Atomizing metals

I was just wondering how this might be done. Let's say I want to atomize some aluminum... do I just blow a high pressure spray of air at the edge of a stream of molten aluminum and catch it some way?

I understand my idea is rather simplistic - possibly ignorant - even dangerous.

Any recommendations?

Ask the telescope people how the do their mirrors Gerry :-)} London, Canada

This may not apply to your application, but I understand that in satellite technology they will "vapor deposit" gold onto the heat shields. I have no idea how it is done, but that might be an alternative to the atomization you are looking for.

Also, I would like to know more about why you need to do this process. Maybe if you give more details, someone could give you a better alternative.

Gerald Miller wrote: Ask the telescope people how the do their mirrors ^^^^^^^^^^^^^^ I believe they vaporize the aluminum in a vacuum, allowing it to condense on the mirror surface. The end result is not "atomized" aluminum, but a very thin clean film.

Blowing a stream of air across molten aluminum would most likely produce fine, irregular, solidified particles. You could probably do the same thing with a file or some sandpaper.

i dont know why, but one thing chemists and engineers (chemical engineers?) are really really good at is making little tiny spheres.. of 'stuff' .. very precise, too.

i think this might fall into the realm of aerosols.

typically, soft materials (plastics, bronze, etc) are sprayed through very specific (precision) nozzles, into a cooler chamber. surface tension makes the sprayed droplets incredibly uniform. small ones are sprayed farthers, larger ones drop closer. i imagine they are sifted/sorted at this point, and resprayed.

i have no idea how one would do this with aluminum, tho.

Yeah, but they'd probably be particles of aluminum oxide, not aluminum.

You can look up "powder metallurgy" on the web and see if there is some info on how the PM materials people do it. Alcan is the leader, or was, in this technology. The most likely way to find out is to ask the PMIA (Powder Metal Industries Association) in Princeton, NJ. They have a website. They publish papers and books. They're the source.

Ed Huntress

If you want to do coating this is pretty simple. You need a bell jar and an alumina coated tungsten fillament.

The part you want to coat with aluminum metal is placed in the bell jar, with line of sight to the source.

Then you coil up some aluminum wire and place it in the basket of the fillament - or you could use aluminum slugs as well.

Pump a decent vacuum in the bell jar - about 1 e-6 torr or so, and then heat the fillament by passing current through it.

Aluminum has a tolerably low melting point and a decent vapor pressure so it will literally evaporate out of the hot surface of molten metal, and that atoms will travel outwards and coat your item.

This sounds complicated but it's really not.

Jim

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|I was just wondering how this might be done. Let's say I want to atomize |some aluminum... do I just blow a high pressure spray of air at the edge of |a stream of molten aluminum and catch it some way? | |I understand my idea is rather simplistic - possibly ignorant - even |dangerous.

But....it sounds like great fun! Rex in Fort Worth

|i dont know why, but one thing chemists and engineers |(chemical engineers?) are really really good at is making |little tiny spheres.. of 'stuff' .. very precise, too. | |i think this might fall into the realm of aerosols. | |typically, soft materials (plastics, bronze, etc) are sprayed |through very specific (precision) nozzles, into a cooler |chamber. surface tension makes the sprayed droplets |incredibly uniform. small ones are sprayed farthers, larger |ones drop closer. i imagine they are sifted/sorted at this |point, and resprayed. | |i have no idea how one would do this with aluminum, tho.

A variation on a shot tower? Rex in Fort Worth

Sputtering they call it.

Might google it. I got

many many more. Martin

Sputtering is another form of PVD (physical vapor deposition) that uses a different kind of source than thermal evaporation.

Sputter guns can provide large rates but tend to provide isotropic (comes in from every direction) laydown of material. You can't do things like shadow.

Jim

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Like many others that replied to the post, I really wonder why you are interested in this, as that may affect the range of options you have for producing the spray. Do you want to make a spray that will then coat some other object? Do you want the aluminum spray to solidify into tons of fine aluminum particles?

