Sciencemadness Discussion Board - Real exploding foam demonstration

Real exploding foam demonstration

deltaH - 26-5-2014 at 09:42

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 :mad:

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]

Zyklon-A - 26-5-2014 at 09:54

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.

deltaH - 26-5-2014 at 10:02

The neat thing is that the decomposition of peroxide generates heat and this heat can be used to evaporate the fuel... nice synergy there

Dornier 335A - 26-5-2014 at 10:09

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.

deltaH - 26-5-2014 at 10:21

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]

unionised - 26-5-2014 at 10:36

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?

DraconicAcid - 26-5-2014 at 10:36

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?

Dornier 335A - 26-5-2014 at 10:47

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.

unionised - 26-5-2014 at 10:49

If there's enough water to stop it being bloody dangerous, then there's enough water to stop the foam burning.

Dornier 335A - 26-5-2014 at 10:52

Is there? The foam consists of bubbles filled with oxygen gas and alcohol vapour and will with no doubt burn.

unionised - 26-5-2014 at 10:54

How does the flame get from one bubble to the next?

Dornier 335A - 26-5-2014 at 10:58

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]

deltaH - 26-5-2014 at 10:58

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]

DraconicAcid - 26-5-2014 at 11:03

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.

unionised - 26-5-2014 at 11:07

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.

deltaH - 26-5-2014 at 11:07

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]

Dornier 335A - 26-5-2014 at 11:09

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.

The Volatile Chemist - 26-5-2014 at 11:11

Lighter fluid seems a cheaper solution, but I don't know of it's volatility (I know of my own volatility, of course, but...)

deltaH - 26-5-2014 at 11:12

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.

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]

unionised - 26-5-2014 at 11:37

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.

Zyklon-A - 26-5-2014 at 11:37

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]

deltaH - 26-5-2014 at 11:39

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!

Dornier 335A - 26-5-2014 at 11:41

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]

deltaH - 26-5-2014 at 11:43

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]

Zyklon-A - 26-5-2014 at 11:54

Quote:

You have quiet the excess fuel there, guess this is the fuel-air explosion variation... interesting idea!

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?

Dornier 335A - 26-5-2014 at 12:02

A bit higher up on the page was a suggestion that water/peroxide/organics mixtures with energy content of more than 0.8 kcal/g can be initiated with a detonator. This corresponds to 54% peroxide according to my calculations with EtOH as fuel.
Mixtures inside the explosive range but insensitive to impact are said to have an energy content of less than 1.2 kcal/g. This corresponds to 72% hydrogen peroxide, again in combination with ethanol. So this means that the foam experiment is safe to conduct, at least with respect to the plausible detonation of the liquid phase.

EDIT:
Zyklonb, cellolose forms a gel with high concentration H₂O₂ which can be detonated by a blasting cap but not by heat or flame.

[Edited on 26-5-2014 by Dornier 335A]

deltaH - 26-5-2014 at 12:06

Thanks Dornier for your most excellent input as always shedding light on the sensitivity of the liquid phase, no doubt of great importance!

Thanks unionised for being safety conscious, I respect that very much!

If anyone makes a youtube clip of this, please do post a link here!

[Edited on 26-5-2014 by deltaH]

bismuthate - 26-5-2014 at 12:13

Well I believe the subject of calcium carbide and hydrogen peroxide has been brought up before here. Perhaps KI and CaC2 with H2O2 in some proportions could yield explosive foam (if done with detergent).

deltaH - 26-5-2014 at 12:19

Interesting idea bismuthate, thanks. Oxy-acetylene foam :cool:

Might be difficult to time the production correctly, what I mean to say, the peroxide decomposition is fast, the acetylene production is not as fast? Perhaps the two won't be mixed properly/uniformly.

If you exclude the catalyst, there is probaby enough impurities in crude industrial CaC2 to catalyse the peroxide decomposition.

I have no idea if one wouldn't also form calcium peroxide, but presumably, this would decompose?

[Edited on 26-5-2014 by deltaH]

Zyklon-A - 26-5-2014 at 12:20

Yes, that's very useful info Dornier.
I went ahead and tried acetone.
About 5 mL of 20% hydrogen peroxide, 5 mL of acetone, several grams of manganese dioxide (and soap) were paced in a beaker. It was ignited with a fuse. Or at least that was the idea. Due to acetone's volatility, it was initiated by my lighter before the fuse even caught!

