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Author: Subject: atmospheric combustion of Al (foil)
kryss
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[*] posted on 3-10-2004 at 12:33


Cleaning it with mercurys the best way - you could try dipping in a solution of Mercuric Chloride - some Hg forms on the surface getting rid of the oxide layer. This, I have read, is then spontaneously flammable in air.

BTW various people have told me that Hg vapour is not toxic - its the salts and the organo forms. Apparently in the middle ages the recommended cure for constipation was to swalllow a pint of the metal.

Then again they also did this with molten lead!
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neutrino
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[*] posted on 3-10-2004 at 13:49


All forms of mercury are toxic. The salts and the vapor are highly toxic, the organo forms (if dimethyl mercury is any kind of indicator) are EXTREMELY toxic, while the metal is relatively safe.
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BromicAcid
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[*] posted on 3-10-2004 at 18:05


Yes, the metal, if pure is relatively safe, not the vapors though. But you can pass it between your hands and swallow it without dying.



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[*] posted on 4-10-2004 at 10:32


Like other people have said, you can use metal mercury and its compounds. The alkylorganomercury compounds frighten me. If you are using mercury make sure you have some good ventilation and do not spill it in a small room.

Although the vapor pressure of mercury at room temperature is only 0.0012 mmHg, the resulting equilibrium concentration of mercury vapor is 1.58 ppm, or about 13 milligrams per cubic meter (mg/m 3 ).

(mg/m 3 ). The TLV for mercury is 0.05 mg/m 3 , more than 2 orders of magnitude lower.

mick
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uber luminal
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[*] posted on 8-4-2005 at 13:53
Stray off topic for corrections


I dont think you could use Hg or Ga to "clean" the Al unless you left the liquid metal over the Al and didnt want a very large "clean" surface. But if you do that, you will find that the liquid metal quickly runs through the grain boundaries screwing up structure formation. (I have recently done an experiment like this, its pretty cool to be able to pick out individual Al crystals which were but 20 min ago part of a large solid chunk of Al. )

The misconception here is that, yes Ga and Hg will penetrate the Al2O3 layer, but only until a small hole is formed. then the liquid will all funnle through it into your metal and slide through the easy grains. So it will not... Clean the metal from its oxide layer the way we want it to. These things do what is called liquid metal embrittalment.(LME is very common, not just in Al, but steel+Zinc or impurities in the heat affected zone of welds, or solder/brazing on certain alloys(just look at the phase diagrams for solb.) but its not some crazy redox or anything. (check a themo/red table, nothing would make sense to break down the Al203... nothing that is considered a metal anyway). What about atmosphere? What about it. its not exposed to the metal. and when you do expose pure Al to air, you have about 0.002 seconds (IIRC, i think it might even be a shorter time frame)to do anything before its protected by the oxide again.

I have read... (in a magazine which I think it total crap, aka Popular Science) under a Theodor Grey article, that the HgCl somehow prevents Al2O3 from forming, and thus allows oxygen to... magically oxidize it, yet not form the oxide layer. I try not to remember things I read from Popular science, so I might have that wrong. but anyway the point of the article was to show that Al could rust apart. when the real point of failure is due to the crystals falling apart!
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uber luminal
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[*] posted on 8-4-2005 at 14:09


Quote:
Originally posted by Mr. Wizard
One side of the foil is rather dull, and may have a PE coating. It was also hard to get a good connection with the alligator clips. A little warming with a flame, and a sniff test will tell me if if it has PE or some plastic on it. I don't think it does, as the use of foil in an oven would lead to a house full of smoke. There are other plastics that will hold up in an oven though, as the turkey roasting bags show. More tests ahead.


Commercial Al foil is actualy very pure al. Can you think of the extra production cost put on a thin film? The dull side vs shiney side is just a gradiant of heat as the foil cools. the dull side gets cooled very quickly and the gloss side has a bit more time to cool off. not much, but you consider its foil, and it doesnt need to loose much. I get the same dull vs glossy metal side when melt spinning metals, which is very very close to the same process ALCOA uses to make Al foil. The coolest part about Al foil, like I said, that it is almost pure (at least for alcoa Al foil anyway) If you could melt enough of it, with enough superheat and flux, you could then make mostly pure Al ingots. Which will be very soft.
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[*] posted on 8-4-2005 at 14:44


Foil is not continuous cast. That would be expensive.

http://www.edusite.com/science/products.htm

On another part of their site they say it's 8111 alloy, which is 97% Al, ~1% Si and 0.75% Fe (according to http://www.matweb.com/search/SpecificMaterial.asp?bassnum=MA... ), about medium alloy as aluminum goes (I'd call high alloy 10-20% content; 6061 places in the 5% range).