If you want a fine coating of aluminum on something else, you probably should look at some form of Chemical Vapor Deposition (CVD). That process is used by many industries and academia to "grow" the coating onto a substrate. Sucessfully doing this probably means building a chamber in which you can control the pressure, temperature, and composition of the atmosphere. Some CVD processes require a gas of some kind to assist in the vapor-phase transport of the material you are depositing. Some materials (perhaps aluminum...) can simply be "boiled" off into a high vacuum chamber and it will deposit on the substrate (Without the need for a vapor-phase carrier). To get good controllable growth, you will also probably have to control the substrate temperature. (i.e., the aluminum source would be heated hot enough to make the aliminum boil off, the substrate will have to be cooler than the source, but perhaps only slightly cooler (i.e., not room temperature)) If you want to coat something big, it might be quite a challenge to build a chamber big enough that can withstand a high-vacuum. You may need a relatively expensive (several hundred $) high vacuum pump depending on the needs of the process.

If you want to create fine aluminum power, (which is pretty much what the sintered powder metallurgy people do), then I think they accomplish that by squirting a thin stream of molten metal (in your case, aluminum) at a (very high speed) spinning disk....When the stream hits the spinning disk it breaks up, and I think in the case of powder metallurgy, the disk is kept cool in order to help the molten metal freeze again.

...if you really still just want a spray of molten aluminum, then perhaps you could modify the powdered metal process. Fire a thin, high velocity stream of molten aluminum at a high speed spinning HOT disk (hotter than the melting temp of Al). (actually, a disk might not be the right shape as that would spray all over the place...you might be able to think of a profile that directs the spray a little better...) You still might have to control the atmosphere in order to prevent creating lots of aluminum oxide instead. I'm not really sure this would work, but it kinda sounds like fun tho... :)

If you get the molten aluminum up to a very high pressure before squirting it through a very small nozzle, that may automatically atomize it. This is essentially what fuel injectors do in diesel engines. Since aluminum also conducts electricity, you might be able to assist the breakup by charging the nozzle (and hence, also the aluminum) to a high voltage. If the molten aluminum stream holds enough charge, that can help the atomization process (I think the auto industry has been doing research on this for the fuel injectors also).

This all seems quite dangerous (except perhaps a small chamber CVD system)...be careful.

Todd

I am not sure why you want to atomize Al but I have done it with a Metco metal spraying gun. We sprayed Aluminum metal on steel to protect it like paint. The Aluminum was actualy bonded to the steel. Metco make many different metals that can be sprayed to any metal. We played with spraying Stainless on to lead. We could not get the Stainless of the lead. The way they do it is have a accetline oxy flame . A spool of the metal you want to spray is fed into the gun down the bore of the flame. It also has compressed air and that was to drive the air motor the sucked in the spool of aluminum thick wire. about .180" The gun sprayed out the Al about three inches and the surface of the steel had Al stuck to it like the sand on sandpaper. Several more aplicatins and you had a total Al surface. You could spray about 4" square a minute. I hope this give you a little information. I happen to have a metco spray gun so if what you are trying to do is what I just discribed I think we could come to an understanding. Don

Aremco.

Jim

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I have, with good results, but it takes a lot of time.

Um... actually...

I was just wanting to make aluminum powder.

Of course, this stuff is all very interesting.

Recommendation on where to buy the aluminum powder?

Very interesting. Thanks.

Well, maybe not tons. I'm not only interested in metalworking, but also pyrotechnics. I feel a little ashamed that so many folks thought I was attempting something as deep as coatings and telescope mirrors.

It's all very interesting, though.

That's a neat idea.

That's why I was thinking of a high pressure air jet at the edge of a molten stream. It is a whole lot easier for a backyard melter than trying to build something that could push molten aluminum through an itty bitty hole.