RogueRose
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Aluminum can composition - plastic layer on inside & outside
There has been some discussion on the composition of Aluminium cans (soda/beer) and I've run some tests with melting and dissolving in NaOH solution.
When putting the can in molten Al, there is a flame that is emitted immediately upon pressing it down into the hot metal along with some blackish
smoke coming from the flame.
I made a saturated solution of NaOH and added some pieces of the side wall of the can. For the first 20 mins or so, bubbles were only emitted form
the cut edges of the can and eventually small corrosion spots appeared over the flat wall piece. After about an 2 hours all the Al had dissolved with
a gross plastic membrane remaining floating on top.
In comparison I placed some foil and Al from a disposable pie pan in the solution and it immediately produced gas along the entire submerged surface.
An equal size piece to the can piece dissolved in just under 2 mins.
Interestingly the top of the can acted similarly to the foil as it emitted much more gas than the sides but not as vigorously as the foil. It took
about 30-45 minutes to dissolve.
I also tried a hot solution of Na2CO3 and was suspecting similar reaction as the hydroxide as many YT videos have suggested this. I was disappointed
that this did not happen with any of the Al pieces. The foil did blacken but no bubbles were really noticeable (may have diffused into the
solution?). I suspect the temp may not have been hot enough as it started at about 190F but dropped over time. Video's showed using water from a
coffee maker then adding carbonate - so I would assume similar temps.
What I'd like to know if whether the NaOH is consumed in the reaction or is it a catalyst and the Al reacts with the water making Al hydroxide.?
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Praxichys
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The aluminum is reacting with the NaOH to form sodium aluminate.
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j_sum1
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I believe that the coating inside is an epoxy lacquer.
https://youtu.be/hUhisi2FBuw?t=4m34s
(The whole video is fascinating.)
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MrHomeScientist
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I had the exact same experience as you, RogueRose (except the Na<sub>2</sub>CO<sub>3</sub> step, I never
tried that). I also had a lot of grey powder left over from dissolving the can in NaOH, which is presumably made of the alloying elements.
As for your question, Praxichys is right. When I did this experiment I used KOH, and it goes via
2Al + 6H<sub>2</sub>O + KOH == 2KAl(OH)<sub>4</sub> (aq) + 3H<sub>2</sub>
So all your aluminum ends up in solution as the aluminate.
More fun facts:
The alloys used in the walls of soda cans are:
3104-H19
http://www.matweb.com/search/DataSheet.aspx?MatGUID=aaaabe41...
3004-H19
http://www.matweb.com/search/DataSheet.aspx?MatGUID=ec6a8753...
For the lid, they use a slightly different alloy:
5182-H48
http://www.matweb.com/search/DataSheet.aspx?MatGUID=430cd3b0...
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