13 replies to this topic

[Gary]

Hi,
I am trying to make some very, very fine aluminium powder in the nanometre particle size range.
Wary of the hazards involved, namely pyrophoricity (spontaneous combustion in air, possibly catalysed by moisture), I might try ball-milling aluminium foil (kitchen foil is readily available) under oil or kerosene, in order to exclude oxygen and moisture and thus prevent a flare-up. After several days of milling, I then intend to remove the oil by dissolving it in a lipophilic (oil-soluble) organic solvent, such as hexane or toluene. Residual solvent can be removed from the aluminium by evaporation at room temperature. (most organic solvents are volatile).
Question is, would the very fine aluminium produced by this method be safe to store without the risk of spontaneous combustion (pyrophoric flare-up?)

[Arthur Brown]

In a word NO!

nano fine Al would be a hazard on several counts! Spontaneous combustion and atmospheric pollution being the first that spring to mind. There are ways of passivating fine metals but always there will be a risk attached.

[al93535]

I don't think you would ever get nano-sized aluminum powder from a ball mill. At least not in that time span, a month maybe... But I still have my doubts.

When you evaporated the solvent from the powder you would have a problem. The aluminum would either 1: heat up and become passivated from the oxide layer forming. 2: heat up and catch fire while it was oxidizing. Either way, its going to do what you tried to prevent it from doing by milling without oxygen.

If you must make the al yourself, which will be far from nano sized, mill the al and open the jar every 4 hours to let in Oxygen so the particles are passivated. This is going to take a long time starting with al foil....

You can purchase nano-aluminum powder, it is extremely expensive, but whats the point really? Better flash? nah...

[seymour]

What do you want to do with the Aluminium? Ideally there will be alternatives that are fairly easy to buy without costing you too dearly.

[FrankRizzo]

Without a lubricant and a carrier solvent, you will not even achieve less than 20micron particles by ball milling. Once the particles get to a certain mass/cross-section ratio, they begin to impact weld with one another, and particle size cannot be reduced further. Lubricants (like stearic acid) dissolved in a carrier solvent will reduce this effect enough to bring the material down to 2-5micron, but will never achieve nano-sized particles (0.01micon).

Commercial nano aluminums are produced by a high-energy electric discharge through a thin aluminum wire in an inert atmosphere (helium, argon, sometimes nitrogen). The wire superheats (evaporates) from a solid to plasma. As the plasma particles contact the inert gas atoms of the chamber, they cool down and condense back to nano aluminum particles. The pressure in the vessel is controlled during the process to favor smaller particles. This is not something you're going to do in the garage successfully.

Edited by FrankRizzo, 24 March 2009 - 09:28 AM.

[Gary]

I was hoping to make ultra-fine aluminium for flash comps intended for use as breaks in shells, inserts and crossettes.

[digger]

I was hoping to make ultra-fine aluminium for flash comps intended for use as breaks in shells, inserts and crossettes.

Why not just buy dark flake aluminium? I have milled aluminium foil to a fine powder, it is possible, it takes ages, you can't get much shredded foil in a big mill jar, simply not worth the effort in my opinion when you can get German Dark in region of £10 - £35 per Kilo depending on what suppliers you have access to.

Edited by digger, 18 April 2009 - 03:39 PM.

[Gary]

Why not just buy dark flake aluminium? I have milled aluminium foil to a fine powder, it is possible, it takes ages, you can't get much shredded foil in a big mill jar, simply not worth the effort in my opinion when you can get German Dark in region of £10 - £35 per Kilo depending on what suppliers you have access to.

I just enjoy making my own pyro materials. Besides, it is probably cheaper to make your own aluminium....you can buy thin aluminium foil in Tescos for a few pence. Put this in a ball mill loaded with suitable media, then wait, wait, and wait... hey presto! Fine aluminium powder. This can then be graded according to particle size by passing though a series of mesh. OK, the time factor is a down-side, but I can live with that. After all, if the ball-mill is outside in a safe location, well away from property or persons, it does not require any 'baby sitting'. All it needs is a little venting every few hours to allow the aluminium particles to oxidise in a controlled, safe manner.

[digger]

I just enjoy making my own pyro materials. Besides, it is probably cheaper to make your own aluminium....you can buy thin aluminium foil in Tescos for a few pence. Put this in a ball mill loaded with suitable media, then wait, wait, and wait... hey presto! Fine aluminium powder. This can then be graded according to particle size by passing though a series of mesh. OK, the time factor is a down-side, but I can live with that. After all, if the ball-mill is outside in a safe location, well away from property or persons, it does not require any 'baby sitting'. All it needs is a little venting every few hours to allow the aluminium particles to oxidise in a controlled, safe manner.

Fair enough, I make a fair few pyro chems myself too. But generally only those that are not readily available like barium salicylate etc etc

I am sure it does not work out that much cheaper at a couple of quid for 300 grams of aluminium foil. One supplier I know of has dark ali at about £7 a kilo. I doubt you would get your home milled stuff to the same quality as a good dark ali either.

Edited by digger, 18 April 2009 - 05:29 PM.

[Gary]

Fair enough, I make a fair few pyro chems myself too. But generally only those that are not readily available like barium salicylate etc etc

I am sure it does not work out that much cheaper at a couple of quid for 300 grams of aluminium foil. One supplier I know of has dark ali at about £7 a kilo. I doubt you would get your home milled stuff to the same quality as a good dark ali either.

I have made small quantities of very satisfactory perchlorate-based flash powder from aluminium foil which has been ball-milled for continuously for 5 days (with occasional venting, of course), then screened through mesh. The fine aluminium powder produced this way has a silvery-grey appearance, and is so fine that the individual particles can not been seen under the naked eye. Not quite German Dark or Indian Blackhead, but good enough to suit my needs.

[cooperman435]

Gary its still no where near dark ali though mate and whilst some class flash as a comp that will report in a small confined tube and make light I class it as something that will self confine under 1g which I assure you (as I know from personal experience) you will never manage from foil no matter how long you mill it for.

[Arthur Brown]

Some serious research into the metallurgy of aluminium may yield a method for manufacturing fine powders. Less time and money could easily buy you pyro aluminium of several grades. Messing with pyrophoric metal preparations is hardly a safe lab practice in a well kitted lab. In a home lab it is approaching suicidal! Realistically if it isn't on the pyro market then you may not need it!

[digger]

Realistically if it isn't on the pyro market then you may not need it!

Very true, however it can be good to experiment with new things that have not been published before. As all we are allowed to do is experimentation anyway.

[Mumbles]

The sieves even approaching the mesh of the standard flash grade Al are extremely expensive and not very accurate anyway. The particle size is measured under a microscope or similar. There are other methods using a suspension of the particles in a liquid and measuring the time it takes to settle.