Aluminium powder through sodium hydroxide reaction

[Dr. Hextromeister]

Hello all.


A method I have been experimenting with for a while is to react aluminium foil with sodium hydroxide in order to produce large quantities of aluminium powder. Once the reaction is complete, the foil should be reduced to a brittle mush allowing for further ball milling.

Due to the caustic nature of the substances used and gases present, a gas mask and a pair of safety gloves are advised. THE FOLLOWING PROCEDURE MUST BE DONE OUTSIDE!






Step 1

Roll pieces of aluminum foil into small balls or cylindrical tubes and place in a container. Soup cans work good (Yes, I know most are made of Al but they are hardly effected by this process).

Step 2

Pour 1/2 a teaspoon of sodium hydroxide onto the foil. Shake the container slightly to ensure spread of the sodium hydroxide.
Step 3

At this point it would be a good idea to put on a gas mask and prepare to stand back.

Measure out around 75 ml of water and begin slowly pouring it over the foil. In around 5 seconds steam and hydrogen gas will start jetting out of the container so stand back until this has completely stopped. After 10 minutes check to see if the aluminium has become brittle enough by poking an old pencil or stick into the crumpled foil. If the foil is dark in colour and falls apart when prodded, it is done.
Step 4

Empty the foil into a seperate container of water to wash away the sodium hydroxide solution. Next, get an old cloth and continue to wash and strain the foil of water a further 4 to 5 times. Once done, crush the ball of aluminium mush and lay it out on a smooth surface to dry for a few hours.

Once the aluminium mush has dried it can be powdered using a mortar & pestle or placed straight into a ball mill.

Also with pictures on my site - http://www.geocities.com/drhextromeister/apm1



Has anyone else experimented with a similar method? If so, what was the purity of the final product like? How well did it perform?


For about £1.00 I can get around 300g of powder. Suggestions for improvement will be highly valued..

[Alexires]

Riiiiiight.

Welcome to Yr 12 Chemistry.

Aluminium is protected from reacting with things like the Air and Water by a layer of Al2O3 around it. The NaOH dissolves this layer thus

Al2O3 + NaOH --> Na+ [AlOH4]-

After that, its just bare aluminium which reacts with the water to form Al(OH)3. (this is from a uni website, I always though it just went to Al2O3 straight away)

2Al + 6H2O --> Al(OH)3 + 3H2

Then this happens.

Al(OH)3 + NaOH --> Na+ [AlOH4]-

I'm pretty sure that if you tried to use your "aluminium" powder in anything, it would do jack shit.

Even if that isn't exactly correct (some of that info was from the net, we are just been taugh what Al2O3 does in the presence of a strong base such as NaOH) your reaction goes from Useful Aluminium --> Useless Crap very fast.

[megalomania]

The premise is actually sound. I use this reaction to generate hydrogen gas, and it does indeed make the aluminum foil "mushy" once the reaction proceeds. I don't agree that you need a gas mask because the reaction is not that vigorous, but safety goggles are of critical importance when working with caustics like NaOH.

The trick is to interrupt the reaction after a short period of time. I always ball my aluminum, but I want complete reaction. I would recommend a flat sheet of foil steeped in a shallow tray of hydroxide solution. Prepare the solution beforehand and you will not have as much trouble.

The partially reacted foil sheet would be considerably weakened after a short time allowing it to be more easily processed.

Now, as to this being suitable for powder I am not so sure. It is quite likely it will be contaminated with the aluminum hydroxide compound that forms when aluminum reacts with sodium hydroxide. Of course the purity and consistency of the final product depends entirely on your intended use.

I am sure many of us are able to replicate this experiment, yes? The man has provided pictures and a walkthrough after all. My two cents worth are only learned conjecture based on what I have experienced with this reaction, but Dr. Hextromeister has actually gotten results with his method, so maybe it works better. Peer review works for me and you...

[Dr. Hextromeister]

Thanks for your input.


Al2O3 + NaOH --> Na+ [AlOH4]-

After that, its just bare aluminium which reacts with the water to form Al(OH)3. (this is from a uni website, I always though it just went to Al2O3 straight away)


That's where we stop the reaction.



I never stated the purity of the powder and I'm pretty damn sure it's not going to be of any technical use in it's current state. What I am trying to do is work on this process to come up with accompanying methods to lower impurities. As Megalomania said, the trick is to stop the reaction once the foil is weakend enough (That's why I suggested a gas mask when monitoring. Believe me, breathing in the gasses HURTS.) allowing for easy ball milling.


None of the aluminium should be dissolved. The foil should still remain, only partially attacked by the NaOH.



