Sciencemadness Discussion Board

Ideas for fine Al and Mg powder

garage chemist - 20-6-2005 at 08:10

Magnesium and aluminium can easily be alloyed together at home, even in a small crucible over a bunsen burner. When a ratio of 50/50 (per weight) is chosen, one gets magnalium, a very brittle alloy which can be crushed with a hammer and ground into a very fine powder with mortar and pestle.

This is ideal for applications like flash powder, but for reduction purposes (like production of white phosphorus) pure metal powders would be better.

For magnesium, my idea would be to make magnalium and then dissolving the aluminium with an aqueous base like NaOH (like the way raney nickel is made). Magnesium is resistant against aqueous bases. This would leave behind a very fine and extremely active magnesium powder (might be pyrophoric, but it could be washed first with alcohol, then with ether and then with a solution of paraffin in gasoline prior to drying to coat the particles and prevent oxygen access).
My worry would be that the magnesium could form a local galvanic element with the aluminium, where the magnesium would protect the aluminium like a sacrificial anode and when it's gone, the aluminium would be the next to dissolve. This would need experimentation.

For aluminium, my idea would be to make a solution of an aluminium salt (aluminium sulfate or chloride) and place a chunk of magnesium in it, which should dissolve and reduce the aluminium ions to the metal, which hopefully separates as a fine powder instead of a solid coating.
Like with the production of lead salts by placing a chunk of lead into a copper salt solution.

What do you think of these methods? Metal powders (at least fine ones) are difficult to get, so I might give this a try some time in the future.

chemoleo - 20-6-2005 at 08:32

Finely divided Mg reacts with water, albeit slowly. The more finely divided, the faster the reaction.
And an aqueous solution of NaOH will certainly contain H2O.
For that reason, I don't think it will work. Unless you dissolve NaOH in a non-aqueous unreactive solvent (pyridine springs to mind). But then i am not sure if the NaOH reaction would work in the first place...

I don't think you'll have much luck there :(

garage chemist - 20-6-2005 at 08:42

Yes, I remember that, some magnesium ribbon thrown into water makes a very slow, but visible stream of hydrogen bubbles. My chemistry book says that it's resistant against basic solutions- but that could mean the same as the stated "resistance" against water.

What about the aluminium powder precipitation from aluminium salt solution + magnesium?

chemoleo - 20-6-2005 at 08:51

Again, aluminium powder reacts with water, something I painfully discovererd when I tried to isolate superfine Al from Al-acrylic paint. Maybe use nonaqueous ionic solvents once again. Not sure if the reaction would work though, nonetheless...

Re. the Magnalium and NaOH- I suppose you have a point. Mg(OH)2 is not much soluble, so it will form a coat on the Mg, which is resistant. While Na[Al(OH)4] is soluble. However, in an alloy, the Mg isn't present as little nanosized particles, it is in fact atomised. Which for sure WILL react with H2O, atom per atom.
The resistance probably refers to blocks of Mg, not atomised Mg.

garage chemist - 20-6-2005 at 09:20

OK, thanks for the help.

I'll think about some possible non- aqueous solvents then...

12AX7 - 20-6-2005 at 09:46

Yeah, magnalium is more or less a solid intermetallic composition of MgAl (not magnesium aluminide, since it's metallic). At room temperature it's about 0.58 mole% Mg (gah, I hate %atw phase diagrams).

Tim

evil_lurker - 20-6-2005 at 10:38

You can grind magnesium, zinc, aluminum and a bunch of other stuff.

This guy did it, and I'm about to add on a similar grinding apparatus to my big gaundy ball mill.

http://www.members.shaw.ca/justin.le/grinder/grinder.html

Anyways quoted from this website, "Magnesium is somewhat problematic because of its reactivity with water. A spoonful of potassium dichromate added to the bath greatly suppresses the amount of bubbling that takes place. I've also used mineral spirits instead of water when grinding magnesium with very fine sandpapers, but this is less convenient."

[Edited on 20-6-2005 by evil_lurker]

Making Aluminium and Magnesium powder with the ball mill.

