Looking for some reactants (things that go boom... ish)

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Eastwinn
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Looking for some reactants (things that go boom... ish)

Postby Eastwinn » Wed Mar 24, 2010 11:18 pm UTC

I'm trying to make a combustion-free cannon. Potato guns are been-there-done-that -- explosions aren't as exciting as they used to be unless there's fiery death close behind. I want to make a cannon that works with a reaction creating pressure that blows some projectile out of the barrel where the reaction isn't combustion. I already have a design in mind that involves the mixing of a liquid and a solid. The obvious choice here is vinegar and baking soda, but the reaction is a bit slow. It'll do, but I'm looking for more spice. Does anyone know of some common reactants (they can be more obscure than vinegar and baking soda) that can create a lot of pressure and react pretty quickly? Also diet coke and mentos is out of the question.
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Re: Looking for some reactants (things that go whimper... is

Postby TaintedDeity » Wed Mar 24, 2010 11:21 pm UTC

Out of curiosity, why no diet coke and mentos?
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Eastwinn
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Re: Looking for some reactants (things that go whimper... is

Postby Eastwinn » Thu Mar 25, 2010 12:07 am UTC

I'd eat them :P

Really I'm kind of a soda addict so I would never choose using soda in a cannon over drinking it. Seems trivial, and it kind of is, but so is wanting a cool reaction.
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Re: Looking for some reactants (things that go whimper... is

Postby TaintedDeity » Thu Mar 25, 2010 12:25 am UTC

That's a good enough reason for me :D
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BlackSails
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Re: Looking for some reactants (things that go whimper... is

Postby BlackSails » Thu Mar 25, 2010 12:29 am UTC

Its more than just pressure that you need for things to fly. You need pressure and you need it fast. Otherwise, you arent going to get very far. And "alot of pressure, quickly" is really just an explosion.

What you are looking for btw, is this: http://en.wikipedia.org/wiki/Entropic_explosion

Do not make TATP. It is extremely dangerous, and will probably bring you to the attention of the FBI.

You could try using a high temperature reaction to drive the sublimation of dry ice.

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Re: Looking for some reactants (things that go whimper... is

Postby Red Hal » Thu Mar 25, 2010 12:35 am UTC

Agreed. The other option is to have the reactants in a second chamber building up pressure which you can then release into the primary propulsion chamber. It would have to be significantly larger than the primary chamber though, to reduce the drop in pressure on equalisation.
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Eastwinn
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Re: Looking for some reactants (things that go whimper... is

Postby Eastwinn » Thu Mar 25, 2010 2:28 am UTC

^ Yeah, that's a possibility. Thanks for the info BlackSails. :D

Oh, speaking of extremely dangerous, I don't anticipate this to be a dangerous project, which is the 2nd reason for avoiding combustion -- the first being that it's boring.
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Re: Looking for some reactants (things that go whimper... is

Postby Minerva » Thu Mar 25, 2010 11:26 am UTC

What about hydrogen peroxide (the highest concentration hydrogen peroxide that you can lay your hands on) combined with some other reagent, (KMnO4 comes to mind but there are other alternatives), that will decompose the peroxide?

Concentrated hydrogen peroxide (50%) is pretty damn violent in the presence of a decomposition catalyst.
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Re: Looking for some reactants (things that go whimper... is

Postby sgt york » Thu Mar 25, 2010 2:19 pm UTC

Dry ice & water would work well, but it can be dangerous.

I've made simple baking soda launchers with my kids. Wine bottles work well...Take the cork and staple about 3" of streamer to it. Pour some baking soda into the bottle, then add vinegar, then put the cork in, streamers down. Swirl to mix (try not to get the streamer wet) and wait. It flies pretty well. Don't worry about shattering the bottle with the pressure; the cork will fail long before the bottle will.

Another fun one is the bottle pump rocket; it uses compressed air from a bike pump to launch a 2L soda bottle pretty high. There are dozens of plans all over the internet, from the simple to the highly complex. Instructables has a simple one to start off with.

