From: fernee@newton.physics.uq.oz.au (Mark Fernee)
Subject: Re: soap- vs. polystyrene- "Napalm" -- GP
Organization: Physics Dept. The University of Queensland
Date: Tue, 12 Jan 1993 03:18:40 GMT

In article <1993Jan11.220134.7559@mnemosyne.cs.du.edu>, rduta@nyx.cs.du.edu (Radu) writes:
|> I see your poing about the gunpowder goig out when submersed, but that is only
|> assuming that the "flame" gets "wet", and since it's does not disolve in water,
|> and the reaction ("burning") is independant of a oxigen source and thus probably
|> wont go out when under water.  But too be sure I'll try it.
|> 
Here is a simple theory of fire. To make and sustain a fire you need three basic
components; a fuel, an oxidiser and heat. The last component, heat, is very important
as it raises the fuel oxygen mix above a certain potential threshold where combustion
can take place. As combustion is generally exothermic, it then supplys the heat
necessary to sustain the reaction. To extinguish the fire you need only remove one
of the above components. Thus water may serve two roles; it may remove the oxygen
source and it may remove the heat. As the thermal conductivity and heat capacity 
of water are very high, it is very good at removing the heat from a fire. Thus
your oxygen contained pyrotechnic mixture must produce sufficient heat to prevent
the surrounding water from extinguishing it. This can either be done by restricting
the burning surface and using the evolved gasses to buffer the burning surface
or using a mixture that burns sufficiently hot and produces enough excess heat
that the cooling effect of the water is not sufficient to lower temperature
below the threshold of deflagration. Many Aluminium and Magnesium containing
mixtures can successfully burn under water. In fact at high enough temperatures,
aluminium and magnesium will act to reduce the water to hydrogen and oxygen, 
making water very ineffective in combating Al/Mg fires. (So don't build your
war ships out of Al/Mg alloys). So unless you restrict the burning surface of
your substance, you will find that this gel will not burn under water. If it
does, I'll eat this computer:)

|> I'm not sure that you will ever be dealing with preasures great enough to cause
|> detonation, unlesss you confine it in a metal container or thick glass.

What sort of powder is it? If it simply a nitrocellulose powder then it requires
a very powerful initiating explosive to detonate it. If on the other hand it
is a double base powder (containing a large amount of NG) then you may use
a compound blasting cap of suitable strength to initiate it. Confining it
in a rigid container will cause the container to explode, but it may not cause
detonation within the explosive mixture, but then again, it may. Either way,
such an exercise would be very dangerous due to the very nasty schrapnel
flying about the place.

|> 
|> What i like most about gunpowder disolved in acetone is that it's very sticky,
|> and sounds like a very effective substitute for napolm.
|> 

Napalm is not a very interesting pyrotechnic substance. It is just gelled petrol
and it burns accordingly. It is great that it is sticky so that if a bursting
charge is used it will stick to any people within range. Nasty nasty. I am 
surprised that no one has suggested putting white phosphorus into the gel
so that those deservingly napalmed individuals can't expect to jump in a 
lake to put the napalm out. Well they can put it out, but if they get out
of the water, it will reignite. I wonder if the thoughtfull individual 
who designed that one also has designed a bomb that only kills small children.


|> radu

Mark.

Organization: Doctoral student, Urban and Public Affairs, Carnegie Mellon, Pittsburgh, PA