I've been ball milling magnesium to a 200 mesh powder without issue, i'm using a rubber container and ceramic media. However last week I opened the
container and tried to see if it was fine enough for my mesh. It wasn't quite ready so I poured it back in and started it milling again.
I don't know quite know how it happened but about 2-3 minutes later it detonated and blew the end off my mill container, filled the area with thick
smoke and started a small fire! Everything turned out ok and the fire went out with some water.
I think the lesson is that magnesium powder is hazardous and ball milling it is likely to result in an incident eventually.Tsjerk - 5-9-2022 at 09:51
You should use some mineral oil when milling it. This is already adviced when milling aluminium, but with magnesium it is even more important.Chemgineer - 5-9-2022 at 12:02
Good advice however I suppose it adds a solvent step to remove the oil afterwards, also I expect the lubrication slows down to milling?Tsjerk - 5-9-2022 at 13:52
Both true, but at least your ballmill won't explode and start a fire.arkoma - 5-9-2022 at 23:29
Water might not be my first choice for possibly burning Magnesium.Rainwater - 6-9-2022 at 03:34
Water might not be my first choice for possibly burning Magnesium.
I second this!!!
Even a class 'ABC' extinguisher can add fuel to a magnesium fire, and many other combustible metals. If I remember correctly a class 'D' is used.
Table salt is another good option but be prepared for the possibility of chlorine gas.
Acid-washed sand and time are good methods to deal with most metal fires
I once got the idea to use an inert atmosphere of "party balloon helium" just to find out that it was roughly 40% He and 60% air. After the fire, I
had some nice green rocks in my mill.
Stay safe. BromicAcid - 6-9-2022 at 13:47
On the one hand, magnesium can form a nitride so finely divided magnesium could potentially still have issues in N2. On the other hand, it's nowhere
near as prone to forming the nitride as lithium is: Case in point - Grignards are routinely run under nitrogen.macckone - 7-9-2022 at 10:42
The explosive properties of magnesium are well documented.
At least you didn't have it fine enough to get a UV flash burn from the explosion.
I always open the container and let it sit for bit every 8 hours or so.
If your ball mill is more aggressive I would suggest a more frequent cycle.
This give the exposed fresh surfaces a chance to oxidize in a more controlled manner.
Some good charcoal (1%) is also useful in coating the surface and won't interfere with most pyrotechnic uses like a solvent might. After all your mix
is probably going to contain charcoal anyway.
For a grignard you probably don't want the powder that fine. It will make generating the reagent too energetic. Of course grignards are finicky and
you may know the material you are working with better than we would. Mateo_swe - 16-10-2022 at 10:13
Wouldnt an oxygen free environment be the best for preventing an explosion?
It wouldnt be the easiest to make in a ball-mill jar but maybe one can just fill the jar with argon gas and close it (as argon is heavier than air)?
The jar needs to be air thight and not let any oxygen in.
Or wouldnt that work?Fulmen - 16-10-2022 at 10:45
How do you plan on emptying the mill? Mateo_swe - 26-10-2022 at 02:54
Just open the mill jar after it has been standing a while so fine dust settles.
Isnt the danger when the milling action is going on and thus might create sparks or elevated temps? Fulmen - 26-10-2022 at 03:34
Reactive metals like magnesium and aluminum has a protective oxide layer that prevents further reactions with air. Milling strips off this layer, and
the heat produced when it reforms can be enough to ignite fine powders. Mateo_swe - 30-10-2022 at 01:16
OK, how would you suggest doing it then?Tsjerk - 30-10-2022 at 01:26
You should use some mineral oil when milling it. This is already adviced when milling aluminium, but with magnesium it is even more important.
Fulmen - 30-10-2022 at 01:31
The general consensus is to open the jar frequently to reform the oxide layer (see macckones answer in this thread). Sadly I can't give you any more
detailed advice as I haven't tried milling reactive powders. But I'm sure there are older threads on the topic.
