[OxideHelium]

Hi guys, as I just began my adventure with chemistry I decided to make my first experiment with milling of aluminium, so I made mill ball, very homemade but it mills great even too great because after 3 days of milling of Al it gave me extremely soft dust, and because this dust is too thin it immediately reacts with Oxygen and autoignition itself when I open metal can with Al-dust, And my first chemical question is:
1, How avoid autoignition ( what substance add to Al to make it proof from oxygene) is there something that can me help?, I heard that stearine or wax could help but I'm not sure that is good idea and if it would be I have no idea how much of it to add to my aluminium ( how much Al and how much stearine in grams),
2, Very sorry for my language, I think I'm more dummy (dummier) than ...
Thanks for answers, and I hope that yours covalent electrons didn't go away during reading of my poem ;-)

[Arkcon]

Aluminum dust is prone to autoignition, but it doesn't always autoignite.  Things you should work on:

1).  Grounding to prevent static charge buildup, while milling n before opening.

2).  An inert gas blanket when opening.  I don't know if nitrogen is adequate, but aluminum dust is very reactive to moisture, oxygen and carbon dioxide.

3).  And you'll need safety protocols for handing a possibly autoigniting metal powder and an inert gas blanket.

My suggestions would be don't try this at home, but people here on Citizen Chemist don't often take my advice in that regard. 

[OxideHelium]

Aluminum dust is prone to autoignition, but it doesn't always autoignite.  Things you should work on:

1).  Grounding to prevent static charge buildup, while milling n before opening.

2).  An inert gas blanket when opening.  I don't know if nitrogen is adequate, but aluminum dust is very reactive to moisture, oxygen and carbon dioxide.

3).  And you'll need safety protocols for handing a possibly autoigniting metal powder and an inert gas blanket.

My suggestions would be don't try this at home, but people here on Citizen Chemist don't often take my advice in that regard. 

1. Of course I didn't ground it during and after milling, Thanks.

2. Yes, I thought to inert some gas into it but didn't do it so far, but also I'm not sure what next, how to get Al from my mill to another container ( if I move it ... it will probably again start fire... Don't you think that?)

Huh You just realized me that I did it in very moisturizing place, Now I know that it is very reactive with oxygen also as you said with moisture but I haven't idea that with carbon dioxide also, wow thanks a lot for advice,

3. Thats right you're really right "to be careful" is nedded but as I said i'm dummy with that things so far, but I learn day by day, and especially with your help I'll be in ONE PART... hahaha.

No I did it in my little shack/garage, so you don't have to be affraid on me.

[Enthalpy]

Additive to aluminium: probably not. Very pure aluminium, or Al-Mg alloys, make a more protective oxide layer, better than more common alloys like Al-Cu and Al-Zn but if the powder is fine enough it won't stop the combustion. And anyway, such soft alloys are difficult to grind.

Stearine or wax: the idea is that they separate the aluminium surface from the air, so a first answer to the amount is "enough to cover the aluminium dust". I mean, not to make a film on each aluminium particle, but to let the whole powder heap sink in the liquid.

You need a compound that doesn't oxidise aluminium, and for that an alkane (paraffin) is great, an ester (vegetable oil, wax...) less sure. It would be wise if that compound were hard to light, since aluminium dust is just too prone to it, so for instance gasoline is excluded. Something like maize oil if it doesn't hamper the grinding process (I ignore that). I'd fill the ball mill with it and keep the aluminium powder in the oil for storage. Diesel oil and heating fuel are thinner liquids than vegetable oils but not very resistant to lighting; a heavier petrol cut (liquid paraffin) would be better.

Please begin with small amounts, have a fire extinguisher of adequate composition at hand (not water) and learn+train to use it, make the operation at a place where a brutal fire isn't damaging, and so on.

[OxideHelium]

Hi guys, Ok I tried mill Al with a wax from candle, but it doesn't work properly because I think I added too much paraffine and I have got some strange thing, something like plasticine or , and doesn't look like dust at all,
I tried burn it but it didn't start fire, but nevermind, I will be tried mill it again with or without wax,
when I will do something "new" I give you info about my "discoveries" HAHAHA.

[Enthalpy]

Sure, tell us!

A solid like wax may well preserve aluminium from crunching by the balls. I'd suggest a liquid instead: Diesel oil or heating oil (their vapour isn't very sound, don't breathe it), liquid paraffin, kerosene for lamps... With a strong preference for one that can't catch fire without a wick.

Making the whole crunching within a liquid seems the safest way, or rather the least unsafe, especially if you keep the liquid for subsequent storage. Once again, please be cautious, choose the location and equipment properly, and think in advance.

[wildfyr]

What about a liquid PEG? Its not very flammable or reactive.

[OxideHelium]

Here I am again guys sorry for that ;-)
Ok or "holy moly" sounds better, cause I had again failure with my Unfriend, very hungry for Oxygene metal called Al, I have milled it again but little shorter than recently without any passive materials so far, but it again combusted (autoignited) but not so fast as during first time,. I have to use materials as those as you had me adviced ( as you have given me advice), but I'm not sure which one to use/ to choose,. First I have to read some more about that materials and we will se.
But there is one thing I'm thinking about, On YT there is a lot short films/movies with milling Al and on "ones" there ain't autoignition/combusting and on the other there is autofire of Al, for example:
https://www.youtube.com/watch?v=2im84pvvYYc here there isn't autoignition but dust is quite good, seems to be very thin, and on this one https://www.youtube.com/watch?v=KV60zhFOC7A was autofire all of his stuff, so in my opinion I have to/ we all have to point (targeted) to make dust not too thin to avoid combustion or use some materials to prevent start fire as you told me.
I hope that nobody/no one will not be angry for me that I used his movies to give you examples.
Movies belong to YT author Brewmaster C and The Plutonium Bunny, by the way maybe I will write to those guys and ask how they do it. Thanks guys and sorry that you had to read my poem again and again.

