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Author: Subject: Exotic thermites & analogs
egloskerry
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[*] posted on 27-4-2007 at 20:01


On the site I got them from, it lists two oxides, red and black. It says the black is FeO.

However, I did get two pounds of each, and I got less black oxide than red. Since FeO has a much lower mol. weight than Fe2O3, two pounds of it should've occupied MUCH more space. So I'm guessing it is Fe3O4 after all.

Are both of them (FeO and Fe3O4) paramagnetic?

[Edited on 27-4-2007 by egloskerry]
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mrjeffy321
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[*] posted on 27-4-2007 at 20:55


You cannot always associate a higher molar weight to a higher density (Compare the molar masses and densities of Radon to Lithium).
FeO: 5.7 g/cm^3
Fe3O4: 5.18 g/cm^3
Fe2O3: 5.24 g/cm^3
They are all relatively close to each other in terms of density.

You could do a RedOx titration of with the Iron Oxide (dissolve it in solution with H2SO4 then titrate with KMnO4 to oxidize all Fe+2 to Fe+3, compare experimental results with what would be predicted for the given oxide).
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egloskerry
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[*] posted on 28-4-2007 at 06:42


Eh, it's not that important. I'll just ask them the next time I order.

But about my earlier post. Would Sb2O3 work, or be considered a thermite? And is it possible to get that thermite datasheet?
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12AX7
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[*] posted on 28-4-2007 at 08:19


Sb is reasonably metallic, it would probably work. Sb2O5 would be even better.

Tim




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egloskerry
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[*] posted on 1-5-2007 at 21:00


I tried 25g each of Cu2O/Al and Fe3O4/Al thermite, figured I'd get some sort of alloy. All I got was a black spot on the piece of concrete. It did, however, burn faster than iron thermite, but slower than copper thermite. I wonder if a ferrovanadium alloy could be made this way.
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JAPS
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[*] posted on 6-5-2007 at 08:41


Hi all, Al and Fe oxide is still the best method.

I use thermite to demonstrate exactly what thermite is capable of burning through, glass, metal etc.
I use either Al / Fe2O3 or Al / FeO(OH) in the weight ratio 1 / 3. The mixture is placed in a 15 to 20cm. diameter flower pot with a piece of thin cardboard over the hole in the bottom.

The pot is placed on an iron support which is about 10cm. over the material to be burnt through. This means that the molten iron flows through the hole in the bottom of the flower pot and directly onto the glass or whatever is under the pot. The material to be burned through is supported by 4 bricks, and under the material is sand.

You don't need fine Al powder for the main bulk, you can use Al pellets ( griess ) or the cuttings from sawing, anything between 1mm. and 2mm. will work fine.

The thermite is packed into the pot until the level is about 3cm. below the rim of the pot. Now you need a cylinder of paper 3cm. long and 3cm. diameter. The paper cylinder is placed in the middle of the pot and the rest of the thermite is filled around the cylinder.

What you now have is a flower pot filled with thermite except for a hole in the center.

I don't use magnesium ribbon to ignite the thermite because it doesn't always work !!

You now need a mixture of Al powder and Fe2O3 ratio 1 / 3. and 7 storm matches.

Using a rubber band connect 6 of the storm matches together about halfway up the wood, and push the other storm match down between the heads of the other matches until the lower part of the head is below the top of the other matches. Place the " Fuse " into the middle of the hole and fill up with the fine powder. You should see the top of the 6 matches and the seventh single match sticking up in the middle.

After lighting the top match you have about 3 seconds to get well clear !!!

Always have a bucket of water and a fire extinguisher nearby.

Note: The flower pot is clay not plastic !
FeO(OH) is rust and is red-brown
All ratios are weight
Griess is small round parts of recycled Aluminum scrap.
Light well away from anything that can catch fire.
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egloskerry
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[*] posted on 6-5-2007 at 20:12


Fe2O3 is known as rust. FeO(OH) is yellow iron oxide.

Your ignition process seems very complicated. You should look at some of the other methods that have been posted.

