atomizing aluminium into powder

[oldmanbeefjerky]

Hello,

 

I just fixed up the broken welder i got from my metalwork class, as well as all the bits needed to use it properly, and i found my self at a disposition, not having anything to weld, so i thought, what could i weld.

It crossed my mind that i couldnt weld the large amount of aluminium chunks i have, since they would burn in the air, or melt and boil away, and thats when i thought,

Could i make atomized aluminium powder, if i were to boil aluminium with an arc, in an oxygen free environment?

 

First i thought two aluminium rods together, 1 ground, the other live positive, but that would mean that allot of aluminium would just end up melting and falling to the bottom of the container. then i thought, what if i use an inert rod for the live positive, and just a ceramic cup holding the aluminium that will be boiled. but then i thought, what on earth could i use? carbon? steel? copper? i dont really know what effect that might have on the powder.

 

The aim is that the aluminium gas produced would sublime on the inner surfaces of the container as aluminium powder, and then a few taps gives me about 2-5 spoonfulls of powder at a time.

initially i would expect the first bits of aluminium gas to burn, but then after a small amount of time the oxygen would be completely consumed. another thing i could do is use some kind of a vacume pump which sucks the gas from the container and through an air filter.

 

What would be the best way to go about doing this? i dont expect to do large batches at a time, nor get much powder at a time, but then again, im not really going to use this at a very fast rate, for stars.

[Arthur]

You scare me! Yes one way of producing small mesh Al is to spray molten Al with inert gas into an inert gas cooling area. As a DIY project that much molten aluminium is likely to kill you if it meets water or flesh. Plan your toy so that there is NO possibility of anyone getting hurt, then move it a mile away. ALL my flameproof firing gear says specifically "no protection against molten metal"

 

Plus all fine fresh aluminium is pyrophoric, til it establishes an oxide coating, it could burst into flame any time.

[oldmanbeefjerky]

when you say "that much molten aluminium? how much do you think im using?

Im only doing a few grams as a time, unless i move to my next big idea which is to do the exact same thing, but run it through a long length of copper pipe, then bubble out through a one way valve going into some oil, to make sure that if there is combustion, it doesnt somehow lead back up the pipe and burn up all the aluminium, as well as keeping it all oxygen free

 

All of this is very small scale.

once there is enough dust inside the pipe, ill just empty it out , put some more aluminium in the ceramic container, and keep on going!

 

even if there was an explosion of the aluminium somehow, i find it almost impossible that it will breach the crucibal, and even moreso that it will cause harm to anyone within 15M of it. safety is pretty straight forwards with this,

what i need to know however is, what would be the best setup of an electrode and some aluminium , to acheive the boiling aluminium i desire, and what electrode should i use (aside from tungsten)?

[Mumbles]

The best setup would probably be to not to do it. I think you have a very delusional view on how this works. Subliming things does not usually give powders. You'd be more than likely growing crystals of aluminum. Also if you're doing this in a container, how do you expect to get the solidified aluminum out without dumping it back into the molten aluminum? You'd be better off with a block of sand paper to get any sort of powder out of those aluminum chunks. Your posts really do not give confidence in most that you can do this is a safe manner.

[Arthur]

OMBJ this thread makes you a likely winner of a Darwin Award.

 

You clearly have little idea of how many things could go wrong and how much pain you could be in when they do. ALL development projects go wrong sometime.

[oldmanbeefjerky]

Perhaps an illistration is in order. Ill show you as soon as its done. Also Mumbles, i am placing a small ceramic crucibal inside a larger ceramic crucibal. the small one will hold maybe 2-5 tablespoons of molten aluminium at a time, tops.

 

 

i didnt include the place where the aluminium would be subliming in under a strong vacume, since i have not yet decided upon how i should do it, or whether i should use my previous idea.

Edited October 29, 2011 by oldmanbeefjerky

[Mumbles]

Might I suggest this setup? Link

 

I did always find it somewhat ironic that you're from Darwin, Aus.

