User
Hazard to Others
Posts: 339
Registered: 7-11-2008
Location: Earth
Member Is Offline
Mood: Passionate
|
|
Ideas on the formation of Al2O3
As we all know Al2O3 can be a usefull catalyst etc.
Well since it might be very easy to make it yourself i thought why not.
Aluminium is converted to its hydroxide by adding lye to Al-foil.
Then it is thermally destroyed by adding it to a porecail beaker which is placed on a very hot hotplate (more than 500 degrees).
If my idea is correct Al2O3 is left behind.
Ive tried this and i found a very porous white left over.
The problem is that there is no way that i can tell anything about the purity of this substance.
Anyone any ideas about this.
Or come up with a better method?
P.S
I would like to keep it as OTC as possible, i know a furnance would be great but i dont have one right now.
What a fine day for chemistry this is.
|
|
|
Fleaker
International Hazard
Posts: 1252
Registered: 19-6-2005
Member Is Offline
Mood: nucleophilic
|
|
Perhaps adding some big blocks or turnings to a dilute mercuric nitrate solution and leaving it outside for a few days might work.
Collect and carefully rinse the product and then calcine.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
Simply eacting NaOH wih Al will produce some sodium aluminate, your process will produce alumina will a high sodium content as well containing most of
any alloying metals.
Slowly add Al to NaOH solution until there is an excess of Al that does not dissolve, alloying metals will mostly remain with the metallic Al.
Keeping it out of contact with air, allow the mixture to settle for at least a few hours; then decant the solution away from the remaining Al.
Now an acid as week as CO2 will precipitate Al(OH)3 for a solution of the aluminate. Sodium bicarbonate works too, add an excess (in regards to the
amount of NaOH originally used) of NaHCO3 to the solution, bring to a gentle boil, cool, decant through a filter. Wash the Al(OH)3 precipitate with
dilute aqueous ammonia a number of times to remove sodium ions. Collect the Al(OH)3 on a filter, allow it to dry. Heating to a bit above 300 C
converts it to AlO(OH), significantly higher temperature to Al2O3.
Aluminum sulfate can often be purchased in garden supply shops, alum can be bought too. Making a solution of either, then adding excess NaHCO3 will
produce Al(OH)3 or AlO(OH) or a mix. Again good washing is desirable.
|
|
|
smuv
National Hazard
Posts: 842
Registered: 2-5-2007
Member Is Offline
Mood: Jingoistic
|
|
| Quote: | | As we all know Al2O3 can be a usefull catalyst etc. |
While there are countless ways of forming alumina, not all aluminas have equal catalytic acitivity. Gamma alumina is most active and is formed by the
calcination of gelatinous aluminum hydroxide at up to 500c (lower temps may provide inferior quality alumina). Gelatinous aluminum hydroxide is
prepared by the precipitation of aluminum hydroxide between pH 7-10 with amorphous alumina being precipitated at lower pH's.
Some ways in which I have seen gamma alumina prepared:
Allow a 10% sodium aluminate solution to stand, it precipitates aluminum hydroxide with time. Filter. Wash thoroughly with water to remove sodium.
Calcinate. Said to be very active.
Pass CO2 through a 10% sodium aluminate solution. Then filter etc. as above. Slightly less active than above.
Treat 8% sodium aluminate with sulfuric acid. Filter etc. as above. Produces a less active product.
Heat a solution containing .05M aluminum chloride and .8M urea. Filter etc. as above. Produces a very active product.
etc.
I based the "activity" upon its effectiveness as an ethanol dehydration catalyst. But should apply to other dehydration reactions. These aluminas
may not be good for dehydrogenation reactions which I believe require different catalyst surface properties (defects in basic as opposed to acidic
sites).
I have experience with the precipitation of aluminum hydroxide from sodium aluminate with CO2. It works well. I also tried the precipitation of
aluminum hydroxide with urea and it requires too dilute of a solution to be useful. The alumina prepared via the CO2 method was fairly active for the
cracking of naphtha and dehydration of ethanol to ethylene.
See:
Ethanol dehydration with various alumina catalysts
J. Am. Chem. Soc. 47(11), 1925, pp 2748-2754
Prep of alumina via urea method as well as another involving succinic acid/urea
Applied Cutalysis, 24 (1986) 25-35
"Titanium tetrachloride…You sly temptress." --Walter Bishop
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
