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Author: Subject: Effect of confinement on low explosives
Trashcanman
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[*] posted on 23-3-2024 at 11:02
Effect of confinement on low explosives


Hello,

I have a question about how much the confinement of a LE like blackpowder can influence the reaction speed.

The reaction rate of a chemical reaction approximately doubles when the temperature is increased by 10 degrees celsius.

increaseOfReactionSpeed=2^((temperatureInCelsius)/10)

Pipe bombs utilize that effect by keeping the hot reaction products close to the unburned powder.

What is the limit of this effect?
Could it be used to create a shockwave with a low explosive if the container had an extremely high bursting pressure? :)

LEcontainer.png - 11kB




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MephistosMinion
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[*] posted on 23-3-2024 at 21:27


As far as I recall even with confinement you won't be able to create the sort of shockwave that is a feature of high explosives using black powder. There is sufficient force to disrupt more sensitive primary explosives and cause them to detonate, this is usually achieved by the physical disruption and "collision" of the LE container after bursting with the primary explosive, as well as the high and instant increase in temperature immediately around the area; rather than any percussive wave created. Close proximity, even physical contact is usually required too.

Edit: to get max results from BP it should also be compressed before granulating. I can't remember is it's 1.7 or .7g per cc but it increases its burn rate in the open significantly once re granulated by gradual cracking and sifting into different grain sizes. There is or was a brilliant article on passfire covering this method.



[Edited on 24-3-2024 by MephistosMinion]
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OneEyedPyro
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[*] posted on 24-3-2024 at 09:09


There are limiting factors at play with any explosive regardless of confinement. There are diminishing returns in burn rate as pressures/temps get higher and at some point must reach a state of equilibrium.
With black powder the degree of diminished returns ramps up quickly at fairly low pressures which is why you could (within reason) safely load just about any weight projectile over any amount of BP in nearly any modern firearm.
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Alkoholvergiftung
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[*] posted on 24-3-2024 at 10:03


Dont underestimate Blackpowder. Normal pressure in an Blackpowder rifle is 1500bar but with blocked barrel it can rise up to 6500bar and that will shatter any barrel.
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OneEyedPyro
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[*] posted on 24-3-2024 at 12:26


Quote: Originally posted by Alkoholvergiftung  
Dont underestimate Blackpowder. Normal pressure in an Blackpowder rifle is 1500bar but with blocked barrel it can rise up to 6500bar and that will shatter any barrel.


I saw with my own eyes a 20 inch piece of steel rebar inserted then welded in place at the end of the barrel of a muzzle loader over roughly 500 grains of Swiss FFF black powder.
We set it off with a string from behind a steel plow blade expecting the barrel to explode. The barrel was pushed backwards with enough force to completely destroy the stock and ricochet off the gravel road landing about 100 yards away. We never did find the rebar.

Point is, the barrel seemed almost fine with no obvious bulges. Even the primer was still in its place and looked normal.
I think it would take a LOT of effort to generate 6,500 bar with BP.
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DennyDevHE77
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[*] posted on 25-3-2024 at 02:54


The flow of stable detonation is determined mainly by the efficiency of the activation processes of chemical reactions
at the moment when the released energy is transferred to the adjacent to the detonation wave front layers of not yet decomposed explosive material, if this efficiency is too low, the detonation front will
move forward with decreasing velocity, and will eventually become a sound wave. And it depends on the nature of the substance or mixture. You will never squeeze more than 400-500 m/s out of black powder, but you will easily get about 3000-3500 m/s on a similar coal dynamo in a strong thick case of large diameter and optimum density. In black powder, the shock (detonation) wave from the detonator primer will quickly turn into convective combustion (combustion where heat transfer processes are carried out by penetration of hot gases between the mixture particles). If black powder is simply set on fire, then detonation will not be possible in principle.

Well obviously mixed substances, where the combustible and oxidizing components are separated, will give a less fast shockwave in the end than organic molecules or homogeneous mixtures.
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Trashcanman
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[*] posted on 25-3-2024 at 12:42


Quote: Originally posted by DennyDevHE77  
The flow of stable detonation is determined mainly by the efficiency of the activation processes of chemical reactions
at the moment when the released energy is transferred to the adjacent to the detonation wave front layers of not yet decomposed explosive material, if this efficiency is too low, the detonation front will
move forward with decreasing velocity, and will eventually become a sound wave. And it depends on the nature of the substance or mixture. You will never squeeze more than 400-500 m/s out of black powder, but you will easily get about 3000-3500 m/s on a similar coal dynamo in a strong thick case of large diameter and optimum density. In black powder, the shock (detonation) wave from the detonator primer will quickly turn into convective combustion (combustion where heat transfer processes are carried out by penetration of hot gases between the mixture particles). If black powder is simply set on fire, then detonation will not be possible in principle.

Well obviously mixed substances, where the combustible and oxidizing components are separated, will give a less fast shockwave in the end than organic molecules or homogeneous mixtures.


Interesting but what do you mean by "coal dynamo"?




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Trashcanman
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[*] posted on 25-3-2024 at 12:48


Quote: Originally posted by OneEyedPyro  
There are limiting factors at play with any explosive regardless of confinement. There are diminishing returns in burn rate as pressures/temps get higher and at some point must reach a state of equilibrium.
With black powder the degree of diminished returns ramps up quickly at fairly low pressures which is why you could (within reason) safely load just about any weight projectile over any amount of BP in nearly any modern firearm.


Thanks for pointing that out.
I suspected that something like that may happen but wasn't sure.




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DennyDevHE77
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[*] posted on 25-3-2024 at 21:09


Well, one of the terms for ammonium nitrate mixed explosives is "dynamos", that is, mixtures of ammonium nitrate with non-explosive propellant without the addition of secondary explosives. And so I meant a typical mixture of 88% ammonium nitrate and 12% coal.
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Trashcanman
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[*] posted on 26-3-2024 at 09:57


Quote: Originally posted by DennyDevHE77  
Well, one of the terms for ammonium nitrate mixed explosives is "dynamos", that is, mixtures of ammonium nitrate with non-explosive propellant without the addition of secondary explosives. And
so I meant a typical mixture of 88% ammonium nitrate and 12% coal.


Ok. Now I understand what you meant and learned a new word :D.
Thank you.




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EF2000
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[*] posted on 26-3-2024 at 11:20


Quote: Originally posted by DennyDevHE77  
Well, one of the terms for ammonium nitrate mixed explosives is "dynamos", that is, mixtures of ammonium nitrate with non-explosive propellant without the addition of secondary explosives. And so I meant a typical mixture of 88% ammonium nitrate and 12% coal.

Proper term is "dynamon" (динамон, Dynammon), see PATR2700, v. 5, D1743.
Dynamons show that AN mixed with anything can detonate, with especially wild compositions coming from our great motherland. Like 85% AN and 15% of flour from pine cones.




Wroom wroom
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DennyDevHE77
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[*] posted on 26-3-2024 at 22:01


Thanks, I'll memorize the correct spelling since apparently the translators don't know it.
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[*] posted on 27-3-2024 at 13:50





Ammonpulver is a smokeless propellant made from AN and charcoal used as a substitute for cordite when resources get scarce (I believe)


[Edited on 27-3-2024 by yobbo II]
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Trashcanman
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[*] posted on 27-3-2024 at 15:18


Quote: Originally posted by yobbo II  



Ammonpulver is a smokeless propellant made from AN and charcoal used as a substitute for cordite when resources get scarce (I believe)


[Edited on 27-3-2024 by yobbo II]



Good to know.




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