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chemical reaction cannon?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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chemical reaction cannon?

Unread postAuthor: randomblahguy » Tue Aug 14, 2007 7:26 pm

hello, im randomblahguy and new to the forums. a couple friends and i want to put together a spudgun before they leave (they're high school seniors, im a junior) and i'd like to get some feedback on a couple of ideas that we came up with.

one of our ideas was using the decomposition of hydrogen peroxide (35%, can be bought online) to provide gas and compress it into a chamber. the decomp will be accelerated by a manganese dioxide (MnO2) catalyst. we've all taken chemistry and know the dangers associated with chemicals and most of us have had our share of acid spills, hair on fire, etc. i calculated the required amount of gas for a certain pressure and volume (2" diameter, 30" length cylinder, small, but good practice for my gas laws and stoich skills 8) )

i saw a bbmg that used the decomp of h2o2 as the source of compressed air. i'd like to know if it could work for a larger scale cannon (because none of my buddies want to buy an air compressor and a bike pump is rather laborious.).

if it may see feasible i would most likely build a small chamber using 2" PVC, and an overpressure valve of some type, and test whether the reaction will proceed under increasing pressure. assuming the chamber is 30in long, about 85 grams of 35% h2o2 will be needed to pressurize the gas to 100 psi. now, thats the ideal gas law...and conditions arent so STP in arizona. since yields and conditions arent so perfect in the real world, i doubt that the chamber will yield 100 psi. im looking more towards whether the reaction would work.

although my friends dismiss this, i'm a little worried that the oxygen could spontaneously combust and do something crazy to the chamber...is that possible? (i'll probably seek advice from my previous chem teacher who let us play with methane bubbles after school...and didnt really care whether we wore goggles or not...as unsafe as it is).

comments, questions, concerns, criticisms are all welcome.
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Unread postAuthor: paaiyan » Tue Aug 14, 2007 7:35 pm

Uh, pardon my idiocy, but is that how they make hydrogen peroxide bombs? There was a guy on a college campus around here last year who blew himself up with one of those. I just want to make sure you're not gonna do the same thing here...
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Unread postAuthor: thespeedycicada » Tue Aug 14, 2007 8:07 pm

you should get a platinum catalyst for the h202 it produces alot of steam much more efficient then the oxegen producing reaction you had in mind although it might be expensive
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Unread postAuthor: randomblahguy » Tue Aug 14, 2007 8:10 pm

no, dont worry, i plan on having some sort of valve release to make sure the pressure doesnt go too high. its a pneumatic cannon, so no (purposeful!) combustion is going to take place unless something weird happens.

what im trying to do is assess the practicality of using hydrogen peroxide to power a pneumatic cannon. not make a hydrogen peroxide bomb...
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Unread postAuthor: Mishkan » Tue Aug 14, 2007 8:14 pm

What pressures have you tested this reaction up to.

Oh yeah, you'd practically be using a steam gun. Look at some of the designs for those and you'll get an idea.
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Unread postAuthor: potatoflinger » Tue Aug 14, 2007 8:37 pm

whatever you do, you should make it a triggered burst disk cannon, and you should make it out of galvanized pipe, just in case it turns into a hybrid by accident.
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Unread postAuthor: thespeedycicada » Tue Aug 14, 2007 8:40 pm

potatoflinger wrote:whatever you do, you should make it a triggered burst disk cannon, and you should make it out of galvanized pipe, just in case it turns into a hybrid by accident.
Thats not a bad idea ill try that for my second hybrid that is if i ever make a first :roll:
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Unread postAuthor: boilingleadbath » Tue Aug 14, 2007 8:51 pm

The point about this being a steam gun is very much true... I believe that, in an abdiatic situation, we find that roughly 40% of the water ends up as steam... which clearly means that you get more pressure than your calculation will tell you.

Due to this heat, you would be best off to do this in a copper or steel (or aluminum, but you'd probably have to order that) chamber.

