Micro-Pitting on Cosmetic Duplex Nickel Chrome Plating

A. Dear Mr Charlie,
This could be on account of imbalance between the wetter and the brightener in your bright nickel bath. If the wetter or additive as it is called in India is depleted, then air bubbles will stick to the metal surface on account of the brightening agent not dissolving in the plating solution fully and making the parts slightly sticky which causes the air bubbles to stick. Try using 1 : 2 or 1 : 3 of brightener to wetter ratio.

An afterthought. Just look into your filtration once again by passing the solution thru Whatman filter in your lab and check if the filter is doing its job. Collect some solution from the discharge end from your filter for this purpose.

A. Charlie Peck,
you have micro-pit problem, I would like check surface tension in your nickel bath. Then prior to bright nickel rinse tank or sulfuric acid tank, wipe the tank wall with wetter and rinse & vacuum. Run the hull cell to duplicate the problem. If after you run the hull cell you cannot find micro pits that means the problem in your tank or parts. When did you change the anode basket bags, sometimes bag material is bad. Make sure bags are wash, and leached with 5% sulfuric acid & small amount of wetter, and washed again.

A. If you have a pitting problem it is more likely to come from another reason rather than chromium but you should find and eliminate your cause of this much chrome contamination. Give more detail as to where on the part pitting occurs, type of bright nickel, pretreatment, treatments you have done on your bright nickel and the improvements or otherwise that you have observed. Common causes of pitting, i.e., holes/depressions in the plate rather than fine speckles; stardust are usually organic in nature: organic contamination, high brighteners, cleaning problems, poor agitation, etc.

A. What base metal are you depositing your nickel over? And is there any other metal layered between the base metal and the nickel? What is the shape of your articles, and are they tubular? The source of your chrome contamination could be chrome trapped under a jig coating if you are using jigs. But as an old time plater who has battled with the quality of Iscor so called "Bright Cold Rolled" steel, this is your base metal; the pitting you describe is possibly the "orange peel" often found in the Iscor product.

Hope I helped a "Gautie"

A. It is difficult to trouble shoot from this distance without seeing the parts or setup. What treatment are you using to treat for chrome? How long is it okay after treatment? Is the stardusting all over? Can you reproduce in a lab plating test, Hull cell or bent cathode. Stardusting is usually particulate rather than gaseous and extra non-pitter should make a difference if it was due to hydrogen.

A. Dear Mr. Ang,

What kind of agitation do you have in your Nickel bath? If you agitate the bath with air, do you use an oil-separator?
For a better investigation you should check your parts directly after nickel-plating. Also you should check, that the pits might come because the design of the party does not allow that the hydrogen/air (from agitation) can escape.
Before the chrome process sometimes it is better to have a low-current chrome activation to solve the "white-washing" effects, depending on base material and process.
What kind of Chrome electrolyte do you have (wetting agents, etc.?).
Did the base material get polished before plating?

Kind regards,

A. Dear Mr.Ang,

What can you do in order to remove all the organics and also the oil, is after the first degreasing you put one bath of static rinsing with normal city water, in order not to pollute your cascade rinsing bath. This one is better then directly go to the cascade rinsing.
The problem by using DI water for the pretreatment process is that it's not too powerful to remove the organics or oils on the parts. It would be better to use the normal city water for all the pretreatment process. The usage of DI water is better for the rinsing just before the plating and also for the post-treatment.

Hope it might help

A. Hi Rick. We assume you can see this defect after nickel plating and before chrome plating? Can you send a picture of it?

I think most platers restrict their use of the word "stardust" to a haze or very fine roughness in the high current density areas. Pitting would seem to be something different, and my first question would be whether the pits are hemispherical and shiny (gas pits / hydrogen pits) or something else.

This is an unusual problem and my first inclination would be to think that either the steel parts are a different size and are receiving a different current density, or zincate contamination is screwing up the steel pretreatment.

Regards,

A. Hi Anthony. Sorry, I don't know the root cause. But even though I don't know why, I suspect it can be solved by copper plating the brass before the nickel plating.

Luck & Regards,

A. Anthony,

Pitting or stardusting is typically caused by a few things that can be identified with some simple tests. If you're able to plate in a hull cell that would speed the troubleshooting up exponentially. First thing to check with pitting is the surface tension, if its too low add wetters. If surface tension is not the issue then it could be dissolved iron in the bath causing the stardusting and iron precipitants can allow that to be filtered out of the bath or complexed so as not to solve an issue. Now if you're seeing roughness as opposed to pitting then you could have particulate in the bath. Anode bags should be checked for rips, agitation discharges should be checked to see if they are kicking up any particulate, and the bath should be filtered either way. Typically particulate will settle on "shelfs" or surfaces that are horizontal to the bottom of the tank and allow particulate to settle.