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kazaa81
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wink.gif posted on 23-3-2005 at 14:30
Copper oxides removing...


Hallo to all,
how can I remove copper oxides from a copper money without destroying it much?
I've 30%HCl, 90% H2SO4 (these are too much strong, I think).

Thanks at all for help! ;)
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[*] posted on 23-3-2005 at 14:40


Heat the copper to red and then quench in water.



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[*] posted on 23-3-2005 at 14:53


table salt and vinegar always worked for me.
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[*] posted on 23-3-2005 at 15:07


HCl in the absence of air should work well. Cold sulfuric acid would probably also work, but make sure to dilute it.
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[*] posted on 23-3-2005 at 15:08


I second the salt and vinegar suggestion. Dilute HCl will also work well. I remember cleaning many pennies with salt and vinegar when I was very young. The combination was quite effective. Curiously, my copper-cleaning solution seemed to increase in effectiveness over time. It took a couple minutes of swirling to clean copper with fresh solution, while solution that had been used for a few days would remove tarnish in the blink of an eye. I never did perform enough controlled experiments to figure out if evaporative concentration of the solution, the introduction of copper ions to the solution, or some other phenomenon caused the increase in cleaning power.

The freshly cleaned copper was gorgeously bright, but it started visibly tarnishing very quickly after the cleaning solution was removed and the metal dried. I don't know what the best way to clean your copper surface and keep it bright would be.




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[*] posted on 23-3-2005 at 17:17


Quote:

I don't know what the best way to clean your copper surface and keep it bright would be


Vaseline?




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[*] posted on 23-3-2005 at 20:16


In the days of yore, I was always amused by putting brown pennies in vinegar, salting them and watching the area in the vicinity of the salt crystals turn pink.

Salt and vinegar also etches nicely (pickled bronze bits I melted and pickled have turned out with shining polarization due to showing the random crystal orientation), the combination of moderately low pH and chloride ions seems to dissolve things nicely. I never noticed dezincification either... I wonder if it will dissolve the top layer (of CuO, Cu2O, then Cu metal (with Zn and Sn oxidized out, turning the surface pink rather than yellow)) on the castings. Hmm, I gotta try that... :)

Tim
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[*] posted on 10-4-2005 at 07:25


I found out by accident at a picnic that katchup cleans pennies very well, with no visable damage to the coin's detail. I'm sure it has to do with the acid from the tomatoes plus salt in the product. Curiously, the pennies don't oxidize as quickly when cleaned this way.
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[*] posted on 10-4-2005 at 07:44


I have a few silver coins lying around, would I use the same solution, or perhaps something else?



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[*] posted on 10-4-2005 at 08:34


kazaa81, you should be reluctant to take any advise that involves heating coins red hot or dipping them in acids. You might just as well put them on a wire wheel buffer. If these are collectable coins you should do some more research. Sometimes coins can be brought back from tremendous corrosion by using electrolysis, this has been demonstrated with items taken from old shipwrecks, but I don't know the procedure. The net result is the corrosion layer is reduced and the metal it actually redeposited on the base metal. An acid dip will remove the corrosion and leave the coin less intact than before you started.
Try putting a coin in a loose wrap of aluminum foil, just enough to cover the coin, and warming it in a solution of NaHCO3 for 15 minutes. This should cause a reduction of the copper salts and a corresponding oxidation of the aluminum foil. Remember not too wrap the coin to tightly, as the solution must get under the foil. This works very well with silver jewelry and plate also. A magnesium plate can be substituted for the Al foil, but the coins have to touch the plate, forming an electrochemical cell.

[Edited on 11-4-2005 by Mr. Wizard]




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[*] posted on 10-4-2005 at 19:09


cyclonite4:
Quote:

I have a few silver coins lying around, would I use the same solution, or perhaps something else?


