Sciencemadness Discussion Board - Alumina (AL2O3) question again

Alumina (AL2O3) question again

mouseear - 14-8-2008 at 05:13

What chemical can dissolve Al2O3 completely? Also can you let me know the test condition?

ScienceSquirrel - 14-8-2008 at 05:27

It depends on your alumina to a certain extent, samples that have been heated to high temperatures can be quite inert.
However it will dissolve in strong mineral acids and caustic alkali solutions eg aqueous potassium hydroxide.

Sauron - 14-8-2008 at 06:12

Yes, but then it won't be Al2O3 any more, will it?

I think he wants to dissolve it, not destroy it.

Mineral acids will produce their aluminum salts and caustics will produce aluminum hydroxides.

I know of no solvent for alumina with which it does not react.

ScienceSquirrel - 14-8-2008 at 06:22

If you have a look back at Mousear's previous posts you will see that they have a theme of removing metal oxides from a metal frit.
I don't think he is bothered if they are dissolved or turned into something else he just wants to get rid of them.

[Edited on 14-8-2008 by ScienceSquirrel]

blogfast25 - 14-8-2008 at 08:00

Fused (annealed) alumina is much, much more inert than one would ordinarily think, as I know from personal experience. It hardly dissolves at all in hot 32 w% HCl for instance. Concentrated sulfuric or strong alkali would do it but only if properly size reduced.

The Bayer extraction process for the extraction of alumina from Bauxite for instance requires grinding finely and extraction with strong NaOH in pressurised digesters, to allow higher temperatures. And grinding and milling annealed alumina is also easier said than done, it's extremely tough...

mouseear - 14-8-2008 at 08:01

Yeah, I just want to move the solid Al2O3 into solution. Does not matter what form it will be in the solution. As long as it can go into the solution, that will be great.

I tried soaking in 10% NaOH at 180C for 2 hrs. Then I analyzed the solution using ICPMS. But I did not see any Al there.

I also used Aqua Regia w/ HF, the same thing. Do not see Al.

The alumina was formed due to high temp, went through the furnace.

Thanks a lot for your inputs.

mouseear - 14-8-2008 at 08:05

I try to avoid the microwave digestion... So no way to disslove it?,

ScienceSquirrel - 14-8-2008 at 08:07

Quote:

Originally posted by mouseear
Yeah, I just want to move the solid Al2O3 into solution. Does not matter what form it will be in the solution. As long as it can go into the solution, that will be great.

I tried soaking in 10% NaOH at 180C for 2 hrs. Then I analyzed the solution using ICPMS. But I did not see any Al there.

I also used Aqua Regia w/ HF, the same thing. Do not see Al.

The alumina was formed due to high temp, went through the furnace.

Thanks a lot for your inputs.

Can't you just ignore it?

It sounds completely insoluble

Sauron - 14-8-2008 at 08:11

Why not dissolve the TNT instead of the alumina? Then filter off the alumina and recover the TNT from solution.

ScienceSquirrel - 14-8-2008 at 08:14

Quote:

Originally posted by Sauron
Why not dissolve the TNT instead of the alumina? Then filter off the alumina and recover the TNT from solution.

Who said TNT?

Mouseear is innocent, he ain't got no TNT I hope!

[Edited on 14-8-2008 by ScienceSquirrel]

mouseear - 14-8-2008 at 08:19

That is funny. But pls d

o not make fun of me. I am serious and asking for help.

[Edited on 14-8-2008 by mouseear]

ScienceSquirrel - 14-8-2008 at 08:29

Sorry about that.

When analysing alumina samples, the following methods are commonly used; fusing with calcium metaborate or sodium carbonate, digesting with 32% hydrochloric acid under pressure.
The following is fairly typical;

http://www.opticsinfobase.org/abstract.cfm?URI=as-16-3-86

[Edited on 14-8-2008 by ScienceSquirrel]

blogfast25 - 14-8-2008 at 11:03

Also fusion with NaHSO4.

Sauron - 14-8-2008 at 13:59

Sorry, it's my bad eyes. I read tnt when what SS posted was frit.

