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Polverone
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Exotic thermites & analogs
Many oxides/salts of less reactive metals can react vigorously when mixed with an appropriate quantity of magnesium or aluminum and initiated by high
temperatures (or, in some cases, by a detonator). The most common of these mixtures, of course, is aluminum and iron oxide.
I've experimented with a few other different mixtures. Anhydrous CuCl2 and aluminum is easy to ignite, though not terribly vigorous. I was able to
wrap some CuCl2 powder in aluminum foil to make a tube and ignite the tube at one end with an alcohol burner. Combustion progressed with a small
amount of pinkish flame (I would have expected green or blue, but it was pink) and considerable smoke, with solid copper being deposited. CuCl2 and
300 mesh aluminum powder burned quickly.
Flour-fine CuO from a ceramics supplier burned with extreme vigor with 300 mesh aluminum in a stoichiometric ratio. I ignited one charge of about 30
grams at night with a hot aluminum/sulfur ignition mixture. The thermite mixture was in an aluminum can with the top cut off and the igniter laid on
top. The CuO/Al burned in a fraction of a second with a hearty "whump!" and shot glowing debris (likely the igniter slag) 10 meters in the air.
A 50 gram charge of the same mixture was initiated in the daytime with 2 grams of HMTD. There was a satisfying flash and explosion, and a large cloud
of brownish smoke (vaporized copper mixed with aluminum oxide) rose above the test site. It is interesting that this mixture yields *no* permanent
gases at STP yet exploded with sufficient force to make the plastic stand holding the charge vanish without a trace.
I have oxides of tin and chromium on hand, which I hope to try at some point in the future. I would also like to try lead salts/oxides, though I fear
excessive sensitivity with these, and also with silver salts/oxides, though I fear sensitivity *and* price with them.
Have any other experimenters here wandered off the beaten path of "standard" thermite?
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Rhadon
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I just experimented with PbO / Al. I put it into a container that was made out of a piece of aluminum foil and tried to ignite it with an alcohol
burner, without success. Though, the aluminum case began to glow and started to melt down, what indicates that some energy was given off (usually I'm
unable reach the mp of aluminum). I tried it once again, with the same result.
So I gave it another try, but this time I put some sulfur on top of the mixture to lower the ignition temperature. It didn't burn as bright and not as
fast as I expected (both components were very fine), but it worked quite well.
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vulture
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That's strange, I've always read that PbO/Al is very sensitive and can explode without confinement.
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Polverone
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I have read the same thing about lead oxide and Al, but I believe the references I had were speaking of minium, red lead, Pb3O4. Also, as I'm sure
anyone who has ever experimented with pyrotechnics knows, particle size makes a tremendous difference. Rhadon, how fine were the particles of your
components? I hope that your experiments are small and cautious. The CuO/Al mixture I used was extremely vigorous, and I would expect that lead-based
mixtures could be even more so.
If you are having difficulty achieving ignition, try placing a 1:1.78 (or just 1:2) mixture of Al powder and sulfur powder on top of your main charge.
This mixture is easy to ignite with a fuse and relatively tame but burns hot enough to melt steel and ignite thermite mixtures of all sorts.
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Rhadon
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Perhaps the ignition was a bit hard because PbO exists in two forms - a red alpha- and a yellow beta-form. I don't know what the difference is,
though.
I used lead hydroxide and heated it until it had a yellow color. This should have yielded the beta-modification. I made it as fine as I could, the
particle size should be approximately like that of flour.
The aluminum I used is very fine. I don't know what mesh it is, but it can be used for painting purposes.
| Quote: | | I hope that your experiments are small and cautious. |
Yes, of course  I only used amounts as small as about 1 g and had 'security
precautions'.
I might try the Al/S mixture for ignition in the next days when I'm in the right mood. There is still some PbO that wants to be used
Does anyone know how sensitive Al/S is?
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Polverone
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Al/S sensitivity
Do you mean sensitivity to heat, friction, impact? I have only tried initiating it with flame. It is considerably harder to ignite than black powder,
but it is still easily accomplished with the flame from a fuse or match. It burns slowly with much heat. Try it, you'll like it ;-)
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Rhadon
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I see, I should have mentioned what kind of sensitivity I was thinking of. Actually, I wanted to know about all three, but primarily sensitivity to
heat and friction. Heat sensitivity because of the ignition temperature and friction sensitivity because it's always good to know how careful you have
to be when mixing the components.
