Nickel bath inexplicably quits plating

[jackf]

I have had my Nickel electrolytic bath go bad twice.. I plate only steel, brass, or copperplate. The problem starts out abruptly with black streaks appearing on the work.These seem to be rising vertically from the lower levels of the tank, as though some stratification has taken place. Shortly thereafter the solution stops plating. I have tried heavy plating on iron sheets to clean up the tank, but even with enormous currents plating is very skimpy or nonexistent. It seems strange that the ion bonds aren't broken with amperes of current, when normal plating takes only a few milliamperes. The ph I measure with a plant type ph meter runs 6 to 7, very acid.

I tried adding brightener but that was no help. I have to start a new tank each time. That works well for a year or two, then suddenly toggles over into this shocking condition.

The process I have worked out is to sandblast or polish the metal, Degrease it thoroughly with carbureter cleaner and rinse in near boiing water, pickle it for a few seconds in dilute Hydrochloric acid, rinse in flowing hot water and immediately put it into the plating tank with the current adjusted for approximately 25 ma per square inch of work surface. I normally allow 2 hours for a useful cosmetic plating and four hours for a hard work surface on tools.
any ideas? Thanks Jack.

[dadkar2]

There is some information needed that could help with your problem.

How large are your tanks?
How much volume do you run through your tanks? (how many sets of anodes have you gone through)
How many rinses do you use between your acid pickle and the nickel?
How do you create aeration in the tank; compressed air or pump?
How old is your brightener? Is it the NEW brightener or the old brightener? (I don't think the old brightener worked very well)

Ken

[dadkar2]

I re-read your post and noticed that you rinse in running water. Is it tap water or distilled?

Ken

[dadkar2]

Also...pH of 6 or 7 is not acidic. It is near center of the scale, or neutral. Your pH needs to run around 4 after adjusting the brightener level.

Your bath temp needs to run around 125F.

Are your anodes corroded or anode bags filled with gunk?

I could guess on...eg, boric acid content depleted...

But without more specifics about your process it would only be guessing.

If the tanks are small enough, eg a few gallons, it's just as well to start over. The cost of analyzing or guessing will eventually exceed the cost of a few pounds of crystals and some brightener.

You could put the solution aside with a heater boiling off the water till you get down to a level where the solution just starts to thicken. Don't reduce it past this point because it will get messy. Bottle that up and take it to a household hazardous chemicals collection site. If it is a few gallons they won't mind.

Ken

[mcaswell]

Black streaks = zinc contamination, probably from some steel parts that were, or had been at one time, zinc plated. Sandblasting these parts blasts the zinc particles into the steel, making it much harder to remove.

Plate a steel dummy to plate out the zinc contamination, then sandblast, acid etch in your acid tank, then blast again.

And of course, only use distilled water in all your processes to avoid possible contamination.

The pH of OUR nickel solution should be approx 4.

[dadkar2]

To remove zinc I keep a bath of old Pickle2 handy. Soak the parts for about 5-10 minutes in the old Pickle 2. Remove, scrub with a brass brush, then soak for another few minutes in Pickle 2. Then rinse, dry, and finally sandblast. Most of the zinc will be gone before it gets to the sandblasting. The acid will also remove some of the rust.

Also if you heavily contaminate your blasting media with zinc, then you will be dealing with this for a long time. Dump it and replace when in doubt. It's pretty reasonably priced.

That's my 2c. Any other suggestions welcome.

Ken