[oldmanbeefjerky]

This has been the third time someone has said that. until i found out what a darwin award was, i always wondered how the fact i am from darwin and the current topic related, whatsmore how they knew i was from darwin. though i now know it has nothing to do with it.

Also Har Har, im serious though. what should i use as the positive until i can get tungsten to boil the aluminium like in a TIG weld?

Also i already collect stamps

[Arthur]

A cup full of molten metal spilt on the floor will flow and if it finds your feet they will be so cooked that they may have to be amputated, likewise if you get molten metal on your hands or face. This is not an area of experiment without risk.

 

The old style method of fine Al powder is to get a belt of abrasive paper under oil and drive it against an aluminium ingot, for hours, then drain the oil off the powder.

[Bonny]

Might I suggest this setup? Link

 

I did always find it somewhat ironic that you're from Darwin, Aus.

 

I almost spat beer all over my keyboard! Too funny!

[oldmanbeefjerky]

A cup full of molten metal spilt on the floor will flow and if it finds your feet they will be so cooked that they may have to be amputated, likewise if you get molten metal on your hands or face. This is not an area of experiment without risk.

 

The old style method of fine Al powder is to get a belt of abrasive paper under oil and drive it against an aluminium ingot, for hours, then drain the oil off the powder.

 

hence why i wont use cup fulls of metal, but rather a a couple spoonfulls worth of metal.

Once i make the crucibal for the aluminium , i will upload a picture, then you can tell me its dangerous.

 

which reminds me, would it be at all any more dangerous to vapourize small cuts from magnesium alluminium alloy wheel rims? in order to get a somewhat better than just aluminium magnalium powder?

im talking aluminium rims with a maximum magnesium content of 10%, not 90% like those old collectable mag rims.

[Arthur]

Can we all sing the "Theme from M*A*S*H" together please starting " Suicide is Painless....."

 

OMBJ You are either brilliant or an idiot it's hard to tell which til you complete your research BUT previous world experience puts a high probability on the latter. There are many more idiots than genius.

 

Powder Al and MgAl is available by the abrasive paper method and for remote operation done under oil can be reasonably productive. The use of Aluminium or MgAl in the molten state involves risk and hazard that you haven't even though about yet. If there is moisture in there it will expand 1400x on it's rise to molten metal temperature and throw out little eruptions of molten metal. Any air at all in the reaction vessel and you have just initiated a metal fire like thermite which cannot be extinguished and will give you flash burns if not thermal burns. Raising a ceramic crucible to molten metal temperatures could well crack it and maybe crack the outer when the molten metal hits it.

 

SO FAR you have too many ways to fail catastrophically which you haven't taken into account. If nothing else please think of your parents, they do NOT want to wait by your bedside to see if you are going to live/be permanently crippled etc.

 

To get supplies have you researched a thread here called Hints and tips for Australians -it's been useful before.

Edited November 4, 2011 by Arthur

[oldmanbeefjerky]

MgAl sounds too dangerous for this.

But using abrasive paper sounds like complete nonsense! everyone says " ball milled aluminium is never good enough for stars", so why on earth would abrasive paper fillings be any better? magnalium maybe, but certainly not aluminium!

 

also, in the amounts i will be using, compared to the real life size if the crucible, even if the lot of it exploded and sprayed everywhere, all would be fine and dandy on my end. i think ill wrap the thing in thick sheet metal, perhaps 1-2mm thick? just to avoid getting splattered on incase the whole lot cracks, falls apart and begins to splatter everywhere. ide rather not be near the thing at all though when i am running it, so i am looking for ways to do this remotely.

[baran420]

G’day

 

Given the sensible advice above regarding the dangers of molten Al and the insistenceyou still show for attempting it..... I have to ask: have you considered one ofthe industry proven (?) methods of pouring a thin stream of molten Al onto ahigh-speed spinning disc and letting the Al coalesce onto the sides of aspecially constructed container? I haveno idea of your workshop experience, materials understanding or your innate levelof self preservation etc etc so I have to say this idea should not be attemptedby someone that has not spent a fair amount of time in a workshop or has not had any foundryexperience.

