Carbonate containing thermites

So I'm not really into pyrotechnics. But last video by Cody's Lab about copper thermite made me wonder "what if you put an easily decomposable compound into such an energetic thermite? Would that make the thermite more dangerous due to high amount of gases being produced?"

So what coulb be such a compound?
I have some ideas. Ammonium carbonate and bicarbonate are one. There is also sodium bicarbonate. One could also add some kind of formate or oxalate. Ammonium oxalate seems interesting. Oxalic acid itself may be a good idea too. Finally, we can add (basic) copper carbonate to the thermite. Or just use Copper carbonate as the main ingredient.

The idea is that copper thermite is energetic but unlike typical explosive it does not produce hot, expanding gases, which is one of the most dangerous things explosives do. We can add some compounds, which produce them when decomposed, however. Or we can use copper carbonate which shoul react like that (I'm aware that CuCO3 is an idealisation):

3CuCO3 + 2Al --> 3Cu + Al2O3 + 3CO2

So if we added such a compounds to our thermite, we would make it produce some gases. But what would be the disadvantages? Well, such a compounds are not very dense. Copper oxide has a density of about 6g/cm^3. Copper carbonate is about 3g/cm^3. What that means, such a thermite has a much lower energy density and may not explode/react as fast as we want. When it comes to other compounds mentioned before, only oxalic acid and sodium bicarbonate are above 2g/cm^3. So, basically , we would add a bunch of filler to our thermite.

All in all, would you rather I throw a regular Cu/Al containg bomb at you or would you rather I put some (how much?) gas producing filler inside? Let's assume you want to survive.

But seriously, is it a completly dumb idea?

Edit: Also what would happen if I made a thermite with something like iron carbonate or other carbonate instead of oxide?
[Edited on 18-6-2016 by MeshPL]

[Edited on 18-6-2016 by MeshPL]

Quote: Originally posted by MeshPL

But seriously, is it a completly dumb idea? Edit: Also what would happen if I made a thermite with something like iron carbonate or other carbonate instead of oxide?

Quote: Originally posted by j_sum1

But it might eject reaction products further.

Quote: Originally posted by Bert

Adding powdered Teflon to thermite is done industrially to "pressurize the effluent"- That is, blow white hot metal out of the reaction at high speed... A purpose being, pyronoll metal piercing torch or similarly purposed linear cutting devices. http://www.google.com/patents/US5372069 Some people want to use the hot reaction products to do work, rather than recover the reduced metals.

Quote: Originally posted by PHILOU Zrealone

It is already known that "moist" Fe2O3 (containing Fe(OH)3) gives troubles/danger with thermite since the H2O liberated as a gas forms at high temperature H2 + O2 then Al takes the O2 and the H2 explodes afterwards into the air.

Quote: Originally posted by blogfast25

Quote: Originally posted by Bert   Adding powdered Teflon to thermite is done industrially to "pressurize the effluent"- That is, blow white hot metal out of the reaction at high speed... A purpose being, pyronoll metal piercing torch or similarly purposed linear cutting devices. http://www.google.com/patents/US5372069 Some people want to use the hot reaction products to do work, rather than recover the reduced metals. In that case the Teflon is an active ingredient, oxidising the Mg or Al in a very exothermic reaction. An SM thread on the subject: http://www.sciencemadness.org/talk/viewthread.php?tid=16741

Quote: Originally posted by Bert

I am aware of various Teflon oxidized photo flash mixtures, this is not one. The original cutting mixture was Aluminum powder/Iron oxides, plus some Nickel oxide to add further heat liberated by alloying the two metals- And a small amount of PTFE powder, which certainly DOES react with some of the Al on decomposing, but also produces propellant gas.

Quote: Originally posted by blogfast25

Quote: Originally posted by PHILOU Zrealone   It is already known that "moist" Fe2O3 (containing Fe(OH)3) gives troubles/danger with thermite since the H2O liberated as a gas forms at high temperature H2 + O2 then Al takes the O2 and the H2 explodes afterwards into the air. Got any references for that?

