[LMB] Gunpowder (WAS OT: Talking of Rocket Ship Galileo)

[Mark Allums]

James M. BRYANT G4CLF wrote:
 > A gun may contain a substance that doesn't
> MA> necessarily "burn"  High explosives merely turn from solid or liquid to
> MA> a gas really, really fast.  There can be flame, because it's a very
> MA> rapid release of energy.
> 
> Some clarification is needed here (for more detail read "Explosive Material"
> in Wikipedia). Low explosives like gunpowder, cordite, "smokeless powder"
> and other propellants burn very quickly and generate a lot of hot gas
> which pushes the bullet out of a gun. High explosives "detonate" - their
> decomposition spreads by means of a shock wave at between 1000 and 10000
> metres per second. They also generate hot gas but since the propagation is
> supersonic there is a powerful shock wave.


Thanks again for keeping me straight.

Thing is, chemical reactions go faster under higher pressures.  So, at 
first, the powder burn is a bit slow.  But the gas generated has nowhere 
to go, so the pressure builds up.  In a vicious cycle, the burning of 
the powder progresses faster and faster--it's all over in a fraction of 
a second.

There was the fire at the rocket fuel factory (the place where they make 
the oxidizer for the shuttle solid boosters).  The factory was doomed 
from the start, but it really surprised them when the stuff had a higher 
order detonation.  There's a great video of it, probably can be found on 
YouTube.

--MArk Allums