 

It would be at the tough end of the DIY scalebut I imagine it to be a more feasible method for obtaining powdered Al fromthe molten state than boiling and sublimation.

 

To drive the said disc, if a discwould even be the best design, you would need a high-read dangerously high RPMsetup. In the absence of a special motor,I could imagine the sort of speed and torque required could be easily obtained bytraining a jet of compressed air onto a well constructed turbine (perhaps theTesla turbine idea to maximise air-turbine coupling).

 

Thinking to myself now I couldimagine a mechanical failure at the RPM capable from using compressed air inconjunction with molten Al could get you more Darwin awards than you could pokea stick at (Apparently even loose bearings have been known to fail spectacularlywhen allowed to reach horrendous velocities from a jet of trained compressedair and these are highly machined and made from exact materials......)

 

Given the justifiably cautionarycomments given here I would not be offended if a moderator deleted this entry.

 

Cheers,

 

AB

 

 

[Arthur]

Given a vacuum induction furnace it would be possible to blow an inert (Noble) gas through a thin film of molten aluminium and make spherical particles. In a similar furnace you could pour molten aluminium onto a spinning ceramic disc and again get spherical particles. However spherical particles are what you don't want! There are methods of making the high surface area particles that we do want BUT these tend to be trade secrets and not released to all and sundry.

 

Given a domestic setup IMO OMBJ you are more likely to hurt yourself that you currently seem to expect. please don't do it.

[asilentbob]

Actually sometimes you do want spherical particles. Usually for various glitters or if the -325 mesh flake you have is just too hot for your use.

 

Spherical is the hardest for the hobbyist to make. So in some regards being able to make a wide size distribution of spherical particles (which could then be screened into fractions) could be seen as the ultimate aluminum powder independent manufacturing capability. You can mill it into flake if need be... But you can't easily or practically go the other direction from flake to spherical. Thus you would always otherwise be dependent on purchasing atomized aluminum powder from companies.

 

Both common methods that I know of, and that have been previously mentioned, are very dangerous and would be difficult to pull off... that said... I have seen some pretty amazing ghetto rigged shit before, so I'm going to have to say that either method is entirely possible... but a complete bitch and not worth it.

 

There is some discussion on Sciencemadness on amateur atomized aluminum production. Mostly hypothetical. IIRC someone did a small scale experiment too with something like a welder and air blower (or probably tig/plasma cutter)... and from what I very vaguely remember the conclusions were that without awesome fabrication skills, cheap electricity, cheap inert gas, and a ton of time and money to spend on optimization the resulting powder would be ridiculously expensive by the high pressure gas atomization route.

 

I think the verdict with the spinning rotor design was that it would require an impractically large setup so that the molten aluminum would have enough time to cool before hitting the walls and the rotor would have to run continuously to keep cool and the aluminum only poured for short periods at a time... all inside a large metal tank (like 10+ ft in diameter) filled with inert gas with a one way check valve... and so it would also be really hard to monitor what is going on inside since you can't really see inside the container. The motor would need to be mounted extremely securely outside and have a shaft extension go inside. Nothing that can possibly melt from the high temperatures can be present, etc... Then there are problems from metal warpage due to the intense heat.

 

For the spinning rotor design... It could probably be done in something the size of a standard US propane tank that has been thoroughly emptied, cut in half, bolt flanges welded on and high temperature washer that wont wick aluminum into it added, gas inlet modified to be where the extended shaft from the motor comes in, on one side of it the molten aluminum would come in, and on the other side you could have a check valve / safety over-pressurization valves and somewhere else on the top an inert gas inlet port... There are numerous difficulties. For one how do you control the flow of molten aluminum so you can let in a very little amount and not too much too fast? You can NOT simply stand there and pour it into a funnel. You need a remotely operated way to add "doses" of aluminum. With such a small volume, it is going to get extremely hot in there very fast, even with just a small amount of molten aluminum, so you will definitely need that check valve and probably a constant stream of inert gas. If the rotor, shaft, or any other moving part is warped by the heat, everything can fail spectacularly in possibly less time than you will have to shut it down... that is if you even notice it before it happens... remember you can't see what is going on inside. With everything getting hot, the sides of the tank will heat up a lot too. You could possibly have part of the tank submerged underwater, or fabricate and weld on a water cooling jacket which would put an extra barrier between the water and the aluminum and be preferred. However... with all this... I think a very large amount of the aluminum will simply splatter onto the walls and coalesce into a foil before cooling off since the inner diameter of the tank is too small to allow the freshly splattered aluminum time to cool while flying through the inert atmosphere. Have you ever tried to solder something, used too much solder and had a ball drip off? Usually it makes it to the floor and spreads out a lot before solidifying. Granted here after it hits the spinning rotor it should be a lot finer, but it still doesn't have enough time to cool off. The gas has to cool it off and its just not flying through enough.