The "BANG!" was massive It certainly didn't detonate, [see below, the gasses may have detonated] but my ears were ringing for a couple minutes.

[Edited on 27-5-2014 by Zyklonb]

deltaH - 26-5-2014 at 12:27

It sounds like the gas phase did detonate, no? We might have a good alternative for the exploding hydrogen balloon experiment...

[Edited on 26-5-2014 by deltaH]

Zyklon-A - 26-5-2014 at 12:31

Yeah, I guess.
I didn't think much of it was gaseous. I lit it within 10 seconds after adding it to the foam.
It was pretty cool, much louder than I expected.

[Edited on 26-5-2014 by Zyklonb]

deltaH - 26-5-2014 at 12:36

I wonder what the foam detonation looks like in slo-mo? Could be pretty neat!

I also wonder if the foam could possibly be facilitating a deflageration to detonation transition in the gas phase? Then again, I might just be tripping

[Edited on 26-5-2014 by deltaH]

Zyklon-A - 26-5-2014 at 12:42

For real! I wish I had a camera with a high speed option.
Dornier 335A could you do a video on it?

Dornier 335A - 26-5-2014 at 12:55

240 frames per second is not enough in this case, sadly. And I don't have any hydrogen peroxide.
Gas detonations usually propagate at around 2000 m/s, so not even Periodic Videos' high speed footage of an oxygen hydrogen balloon shows any delay at all. http://youtu.be/qOTgeeTB_kA?t=3m54s

deltaH - 26-5-2014 at 13:02

Also, sound travels faster through liquids than gas, so perhaps the foam detonation is faster than a purely gaseous one? Then again, the foam might have a retarding effect, we simply don't know as of yet. My money is on an enhancement

[Edited on 26-5-2014 by deltaH]

Zyklon-A - 26-5-2014 at 13:27

A high speed video, even if it doesn't capture the the wave will certainly look better than seeing a pile if foam, touching a flame to it, hearing a bang, and the pile of foam's gone.
I'll email periodic table of videos and ask if they can make a video on it. They've asked for video suggestions several times.
[edit] I'm not sure whether foam would help or not, it'd be rather hard to find out.

[Edited on 26-5-2014 by Zyklonb]

deltaH - 26-5-2014 at 14:09

That would be great Zyklonb, thanks.

[Edited on 27-5-2014 by deltaH]

Zyklon-A - 26-5-2014 at 15:38

OK, I sent the email. Can't say I expect them to make a video, but hopefully they do.

The Volatile Chemist - 26-5-2014 at 17:51

That'd be nice. What's their email?
As a side note, you might show them this post, to proove there is interest in the subject.

woelen - 26-5-2014 at 22:56

I read this thread with pleasure, but I also have concerns about safety. The toothpaste demo usually is done at quite a large scale with a lot of foam. If foam with pure oxygen/fuel mix is ignited at such large quantities, then you might get really nasty accidents (e.g. blowing out windows, or blowing out your ear drums). Glass may be shattered and the fire ball may become so large that it engulves the person who ignited the massive amount of foam.

I would say, keep on thinking and experimenting, but use your common sense and stay safe. I think Zyklonb's experience with a small amount of acetone demonstrates what can happen with large amounts.

deltaH - 26-5-2014 at 23:27

Thank you woelen, I have added a warning to the opening post emphasising these points for users who may read it for the first time. Please feel free to modify it if you feel I have left out something important.

As always, safety first people please!

[Edited on 27-5-2014 by deltaH]

The Volatile Chemist - 27-5-2014 at 02:54

Being at a lack of resources, would MnO₂ and H₂O₂ work for foaming? I've never really done it with more than a few mL of peroxide, would it 'foam' enough?

deltaH - 27-5-2014 at 02:59

Zyklonb did it using MnO₂, so should be fine, but one needs a tiny amount of liquid soap to get it to foam.

[Edited on 27-5-2014 by deltaH]

The Volatile Chemist - 27-5-2014 at 03:17

Quote: Originally posted by deltaH

Zyklonb did it using MnO₂, so should be fine, but one needs a tiny amount of liquid soap to get it to foam.

