RogueRose
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Grinding/Sanding Aluminum blocks for powder - question on speed & sensitivity
I didn't see an Introductions forum so I did not post there. I've been reading this forum for some time and found it quite helpful in many area. I
thank all those who so helpfully contribute to the community and hope that I may also become helpful in the future. Now to the question.
I have some blocks of aluminium (99.5% pure supposedly) and I would like to make some aluminium powder for some various experiments. I've seen many
methods of making powder but the method I that is available to me has some issues I would like to explore first.
The grinding cylinder will be 8-12" diameter and 12-24" long lying horizontally with the bottom 2/5's (or so) submerged in water. I plan on silicon
carbide grinding material with 80-120 grit (maybe alternate as each strip is 1.5" wide & applied at a 45 degree angle - like how paper tubes are
made). RPM will be 20-50, depending upon the diameter.
I don't know if i t is better to have the Al blocks submerged with the cylinder pulling/pressing down or have the blocks on the top with it pressing
down on the cylinder. Caking of the grinding medium is a concern but am curious as to whether the water will pull the grounds off or if I need to use
something like beeswax (mentioned in other grinding processes) applied prior to grinding. I was wondering if some kind of brush may be helpful to
remove any grounds from the grinding medium (steel or brass brush possibly??)
Preventing oxidation of the grounds is of high importance. The grounds will enter a ball mill once dried. I would like to make dark/blackhead AL and
have read charcoal is used. Can the Al be ground while damp? I would think this wouldn't be wise as the charcoal may be repelled when near the water
(both charcoal & Al powder float and act strangely in water). So I am wondering the best way to dry and prevent oxidation.
I am concerned that the AL powder may be difficult to collect and was wondering the best way to remove it from the grinding machine (a skimmer to
catch the floating & something to suck up the sludge on the bottom - then filtered & dried?).
Is there any specific charcoal that should be used? I've seen Willow but also seen BBQ briquettes being used. I could make Oak, Ash, Cherry,
mulberry, pine & a lot of others if this would be better.
If anyone has any suggestions or concerns I would very much appreciate hearing them. I am quite aware of the nature of Al powder as far as it's
potential for flashing (I have heard that water may cause this but it seems it is more likely when the powder is damp, not submerged, and when the
water is slightly acidic).
Thank you for any help provided and I look forward to some interesting conversations on this board!
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Bert
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Thread Moved
16-6-2014 at 23:47 |
Bert
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The process used for commercial pyro grade black Aluminum that results in carbon admixture is quite different from what you imagine.
As I understand the original German process:
Multiple layers of Al foil were rolled and beaten very thin, with a sheet of paper between each layer of Al to prevent the layers being fused together
by the pressure. The resulting Aluminum foil/paper sandwich was heated in an inert atmosphere, carbonizing the paper. Resulting Al foil/charcoal was
then milled, breaking the Al foil into the desired grade of Al "flake" powder, mixed with perhaps 2% by weight of charcoal & 2% stearine. The
charcoal is said to aid in lowering ignition temperature of this powder by providing a lower ignition temperature fuel when used in perchlorate
oxidized flash mixtures not containing Sulfur or antimony sulphide. It may also serve as an anti cakeing agent.
[Edited on 17-6-2014 by Bert]
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PHILOU Zrealone
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I would avoid Al grinding/sanding under water...it will make a layer of Al hydroxyde and free some H2 when naked Al will contact water and dissolved
oxygen.
Ultrafine Al powder (UAP) is made like this:
Aluminium wire is exploded by intense electric current under Helium or Argon atmosphere. Once cooled freezing a stream of dry air is introduced into
the reactor at a very slow speed and under powder mixing because the super-reactive Al powder may catch fire and burn forming exothermically AlN and
Al2O3.
When this is done and that air has had the time to react slowly at negative temperature, temperature is raised to ambiant T°. That way a very thin
oxyd layer is obtained onto the Al powder. The powder looks like dendritic thunderbolts and has a very high specific surface and a lot of reactive Al
per mass.
The powder can be lightened by a candle flame or the spark of a lighter...it starts localy red then suddently it becomes hyper bright and the burning
zone expands fast to the all powder.
Mix of this with ammonium nitrate prills burns generating star sparks like a sparker.
The powder is very light and density is like 200-350g per L.
It increases specific impulse of Al based powders by 15-40% vs other Al powders.
This powder can be pressed to create Al sponges than can absorb TNT to make thermobaric explosives (a first explosion expands and vapourises the Al
powder that burns all oxygen and nitrogen from the air...once it cools down a strong depressurisation occurs with a kind of implosion effect)...In
such explosions the wind blows twice  
I got a few 100gr of that UAP by a good friend of mine.
[Edited on 17-6-2014 by PHILOU Zrealone]
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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aga
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To get a really fine powder and also keep the impurities down, i would put a large chunk of steel in the chuck of a pillar drill (aka bench press
drill) and simply press down on a chunk of Aluminium held in a vice.
Add a plastic container (e.g. cut-down water bottle) under the vice to catch the powder.
If the Aluminium is a bar, put that in the chuck instead, and grind down on some steel.
Whichever way, grind as Slowly as possible so as not to blow all the Al dust away.
Sanding the Al will inevitably include silicon, glue and whatever the backing is made of.
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PHILOU Zrealone
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Quote: Originally posted by aga  | To get a really fine powder and also keep the impurities down, i would put a large chunk of steel in the chuck of a pillar drill (aka bench press
drill) and simply press down on a chunk of Aluminium held in a vice.
Add a plastic container (e.g. cut-down water bottle) under the vice to catch the powder.
If the Aluminium is a bar, put that in the chuck instead, and grind down on some steel.
Whichever way, grind as Slowly as possible so as not to blow all the Al dust away.
Sanding the Al will inevitably include silicon, glue and whatever the backing is made of. |
Aluminium oxyde layer is corundum with hardness of 9 on Mohs scale... above 5-6 minerals can't be scratched by iron....so the tiny Al oxyd layer will
by reaction abrase the iron and you will have a little iron (and iron oxyde) into your Al powder.
[Edited on 19-6-2014 by PHILOU Zrealone]
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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aga
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Is there a way to get Pure Al powder ?
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PHILOU Zrealone
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As explained a few posts earlier, explosion of pure Aluminium wire by strong electric arc in vaccuum or under inert atmosphere.
Alternatively grinding with corundum ballmills 
Low quality (opaque) 1cm diameter Rubies stones can be bought for less that a few € (between a few stones per €) but it can go up to 5€ for
stones of 3cm diameter.
Last but not least...Sand paper is also "Emery paper" the tiny stones glued on the paper are corundums or spinellas thus mostly Al2O3.
Emery
[Edited on 20-6-2014 by PHILOU Zrealone]
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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