Problems with Bright Nickel Plating Baths

A. Billy:

This question about stardusting was asked in our forum and a electroplating chemist answered it. Here is his answer.

His problem, if he is using brighteners, could be:

1) excess brightener
2) insufficient leveler
3) insufficient carrier
4) pH too high
5) insufficient air agitation

Hope this helps!

A. Stardusting is sometimes caused by precipitation of calcium or magnesium salts in nickel plating solutions. Check to see if hard water is used to make up evaporation losses. The fact that it settles on shelf areas indicates that this could be the problem.

A. Make sure that your boric acid content is not supersaturated. You probably have boric crystals that are settling in your parts. A quick way to check is to take a sample of the bath in a beaker [beakers on eBay or Amazon] and let it cool to room temperature and if you see crystals forming fast like an hour or two then the boric is to high. To remove it simply cool your entire bath for several days with no agitation and simply scoop the boric acid from the tank bottom.

A. It is important to know how you are re-activating the copper before nickel plating. If your supplier does not find anything wrong with the nickel bath per se, it is probably in the activation/cleaning of the buffed copper. Also, this type of problem sometimes can occur due to high organics in the copper bath. A carbon treatment of the copper could solve this problem.

A. The fact that it is only on the top surfaces would indicate it is insolubles in the nickel tank. When the trouble occurs, take a liter and filter through a buchner filter funnel, rinse and examine the filter paper under low magnification. If iron contamination then will be brown ppt, if calcium whitish, black nickel sulfide etc. Check anode bags. Do similar check on outlet of filter to ensure there is nothing passing filter. Check air source for particulate contamination.

To check if the problem is coming from a source before the nickel, wipe one piece on a top significant surface just prior to going into the nickel and see if any difference between this and the part next to it

A. If you feel any roughness in the areas of a "stardust" more likely you are dealing with the solids: check your bags, filtration, PH, concentration of boric acid, temperature, condition of your racks(to eliminate contamination from previous operations), conditions of your air source, especially presence of oils and solids in the air. Also it's highly recommended to make the Hull cell test to see the area of C.D. where the problem appeals. If it's on a high C.D. area repeatably, then consider a possibility of high level of organic contaminations as well and full bath chemical treatment (hydrogen peroxide, 5.5 pH, carbon)would be necessary to perform. Also pay attention on the carbon dust like a source of organics and roughness from solids, so make sure the mesh of your filter cartridge is correct to halt any solids (I'm using 1 mkm).

A. First I would recommend to improve filtration. If the problem is mainly on the "shelves" it is probably a result of poor filtration. The second parameter is the quality of the water used in the plating solution and in the rinses.

A. Hi Enrique. The picture probably helps to confirm the problem you have in mind, but what you are finding unsatisfactory is not as obvious as you might think :-)

Are you the customer or are you from the plating shop? How big is the part, maybe 1" x 2"? What is it made of, cast brass? It's hard to judge/guess what you consider bad about this part based only on a low resolution photo --
1. There are several scratches.
2. There looks to be a grainy unpolished area near the lower right.
3. There may be blistering but I can't tell.
4. Photos can be deceiving but it looks like the part wants quite a bit more vibratory finishing before plating.

Tell us more.

Regards,

A. Hi Enrique. If the volume supports it, the parts ought to be plated on proper plating racks rather than simply wired. The best bright nickel plating requires a current of about 40 amps per square foot, and it can be difficult to get consistent bright nickel on parts that are flopping around on wire such that the current density varies; and small gauge wire may be limiting it as well.

I don't have enough experience to guess why the parts are discoloring a day later unless the nickel plating is just very thin in those areas for the reasons I mentioned. Good luck.

Regards,

A. Good day Enrique.

It might be a number of conditions which are responsible for the nickel plating darkness/thin deposit which turns grey.
Firstly, check for metallics, as they show up in the LCD area.
A quick fix/check would be to dummy plate at LCD 2-5 ASF overnight. Copper can cause LCD darkness.
Check bath concentrations and pH, making sure they are in operating parameters.
Excess brightener/insufficient carrier also causes poor/dark LCD coverage.
Organics can also cause dark LCD. Try carbon on your filters, but remember carbon removes brightener and wetting agent.
Try a hull cell panel to determine the solution after trying the above possibilities.

Hope this was helpful.

Regards,

A. Hi Kevin. The general idea of "star dusting", as you'll read on this thread, is micro-roughness due to deposits of tiny particles rather than pitting; so I'd agree with you at least that far. I wouldn't want to discourage anyone from trying to more precisely define it for you, but I think all you can really get is this "general idea" because when something starts out from slang it rarely gets more precise as it's bandied about in thousands of locations around the world. For example, Parthasaradhy .
claims it is peculiar to plating on plastics, but others certainly disagree.

I see the term used in at least 6 other threads on this site, and if you review them you'll see that some knowledgeable people may consider "shelf roughness" as stardusting whereas others agree with you that it might look like what shelf roughness looks like, but if you have shelf roughness, that's not stardusting :-)

Can you try a Hull Cell at a slightly higher or lower temperature to see if precipitation of supersaturated boric acid or other salts is less problematic at higher temperatures? -- not to solve the problem, but perhaps to indicate that it is an oversaturation problem? Did you try an elevated temperature carbon treatment, or just run the solution through carbon at 140 °F? Good luck. Hopefully someone who actually has experience rather than just book knowledge will chime in :-)

Regards,

A. Lyman,
STAR DUST PROBLEM
1) Check the part, it is roughness or pit
pits-- check surface tension of your nickel tank, maybe you need to be add wetter.
2) Check if your filter is plugged up or blew filter powder into the tank; clean the filter and repack.
3) Check anode basket bags, may be ripped, change the bags.
4) Check your incoming parts -- may be poor metal -- pits on part before you plate or parts are not cleaned good (compound left on part).
5) Parts fell in the tank so long -- pull out parts from the tank & clean the tank

A. Your Boric Acid concentration is too high for the temperature that you are running, and in air when the solution evaps, well, boric acid is white.