Lambda - 20-6-2005 at 17:01

Quote:
Originally posted by Lambda on 14-6-2005
Reagents and Apparatus Acquistion / Woo hoo, I built a working ball mill!!! /

http://www.sciencemadness.org/talk/viewthread.php?tid=3957
Quote:
To make aluminium powder, I used the steal tumbler with brass balls. It scared the birds out of the trees when it was on !. I allso added some stearic acid (~5%) to coat the aluminium powder, and opend the tumbler from time to time to let it react with the air. As a starting point, I used finely snippered aluminium foil, as what you would expect if made from a coffee grinder.


The longer this Ball Mill opperates, even up to 3 - 4 weeks, the finer your powder. It can even become dangerousely fine, and become pyrophoric. The stearic acid works as a coating agent to protect the powder from atmospheric oxidation.

This coating layer may be removed by a sutible solvent. This solvent may not contain halide groups, as would be used to preform a Grignard reaction. Maybe Tolueen will work fine.

CAUTION !!!! This fine powder is extremely dangerous, for in it's dry form it will ignite in the air in an explosive manner !. Furthermore, mixtures of this powder with many organic solvents and in perticular halide containing solvents like chloroform are powerfully explosive. These mixtures are known to detonate for no apparent reason. A slight vibration may trigger it off. Even water and aluminium powder (stychiometric) is known to detonate with more explosive power than that obtained by TNT.
Quote:
Ignited aluminium or magnesium powder can blind you permenantly !

garage chemist - 21-6-2005 at 00:36

On a german university site, I found an experiment to the recycling of aluminium.
They first mix 45g NaCl, 45g KCl and 10g NaF (I need to make this from my 40% HF, not fun), melt the salts together and then add pieces of scrap aluminium. They melt under the molten salt and the aluminium oxide coating dissolves (it forms some kind of complex with the fluoride). After cooling and breaking up the fused salts, a perfectly shiny aluminium blob is obtained.

This sounds like the perfect procedure for production of magnalium, since it eliminates the need for a protective gas and prevents oxidation of the metals. One would first melt the required amount of aluminium under the salts and then add the magnesium in solid form, under gentle stirring.

I'm so interested in magnalium since it is really easy to powder and a ball mill would produce a much finer powder from it as it could ever do from aluminium.

For production of magnesium powder from magnalium by dissolution of the Al, one could add some dichromate to the NaOH solution to protect the Mg powder and eliminate its pyrophoric tendencies.
Not sure if it will work though... you also need to use protection against the carcinogenic dichromate spray mist from the hydrogen production.

Or just use the plain magnalium... you don't even need a ball mill to make a powder fine enough for use in flash. Mortar + pestle is enough.



Hey, what about dividing the pure metal (Al or Mg) in the salt melt by strong agitation? We could melt aluminium + the salt mixture in a CLOSED crucible and then shake it up really strong until it has cooled down and solidified.
The shaking of molten sodium in an inert solvent is the standard method for production of fine sodium powder for some applications where solid Na reacts too slowly. The sodium is divided so finely that the suspension (in, for example, xylene) looks like milk.
This could be a method for production of spherical Al and Mg. For turning it into flake (for use in flash powder), short ball milling would suffice.


[Edited on 21-6-2005 by garage chemist]

12AX7 - 21-6-2005 at 09:34

You can use straight chlorides for a cover flux. Try an eutectic between any of the four NaCl, KCl, CaCl2 and MgCl2. Fluorides I'm told are nice but not strictly necessary (you can use 5% CaF2 as well). The problem is a little oxygen and steam dissolves in it, oxidizing the metal anyway to produce sticky MgO (not very fluxed, unlike Al2O3 which happily floats in the salt), also adding hydrogen to the melt, leaving it full of bubbles on solidification. Not only that, magnesium is lighter than the salt melt, so although it will protect it as a film, it will oxidize much more than aluminum does.

