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ShadowWarrior4444
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| Quote: | Originally posted by UnintentionalChaos
It forms from the absorbtion of carbon dioxide by the solution. Carbonic acid being a stronger acid than aluminum hydroxide displaces it from sodium
aluminate forming sodium carbonate and the aluminum hydroxide precipitates. |
Hmmm, there shouldnt have been much CO2 in the chamber--it was under positive hydrogen pressure the entire time. I suppose I'll run another test after
flushing the vessel with difluoroethane ('heavier' than CO2.)
This may also be a useful way to make alumina powder for crucible and abrasive manufacture at home. Disolve the foil, let the impurities settle,
decant and expose to CO2. I wonder if the NaOH can be recovered as well. Probably with the use of CaO and a bit of heat. Can Ca(OH)2 be used to
dissolve aluminum in a similar fashion?
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12AX7
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Incorrect, aluminic acid is slightly stronger than carbonic. I have crystals of sodium aluminate (originally the hydrate, but now dehydrated) which
are quite stable in air in regards to hydrolysis.
Probably, alumina hydrate was supersaturated and only precipitated after some time.
If you had an excess of aluminum, continued corrosion certainly occurs, where the basic sodium aluminate solution (or acidic aluminum chloride
solution, or...) is essentially catalyst, yielding more white goop.
Ca(OH)2 is certainly basic enough, but don't expect to make calcium aluminate (the cement).
Tim
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ShadowWarrior4444
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I am fairly certain that the aluminum was not in excess, if anything the sodium hydroxide was.
It may be likely that alumina hydrate was supersaturated, however it did not precipitate on cooling, only after standing 16 hours at room temperature;
this leads me away from saturation theories and more toward hydrolysis theories. Could sodium aluminate hydrolyze over time in the presence of a
strong base?
The precipitation pattern may be of interest as well, it seemed to have a geological appearance. A bit like a porous rock, or a tangle of vines. Upon
jarring the container slightly, the formation broke up into fine white powder which settled.
[Edited on 7-2-2008 by ShadowWarrior4444]
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12AX7
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Hey, alumina hydrate is a refratory compound, it could take a while to form even a small crystal lattice. Or something.
Crystallizing a considerable time after cooling is *exactly* what supersaturation can do.
Tim
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