[Edited on 27-5-2014 by deltaH]

Great! I'll be trying a small amount in the near future, gotta get some peroxide.

Zyklon-A - 27-5-2014 at 06:01

Quote: Originally posted by The Volatile Chemist

That'd be nice. What's their email?
As a side note, you might show them this post, to proove there is interest in the subject.

Yes, I included a link to this thread. I'll post the email in a few hours, I'm on my phone now and it's a pain in the @$$ to find stuff, ect. Or I might just forward it to whoever asks.
[EDIT] Here it is:

Quote:

Hello, periodic videos.

I'm not sure if you guys are still doing high speed videos or not.

Me and several members on the chemistry forum sciencemadness, where discussing variations of the classic "elephant toothpaste" demonstration. The idea is, rather than just using hydrogen peroxide, liquid soap (to produce foam) and a catalyst (generally potassium iodide) we added a volatile liquid fuel as well. The pillar of foam is then ignited. The reaction is quite impressive.

Depending on several factors, it might burn with "whoosh" or a loud "bang!"

I was able to get the fastest reaction using acetone, but methanol, ethanol and isopropanol all gave great results too.

With the acetone, I believe the gas phase did indeed detonate.

I used 20% hydrogen peroxide, but 30-40% would surely be even better.

I think it would make a great video, to show the reaction in high speed. I tried several other ideas too, like bubbling hydrogen through the foam, acetylene would probably be even better.

Here is the thread were it is being discussed:http://www.sciencemadness.org/talk/viewthread.php?tid=30447
...
Anyway, I hope to here back from you guys.
Regards, Amos Backstrom.

[Edited on 27-5-2014 by Zyklonb]

deltaH - 27-5-2014 at 08:28

Looks good Zyklonb, thank you.

I'm started to think of some interesting things one might do with such exploding foams that could facilitate learning / be good for demo's, taking advantage of the fact that working with these foams allows one to hold a combustable gas mix in the open temporarily.

Something that has come to mind is preparing a small amount of foam and loading tens of foam millilitres into a small rolled paper cone that has its pointed end cut off so to make a second smaller hole there, then lighting it through the narrow end with a match tied to a wooden rod, the idea being to make a little mini vortex cannon using the foam.

When directed at light stacked objects some short distance away from the larger opening (say 0.5 - 1m away), perhaps this could collapse them, for example maybe a stack of light-weight inverted polystyrene cups.

I think so long as one keeps the size small and works with paper and such and wears eye and ear protection, this could be reasonably safe.

I would use alcohol not acetone to tone it down a bit.

I'm reasonably sure the paper cone should be afixed to something with some duct tape.

Does this sound too dangerous / stupid thing to do?

[Edited on 27-5-2014 by deltaH]

Zyklon-A - 27-5-2014 at 09:21

No, that sounds fun, I'd like to try that sometime.
I'm not entirely sure what kind of setup you're talking about though, could you upload a picture from "Paint'' or something?

deltaH - 27-5-2014 at 09:35

Something like this...

Maybe someday this...

https://www.youtube.com/watch?v=2VpLRpcL9CA

Sorry, too lazy to draw the foam, but basically you'd scoop some foam into the open cone vertically, then tape it down with some duct tape so that the cone lies on its side and will naturally point upwards at a slight angle.

[Edited on 27-5-2014 by deltaH]

Zyklon-A - 27-5-2014 at 11:07

Ah, I see. It took a while, but it makes sense now.
I wish I had a better fuel, almost out of isopropanol, don't have any more methanol, and my ethanol is too dilute.

Maybe if I diluted acetone it would be safer?
Anyway, it's something I want to try when I get home, I've never made a vortex cannon before, but it sure would be fun.
[EDIT] The "cone" would have to be quite strong right? Based on how loud the explosion was. And that was un-confined

[Edited on 27-5-2014 by Zyklonb]

deltaH - 27-5-2014 at 11:51

I'd avoid acetone at all cost due to it detonating if it were me (that would probably shred the cone), I'd rather go for the alcoholic version so as to get a fast deflageration, but not a detonation (hopefully).

Again, safety first please! Goggles/face shield and ear muffs a must (the latter in case it detonates again).

