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Study of Oxidation on Coins

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by

Emily Liang

on 1 February 2016

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Transcript of Study of Oxidation on Coins

How long does it take for coins to oxidize?
First of all, what is oxidation?
In Conclusion:
Sunday, February 10th, 2013
Week #1
I'm going to leave four coins (a quarter, a dime, a nickel and a penny) out on a place where they will be exposed to the weather, rain or shine. Without ever moving or cleaning the coins, I will document their progress towards oxidation in the manner of photos and observations in the form of notes. This recording of results will continue for 3 weeks, by the end of which I will construct a conclusion and refer back to the hypothesis to see if I my predictions were correct.
Week #2
My hypothesis was incorrect as only 1 out of 4 of the test subjects began oxidizing at all. I did not take into context how much the different plating would affect the progress of the coins, but it turns out the the outer layer has the most affect on how long the coins will last, rather than the material it is mostly made out of. It seems that most coins are specifically designed to be durable under moisture and other types of weather it encounters. The nickel plating on the quarter, nickel and dime protect it from the brunt of the moisture, despite that fact that these coins are mostly made of steel, which rusts easily. The penny has not fared so well, because of it's copper plating, which rusts far more easily and is not quite as impervious to moisture. Coins are man made, and thus mostly shielded from the forces of nature. If I were to do this project again, I would probably try to test the coins out on man made mixtures to see if they would corrode the coins more successfully.
Oxidation is a chemical reaction that involves the moving of electrons. It is one half of the redox reaction.
Redox reactions are concerned with the transfer of electrons between species. The two types of redox reactions are called oxidation and reduction.
Oxidation
Reduction
loss of electrons
gain of electrons
increase of oxidation state by ion, molecule or atom
decrease of oxidation state by ion, molecule or atom
Specifically, oxidation is the interaction between oxygen molecules and other substances it may come across.
Sometime oxidation is a good thing, such as when it forms extra-durable
andonized aluminum
but sometimes, it is also destructive, such as when it forms a substance called
rust
So, what's this got to do with coins?
We all know that coins aren't just one type of pure metal- it's a mix of all different types of metals.
This mix of metals gives coins their colour, lustre and durability.
Because coins are cycled between a large number of people and places, they must be very resilient.
But just how durable are they?
Coins were not made with full time exposure to the elements in mind...
So how will they fare when put to the test under the natural elements?
Hypothesis:
Because coins are not made of pure substances, and are metal compounds, I think that the oxidation rate will be different from that of the pure substances that make up a coin. I predict that to be fully oxidized, the coins will take twice as long as the pure substances that create it because coins are specially crafted to be resilient. Steel will begin to rust once it come is contact with water, and since coins are predominantly steel with a thin plating of nickel/copper, I think the coins will rust within 3 weeks.
Test subjects:
1 x 2007 Canadian Quarter
1 x 2011 Canadian Dime
1 x 2009 Canadian Nickel
1 x 2009 Canadian Penny
94% steel, 3.8% copper, 2.2% nickel plating
92 % steel, 5.5% copper, 2.5% nickel plating
94.5% steel, 3.5% copper, 2% nickel plating
94% steel, 1.5% nickel, 4.5% copper plating
Weather: Sunny and dry
Observations: Coins still looking new and shiny. At this point in time, the coins are still in very good condition, with the exception of a few scratches.
Day 1:
Day 2:
Monday, February 11th, 2013
Weather: Drizzling lightly
Observations: All coins covered with thin layer of water. Quarter, dime and nickel still looking the same. Penny shows slight signs of discoloration.
Edges of imprint are turning brown- water stains or first signs of oxidation?
So how is this project going to work?
Day 3:
Tuesday, February 12th, 2013
Weather: Minor to Moderate rainfall
Observations: Weather has not yet affected the quarter, dime or nickel at all. Penny shows some progress towards oxidation.
Clarified: Not water stains
Day 4:
Wednesday, February 13th, 2013
Weather: Slightly cloudy and dry
Observations: Nickel plating on quarter, dime and nickel seem to be protecting it from oxidizing. Penny is beginning to turn brown. Surface of quarter is becoming slightly clouded.
Day 5:
Thursday, February 14th, 2013
Weather: Drizzling very slightly/cloudy
Observations: The slight clouding on the quarters was a water stain- still unaffected by water. Penny continues oxidizing gradually.
Day 6:
Friday, February 15th, 2013
Weather: Sunny and dry
Observations: Quarter, nickel and dime have not oxidized whatsoever. Penny's brownish discoloration has begun to turn green.
Day 7:
Saturday, February 16th, 2013
Weather: Rainy in the morning, then sunny
Observations: Green discoloration on penny has turned black. The quarter, nickel and dime seem impervious to rusting.
Testing Area:
I'll be putting the coins here to expose them to weather.
I'll be putting the coins on the balcony ledge here.
Day 8:
Sunday, February 17th, 2013
Weather: Cloudy and damp
Observations: The penny's progress in oxidizing seems to have slowed down. No new signs of oxidation.
Day 9:
Monday, February 18th, 2013
Weather: Cloudy and damp
Observations: Penny's discoloration has darkened. No visually noticeable change on quarter, dime or nickel.
Day 10:
Tuesday, February 19th, 2013
Weather: Sunny
Observations: No new progress.
Day 11:
Wednesday, February 20th, 2013
Weather: Raining
Observations: Not much discernible change. Maybe water is also cleansing the coin at the same time?
Day 12:
Thursday, February 21st, 2013
Weather: Raining
Observations: Face of penny is almost completely coloured black. No other signs of change.
Day 13:
Friday, February 22nd, 2013
Weather: Raining
Observations: No new signs of progress.
Day 14:
Saturday, February 23rd, 2013
Weather: Sunny
Observations: Different platings on the coins seem to be affecting their oxidation rate.
Sunday, February 24th, 2013
Week #3
Weather: Drizzling
Observations: Coins do not seem quite as shiny anymore. Has the weather dulled their lustre?
Day 15:
Day 16:
Monday, February 25th, 2013
Weather: Cloudy and damp
Observations: Face of penny is almost completely discoloured. Other coins still impervious to oxidation.
Day 17:
Tuesday, February 26th, 2013
Weather: Drizzling
Observations: No new progress.
Day 18:
Wednesday, February 27th, 2013
Weather: Cloudy and damp
Observations: No new progress.
Day 19:
Thursday, February 28th, 2013
Weather: Moderate rainfall
Observations: Penny's colouring has turned very dark.
Day 20:
Friday, March 1st, 2013
Weather: Heavy rainfall.
Observations: No new progress on coins.
Day 21:
Saturday, March 2nd 2013
Weather: Minor rainfall.
Observations: No new progress.
Before:
After:
A side by side comparison of the coins progress from beginning to end.
Day 1: Sunday, February 10th, 2013
Day 21: Saturday, March 2nd, 2013
As a result, I've learned that coins were indeed made to withstand the elements. It also turns out that however symbolic a copper penny may be they are expensive and not all that durable. Someday in the distant future, some archaeologists or going to find some very durable coins.
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