 

Really the aluminum dosing system is probably the most difficult barrier. How does an amateur fabricate a high temperature valve that actually has heating coils in it to keep the aluminum above its melting point at all times? How is this valve remotely actuated? How is it incorporated into the tank without heating up the tank itself too much?

 

If you insist on continuing to try to atomize your own powder, I'd at least suggest you attempt to start with something like lead-free tin solder or other lower melting point metals first and slowly work your way up to aluminum. You should also do a hell of a lot of deep research on how its done in industry.

 

Hopefully this is more helpful than flaming.

 

 

EDIT: If you want to see what I mean about expensive, use a plasma cutter with nitrogen or more expensive argon and make a bunch of cuts through aluminum with something non-flammable underneath to catch the particles. Take into account estimated electricity and gas usage prices per whatever weight of aluminum powder you are able to recover. Then consider that some of the particles recovered are too large to use for pyro, so screen them out and recalculate.

Edited November 4, 2011 by asilentbob

[Arthur]

One of the useful attributes of the usual 50/50 MgAl is that it is very weak as metals go, it almost crumbles by hand, so it is easily milled by light duty machines. Using an alloy strong enough to make anything will result in a MgAl that needs a milling machine not a ball mill.

[50AE]

Ball milling aluminum shaving from sand cast parts (engine parts, some silicon content) from my experience makes spheroidal shapes. I might take a microscope to justify it, but by eyeballing it, the visible particles look like small balls and the powder that is less than 175 mesh ignites hard with potassium chlorate and burns slowly.

[Arthur]

From your first post "The aim is that the aluminium gas produced would sublime..."

 

However Aluminium melts at about 660C and vapourises at ~2500C so there is no sublimation possible. If vapourised Al hits the side of the container you will have a metallised finish nice and shiny like foil food packaging but nothing to recover as product.

 

Realistically the Al we love for pyro comes from an industrial mill and the precise mill conditions are what make the different particle sizes. The problem is that under some conditions the particles will agglomerate again so there will be a limiting minimum size.

[oldmanbeefjerky]

Hmm, that has given me alot to think about, but i will try powdering solder first by the arc method. if that fails, ill still have a makeshift arc furnace which im sure ill find uses for in the future, such as perhaps with a weaker power source subliming charcoal into a super fine powder, which im sure i will find use for somewhere.

 

im not going to consider at all the high speed disc to spray the liquid into atomized particals. too many things can go wrong at those freakishly high speeds.

 

Also, the argon i get is free. they are old gas tanks from the dump which i am allowed to empty, still at a maximum of 10% capacity, unlike the propane and oxygen tanks, and oddly also chlorine, which are considered too dangerous to go near, but not too dangerous to simply allow to explode or leak.

[asilentbob]

Subliming charcoal? Haha, no.

 

I don't think powdering solder by boiling it off will work very well.

 

You need to melt it, then blow it, as with a plasma cutter.

 

If you want a project you can do with an arc furnace, look into DIY calcium carbide.

http://www.metallab.net/arcmelt.php

[oldmanbeefjerky]

thats one of the things i intend to try.

also, once i figure out how, i intend to blow the hot vapours through some cooling pipes.

But i think just making the furnace to begin with should be top priority, rather than make plans that ill never be able to carry out. molten metals are fun! and i intend to make a hobby of it!