SpudFiles

Hi peeps - new member on the forum.

I have just clicked the link to the forum after rediscovering spud gunds while boredly reading wiki.

I built a few home made cannons abotu 10 years back, but none since.

Reading through the forums I haven't yet read of anyone using the fuel mixture that I used to get some very impressive results with: Hydrogen Peroxide and Potassium Permangenate solution + butane(or other "fuel" - as oposed to "oxidizer").

Potassium Permangenate reduces(? its been a while) hydrogen peroxide (H2O2) to water (h2o) in a catalytic reaction that produces gasseous oxygen (H2O2 + KMnO4 = KMnO4 + H2O +O2)(or something similar).

With my first batch of cannons I ran into the common problem of having too rich a mixture after the first firing as all the O2 had been burnt. I tried all sorts of things form fans to blowing down the pipe with a compresor to try and get some o2 in the tube and lean out the mixture.
Once I discovered the H202 reaction above, things got a lot more powerful as I could produce Oxygen in the tube more or less at will. And as the reaction is catalytic, only a small amont of KMnO4 is required as you only need to slosh more H202 into the chamber and it will mix with the KMnO4 and it will fizz away and give off more O2.

Ultimately this mix proved too much for our cannon, with the last firing destroying our beercan and gaffatape masterpiece and left my mate deaf and purple for 3 days (I was at a safe distance)...we never found the projectile - Insert "at your own risk" discalimer here.....

(sorry if I am telling my Gran how to suck eggs -like I said, i couldnt find any reference to this method)

Look at some of Rambo's cannons. They are very creative and look fun to build.

Rambo uses this method a lot. One could even say it's his "thing".
We've also been talking about using MnO2 instead of KMnO4. I've been looking into it myself, recently and I have a couple of questions:
1. I hear the reaction is quite exothermic. Just how hot of a reaction are we talking about here?
2. How concentrated is the peroxide you use and where do you buy it from?
3. Where do you get your permanganate from?

Sounds like I will need to take a look at this "rambo"s stuff then

1. I cant remember any significant heat being generated, I certainly never burnt myself with it or anything - there might be if it is done in larger quantities, but I was only using a few grams and a couple of ml at a time. Potassium P, will produce a VERY exothermic reaction when mixed with glycerine - in case that is what you were thinking of...?

2. I think the H202 was 10% solution, I believe you can get up to 30% for bleaching hair. I got it from Chemists/Pharmasists/drugstores in the UK - just say it is for anitseptic/hair bleaching.

3. Again, Chemists shops in the UK. used as an antiseptic or say you want it to grow crystals. Kids Chemistry Sets, often have Pot P in them, and it can usualy be ordered from the people who make the set to replce it when it runs out.

FiveseveN wrote: 1. I hear the reaction is quite exothermic. Just how hot of a reaction are we talking about here?

i did that once, it gets hot, really hot, if you live in cold weather, have a few bottles of h2o2, a few D sized alkine batteries, and a swiss army knife on ya, it should warm you up, great emergency hot pack, takes no less than 30 sec to be really hot, think apartment heaters, and then some...

The decomposition of H2O2 releases 85 kj/mol, and the 3% stuff easily avilable is about 1 mol H2O2/liter solution.

With the specific heat of water being 4.184J/g/K, that's a temperature rise of about 20* C.
That is, it gets warm. Now, with 30% or something, a large portion of the water will turn to steam.

That would probably explain why I never noticed significant heating when I used it then...

H2O2 100% should give about 800 C(we don't forget that it's rocket fuel).If I use more then 5-10% it releases a lot of steam and the gun missfire All these guns have a very bad noise/power ratio.

You could use that for a pneumatic if you get enough steam.