Small change is a big headache for many governments as the cost of producing a coin is often more than the coin is worth. A US five-cent nickel can cost up to seven cents to make, so the US mint and the National Institute of Standards and Technology (NIST) are working on a version of the coin that is 40-percent cheaper, but is still as tough as the old one and maintains compatibility with modern vending machines.

When coins were first invented, the principle behind them was simple. They contained as much gold, silver, copper, or nickel as the coin was worth and was stamped to prove this and to prevent clipping (cutting off some of the coin for the metal value) or counterfeiting.

Unfortunately, modern economics has turned this completely on its head. Today, a coin is essentially a promise of credit saying that the government of issue backs the worth of the coin. This means that mints spend significant time redesigning coins to reduce the amount of precious metal they contain to keep ahead of inflation and production costs while retaining their other qualities both practical and aesthetic. The latter is surprisingly important because the value of currency is heavily dependent on how much people trust it and a coin that doesn't "feel" right can have a real economic impact.

According the NIST, designing the new US nickel means not only keeping down costs. It also means making sure that it doesn't corrode, that the new alloy can take a sharp image, tarnishing is kept to a minimum, the coin has the same thickness as the old one, and that it has the same magnetic and electrically conductive properties, so it won't be rejected by the coin sorters in vending machines or bank counters. In addition, it has to conform to the US Mint facilities in Denver and Philadelphia.

The new design takes advantage of the NIST's 2001 Materials Genome Initiative (MGI) that's designed to speed up materials development while keeping down costs by using computational and IT tools. Essentially, this involved setting the desired specifications for the new coin, then reverse engineering them. This included addressing problems like making the color of the alloy match the current silvery sheen with not too much orange or yellow.

By trying to match the desired parameters using computer models that predict how various metals will interact with one another, the researchers came up with an alloy of copper, nickel, and zinc that is 40 percent cheaper to manufacture. This modeling also kept costs down by reducing the need to make experimental batches.

"Within a year, we were able to put together a framework for designing an alloy, identifying and using our model to get the correct alloy, and then moving forward and actually making the prototype, testing it out and finding out that we did meet all of our goals," says NIST project leader and materials engineer Eric Lass.

The team says that the process will not only save the US government millions of dollars, but also has applications in industry for more resilient electronics, as well as the ability to control the color of metal products.

Source: NIST