Tightly rolled up paper is pretty strong and relatively safe should it blow (pieces don't travel far). Just be weary that the cone could shoot back loose of your taping, so don't stand right behind it.

[Edited on 27-5-2014 by deltaH]

PHILOU Zrealone - 27-5-2014 at 12:33

When working in soap factory, alcohol (ethanol) or volatile solvents where used as foam killers!
So the use of aceton, ethanol, methanol, isopropanol tends to destabilise the foam...it will last much less time than without the solvents.

There can be options if you find a tickener stuff that gelifies with such solvents...we used special stuffs to make soap consistent in the high duty liquid departement of Procter&Gamble but I don't remember the name.

I suspect polystyrene-aceton might be an option or methylcellulose glue for wall-papers.

The PS-aceton might allow to make a foam with H2O2/acetylen that becomes solid under drying since PS is fully soluble in aceton but leaves a fine pellicule of PS if allowed to stay in the air. This becomes brittle when completely dry. For demo in closed environment don't play with it in big amount and stay away from heat sources or glass!
If energetic properties are searched...for better OB a little excess of oxygen over acetylen is wished as polystyrene introduce some extra carbon rich fuel.

One might even imagine a PS foam with only pure oxygen in it.

as a safer very flammable plastic foam.

[Edited on 27-5-2014 by PHILOU Zrealone]

deltaH - 27-5-2014 at 23:10

Great and thanks for the suggestions PHILOU!

There are also various supermarket OTC gums available that should stabilise foams by adding a very small amount (~0.5 - 1 wt. %), things like xanthan or guar gum for example, I have both in my kitchen.

The thickened liquid then probably wouldn't even require soap at all, it would form a dense mass of foam (very small bubbles). However, my gut feeling tells me that such dense masses will tend to detonate instead of deflagerate when ignited because 'containment' is stronger and also the pressure in the bubbles is slightly higher.

I remember when I was studying as an undergrad being taught that for very small bubbles in liquids, the internal pressure inside the bubble increases as the bubble diameters decrease (due to surface tension) otherwise known as Laplace pressure. This becomes dramatic when bubbles become very small (e.g. microbubbles). This would make the gas mix far more detonatable I would imagine.

Where γ = surface tension and dP = the difference in pressure between the inside and outside of the bubble.

This could be a big advantage for employing foams, but again, the bubbles need to be micron sized if you aiming for detonation I would guess.

A side effect of this principle is that as you form smaller bubbles, the need for a volatile fuel becomes more important because there may otherwise not be as much fuel evaporating into the gas phase.

While perhaps purely academic/commercial, dimethyl ether could be a great fuel (maybe even close to 'ideal') for such purposes because it is very volatile, but dissolves in water to the tune of 71g/l. Furthermore, it one of those special ethers that don't form peroxides AFAIK. Unfortunately, it's not OTC in any products that I know of. Perhaps this might stimulate someone to suggest something a little more practical, but along the same lines?

Ordinary diethyl ether is also slightly water soluble, though this can form explosive peroxides, so again the same danger as with acetone...

EDIT: PHILOU, won't the styrene solution in acetone precipitate as soon as one add it to the large volumes of hydrogen peroxide?

[Edited on 28-5-2014 by deltaH]

PHILOU Zrealone - 28-5-2014 at 11:46

The tinier the bubbles implies also more surface of defined thickness --> in theory at a certain stage the bubble diameter will be equal to the bubble wall thickness (or even tinier) then the OB will be less good.

PS will precipitate if done in one shot but one can make drop by drop fall of aceton/H2O2 into PS/aceton/catalyst...under mixing. That way we made, at P&G, 80% silicon solution into alcohol suspendable into water with a viscosity of 10 cps...that silicon was >200.000 cps.

deltaH - 28-5-2014 at 11:52

Quote: Originally posted by PHILOU Zrealone

The tinier the bubbles implies also more surface of defined thickness --> in theory at a certain stage the bubble diameter will be equal to the bubble wall thickness (or even tinier) then the OB will be less good.

I didn't quite understand how this affects OB, can you ellaborate please?

[Edited on 28-5-2014 by deltaH]

PHILOU Zrealone - 29-5-2014 at 03:11

Quote: Originally posted by deltaH

Quote: Originally posted by PHILOU Zrealone

I didn't quite understand how this affects OB, can you ellaborate please?