Maybe a thermite test is in order? :)

[crazynlazy]

If you're worried about any kind of impurities in the form of aluminum hydroxide, why not just wash the solution of sodium hydroxide, aluminum and alleged aluminum hydroxide with an acid? If hydrochloric acid was use the two bases would react as follows:

4HCl + Al(OH)3 + NaOH --> NaCl + AlCl3 + 4H2O

At this point the sodium and aluminum chloride can be filtered out because of their solubility in water, and any remaining undisolved solid can be extracted and ball milled for further use. The only problem after that I can see in this reaction is the amount of aluminum in the final product.

[ultma]

If you're worried about any kind of impurities in the form of aluminum hydroxide, why not just wash the solution of sodium hydroxide, aluminum and alleged aluminum hydroxide with an acid? If hydrochloric acid was use the two bases would react as follows:

4HCl + Al(OH)3 + NaOH --> NaCl + AlCl3 + 4H2O

At this point the sodium and aluminum chloride can be filtered out because of their solubility in water, and any remaining undisolved solid can be extracted and ball milled for further use. The only problem after that I can see in this reaction is the amount of aluminum in the final product.


HCl would not be a good choice. It likes to react with Al often violently :eek:

[good1]

Aluminium powder can be obtained from Fibreglass and polyester resin outlets.
>www.polyfibre.co.uk< Under powder and pigments,subheading Metal Powders.Used for, in theri words "Sintered metal powder which provides a true metalic finish in castings and laminates".

Any good.?

[DONMAN]

I really weak acid might do well in this situation... BUT DEFIANTLY not HCl. You may want to use some vinegar on the weakened aluminum foil before you powder it.

[Frunk]

I really weak acid might do well in this situation... BUT DEFIANTLY not HCl. You may want to use some vinegar on the weakened aluminum foil before you powder it.

I've been able to get vinegar to attack very fine steel wool, but I somehow doubt the vinegar will attack the otherwise chemicaly resistant aluminium oxide passivation layer. Do-it-yourself paintballers that want to anodize their own aluminium use NaOH to strip it and previous anodizing for a reason... Last time someone tried acids, even HCl, it only removed the oxide layer in spots then hollowed the metal from that spot on. Bases are good against Al2O3 and vinegar is very likely too damn weak.

[DONMAN]

True, but possibly some diluted sulfuric. The thing is you need it to be a slow reaction, as that makes it much easier to control. Vinegar is way to weak, even concentrated HNO3 has a hard time breaking that layer down on aluminum.

[Meawoppl]

Sounds like a grain boundary attack to me. Have you tied any other types of Al? Most cast objects are 6% Si and should be considerably more resistant to this method b/c of the phase separation.

[Dr. Hextromeister]

Ok, I've recently treated some aluminium foil to a dilute solution of sulphuric acid.


The results look good. The foil is now hard and brittle, making the powdering process a whole lot more easier.

[nbk2000]

If there was an alloy of aluminum and X, where the X could be dissolved out without attacking the aluminum, wouldn't that make aluminum powder?

[Microtek]

Dr Hextromeister: How much Al foil do you use in your process? In the method you describe, it seems that practically all of the NaOH must react to form the aluminate. How much is "half a teaspoon" when you measure it? 5 g? 40 g NaOH will react with about 27 g Al.

Conserning the workup, I would wash the powder in dilute HNO3. Nitric does not attack Al very readily due to the oxide coating as has been mentioned above, but we are not interested in removing the oxide coating anyway, just the hydroxide. Acetic acid is probably just as good.

[panzerkampfwagen]

How about electrolysis of molten (350C)/aqueous Aluminum Sulfate? If the electrodes are aluminum, with nothing more reactive to consume, the resulting sulfate group or sulfuric acid would consume the electrodes, leaving the aluminum to either precipitate at the bottom or create a film over the electrode which, if removed periodically, would be fine enough to break into a powder. Aluminum sulfate is very cheap and is used in making potting soil more acidic and is therefore available at any sort of gardening/plant/home store. I would not, however, advise being anywhere near it since it may or may not produce gaseous sulfuric acid which is not fun for your lungs.

[panzerkampfwagen]

How about aluminum oxide and phosphorous? Aluminum oxide, being ionic, is easy to powder and phosphorous reacts readilly with any oxides. I have used a similar process for silicon with silicon dioxide and magnesium. In that process, the two are heated until it begins to, and then stops making cracking noises. It is then poured, while hot, into dilute hydrochloric acid, forming pure silicon and an interesting mushroom cloud of semi-dangerous gas, as well as hydrogen gas. The pure chemical rains down as a powder. The HCl may or may not be necessary, but it may be worth a shot. Aluminum Oxide can easily be produced by anodizing aluminum or using mercury as a catalyst, if you happen to have some old thermometers handy.