[Enthalpy]

One had luck and the other had none. The powder that caught fire had been milled for longer, but the time depends on the ball size, shape, container... You can't rely on that for your safety.

As a protective liquid during milling and storage, I would stay away from alcohols, because freshly deformed aluminium surfaces are badly reactive, and trust hydrocarbons instead.

I found in hardware shops a solvent composed of "isoalkanes C9-C13". It is nicely thin, hence milling may proceed (hopefully), but it still doesn't catch fire with a lighter (check it). Supposedly low toxicity, an advantage over heating oil or Diesel oil.

Repeating: please take precautions. Such a powder may detonate if dispersed in air.

[Enthalpy]

This thread reminds that other one
http://www.chemicalforums.com/index.php?topic=91121.msg325984#msg325984
because aluminium powder can be suspended in a ramjet or scramjet fuel for "easier" handling. So:

• Milling the metal or metal-containing compound under a non-oxidizing liquid looks simpler and safer than in a gas.
• This liquid can be a fuel that will burn in the jet engine. No bare metal powder, safer production.
• More liquid can ease milling. The excess can be removed after milling, for instance by evaporation, and serve again.
• Jet fuel is one option. Other compounds, including some I suggested in the other thread, may be possible - if fresh aluminium provokes no unwanted reactions.
• Alkylation units at refineries produce low-freezing branched alkanes. The fraction too heavy for gasoline would make a nice speciality jet fuel (and rocket fuel).
• Aluminium increases much the fuel consumption. AlH₃ and LiAlH₄ save fuel mass. Coated with aluminium, they are not pyrophoric. Demonstrated for rockets, unclear for jet engines.

Whether a slurry clogs the injectors remains to see. It must erode the pumps. And I'm not convinced that we want LiOH, LiAlO₂ nor even nano-Al₂O₃ in our atmosphere. Finally, while suspensions of LiAlH₄ and AlH₃ bring a little bit more performance to liquid rocket fuels, Al isn't worth it.

[pcm81]

Since i had a thermite related hobby before, here are couple suggestions about milling aluminium and other metals.

1. DO NOT OPEN THE CAN UNTIL DUST SETTLES. The aluminium in your jar is airborne and will catch fire when exposed to additional oxygen when you open the can. Let it settle out of the air before opening the milling jar. Basically set it aside for 15-30 minutes after milling is done before you open it.
2. Do not use steel balls in ball mill. When you are "properly" milling any metals you should use non-sparking milling medium like lead slugs or ceramic grinding media. Ceramic media is lighter than steel and lead will work soften overtime, so both choices are whole lot slower than steel balls, but whole lot safer as well. Steel balls can spark inside your ball mill causing aluminium powder to ignite inside the ball mill.
3. Some people add graphite to the ball mill to create carbon coat on the aluminium particles preventing oxidation of aluminium. This keeps aluminium reactive for longer since it won't form aluminium oxide skin.

[OxideHelium]

Hi guys and maybe gal(s) also, Ok I had failure again, hihi :-),

reply to pcm81

1 Yes, I was opening can until dust settled, so it was my error, I think it is quite good idea to live milling jar in peace until dust sets at the bottom.

2 I don't have any other milling medium to mill it, so I have to use steel balls, but there isn't problem with sparking from steel balls when can is closed at all, problem begins during open can ( about 10-30 sec from open to start fire).

3 Again good idea I think, to add graphite to prevent it from combustion, I will try it, and soon (1-2 week) I will give you answer that it works or not,

At the end,

My last try with milling and avoiding combustion was 50/50 cause:

I didn't have autoignition because I added some king of alkanes called paraffin oil, so it prevented from autostart fire but it (my dust) changed from dust to mud, and amount of it was microscopic,.

thanks for answering to me and again sorry for my "excellent language" :-())).

Take care, keep far from fresh aluminium dust ( haha), and so long, your metachemist OxideHelium.

[Enthalpy]

[...] I added [...] paraffin oil, [...] my dust changed to mud, and the amount was microscopic.

One explanation I like is that the paraffin oil is a good lubricant, that is, its viscosity suffices to prevent the metal-to-metal contact between the balls. So the aluminium chips are not crushed nor squeezed by the balls. Fail.

The answer would be a bad lubricant, whose viscosity drops when the film is thin, so it doesn't prevent the balls to touch an other. One known bad lubricant is silicone oil. Manufacturers: Wacker, Bluestar (Rhodorsil) and others.

Even thin silicone oils (with short molecules) are hard to light. Not the ones with 0.6mm²/s viscosity, but already the oils with 3mm²/s have a flash point of +75°C. These should be decently safe against fire.

Silicone oils are bad candidates as fuels and would be removed in such uses. The light silicones with 3mm²/s can be evaporated a bit above +150°C. A process where the aluminium powder goes from the silicone to the fuel without touching the air is necessary; keeping the powder wet all the time would be better.

A good fuel that is a bad lubricant would be better, to avoid the silicone and the transfer.

Marc Schaefer, aka Enthalpy

[OxideHelium]

Hmm... I thing that first I have to learn more before "DO" something, so I Stop to make experiments until I read about something that I want to do, I must read and read more,. But I THANKS you for yours answers for me about my problem,. But so far I stopped testing with this strange flamable metal (hihi),.