[Edited on 28-5-2014 by deltaH]

-PS has a density of 1040g/L what is roughly 10 moles/L monomeric unit.
-Pure O2 being a gas, MM= 32g/mole with a molar volume of 22,41 L/mol at SPT --> 1L of O2 at standard T° and pressure weight about 1,428 g.

C6H5-CH=CH2 + 10 O2 --> 8 CO2 + 4 H2O
To get perfect OB (0%) one would need 10 moles of pure O2 per mole of PS monomer.
So 224,1 L O2 (320g) for 0,1L PS (104g)...

The weight ratio between O2/PS must be 320/104 = 3,077
The volumic ratio between O2/PS must be 224,1/0,1 = 2241
So if the volume of the bubble becomes equivalent to the volume of PS...it becomes evident that you will be very deficient at oxydiser/comburant (O2) what means bad OB.

So tiny bubbles yes to favourise the intimate mix but not too tiny.

This effect is comparable to the effect of oxyd layers of Aluminium powders....
The oxyd layer remains relatively constant but if the size of the Aluminium spheres/granules becomes tinier at a certain point the oxyd layer can't be neglected because it induces a dead weight...if the sphere becomes 2 times the oxyd layer thickness; then there is no more aluminium to burn!

deltaH - 29-5-2014 at 05:08

Ah ok, I'm with you now, you were referring to the case where the bubble walls are the fuel, my brain was still stuck in the mode of thinking of vapour fuels only... I have my blond moments

On a side note, I was walking today on our beach promenade and noticed heavy persistant foams washing over again because of turbulent seas. We're having stormy weather. Anyhow, the spots where this foam forms thickest is also the spots where we have a lot of brown algae washing up and these gets churned and smashed on rocks by heavy wave action.

Why am I mentioning this?

Because brown algae is the source from which commericial alginic acid, typically as sodium alginate, is extracted, so... that reminded me that alginate could also be an OTC foam stabiliser for the alcohol foam mixtures.

Where does one find this stuff? It's typically used to prepare liquid antiacid syrups, usually in the sodium alginate form with some sodium bicarbonate added. In South Africa, this is sold as the popular brand Gaviscon. I also have this in my kitchen

It's worth a try perhaps.

... poor cars (not my image and an old one at that gotten off the net!) A shot of the three anchor bay area in Cape Town after a storm showing the foams I'm talking about

[Edited on 29-5-2014 by deltaH]

DraconicAcid - 9-6-2014 at 12:55

Quote: Originally posted by Zyklonb

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.

I tried this, too. 5 mL each of isopropanol and 30% hydrogen peroxide, and a bit of dish soap. Adding KI caused a much slower foaming than I had expected; lighting it caused a large flame, which went snap! crackle! pop! like a breakfast cereal, and spat brown flaming foam all over the place.

kecskesajt - 11-12-2014 at 10:43

Put some CaC2 and MnO2 into H2O2 with dish soap.Powaaaaaaful explosion.Use in really small amounts like a few bubbles.To make a deflagration,bubble some propane or methane into soapy water.

deltaH - 11-12-2014 at 11:47

Quote: Originally posted by kecskesajt

Put some CaC2 and MnO2 into H2O2 with dish soap.Powaaaaaaful explosion.Use in really small amounts like a few bubbles.To make a deflagration,bubble some propane or methane into soapy water.

Hmm... interesting variation, thanks for sharing!

[Edited on 11-12-2014 by deltaH]

chemrox - 11-12-2014 at 21:41

Federoff ?complete references and an explanation of "elephant foam" would improve this thread for those of us not "in the know."

Bert - 11-12-2014 at 22:08

The acetylene/O2 bubble foam version could at least be a bit safer from premature electrostatic discharge ignitions than the balloons and plastic bags filled from oxy acetylene torches that so many have injured themselves with-

Including myself, many years ago. Ouch.

deltaH - 11-12-2014 at 22:38

The peculiar/wonderful thing about this experiment from a demo point of view is that your start with a fuel (CaC2) which goes on to produce a far more energetic fuel fuel (C2H2) by "gaining of water" (strictly speaking by reacting with water) and an oxidant (H2O2) that goes on to produce a far better oxidant (O2) with loss of water. So while CaC2 + H2O2 would not explode directly easily, suddenly you get something that is extremely energetic in the gas phase even when very wet! Really cool chemistry I think.

