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deltaH
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Real exploding foam demonstration
I was thinking today about the concept of making a real exploding foam demonstration by combining the elephant toothpaste demonstration with a
volatile fuel so that the resulting foam generated could be ignited... spices up the traditional demo for a double wow effect 
Unfortunately searching for exploding foams keeps turning up the traditional elephant toothpaste experiment, not exactly what I had in mind 
What would be a good OTC fuel to use for this, methylated spirits?
Anyone tried something like this and care to share?
Thanks!
WARNING:
Exploding foams have now been shown by contributors in this thread to readily detonate with a very load report that can damage hearing and might even
break windows on a large scale. This should not be conducted on large amounts of foam, a few millilitres at a time is plenty and avoid any easily
shrapnel producing materials (e.g. glass). Be aware that volatile fuel vapours from the foam can ignite unintentionally from some distance away
and that the demonstration can produce a fireball. Treat this demonstration with the utmost of respect!
[Edited on 27-5-2014 by deltaH]
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Zyklon-A
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I've tried something like this, basically I just did the regular elephant's toothpaste, and then bubbled hydrogen in the foam. It's hard to
know how much to add, but it has always given a nice boom!
I hadn't even thought about using a liquid fuel, but it seems like a cool idea.
Seems like any flammable liquid that doesn't react with the oxygen generation should work.
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deltaH
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The neat thing is that the decomposition of peroxide generates heat and this heat can be used to evaporate the fuel... nice synergy there 
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Dornier 335A
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You could use alcohol. I've seen and done a variation on this experiment, where ethanol and 30% H2O2 are mixed in a small
beaker. The mixture is ignited and then KI solution is poured into it causing a massive fireball. It works well with acetone too but acetone and
hydrogen peroxide are not something one wants to mix for a certain reason.
I'd say you could go with ethanol and 30% hydrogen peroxide in a 10:90 ratio by volume. Don't forget to tell us how it went if you decide to try it.
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deltaH
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Thanks Zyklon and Dornier. Yes I'd avoid the acetone too, but spirits should be relatively safe I would think, plus
all the water in the foam would flash boil to steam so it would be relatively quenched compared to the un-foamed version.
A quick back of the envelope calculation reveals that a 10:90 mix is close to optimal for an ethanol / 50% hydrogen peroxide mix...
assuming you evaporate all the alcohol.
EDIT: The main danger with using acetone is not disposing of the acetone peroxide solution properly, for example, leaving a small residue in a closed
bottle and forgetting about it. Even without catalyst, at high peroxide concentration and sufficient time, this can form a dangerously sensitive
substance. One simply needs to be aware of potential hazards than can arise.
[Edited on 27-5-2014 by deltaH]
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unionised
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A bit of thought suggests that if "10:90 mix is close to optimal for a ethanol / 50% hydrogen peroxide mix " then that mixture should be able to
detonate.
Does it still seem like a good idea?
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DraconicAcid
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Dornier- you say you've done this. On what sort of scale? And can you actually ignite a mixture of 10% ethanol and 90% aqueous hydrogen peroxide?
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Dornier 335A
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Unionised, 10:90 of that mix is indeed close to oxygen balanced but I don't know if it would be able to detonate with as much as 45%
water. 80:20 of 100% peroxide and ethanol would certainly be high explosive.
DraconicAcid, I did it with 1 ml of each liquid on a watch glass. I've seen it done with 10 ml or so, in a tiny beaker.
90:10 would be close to optimal for the experiment deltaH describes. The liquid mixture can't burn at room temperature however.
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unionised
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If there's enough water to stop it being bloody dangerous, then there's enough water to stop the foam burning.
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Dornier 335A
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Is there? The foam consists of bubbles filled with oxygen gas and alcohol vapour and will with no doubt burn.
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unionised
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How does the flame get from one bubble to the next?
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Dornier 335A
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Heating the bubble so it bursts. The whole mass of water doesn't have to turn into superheated steam like it would have to do in a detonation. A quick
deflagration will also physically break the bubbles to release the gas.
[Edited on 26-5-2014 by Dornier 335A]
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deltaH
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I think the 'does this burn' debate is somewhat moot, if I recall correctly, mythbusters demonstrated methane foams burning once... or something like
that.
EDIT: Here it is:
https://www.youtube.com/watch?v=gXcug7RqPgs
[Edited on 26-5-2014 by deltaH]
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DraconicAcid
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Foams of methane will easily burn (I often do the "flaming hands of death" demo, where I scoop up natural gas as a foam and hold it over a candle
flame), but what's written above suggests lighting the liquid before making it a foam.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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unionised
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It's perfectly possible to get foams to burn. That was never in dispute so it's hardly moot.