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Rhadon
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In the last days I experimented with Al/s. Before applying it to PbO/Al I wanted to try igniting the ordinary Fe3O4/Al thermite with it. I did so
three times without having success. Since this was probably due to the very small scale, I wanted to give it another try with about 15 g of Fe3O4/Al.
Unfortunately, I didn't have enough Fe3O4, so I searched for another metal oxide in my lab. I selected MnO2.
About 14 g of MnO2/Al could be ignited easily with Al/S, and the reaction worked unexpectedly well, even though it was not as vigorous as Fe3O4/Al, of
course.
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Madog
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i have used PbO/Al once. it was easy to ignite but not as good as i expected. Al/S sounds interesting.
Most people outgrow their pyro tendencies, we are the ones who\'s tendencies outgrew us.
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KABOOOM
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Kwel
here (Iran) teenagers make a kind of very dangerous torpedo using red lead and a kind of very fine bright aluminum powder (the word we use in persian
does not mean Al powder and its main use is for painting and things like that to add brilliant effect)
anyway, here is how they make the kwel torpedo
1. mix the Pb3O4 & Al powder very carefully
2. sprinkle half of the powder on a sheet of plactic bag then cup the sheet then put some stone in it and pour the rest of the powder now wrap the
above part of the cup-form till you have a ball with a plastic-bag wall (that contains Pb3O4-Al mix and pieces of stone in the middle)
3. (the most foolish part!) wrap the ball with electric-tape very TIGHT!!!!!
this torpedo is Terribly sensitive to impact there is no need to throw it very hard
it's Incrediblly powerful. many kids have been injured and even died with the torpedo
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Polverone
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Red lead & aluminum
Have been used to create crackling microstars ("dragon's eggs") in the past, but the toxic lead is now replaced by bismuth trioxide (at least in US
fireworks). I was aware that the mixture was explosive but didn't realize it was so sensitive. Impact-explosives can be fun but are generally a bad
idea from a safety standpoint.
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PHILOU Zrealone
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There was an extremely good post about thermites on alt.engr.explosive NG that was posted by Don Haarman 2 or 3 month ago!
You have a very long tale very instructive that explains all you want to know about all kinds of themites with various oxydes!
See:
Subject:
Re: extinguishing thermite
Date: Sat, 03 Aug 2002 02:05:43 GMT
From: "donald haarmann"
Organization:AT&T Worldnet
Newsgroups: alt.engr.explosives, sci.chem, rec.pyrotechnics
References:1 , 2 , 3 , 4 , 5 , 6
Then you would have 18 pages of pleasure! I don't put those here since they are there! and I'm not sure this reply case has enough memory to hold 18
pages!
PH Z
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Polverone
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Oh, indeed
I have seen this message. It contains much excellent material. He also cited "Civilian and Military Pyrotechnics" within that message, I believe,
which is what inspired me to scan it.
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PHILOU Zrealone
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To be honnest...think a bit to what will happen if you blast a thermite mix?
It will spray all arround and take the reactants away from each other fast before they have had the time to react!
Even a fast exploding thermite won't exceed 500m/s while any low detonation is over 1,5km/s so better use only the Al/Zn/Mg powder in the explosive
immediately because the other metal oxyde will be only dead weight-inert body!
PH Z
   
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Polverone
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I found a reference on Usenet (yes, I know, not exactly a peer-reviewed source) to exploding CuO/Al thermite mixes which inspired me to try it myself.
It may be because of the relatively small charge in a confined area, but I am fairly certain that almost all of the CuO/Al mix reacted without
dissipating (when I initiated a pill bottle of the mixture with HMTD). When I've had mixtures containing Al fail to completely react/detonate, it is
very easy to see the powder on nearby surfaces. There was no residue left behind in this case, not the smallest fragment of plastic or the merest hint
of aluminum. Bear in mind that I was using very fine and well-mixed powders, whereas traditionally thermite is made with coarser materials.