And I feel I have to tell you, it is EXTREMELY DANGEROUS to throw water on a thermite reaction. The temperatures are capable of flash boiling the water and potentially causing a small explosion. Also, water won't put it out, since the metal oxide supplies the oxygen. A fire extinguisher won't work either for the same reason. The only way I could imagine would reliably stop the reaction is to scatter the reactants so they are no longer in a confined area.
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UnintentionalChaos
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[*] posted on 6-5-2007 at 20:56


Not only flash boiling, but the molten metal is quite capable of stripping oxygen from the water and making a cloud of hydrogen which then explodes/combusts with environmental oxygen



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12AX7
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[*] posted on 6-5-2007 at 21:25


I suspect he meant water for cooling things not reacting or intensely hot. Obviously dumping water on thermite is not going to go well.

Incidentially, why allow hydrated iron oxide? Doesn't that make a lot of gas? I've had Fe(OH)3 explode when I've slowly heated mixtures containing it! I would only ever burn calcined rust (which has a dark red-brown color, with almost a purple tinge to it).

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egloskerry
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[*] posted on 7-5-2007 at 23:49


And also, Fe3O4 is going to work MUCH BETTER than Fe2O3. In my experience with Fe2O3, a sustained reaction is difficult.
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[*] posted on 8-5-2007 at 11:24


I also had problems with Fe2O3 but when I used finer Al powder it worked. It burned very fast and the iron was scattered around so I belive that it couldnt melt through a metal plate. It should burn slower.



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egloskerry
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[*] posted on 8-5-2007 at 17:25


What mesh is your Al? Mine is 625.
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[*] posted on 9-5-2007 at 03:05


I don't know. It is a silver powder and it floats in air. It is reagent grade. I got it from school.



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[*] posted on 9-5-2007 at 11:00


Sorry about any misunderstandings !

Rules and regulations require that a fire extinguisher and a bucket of water are on site when I make the demonstration ( makes sense ). It would be classed as an attempted suicide if I were to empty the bucket of water over 2 or 3 kilos of burning thermite ( probably worse than pouring water over burning fat in the frying pan ). Accidents can happen, and sometimes the thermite tends to spit out unexpectedly. Molten iron on someones clothes would not be very nice, so the water is not a bad idea !!

The FeO(OH) burns louder than the Fe2O3, probably due to the attached water crystals, I would also say it tends to burn slower.

I would hazard a guess and say if you were to ignite a 3 kilo mixture of thermite using fine Al powder ( < 50µ ) and Fe2O3 you would get an enormous flame ( maybe an explosion ) and molten iron spread around in a 15 meter radius. Nice to watch ( in the middle of a corn field ) but that 's not the object of the exercise.

The main bulk of the thermite must be Al around the 1mm to 2mm size, this reduces the speed of the reaction and results in the molten iron pouring out of the hole in the bottom of the pot.

The ignition method that I described is what I use when I'm testing. When viewers are present I start it electric from 20 meters. For both methods I still use the primary of powdered Al and Fe2O3. This may appear complicated, but it hasn't failed yet !!
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[*] posted on 12-5-2007 at 06:46


Hi Zink.

If the powder that you have is what I think it is, then your bright and shiny ( air float ) Al powder is used in the paint industry. If you get it on your fingers then your fingers become a shiny silver color.

It is anywhere between 75µ and 1µ and was made from Al foil. The foil was first cut into small pieces and then milled with some stearic acid to polish it.

The powder is usually mixed with linseed oil ( or similar ) so that it can be applied to canvas.

It's also quite expensive !!

Use a fine dust mask when handling it !!

[Edited on 12-5-2007 by JAPS]
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[*] posted on 12-5-2007 at 07:35


Hallo 12AX7,

Absolutely correct. The FeO(OH).xH2O is heated up slowly to 230°C for 2 hours. ( Just for interest ) The cooking pot is covered and fixed with a cloth in case of ( volcanic eruptions ). There are usually about 4 kilos in the pot. The starting color is brown-black and ends up at red-brown.
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[*] posted on 29-5-2007 at 16:08


Quote:
Originally posted by egloskerry
And also, Fe3O4 is going to work MUCH BETTER than Fe2O3. In my experience with Fe2O3, a sustained reaction is difficult.