Lastly, you can do away with reactants entirely and go medieval on it. Trebuchets are fun and surprisingly easy to build. catapults are fun, too, but they wear out quickly.

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Eastwinn
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Re: Looking for some reactants (things that go whimper... is

Postby Eastwinn » Thu Mar 25, 2010 5:10 pm UTC

Minerva: That seems like exactly what I'm looking for. I'll test some transition metals on 3% hydrogen peroxide today and see how it works, then plan to find some better concentrations. Thanks.

Edit: The best reaction I could get was between silver and hydrogen peroxide, but it was particularly slow. :/
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Re: Looking for some reactants (things that go whimper... is

Postby justaman » Thu Mar 25, 2010 8:26 pm UTC

Wikipedia says potassium permanganate and glycerol produces a violent combustion reaction if that's any help. I know you were trying to avoid combustion rxns, but that one is a bit different to the standard, as in two fairly innocuous chemicals mixed together.

I'd also like to be the voice of reason and say please read the MSDS's and dispose of any waste properly.
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Re: Looking for some reactants (things that go whimper... is

Postby BlackSails » Thu Mar 25, 2010 8:53 pm UTC

Eastwinn wrote:Minerva: That seems like exactly what I'm looking for. I'll test some transition metals on 3% hydrogen peroxide today and see how it works, then plan to find some better concentrations. Thanks.

OOPS: The best reaction I could get was bewteen silver and hydrogen peroxide, but it was particularly slow. :/


How fresh was your peroxide? It can break down after a while.

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Eastwinn
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Re: Looking for some reactants (things that go whimper... is

Postby Eastwinn » Fri Mar 26, 2010 12:52 am UTC

Oh shit it didn't even cross my mind that it had been sitting in that clear glass bottle for ages. XD

Okay, repeating this experiment later then.. good call.
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Re: Looking for some reactants (things that go whimper... is

Postby Seraph » Fri Mar 26, 2010 1:55 am UTC

Minerva wrote:What about hydrogen peroxide (the highest concentration hydrogen peroxide that you can lay your hands on) combined with some other reagent, (KMnO4 comes to mind but there are other alternatives), that will decompose the peroxide?

I recommend liver as a catalyst.
You're going to want something better then 3% for an interesting reaction.

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Re: Looking for some reactants (things that go whimper... is

Postby ducksan » Fri Mar 26, 2010 3:05 am UTC

I'd have to say carbon dioxide generation is the safest. It is roughly the only gas you can generate completely safely (besides explosion risk) in a home environment; the remainder of the gases are flammable (e.g. hydrogen), require corrosives to make (oxygen, high% peroxide can flip a shit and make a lot of heat, IIRC), or are themselves dangerous (chlorine, etc.)

Seconded: Don't make acetone peroxide. It is called the "Mother of Satan" for a reason. You try putting three peroxide groups that close to each other without trouble.
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Re: Looking for some reactants (things that go whimper... is

Postby Tass » Mon Mar 29, 2010 12:12 pm UTC

Seraph wrote:
Minerva wrote:What about hydrogen peroxide (the highest concentration hydrogen peroxide that you can lay your hands on) combined with some other reagent, (KMnO4 comes to mind but there are other alternatives), that will decompose the peroxide?

I recommend liver as a catalyst.
You're going to want something better then 3% for an interesting reaction.


Yes. Three percent would be dull even if it was fresh. If it is aged and down to two it doesn't help either. Get some 40% or better.

Usual catalysts include potassium iodide, potassium permanganate, mangane dioxide, liverjuice, or if you are okay with poisonous substances: lead dioxide.

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Re: Looking for some reactants (things that go boom... ish)

Postby Dave_Wise » Mon Mar 29, 2010 1:17 pm UTC

Potassium and water? Thing is, the hydrogen ignites, so technically it's still combustion. Bugger.
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Re: Looking for some reactants (things that go whimper... is

Postby Minerva » Mon Mar 29, 2010 4:24 pm UTC

Eastwinn wrote:Minerva: That seems like exactly what I'm looking for. I'll test some transition metals on 3% hydrogen peroxide today and see how it works, then plan to find some better concentrations. Thanks.

