Can you over mill Aluminum powder?

[Brightthermite]

I found I was running low on Al powder and needed to make some more. I used some heavy duty great value brand foil and milled it for right around 3 days. I checked on the powder today and found it to be much more reactive then the powder I was running low on.

 

The original batch I made around a year ago and milled it for at least two week, I remember it was for a long time. I do not remember what kind of foil was used. It is just as reactive as the day I made it but no where near as reactive as the new batch I just finished today. The new batch was milled with much less media then the previous batch was milled with.

 

The old batch is off grey color while the new batch is a darker grey, like dark soft pencil lead. I did a smudge test on a piece of paper and they're smudges are identical.

 

So is it possible that I somehow over milled the Al, or is it just that the powder I made year ago never got as fine as the powder I finished today? Does the brand and type of foil make a huge difference?

 

[dagabu]

Luckily, O2 got into your ball mill or you may have had a hot mess on your hands. It is widely recommended that you open the mill jar every few hours to allows O2 in at intervals.

[Brightthermite]

Luckily, O2 got into your ball mill or you may have had a hot mess on your hands. It is widely recommended that you open the mill jar every few hours to allows O2 in at intervals.

Oh no, the powder was not milled for 3 days without being allowed to vent. When I say I checked it I just mean that I tried to light a small sample with a match.

[SeaMonkey]

For those who like to make their own Aluminum Powder

a video from Elemental Maker.

 

Pre-treating the Aluminum will make a difference.

[Arthur]

LONG ago one member posted some information that he found by viewing some powdered aluminium through an electron microscope. His findings were that though there was a lot of Al present there are other ingredients (In the 2% range), IIRC his findings pointed to charcoal being present as if there was charred paper in the pre-milled mix. It's been suggested before that pure Al ball milled will reach a fineness where no further reduction occurs due to re-agglomeration. Perhaps the "other ingredients" are there to modify the usual milling process of aluminium.

[zZz]

LONG ago one member posted some information that he found by viewing some powdered aluminium through an electron microscope. His findings were that though there was a lot of Al present there are other ingredients (In the 2% range), IIRC his findings pointed to charcoal being present as if there was charred paper in the pre-milled mix. It's been suggested before that pure Al ball milled will reach a fineness where no further reduction occurs due to re-agglomeration. Perhaps the "other ingredients" are there to modify the usual milling process of aluminium.

I don't understand how other ingredients affect to the milling process .

Were they there to reduce the possibility of an ignition? Or to help to get finer powder ?

Edited February 21, 2020 by zZz

[Arthur]

Pure aluminium in a ball mill forms spherical particles that get smaller until the competing process of particles rejoining forms a limiting fineness.

With the right additives and pretreatment the aluminium tears into smaller particles with much more surface area than spheres, and keeps getting finer as milling progresses. IIRC he said that the particles may be charcoal, which may have come from paper. Someone else here may also have access to an electron microscope and maybe the time to use it..

 

Probably the unspecified ingredients are part of the reason why some people swear by each of the named brands of "dark Aluminium", each brand being subtly different to have a similar function without infringing a patent or ten.

[Piccaso]

I will add that yes you can over mill it for a particular use. Where as the smaller particles will be great for reactivity they will not be as useful for other formulas that need larger particle sizes. The previous posters are right though it will only get so fine before being just hammered back into itself without some other additive or process to stop this from occurring. Read up on nano metal particles used in thermite or other energetic materials. I find this topic of metals used in energetic materials very interesting and read just about every book on the subject I can afford to purchase. To bad for me a lot of these texts are very limited in their printing and are therefore very expensive and hard to come by. When I took up this hobby seriously I was encouraged to read before doing anything. I find this to be the most useful bit of advice I have ever received.

[Arthur]

I've seen somewhere (COPAE?) electron microscope images of aluminium powder, The usual mesh cuts all looked like balls,BUT the finer black aluminiums all looked like torn fabric. There was a rating of surface area per unit diameter, which definitely showed that the particles must be very ragged, not even nearly spherical.

 

ISTR that previous comments have postulated that the ingredient used to make "black aluminium" was the aluminised paper that does or did go between the cigarettes and the cardboard packet, heated to add both charcoal and a heat temper to the metal. Which goes with Elemental Maker's suggestion that the ingredient could be a fired mix of an alternating stack of newspaper and cooking foil sheets.

[ronmoper76]

i have millled ALOT of homemade aluminum powder.... with no additives and with and i noticed a few interesting things. First was just aluminum and a little charcoal it worked great and a spoonful of it burnt quite quickly very similar to a video on youtube. Next i tried stearic acid. and i also tried graphite. they all seem to burn very quickly and glow super hot,showering sparks everywhere if tossed in the air. I also have store bought dark indian powder from a reputable supplier that burns similar but i must say,slower than my home made aluminum. I yet tried another that had magnesium added instead of a carbon like charcoal and it preformed enexpectedly,a spoon of it burns almost instantly,flameless and makes a slight pop sound,like aluminum on steroids.... all of the above made excellent different formulations,they all work well,i feel my own is notably better but unnecessary i believe because they all seem to get the job done......When i added stearic acid it doubled my milling time to get to the same small particle size,actually made it harder,plain airfloat charcoal seemed to be the fastest, long since moved to other things now but wanted to add my thoughts and results.

[ronmoper76]

charcoal makes a huge difference,it makes the aluminum burn significantly faster,i never added over 5% . I notice mine is way fluffier and less dense.I have a quart of each i just weighed and my own weighs half as much as a quart of indian blackhead. Burn tests in a spoon are WAY different to,Its very fascinating to me but dont understand why. one of each above,can you tell which is which?

