Thickening shaped metal foil by electroplating

[TSTwizby]

I've been looking into information about doing this, but the specificity of my question makes it difficult to effectively research.

I want to take metal foil, preferably something easy to find online or in a store as 36-gauge (.005") or thinner, though not thinner than typical household aluminium foil, and coat it on both sides with tissue paper. From experience, I know that this can be easily folded into various shapes without tearing the foil, as the tissue feels most of the strain from folding and softens the metal's creases. After folding it into a particular shape, the outer layer of tissue is removed by soaking in a solvent and scrubbing lightly, leaving a clean metal surface along the outside of the shape. I then want to thicken the outer layer of metal, preserving the details of the folded shape as much as possible, so that it will no longer easily deform.

My current plan uses copper foil (38 gauge, which is too thick, but is serviceable as a proof of concept). I attach the tissue paper using diluted white glue, clean the tissue and glue off using acetone, and then plate in a solution of citric acid and copper sulfate. This results in a very fast, noticeably thick coat on the copper foil, but it is somewhat uneven and tends to rub off easily. I believe that this is at least in part due to a thin coating of plastic on the foil, most likely intended to prevent oxidation of the surface, which my current preparation method does not completely clean off.

Does anyone have suggestions as to other things that might be causing my difficulties, and possible ways around them, or else reasons why this is unlikely to work no matter what I do?

 

[bdd4]

I worked as a Quality Control Inspector for the U.S. government and had assignments that require me to witness electroplating processes being applied to a product being sold to the government by a company. What I recall is that an item to be plated went through a cleaning process before the plating process.
I suggest a couple of things: (1) Call a plating company and ask them how to clean, (remove the protective coating) on the material you plan to plate,
(2) Buy shim stock which comes in the thicknesses you are working with and even perhaps thinner, from a metal supply company. It is possible it is not protectively coated. Even if you are not in the U.S.A.you can check online with a company I use when I need project materials. The company is McMaster- Carr. Just do a Google search for their exact URL. I hope I have offered somethings useful.

 

[herm0016]

bdd is correct. before plating you will need to clean in something strong, parts are usually dipped in acid, then a neutralizing agent, then a rinse stage. what are you using for a power source? You should be able to plate copper from CuSo4 using a small dc power supply and nothing else in the solution. 6v lantern batteries work well, or get a small adj. supply from a science supplier or http://www.goldmine-elec-products.com/ arrange the copper strips around a bowl and put your part in the center to be plated.

ex: http://cheserver.ent.ohiou.edu/ChE455/ChE455web/Lab_Sessions_files/EH2-Plating.pdf

 

[TSTwizby]

Thanks for the recommendations. I had not heard the term 'shim stock' before, which should make getting material much easier.

What I've done so far has just been with ordinary 1.5V AA-batteries, which is plenty for the fairly small-scale work I'm doing.

I've gotten some conflicting information about what to clean the copper with, some people are saying just acid and some are saying just a solvent. I'm pretty sure the copper is coated with a thin layer of plastic, which suggests to me with my limited experience that I should first use a solvent and try to scrub the plastic off and then clean with acid to remove any surface oxidation.

 

[herm0016]

a higher voltage will be better, plus you will get more current out of a lantern battery. I would find some stock with no coating. it may even work better to plate stainless or aluminum with copper. stainless will be stronger in the long run. I'm not sure of the difference using dis-similar metals and similar metals.

another thought: if it was plating evenly across the surface, the "coating" must be conductive. if it was a plastic coating, you would get bubbles only around the edges. are you sure its not the citric acid? it would seem like this would make the Cu+2 ions into CuO+ ? not sure on my charge balance. the CuO would not stick to the CU nearly as readily as the Cu+2.

 

[TSTwizby]

That's a good point about the coating, I did not notice an especial excess of activity around the edges of the foil. That said, whatever it is, it does indeed seem to prevent the copper from tarnishing. Perhaps more investigation is necessary.