Edit: The best reaction I could get was between silver and hydrogen peroxide, but it was particularly slow. :/


Silver is often used as the basis of the catalyst pack in H2O2 monopropellant rocket engines. But the peroxide has to be quite concentrated - certainly more than 3%, and almost always 50%-90%.
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Re: Looking for some reactants (things that go boom... ish)

Postby TescoPeeledPlums » Mon Mar 29, 2010 5:45 pm UTC

Minerva wrote:
Eastwinn wrote:Minerva: That seems like exactly what I'm looking for. I'll test some transition metals on 3% hydrogen peroxide today and see how it works, then plan to find some better concentrations. Thanks.

Edit: The best reaction I could get was between silver and hydrogen peroxide, but it was particularly slow. :/


Silver is often used as the basis of the catalyst pack in H2O2 monopropellant rocket engines. But the peroxide has to be quite concentrated - certainly more than 3%, and almost always 50%-90%.


I high school I did a case study a while ago based on how potato had a naturally-occurring H2O2 catalyst in it. The potato now serves a double use, you are welcome.
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Seraph
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Re: Looking for some reactants (things that go boom... ish)

Postby Seraph » Mon Mar 29, 2010 7:20 pm UTC

The catalyst in potato is really slow.

In fact I usually use potato and liver + hydrogen peroxide as a chemistry demonstration to show how catalysts can affect reaction rate.

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Re: Looking for some reactants (things that go boom... ish)

Postby burkleypatterson » Mon Mar 29, 2010 9:39 pm UTC

I'm working on a similar project. Basically all i've done is modify my potato launcher to use dry ice and warm water, as per BlackSails suggestion. It works brilliantly! Just remember, dry ice bombs are a felony, so pass it off as a dry ice "rocket"

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Re: Looking for some reactants (things that go boom... ish)

Postby opsomath » Thu Apr 01, 2010 11:05 pm UTC

The trouble is, everything I can think of that would produce a lot of pressure fast is as dangerous as an explosion. Examples: hydrochloric acid (muriatic acid) and aluminum foil, lye solution (NaOH) and aluminum foil, the aforementioned hydrogen peroxide/catalyst mix. The first two make hydrogen gas which is very very flammable, the latter uses oxygen which MAKES things flammable. The best catalyst if you still want to use peroxide will probably be MnO2, which you can get by sawing open a std. alkaline battery and digging the black stuff out. (It's a paste of MnO2, carbon, and some alkaline salt which is probably KOH. You can use it as is. Dispose of it and handle it carefully as it is generally doped with various heavy metals.) 35% peroxide will exothermically decompose VERY violently into live steam and oxygen gas under its influence and would make a great propellant, but you would have to be VERY careful; a spark could ignite your apparatus even if it was made of something noncombustible under normal circumstances such as PVC.

One I would like to suggest is baking soda/muriatic acid or baking soda/sulfuric acid. These are far more reactive, concentrated acids than vinegar, and will generate CO2 (relatively safe) super-fast upon mixing. Sulfuric acid is available in concentrated form as a drain opener, and muriatic acid as a pool cleaner. The acids can burn you, but baking soda cannot and if you use an excess of soda then your byproduct will be Na2SO4 which is pretty much safe.

Disclaimer: This information is for purposes of chemical education only. You should not attempt any of the experiments described unless you are qualified in knowledge and legally permitted by your area authorities to do so.

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Re: Looking for some reactants (things that go boom... ish)

Postby BlackSails » Thu Apr 01, 2010 11:15 pm UTC

There is something you could do with aluminium trihalide, if I remember my orgo at all.

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Re: Looking for some reactants (things that go boom... ish)

Postby opsomath » Wed Apr 07, 2010 3:27 pm UTC

That reminds me...the sulfuric acid/sodium bicarbonate mix has been used as a propellant before, eg. in old-timey fire extinguishers.

http://en.wikipedia.org/wiki/Fire_extinguisher


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