What is a safe way to process homemade magnalium?

[AdmiralDonSnider]

Today I experienced the second accident in the post-processing of homemade magnalium. Although both accicents might have been caused by actions that may be regarded uncautious by members, I do however suggest to pin the topic in order to prevent others from making the same, probably fatal, mistakes.

 

I make my magnalium at home. Up to about one month ago I have always ground the mix of chunks and grains - resulting from crushing magnalium ingots with a hammer - in small kitchen macerators/blade mill style machines which are intended to grind nuts and similar stuff. I knew the method is suboptimal but ASSUMED it is acceptably safe. Sure, I had experienced a short-circuit earlier (which likely resulted from metal creeping into the motor over time), but the method still seemed rather safe.

But I immediately ceased to process the metal that way when I had a blade mill almost explode in my hands while milling magnalium. The blade action, as never before, seemed to have caused enough energy to actually make parts of the metal IGNITE which shot the machines locked-in-place safety cap up one meter high with a simultaneous bright white flame of BURNING METAL and loads of smoke. Jugding by the amount of spilled metal, luckily, only a very small part of the material had ignited, but I still got the shock of my pyro career and was lucky enough that I have not been seriously injured except minor burns on my thumb and fingers.

 

Today the second accident took place. I did not cause me any harm, but destroyed some of my equipment.

Experienced readers might moan when they read that I was trying to reduce magnalium in a BALL MILL, but the truth is that I WAS NOT AWARE of the actual DANGERS although I have done loads of reading in both books and forums, and although I have even read a warning adressing the dangers of grinding *magnesium* in a ball mill, printed in Sponenburghs booklet on amateur mills. I, however, have NEVER READ ANYWHERE that milling magnalium in a thoroughly cleaned mill jar with non-sparking media might result in an EXPLOSION, which is exactly what happened today after only about one minute of grinding. A familiar white flame shot out of my mill jar and actually ripped it into the two pieces of pipe out of which is was glued together with strong pvc cement. Luckily the jar easily failed, otherwise a pressure buildup could have caused a more serious accident. Out of respect I had started the device remotely from a safe distance, thus I was not injured in any way.

 

I encourage others to jump into discussion and share their thoughts on what they may believe to be uncautious behavior or a predictable event. I, however, repeat that I have NEVER read that something like this may (or is even bound to?) happen with magnalium. I thought ball-milling the straight metal would be safe. Others may still do so. This is why I find it so important to share this experience as a warning.

 

Based on that I am left with two questions:

- What did actually cause the explosion is a non-contaminated jar using lead media?

- What are the left SAFE ways of post-processing magnalium to a fine (63µ) powder, as both blade and ball milling obviously are NOT SAFE!

 

 

 

 

[Bobosan]

Glad you are all right.

 

Could possibly the mg/al alloying process had ferrous metal introduced?

 

It sounds like you have been doing this home process a while before and just recently began experiencing problems.

[LambentPyro]

Thankfully you are okay. Rarely are pyro accidents small. The problem is, Aluminum is super stable and burns at a very linear rate. Magnesium on the other hand is very different. It is unstable and very powerful. It does not need to be finely powdered, like Al does, to make a very powerful flash in the presence of oxidizers. Actually, it does in fact oxidize quite quickly when exposed to steamy/humid environments. With that in mind, Mg's strength, and Al's stability is combined to make an excellent metal. Why am I saying all of this that you already know? It matters, making an alloy is just making a mixture homogeneous, milling Mg in equal parts of weight is still the same as milling Mg/Al. Mg/Al must spark much easier than Al alone, and gets its pyrophoricity from the Mg. May I ask what media you were using? I would use a non-metal for milling metals such as Zirconia. Metal and metal sparks, I am not willing to test that statement either. The way I see it, Lead can spark with steel just as Lead can spark with say, Copper, maybe a small difference in tendency, but it still happens. Edited January 13, 2014 by LambentPyro

[uncrichie]

""The way I see it, Lead can spark with steel just as Lead can spark with say, Copper, maybe a small difference in tendency, but it still happens.""

 

LP, you just caught my attention with the above statement. I just this weekend finished filling several hundred 3/4" pieces of 1/2" copper pipe with hardened lead to use as ball milling media. Can you elaborate on the lead/copper sparking theory, you have me very worried now.