Edited February 24, 2021 by ronmoper76

[dlking59]

I've read that the "dark" aluminum came from the dark/black lid on the containers the aluminum were shipped in. In another article the author stated the "dark" came from app. 5% charcoal/graphite added to keep the aluminum from clumping and flow more freely. Which is correct ? I don't know, but I have seen black lids on containers and the charcoal for anti-clumping free flowing makes sense. Kind of like cab-o-sil added to P. perchlorate.

[ronmoper76]

both aluminums in the pictures above are in a clear cup and one of them is indian dark flake 2 micron the other some shit i made from reynolds wrap with charcoal added,neither one is black.......it turns darker the smaller the particles get till they no longer reflect light they are so small and thus its called dark aluminum.

Edited February 26, 2021 by ronmoper76

[SharkWhisperer]

.it turns darker the smaller the particles get till they no longer reflect light they are so small and thus its called dark aluminum.

That comment alone reflects your very incomplete knowledge of the physics of light, and has absolutely nothing, zip-zero to do with the perceived color of Al powder. That statement is entirely inaccurate. You really need to do some additional reading on the difference between bright and dark Al because it's clear that you have not. And the commercial manufacturing processes used to arrive at both. "...no longer reflect light they are so small..." is about the most ignorant statement I've read on here in awhile.

 

And you are propagating misinformation. In this case, mostly harmless. But given that you are prone to illogical explanations, I can easily envision that you also propagate misinformation that is dangerous to yourself and anybody naive enough to listen to it.

[ronmoper76]

i did reply back but im editing. I will be damned if im going to bicker with a keyboard to someone i never even met or spoke to in my life. i will never reply to anything other than my own post again to appease whomever it may be. i joined this forum for research and info that pertains to a hobby i have and for zero else. thank you for correcting me and the wealth of knowledge,im gonna go sit in the back of the bus now.

Edited February 27, 2021 by ronmoper76

[SharkWhisperer]

i did reply back but im editing. I will be damned if im going to bicker with a keyboard to someone i never even met or spoke to in my life. i will never reply to anything other than my own post again to appease whomever it may be. i joined this forum for research and info that pertains to a hobby i have and for zero else. thank you for correcting me and the wealth of knowledge,im gonna go sit in the back of the bus now.

There are many, many fireworkers with exhaustive knowledge on all topics pyro here that would be more than happy to share with you--IF they trusted that you were not a complete idiot with a high likelihood of injuring themselves or others, or one who dispenses "knowledge" that is nonsensical, as you clearly have. You're welcome to remain on the back of the (short) bus if you wish. Better, perhaps, would be to ask (after thorough research, including past threads on this site or others) logical questions that we're happy to answer. BEFORE you share your misguided and uneducated "opinions" or, in this case, outright wrong interpretations of simple facts.

 

This is not a Reddit fireworks/pyros forum. We are not teenagers (although teenagers are welcome) exchanging stupid, dangerous, or unproven ideas/designs. You are clearly a newbie.That's fine. We all were once. But you've got a lot of learning to do before you can authoritatively offer advice--and I'm sorry, but your Al particle size/light wavelength explanation was just plain ridiculous. We WANT you to advance. But we will not tolerate idiots perpetuating bad advice or nonsensical non-scientific explanations. We're working with energetic compounds that can kill you dead. Guesses and suppositions have zero place in this art/science/sport.

 

You are not shunned. But I strongly suggest that you spend several hours reading the many, many past threads on bright vs dark Al and educate yourself deeply, for your own good (the information is there), and as a prerequisite before you are "qualified" to offer other newbies pyro advice. I think you've learned that if you make "educated" guesses that are simply wrong, or promote dangerous practices (for yourself and others) that your lifespan here and your welcome will be short lived. Oppositely, if you want to learn pyro, safe as possible, you're at the right place.

 

SW

[Mumbles]

There is some confusing information out there if you haven't had the time to do a deep dive or had some seasoned pyros explain it. A lot of it is from suppliers operating during the heyday of the American pyrotechnic manufacturing industry. There is a difference in dark or black aluminum, and what is sometimes called blackhead aluminum. The "head" portion makes this particular distinction. dlking59 alluded to this. Back in the day, flake aluminum was available from a few suppliers. I don't recall which one exactly the "head" thing is in reference to, but I want to say probably Eckart or Oberon. Those were colloquially referred to by the color of the drum head. There was blackhead, which is a dark aluminum. There was also at least a yellowhead and bluehead aluminum. I don't recall off-hand what exactly they were, but I believe one was a bright flake and one was a dark flake more equivalent to 809 or american dark, around -325 mesh instead of single micron.

 

Dark aluminum was not originally made by adding charcoal, but it was a by-product of production. It was produced from aluminized paper. Think something similar to foil gum or fast food wrappers, or the tops of cigarettes. This was stamp milled to a very fine aluminum. The paper backing helped to prevent the aluminum from being fused back together and provided some additional weight or thickness to get it stamped thinner. The paper was then burned off, leaving some carbon behind. There is some speculation that this process may have also produced surface aluminum carbide, which may have enhanced reactivity. Stearic acid was also added during the process for similar reasons to prevent fusing and laminating back together and protect the surface. Adding charcoal to aluminum while milling it basically is just an anti-cake and fluffing agent most likely.

[kingkama]

I find this table of uses and grades of alluminim powder, mumbles is obviously right but this chart would be a a god integration.

Edited March 2, 2021 by kingkama