Quote: Originally posted by PHILOU Zrealone

1°) Thermal decomposition of water (thermolysis) happens at elevated temperatures and water molecule split back into its atomic components H2 and O2. It is very low yielding at ambiant T°, but increases with T° (about 3% at 2200°C and nearly 50% at 3000°C). 2 H2 + O2 --Ear--> 2 H2O + heat 2 H2O + heat --Ead--> 2 H2 + O2 Energy of activation of reaction (Ear) is much tinier than Energy of activation of decomposition (Ead) so when the system is at high T° Ear and Ead are negligible vs the energetical state of the molécules (Energy System > Ead > Ear) so reaction happens in both sides at the time with a theorical maximum at 50%. 2°) From https://en.wikipedia.org/wiki/Thermite - Hazards If, for some reason, thermite is contaminated with organics, hydrated oxides and other compounds able to produce gases upon heating or reaction with thermite components, the reaction products may be sprayed.

Quote: Originally posted by blogfast25

Quote: Originally posted by PHILOU Zrealone   1°) Thermal decomposition of water (thermolysis) happens at elevated temperatures and water molecule split back into its atomic components H2 and O2. It is very low yielding at ambiant T°, but increases with T° (about 3% at 2200°C and nearly 50% at 3000°C). 2 H2 + O2 --Ear--> 2 H2O + heat 2 H2O + heat --Ead--> 2 H2 + O2 Energy of activation of reaction (Ear) is much tinier than Energy of activation of decomposition (Ead) so when the system is at high T° Ear and Ead are negligible vs the energetical state of the molécules (Energy System > Ead > Ear) so reaction happens in both sides at the time with a theorical maximum at 50%. 2°) From https://en.wikipedia.org/wiki/Thermite - Hazards If, for some reason, thermite is contaminated with organics, hydrated oxides and other compounds able to produce gases upon heating or reaction with thermite components, the reaction products may be sprayed. Those bits are well known and not disputed. But that moist thermites can cause secondary hydrogen explosions remains unproved speculation as far as I'm concerned. [Edited on 20-6-2016 by blogfast25]

Ah OK got it.

I have trown a few drops of H2O on 3100°C overheated iron surface from acethylen/N2O blowtorch and it makes a nice explosion with a clearly visible flame...
If following you no H2 and O2 are produced... where does the flame come from?

For the rest:
http://www.sciencedirect.com/science/article/pii/0038092X779...
"Hydrogen production from water utilizing solar heat at high temperatures ..."
They mention a low temperature acheived with...iron oxyde...but to be practical, you need to flash cool the product of reaction below the explosion/inflamation T° of H2/O2 what is technically hard. This process would ensure the storage of solar energy into H2 with a good yield...although I think electrolysis is much safer and higher yielding.

This is also interesting http://www.eolss.net/sample-chapters/c08/e3-13-03-01.pdf
Especially the graphs of products of reaction at the end as the function of T°

But I'm a true believer and open minded about sceptical people
So here another possible explanation:
Overheated Al powder and H2O stil produces Al2O3 and H2 at high temperature...this explains that ultrafine Al powder water gels are detonable...or propellant (see ALICE tread).
So even if the decomposition of water into H2O doesn't happen stricto senso from the heat, it will from the heat of the Aluminium acting like Mg would or an alcaline metal...


[Edited on 20-6-2016 by PHILOU Zrealone]

@Philou:

Again, that water can be thermally cracked and reacts with hot electropositive metals to form hydrogen and metal oxide is not in dispute here.

These would be necessary conditions needed to make happen what you claim. But are they also sufficient conditions?

That’s not clear when you look at the situation more closely.

Thermites ‘burn’ by means of a reaction front that propagates in spatial dimensions. For example, schematically in just one direction, the reaction zone propagates in the x-direction:



Temperature gradients cause heat fluxes (the wider arrows) from the hottest to cooler zones, in particular to the unreacted zone (highest temperature gradient). This is of course needed to make the reaction self-sustaining.

T is a function of both time and x, probably something like:

$$\frac{\partial T}{\partial t}=v(x)\frac{\partial T}{\partial x}+\kappa \frac{\partial^2T}{\partial x^2}+\frac{1}{\rho c_p}Q(x)$$
... a heat conduction advection equation where v(x) is the propagation speed of the reaction zone, kappa(x) the thermal diffusivity of the material and Q(x) the heat generated by the reaction.

The point is though that the temperature profile of the unreacted zone could easily allow the water to evaporate off (at T_w, about 100 C), well below the temperatures needed to thermally crack the water or for it to react significantly with any hot metal.

