Sciencemadness Discussion Board

Aluminium powder using acid method

Vikascoder - 3-5-2012 at 02:21

Getting extremely fine powder is a very big problem for a normal person. So to solve this problem i was thinking whether aluminium powder can be formed by reacting aluminium with concentrated sulfuric acid then displacing it with magnesium . This method works for preparing zinc powder by reacting it with hydrochloric acid then displacing it with magnesium. So i want to ask can aluminium powder can be prepared this way by reacting aluminium with sulphuric acid then displacing it with magnesium.

woelen - 3-5-2012 at 02:40

I never tried this myself, but I do not expect that this works. Aluminium is very reactive and easily reacts with water, when its oxide layer is removed. You can see this reactivity if you take aluminium and add a solution of copper chloride or copper sulfate plus sodium chloride to it. This mix destroys the oxide layer and then you see vigorous bubbling and formation of flocculent Al(OH)3 while it reacts with water.

Vikascoder - 3-5-2012 at 04:38

I think it would works . Because when i had tried this method i got extremely fine powder aluminium though i have not tested it till now. By the way industrially how german dark head black aluminium powder is formed.

Adas - 3-5-2012 at 08:53

German dark Al also contains 5% of carbon to enhance its performance. Probably you can make Al this way, if it doesn't react too fast with water.

And reacting Al with H2SO4 is rather a slow process, buy some Al2(SO4)3 instead.

barley81 - 3-5-2012 at 10:19

There is a tutorial on instructables for making aluminum powder. Shredded Al foil and charcoal are put into a rock tumbler with steel marbles for several days. After sieving, I got a moderately fine powder that burned very brightly when lit using a torch. I have no way of measuring particle size, though.

Sorry if this is OT. I thought it might be useful.

[Edited on 3-5-2012 by barley81]

Neil - 3-5-2012 at 14:43

Steel bearings may spark, that would be bad...

Check out the posts by 'the wizard is in'. He laid out safety data and bemoaned the dangers of a spark in a drum of powdered aluminum on several occasions.

barley81 - 3-5-2012 at 14:51

Ooh. I should've done some research last year before going ahead with that. Most of the aluminum was really coarse because of the way I shredded it. In that case, lead/antimony non-sparking media would be better.

lagerdale - 6-5-2012 at 18:47

Quote: Originally posted by woelen  
I never tried this myself, but I do not expect that this works. Aluminium is very reactive and easily reacts with water, when its oxide layer is removed. You can see this reactivity if you take aluminium and add a solution of copper chloride or copper sulfate plus sodium chloride to it. This mix destroys the oxide layer and then you see vigorous bubbling and formation of flocculent Al(OH)3 while it reacts with water.


Isn't that what mercuric chloride also do to aluminum?

If yes, why do people use toxic mercuric chloride to strip the oxide layer of aluminium, instead of safe copper chloride?

DougTheMapper - 6-5-2012 at 19:56

What about the thermal decomposition of aluminum oxalate?

FeC2O4 decomposes easily with heat to extremely fine Fe and CO2 - so fine, in fact, that it's pyrophoric.

I wonder if Al could behave the same way. On the other hand, Mg has sufficient reduction potential to strip O from CO2 so the same could be said about aluminum. However, IIRC the decomposition of oxalates are generally at lower temperatures than, say, the ignition temperature of aluminum in oxygen. Then again, it might be fine eno9ugh to be pyrophoric.

I am about to go to bed but I will try this tomorrow after work and see what happens, and whether Al will react directly with oxalic acid (It may passivate it; it's used for anodizing) or if I'm going to have to make some AlCl3 (Al dissolved in HCl) in solution first, add the oxalic acid, and heat to remove HCl. We shall see.

I have doubts about this method though... aluminum oxalate occurs as a tetrahydrate and the water of crystallization might destroy the hot aluminum powder.

[Edited on 7-5-2012 by DougTheMapper]

AndersHoveland - 6-5-2012 at 20:33

Quote: Originally posted by Vikascoder  
i was thinking whether aluminium powder can be formed by reacting aluminium with concentrated sulfuric acid then displacing it with magnesium.

If you intend the aluminum powder for pyrotechnic use, and have magnesium, there is a more practical route.

A mixture of aluminum and magnesium can be melted in a steel container, without much difficulty, using a propane torch applied underneath. This forms a brittle "magnalium" alloy, which can then be hammered into a fine powder. Magnalium has many of the advantages of magnesium, while being much more resistant to corrosion, for use in pyrotechnics.

woelen - 6-5-2012 at 23:19

Quote: Originally posted by Vikascoder  
I think it would works . Because when i had tried this method i got extremely fine powder aluminium though i have not tested it till now. By the way industrially how german dark head black aluminium powder is formed.
Are you sure about that? Could you please provide us with a reference or link which elaborates on this? I am very doubtful about your claim. You did not test your powder, so that is the first you need to do and you also have to show that it really is aluminium and not unreacted magnesium powder. At this moment I am not yet convinced, but I remain open for new ideas.

bbartlog - 7-5-2012 at 05:27

Quote: Originally posted by DougTheMapper  
What about the thermal decomposition of aluminum oxalate?
FeC2O4 decomposes easily with heat to extremely fine Fe and CO2 - so fine, in fact, that it's pyrophoric.
I wonder if Al could behave the same way.
[Edited on 7-5-2012 by DougTheMapper]


No. Aluminum is too readily oxidized for this to work. The pyrolysis of some transition metal oxalates does yield (some) elemental metal (nickel, silver, iron, copper at least), but from aluminum oxalate you get alumina. Not a bad way to prepare finely divided alumina, as a search on 'pyrolysis of aluminum oxalate' will inform you, but useless as a way to aluminum powder.