How to do copper plating
Q. I'm an absolute beginner in electroplating. I would like to copper some iron pieces (plate, pipe); so I've turned or filed to the desired dimension and shape. I've prepared a solution of copper sulfate [linked by editor to product info at Amazon] CuSO4 (
200 g/l) and H2 SO4 (
5 g/l) in water (deionized). When I've used this solution with a copper wire as anode and with 10 mA/cm 2 as maximum, the result was very bad. A lot of copper has deposited on iron but rinsing it under water-tap the copper goes away. So I've reduced current density also to zero: if I put iron in the same solution the result is the same: a lot of copper badly attached on iron, and under the copper the iron was oxidized (dark color).
Further attempts (current density between 0 and 100 mA/cm 2 ; no H2 SO4 or more than 10 g/l; CuSO4 from 50 g/l to 200 g/l) have produced the same result: I've also tried various polishing by inorganic (HCl, H2 SO4. NaOH) and organic (tetrachloroethylene, turpentine, Acetone [linked by editor to product info at Amazon] ) solvents. Temperature of bath has always been around 18 °C. Only if I put iron pieces in the bath for few seconds and then rinse it, I can get a very very thin copper deposit (I was not able to measure it with .01 mm caliper) that's well attached to iron, but it's so thin that it isn't useful at all.
Where am I wrong? Many thanks in advance.
A. Hello, Lapo. If you (or a reader) wish to demo copper plating for a school science project, we have an FAQ: How Electroplating Works . that will give you easy instructions for the project.
But sorry, your approach won't work for functional electroplating applications because copper is more "noble" than iron and will (as you saw) deposit on steel or cast iron without any current applied. This is called an "immersion deposit" and it usually has virtually no adhesion. Still, make sure that your component is absolutely clean (waterbreak-free) and that current is applied to the part before & while it goes into the plating tank ("hot entry") because that will help a little towards discouraging immersion plating.
The preplate cleaning should consist of caustic cleaning (detergent and NaOH) followed by an acid dip (HCl). But for onesy-twosy work you can scrub the part with a tampico brush and powdered Pumice [linked by editor to product info at Amazon] as an alternate to caustic cleaning, and use a diluted HCl for activation.
For functional copper plating on steel you need to either electroplate an initial layer from a nickel strike bath, or from a copper cyanide (very dangerous poison) bath before you will be able to use the copper sulfate bath; these will
not immersion deposit. You probably will be best off with proprietary additives (brighteners) to get good, bright, plating.
Electroplating involves working with very hazardous chemicals, so it may not be an ideal casual hobby. If your desire is simply to get copper plating on the parts, as opposed to doing copper plating as a hobby and learning experience, plating is a jobshop industry and there should be a commercial plating shop available in your area. Good luck!
Ted Mooney, P.E. RET
Pine Beach, New Jersey
A. It is not something you would let children do without supervision, and some people might not find it impressive, but I did find a way to plate coins with copper metal. If you insist on trying to plate outside of an industrial environment, at least you won't be using concentrated acids, metal salts, and etc.
I tried to find a way to do this using only nontoxic chemicals (aside from the copper itself), but I needed to use some ethylene glycol. This stuff is toxic, has a sweet taste (or so I am told), and pets and children might be tempted to taste it, so it must be handled by adults and stored in locked cabinets. On the other hand, anything containing copper is not good to drink, and there is enough salt in this solution to act as an emetic.
All of these tests should be done under adult supervision, and the learning experience is bound to be better this way. Depending on the age of the witnesses, you can cover all sorts of exciting things, from cleaning coins with toothpaste to chemical calculations of normality and concentration to electrochemical equivalents. Except for the brightening agent, all other supplies are household items. The ethylene glycol should be stored in childproof areas, and the test solution should be dumped at the end of any experiment. All containers should be labeled, even as you are using them, as a matter of normal laboratory practice.
The solution described is low in the concentration of copper, as far as plating solutions go. If all of my electrolysis converted my copper anode to copper ions, and all of it ended up in the sewer we are talking about:
e =i x r
1.5 =i x 15 ohms
i x 15 = 1.5
i = 0.1 amps
If you run the cell for 2 hours, that's 0.2 ampere hours. Looking up cupric ion, we see that we deposit/dissolve 1.19 grams of copper metal per ampere hour. So the most we could dump down the drain is 0.24 grams, not an ecological nightmare. The final concentration of the cell of 100 cc, after 1 hour of electrolysis, could reach 2.4 grams/liter (this is unlikely, as gassing is very evident, indicating that we are not operating at 100% efficiency).Source: www.finishing.com