Exotic thermites

[Differential]

I've tried a few varieties of thermites, and had good luck with iron oxide, copper(II) oxide, and anhydrous copper sulfate. Typically I do 10 grams or less, as an unconfined powder. However, I tried copper carbonate and had no reaction - I was expecting the carbon to be reduced, and possibly reigniting in air. Has anyone else tried this?

[Mumbles]

I think you might just be running into a thermodynamics issue. Going from copper carbonate to copper oxide (and releasing/burning CO2) is going to be energetically uphill. It's not surprising to me that the reaction isn't self-sustaining. I suspect you'd need added direct heat for a period of time before it finally gets going.

[Differential]

Magnesium ribbon will react with dry ice, and aluminum is similar to Mg in terms of reactivity.

 

2 Al + CuCO3 should yield Al2O3, C, and Cu.

Hf Al2O3 = -1670 kJ/mol

Hf CuCO3 = -595 kJ/mol

 

So the reaction should release about 1,075 kJ, or about 6.0 kJ per gram of reactants. Copper oxide thermite will only release 4.1 kJ/g. That's why I'm confused.

 

The few articles I did find on the reactions between Al and CO2 mentioned temperatures of 1,000+ C, so you could be right.

[Mumbles]

Overall it is energetically downhill, there is just an activation energy due to the first step in the reaction.

 

CuCO3 ---> CuO + CO2

 

This reaction is 45.5kJ/mol uphill, though thats .368kJ/g. Apparently that's enough to impede it from self-sustaining from the start. I know that Al/CuO burns just fine.

[pyrojig]

Now bind this mixture with a NC laq. in a "wet mix" and see the reactivity go very energetic. I guess this could be attributed to a very intimate mix bound and granulated . I hear it can be almost explosive in nature . Not sure if it can be better for target mix or if the NC will desensitize it. I imagine it wont matter either way. . If one where to make this mix I would make sure that all starting chems are very fine in particle sizes .

[pirobot668]

From what I have read/seen, copper thermites tend to explode. The mechanism is assumed to be due to thermal conductivity.

The copper simply 'passes along' heat more rapidly, so the pressure/heat/burn-rate spiral runs away very fast.

I have done some bits of work with NC lacquers/Cu-thermite as well. 3mm cubes, lightly primed with potassium perchlorate/silicon powder/dextrin.

The cubes zip around like little rockets, then pop and bang for a bit. Sometimes a fragment willl split several times. Blue-green flash, pretty!

That was years ago, I will see if I can find my notes.

[otto]

@ pirobot668 - I'm intrigued. That sounds like interesting star material to me.....

 

Then again, what do I know? I'd certainly be interested in those notes!

 

/m

[GMetcalf]

From what I've read, I believe a Copper Oxide/Magnalium mix can be used to produce a Dragon's Egg (by binding with Nitrocellulose). So the popping effect isn't at all surprising!

 

The colour is though and I would love to see those notes pirobot668! I'm currently working on some coloured star formulae which don't utilise Potassium Perchlorate or Chlorate and I'm currently working on a blue star utilising the Copper Oxide/Aluminium thermite reaction as a starting point...

[ddewees]

I played with cu/mgal stars before (recently), and they do in fact explode (for the most part). The smolder stage was far too long though, often taking several seconds in between flashes. Neat stuff though, it caught me off guard.

[niemand01]

A while ago I had some fun with different thermites the more exotic ones being with sillicium and manganese oxide to isolate the corresponding metals. Eventually I even got titanium oxide thermite to work. After that I did some experimenting with thermate tried out different oxidizers etc. Anyway would anybody happen to know why they use Barium nitrate as an oxidizer in commercial thermates ?

[dave321]

i think its to lower the ignition temperature and ease the ignitability.

don't they also use sulphur in the same composition for the same reason

[niemand01]

Yes they do use sulfur but I was thinking more of why not use lets say the cheaper Potassium nitrate ?

Edited May 7, 2015 by niemand01

[Joyburger]

I believe they use barium nitrate in order to cause the evolution of gases that will project molten material forward as the thermate burns. It's better for the actual task of burning through stuff, but not particularly aesthetic.

Edited July 8, 2015 by Joyburger

[Mumbles]

According to the patent, the barium nitrate lowers ignition temperature, adds a flame, and increases the thermal effect. Exactly what the increased thermal effect means or actually mechanistically happens is unclear.

 

http://www.google.com/patents/US6766744

[pyralex]

Magnesium ribbon will react with dry ice, and aluminum is similar to Mg in terms of reactivity.

 

2 Al + CuCO3 should yield Al2O3, C, and Cu.

Hf Al2O3 = -1670 kJ/mol

Hf CuCO3 = -595 kJ/mol

 

So the reaction should release about 1,075 kJ, or about 6.0 kJ per gram of reactants. Copper oxide thermite will only release 4.1 kJ/g. That's why I'm confused.

 

The few articles I did find on the reactions between Al and CO2 mentioned temperatures of 1,000+ C, so you could be right.

how can i react MG with dry ice? that seems fun

[taiwanluthiers]

Seen it in a chemistry demonstration once... Professor lights a Mg ribbon and places it in a block of dry ice. The Mg burns far more fierce as though it was in oxygen.

[boneleg]

Its fun to use less reactive metals spiked with a little magnesium to keep the reaction going.

http://www.youtube.com/watch?v=qFnp2j5pmMA

[Puls0r1]

how about trying magnalium instead of just aluminum.