If you want pure alloy, you need to find some spare aluminum wire. I've cast 1" square bars and they are soft enough to bend with difficulty by hand.

Tim
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[*] posted on 8-4-2005 at 15:07


HgCl doesn't have any significant effect on the oxide layer, but the mercury that forms when the salt reacts with the aluminum does.

For a video of this, look here. Make sure to watch the video, it really is quite interesting.
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[*] posted on 9-4-2005 at 02:27


WTF is mercury paste? Why doesn't he name the real chemical, HgCl2?
I'm almost sure that some HgCl2 solution was poured on the aluminium in the video.
The interesting thing is that a very small amount of HgCl2 (a fraction of a milligram) is enough to destroy unlimited amounts of aluminium. The oxide crust keeps on growing on the "infected" parts because the oxide that forms is in the form of a porous mass that allows air to get to the bare metal just as it is the case with iron.
The infected parts need to be cut or sanded off in order to stop the destruction.
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[*] posted on 9-4-2005 at 13:05


Does a catalytic amount of HgCl2 destroy unlimited pure aluminum? I know it won't oxidize an unlimited amount of common alloys, at least not at a reasonable pace. A few milligrams of HgCl2 dissolved in methanol will attack the bottom of an aluminum can vigorously soon after evaporation, but the reaction slows to a standstill after not much time. I need to find some old aluminum electrical wire.



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[*] posted on 9-4-2005 at 13:40


I haven't tried it out, but I read at least once that superficially amalgamated aluminium will be completely oxidised by air.
I may be wrong on this one, though. I wondered why the oxide crust in the video was black. Perhaps the Hg particles are moved away from the aluminium with the growing porous oxide?
This would need experimentation to find the answer.

[Edited on 9-4-2005 by garage chemist]
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[*] posted on 9-4-2005 at 17:47


yea the video's black powder is... weird? Perhaps its a difference of Al alloys? The size of the crystals has something to do with it too. Al that has been heated and left in an oven for a long period of time and let cool slowly , the crystals would be a lot larger than Al injected into a mold and cooled quickly. I tried this today with 99.99% Ga metal with a 6061 Al stock(small grain boundaries). It had grey powder which I was able to scrape off. the grey was light grey, not this black.

The Ga does penetrate into the Al, but seems to be driven further by additional heat. Also the Ga sits on the Al in a silver bubble... for a long time with nothing happening. (long time as in, longer than I wanted to sit there and wait for it). So, (like the video) I used something sharp inside the Ga and scratched the surface. Then stuff happens.
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neutrino
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[*] posted on 9-4-2005 at 18:37


An injection molded girder?:o
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uber luminal
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[*] posted on 10-4-2005 at 19:19
should probably make a different thread on this side topic but...


what do you mean by...

"An injection molded girder?"

I was just saying that crystal sizes will be different depending on how the Al is processed.

I have further tested, and concluded that its not heat which drives the Ga further into the Al, but stress. Heating the Al causes expansion and compression at unequal rates throughout the entire pieces, providing strain. The Ga seems to sink further into these area's.

This makes total sense, since this happens in the heat effected zone of welds.(or can happen)
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[*] posted on 11-4-2005 at 02:00


I was referring to the girder/beam in the video. I would think that something like that wouldn’t cool so quickly due to its size.
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[*] posted on 11-4-2005 at 07:02


Well, they don't cast shapes like that, it's either extruded or rolled. Probably extruded. Since this is done at high temperature (where grain growth occurs), it has to be heat treated (usually to T6) to regain strength.

The grains could be oh... anything from 10 thou to 1/8" across, on average. You'd have to do a slice, polish and etch to be sure, but you also need the beam on hand to do this...

Say, after gallium treatment, can you roll the aluminum apart into grains? Can you dissolve it in the structure by heating? (To heat treat aluminum, the metal is heated just below the boiling point, where (solid state) solubility is greater for such additions as copper, magnesium and silicon, then cooled faster than the solution can precipitate to eventually produce an extremely fine dispersion of hard, brittle particles.)

Tim
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[*] posted on 12-4-2005 at 06:14


Well, page 2 seems to have nothing to do with the original post.

I, and I'm sure many others would be really interested in a way to ignite aluminium (foil) at STP.

I have to say, Polverones thought that a class would be mesmerised by baking foil burning has just got to be correct.

Anyone got any further yet.

