condennnsa - 25-8-2010 at 23:23
Hi, I just come across this rocket propellant on the internet
http://en.wikipedia.org/wiki/ALICE_(propellant)
Apparently, it's just a mixture of ice and extremely fine aluminum powder. Now I thought that one would need a moderately strong oxidizer to be of use
in propelling rockets, but water...?
Is the reaction between water and aluminum really so exothermic?
The only reaction that I can think of between H2O and Al would be something like 3H2O + 2Al -> Al2O3 + 3H2, then the hydrogen would in turn burn
with atmospheric O to form water again
[Edited on 26-8-2010 by condennnsa]
woelen - 26-8-2010 at 00:27
The reaction between aluminium and water indeed is very exothermic. Aluminium reacts with water, but the formed oxide covers the metal and this
prevents further reaction. If in some way one can prevent the formation of a tight oxide layer then the reaction of the metal and water is very
exothermic and quite dangerous in larger quantities.
One way to cause the oxide not cover the metal but form a flocculent precipitate instead is the addition of a combination of copper(II) ions and
chloride ions to the water. Just dissolve some NaCl in water and add aluminium foil. This gives no reaction. In some other water dissolve some copper
sulfate, again no reaction with aluminium foil. Now, mix the solutions of copper sulfate and sodium chloride and add aluminium foil. A vigorous
reaction starts and quickly all foil is converted to a grey somewhat flocculent mass. A lot of heat is produced.
Now imagine what happens if instead of the compact foil, you add finely powdered aluminium to a solution of table salt in which also some copper
sulfate is dissolved. The powder at once reacts, giving a plume of steam and a lot of heat.
The copper-chloride combination does some very specific trick, it prevents adherence of the formed oxide to the aluminium metal. Probably it has to do
with intermediate complex formation, but I'm not sure about that. Some of the copper also is converted to metal, but this is not the cause of the
violent reaction, only a tiny fraction of the copper reacts to metal, while a lot of aluminium reacts. It also is specific to the combination of both
chloride and copper(II) ions.
Other combinations also bring about such reactions, e.g. copper(II) + bromide, and also mercury(II) + chloride.
So, I can imagine that a mix of water and very fine aluminium powder can act as rocket propellant, but some additional agent is needed, which has the
effect, described above, but only at elevated temperature. Copper(II) + chloride is not suitable, because that already at room temperature causes
violent reaction.
12AX7 - 26-8-2010 at 09:39
This thread needs a video,
http://www.youtube.com/watch?v=CRLMsiC-SgM
Tim
bbartlog - 26-8-2010 at 11:02
I would assume that in an ALICE rocket the aluminum and ice are somehow combined *without* the aluminum acquiring an oxide coating. Maybe ice at a
sufficiently low temperature won't react even with naked Al. I suppose if I read about the Purdue experiment I would know.
The CuCl2 plus Al reaction has been on my mind of late as a way to obtain AlCl3. Problem being that it may not proceed readily except in aqueous
medium, which defeats the purpose. Doing it as a solid thermite reaction might work but the exotherm would have to be handled somehow. Seems like
there is a small chance that some other solvent would work, too...
hissingnoise - 26-8-2010 at 11:38
Boris, the title of this thread brought rabbit-holes, Lewis Dodgson and looking-glasses to mind.
The Al - Ice bit took a worryingly long time to register - I'd better cut down on bud, or even, perish the thought, give it up altogether.
The idea of fuelling rockets with frozen water and aluminium is exquisitely bizarre. . .
BTW, only joking 'bout giving up my raison d'étre!
12332123 - 30-8-2010 at 07:14
I wonder if a suspension of aluminium powder in a room temperature polymeric hydrogel could give similar performance and environmental credentials but
with the added advantage of long-term storage stability at room temperature. Perhaps the performance (specific impulse) could even be improved by
gelling a solution of ammonium nitrate rather than straight water, though at that level of complexity I suppose you might as well consider using
standard composite propellant.
franklyn - 30-8-2010 at 10:20
Theoretically , Aluminum and water yields 1760 Kcal per kilogram of reactants.
Good luck with that. This has never been shown to occur on it's own without
added oxidizer. The test cites nanoscale aluminum which is NOT a fine powder.
Producing it is the real point of interest not the stunt application. Realistically ,
Magnesium is the only thing which does burn in ice. A poor use of available
enthalpy as it is in part consumed by the phase change. Adding chlorine to
promote reactivity defeats the objective of " envioronmentally friendly ".
Put this in the category of never to see practical use.
Far more sensible is the utilization of hydrated salts such as Ammonium Alum
Al2(SO4)3 • (NH4)2SO4 • 24H2O , Aluminum Sulfate Al2(SO4)3 • 18H2O ,
Epsom salt Mg(SO4) • 7H2O , all of which blend well with Ammonium Nitrate.
Nitrocellulose ( Gun Cotten ) can be used as a binder , using just enough of the
energetic material to promote the desired combustion without risking detonation.
.
franklyn - 4-9-2010 at 12:06
This paper has some relevance to propellant applications
Atomic Layer Deposition of Oxidizer Coatings on Aluminum Nanoparticles to Fabricate Superthermite Explosives
http://handle.dtic.mil/100.2/ADA419512
Redirects to :
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA419512&Locati...
.