jimmyboy - 29-10-2005 at 15:26
I am guessing this i really trivial but i cant seem to find a easy source for fine alumina powder anywhere (i hate ordering things) - i was wondering
if simply burning aluminum turnings with potassium chlorate would suffice - then take the white powder that remains and place in water - pour off the
KCl and retain the solid (aluminum oxide is insoluble from what i understand) - anyone have a more efficient way - or maybe a source i havent thought
of?
The_Davster - 29-10-2005 at 15:42
I am not sure how controllable that reaction would be
. How about the following:
Al +KOH +H2O-->Al(OH)4-(aq) +H2
Al(OH)4-(aq) +H2SO4-->Al(OH)3(s)
2Al(OH)3-(heat)->Al2O3 +3H2O
Just make sure in the second step to use a stoichiometric ammount of sulfuric or
Al(OH)3+H2SO4-->Al2(SO4)3 +H2O
will occur.
Or, as Al2(SO4)3 is a common garden chem:
Al2(SO4)3 +OH- -->Al(OH)3(s)
2Al(OH)3-(heat)->Al2O3 +3H2O
EDIT:Again use stoichiometric base in the rxn above or aluminates will form.
[Edited on 29-10-2005 by rogue chemist]
12AX7 - 29-10-2005 at 15:43
Precipitate alumina hydrate from solution (alum, aluminum chloride or sodium aluminate), wash, dry, calcine to alumina? How alumina-ific does it have
to be?
Tim
jimmyboy - 30-10-2005 at 15:12
hmm aluminum sulfate is for gardens? that could be good - a propane torch to decompose it - or swap it out with the hydroxide and do the same - there
is some confusion about the temperature you have to use to decompose - i have 2 sources telling different things - one says aluminum hydroxide is
simply hydrated alumina the other states you need over 1000 deg C to decompose - any ideas?
here
http://www.chemicalland21.com/arokorhi/industrialchem/inorga...
and here
http://www.absoluteastronomy.com/encyclopedia/b/ba/bayer_pro...
The_Davster - 30-10-2005 at 15:31
Brauer gives a value of 1100C for the conversion of Al(OH)3 to Al2O3, but the mineral "diaspore" decomposes to Al2O3 quickly at 500C.
Aluminum hydroxide is not simply hydrated(in the chemical sense of the word) aluminum oxide, that is a remanent from an archaic nomenclature system
BromicAcid - 30-10-2005 at 19:21
The thread on castable refractories has a good section on alumina from aluminum in bulk form with mercury and or a mercury salt and it gives good results with
minimal effort and chemicals once started. There is also the thread titled mercury and aluminum that focuses on this particular reaction.
jimmyboy - 31-10-2005 at 12:34
well i found a ceramic store fairly close that sells it for 2 bucks a pound - since its nontoxic i guess i can do that -- also have seen that its an
ingredient in some silver and brass polishes - seems they mix it with petroleums but the sulfate can be had at lowe's - home depot so thats
another route as well 
- i also see that they use it in toothpaste as well?? this
is the same stuff they use in grindstones - yipes
[Edited on 31-10-2005 by jimmyboy]