Mike.
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[*] posted on 12-4-2005 at 11:42


I remember pulling arcs from a MOT (2kV 0,5A-no current limiting, the MOT got very hot!) with rolled aluminium foil as the electrodes and occasionally an extremely bright blue spark flew away from the Al and rolled around on the table a bit before going out.
With a NST, this didn't work because of not enough amperage.
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[*] posted on 12-4-2005 at 12:30


I've got a 50V power supply with 15mF (15,000uF) filter cap on it. Sometimes I disable the circuit before turning it off, so I'm left with 19 joules stored... I've shorted it with aluminum foil before and to my amazement, it EDM's nice spots in it. It also produces the distinct "metal fume" odor (characteristic of zinc, magnesium and other flammable metals I'm sure), presumably from colloidial alumina floating around.

Any power supply without current limiting and a good couple 50 amps pulse capacity will work I'm sure...

Not much for keeping it burning though.

Which reminds me, I can melt aluminum (and the surface oxide) under a carbon arc, it dances, boils and makes a nice shadow of white oxide deposit on the work surface. Not self-sustaining.

Tim
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[*] posted on 30-10-2019 at 10:24


Have you tried to paint the foil with a strong solution of KNO3, and letting it dry in the sun to form a KNO3 layer? Then roll up / fold up and try to burn. I'll try this when I am next home.
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[*] posted on 30-10-2019 at 11:56


One time I balled some aluminum foil around 3 or so tablespoons of KNO3 and placed it in the hot coals of a fireplace and gently proded it as the foil softened. It started to emit flickers of white light and then it caught. For several seconds the room was immensely bright.
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[*] posted on 31-10-2019 at 04:27


Quote: Originally posted by uber luminal  

The dull side vs shiney side is just a gradiant of heat as the foil cools. the dull side gets cooled very quickly and the gloss side has a bit more time to cool off. not much, but you consider its foil, and it doesnt need to loose much. I get the same dull vs glossy metal side when melt spinning metals, which is very very close to the same process ALCOA uses to make Al foil. The coolest part about Al foil, like I said, that it is almost pure (at least for alcoa Al foil anyway) If you could melt enough of it, with enough superheat and flux, you could then make mostly pure Al ingots. Which will be very soft.


That's actually wrong.
If you pass one foil between rollers it will be shiny on both sides.
For economical reasons, 2 foils pass between the rollers.
Facing the roller: shiny
Facing the other Al foil: dull




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[*] posted on 3-11-2019 at 06:04


I like the carbon additive approach, viewing it from the perspective of its possible interaction at elevated temperatures with the Al2O3 protective layer on Aluminum foil. As support, see this paper at https://www.nrcresearchpress.com/doi/pdf/10.1139/v63-095 and also per this abstract: "Reactions Between Aluminum Oxide and Carbon The Al2O3—Al4C3 Phase Diagram" at https://ceramics.onlinelibrary.wiley.com/doi/abs/10.1111/j.1... , and the comment:

"Because of the high reactivity of aluminum carbide and all the intermediate compounds with moisture and oxygen"

with the proposed use of KNO3 here as the oxygen source.

A possible interesting variation would be to further pretreat one side of the Aluminum foil with the outer part of a sooty flame (like from say burning turpentine).

Why soot based carbon? To quote a source ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5324401/ ):

"In contrast, the organic carbon (which in the case of methane flame soot is dominated by aliphatic species) is highly reactive, undergoing first the addition of oxygen-containing functional groups and ultimately the loss of organic carbon mass from fragmentation reactions that form volatile products"

where aliphatic refers to hydrogen/carbon open-chain compounds with no rings irrespective of the presence of single, double, or triple bonds.

Note, per a source ( https://www.tandfonline.com/doi/pdf/10.3402/tellusb.v41i3.15... ) "soot consists of pure elemental carbon along with highly polymerized organic matter."

Particular carbon surfaces, like heated soot (which per https://www.ncbi.nlm.nih.gov/pubmed/21824643 consists of black carbon (BC) and organic carbon (OC) particles, where OC on further heating can generate pyrolytic elemental carbon (PEC) ) may result in a faster (from a generated PEC presence per same source) ignition reaction process with Aluminum foil.

[Edited on 3-11-2019 by AJKOER]
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[*] posted on 3-11-2019 at 17:35


Has anyone checked that the heat released by the combustion of aluinium metal in air is enough to,
raise the temperature of metalic aluminium to melting point, and vapourise it ?




CAUTION : Hobby Chemist, not Professional or even Amateur
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