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Chemrox, there is such a HUGE number of demo's and explanations about the related "elephant foam" experiment on YouTube and online, that I feel it is redundant...

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Bert, I too was thinking about your misfortunes with acetylene!
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An interesting question occurred to me, with the speed of sound being much greater through water than gases, does this mean that the acetylene/O2 foam would detonate at a much higher velocity because of propagation of a detonation (in part) through the liquid phase that initiates the remainder?

This could be an awsome experiment for professionals with high speed camera's.

[Edited on 12-12-2014 by deltaH]

Microtek - 12-12-2014 at 01:05

I would think that the liquid layer (ie. the interface between bubbles) is too thin and that the density variation will cause too much diffraction of the propagating detonation to actually speed up the process. In fact, I think it would slow it down.
Only one way to find out for sure though...

careysub - 12-12-2014 at 07:34

Quote: Originally posted by Microtek

I would think that the liquid layer (ie. the interface between bubbles) is too thin and that the density variation will cause too much diffraction of the propagating detonation to actually speed up the process. In fact, I think it would slow it down.
Only one way to find out for sure though...

You are right - they would slow it down, to the extent that they do anything at all (which I question).

In general, detonation/shock waves slow down when they encounter denser materials, they do not speed up. They aren't sound waves - though sound waves are the limiting case of a weak shock wave. Once a shock wave degrades into a sound wave it is no longer a shock wave.

But the thickness of a bubble wall is on the same order as the thickness of a detonation front. I doubt any discernible effect would be encountered unless the foam bubble wall was unusually thick (dense polymer foams would be an example).

Plane detonation/shock fronts are stable, tending to suppress irregularities that develop.

careysub - 12-12-2014 at 07:53

A stoichiometric foam consisting of oxygen as the oxidizer, and a polymer fuel would have to be pretty light, like an aerogel.

If the average polymer composition was CH2 then the oxygen gas bubbles would outweigh the polymer 3.4:1. If it was highly unsaturated, and on average close to being just C, then it would be 2.7:1.

Metacelsus - 12-12-2014 at 08:55

What if the polymer were energetic itself? (Polyvinyl nitrate, for example.) The oxygen would then just provide OB, but the polymer would be doing most of the job.

deltaH - 12-12-2014 at 10:04

It could be beneficial for the energetic polymer to be soluble in the peroxide solution so that it could harden somewhat when the peroxide decomposes.

In fact, it would probably be even better if the starting mixture has the consistency of a putty that one mixes with a very weak peroxide decomposing catalyst by kneading and then wait for the "dough" to puff up like bread.

Perhaps it could even be two putties that one mixes together by kneading, like what's done with epoxy putty.

Any ideas for a soluble energetic polymer with thickening properties anyone?

[Edited on 12-12-2014 by deltaH]

careysub - 12-12-2014 at 13:02

If you had an explosive polymer (or polymer mixture) and foamed it, then you would obviously have explosive foam, and the denser the "foam" the more energetic per unit volume. In the high density limit, not very "foamy", and not what people have in mind here I think.

The other route is to use an explosive gas mixture, and the foam forming material simply holds the gas in place.

Or you could do both.

When I was a kid a few times I set off acetylene/oxygen explosions, with a balloon, or in a buried container. On one occasion I buried a heavy glass bottle so that that the rim was flush with the ground.

I added CaC2, peroxide, and whatever I was using to catalyze oxygen release and set it off with a long kitchen match.

The first few times it made a nice loud bang. Then there was a very different explosion, I didn't really hear it exactly, it felt more like being slapped in the face. And the bottle hole was gone. I excavated and discovered the bottle had shattered into little pieces. I presume the last explosion was a true detonation.

Bert - 12-12-2014 at 13:08

Aim for 50% acetylene or just a bit under. Initiate with a small high explosive booster, not a flame. Much more reliable...

Potential Destructiveness of Gas Detonations -US Bureau of ia Mines

[Edited on 12-12-2014 by Bert]