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Offline mafiaparty303

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Re: Melting Coins
« Reply #15 on: December 31, 2006, 05:24:35 AM »
I have a question about this,

I learned about being able to (easily) melt pennies made after 1982 which are made mostly of zinc, I took a small aluminium (tin) can and built a fire in our backyard fireplace, after I had some good red coals I put a couple pennies in the can, put the can in the fire and waited, after a couple of min. the pennies had melted, I took a bucket of water, poured the molten zinc into the water and you get very shiny weird formations of zinc, the zinc looks very pure plus I had a lot of slag left in the can and only the shiny molten zinc poured out of the can since I doubt the fire was hot enought to melt the copper.

How pure do you guys presume this zinc to be? To me it looks VERY pure since there are no uneven shades of shiny grey or anything to make it look not 99.9 % pure.


Is there a way to test how pure it is?
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Offline billnotgatez

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Re: Melting Coins
« Reply #16 on: December 31, 2006, 04:03:08 PM »
Are you sure that you did not get the alloy brass?

Offline mafiaparty303

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Re: Melting Coins
« Reply #17 on: December 31, 2006, 04:32:44 PM »
pretty sure since its very shiny like silver (you can see your own reflection in some parts) plus its not that yellowish brown color that brass has, plus I doubt the fire I build has the power to melt the small percentage of copper in the pennies

woulfn't it be better to store zinc in water since they dont react, they it wouldn't tarnish.
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Offline billnotgatez

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Re: Melting Coins
« Reply #18 on: December 31, 2006, 04:45:06 PM »
Water has many dissolved gases in it typically. One of these gases could be oxygen.

Offline EccentricHeather

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Re: Melting Coins
« Reply #19 on: December 31, 2006, 05:34:51 PM »
According to the "Red Book", the post-1982 composition of Lincoln cents is:

plating:  pure copper
core:  99.2% zinc; 0.8% copper
Total content is 97.5% zinc; 2.5% copper

So the zinc core is reasonably pure, but there is a little copper in it.  I wonder how much of the copper plating might dissolve into the zinc when the coin melts.  I have melted these coins in the past, but I haven't looked into this in detail.  If you want to get the purest possible zinc out of it, it might be wise to remove the copper plating first, perhaps by dipping it in acid until the plating dissolves.  (That might dissolve a lot of the zinc as well; perhaps someone else here has a better idea.)

There are other zinc coins around.  During World War II, Nazi Germany produced small-denomination zinc coins for Germany and occupied territories.  Many of these coins are cheap and plentiful, and most of the surviving ones are in bad shape as they have corroded over the years.  I don't know how pure the zinc is, and I haven't tried melting any, but at least they wouldn't have the plating to deal with.

If you want another metal with a low melting point that is relatively inexpensive and easy to obtain, look for bismuth.  It will easily melt over a stove, and unlike many heavy metals, its toxicity is low.

Heather

Offline mafiaparty303

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Re: Melting Coins
« Reply #20 on: December 31, 2006, 05:52:48 PM »
Thanks for the info. Isn't bismuth the metal that crystalizes in weird shapes? Because I remember seeing these metalic things at a hobby store near here and they looked like the bismuth crystals I have seen on the internet. Maybe they still have them...

Ive also bought some clay because I'd like to mold some of the zinc into little ingots, Ill post some pictures if I get to it.
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Offline jdurg

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Re: Melting Coins
« Reply #21 on: December 31, 2006, 06:32:51 PM »
ALL metals will crystalize if pure and cooled slowly.  It's the cooling part that is a pain in the ass since many metals melt at such high temperatures that it's difficult to cool them down slowly.  Bismuth is one of those metals that will cool quite slowly as it's melting point isn't all that high.

