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topic 59491

Producing functional acid copper electroplating solution from vinegar



December 13, 2013

Q. Hello,

I'm a French hobbyist who just got started with electroplating, and am attempting to produce a functional plating solution from vinegar - that is, a solution that can effectively plate small items with high repeatability. Please find below a brief summary of my experiments and observations, and my questions.

Setup:
I started with 0.75 l white vinegar (8% acetic acid) mixed with a pinch of standard table sea salt, sitting in a roughly cylindrical glass vessel of around 10 cm diameter. The anode is a thick copper wire formed into a spiral, to ensure rough uniformity of the electrical field in all directions. I have used several cathodes - please read on.

Experiments:
I did not add copper sulfate to the vinegar, so I had to charge the solution in copper ions first. To do that, I used a 15V, 3A rectifier. A steel nail was used as a cathode, standing about 5 cm from the anode. The rectifier was then left on for about 5 hours at full voltage (15V). During those 5 hours, the current rose from about 10 mA to 600mA, and the solution became dark blue, which shows that the vinegar now contains ions. I know that steel cannot be copper plated - it just happened to be the first metal object I found, and the goal of experiment was just to charge the solution anyway. The nail got covered with a thick layer of a black, sooty, brittle copper deposit. Vigorous gassing was observed at the cathode - H2 production, a symptom of reduction at the cathode and basification of the plating solution.

I then decided to try and plate something - a brass nail, which can be copper plated as it is positioned adequately relative to copper in the redox chain. The nail was lightly sanded, and wiped. I didn't wear gloves, or wash the nail.
The aforementioned setup was used, with a tension of 1.75V, which resulted in a 10mA current. Very slight bubbling was observed, and after less than a minute a smooth, matte copper deposit was visible on the nail. I plated for 2 hours, then took the nail out to examine it. A reddish, powder-like deposit was visible, and could be removed at a single touch. No "soot". Below was a very thin layer of copper - a proof of principle for my setup.

Questions:
Using anything more than 10 mA results in gassing at the cathode, which is not ideal for smooth plating. I wonder why - the solution is dark blue, so should contain copper ions. Perhaps there are not enough copper ions in the solution? Or perhaps the solution is not acid enough (I am not equipped to test pH at the moment), or has lost too much acidity due to reduction? Or is the fact that the cathode was clearly not well prepared (no washing, etc.) enough to explain this behaviour? The layer produced in 2 hours is much too thin to be viable, and higher current would help, but I cannot achieve it at this time.
Also - what about the reddish powder? How can I avoid that? Should I clean the object being plated every now and then to remove the powder?

Thanks enormously for any pieces of advice and insights that you can provide me with!
Best regards from Paris,

Jeremie

Jeremie Marronnier
hobbyist - Paris, France


December 19, 2013

A. Hi Jeremie. With no means to measure the pH, what I'd probably do is mix 50:50 your plating solution and fresh vinegar. I suspect you consumed virtually all of the acidity of your original vinegar by applying 15 V to dissolve copper into it. Finishing.com's copper plating experiment was designed for grammar school children to illustrate the principal and was never intended to produce robust and functional plating. I don't think you can make a functional copper plating solution from vinegar, but don't let my negativism discourage you -- maybe you'll surprise us.

The question about whether failure to clean the materials or wear gloves was a problem is, unfortunately, unanswerable silliness: you've presented a huge completely uncontrolled variable which you simply must fix before continuing :-)

Regards,

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


December 19, 2013

Q. Hello Ted, and thanks for your reply. Here is follow-up information:

1. I now use gloves and wash the object to plate (soap and water, plus a quick dip in vinegar). As this point I cannot see any measurable difference, but at least it can be said that the object is more or less clean :)
2. I have measured pH to be around 4. As far a I understand proper pH for an acid copper plating solution should be between 3 and 5, roughly speaking. Is that correct?

Thanks again,
Cheers,
J

Jeremie Marronier
- Paris, France


December 19, 2013

A. Hi Jeremie. The Electroplating Engineering Handbook suggests (although this is for copper sulphate baths): "... powdery deposit: Check for low acid content, excess current, low temperature, low chloride content."

It's hard to say what is the right pH for an acetic acid bath (which doesn't seem to be covered by the standard literature), but fluoborate baths run from a pH of 0.2 to about 2.0, so it's certainly possible that your pH is too high. Again, I'd mix with half fresh vinegar (probably with pH less than 3.0) and try to bring the pH down.

Regards,

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


December 19, 2013

A. Hello Jeremie,
I just wanted to add a few comments. Because you are using acetic acid instead of a 8 - 10% v/v sulfuric, the Cu ion movement will be slower to start with. As Ted mentioned, your acidity dropped because you had to charge the solution with Cu at a high current density. On the subject of Cu ions, there is nothing in the solution to facilitate anode corrosion. Normally the chloride ion in acid Cu plating solutions is 60 - 85 ppm. Once the solution is charged with Cu and you go to plate at much lower current densities, you are not dissolving the Cu you need from the anode, and are relying solely on the ions in solution to plate. After hours of plating the Cu concentration in the bath drops so low that the deposition rate slows dramatically. The deposit you are getting is a result of low acid and Cu concentrations, and the lack of a chloride ion. One way to check how much Cu you have in solution is to weigh the Cu wire anode on a gram scale before and after charging the solution. This will give you the grams per liter metal concentration in your solution. Good luck with your experiments!

Mark Baker
Process Engineer - Malone, New York, USA


December 20, 2013

! Dear Ted and Mark,
Thanks again for your detailed replies. I should have stated up front that I don't question the infinite superiority of industrially made solutions (with sulfuric acid and brightener). I'm very curious about the process and those experiments are a good way for me to get acquainted with the chemo-physical processes involved in plating; and as a hobbyist I'm not (so far) extremely demanding about the end result.
Indeed, considering your answers it looks like my pH is too high. I'll try to dilute the solution as you advised, Ted, either with "industrial" (cleaning) vinegar, which has 14% acetic acid, or with a more concentrated solution, easily found at the chemist's.
The sooty deposit is probably the result of a combination of factors - low acidity, unstable concentration of ions, and too high a current for the ion concentration. Mark, what you say about very low currents not being enough to dissolve ions in the solution because of the lack of chlorine might explain another of my observations - that for a given experiment, the start current (i.e., what I get with a reference voltage), is always lower than in the previous experiment. It seems to indicate the solution cannot replenish itself properly.
I'll continue experimenting -- once again, as a hobbyist, I'm not after industrial quality, and it's much easier to deal with everyday products than to manipulate sulfuric acid when you haven't got a proper workshop to start with :)
I'll keep you posted on the next experiments.
Thanks again for your help and explanations, and since we're almost there, Happy New Year!
Cheers,
J

Jeremie Marronier
- Paris, France


December 23, 2013

thumbs up signHello again Jeremie,
Thank you for your last comment, Happy New Year!

Mark Baker
Process Engineer - Malone, NY USA


December 24, 2013

A. Old Weils potassium sodium tartrate bath:

150 gms potassium sodium tartrate
30 gms copper sulphate
80 gms NaOH
1 lit water
copper anodes

According to Ktehismus der Galvanoplasteik u.galvanostegie,Leipzig 1888.

Hope it helps and good luck!

Goran Budija
- Zagreb,Croatia

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