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Author: Subject: Making magnesium powder in a blender - risk of fire?
RogueRose
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[*] posted on 9-3-2019 at 16:56
Making magnesium powder in a blender - risk of fire?


I found that the case of an old laptop I took apart was magnesium, both the top and bottom along with some internal support structures. I was able to put much of it through a paper shredder, a cross-cut shredder and it chips it up really nicely so I have some "shredded" magnesium.

The blender has a glass body and stainless blade, which is the only thing I can think of being an issue, if there is any ferrous material inside the shred, a spark could ignite the Mg, but I went through piece by piece (along with a magnet) and there's nothing other than the blade and Mg pieces.

The blender works really well and after about 3 mins I see no wear on the blade (unlike the glass.... that ate the blade up but glass has a higher hardness than steel, Mg, MUCH less). I thought I would stop and see if anyone thinks there is a risk of fire with this.

The container is air tight - sealed with some plumbing putty. IDK if there is a problem with oxidation like when milling Al powder when it comes in contact with O2 (catching on fire). I haven't heard of Mg being as much of an issue and I'm not getting as fine a powder either.

So, is there a risk of fire from O2 and can the blades create any sparks on anything that isn't from blade material (I suspect no, though I really don't want a 4000-5000F fire on my hands).
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greenlight
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[*] posted on 9-3-2019 at 21:22


I would be damn careful doing that in blender and avoid it if you can buy the Mg elsewhere.
Magnesium has the same problem as aluminium powder but even worse when milling it. The finer it gets, the higher the risk.
Mg reacts so well with oxygen because of its two outer valence electrons that it wants to lose while oxygen wants to gain two electrons for a full shell.

Be extra careful when opening the blender after you have milled it, that's when most accidents happen. Don't mill it too fine in one go before opening the lid. I have read that when ball milling it the jar has to be opened every hour to make the process safer.

If the blades of your blender are stainless steel there shouldn't be risk of sparking as you can buy mill media that are stainless steel balls.

I don't know what your use for the Mg powder is (I'm guessing pyro) but you will probably want to coat it as well for storage as it will get oxidized by the air even in a proper storage container.

Just be careful as the burns will be bad and the fire hot if something goes wrong.






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RogueRose
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[*] posted on 9-3-2019 at 23:10


Quote: Originally posted by greenlight  
I would be damn careful doing that in blender and avoid it if you can buy the Mg elsewhere.
Magnesium has the same problem as aluminium powder but even worse when milling it. The finer it gets, the higher the risk.
Mg reacts so well with oxygen because of its two outer valence electrons that it wants to lose while oxygen wants to gain two electrons for a full shell.

Be extra careful when opening the blender after you have milled it, that's when most accidents happen. Don't mill it too fine in one go before opening the lid. I have read that when ball milling it the jar has to be opened every hour to make the process safer.

If the blades of your blender are stainless steel there shouldn't be risk of sparking as you can buy mill media that are stainless steel balls.

I don't know what your use for the Mg powder is (I'm guessing pyro) but you will probably want to coat it as well for storage as it will get oxidized by the air even in a proper storage container.

Just be careful as the burns will be bad and the fire hot if something goes wrong.




Thanks for the reply. I don't have a lot of experience with Mg or Al milling and I think I was remembering that magal might not be as pyrophoric..? Maybe it is the same. I think I'll add a little stearic acid to the mix and keep the batches small. From what I see the pieces aren't really a powder, more like large flake, so I think that is probably less dangerous than a very fine powder.

Thanks again for the suggestions!
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Metacelsus
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[*] posted on 10-3-2019 at 08:53


I would suggest to do it outside, and have the switch to turn the blender on a safe distance from the blender. You can load it up, walk back, then turn it on. If it starts to burn, you can cut the power and wait until the fire burns itself out. This way, you only risk the blender, not yourself.