In regards to the purity of your zinc, you probably have about 96 to 97% pure zinc.  Just because the temperature of the fire wasn't hot enough to melt copper doesn't mean that the copper didn't dissolve in it.  Salt dissolves in water, but that doesn't mean that the water has to be at the melting point of salt.  Gold will dissolve in mercury even though the mercury isn't at the melting point of gold.  Copper will dissolve into liquid zinc forming a completely normal looking blob of zinc. 
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Offline mafiaparty303

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Re: Melting Coins
« Reply #22 on: December 31, 2006, 06:34:38 PM »
o ok, that I didn't know about the copper being able to dissolve into the zinc regardless of the heat applied
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Offline jdurg

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Re: Melting Coins
« Reply #23 on: December 31, 2006, 06:38:49 PM »
o ok, that I didn't know about the copper being able to dissolve into the zinc regardless of the heat applied

Yup.  That's the basis for a pretty neat demo involving a penny.  You take a penny and dip it into some HCl and then some NaOH to make sure that the copper surface is clean.  In a fairly concentrated dish of NaOH, you add some zinc powder/filings and soak the penny in there, completely covered by the zinc.  This will result in a thin layer of zinc adhering to the cent's surface.  Now take that penny and put it into a bunsen burner flame.  The zinc will melt and the copper will dissolve in the zinc forming a VERY thin layer of brass on the surface.  (As it's mostly Cu on the surface and just a small part of zinc).  The penny will now look golden in color as the copper dissolved into the zinc forming an alloy.

You can also take a modern penny and put it into a bunsen burner flame, and after a while the penny will turn silver in color as the molten zinc below the surface alloys with the copper on top.
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Offline mafiaparty303

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Re: Melting Coins
« Reply #24 on: December 31, 2006, 06:43:20 PM »
ya I remember doing that in middle school, we had all these diferent types of pennies and zinc and HCl now i remember.

Does anyone know where I can get some acids (HCl and other basics) in small quantities just to conduct some experiemtns? At a fairly low price too.
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Offline jdurg

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Re: Melting Coins
« Reply #25 on: December 31, 2006, 06:54:01 PM »
You can get fairly large tubs of "experiment quality" HCl from pool supply stores, or some home improvement stores.  (Muriatic acid is used in pools, and is also used to clean brick and concrete).  Many drain cleaners contain somewhat impure sulfuric acid which can be cleaned and purified if you have the time and patience.
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Offline billnotgatez

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Re: Melting Coins
« Reply #26 on: December 31, 2006, 07:05:22 PM »
There are two sticky posts at the top of the below page, which is a sub-forum to this forum. Inside those stickies are links. Below is also a copy paste from two of the links.

+  Chemical Forums: Chemistry Forum, Chemistry Question, Chemistry Help
|-+  Chemistry Forums for Students of Chemistry
| |-+  Citizen Chemist
| | |-+  Buy/Sell/Trade/Borrow Chemicals, Glassware and Instrumentation (Moderators: Mitch, billnotgatez)

Quote
hydrochloric acid     HCl     Masonry Cleaner     Muriatic acid (the common name for HCl) is used in swimming pool maintenance. It is also sold as masonry cleaner and is available at the hardware store. Percentages vary but concentrations as high as 35% can be found easily.

Quote
Hydrochloric Acid

Formula: HCl (aq)
Synonyms: –

Suppliers:
1. It is the active ingredient of some heavy duty "Patio Cleaners" sold by hardware stores.
2. It is the active ingredient of some toilet bowl cleaners. Unfortunately, a lot of these are too impure to be of much use.
3. It is sold by some swimming pool suppliers as a "pH Minus" (i.e. an agent to decrease the pH of water). It may be sold by name, or as "Muriatic Acid".
  Pool Plaza (USA)
4. Some alternative photographic suppliers sell it.
  JD Photochem (Canada)
  Photographers' Formulary (USA)
  Rayco (UK)
Silverprint (UK)
5. Some art suppliers catering to serious artists sell it.
  Kremer Pigments (Global)


Offline hopeful

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Re: Melting Coins
« Reply #27 on: January 02, 2007, 06:11:39 PM »
if you are just looking to play with metal casting bismuth melts very very easily...bit sure of the temp but i did it easily with a butane torch. Noted this is not the cheapest metal but once melted you can form some pretty nifty crystals with it.

Offline ArtCelled

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Re: Melting Coins
« Reply #28 on: March 22, 2007, 12:10:14 PM »
I tried melting aluminum, but i forgot dat aluminum cud oxidise sooooo fast dat it all got powdery. i melted aluminum wid da flower pot thing. suggest me something !

Offline Borek

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Re: Melting Coins
« Reply #29 on: March 22, 2007, 03:06:38 PM »
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