Nickel And Steel - How To Detect Difference Between Them?

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Author	Replies: 8 / Views: 9,372
harrison2 Pillar of the Community Mexico 1304 Posts	Posted 01/19/2013 12:23 am So, as we all know, there are some coins that are pure nickel and some that are steel. Hypothetically speaking, imagine two coins that are identical, but one is steel and the other is pure nickel (which is also a magnetic material). How can one tell which is which? Report this Post to the Staff

argentum Pillar of the Community United States 1195 Posts	Posted 01/19/2013 01:14 am Presumably, these two hypothetical coins are identical in design and volume. Take the mass of the two coins. One coin should be found to have the same density as pure Ni and thus is the Ni coin. If both are found to have the same density, then we need another diagnostic. Edited by argentum 01/19/2013 01:15 am Report this Post to the Staff
sel_69l Bedrock of the Community Australia 21788 Posts	Posted 01/19/2013 04:47 am More presumably these two hypothetical coins would be of identical design weight and diameter, so they could be used in vending machines. One coin would be pure nickel and the other nickel plated steel, and BOTH would be magnetic. So how would you tell them apart? Pure nickel has a density of 8.88 g/cc, steel a density of 7.85 g/cc. The pure nickel coin, being slightly denser, would be a tiny bit thinner, 11.6% thinner in fact. If the pure nickel coin is exactly 1.00 mm thick, the nickel plated steel coin would be 1.16 thick. You need a better quality micrometer gauge to measure down to 1/100th of a millimetre, but a poorer quality gauge should be able to pick a 0.1 mm difference, but a problem arises with worn coins in this regard. So how do you tell them apart? The nickel plating on the steel coin would show signs of wearing thin. Much better to look for a date! Most mints would only change the metal upon the change of the date also. ---------------------------------------------------------------------------------------------------------------- I will make it a bit harder: How would you pick them apart if one was nickel plated stainless steel, and the other pure nickel? It can STILL be done! Report this Post to the Staff
CaptainFwiffo Pillar of the Community United States 4132 Posts	Posted 01/19/2013 2:33 pm Isn't there likely to be a difference in the strength of the ferromagnetism between the two coins? I don't know enough about the subject to say how useful that would be... Their Curie temperatures are different, so nickel loses its magnetism at a significantly lower temperature than steel (though it might still be hot enough to damage the coin). A microscopic examination of the crystal structure would probably work, but you'd have to have known samples to compare against and some knowledge of metallurgy. Report this Post to the Staff
yotie Pillar of the Community United States 3077 Posts	Posted 01/19/2013 2:40 pm taste? Report this Post to the Staff
harrison2 Pillar of the Community Mexico 1304 Posts	Posted 01/19/2013 2:47 pm yotie, you mean like stick it in your mouth type of taste? What I am working with is a subject that is brass plated and I'm told it is nickel underneith, but I don't really trust the seller. I would be more likely to believe that it's plain ol steel...but really don't know. This has been educational at least! Report this Post to the Staff
sel_69l Bedrock of the Community Australia 21788 Posts	Posted 01/19/2013 4:10 pm CaptainFwiffo: I deliberately left out the facts about the difference in ferromagnetism, hoping someone else would pick up on it. You did! It's a common diagnostic test, and is is used in vending machines. Most vending machines don't know the difference between coins and metal disks, so testing for differences in disks are followed. Report this Post to the Staff
harrison2 Pillar of the Community Mexico 1304 Posts	Posted 01/19/2013 4:21 pm Isn't that basically how the Ryedale machines work? Report this Post to the Staff
CaptainFwiffo Pillar of the Community United States 4132 Posts	Posted 01/19/2013 6:30 pm Rydales (to my understanding) use the same mechanism that metal detectors do for differentiating types of metals. Zinc "sounds" different than copper to a Rydale. I would think nickel and steel would be clearly different, but some metals are quite similar by that measure too. That's why aluminum pop-tabs are so irksome to dirt fishers - they sound like gold. (I am not a detectorist or Rydale person myself, so I could have this all wrong). Report this Post to the Staff
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