Questions about Immersion Plating / Replacement Plating

A. Hi Debra. You are describing "immersion plating" processes. You may already know that you can deposit copper on an iron nail simply by putting it in a solution of copper sulphate [on eBay or Amazon](this is sometimes demonstrated in science classes in school).

Similarly, you can deposit gold on almost anything, silver on almost anything but gold, and copper on almost anything but silver or gold by the same immersion plating mechanism. These metals are more "noble" than the "baser" or "more active" metals you deposit them on, and what happens is a little of the metal you are plating onto goes into solution, and in turn some of the copper, silver, or gold plates out of the solution. A term you could study to understand this is "electronegativity".

Actually, this is how most batteries work, too. The "anode" material plates out onto the "cathode" material, and generates voltage while it does. You can search youtube for "lemon battery" videos.

One limitation of immersion plating is very limited thickness because, as soon as you have a few atoms thickness of the noble metal completely covering the substrate, the base metal is no longer exposed to the solution, and the "battery" is dead, so the deposition stops. So the thickness you can deposit is very thin.

The suppliers of consumer products supply the safety information, and the government regulates those sales and the disclosure of the safety information, so I don't like to add or detract from it except with common sense info like urging you to wear rubber gloves [on eBay or Amazon] and goggles [on eBay or Amazon], and make sure you have good ventilation. Best of luck.

Q. Ted,

Thanks so much for your reply! I hope you don't mind me following up. I was kind of confused by your reply a little bit though. This is what you are saying (I think!).

When you say that you can't deposit silver on gold, or copper on silver and gold, do you mean you can't on real gold and silver, or anything with gold or silver finish? I know you're probably real busy, I hope you don't mind me asking. I really appreciate it.

Thanks,

A. Hi again. It makes no difference whether the item is solid silver or silver plated. In "immersion reactions" a more noble metal is deposited on a less noble metal by the mere difference in their electromotive potential because that comprises the "battery" to drive the reaction.

As soon as you open the question up to "electroplating", as opposed to "immersion plating" though, you can plate almost any metal onto almost any other metal (this is actually a slight simplification, there are a few problems and no-nos, but the point is that you are no longer limited to plating more noble onto less noble) because you supply the electricity to overcome the differences in electromotive potential.

A. Hi Erdem. I would say that "1" and "3" are the same thing.

I don't think I've ever heard the phrase 'under-potential deposition', so I'd like to hear it in context, but it sounds like the same thing.

Regards,

A. Underpotential deposition basically means that a metal is deposited on a surface/metal and the depostion takes less potential(Volts) that is naturally required to deposit the metal from the electrolyte to the substrate object.. For example to deposit Tin metal on Copper would take at least 0.200 volts(difference from their respective half cell potential), but how is this achieved? Outside sources or chemistry is used for example in the coating of Tin to Copper metal Thiurea is used to lower the half cell potential of copper and tin will deposit directly on Copper, but no displacement plating takes place.

I would like to add to your list another technique and is actually a very old one(1800's), but it has it's merit none the less, and that is what is called, "Contact Plating" where a noble metal comes in contact with a less noble metal and becomes the anode(negative charge) of the galvanic cell and the metal that is in solution starts to plate on top of both the less noble metal and the noble metal, I view this as nature's natural electroplating as it uses the metal and electrolyte electromotive force to drive a electrochemical deposition.

For example, coating a Silver Ring with Copper using a container, a steel plate and a solution of Copper sulphate. The Silver metal that is in contact with the steel plate is coated with Copper when the CuSO4 solution is poured on the container.

A. I would like to point out that further research on the underpotential deposition effect of Thiourea [on eBay or Amazon] on Copper metal has been researched as a Palladium chloride activator alternative on the Electroless Nickel process for Copper Circuit Boards,

Here is the most recent research on this:
http://www.cbe.buffalo.edu/people/pdfPub.jsp?id=3483

And while it only talks about Nickel, I am almost certain that other metals can be deposited (at least as seed layers), for example, Cobalt and/or Iron, Chromium