The tarnish on silver from open air @stp, I think is Ag2S rather than any silver oxide. So you can remove the Ag2S to reveal Ag, or you can just reduce the Ag2S to Ag instead. Check a SRedP listing to see what you have that will do this. I think the most common thing is to place Al foil into a small bath of hot water with some ions that will not beat the red potential you are aiming for. (like Baking soda). I have done this before, just by heating up water in a glass measuring cup (the heat is to speed up the rxn.) in a microwave. insert some Al foil strips and add a spoon of baking soda. Dip your coins in (assuming they really are silver on the outside) and it should happen in seconds. Then you have water that smells of eggs :)
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[*] posted on 12-4-2005 at 00:59


I'm certain they are silver ;) thanks for the tips. I have a certificate saying they are 99.9% silver, the coin being 17.016 grams in weight. I got it from a garage sale for $1 (good deal methinks :D ). Maybe I could just use it for chemistry?



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[*] posted on 12-4-2005 at 01:05


i have a better idea. Send the silver coins to me...
I can seperate the silver from the other metals, or just recast it into something else (like my pocket).
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[*] posted on 11-6-2005 at 16:47


Is there a way to use electrolysis to dissolve the copper oxide in solution without ruining the copper?
I need to clean some scrap copper to sell it (anywhere from 20 to 100+ pounds).
I did experimented in small scale using a solution of epson salt in water (one pole was the copper to clean) but apparently it leaves a lot of oxide on the wire.
Any suggestion that is cheap to remove the oxide only?


(The vinegar/salt method dont work because:
Vinegar solution saturate too fast and after 5 minutes the copper oxidize again.)

[Edited on 12-6-2005 by Archimede]
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[*] posted on 11-6-2005 at 17:45
Copper oxide ?


Copper oxide, often turns to copper carbonate by the interaction of CO2 and watervapor in the air. Take a look at those nice green chirch roofs, which were originally made of "pure" copper. Throughout the years they turn green due to copper carbonate.

Many copper salts are soluble in ammonia (house hold ammania containing about 5% ammoniak).

BRASSO, a well known copper polish, has a soft grain abrassive and.....yes, ammonia!!!.

Additional advantages of BRASSO (international trade name), is that it leaves an oil/wax residue behind, as to protect the copper surface from future attacts by carbolic acid and H2S. Sweat, from your fingers, is allso a well known copper surface "killer".

Often the biggest challange is to not damage the coin, and lower it's value.

A well known coin collector and sales man that I know in Holland, even refuses to use BRASSO, or any other chemical cleaning agent. He uses soft grain abrassives in the form of powder and water (not WIM, it contains calcium hypochlorite). A soft grain like chalk may work fine, and then you may protect the coin by "NON ACIDIC" vaseline.
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[*] posted on 11-6-2005 at 18:24
Fast, but very dangerouse !


To get realy fast results, the following may be done:

1) First remove any grease or fat residue by means of ammonia.

2) This ungreased copper may then be dipped in dilute nitric acid. ***

***Nitric acid reacts with copper, copper oxide, copper carbonate etc. This is a fast reaction, producing a lot of DEADLY NO2 GAS. This nitrogen dioxide gas forms nitric acid in your lungs. You may feel fine, untill about 6 hours later. They may not be able to save your life then, because your lungs will no longer be able to take up air to breath, due to servere lung damage !!!.
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[*] posted on 12-6-2005 at 02:02


Ouch! Just dip it in HCl. CuO(.CO2, etc.) + 2HCl = CuCl2 + etc., while Cu metal is too positive to displace H+.

If it corrodes after removing, well obviously, you have to wash it off good, possibly with help from a baking soda solution, and spray with WD-40 to get rid of any water and oil the surface.

Tim




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[*] posted on 25-6-2005 at 19:40


I found some muriatic acid 31.5% and just pouring a little bit on the copper INSTANTLY it turn it shiny like new. I then rinsed it with water and noticed that in 5 minutes the copper was turning dark again so I used the WD40. Tomorrow Ill check how it is.
To get rid of the acid I poured in it a small box of baking soda and the 'disposed' of it :(
Any better way to do get rid of it? or can I use that for something else? (HCl+CuOx)
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[*] posted on 25-6-2005 at 19:57


If you don't want to use much, don't... dilute it with some water, maybe 1:3 or 1:4. It'll work a little slower but no problem. Then just flush it down the sink with a lot of water (unless you have iron or stainless steel pipes, which will be corroded; then it might be a good idea to neutralize until bicarb stops fizzing).

Tim




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