PYRO: Pyrotechnics

James Rogers (
Tue, 24 Dec 1996 17:39:49 -0800

>> Although a magnesium/manganese dioxide/potassium chlorate mixture doesn't
>> have any explosive properties, it is *very* exothermic. Thermite+.
>> Definitely a lot of fun.
>Actually, it was seriously explosive. An enclosed spoonful or so (I don't
>know the exact amount since a friend with a death wish did the actual
>mixing) was enough to blow a coconut and a silly hat into oblivion, and
>leave a one meter wide crater in packed soil.

Hmmm... Something isn't consistent here. If there was an explosion, it
would have to be mostly due to the extremely exothermic nature of the
mixture. The only component capable of explosion is potassium chlorate,
which tends to be a pretty poor explosive, *especially* without the presence
of an organic fuel. It was probably a mostly exothermic explosion (as
opposed to deflagration or detonation).

Which leads me to question the one meter wide crater. Unless the charge was
buried, this number is *way* too large. Using military explosives, this
would require a block of TNT, which has an order of magnitude more power
than potassium chlorate under the best of circumstances. The crater may
have seemed large at the time, though. Either that or there was *a lot*
more than a couple spoonfuls of the chlorate mixture. What kind of depth
did you get?

>> I assume the potassium chlorate was to make ignition easier? I certainly
>> commend you on your choice of manganese dioxide. Not the most commonly used
>> metal oxide, but definitely the best for this application. Net thermal
>> output is 25-35% higher than iron oxides.
>Well, the idea was to use the catalytic reaction between the manganese
>dioxide and the chlorate that releases oxygen; I guessed it would make
>the otherwise strong magnesium-chlorate reaction stronger. In retrospect,
>I doubt that was the real reaction, but the combination was definitely
>powerful. And it made me nervous, I have never liked chlorates...

Chlorates are very unstable. Can't be mixed with ammonium salts or anything
with sulfur unless you have a death wish.

>> 1) Replace magnesium with aluminum. A little harder to ignite, but it
>> significantly boosts the thermal output.
>One fun experiment we did (it was a young scientist association in
>southern Stockholm) was to make thermite using copper oxides. It managed
>to vaporize coke cans quite nicely.

And I think it ignites easier too.

>Ah, the reckless days of highschool. I still remember when one experiment
>blew up, set fire to a small field of grass and rained metal pieces over a
>large area. The police arrived, only to find a group of youngsters in
>white lab coats carrying electric gear and gas masks (another of my
>less-than-safe inventions: yellow cadmium fog) arguing about how much zinc
>there ought to have been in the mixture. They just looked pained when we
>started to explain :-)


I was fortunate in that I lived in a rural area during most of my
experimentation. No one cared what we did out there.

One of my horror stories was I accidentally discovered (very
unintentionally!) how to spontaneously and rapidly decompose nitric acid.
The red, noxious cloud of nitrogen trioxide would have covered a city block,
all from 250mL of nitric acid. Thankfully, my parents weren't home at the
time. Interesting reaction. Nothing happens for 10 or 15 minutes and then
suddenly... (When synthesizing PETN, follow the temperature recommendations

-James Rogers