Exploring the Grain Size of Ferrous Coins

By Taylor Haddix & Alex Bodulow

The History of Coins • Coins were first introduced as a currency around the 5th

or 6th century BCE

• The first coins are speculated to have been minted on the Greek island of Aegina.

• They were first made with electrum, an alloy of silver and gold

• Electrum was typically 55.5wt% Au and 44.5wt% Ag

• Coins have slowly been fading out due to paper money

• In the mid 2000’s their were more than $1billion in dollar coins in the US Federal reserves.

How Coins are Made TodayHow It's Made• Material is cold worked into long strips• Blanks are punched from strips then

annealed• Blanks then go though rimming

machine that presses the edges flat• Finally blanks are pressed

500 Lire(Italian)• 500 lire = 32 cents in US Currency• Core: Aluminum-bronze alloy• Ring: Stainless Steel

1 Peso(Mexican)• 1 Peso = 0.073 US Dollars• $1 Nuevo Peso = $1000 old Peso• Core: Aluminum-Bronze• Ring: Stainless Steel

Two Pence(British)• 2 Pence = 3 Cents in Us Currency• Often pronounced two pee - is a unit of currency

equaling two one-hundredths of a pound sterling• Copper plated Steel

5 Cents(Canadian)• 5 Cents Canadian = 4 Cents Us Currency• Smallest valued coin in Canadian currency• Coins are now made of Copper-Steel ally

plated with Nickel• 94.5wt% steel, 3.5wt% copper, 2wt% nickel

plating

5 Peso(Mexican)• 5 Peso= 37 Cents Us Currency• Peso means weight in Spanish• Core: Aluminum-Bronze Alloy• Ring: Stainless Steel

Semester Project - Outline

Materials & Techniques

• We used two different etching solutions:

• For coins 2, 3, and 5 – 1 Peso, 2 Pence, and 5 Peso – the grains were exposed best with the H20, HCl, FeCl3 solution.

• 10 parts H20, 5 parts HCl, 1 part FeCl3.

• For coins 1 and 4 – 500 lire and 5 Canadian cents – the grains were exposed best with the ethanol and nitric acid solution.

• 95% ethanol 5% concentrated nitric acid.

• After rubbing the etching solutions on the coins, we air dried and examined the samples under the microscope

• This process was repeated up to three times to achieve the best grain definition

Materials & Techniques • What does etching and polishing a surface achieve?

• How does an optical microscope work?

• Polishing a surface allows light to have a uniformed surface to reflect off of (similar to a screen)

• Atoms along the grain boundaries are more chemically active. Therefore they dissolve quicker than those composing the grain.

• Etching solutions also help to smooth the surface

• Can break down bumps which sanding cannot

*Both of these figures are from - Materials Science and Engineering an Introduction by W.D. Callister, 8th ed.

Grain Analysis • Why analyze grains

• Size can reveal hardness of a sample

• How quickly was the sample cooled

• Mobility of dislocations

• Elongation of grains can reveal if a material has been subjected to an applied stress (Cold Working)

• Able to determine the microstructure

• Number of phases present

Under-etched Over-etched

COIN #1 - 500 Lire

COIN #2 – 1 Peso

COIN #3 - 2 Pence

There are approx.158.78 grains/inch

COIN #4 -5 cents (Canada)

COIN #5 - 5 Peso

References

• Coinage http://www.ancient.eu/coinage/

• Electrum http://en.wikipedia.org/wiki/Electrum

• Dolar coin fact http://www.npr.org/2011/06/28/137394348/-1-billion-that-nobody-wants

• Peso Image http://en.numista.com/catalogue/pieces585.html• 500 lire image http://en.numista.com/catalogue/pieces6354.html• 5 peso Image http://www.coinfactswiki.com/wiki/Mexico_2011_5_pesos• 2 Pence Image http://en.numista.com/catalogue/pieces11055.html• Canadian Nickel http://www.flickriver.com/photos/lawrence_chard/sets/72157628651831179/• Coin Facts wikipedia.org• How It’s Made Video https://www.youtube.com/watch?v=X-tX4LoK-Lw