The Chemistry of the Loonie

But in Canada we already had a large, white metal dollar coin. And people refused to use it.

The solution: make a golden coin and make it smaller.

Sherrit Gordon Limited came up with the idea of using a nickel core and coating it with a copper-tin alloy to give the coin a golden color.

But how to apply the coating?
That's where chemistry comes in.
Sherrit already had a process for electroplating nickel onto a steel core. Why not, then, electroplate copper and tin onto a nickel core?

Back in the lab the chemists set to work to find out if this could be done.

They started by suspending a nickel plate in a beaker of alkaline solution containing copper and tin ions. Copper plates were introduced and connected to a direct current power source so that nickel and copper became cathode and anode, respectively, of an electrolytic cell. Under the influence of an applied voltage, copper and tin ions are attracted to, and deposit on, the nickel cathode.

As the researchers scaled up the process from the laboratory bench to commercial production, they determined that the critical components of the electrolyte were copper, tin, potassium hydroxide and potassium cyanide. They also found that not only were the individual concentrations important, but so were some of the component ratios, such as Cu to KCN and Sn to KOH.

The chemists invented a technique to ensure that the copper anode oxidation rate exactly matched the rate of copper ion removal from solution, and also to ensure that adequate current density was always maintained.

They also devised sophisticated analytical procedures and chemical makeup systems, including automatic titrators and X-ray fluorescence, to ensure rapid response to any change in the electrolyte composition. The whole process required an unusually high degree of control to meet the tight deposit composition range (11.4 to 13 percent tin, the remainder copper) that gives the optimum combination of color and resistance to tarnish and wear.

In 1986, Sherritt's copper-tin alloy plated nickel coin was chosen by the Royal Canadian Mint for the new dollar coin that was to bear the traditional Voyageur canoe design. But on the way to the Mint in Winnipeg the coining dies went missing. To avoid counterfeit coins turning up in future, the Voyageur dies were scrapped and another design from the Mint's archives was chosen--the loon. And on June 30 1987 the first loonies saw the light of day.

Sherritt now has a patent for this unique use of copper-tin alloy as a surface cladding for coins.