE THEM, AS PLASTICS ARE BASICALLY INERT TO E-N CATALYSTS.

WHEN VERY FINE PARTICULATE ADHERES TO THE SURFACE OF PLASTICS WE USE THE TERM SEEDING WHICH IS NOT EXACTLY ACTIVATING BUT IMPLANTING METAL PARTICLES THAT COULD BE ACTIVE AND INITIATE REACTION.

WHY SOME TANKS REACT AND OTHERS DO NOT COULD BE RELATED TO DIFFERENT ACTIVITY IN THEIR SOLUTION, PRESENCE OF MAGNETIC EQUIPMENT NEAR THE TANK, HOT SPOTS, AND A NUMBER OF THINGS THAT WOULD BE IMPOSSIBLE TO DEAL WITH THRU THIS VIA.

GOOD LUCK.

A. Sorry, Mr. Bac, I don't personally know. Did you make this yourself, or buy it from Atotech, Palm International or another electroless nickel specialist? Those commercial units come with instructions, and maybe you can find those vendors' instructions on the internet. Good luck.