Pat Flannery writes:
David Spain wrote:
'Fast' explosives aka superexplosives, allow the reaction to progress
at the theoretical maximum speed, the speed of sound through the
material.
The only thing I can think of in this regard is Primacord, a super fast
burning detonating cord used for high explosives that burns at a rate of
7,000-8,000 m/s: http://en.wikipedia.org/wiki/Detonating_cord
...which seems a lot higher than the speed of sound in the material it's made
from, which is a variable that depends on density.
That would mean it's burning at around 16,000 mph, which seems high for sound,
even going through solid lead.
Pat
I gotta learn to stop posting based on recollection.
I WAS WRONG. Well sort of...
I quick review of what's available on the Internet delineates between
between the shock wave that initiates the chemical reaction vs the
chemical reaction itself.
The 'detonation wave' can proceed through the material at supersonic
speed (relative to the material). It physically displaces (compresses)
which heats the reactant which then reacts sonically after the
'shock discontinuity' wavefront passes. [1]
The speed of the detonation wave is aided by an increase in the
density of the material. According to US Patent 4913053 Primacord uses a
process of heating and high pressure to boost the detonation velocity
of the fusing by 15-20% [5].
Technically its not 'burning' or reacting at that speed, and again
taking a risk IIRC, that is why there's no discernible flame front
in a detonation as opposed to a deflagration. The chemical reaction
happens after the supersonic shock wave passes through the material
which would make it appear to be 'burning' (aka reacting) all at once.
To pick this apart a bit I focused on one type of explosive, RDX
and came up with this:
Explosive velocity: 8750 m/s [2]
Speed of sound in RDX: ~3300 m/s [3], [4]
Thus the shock wave propagates through the material at roughly
2.65x the speed of sound in the material.
Sources:
[1]'Toward Detonation Theory' by Anatolii Nikolaevich Dremin page 4 para 3
a description of ZND theory.
http://books.google.com/books?id=pZL...gbs_navlinks_s
[2]
http://en.wikipedia.org/wiki/RDX
[3] Molecular Dynamic Simulation of Nanoindentation of
Cyclotrimethylenetrintramine (RDX) Crystal
http://www.mrs.org/s_mrs/sec_subscri...ction=detai l
Google search of 'speed of sound in RDX crystals' yields a reference to this
paper with the quote 'the indentation speed is 200 m/s which is 6% of the
sound speed in RDX' this calculates to 3,333 and 1/3 m/s.
[4] The elastic constants and related properties of the energetic
material cyclotrimethylene trinitramine (RDX) determined by
Brillouin scattering by Haycraft, Stevens and Eckhardt.
http://digitalcommons.unl.edu/chemistryeckhardt/2
See the sound velocity diagrams in Fig 3. I noted the logitudinal mode curves,
esp. the ones from the ultrasonic works of Scwartz and Hassul which are in
close agreement at around 3300 m/s.
[5] US Patent No. 4,913,053 McPhee for Western Atlas International Houston TX.
'Method of increasing the detonation velocity of detonating fuse'
http://patft.uspto.gov/netacgi/nph-P...&RS=PN/4913053
----
Sorry,
Dave
PS: And boy, if this post doesn't end up on a NSA server somewhere,
somebody is asleep at the switch....