[pyrojig]

""The way I see it, Lead can spark with steel just as Lead can spark with say, Copper, maybe a small difference in tendency, but it still happens.""

 

LP, you just caught my attention with the above statement. I just this weekend finished filling several hundred 3/4" pieces of 1/2" copper pipe with hardened lead to use as ball milling media. Can you elaborate on the lead/copper sparking theory, you have me very worried now.

Lead media is not going to spark with anything . This is a ill advised statement.

 

 

 

As far as Admirals statement it sounds like a static spark or maybe the dust creeped into the housing of the motor and was ignited by the brushes like what happened to mumbles .

As for the mill accident , that is a mystery. If in fact the media was lead ( which is a poor choice for grinding metal) then the cause may have been static buildup from the Sponenburgh mill. The pvc is a poor choice for a mill jar for anything energetic or prone to static . As stated earlier there may be a iron contamination, very possible with automotive metal.

 

I have been just plain lucky so far. I do the same thing with milling the magnal in a thumbler 12 # mill. The media is Zirc. and it does a wonderful job.I use the water quenching process now, as it reduces the metal to a popcorn thin flake . To this I hammer it to a finer metal under the water then screen dry, then mill. I however wonder if it is the rubber lined jar is protecting this from happening ( static issues). The use of lead will end up in destroyed media as it will look like a christmas decoration after being embedded with magnal . I use automotive grade metals which are impure , and have trace metals of others in it. I however have not had any explosions or other issues so far,BUT......................... after hearing your story I am a bit concerned and will take extra precautions to minimize any possibilities in-case a mishap should happen.

[Mumbles]

We were just talking about this in the chat.

 

What sort of container do you use to melt the MgAl in, and is it possible it could have contaminated your product with a little rust? That might cause a mini-thermite reaction that could have caused your mishap. Al and Fe2O3 react fairly violently and can be initiated by impact.

[schroedinger]

Also, did you add charcoal or some wax?

 

I would assume, that adding these also would increase safety, specially as it inhibits oxidation witch will occur a lot at the beginning.

Also did you hammer mill the mgal and dirctly add it to the mill or did it had some time to oxidize?

[nater]

The few I know who mill metals, do so with much care. The milled metals can become pyrophoric and spontaneously ignite when oxygen is introduced. Is it possible this is what you experienced?

[a_bab]

Giving the short amount of time your mill blew up I think I *know* the cause.

 

There were some other MgAl milling accidents reports on the PF. However all are ignition type accidents - moreover the ignition occures when the mill is emptied. Depending on the situation one can have a flare up or just a silent burn of the milled powder. These are all caused by the pyrophoric nature of the fine metal.

The flare up can occur when the container contents are spilled, and the airborn fine dust will cause a hot, blinding flash. Or, the ignition may be delayed and one can witness the sudden ignition and the silent burn of the settled powder.

Now, all of these accidents have a thing in common: long milling time. It seems like more then an hour of milling will likely cause an ignition when the container is opened.

 

Usually the amount of oxygen is slowly consumed in the mill as it reacts with the metal particles. It would be interesting to know by what extent - the truth is however that it takes little oxygen to cause a flare up in the container, and the sudden raise of pressure will crack the container open or pop the cap, spill the hot contents, and the subsequent large flare will be percieved as a sometimes loud explosion, as the milled MgAl burning reaction is fed on the external atmosferic oxygen. This would be a mini-FAE actually.

 

Now, all these accidents reports I have collected always used steel or zirconia milling medium.

One certainly used rusted bearing balls so the initial flare up cause is obvious. (thermite type reaction).

 

But... you've used hardened lead.

ALL lead oxides react violently with Mg and Al. Think about crackling compo.

Moreover, lead is always oxidized. Sure, a thin layer it is but if we add up the amounts from all the milling balls/slugs I'm sure it will be in the grams range. All it takes is one reaction then the rest of the balls will be "fried up" as the lead oxide is consumed.

 

I guess some pics of the media will prove my theory.

 

I'm glad your accident did not have any serious consequences, and that you posted it.

Better yet I'm glad you did use the usual safety procedures (remotely turning the mill) although you never "felt" like it can happen.

[AdmiralDonSnider]

First of all let me thank you for your participation. Glad you are helping me discover the reasons of what happened.

 

The problem is, Aluminum is super stable and burns at a very linear rate. Magnesium on the other hand is very different. It is unstable and very powerful.