[Edited on 20-6-2016 by blogfast25]

Quote: Originally posted by blogfast25

@Philou: Again, that water can be thermally cracked and reacts with hot electropositive metals to form hydrogen and metal oxide is not in dispute here. These would be necessary conditions needed to make happen what you claim. But are they also sufficient conditions? That’s not clear when you look at the situation more closely. Thermites ‘burn’ by means of a reaction front that propagates in spatial dimensions. For example, schematically in just one direction, the reaction zone propagates in the x-direction: Temperature gradients cause heat fluxes (the wider arrows) from the hottest to cooler zones, in particular to the unreacted zone (highest temperature gradient). This is of course needed to make the reaction self-sustaining. T is a function of both time and x, probably something like: $$\frac{\partial T}{\partial t}=v(x)\frac{\partial T}{\partial x}+\kappa \frac{\partial^2T}{\partial x^2}+\frac{1}{\rho c_p}Q(x)$$ ... a heat conduction advection equation where v(x) is the propagation speed of the reaction zone, kappa(x) the thermal diffusivity of the material and Q(x) the heat generated by the reaction. The point is though that the temperature profile of the unreacted zone could easily allow the water to evaporate off (at T<sub>w</sub>, about 100 C), well below the temperatures needed to thermally crack the water or for it to react significantly with any hot metal. [Edited on 20-6-2016 by blogfast25]

The cracking and crackling recombination explosion occurs almost instantaneously as compared to the typical reaction time of the thermite...there should be no delay H2 and O2 is a detonating mix so when slighly cooled and in contact with a hot spot it recombines immediately.
True that such an event is hard to prove because the witnesses leaves the crash site during the incident .

On an energitical level nothing should distinguish H2O explosion by vapourisation vs H2O vapourisation (explosion) then decomposition into H2 and O2 and recombination into H2O...

Sole solution to cut the debate is a good spectroscopic photographic device proving the presence of H2 into the burning flame/melt.
I don't have that .

Or a filmed carefull comparative study of the mechanical work of
-Fe2O3/Al thermite vs Fe2O3/Fe(OH)3/Al thermite
-CuO/Al thermite vs CuO/Cu(OH)2/Al thermite
With the very same ingredients and overal the same amounts of Al/Fe and Al/Cu.

The 1D idealisation is maybe good for an horizontal cigarette burning of low diameter. Nice equation and graph by the way!

In 3D, you have also to play with:
-heat flux going upside from air bubbles (gaps into the initial powder) (density gradient)
-radiative heat flow all direction with efficiency depending on heat capacity of the various medias (air, Al, Fe2O3, Fe, Al2O3, H2O(g)).
-sparkling propagation upside and outside (downside is too resistant)
-flowing of denser metal going downside (density gradient)
-the mather contraction creating gaps/cavities that collapse allowing unreacted powder to fall downside
-convection of the molten metal and flux (liquid Fe2O3/Al2O3)
-coalescence of gases, liquid flux, molten metal

All this is just way to complicated to put into simple equations.
Reality is much more chaotic

[Edited on 20-6-2016 by PHILOU Zrealone]

Quote: Originally posted by PHILOU Zrealone

All this is just way to complicated to put into simple equations. Reality is much more chaotic

If we can successfully model something like Rayleigh–Bénard convection we can probably also model temperature gradients in a thermite mixture. The question is really not 'can it be done?' but rather 'is it worth doing?', which in the thermite case I'd say is 'No'.

In summary, I'd be far more convinced by your claims if they were accompanied by good old direct evidence.

[Edited on 20-6-2016 by blogfast25]

I wouldn't call it a thermite, but I was surprised to discover that sodium carbonate can act as an oxidizer; mixed with magnesium powder, it produces an impressive flare. Potassium carbonate is also used in "yellow powder":
http://www.amateurpyro.com/forums/topic/755-yellow-powder/

I just tried out a mixture of 5.5 g basic copper carbonate and 4.5 g Mg powder (ie, a 33% excess of Mg to O). Ignited with Mg ribbon, it flared up, much tamer than CuO thermite. The flame was bright but had no particular color. What was most striking was this purple-red residue it left on the ceramic I ignited the mixture on, presumably a thin deposit of copper:

Quote: Originally posted by mayko

What was most striking was this purple-red residue it left on the ceramic I ignited the mixture on, presumably a thin deposit of copper: