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LiveWire
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HE + Flash Powder
I was thinking of ways to make flash powder burn faster (for a brighter light), and I remembered that aluminum is sometimes mixed with PETN. So I was
wondering, would it be possible to mix flash powder with a high explosive such as PETN? I'm thinking that the HE would serve to propogate a
shockwave, therefore making the flash powder burn several times as fast. Of course, the amount of oxidizer in the flash would be adjusted for proper
oxygen balance.
Theoretically, would this work? If we assume that our flash composition by itself burns at 400 m/s, I think a PETN+flash mix could easily reach 4000
m/s, therefore increasing the speed and peak brightness by a factor of 10.
I'm also thinking that maybe the duration that the burning aluminum or magnesium particles give off light is long enough that it doesn't really matter
if the velocity of the explosion is 400 m/s or 4000 m/s.
Any thoughts?
By the way, I am a newbie; my apologies if I've said or done anything stupid.
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Lambda
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Aluminum powder is used in combination with many CNO high explosives to enhance the Blast effects, and hence more volumetric energy output of the
same. One mechanism involved, is a secondary reaction in witch CO2 acts as Oxidizer, and is thus Reduced by the Aluminum to CO.
3 CO2 + 2 Al --energy--> 3 CO + Al2O3
"Chemistry Of Pyrotechnics - Basic Principles And Theory - By John A. Conkling (1985)" is a good read in respect to the theory of color, temperature
and compositions. Aluminum (Thermite) is also used as ignitor in various FAE (Fuel Air Explosives) compositions together with High Explosives. IIRC
Aluminum can double the energy output of a high explosive up to an Al content percentage of ~32% (Explosives - 5th Edition - By Köhler, Meyer &
Homburg - 2002) (?).
[Edited on 20-2-2006 by Lambda]
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Boomer
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Which is why it usually *decreases* VoD and brisance. It also tells you the light will be generated mostly *after* detonation.
In other words, go with flash and use the finest Al you can get. If that's too slow, shock some argon with a HE! 
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halogen
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Either that or have excess oxidiser
F. de Lalande and M. Prud'homme showed that a mixture of boric oxide and sodium chloride is decomposed in a stream of dry air or oxygen at a red heat
with the evolution of chlorine.
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Fulmen
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"I'm also thinking that maybe the duration that the burning aluminum or magnesium particles give off light is long enough that it doesn't really
matter if the velocity of the explosion is 400 m/s or 4000 m/s."
I think you've answered your own question here. The light isn't produced by the reaction itself but by hot glowing particles of aluminium oxide, and
this will produce an "afterglow" no matter how fast the powder burns.
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artem
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| Quote: | Originally posted by LiveWire
So I was wondering, would it be possible to mix flash powder with a high explosive such as PETN? I'm thinking that the HE would serve to propogate a
shockwave, therefore making the flash powder burn several times as fast. Of course, the amount of oxidizer in the flash would be adjusted for proper
oxygen balance...
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The light output depends on the balance of temperature, size of the fireball and time of oxidation. The velocity of the deflagration/detonation is the
secondary factor, for example, strong shock wave "activates" the metal surface and increase its temperature, so, metal particles burn immediately.
Detonation products of HE also increase the fireball and serve as the source of oxygen for metal.
But when the metal particle size - and time of combustion is very small, part of the oxidation energy go to the blast wave, also the fireball is not
very big (for example, in the Zr-KClO4 for photoflash it was recomended to use Zr as the mix of fine and coarse particles - see US patent 5821451).
That's why, there is an optimum for the size of metal, and ratio HE/Me. There is no need to use the oxidizer except HE itself, only small amounts of
Na-Sr-Ba salts are usefull to increase luminosity.
The most powerfull modern light sources containes only layer of HE + layer of Al on it, the mass ratio ~1, the excessive Al oxidize in the air.
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quicksilver
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This also invites the element of visable light vs. total output generated. I have seen experiments w/ Zr and various other metal fuels. Some
generating more UV for photography in unique circumstances.
The responses to your query are right on the money. I would add that there are a great variety of metal fuels available; some of the Al powders used
in military & industrial applications also contain carbide, carbon, teflon, etc. This may aid in increasing intensity in many cases (as would fuel
particulate size and shape, of course). In an oxidizer/fuel mixture PETN would not detonate but simply add to the fuel burn ratio and may actually
lower the total generated light output. I have read that fuel/oxidizer mixtures could be mfg at the sub-sieve level via a "whet-mix" process. This
would be more in line with the target concept.
A common one with lots of UV:
Zirconium.........................................28
Zirconium hydride.................................7
Magnesium.........................................7
Barium nitrate....................................30
Barium oxyde......................................25
Carbon fuel.......................................5
Shimizu's #11 report comp: Utilizing a sub-sieve size element would be competitive from a visable light output. But introducing more fuel or a slower
burning fuel would be counter productive.
Potassium perchlorate...................64
Aluminum (Oberon dark).................23
Sulfur............................................13
In his lectures on the subject he spoke of the balence and speed [of burn] being the major factor.
The Standard Military flare comp for both the US & EU is:
Teflon..........................................44
Mg (twin grade; 4u/60u).............54
NC Laquer...................................12
Unfortunatly this flare is also explosive and has resulted in a tragic accident in a US plant a few years back. However it can be mfg in the multi
million candle power level.
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nitro-genes
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And for those few not having zirconium hydride...  There is a common photoflash
in the pyrotechnical compositions database with a remarkable lightoutput which is used in the M120A1 and M112A1 flare cartriges. A pile of 10 grams in
the open, in total darkness is an experience I wont forget easily. The first minute I wasn't able to see almost anything and it took several minutes
before the white image of the flame itself had totally dissipated from my retina. 
Be carefull though, this flash is almost as fast as the regular 70/30 perc/alu. The ten grams in the open I did already made a deep thumping like
sound and was on the edge of deflageration I think. Of coure I used my own home made 400-500 mesh flake alu from aluminium foil (quite different from
20 micron atomized!), so that might also be to blame. The composition
defenitely emits more light than any other flashpowder I have ever made containing aluminium. I think the combination of the barium ions and the
availability of chlorine from the perchlorate is responsible for this increased light production. More energetic quantum state of the barium ions
during the reaction? (and thus fall back, emitting photons). Or more photons in the visible light area? I do know chlorine donors are necessary for
coloured compositions forming a more deeply coloured complex with cations upon excitation. Barium containing compositions should be green, but I have
percieved the flame of this composition as almost pure white. Maybe this is because of a too high reaction temperature?
Edit: Just checked Shimizu: only at a very high temperatures
(Mg as a fuel) and with a supplemental chlorine donor
barium is green, without it it is bright white. Explains
why it is used in the photoflash...
Composition in weight parts:
Aluminum (20 micron; atomized).....................40
Potassium perchlorate (24 micron)..................30
Barium nitrate (150 micron).............................30
I have also found a simple composition of sodium nitrate and magnesium/aluminium to be very bright, although slightly less than the photoflash
above...
About mixing petn with flash: In fairly rich mixtures with petn, I think the petn would detonate, leaving a cloud of dispersed flashpowder which would
combust afterwards. I think the flashpowder would not be able to keep up with the very fast detonation wave of petn. It had something to do with the
extremely high temperatures needed to keep the products of the deflageration of flashpowder (aluminium oxide and potassium chloride) in the gasious
state. The condensation front of these products interferes with the thermal reaction wave and does not permit a real accelarating shockwave to
develop. (Taken from the endless debate about detonating flashpowder )
[Edited on 23-2-2006 by nitro-genes]
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LiveWire
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Many thanks to everyone who replied!
Lambda: I can't get those books here, everything is so regulated. (You can't even get nitrates without having to answer a load of questions!) Is
there anywhere I can get such information online?
Fulmen: "The light isn't produced by the reaction itself but by hot glowing particles of aluminium oxide, and this will produce an "afterglow" no
matter how fast the powder burns."
Well, if the afterglow dies out before the rest of the powder burns, it would be much less bright than it would have been if the reaction spread fast
enough to ignite all of the aluminum before the glow of the first ones fades. So the question is, does the glow last that long?
artem: "The most powerfull modern light sources containes only layer of HE + layer of Al on it, the mass ratio ~1, the excessive Al oxidize in the
air."
Just pure HE under pure Al? This is very interesting, is it being used in any application? Would the oxygen from the HE reach the aluminum before it
all spreads? I see how using Al without an oxidizer would increase the fireball size, but how does this improve light intensity? I mean, the
particles give off the same amount of light regardless of where they are.
By the way, isn't magnesium better at giving light than aluminum? Wikipedia says that military flashbangs use magnesium powder and ammonium
perchlorate. I suppose they don't use the HE+Al because it would be potentially dangerous, right?
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artem
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| Quote: | Originally posted by LiveWire
artem: "The most powerfull modern light sources containes only layer of HE + layer of Al on it, the mass ratio ~1, the excessive Al oxidize in the
air."
Just pure HE under pure Al? This is very interesting, is it being used in any application? Would the oxygen from the HE reach the aluminum before it
all spreads? I see how using Al without an oxidizer would increase the fireball size, but how does this improve light intensity? I mean, the
particles give off the same amount of light regardless of where they are.
By the way, isn't magnesium better at giving light than aluminum? Wikipedia says that military flashbangs use magnesium powder and ammonium
perchlorate. I suppose they don't use the HE+Al because it would be potentially dangerous, right? |
Yes, just pure HE under pure Al, it?s well known device.
Yes, the ignition and initial burning of Al is due to oxygen of detonation products. During the fireball expansion, some air is involved in it, giving
additional O2.
When the ratio metal/HE>>1 or when BP(or flash) is used instead HE, magnesium is much better. As for HE, difference is not great, but flake Al
is more available, more safe to handle and more stable, then ultra-fine grade Mg. Probably, MgAl is the best choice.
As for flashbangs with Mg+ammonium perchlorate and others, they are VERY hazard when manufactured, when stored (they are more sensitive to fire and
shock, then common PBX), they are more dangerous in use (blast wave TNT- equivalent of KClO4/Al ~0.55-1.3 - see PEP1990-03-115, for mix with NH4ClO4
the value > RDX), and their performance is less.
The append article describes devices, which are not HE+Al, but some ideas are interesting.
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artem
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the article:
Attachment: FLASH BANG DEVICES.doc (353kB)
This file has been downloaded 3111 times
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Lambda
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LiveWire,
I will upload them for you to Madhatter's FTP services.
Chemistry of Pyrotechnics - Basic Principles and Theory - By John A. Conkling (Marcel Dekker - 1985) 108s(d).pdf (1.58 MB).
Can be found in the folder:
UPLOAD / Lambda / Pyrotechnics /
Explosives - 5th Edition (Completely Revised) - By Rudolf Meyer, Josef Köhler & Axel Homburg (Wiley-VCH - 2002) 436s.pdf (2.38 MB).
Can be found in the folder:
UPLOAD / Lambda / Explosives /
Note:
Please give me a day to find these books.
Additional information:
Are now both available !
[Edited on 24-2-2006 by Lambda]
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quicksilver
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| Quote: | Originally posted by nitro-genes
About mixing petn with flash: In fairly rich mixtures with petn, I think the petn would detonate, leaving a cloud of dispersed flashpowder which would
combust afterwards. I think the flashpowder would not be able to keep up with the very fast detonation wave of petn. It had something to do with the
extremely high temperatures needed to keep the products of the deflageration of flashpowder (aluminium oxide and potassium chloride) in the gasious
state. The condensation front of these products interferes with the thermal reaction wave and does not permit a real accelarating shockwave to
develop. (Taken from the endless debate about detonating flashpowder )
[Edited on 23-2-2006 by nitro-genes] |
PETN in a physical mixture w/ an oxidizer/fuel if SIMPLY EXPOSED TO THE SPIT OF A FLAME via a fuse couldn't detonate primarly due to the lack of
detonation wave formation. - Now if the material were isolated or layered, would there be a capasity for a "cook off" is in DDT? Most likely not. PETN
is not a great candidate for that. MHN may work well in that instance but not PETN. It's sensitive but not that sensitive as a boarderline
primary-type explos. (such as MHN)
Shimizu found that flash does detonate IF initiated w/ a primary explos (via a BC). The same concept exists when we have a physical mixture of PETN
and oxidizer/fuel - we would need a primary to initiate; flame would not privide the nesessary stimulus. The "debate" over flash detonating really
gets back to HOW that flash is initiated. IF we were to place in intimate contact a primary and initiate that we would see a mild detonation of
2300mps w/ a standard 70/30 flash (Shimizu '98 seminar at U.HN). But when dealing with initiation via a simple fuse only one comp of flash has even
pushed 1100mps (#11) and then only at mass levels beyond self enclosure (50gr +). IF we define detonation as simply speed then, it's a done deal.
Actually some of the best research done in that area was not from seminars by the APG or other pyro folks but the U.S. DoD contractors who worked w/
flare systems - many of whom had serious troubles / accidents w/ their plants. Manufacturing studies available to the general public are tough to find
but worth the effort.
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LiveWire
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artem: Thanks for the article!
Lambda: Thank you! Currently I'm waiting for Madhatter to reply to my U2U for ftp access; I'll check out the books as soon as I get my account.
quicksilver: Of course, I meant detonated with a cap; I didn't expect the PETN to do DDT.
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nitro-genes
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| Quote: | Originally posted by quicksilver
Shimizu found that flash does detonate IF initiated w/ a primary explos (via a BC). The same concept exists when we have a physical mixture of PETN
and oxidizer/fuel - we would need a primary to initiate; flame would not privide the nesessary stimulus. The "debate" over flash detonating really
gets back to HOW that flash is initiated. IF we were to place in intimate contact a primary and initiate that we would see a mild detonation of
2300mps w/ a standard 70/30 flash (Shimizu '98 seminar at U.HN). But when dealing with initiation via a simple fuse only one comp of flash has even
pushed 1100mps (#11) and then only at mass levels beyond self enclosure (50gr +). IF we define detonation as simply speed then, it's a done deal.
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Yes, 2300 m/s was indeed mentioned for chlorate flash, and slightly lower for perchlorate based flash by Shimizu. But almost every definition of
detonation I could find involves the formation of a shockwave or pressurewave. Pressure means expanding gas, but since no gas is formed in
(Per)clorate/Al based flash compositions there simply is no pressure wave...
But the lack of gas formation in flash compositions has another effect: The tremendous heat formed by the oxidation of aluminium cannot diffuse away
from the reaction because no gas is produced. So instead an accelerating thermal wave is formed that can reach 1100 m/s and is limited by the speed of
condensation of the reaction products.
This is the theory, but if it was the whole truth than you would expect that initiating a maximally compressed flashpowder sample by a fuse would have
a faster burnrate than a non-compressed sample, since the air inclusions would be an isolation for the accelerating thermal wave. This is however not
the case. For initiation with a fuse there is a optimal density which is about 1g/ml. So I think there is a sort of a trade-off between the amount of
air inclusions that can form a pressurewave and the slowing down of the thermal wave by isolation effect of the same inclusions... Of course there is
also the intramolecular breakdown of the chlorate /perchlorate ions itself, like in Cheddites that might aid in the formation of a temporarily
pressure wave (until the formed oxygen gas encounters an aluminium particel), this effect may become more inportant when using a blasting cap to
initiate the flashpowder. In my opinion this theory is supported by the fact that the 2300 m/s is lower, but close to the detonation velocity of the
chlorate based Cheddite. Does anybody know what happens with the burnrate if one would initiate fully compressed flashpowder with a blasting cap? Just
curious...
Probably all these effects come in to play somewhere, so lets just call it deflanation or detoflageration or.. or...
I'm starting to talk shit here (if not the whole post)...No more beer for me
[Edited on 6-3-2006 by nitro-genes]
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12AX7
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Well, considering the speed of the reaction...did you think to consider 8Al(s) + 3KClO4(s) > 4Al2O3(g) + 3KCl(g)? Al2O3 might be a stretch but KCl
is certainly volatile above its melting point.
I mean, duh, how else does a salute explode? Contained air? It might expand by 10 or 20 times, but that's it. 10atm isn't even enough to bust a
stiff soda bottle! (Well maybe)
Tim
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artem
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| Quote: | Originally posted by nitro-genes
But the lack of gas formation in flash compositions has another effect: The tremendous heat formed by the oxidation of aluminium cannot diffuse away
from the reaction because no gas is produced. So instead an accelerating thermal wave is formed that can reach 1100 m/s and is limited by the speed of
condensation of the reaction products.
...
Does anybody know what happens with the burnrate if one would initiate fully compressed flashpowder with a blasting cap? Just curious...
[Edited on 6-3-2006 by nitro-genes] |
About of gas formation in flash compositions: the explosion temperature is enough to evaporate all KCl and part of MeO. The condensation takes place
during and after expansion. This is the reason of high blast effect of the flash. Generally speaking, flash detonation is simular to AN-mix, that's
why, it easily detonates at density ~ 50%TMD. But it is more hard to initiate flash at high density because its components are not explosive- even
such as AN. But it is not impossible for some mixes, this is the question of particle sizes, charge diameter and initiation conditions.
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Chris The Great
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I read at the temperatures generated in flash, the Al2O3 breaks down into Al2O and O2 which are both gas at the high temperatures.
I think it was a google archive usenet post where I saw this.
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nitro-genes
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| Quote: | Originally posted by 12AX7
Well, considering the speed of the reaction...did you think to consider 8Al(s) + 3KClO4(s) > 4Al2O3(g) + 3KCl(g)? |
Yes, I already metioned KCl and Al2O3 to be the main reaction products in an earlier post...
| Quote: | Originally posted by 12AX7
Al2O3 might be a stretch but KCl is certainly volatile above its melting point. |
It's not the melting point that matters, but the boiling point I think. There is too little time for evaporation, especially considering the pressure
factor too. For KCl this is 1400 deg C in stead of 700 deg C and for Al2O3 it is the order of 3000+ deg C!
| Quote: | Originally posted by 12AX7
I mean, duh, how else does a salute explode? Contained air? It might expand by 10 or 20 times, but that's it. 10atm isn't even enough to bust a stiff
soda bottle! |
Let's consider that the only pressure produced in a container with flashpowder is indeed from the heat expanded air present in the flashpowder...KClO3
has a density of 2.32 g/cm3, aluminium 2,7 g/cm3. If we take the optimum density of flashpowder (1g/cm3) this means more than half of the space in a
container filled with flashpowder is actually air. (unreactive nitrogen) Although I'm not sure if aluminium nitride isn't produced too...
If we take 3000 K as the maximal temperature reached and apply the combined gas law, (which we can do since the amount of gas moles ideally remains
the same, assuming the container would not rupture):
(p * V)/T (1) = (p * V)/T (2)
the difference in temperature is about 3000 K, so the product (p * v) (2) must become 3000 times as big. Assuming the container would not rupture, the
volume remains about the same too (also assuming that the reaction products occupy about the same volume as the reactants), This would mean that under
ideal confinement flashpowder could maximally generate a pressure of 3000 times atmospheric pressure! Quite different from 10 or 20 bar!
On second thought, it is likely that under these extreme conditions even the nitrogen would react with the aluminium.
making my story a load of bullshit.
| Quote: | Originally posted by artem
About of gas formation in flash compositions: the explosion temperature is enough to evaporate all KCl and part of MeO. The condensation takes place
during and after expansion. This is the reason of high blast effect of the flash. Generally speaking, flash detonation is simular to AN-mix, that's
why, it easily detonates at density ~ 50%TMD. But it is more hard to initiate flash at high density because its components are not explosive- even
such as AN. But it is not impossible for some mixes, this is the question of particle sizes, charge diameter and initiation conditions.
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I know the explosion temperature is high enough to bring some of the reaction product in the gassious state. But I thought that the thermal reaction
wave and the condensation area were very close together. Like a zipper with two zipper mechanims, one opens it up, but the other right behind it
immediately closes it again. So, I was wondering whether the pressure produced by the KCl beeing in the gassious state would have the time to actually
deliver a certain amount of work on the surrounding air, thus creating a pressure wave. I always thought that the blast effect mainly involved the
heat expansion of the surrounding air, like with thunder. But appearently it doesn't...But it is strange though, since I have found flashpowder to be
alot less brisant then cheddites. (Involves pipe bombs from pressure rated steel, and K3wlisch stories from my early days) They should have about the
same brisancy considering KCl to be the main factor producing a pressure wave, and both having about the same detonation velocity...Then again only
the Cheddite was initiated by a blasting cap... Btw, thank you for the document about flash devices! Interesting stuff...
| Quote: | Originally posted by Chris The Great
I read at the temperatures generated in flash, the Al2O3 breaks down into Al2O and O2 which are both gas at the high temperatures.
