I heard that you can not put out a thermite reaction because it is self oxidizing and does not need ambient oxygen to burn. If this is true i do not see any reason why you could not have a thermite reaction in a vacuum.
That’s correct. Once ignited, there’s no practical way to stop it. It will continue to burn in a vacuum.
Yes, it can burn in a vacuum.
If thermite will burn in a vacuum, then it will certainly burn in the thin atmosphere of Mars. I was thinking since Mars’s soil is red due to iron oxide, could you send enough aluminum powder to Mars to get the correct ratio for a thermite reaction and truly make Mars the Hell of our solar system?
I think Hell is currently on Venus.
Thermite is composed of an unoxidized metal powder mixed with an oxidized metal powder. Common variety is aluminum powder mixed with iron oxide (rust). Given sufficient heat to start the reaction, the iron gives up its oxygen and the aluminum takes it, releasing more heat to sustain the reaction.
No outside source of oxygen is needed, which makes a thermite reaction nearly impossible to stop until the available reactants are consumed. However, the presence of a vacuum adds an interesting factor, in that the gases (the particular gas of interest here being oxygen) generated by the reaction are no longer confined to the reaction zone by ambient pressure. Absent any real demonstration, it’s unclear to me whether the reaction could continue, or whether the oxygen would rapidly disperse out of the reaction zone and terminate the process before the reactants are consumed.
So a thermite reaction can definitely sustain itself in an oxygen-free atmosphere…but can anyone provide a cite that shows whether the reaction can sustain itself in a zero-pressure environment?
Is the oxygen becoming gaseous at any point in the reaction? I was under the impression that within the molten, reactive mass, the aluminium was tearing the oxygen atoms directly off the iron. If that’s correct, then a vacuum should make little difference.
Im not sure exactly what they are saying but they mention thermite and vacuum. Can anyone translate to undergraduate?
I’m pretty sure the aluminium is reacting directly with the iron oxide, and yanking the oxygen atoms straight off it. If the reaction relied on the exchange of oxygen in gaseous form, it would be possible to quench it with some inert gas, which definitely isn’t the case. Even at atmospheric pressure, the violence of the reaction would expel gaseous oxygen before it could be consumed, so that can’t be happening.
Thinking of a modern art project?
Even if you could burn off the entire surface of Mars with this type of reaction, it wouldn’t burn indefinitely; once all the oxygen has been gobbled up by the aluminum, the reaction stops. Moreover, the Martian soil isn’t pure iron oxide. It’s about 50%-60% silicon dioxide (compared to about 15% iron oxide, along with significant fractions of alumninum, magnesium, calcium, and sulfur oxides.) That said, it’s possible that some of these other oxides could also serve as a fuel source for a thermite reaction. Any chemists out there want to comment on the oxidizing potentials of these other metals?
My vote’s for Io.
I believe that what they’re saying is that, once the reaction gets going, the aluminum will take O2 from the atmosphere as well as from the metal oxide. This is why thermite mixtures that have “excess” aluminum burn hotter than thermite mixtures with the “correct” balance of ingredients.
Incidentally, that’s how I ruined my vacuum.
I don’t know what the activation energy is of the thermite reaction (too lazy to google)
But couldn’t you rapidly cool the thermite to put it out? I get that it’s in a vacuum so there’s no air to cool. But contact cooling of the thermite itself, wouldn’t that be enough to put it out if you could do it fast enough?
I suspect you could blast it with a fire hose. That would not only cool it, but it would physically separate the powder grains.
Hitting burning thermite with a fire hose may cause an explosion, and at a minimum distribute molten metal over a wide area. If enough powder clumps together, it will keep burning while wet, and if there is excess aluminum the reaction can strip oxygen from water molecules.
Fire hose, bad idea. Best bet is let it burn out. It will run out of aluminum eventually.
From the British show, The Brainiacs:
http://video.google.com/videoplay?docid=5735009028560517081#
It is possible that all of these oxides could also serve as a fuel source for a thermite reaction.
for every:
perfectly balanced
2_fe2O3 → 4_Al203 heat of formation is -1.528KJ
vs 3_SiO2 → 2_Al203 heat of formation is -.367KJ
so magnetite is 4.16 X better oxidizing agent then sand
but this doesn’t account for specific heat
but if SiO2 were 60% and rust 15 then rust would only be doing 4% more work than the sand.
I digress
Why wouldn’t it? It has everything it needs to burn. The pressure seems immaterial.
Ordinary flames can conceivably have a problem in a zero-G environment, since
zero-G lacks convection to pull away the heated exhaust gases. A zero-G flame can conceivably smother itself. But the thermite doesn’t have that problem, either – it has its own oxygen supply. (I don’t think, in a practical zero-G environment, and ordinary flame would have a problem, either – any existing currents would sweep the CO[sub]2[/sub] away.)
Candles snuff themselves on spacecraft-- It’s been tried. Larger fires can (unfortunately) be self-sustaining, though.
One possible catch with thermite in vacuum: You need pretty high temperatures to get it started. On Earth, the usual method is a magnesium fuse, but that does require atmospheric oxygen. I’m sure there are other ways to get the required temperature, though.
Hmmmmm… How about ill-tempered, mutated sea-bass with fricken laser beams attacked to their fricken heads?