16 replies to this topic

[Gary]

Hi,

I have some magnesium turnings, from which I wish to obtain magnesium in a powdered form.
I am aware of the dangers involved in ball-milling metals, notably pyrophoricity (many metals have the potential for undergoing spontaneous combustion when exposed to atmospheric oxygen in finely divided form).
Would it be safer to ball-mill my magnesium with the inclusion of an oil (such as linseed oil) to pervent the exposure to atmospheric oxygen?
What are your thoughts on this?
Could the same be done with other metals, such as aluminium or titanium?
I could use acetone to wash-off the oil after milling is complete, but first I need to find out whether finely powdered Mg is reactive with acetone (like it is with water or alcohol).
In the eventuality of a fire, there should be no real danger, since I do my ball-milling in my spacious garden, well away from the house.

[Gary]

No replies, then?
Yes, I have searched the forum!

Edited by Gary, 07 August 2008 - 02:30 PM.

[Mortartube]

I can only say give it a go with a smaller amount than you would normally mill. It sounds perfect in principle.

[bigtonyicu]

It would work but, you're only delaying the problem to a certain extent.

First of all the oil would have 2 unwanted side affect, it would drastically increase the milling time for 2 reasons reduce friction but more importantly it would act like a heat sink drawing away heat from the metal and drastically increasing the time required to impact harden the metal, depending on the amount of oil, it might even making impact hardening impossible.

But more importantly it will not necessarily prevent pyroforic reaction from taking place, it will only dalay it and possibly cause it to happen in a less violent and in a more controlled manner.

I personally think filling your tube with Argon/Helium/Pure Nitrogen is a much safer alternative and it allows you to include boric acid during the ball milling process; the boric acid will protect the surface of the aluminum while it won't entirely eliminate the danger it will reduce the risk significantly of the metal reacting once exposed to air.

Might I add that before opening the tube, the tube should be allowed to rest for several hours to allow the heat built up during milling to dissipate and to and the airborne aluminium to settle in the bottom.

but a much faster and more efficient way of making you alunium is in a hammer mill... but since most of us don't have one of those and we all have ball mill, it's worth trying.

[Bonny]

I've never tried ball milling Al, never needed to. For MgAl, I crush the ingot with a hammer and then run it through a 20 mesh screen (IIRC). Anything passing the 20 mesh goes into the ball mill and the rest is re-crushed or coffee milled, then into the ball mill. I usually save some of the coarser stuff for fountain and to add to comets. One guy I know crushes his MgAl with a meat grinder and says it works well.
I once processed some Mg turnings that I got from drilling a piece of Mg. I put them in the coffee grinder for a few seconds, and then ball milled. I stopped the mill maybe every hr or so, let it sit for a few minutes and then opened to air it out, before continuing to mill (I also do this with MgAl).
The end product with the Mg was -100 mesh, in a sort of flake/needle form. With the MgAl I can easily mill to pass 250 mesh which is the finest screen I have.

Mg should be fine to wash with DRIED acetone (not sure exactly how to dry it, but the info is out there somewhere). the Mg can then be coated with linseed oil or potassium dichromate.

@bigtonyicu: I don't really understand any reason to add boric acid to the mill when processing Al to act as a coating, I would think of adding stearic acid/strearine if anything... And with using a gas isn't the risk usually when the jar is opened? If that's the case i don't see how the gas would really help as the jar must be opened at some point.

[pyrotrev]

I tried milling pure Mg and found it quite difficult, it's a relatively soft metal and seems to just deform rather than breaking up. MgAl is much easier to powder.

[Bonny]

I tried milling pure Mg and found it quite difficult, it's a relatively soft metal and seems to just deform rather than breaking up. MgAl is much easier to powder.

When I milled the Mg I don't remember how long the mill ran (about 2 years ago) but I think it easily totalled several full days.

[Gary]

Many thanks for your suggestions. I think I'll try using an inert gas (helium springs to mind) to provide my magnesium with an oxygen-deficient atmosphere whilst milling.

[Bonny]

Many thanks for your suggestions. I think I'll try using an inert gas (helium springs to mind) to provide my magnesium with an oxygen-deficient atmosphere whilst milling.

It may prevent an issue while milling, but keep in mind the Mg WILL be exposed to air when the jar is opened...be careful.
Also, I would go with Argon over helium, it is cheaper for one and is also heavier than air, therefore it will displace the air as you blow it into the jar.

Edited by Bonny, 08 August 2008 - 05:26 PM.

[seymour]

Butane is another option.

[nimrodmr4a]

Butane is another option.

Correct me if im wrong, but isn't butane flammable ? If he is trying to avoid a pyroforic reaction, then butane isn't a good option, a small spark could ignite it.

[Pretty green flames]

If you have 100% butane in the milling jar then there really isn't a danger, no air (oxygen) present, so an explosion is unlikely unless your jar has a leak.

[pyromaniac303]

Maybe one way to do it is to actually allow the reaction to happen slowly during the milling, to prevent a sudden inrush of air and rapid heating. You could try modifying your mill jar with a small plug of foam/sponge in the centre of the jar which will allow air to pass through but no product to escape. This is only an idea though, not tested it, probably somone with more experience milling metals will tell me why this won't work.

[Arthur Brown]

Hi,.................
In the eventuality of a fire, there should be no real danger, since I do my ball-milling in my spacious garden, well away from the house.

Down the garden is just where the neighbours will see everything if there is a fire! You do not usually miss a magnesium fire - think bright then multiply by100!

Property damage is undesireable but upsetting the neighbours could cause you much more harm and local ill feeling.

Can you not buy magnesium powdered to the size and style that you want? Magnesium from a chemical supply house should have a specific analysis, magnesium found as supposedly magnesium castings at a scrap yard will have no known analysis.

[cooperman435]

A pyroforic reaction is inevitable if milling uncoated metal so the only answer is to control it from an undesirable result Ie ignition.

The reaction is basically the oxidisation of exposed metal surfaces and as the metal is ground smaller and smaller the surface area goes up in comparison, this increase is I believe exponential in that the surface area increases much faster the smaller the particles get. 100# particles don't have 10 x the surface area of 10# particles but many many times more and 400# has many hundreds (maybe many thousands) times more than the 100#

I personally believe milling with an amount of linseed oil may cure the pyroforic reaction as it will be evenly distributed on the particles and will create a protective layer when exposed to the atmosphere. This will basically do the same as we already use it for on iron filings and magnesium.

If not then opening the jar regulally will allow air and therefore oxygen into the jar and allow the surface of the freshly milled metal to oxidise slowly and in a controlled manner preventing or at least reducing the chances of an accidental ignition which would only occour when opening the jar with the rush of air entering the now oxygen starved mill jar (oxygen starved due to the reaction inside the jar with what oxygen was available but not replaced)