 

One problem is in a home process you can´t be 100% sure that all of the Mg used in the process has thoroughly melted. Sometimes there are gas bubbles in the melt in which traces of unmelted metal are preserved even after a long period above melting temp.

 

As for the mill accident , that is a mystery. If in fact the media was lead ( which is a poor choice for grinding metal) then the cause may have been static buildup from the Sponenburgh mill. The pvc is a poor choice for a mill jar for anything energetic or prone to static . As stated earlier there may be a iron contamination, very possible with automotive metal.

 

Could possibly the mg/al alloying process had ferrous metal introduced?

 

What sort of container do you use to melt the MgAl in, and is it possible it could have contaminated your product with a little rust? That might cause a mini-thermite reaction that could have caused your mishap. Al and Fe2O3 react fairly violently and can be initiated by impact.

 

The media was hardened lead.

 

As you are all suggesting an iron contamination that is indeed possible. The melting container was a cocktail shaker made of stainless steel, which does however seem to become thinner very slowly, losing very thin plate-like layers. That obviously means an iron contamination, which seemingly has not bothered me enough to leave milling undone.

 

Also, did you add charcoal or some wax? I would assume, that adding these also would increase safety, specially as it inhibits oxidation witch will occur a lot at the beginning. Also did you hammer mill the mgal and dirctly add it to the mill or did it had some time to oxidize?

 

I did not lubricate in any way. The MgAl however was stored in the hammered state for at least two weeks before milling. Also the mill exploded during operation so I doubt the event has something to do with pyrophoricity.

 

 

Given that the event seems to have been cause by sparking from iron contamination (I assume the possibility of such can never be excluded fully and reliably) what ways of processing the metal safely remain?

Edited January 14, 2014 by AdmiralDonSnider

[AdmiralDonSnider]

a_bab, thank you too for posting. I wrote my answer post while you were writing.

 

The lead theory seems very plausible, too. I leave this up for discussion.

[BengalFlair]

A couple of years ago I had an accident with kitchen mixer grinder like you which exploded just after starting but earlier than that, during 15/20 years I did the same and never faced such situation. So I spent some sleepless night to find the reason of that and thought what I did that had not done earlier. Suddenly a vital point came to my mind.

Earlier I used to crush the large chunks (bought from market) with a big smoosher (I have often noticed to make it spark during crushing), sieved out the large and put it to the grinder which passed trough a 30/40mesh. So there were no large chunks in the grinder at all. But on that day I just crushed and put it to the grinder without sieving. Obviously there were some large chunks in the grinder with the fines and now I am pretty sure that the spark were generated by the large chunks for their mutual collision or with the blade of the grinder which forced the fine floating particle of the grinder to react with air. I think mutual collision of larger chunks or granules might be a reason of spark to your ball mill also. I also noticed that high mg content mgal is more prone to spark during crushing with smoosher.

 

As all required mesh size of mgal is not available locally and no other safety process of milling is known to me, I am being bound to mill my stuff with that grinder again (obviously starting with 30/40mesh in a safety place, operating from remote and sieving out the fines repeatedly after 2/3min of grinding). Till date I have not faced any problem at all.

[schroedinger]

Well looked up the lead oxides li e a_ bap mentioned.

From sounds vedy reasonable to me. Lead form leaddioxid as a stable oxide, but thats is a really strong oxidizer which likes to give up the oxigen. Combininb this with some pyrophoric fresh made metallic surfaces ( surface just after breaking a particel ) should make nearly a flash like powder ( exept for the fact that it is really fuel rich).

 

So after all, it looks like ceramic, zirconia, steel or brass are the best way to go. But lead doesn'look reasonable

[LambentPyro]

I like that Iron Oxide theory, it makes perfect sense.

 

As far as milling metals with metal media, I would NEVER do it, you're risking your expensive equipment, property, and potentially yourself. Copper may not spark with lead, but what makes more sense? To mill Copper, Steel, Aluminum, etc. with Lead media? Or use other media such as Zirconia. It's a combination of logic and common sense.

 

As always,

Stay safe and think twice.

Edited January 14, 2014 by LambentPyro

[AdmiralDonSnider]

While the lead theory has disturbed me enough to never again mill MgAl with lead media, it does not explain what happened in the blade mill. The blade mill accident involved the exact same batch of magnalium that caused the mill explosion.