But what I'm saying is that if the oxidiser and fuel are premixed before it's turned into a foam you have a material with about a thousand times the
density and that's likely to do a lot more damage if it ignites.
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deltaH
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I suppose if one carefully poured the alcohol so that it forms a layer temporarily over the peroxide -- you could ignite it?
But to be honest, I am more interested in the foams because they temporarily 'hold' the gas mix for you, whereas the non-foam version burns it as it
forms.
Anyhow, as for the 'will it detonate' debate, I do not know, thought without proof, one has to assume that it might and treat it as such.
[Edited on 26-5-2014 by deltaH]
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Dornier 335A
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The foam is supposed to be lit after it has formed, that's at least how I interpret deltaH's description. The other similar
experiment, the one I have tried, is done with a 50/50 mix of alcohol and hydrogen peroxide which is ignited before the catalyst is added.
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The Volatile Chemist
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Lighter fluid seems a cheaper solution, but I don't know of it's volatility (I know of my own volatility, of course, but...)
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deltaH
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Quote: Originally posted by Dornier 335A  | | The foam is supposed to be lit after it has formed, that's at least how I interpret deltaH's description. The other similar
experiment, the one I have tried, is done with a 50/50 mix of alcohol and hydrogen peroxide which is ignited before the catalyst is added.
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Yes this was my intention, the foam acting as a temporary 'vessel' for the gas mix of sorts... so that one could ignite it all at once at a later
stage instead of flaming it as it forms. I suppose a balloon without the foam would also work, but the foam just seems like more fun and ??less likely
to detonate??
Granted, this would have to be done with due respect for safety.
As for the lighter fluid, I don't think you would get good evaporation without forming a homogeneous mix, hence why I was thinking of a soluble fuel.
[Edited on 26-5-2014 by deltaH]
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unionised
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What I'm concerned about is that a mixture of fuel and peroxide might ignite/ detonate if dropped on the floor or "looked at in a funny way" before
you foam it or ignite it.
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Zyklon-A
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I did a little test with 10 mLs of 20% hydrogen peroxide and 20 mLs of 95% isopropanol. (And liquid soap for foam)
I don't have any iodides at the moment so I used MnO2.
The first time it made a nice "pop".
But after that it made some pretty good booms!
It splattered flaming liquid all over the lab too.
It's pretty fun to say the least.
Why not acetone? Is there a risk of making AP? I thought it needed a HCl catalyst.
[EDIT]typo
[Edited on 27-5-2014 by Zyklonb]
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deltaH
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| Quote: Originally posted by Zyklonb | Wow, this thread seems to be getting pretty big fast.
Anyway, I did a little test with 10 mLs of 20% hydrogen peroxide and 20 mLs of 95% isopropanol. (And liquid soap for foam)
I don't have any iodides at the moment so I used MnO2.
The first time it made a nice "pop".
But after that it made some pretty good booms!
It splattered flaming liquid all over the lab too.
It's pretty fun to say the least.
Why not acetone? I'd there a risk of making AP? I thought it needed a HCl catalyst. |
You have quiet the excess fuel there, guess this is the fuel-air explosion variation... interesting idea!
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Dornier 335A
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I checked Fedoroff under Hydrogen Peroxide Explosives. 60% or stronger solutions of hydrogen peroxide combined with organic fuels are detonatable
mixtures. Mixtures with paraformaldehyde, cellulose, glycerol, MeOH and EtOH are mentioned. I wouldn't be too worried about a mixture with 50%
peroxide. And there's no risk at all with 30%.
[Edited on 26-5-2014 by Dornier 335A]
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deltaH
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| Quote: Originally posted by unionised | | What I'm concerned about is that a mixture of fuel and peroxide might ignite/ detonate if dropped on the floor or "looked at in a funny way" before
you foam it or ignite it. |
I understood what you meant -- the sensitivity of the liquid phase is unknown to us (EDIT: not anymore thanks to Dornier), but if
this were sensitive, I think we would have known about it as people would have been making it with more neferious intentions...
[Edited on 26-5-2014 by deltaH]
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Zyklon-A
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| Quote: |
You have quiet the excess fuel there, guess this is the fuel-air explosion variation... interesting idea!
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Yes, intentionally. It also allowed me to run it more than once, by replacing the peroxide. I just blow the flame out.
How would one detonate a mixture of cellulose and H2O2? Perhaps make a paste of cellulose powder and conc. peroxide?
Do any of you guys have >60% H2O2?
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