I made about 10 pounds of magnalium without flux by melting aluminum then adding the tranny cases, I probably lost a pound or two of metal to combustion but I've still got more than plenty of magnalium to last me. Well, unless I want to do a 10 pound thermite pour.
Looked something like this, but with more slag mess: http://webpages.charter.net/dawill/Images/PouredIngot.jpg
Finished: http://webpages.charter.net/dawill/Images/Magnalium.jpg :P

Tim

12AX7 - 21-6-2005 at 09:37

Missed this...
Quote:
Originally posted by garage chemist
Hey, what about dividing the pure metal (Al or Mg) in the salt melt by strong agitation? We could melt aluminium + the salt mixture in a CLOSED crucible and then shake it up really strong until it has cooled down and solidified.


Well let me put it this way, I've recovered bulk metal (and suprisingly little Al2O3) from aluminum filings, so it does flux it. But I wasn't trying to emusify it, either.

You're welcome to try!

Tim

garage chemist - 22-6-2005 at 03:10

My 1kg of scrap magnesium plates from ebay just arrived (the seller claimed them to be 98% pure, I'm not certain on the purity though).
It's quite easy to cut with a wood saw, but a metal saw doesn't work nearly as well. A wood file easily produces quite an amount of coarse filings from it. I might try ballmilling those... if I get around to building a decent ball mill, my old one broke because it was made of lego:D.
A strip of the material burns like magnesium is supposed to do, but it doesn't catch fire that easily, it first melts, forms a drop and then very slowly catches fire. Then the whole strip burns, though. Any ideas on how I can test the purity?
What do you mean by "tranny cases"? Is that another source of magnesium?

I'll try to make magnalium, it won't be easy though since I don't have a furnace, only a smallish bunsen burner and an iron crucible for it.

darkflame89 - 22-6-2005 at 04:21

At what temperatures does the eutectic chlorides melt?

The_Davster - 22-6-2005 at 05:07

Could you just dissolve a small amount of the alloy in limiting dil. nitric acid and find the pH of it. If sugnificant Al is present it will be acidic and if it free of Al it should test neutral. Unfortunatly this does not tell if any other metals are present.

garage chemist - 22-6-2005 at 09:14

OK, I made magnalium in my crucible (7g Mg + 8g Al), it was no problem once the aluminium was molten. The solid Mg melted in the liquid Al in less than 5 minutes and became one with it on stirring with a wire. On exposure to air, it slowly caught fire and burned with a red glow. Putting on the lid stopped the fire, so it doesn't react with nitrogen.
The cooled alloy had the same mechanical properties as glass: hard, but brittle.
I managed to get a grey, fine powder by crushing with a hammer and grinding it in a mortar for 20 minutes.
Mixing 1 part of this with 2 parts KClO3 produces a mixture that burned at moderate speed with a crackling sound and very bright light, but no flash powder. Even coarse Mg powder burned much faster with KClO3.
So magnalium is unsuitable for flash powder, but excellent for bright white flare
compositions and stars.
Ball milled magnalium could be a totally different story though, because this would make a much finer powder than what could ever be obtained from Mg or Al.

I put some of the magnalium powder into water and added some NaOH to dissolve the Al and leave behind ultrafine atomized Mg.
But surprise, the magnalium turned out to be completely inert to even hot NaOH solution! No hydrogen was produced.

Next experiment was to dissolve some Al2(SO4)3*18 H2O in water and add magnesium filings to precipitate Al from solution as a fine powder. Nothing precipitated, the Mg just dissolved and lots of hydrogen was produced.

So my two ideas proved to be useless... so I need to build a ball mill to make my magnesium and aluminium powders.

[Edited on 22-6-2005 by garage chemist]

12AX7 - 22-6-2005 at 10:26

Sounds about right. My VW transmission case is probably 95% pure (AS41 I suspect, 4% Al 1% Si), it melts with speckles of burning, then around bright red glow it finally starts burning at the thermite-igniting white heat. Water also quenches it.

I'm not suprised Al sulfate didn't make aluminum, both react with H2O on contact to produce hydroxides.
Quote:
Originally posted by darkflame89
At what temperatures does the eutectic chlorides melt?


Depends. NaCl + KCl (equimolar) has the highest at 1215°F = 657°C, convieniently just suitable for aluminum. K2MgCl4 has a melting point of 423°C. 33% NaCl + 67% CaCl2 melts at 939°F.

Tim