My main worry, however, is that you would have MnO2 contamination in the chamber after the shot; this would make it darn difficult to continue using the launcher. A copper chamber would be better in this regard than a steel one, being smoother inside.

I think the best option may be to build a burstdisk gun and just tip over an internal container of H2O2 to fire. This doesn't afford much time to aim or such, but will yeild the most power and is certainly the simplist. Plus, the internal container could be disposable, making contamination a non-issue.
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Unread postAuthor: jimmy101 » Wed Aug 15, 2007 10:33 am

This is really a STUPID idea.

Why go F'ing around with 35% H2O2?

You'll need to make sure that all components of the gun, including the safety relief valve's seat material, and the ammo, are compatible with the H2O2.

H2O2 reacts with many organics (spuds?, PVC?) to form peroxides. Peroxides are flammable, explosive and sometimes contact explosives. There is a chemistry adage: "Peroxides Kill Chemists". So, even people with more than high school chem. have trouble with H2O2.

In the normal operation of the gun you'll be spraying H2O2 and catalyst down range.

When a PVC spud gun fails it is bad but people don't usually get hurt too much. If your H2O2 powered gun fails you'll get sprayed with hot 35% H2O2. That is not good. (Grocery store H2O2 used for bleaching and disinfecting is ~3% H2O2.)

Much better to make either (1) a combustion gun (cheaper and makes more noise) or (2) a compressed air gun powered by CO2, bottled air, propane etc.


Besides, wanna bet anybody buying 35% H2O2 ends up on an FBI watchlist somewhere?
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Unread postAuthor: paaiyan » Wed Aug 15, 2007 10:58 am

As much as I agree that this is a dangerous thing to do jimmy, I have to point one thing out. h2o2 *is* a peroxide. Hydrogen peroxide to be exact. But he is correct, some of the compounds formed by the reaction of peroxide with other substances can be quite dangerous. That's why I was asking about the peroxide bomb thing, I wouldn't want anyone blowing themselves up.
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Unread postAuthor: MisterSteve124 » Wed Aug 15, 2007 11:43 am

Yeah much easier, safer and better just to use air or spray for a combustion. But if you're going to do that I would only use metal. Because you don't know how much pressure it will make or if the chemicals will ruin PVC.
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Unread postAuthor: benstern » Wed Aug 15, 2007 1:31 pm

Only the french use chemical reaction spudguns "patators" and like everything else they do, they fail epically at it.
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Unread postAuthor: thespeedycicada » Wed Aug 15, 2007 2:16 pm

there are two h202 reactions i know of 1 makes oxygen the other makes super heated steam using either silver or platinum both make an insane amount of steam.Enough of it to launch big model rockets.I dont know how much pressure the oxygen reaction will make but im guessing the steam reaction will produce more.There is also no nedd to buy and use manganese dioxide just look at the msds info on it :shock:
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Unread postAuthor: Skywalker » Wed Aug 15, 2007 2:38 pm

Nah, I don't think it's a good idea. Why waste a perfectly good explosive/rocket fuel on a silly pneumatic gun?! :lol: I think you'd be much better off buying a compressor or putting up with a bike pump. That's what the rest of us do, anyway.

but just fyi, manganese sucks. use baking/brewing yeast. And whoever said platinum is crazy. :roll:
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Unread postAuthor: thespeedycicada » Wed Aug 15, 2007 3:12 pm

Skywalker wrote:Nah, I don't think it's a good idea. Why waste a perfectly good explosive/rocket fuel on a silly pneumatic gun?! :lol: I think you'd be much better off buying a compressor or putting up with a bike pump. That's what the rest of us do, anyway.

but just fyi, manganese sucks. use baking/brewing yeast. And whoever said platinum is crazy. :roll:
hydrogen peroxide is not an explosive because it wont combust and platinuum is a catlyst for the reaction why is that considered crazy?
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