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"Chemistry of the Loonie"

March 10, 2010

I am doing a research project on the Chemistry of the Loonie. As I am in Chemistry AP, many people cannot help me.

As far as I know, a Loonie is made of a nickel core and is electroplated with copper first, then tin to prevent corrosion. However, I do not understand how this occurs! Is the copper ions in an electrolyte solution, while tin is the anode, and the nickel core is the cathode? If this is the case, does this reaction require an external power source such as a battery?

What I am interested in is how the tin is plated to the copper. Also, I would be interested in discussing the half and net reactions involved in coating the Loonie.

Loren C.
Student - Edmonton, Alberta, Canada

March 11, 2010

Hi, Loren. The Royal Canadian Mint in Winnipeg is open for tours, but whether you could see the plating is another issue :-(

My understanding is also that the core is nickel, but I believe it is plated with bronze (copper and tin alloy) rather than copper and tin in sequence. This is probably more for appearance than corrosion resistance. Yes, an external power supply is necessary to drive the deposition of bronze onto nickel. The nickel blank is indeed the cathode. Presumably there are both tin and copper anodes involved because in a production process like this, having one of the metals dissolved only as a salt would mean that the operation is not an equilibrium process and would require extra maintenance to keep in balance (but I have not seen RCM's operation).

The reactions are fairly simple: the copper and tin are ionized at the anode into positively charged ions which migrate through the solution to the cathode where they meet up with their electrons and are reduced back to metal. Sorry, I don't know the oxidation state of the two metals while ionized because I don't know what the bronze plating process is, and the metals may ionize at different oxidation states depending upon that.

The nickel core is soon to be replaced by copper and nickel (alternating layers) plated steel.


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

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