[JouMasep]

If there was an alloy of aluminum and X, where the X could be dissolved out without attacking the aluminum, wouldn't that make aluminum powder?

It certainly would –on the face of it.

The problem would lie in finding in “X”. This metal would have to be more electropositive than aluminum itself, so as to be preferentially oxidised. And we would then have to find the right reaction conditions.

This, together with the alloying of Al + X would be the major problems. (It would have to be done in an inert atmosphere) Forget about something like an Al / Na alloy and dissolve with sodium hydroxide of course –no metal would remain! Perhaps a reaction with an acid in solution of an alcohol? ‘Seems tricky.

(BTW the reverse of the proposed reaction is done all the time of course. Raney nickel is made by alloying aluminium with nickel and then removing the aluminium in a KOH solution. Nicely leaving a lot of activated hydrogen -as evolved- on the huge nickel surface)

[Gumby]

This all seems like a lot of work to get something that can easily be purchased...

[nbk2000]

Everything that is banned today, used to be easily purchased in days past, so what's your point?

[Dr. Hextromeister]

After treating a batch of crunched up aluminium foil with sulphuric acid solution there is now a coating of aluminium sulphate (Correct?) formed on the Al pieces. The foil now practically turns to powder when pressed on a hard surface, even more so than when treated through the sodium hydroxide method.


Any further advice on purification steps to ensure quality?

[penguin6636]

Quick question here: Because raw Al reacts so well with oxygen forming the oxide layer, if you have synthesized Al powder (or just filed down some Al) wouldn't the fine Al particles increase your total surface area of all the Al you have and form an oxide layer on your powder?

[Skean Dhu]

Penguin: That is a problem when making aluminum powder, Which is why unless you have an inert atmosphere using power sanders is counter productive, as is a water cooled grinder since the same product will result, useless alumnium oxide.

I recently saw a demo involving pyrophoric Iron particles that had been made from Iron Oxalate. Simply you take Iron Oxalate in a test tube and loosely seal one end, and heat the Iron Oxalate(apparently yellow) until the entire sample turns light grey. The process is detailed here
http://www.chemsoc.org/pdf/LearnNet/nc/classicdem_nc9.pdf

Now couldn't one simply acquire some Aluminum oxalate? and through the same process get pyrophoric aluminum? Granted this makes mixing into compounds and storage somewhat problematic, but wouldn't the reactivity be worth the trouble?

[FUTI]

to Skean Dhu: I doubt that is posible to obtain pyrophoric Al that way. IIRC Al can't be obtained through coal (carbon) based reduction like iron. That is at least what textbook say about the subject. Since knowledge is growing thing let give it a grain of doubt and say we won't know unless try it out. I have read some crap book that among other things stated archeological findings from the grave of some Chinese general. They dettermined the elemental composition of the sash (buckle?) found there and it contain 3 metals and one is Al what buffled me. Apparently the item is original (not fake) dated by isotopic analysis etc. How on Earth they made it in those days is beyond me.

This process you posted is based on oxalate tendency to decompose under heat making carbonmonoxide in process which can reduce iron(II)oxide made in the same process. Also note of warning - be cautious when doing that experiment since not only CO is toxic but it is very good ligand molecule that I'm positive to be able to make cluster compounds with iron which are liquids with low boiling point and those are also prone to decomosition back into iron and CO. So there you go, scale of process and design of reactor can mean difference between life and death.

[JouMasep]

Everything that is banned today, used to be easily purchased in days past, so what's your point?

NKB is right, if you are complacent about buying stuff, what do you do if the authorities cut off all supplies?

And I like to think out of the box as much as the next guy (see my feeble attempt at irony above)

But if we do have very adequate (OTC) methods already, I ask (in contrast to said attempt): is there not a point at which the discourse can become “too much”

With respect to the ingenuity of the concept per se, I say (to take an example) “aluminum oxide (from foil and broken thermometers) and phosphorous” to yield Al powder is well beyond practical limits. And how OTC is phosphorous anyway?

I’d much rather make an elaborate Al powdering device than my own little phosphorus factory –so as to produce nice quantities of Al powder for as long as I want.

Sometimes there is no decent chemical route to getting something that we can get so well by mechanical means. As nothing on this page -or anything you’ll find on the web or in publications- comes close, Al powder seems to be a point in case to me.

[flashpoint]

Dr. Hextromeister,

Any luck with the thermite composition, using this Al powder?

[jimmyboy1]

Take some aluminum foil and heat it on one side with a propane torch - this will oxidize one side and crystallize it causing a lot of stress on the foil - it will be very brittle afterwards and easy to crush - you will get a 50/50 mix of the oxide and aluminum metal.