It's been years since I've done the thermite reaction, but I used to use rust (a mixture of Fe2O3 , FeO(OH) etc, exact composition depending on what and how it rusted). I managed to get repeatable meltings of steel can lids, etc.

Come to think of it, my whole batch of rust had been obtained from the outside of a rusted, 55-gallon steel burn barrel. I am guessing the frequent use of the burn barrel drove out quite a bit of the moisture from the rust. It had a deep red-brown color, rather than a muddy ochre color.

I think the ignition method of JAPS sounds pretty good.

I used to ignite my Fe2O3 / Al thermite with a KNO3 / S / C igniting mixture, basically a variant of "green mix". I recall the trick was to get an orange-hot molten globule of burning nitrate-sulfur mixture that would concentrate the heat. It worked, even when the Al wasn't that fine.
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[*] posted on 31-5-2007 at 23:06


I've found that if you want to make a relatively large charge of thermite, and you don't have access to large amounts of Al-powder, you can do as follows:
Un-roll a length of Al-foil corresponding to 1 part by weight. Measure out 1 part by weight of Fe2O3 and sprinkle it on the foil. Roll up the foil to form a long cord with a Fe2O3 center and load this cord into a container and ignite with regular thermite. It works quite well and is a very cheap way of making thermite charges.
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[*] posted on 1-6-2007 at 14:53


Some day I'm going to have to take a few shovelfuls of aluminum cutoffs and swarf and mix with as much iron oxide (probably mill scale) as needed. Then ignite with a few pounds of maybe 20 mesh (aluminum filings), then ignite that with ground thermite (Fe2O3 powder and ground magnalium +100 mesh is what I usually cook up). And ignite that with, say, magnalium (10 mesh, and some 100 mesh), charcoal and KClO3 (makes a sparkler from hell!) and a fuse.

Tim




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[*] posted on 4-6-2007 at 09:54


A strange thought occured to me and I think this might be as good a place to ask as anywhere (my apologies if it's been asked elsewhere; the search didn't find it).
Can you get a mixture of powdered aluminium and ammonium chloride to "fire" like a thermite?
I think the reaction to give H2, N2 and AlCl3 should be exothermic but I don't have the oportunity to try it (my neighbours would call the police). If it does work then it will produce a lot of gas so it might be more "explosive" than a lot of conventional thermites.
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[*] posted on 5-6-2007 at 01:51


12AX7, make sure you put it in a flower pot and let the Fe drip onto something or in a mould.
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[*] posted on 7-6-2007 at 09:55


That'd be a big flower pot.
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[*] posted on 7-6-2007 at 14:33


Yeah, probably loose sand fill and an anvil mold or something.

Would need testing to see if I can get any even slightly controlled composition...be a shame to burn 200 pounds of thermite only to have it crack from gobs of sulfur and carbide or oxide in the metal!

Tim




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[*] posted on 7-6-2007 at 16:40


Unionised... I think it would simply be a reaction of HCl and Al, right? when you heat up the NH4Cl, it will decompose to HCl and NH3, at least at the normal thermite igniton temps - and the HCl will react with the Al, presumably. The H2 generated might burn in the air, together with the ammonia, if high temps are maintained. Perhaps a neat way of making anhyd AlCl3, when doing this in an evacuated container? Somehow I doubt though the reaction of HCl gas and Al powder is vigorous enough to be selfsustaining (while decomposing more and more NH4Cl).



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[*] posted on 7-6-2007 at 18:02


NH4Cl is a common reagent to make chlorides, isn't it? Al(OH)3 + 3 NH4Cl --> 3 NH3 + AlCl3 + 3 H2O would be the reaction (using reactive alumina hydrate, since alumina is so refractory), although it seems odd that so much water would escape voluntarily from aluminum chloride.

Oh yeah, that's right- an NH3.AlCl3 adduct forms, dunnit? Lewis acid, lewis base, lewis salt as it were!

Tim




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