 

I can virtually exclude the above mentioned theory that large chunks of metal caused the sparking due to the blade action, as I have always had those large chunks in my batches for the blade mill and nothing happened over years.

 

I come to the conclusion that the most plausible theory explaining both accidents is iron respectively rust contamination and a resulting thermite reaction with the aluminum due to shock/friction.

Will metallic iron alone suffice for the initiation or must there be any rust present? I know the former will react to form the latter, but also here, I assume that also in my previous batches there has always been some iron from the cocktail shaker wear. This time there was definitely some rust involved.

[a_bab]

One thing is clear: all you need is a flame in the finely divided metal/air suspension to make the content go kaboom. This is what I call "reactive content" since it will change the state dramatically if it ignites, just like the BP would do in the mill.

When milling metals an inert gas atmosfere is always provided. In practice this can be easily done with a flush of CO2 for instance [hint for safe® milling]

 

So it all boils down to what caused the ignition. The facts are:

-magnalium can spark if hit (did you ever witness sparks when you broke the large chunks with the hammer?)

-magnalium reacts with iron and lead oxides

 

I would advise you to read some material about metal milling (there are books on the subject).

[nater]

You don't even need a flame or a spark. Certain finely divided metals, aluminum for one, will spontaneously ignite when exposed to oxygen at room temperatures. They are often stored and processed in a solvent or under a blanket of an inert gas. As I mentioned above, utmost care needs to be taken when milling metals down. A standard approach, allow oxygen to be introduced risking the chances of an accidental ignition. I don't consider this something to be safe enough to attempt on my own.

Edited January 15, 2014 by nater

[a_bab]

He did't mill for long enough to create pyrophoric magnalium.

Besides the oxygen is long gone before you get pyrophoric magnalium, slowly consumed by the MgAl itself.

The solvent for Al milling is a lubricating agent, and it acts same as water in a blender.

 

One method is to avoid pyrophoric ignition is to let the air in the container from time to time.

 

He had enough fines and oxygen to cause the container pop with all the rest. What caused the ignition is the question.

 

Either way, milling metals is asking for trouble... eventualy.

[LambentPyro]

Either way, milling metals is asking for trouble... eventualy.

+1. I agree with this, I am happy buying my Magnalium, it is somewhat expensive, but I tend to use star formulas with low Mg/Al content. I am satisfied with the process I have now.

 

However, later in life, I'd be willing to make it for experience, and other things like casting media is something I'd be interested in doing too.

[mabuse00]

Sorry for your misadventure and thank you for the report.

 

At least your not hurt, equipment can be replaced...

 

after only about one minute of grinding

So there must have been a lot of oxygen in the barrel - and maybe already some fine dust from the earlier crushing process?

 

 

Concerning the leadballs, hardened or not, I can imagine them to be ground down rather quickly with magnalium, or is that a false assumption?

 

 

 

I am happy buying my Magnalium, it is somewhat expensive, but I tend to use star formulas with low Mg/Al content. I am satisfied with the process I have now.

I don't think the authorities in his country would like to see the admiral making his own fireworks. There is no legal way to do it. So the idea is usually to avoid pyro shops to fly under the radar, even if you pay more money in the end. Especially Americans often overlook that fact.

Edited January 15, 2014 by mabuse00

[Mumbles]

I never would have thought to mill any metals with lead due to it's general softness. Even the high hardness alloys of lead are still significantly softer than basically anything we'd want to mill except for maybe pure aluminum. The oxide thing, which I never really considered before, would certainly put it in another class of hazard for me.

 

My material of choice for milling metals would still be a spark-resistant grade of stainless steel. There is really no corrosion to worry about, it's quite hard, and the sparking issue is not really a factor. Others have used ceramics (alumina and zirconia), but I'm not entirely comfortable with that. Alumina certainly sparks quite proficiently. Anyone who tells you differently is full of shit or has no idea what they're talking about. Go in a dark room and hit two balls together and you'll see. Whether those sparks are capable of doing any harm is another matter entirely though. I'm not as sure about zirconia. If I could get a deal on the media like we could a few years ago, I'd be all over it, but at market prices I'll pass.

 

With some of the issue I read about from milling MgAl, I think just stick with buying the fine stuff for stars. I'd be willing to make the less available coarser material for dragon eggs and some of the sizzling comets. I'm more comfortable dealing with larger material, and might be able just do that much in a blender. Again, this really isn't an option for everyone.

