White Yeti
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The strongest base that does not react with aluminium.
Hello everyone,
Obviously, we all know that aluminium reacts with NaOH and the like, but what is the "strongest" base that does not react with aluminium?
The strongest bases I can think of are Na2CO3, NH4OH and bleach.
Ultimately, I would like to make a half cell that favours this electrochemical reaction:
Al + 4OH- ---> [Al(OH)4]- + 3e- +2.33V
Any suggestions?
[Edited on 10-21-2011 by White Yeti]
"Ja, Kalzium, das ist alles!" -Otto Loewi
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bob800
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I've seen a Nurdrage video on this principle, but he doesn't use an alkaline electrolyte (he uses table salt): http://www.youtube.com/watch?v=_FxIzMwOF00&feature=relmf... . However, he uses iron as the cathode, which reacts with water and oxygen to
produce iron hydroxide, which then reacts with the aluminum to produce aluminum oxide. There's equations in the video to explain everything.
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White Yeti
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I've seen the raging nurd's video on aluminium air batteries as well. I've actually made aluminium batteries for a long time before he posted the
how-to video. The ideal design of an aluminium air battery calls for an anode half cell that is very basic (but not too basic) while the cathode half
cell is fairly acidic.
I didn't like the way he talked about how aluminium hydroxide is insoluble, because at higher pH, aluminium hydroxide forms a water soluble complex
ion, [Al(OH)4]-.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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bbartlog
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NH4OH will attack aluminium. More generally I'm not so sure that what you want exists: aluminium will react with water, and anything that raises the
pH sufficiently should dissolve the passivating coating that would otherwise halt this reaction.
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Erbium_Iodine_Carbon
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To get Al(OH)3 you could try this:
1) Dissolve Al with a sodium hydroxide solution containing a known amount of NaOH
- 2 NaOH + 2 Al + 6 H2O -> 2 NaAl(OH)4 + 3 H2
2) Add 1 mol of HCl for every mol of NaOH to precipitate an Al(OH)3 gel (add a little extra acid to make sure all Na+ is converted to NaCl)
- NaAl(OH)4(aq) + HCl(aq) -> NaCl(aq) + H2O + Al(OH)3(s)
3) Add a water miscible solvent like ethanol or acetone to the gel to form amorphous Al(OH)3 powder
4) Filter the solution and wash the filtrate with water to remove solvent and dissolved NaCl
5) Profit
Edit: Sorry, just realised you were going for a battery, not making aluminum hydroxide :/
[Edited on 23-10-2011 by Erbium_Iodine_Carbon]
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AndersHoveland
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Have you considered "silver alkanes" ? Ag-CH2-CH3
Such compounds act as potent bases.
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White Yeti
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I have not considered silver alkanes. I'm trying to make a battery nonetheless, I don't really want to use precious metal compounds, just to lower the
pH of a solution.
However, since I did not explicitly mention that in the thread, I'm the one to blame.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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froot
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I would look into anhydrous polar solvents that won't passivate Al and won't react with OH- ions while providing ion transportation between the
electrodes - if there's such a thing. I have read an article linked somewhere here about producing alkali metals from their salts by electrolysis in
propylene carbonate. May be a good place to start.
How would you construct the O2 cathode?
Edit: Link added for Li-air cell which may have some bearing on this:
http://www.unb.ca/fredericton/science/chem/smcgrady/group/sh...
[Edited on 25-10-2011 by froot]
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Intergalactic_Captain
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Without knowing the design of your battery, I'd add K2CO3 and NaHCO3 as possible electrolytes that won't contribute to undue corrosion.
...OT, but with froot bringing up propylene carbonate (as in organic or aprotic electrolytes) - I've always wondered if say some toluene with
diisopropylethylamine in it or DMSO with a little salt thrown in might work as the electrolyte in the copper/iron battery. Not that familiar with
aluminum battery technologies though.
If you see me running, try to keep up.
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AJKOER
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Quote: Originally posted by bbartlog  | | NH4OH will attack aluminium. More generally I'm not so sure that what you want exists: aluminium will react with water, and anything that raises the
pH sufficiently should dissolve the passivating coating that would otherwise halt this reaction. |
Per my direct experiments, this comment is on the mark.
As a further clarification, the source of the Aluminum is important as it may have been heated treated or an alloy added, to increase the passivity.
How to further the passivity may be a more fruitful research.
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