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XeonTheMGPony
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[*] posted on 10-3-2019 at 09:34


This is why carbon is oft added to pyro Al, or Mg, it coats and helps lubricate the powder
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Heptylene
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[*] posted on 10-3-2019 at 09:39


Can't you fill the blender with something inert, liquid or gas?
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greenlight
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[*] posted on 10-3-2019 at 11:14


Quote: Originally posted by Metacelsus  
I would suggest to do it outside, and have the switch to turn the blender on a safe distance from the blender. You can load it up, walk back, then turn it on. If it starts to burn, you can cut the power and wait until the fire burns itself out. This way, you only risk the blender, not yourself.


The problem isn't so much when the blending/ milling is happening, it's when you open the container and expose the fresh Mg to atmospheric oxygen. A remote way of slowly opening it would be good.

@Heptylene, the under inert conditions reminds me of an old explosives and weapons forum thread about blending aluminium to powder in a blender under oil or water. I cant remember details exactly, I will have to see if I can find the results anywhere.




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Heptylene
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[*] posted on 10-3-2019 at 14:40


You might fill the blender with CO2 gas. I don't think Mg reacts with CO2 at low temperatures. If it doesn't then it would be as simple as putting a small chunk of dry ice inside the blender and waiting for it to fill the blender with CO2.

Maybe diesel could be used as an inert liquid: it's not too viscous, and has flash point higher than room temperature (so no ignition even with a spark at room temp). However, blending for a long time will heat up the liquid, possibly above its flash point.
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mayko
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[*] posted on 10-3-2019 at 16:24


If it can get the activation energy, magnesium will burn even in dry ice:
https://www.youtube.com/watch?v=_xCbal2YyaE

I don't know if eg static electricity could set it off but I also don't know if I'd count on finely divided magnesium in CO2 being inert! :o

[Edited on 11-3-2019 by mayko]




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Tsjerk
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[*] posted on 10-3-2019 at 23:31


Use some mineral oil.
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XeonTheMGPony
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[*] posted on 11-3-2019 at 03:39


there is a reason carbon has been used for centuries, all these exotic ideas all have thier own post work up issues.

When it comes to making fine metal powders the name of the game is to precoat them with some thing inert to what your doing, for pyro this is carbon, for chem, elemental carbon can (I think at least) be washed off or most part will ignore the reaction.

Caution is still needed on opening, very slowly open a bit and close to allow the initial protective oxide layer form slow enough as to not generate heat enough to get a runaway going (burning)

Blender / ball mill the only difference is speed more or less when it comes to the objective.

My larger concern would be wrecking a blender! By burning the motor out.
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Tsjerk
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[*] posted on 11-3-2019 at 08:42


Can anyone explain me why carbon would be better than mineral oil? It can easily be washed of with acetone.
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[*] posted on 11-3-2019 at 09:01


Quote: Originally posted by Tsjerk  
Can anyone explain me why carbon would be better than mineral oil? It can easily be washed of with acetone.


The mineral oil might form a paste or a sort of dough as the particles get finer and finer that will not blend easily or eficiently.

The mineral oil sticks the particles together much more strongly than the carbon does (at least I think that's the reason)
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Tsjerk
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[*] posted on 11-3-2019 at 09:11


Then use thinner oil.
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Felab
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[*] posted on 11-3-2019 at 13:21


Quote: Originally posted by Tsjerk  
Then use thinner oil.


This would partialy mitigate the problem but no matter how viscous the mineral oil is it will always clump up the magnesium to a certain extent. If the aplication it will be used for is sensitive to carbon(I don't think that carbon will be a problem in most cases) well then you can use mineral oil but it will probably take much longer.

An advantage of using mineral oil though would be that very little powder would be suspended in the air so less risk of an explosion.
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[*] posted on 11-3-2019 at 14:31


The question is what the purpose is the powder is going to be used for, or did I missed that?
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[*] posted on 11-3-2019 at 16:41


Just FYI, the engine's crankcase of vw beetle's are magnesium, can be a cheap bulk source

https://www.youtube.com/watch?v=nhY0xzKcPoE

[Edited on 12-3-2019 by kulep]

[Edited on 12-3-2019 by kulep]
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