55 replies to this topic

[BigBang]

Hi all, i did my search and couldnt find the answers to my 2 questions, so here goes:

Question 1, i milled Mg powder that started at 50mesh and got it down to approx 200mesh, but it went from a nice shiney silver to a nasty black colour and became not as reactive as one would expect Mg of that size to be, what went wrong. Did it oxidise? If so, why did it go black, MgO is white.

Questin 2, i have Al powder which is 350mesh atomised. Would i be wasting my time milling this, trying to get it fine enough for use in flash. Would it get significantly finer? Thanks

[broadsword]

Questin 2, i have Al powder which is 350mesh atomised. Would i be wasting my time milling this, trying to get it fine enough for use in flash. Would it get significantly finer?  Thanks

In answer to question 2, Yor would be doin well to make it finer but the aluminium used in flash is aluminium 'flake' so your atomised aluminium would never really be up to making flash powder.

[PyroKid]

Hi all, i did my search and couldnt find the answers to my 2 questions, so here goes:

Question 1, i milled Mg powder that started at 50mesh and got it down to approx 200mesh, but it went from a nice shiney silver to a nasty black colour    and  became not as reactive as one would expect Mg of that size to be, what went wrong. Did it oxidise? If so, why did it go black, MgO is white.

Questin 2, i have Al powder which is 350mesh atomised. Would i be wasting my time milling this, trying to get it fine enough for use in flash. Would it get significantly finer?  Thanks

With regards to question 1, the thing which first springs to mind is that an oxidisation reaction has occured, however, as you have stated above, magnesium oxide is indeed white in colour.

The other option which comes to mind is that perhaps the magnesium powder had reacted with the milling media.

What material are you using for the milling media and the milling jar?

[alany]

Fine Mg is a dark grey clumpy powder, so that is pretty normal unless it is really black like charcoal. All fine metals in a pile look grey because they trap light in their rough surfaces even if the individual particles are still as shinny as freshly cut Silver.

Take this Magnalium for example, coarse it is very shiny:

http://nexus.cable.n...0-mesh-MgAl.jpg

But once it starts getting "fine" it goes quite grey looking. Although this sample is only -100 mesh so there is enough bright flakes left in it to make some small bright spots:

http://nexus.cable.n...0-mesh-MgAl.jpg

(Excuse the filthy keyboard and hands in the photo!)

The oxides of Mg are indeed white, but the nitride is greenish yellow and the sulfide is a redish brown. The overall oxide/nitride/carbonate/hydroxide/sulfide layer that forms on the bulk metal after handling looks grey brown to me.

[BigG]

In answer to question 2, Yor would be doin well to make it finer but the aluminium used in flash is aluminium 'flake' so your atomised aluminium would never really be up to making flash powder.

Broadsword - you are incorrect. The actual milling will turn atomized aluminium into a flake one. In many cases this is how flake aluminium is made in the indestury. of course, with the lack of very good shive, it will be next to impossible to know the new size of your mashed aluminium.

Note that very fine alumnium can catch fire the moment it is removed out of the jar.

Edited by BigG, 01 February 2005 - 11:03 AM.

[broadsword]

But i have always been lead to believe that atmised aluminium isnt really up to the job of FP? Is this incorrect?
But how does milling make it into flake? DO you use the same technique as milling BP?

[RegimentalPyro]

Atomised aluminium is just small spheres of Aluminium.
Flake Aluminium is small flat flakes of Aluminium

The ball mill process turns Atomised into Flake quite well by crushing the small spheres between the milling media.

Imagery that might help you understand this process is as follows. Imagine an apple placed under an 1 ton weight. You'd have something approaching a very flat flake of apple afterwards.

[Richard H]

Atomised aluminium is useless for flash. Flake powders are far more reactive owing to their greater surface area. It might be possible to mill an atomised powder to something resembling more of a flake powder, with the action of the ball mill flattening out the aluminium spheres into flakes.

Personally I mill aluminium foil for around a week to produce my own aluminium bright pyro powder. The product is good for stars, falls, and comets.

[BigG]

Imagery that might help you understand this process is as follows. Imagine an apple placed under an 1 ton weight. You'd have something approaching a very flat flake of apple afterwards.

that is a great description. You don't mind I'll be using this in one of my lecture, do you?

[BigBang]

Ok, for the Mg milling i am using stainless steel BB's, im not sure if thats the best type to use. Someone suggested using marbles...........good idea?? I know fine powders are dark greyish, but my Mg is actually black, like German dark Al. Im not concerned about the colour, just that it seems rather unreactive. This suggests to me that some sort of reaction has taken place, but what??

Re the Al, im going to start milling today and i'll let you all know the results in a few days. I am aware of the dangers of milling metals, so i'll be careful!



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[s2525]

Although im aware people have said it doesnt im sorta sure steel sparks.Also no marbles why would you want tiny bits of glass in a firework.

[sasman]

I am very intrested in this Topic! i have yet to try to Powder Magnesium and i'm hoping to read peoples actual real life results.. i have about 5Kg Mg which has to be reduced in mesh size


Milling Aluminium and Magnalium has proved very easy..

Magnalium 50/50 Mg/Al.. Very easy to mill..after only a few hours in the mill the magnalium passed a 300 mesh screen..


Aluminium mills far easier than i had thought..i followed Richard H.. and tried his method of ball milling thin strips of Al foil and it works very well.. it just takes time.
.Milling was stopped after about 5 days and most of it passed 200 mesh.

I bought an Electric paper shredder to make cutting the Al foil easier..

Also of intrest is milling Ti/TiFe i will try this later in the months to come...when the weather warms up!

[ProfHawking]

At the moment i use atomised aluminium for sparky things, and dark flake for flash, not that i need much.
It is expensive tho. If i milled atomised, or foil in my ball mill with lead shot, how risky is the process of oxidisation?
Would it be possible to make a non-airtight lid that say has a foam lined hole on it, to let air in during the process but not let powder/shot out? or would that cause problems?

[RegimentalPyro]

how risky is the process of oxidisation?

The best way to avoid a pyrophoric flareup is to open the milling jar every couple of hours or so. That way it gives the metal powder a chance to form the protective oxide covering *slowly* over the milling process rather than all in one go [which is the risky bit]

[Loci]

Would it be possible to make a non-airtight lid that say has a foam lined hole on it, to let air in during the process but not let powder/shot out? or would that cause problems?

I would be thinking more along the lines of setting the mill so it was at an angle, rahter like a cement mixer, so you could have holes drilled in the top and not be too worried about the Al getting out, although you might want to put a filter of some sort over the lid

Fraser