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Rhadon
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SiO<sub>2</sub>/Al
I heard that a thermite mixture consisting of SiO2/Al is used to make elemental Si (but not commercially). Has anyone ever tried this?
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Polverone
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Where did you hear this?
I've heard the same thing just recently. I can't remember if it was from a large inorganic chem book I've been reading, or Usenet messages, or
Military and Civilian Pyrotechnics, or something else.
In any case, the Unknown Reference stated that magnesium could be used to reduce SiO2 to silicon, but that some magnesium silicide would also be
formed. It further stated that if an excess of aluminum powder were used instead, no silicide would form and the impurities could be removed by
dissolving them in NaOH solution.
This sounds well worth trying... not that I have any use for raw silicon.
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Rhadon
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You guessed it
The source is an inorganic chemistry book. I don't have it at hand for reference since it is from the library, but if I remember correctly the
procedure recommends to clean the final product by boiling it for some time in HF and washing it with water afterwards. This will also remove
SiO2 impurities.
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Rhadon
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SiO2 / Al experiment failed
I tried the SiO2 / Al thermite mixture recently, the SiO2 coming from unpurified window glass (composition should be about 72%
SiO2, 14% Na2O, 9% CaO, 4% MgO and minor amounts of other additives). Yes, it was highly polluted, but I thought that
1/4 of impurities wouldn't stop the reaction if it has finally started. Since I expected that it would be hard to ignite, I did
it in several steps as shown in the figure below.
Up to the point where the SiO2 / Al should be ignited, it worked all well. But the latter was left back unreacted, having a thin crust of
scoria on its top. Probably the temperature which is generated in the reaction between MnO2 and Al wasn't high enough, or it was due to the
impurities.
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a_bab
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Great pics Xoo ! The Lead oxide/Al is similar : very bright and fast.
Rhadon, for your reaction you must use sand (nearly pure SiO2), not glass powder. Also the crusty residue (Al2O3 + Si) must be reacted with HCl. If Mg
powder is used instead of Al, you'll get also silane (SiH4) generated by the reaction with HCl. This is a pyrophoric gas (and very toxic as well). The
remainings might be pretty pure Si.
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Polverone
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Good pics. I'm kind of surprised that you were able to get 3 pictures. When I tried this mixture, it burned extremely fast - almost like flash powder.
Now of course you should try the next step: explosive initiation!
BTW, did you just use an ordinary fuse to light this mixture or did you use some sort of priming mix too? I think it is sensitive enough that you
might get it going with just a big hot fuse, but I always used an Al/S prime mixture (when I wasn't using a detonator).
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Polverone
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That flash circuit does sound like a viable method for initiation. If I were you I would try it.
When I explosively initiated my CuO/Al thermite, I placed the mixture (about 30 grams) into a narrow pill bottle. I placed a straw filled with HMTD
down the center of the mixture as my detonator. I didn't cap or reinforce the pill bottle in any way.
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a_bab
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Since the Cu/Al mixture is capable of a very fast burning (same as Pb3O4/Al), and I have vaste experience concerning the last one, I can say that if
initiated with a detonator even open (a pile on a sheet of paper with the det. in the middle) the mix will explode (I don't say detonate), so it'll
explode with a loud report and a deep soud (=low speed). And if is confined enough (a motor rocket) it'll eplode for sure every time. It's very
reasembling with the whistle powder from this poit of view (used to make nozle-less rockets)
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Boob Raider
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I wonder if .......
the PbO2 from car batteries would make a good incendary with Al powder. And NiO2 with Al powder. Also if one were to make fine granules with the
thermite mix and pack it loosely around the ignition charge ..... it should generate a large heat explosion. Finer granules would make an intense heat
explosion and coarser granules would work great as incendaries.
I had set off a charge once of Aluminized BP surrounded by Hexamine soaked in naptha ...... and DAMN did it put out a heat wave. (I miss those days when I could buy kilos of hexamine as camp fuel)
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madscientist
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I would think that PbO2/Al mixes would be violently explosive and dangerously unpredictable.
I weep at the sight of flaming acetic anhydride.
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