Whistle powder accident

[The Crazed]

The other day my friend got a little board and thought he would try something new. He got a formula from UNITEDNUCLEAR and tried it. The formula was as fallows:

Potassium Perchlorate 70 %
Sodium Benzoate 30 %

I know whislte powder was pretty powerfull but My friend had tried it before and it just kind of made a flame and smoked a little. He had mixed a total of 50g of it and put it inside of an aluminum tube that was 1/8" thick and 1" in diameter. When the mixture first burned it just made a big flame, then it the flame got bigger and then there was an "earth shattering boom..."[/url]:confused:
Please tell me what went wrong and how to fix it.

Here is a link to some pics:
www.coolpyrostuff.tripod.com

[EP]

It was probably too loosely packed. When pressed very well into a tube it will burn like a rocket propellant and whistle, but packed loosely, will burn fast enough to explode. This is called surface area...

oh, and this is the wrong section. It belongs in low explosives.

[chicomalo]

Yes, that's what went wrong -- when not packed tight, the surface area is too large and thus the composition burns too fast to work as a rocket propellant. Next time, pack it in using steady pressure -- whistle mix is sensitive to shock, and I have found that it can be set off with a moderate blow from a hammer.

[Marvin]

I think its not a surface area problem as such. You get a standing wave formed in the tube which modulates the burning rate. High pressure increases the burning rate, which produces relativly more gas, amplifying the pressure wave. This is where the sound comes from, but becuase of the very high difference in burning rate, whistle mixes are a nats width from undergoing a def to det transition. If you compair with mercury fulminate, you remove all the air pockets by compressing enough, it becomes dead pressed, and wont undergo a def to det transition on its own, but can still be detonated by a shockwave. Surface area problems in rockets tear the casing/destroy the rocket becuase they are operating at pressures close to rupture, but whistle mix which is unchoked, detonates. I'm interested in the fact perchlorate works with benzoates, becuase Ive read only chlorates work for gallic acid mixtures. I think a 1 inch pipe was probably a bit on the large size for whistle, and a metal container is just asking for trouble.

[vulture]

I've had numerous weird experiences with chlorate whistle mix.

- A well pressed rocket engine filled with whistle mix with core and treated with oil, exploded with a sharp bang immediatly after ignition, no flame visible or whistling sound audible.
The hard and sturdy commercial rocket casing was reduced to tiny shreds and partially vaporized.
There was no nozzle.

- loose, unconfined whistle mixed burned very fast and fiercely, but no bang.

- loose, confined whistle mix (approx 45g) in a hard cardboard tube with cement endplugs exploded with a deep thunderous boom which was heard up to more than 2km away, where dogs started barking...

[Terry Collins]

When I recall it correctly, the high pitched wistle sound is produced by packing this mixture in a (one end open) tube with two different density's alternating. And the packing density (of course) affects the burning speed so the mixture burns fast-slow-fast-slow-fast- at high speed, creating the high pitched sound. And I believe that the part of the mixture that is loosely mixt will burn faster than the part being more pressed.

And this mixture is very sensitive and fast burning (it must be, because else it would not produce sound when ignited in an open tube).
So this maybe explains the accidents: it's so sensitive/fast burning that when packed too tight with too much confinement (even confinement created by it's own mass/amount) it will cause an explosion (maybe even a detonation).
Of course in a closed tube/container it will give always an explosion.

So this 'wistle mixture' will not wistle by itself when ignited of course:) you will have to pack it at certain alternating density's in a certain tube with a certain amount. So I would say: too difficult.

But then again, I could be totally wrong

[kingspaz]

next time put it in the right section.
moving to pyrotechnics....

[a_bab]

No offence Terry Collins, but:"So this 'wistle mixture' will not wistle by itself when ignited of course you will have to pack it at certain alternating density's in a certain tube with a certain amount. So I would say: too difficult. But then again, I could be totally wrong"

Well, you are wrong indeed. It's impractical and impossible to press the whistle mix in alternate densities layers because since sound it's a high one (several KHz), so this means thousands of layers with your "method". The high pitch sound is because of the SPEED of burning; it's just a whistle effect. The speed of these compositions can lead to an explosion in fact, hence the imposibility of making a nozzle rocket with this kind of mix. The slightest confinement, a crack in the pressed mix, a "too loose" pressed powder will lead to a CATO (read salute).

[Microtek]

It is by no means impossible to make rockets with whistle mix. The most succesful rockets that I have made were using a KClO4 whistle mix that was pressed firmly. They had a core and a nozzle of the same diameter and endplugs made of epoxy. They were gyrojet sized and almost as fast, though quite light. On a very few occasions, I would have a CATO when I had made the endplugs too thin and they were pushed out. Otherwise I never had any problems with them.

[NickSG]

You both are very lucky niether of you were hurt. Metal shrapnel could have easily killed, or serioulsy injured both of you. From now on, just use regular paper cases.

Whistle mix is a very powerful explosive. In my experience, it isnt that unstable, but you should always respect is and handle it carefully. Even slight confinement will make a loud and powerful explosive, such as a paper tube with walls only 1/16 inch thick. Even if you pack it, if there is empty space left in the tube, the after handling, the mix will just go right back into a powdered state. If I were you, do what I do and mix in a small amount of water, and maybe dexitrin, and then pack it into the tube. It still whistles, and there is a much lower chance of the mix going back into a loose state and exploding.

[kingspaz]

or try 2-4% vaseline as this makes it cling together. i haven't tried this with whistle mix but it works with H3.

[werewolf]

If you had access to a pressing drill like the ones for rocket making or similar you could use that to press the whistle mix very well.

[Anthony]

I wouldn't say "very" well, there's not a lot of leverage in a drill press.

[Sparky]

Whistles don't have to be pressed very hard. A vice will work for small whistles (and possibly larger ones, I don't know). My friend has tried adding vaseline to 70/30 potassium perchlorate/ potassium benzoate. It does make it easier to press and a little easier to work with but it slows the burn and makes it not whistle (maybe he added too much?). It also gives a large orange flame (from the carbon I suppose). Potassium benzoate tends to clump together a lot which makes it hard to mix since you shouldn't really stir relatively sensitive mixes like whistle. Magnesium carbonate can supposedly be used as a free flowing agent in around 3% but I suppose it might slow it down or ruin the whistle. Cab-O-Sil is much better and you can use much less (~0.1%).

[mr.evil]

be sure your sodium benzoate is a fine powder, otherwise it will burn in flashes. (i guess they will produce little shocks wich can detonate the whistle mix).

[vulture]

Let me get this straight, you are wanting to make nozzles out of whistle powder which should then guide the trust they generate themselves???

Have you ever made whistle powder? A cast piece of whistle powder will burn up in a flash and if you're lucky without a bang!

Not to antagonise you, but I strongly suspect you have not yet made or burnt any pyrotechnic composition.