In any case the suggestion about getting new uncoated foil is certainly one I will act on. I'm unfamiliar with stainless steel plating, but the problem with plating aluminum is that without using dangerous and difficult to acquire chemicals (mainly cyanides) the oxide coating that invariably forms on its surface makes getting a stable plate almost impossible.


Could you explain some of the chemistry behind the Cu+2 -> CuO+? I'm having trouble seeing why that would be more likely with citric acid than with other acids. Unless it's just because, as an organic acid, to pull off an O it just needs to spit out water and CO2? In any case, I used it because it does a very good job of cleaning pennies, which would seem to suggest that it would inhibit oxide formation, but I'm far from an expert.

 

[herm0016]

i am not well read in chemistry.

it seems that a more simple acid would be better or none at all in the solution.

i do know citric acid will bind to metals in this process: https://en.wikipedia.org/wiki/Chelation
https://en.wikipedia.org/wiki/Citric_acid

and is used for this process on stainless:
https://en.wikipedia.org/wiki/Passivation_(chemistry)

 

[DrDoug]

Something up my old alley! I used to manage the plating baths at a shop many years ago. Proper metal prep is key to a good plating job. After mechanical cleaning/polishing, the old shop I worked at used 'forward current' (as if plating) while the part is immersed in a sodium hydroxide-based cleaning bath, followed by thorough scrubbing and a two-stage clean water rinse. This is followed by a 30 second soak in hydrofluoric acid (seriously toxic stuff). After another two-stage clean water rinse, if the item is copper and needs more copper then it is sent off to the acid copper tank for plating. This tank used high purity sulfuric acid and copper/phosphorus anodes. If a metal is problematic for initial plating we would use a copper "strike" bath of cyanide and pure copper anodes, then send it to the acid copper bath.

While proper metal prep and bath purity/volts-amps are some of the problems you will face, a bigger problem is that metal deposition in plating is not uniform. A large part of this is that metal doesn't like to deposit into deep draws or areas not directly exposed to the anodes. You can get good plating results if your part isn't too complicated and all sides have exposure and are fairly equidistant to the anodes.

Just thought I would toss out some industry info related to electroplating, I hope it helps you understand the issues related to it. Good luck!

That's a good point about the coating, I did not notice an especial excess of activity around the edges of the foil. That said, whatever it is, it does indeed seem to prevent the copper from tarnishing. Perhaps more investigation is necessary.

In any case the suggestion about getting new uncoated foil is certainly one I will act on. I'm unfamiliar with stainless steel plating, but the problem with plating aluminum is that without using dangerous and difficult to acquire chemicals (mainly cyanides) the oxide coating that invariably forms on its surface makes getting a stable plate almost impossible.


Could you explain some of the chemistry behind the Cu+2 -> CuO+? I'm having trouble seeing why that would be more likely with citric acid than with other acids. Unless it's just because, as an organic acid, to pull off an O it just needs to spit out water and CO2? In any case, I used it because it does a very good job of cleaning pennies, which would seem to suggest that it would inhibit oxide formation, but I'm far from an expert.

Regarding plating aluminum, we worked out a process where we mechanically cleaned and polished the aluminum, then dipped it in nitric acid for 30 seconds and followed that with a flash of acid nickel plate. Once we had it flashed with nickel we rinsed it and sent it off to the acid copper bath to put a bit of metal on it and then we treated it like any other process after that.

No cyanide bath necessary! One of our test subjects is still under the hood of my car (an aluminum buck tag for my Ford Mustang). I also did my aluminum ignition key but I wore the lock cylinder out years ago and have since replaced it.

 

[mindless1]

a higher voltage will be better, plus you will get more current out of a lantern battery.

Lantern batteries of the common chemistries ("Heavy Duty" or alkaline) may have high Ah ratings but their internal resistance make them incapable of as much current as 4+ x AA NiMH, NiCd, or 2 x Li-Ion.

For example an Eveready (4 x F-cells, let alone the stingy 4 x D-cell designs) alkaline lantern battery Ri is 0.9 ohms (@ 70F temp) with voltage dropping rapidly at a mere 300mA.