I need a bigger monitor. Also a new intraocular implant. Also new retinas.

ShadowWarrior4444 - 14-8-2008 at 15:43

I'm a fan of ionic liquids for dissolving oxides, however it may not be all that successful for alumina--you'd need to look through the available ionic liquids.

Superacids might be effective, too. Even attempting HBr or HI may work. Perhaps a mix of HCl and Br?

kilowatt - 14-8-2008 at 19:25

Fused cryolite (Na3AlF6) will dissolve aluminum oxides. This is what they use in industry to prepare electrolyte for aluminum extraction from its refined bauxite ore. Such solutions melt at considerably less than 1000°C.

chloric1 - 15-8-2008 at 02:33

Quote:

Originally posted by kilowatt
Fused cryolite (Na3AlF6) will dissolve aluminum oxides. This is what they use in industry to prepare electrolyte for aluminum extraction from its refined bauxite ore. Such solutions melt at considerably less than 1000°C.

Exactly, and calcium oxide, sodium carbonate, or the respective borates with fusion might work. Then the mixture should be more soluble in acids/alkalies for workup. Need to look for that 1950's patent on generating HCl soluble slags in boron thermite. The basic theory is you add calcium oxide to the thermite and the slag is easier to remove since aluminothermic boron does not separate well from the slag and hence must be removed chemically.

Aha! found it. It was actually from 1962 but filed 1956.

[Edited on 8/15/2008 by chloric1]

Attachment: US3016288 ALUMINOTHERMIC_PROCESS_OF_MAKING_BORON[1].pdf (239kB)
This file has been downloaded 2207 times

blogfast25 - 15-8-2008 at 04:30

I've done the Brauer procedure for AlB12 but with chlorate instead of sulfur. Hard to recover the product though...

chloric1 - 15-8-2008 at 14:46

Really thats great! Does the aluminum sulfide make aluminum oxide easier to separate from your regulas? I would like to try this with calcium oxide added in. Of coarse the boost will have to be increased according to the specific heat of Calcium oxide. Would 10% remove the Al from AlB12 I wonder? It should at least help remove/loosen the calcium aluminate.

Related question MgO in stomach acid

gregxy - 15-8-2008 at 15:00

I have some MgO pills (dietary magnesium suppliment).

When I have eaten them they don't seem to dissolve very well, so I was curious of I get anything out of them.

So I tried disolving them in vinegar. Even after heating they
did not dissolve to any extent that I could determine.
I expected them to form magensium acetate which should
be water soluable.

Next I tried 30% HCl. This did disolve them (and the solution
got warm).

So I am wondering if stomach acid is strong enough to dissolve them. Any ideas?

Magnesium is supposed to help you sleep.

ScienceSquirrel - 15-8-2008 at 16:05

Vinegar is a very weak solution of acetic acid.
Some antacids are calcium carbonate and they disssolve in the human stomach so I would guess that your magnesium oxide tablets dissolve without any problem.

blogfast25 - 16-8-2008 at 05:31

Quote:

Originally posted by chloric1
Really thats great! Does the aluminum sulfide make aluminum oxide easier to separate from your regulas? I would like to try this with calcium oxide added in. Of coarse the boost will have to be increased according to the specific heat of Calcium oxide. Would 10% remove the Al from AlB12 I wonder? It should at least help remove/loosen the calcium aluminate.

Yes, the aluminium sulfide makes all the difference. This is most apparent in the SiO2 thermite, where boosting with Al/sulfur is the standard procedure. See here and here. With sulfur, the stinky alumina/aluminium sulfide slag literally falls apart when immersed in water (Caution: much H2S is generated!) Mechanically, the slag is also soft and breaks up real easy.

The same thermite, with the Al/S system replaced with Al/KClO3, yields the hardest slag I've ever come across, so much so that the globules of Si metal are practically irrecoverable from the slag: for some reason Si produced in this way sticks to the alumina/fluorite slag mix like mad...

Reducing the amount of Al in the boron oxide thermite simply yields less AlB12, not pure boron.

Never tried slagging with CaO but it's on my list of things to do before I die..

[Edited on 16-8-2008 by blogfast25]