[BengalFlair]

Magnalium just not only spark on hitting but also makes a crackling sound while sparking. I have often noticed a long bluish-white spark with a crackling sound coming out during crushing large chunks with a smoosher. This character of mgal is well known to me from my school age and till then I learned not to ram the composition containing mgal.

So it is obviously not too wise just to select a non sparking media but load the ball mill with a highly spark prone materials like mgal especially with large chunks which have higher momentum.

 

Incidence not always takes place with same manner repeatedly but there always would be some logical probability.

According to your statement your mgal was not a homogeneous mixture of mg and al so it may vary from batch to batch and even chunk to chunk and I experienced that the higher mg content mgal is more prone to spark.

 

You have stated that you used cocktail shaker made of stainless steel.That might cause some stainless steel contamination but where did the rusts come from which establish the ferro-thermite theory and as far as I know ferro-thermite is quite insensitive to shock and friction (Shimizu stated a little sensitive to friction and especially the red thermite). I have just tested a sample of3 (fe2o3):1(mgal200m) wrapped in a thin al foil on a steel plate and tried to ignite it with hundreds of dead blow of a 1kg hammer but I failed.

[schroedinger]

It`s propably more the lead themite reaction happening here.

 

Also don`t forget about the fact that you get fresh surfaces during milling, which aren`t oxidised and quite reactive. Your 200# mgal is allready oxidised and lost heaps of it's reactivity for that reason.

[BengalFlair]

Also don`t forget about the fact that you get fresh surfaces during milling, which aren`t oxidised and quite reactive. Your 200# mgal is allready oxidised and lost heaps of it's reactivity for that reason.

 

You must also keep in mind that I hit it on a steel plate with a 1kg iron hammer repeatedly more than hundred times which certainly broke the mgal into lots of finer particles than 200m and exposed the fresh surface of mgal to react with. Hence the reactants got enough chance to collide each other intensely to initiate the reaction.

 

It`s propably more the lead themite reaction happening here.

 

 

 

I have also some logic against lead oxide theory also.

Due to contact with air naturally, lead begins to tarnish by forming a very thin layer on it. The layer is a complex mixture of compounds containing significant amounts of carbonates and hydroxycarbonates but not only oxides and they are quite stable and have very less reactivity with respect to lead tetraoxide which we use to make dragon eggs.

Further more, after a few revolution of the mill from the beginning the hard mgal would rub almost of that entire layer out and distribute it in form of some micron particles through out the mill jar almost evenly which is less than a gram hence reducing its reactivity further again to the mixture to initiate a reaction. “The ratio of the oxidizer to the fuel (by weight) also has an influence upon the sensitivity”-Shimizu.

 

In spite of that if we have to believe the lead oxide theory then we must immediately stop to mill bp with lead media. Because lead has three oxides PbO,PbO₂ and Pb₃O₄ out of which PbO₂ is highly reactive and shock and friction sensitive with sulfur, a main ingredients of bp.

Who knows which oxide would form according to lead oxide theory!!

[Mumbles]

The fact that you used a deadblow hammer and wrapped it in Al foil basically make your assessment that the mixture is not sensitive quite skewed. Deadblow hammers are not meant to deliver a significant impact, just kill the rebound and bouncing. You are not delivering as much impulse as you think. Additionally the process of wrapping the mixture in aluminum foil probably protected the mixture. It absorbed some of the impact, embedded the particles into the foil itself, and potentially isolated the mixture from rubbing against itself by confining it in such a way.

 

A sample of MgAl thermite is actually fairly sensitive in my experience. If you used an unsupported mixture, and a solid hammer, it should not take all that much effort to set off. There are chemistry demonstrations where you strike together a rusty ball bearing, and one covered with aluminum foil. It does not take all that much effort to get it to visibly and audibly react. Lead is going to be much more sensitive than iron. It should be on par with aluminum or magnalium and copper oxide.

 

Shimizu's statements about the ratio mattering take into account the bulk composition. Since the mill in this case was not running all that long, I don't think we can discount the idea of a locally more balanced ratio. It might have been a one in a million occurrence, but I'm not ready to discount it.

 

I think you're just grasping at straws with this this sulfur and lead oxide thing. There are a series of reactions that in theory will go forward, but the energy produced is either negative or pretty weak. The reaction of lead and sulfur alone is more exothermic than any of the reactions that exist between sulfur and the oxides.