I think it was a google archive usenet post where I saw this. |
Interesting, never heard this before...
[Edited on 6-3-2006 by nitro-genes]
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12AX7
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| Quote: | Originally posted by nitro-genes
(p * V)/T (1) = (p * V)/T (2)
the difference in temperature is about 3000 K, so the product (p * v) (2) must become 3000 times as big. |
Err? Absolute temperatures PLEASE!
(PV)<sub>1</sub> / 300K = (PV)<sub>2</sub> / 4000K (I'll be optimistic for you!)
Rearrange:
(PV)<sub>1</sub> / (PV)<sub>2</sub> = 300K / 4000K
Well, take the reciprocal.. and you get what, 13 times?
Tim
[Edited on 3-6-2006 by 12AX7]
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LiveWire
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13 atmospheres is 13 kilograms per square centimeter, 182 pounds per square inch. That's more than enough to break cardboard, plastic, and maybe even
rupture (not shatter) a thin metal pipe.
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nitro-genes
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ROFL
I was really to fast there, of course your right... Damn, and I used to be
really good in physics back in high school (embarrassed), how on earth did I ever survive all the math at university?!
[Edited on 6-3-2006 by nitro-genes]
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12AX7
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| Quote: | Originally posted by LiveWire
13 atmospheres is 13 kilograms per square centimeter, 182 pounds per square inch. That's more than enough to break cardboard, plastic, and maybe even
rupture (not shatter) a thin metal pipe. |
Yeah, but not the thick ones commonly used in pyro. I bet an M-80 can go to like 300PSI or more before failing. Matter of fact that would be an
interesting test to make.
Tim
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artem
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| Quote: | Originally posted by nitro-genes
I know the explosion temperature is high enough to bring some of the reaction product in the gassious state. But I thought that the thermal reaction
wave and the condensation area were very close together. Like a zipper with two zipper mechanims, one opens it up, but the other right behind it
immediately closes it again. So, I was wondering whether the pressure produced by the KCl beeing in the gassious state would have the time to actually
deliver a certain amount of work on the surrounding air, thus creating a pressure wave. I always thought that the blast effect mainly involved the
heat expansion of the surrounding air, like with thunder. But appearently it doesn't...But it is strange though, since I have found flashpowder to be
alot less brisant then cheddites. (Involves pipe bombs from pressure rated steel, and K3wlisch stories from my early days) They should have about the
same brisancy considering KCl to be the main factor producing a pressure wave, and both having about the same detonation velocity...Then again only
the Cheddite was initiated by a blasting cap... Btw, thank you for the document about flash devices! Interesting stuff...
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The brisance of Al/KClO3 vs diameter(d=0.95g/cm3, KClO3<0.3mm!, cap N8):5.4mm(40mm), 16.73(58mm), 21.55(77.5mm).
So, its brisance is the same as for org.fuel/KClO3-mixes.During expansion, additional energy is transfered to the blast wave, and blast TNT-equivalent
is higher.
Few mg of ultrafine KClO4+nano-Al mix on the end of knife, when exposed to flame, breakes the end.
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nitro-genes
International Hazard
Posts: 1048
Registered: 5-4-2005
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What an experiment, putting 5 kg of flash in a house and see what will happen. Wouldn't want to carry 5 kg of flashpowder around though, 1 gram in a
strong paper tube is more than enough for me.
I don't want to sound like a leech, but do you also have some documentation about this nano- aluminium compositions? I've managed KClO3 and magnesium to detonate in milligram quantaties, but not
showing the extreme brisance of course. My magnesium wasn't nano-sized.
I found out that making nano-aluminium doesn't seem that hard. It is made by ball milling aluminium powder under a oxygen lacking atmosphere. In most
cases they use a nobelgas for that, but I wonder if nitrogen would be feasable too. I have a lortone rocktumbler for making my own aluminium powder,
it has a rubber barrel and can be made airtight with a little effort. The darker the aluminium becomes the more pyroforic it gets and the more oxide
is formed. How do they solve this for the nano-aluminium? Do they apply a special coating? And if so, wouldn't you end up with more coating than
aluminium, considering the small particle size?
[Edited on 9-3-2006 by nitro-genes]
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