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hiperion42
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[*] posted on 25-8-2009 at 00:15
thermobaric test


Hi all

I saw a video on youtube showing different
types of explosives (plastic/FAE/thermobaric)

http://www.youtube.com/watch?v=FYg17YrgWlk

at 5:47 they test a thermobaric charge and
i was wondering if anyone has an idea
whether this was deflagration or a full detonation?

i think its clear that the metal additive used did more
then just add to the incendiary effect of the blast.

tnx!

David

[Edited on 25-8-2009 by hiperion42]
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Rich_Insane
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[*] posted on 27-8-2009 at 10:27


Thermobaric explosives use the O2 as an oxidizer I believe. I think it's a detonation that basically burns up and uses O2.

There is a detonation from some HE lump in the middle (plastic explosive, probably some RDX-based plastic explosive), this is surrounded by solid fuel, perhaps Al powder, or an organic propellant, with a very small amount of oxidizer, clumped together. Metal shard increases the effect.

It's basically very hot, and very energetic, due to the fact that Atmospheric O2 is being used.

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rbick
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[*] posted on 11-9-2009 at 13:52


I was unable to watch the video due to the server I´m on. However, it is a common misconception that all thermobaric charges use atmospheric oxygen. A thermobaric charge does not need to use atmospheric oxygen to be considered thermobaric. All oxygen can be present in the chemical structure of the explosive mixture and the oxidation of the metal powder still slows the blastwave and increases heat output, resulting in the desired thermobaric effect. These effects are a slower moving, stronger pressure wave and high heat production, hence thermo (heat), and baric (pressure). This is especially useful when destroying caves or harder structures where atmospheric oxygen may be inadequet.

There are charges however, such as the thermoberic version of the RPG invented by the Russians, that do require oxygen from the air. I think the ratio was something like 70% Al powder 30% TNT. The Al surrounded the spherical TNT booster charge. Anyway, thought this information might be interesting. Cheers :)




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Rich_Insane
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[*] posted on 11-9-2009 at 14:20


Really? . I do know that there is such thing as "true thermobaric" and "false thermobaric". A lot of explosives have Oxygen in their structure. If an explosive gives off O2 to make a thermobaric effect, I would suppose that that O2 would become part of the atmosphere.

Thermobaric RPG rounds (the TGV-7V?) has been described as a charge as powerful as a 155 mm Conventional artillery shell.

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rbick
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[*] posted on 12-9-2009 at 12:33


All explosives have oxygen in their structure. An explosive won't give off oxygen to create a thermobaric effect though. There are oxygen positive explosives which means that there is MORE than enough oxygen in the chemical structure to oxidize all components. For example, we can look at ETN (Erythritol Tetranitrate). PETN's cousin.

C4H6N4O12 → 4 CO2 + 3 H2O + 2 N2 + ½ O2

Understand that carbon and hydrogen are assumed to form CO2 and H2O given enough oxygen, however this isn't always completely the case. Again, it is assumed to make this easier.

As you can see in the simple explosive decomposition formula of ETN, a half mol of O2 remains. This makes ETN an oxygen positive explosive. There is an equation to find the exact percentage, but that isn't for here.

Anyway, whether an explosive is oxygen positive or negative has nothing to do with making a thermobaric explosive. The creation of a sustained, slower moving shockwave and the generation of heat is required. To do this, metal powders are added to traditional high explosives, as we discussed before. Liquids and aerosols are also used in thermobarics, but fine metal powders have become very popular, especially in the home experimenters world. The previously mentioned sustained shockwave and heat generation can be achieved from using thermobaric charges that use O2 from the air and charges that already contain enough O2 in their chemical structure.




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ammonium isocyanate
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[*] posted on 12-9-2009 at 13:15


It's not entirely true that all explosives have oxygen in their structure...

True, I can't think of a commercial secondary high explosive without oxygen, as most (all?) are nitrated compounds (unless you count AN mixtures, which are nitrates + fuel). However, some explosives, i.e. azides (such as lead azide), acetylides (such as silver acetylide), and nitrogen halides contain no oxygen and are very much explosive. IIRC tetrazole derivatives contain little or no oxygen and are very explosive.

Anyway very interesting explanation of thermobarics.




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rbick
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[*] posted on 13-9-2009 at 09:09


Yes you're right. I was thinking of common secondary HEs like TNP, TNT, RDX, ect but did not specify. Thanks for the correction.



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[*] posted on 15-10-2009 at 15:56


Quote: Originally posted by rbick  
I was unable to watch the video due to the server I´m on. However, it is a common misconception that all thermobaric charges use atmospheric oxygen. A thermobaric charge does not need to use atmospheric oxygen to be considered thermobaric. All oxygen can be present in the chemical structure of the explosive mixture and the oxidation of the metal powder still slows the blastwave and increases heat output, resulting in the desired thermobaric effect. These effects are a slower moving, stronger pressure wave and high heat production, hence thermo (heat), and baric (pressure). This is especially useful when destroying caves or harder structures where atmospheric oxygen may be inadequet.

There are charges however, such as the thermoberic version of the RPG invented by the Russians, that do require oxygen from the air. I think the ratio was something like 70% Al powder 30% TNT. The Al surrounded the spherical TNT booster charge. Anyway, thought this information might be interesting. Cheers :)

russians use for a base charge mixture of isopropilnitrate + alloy of magnesium with aluminium, and for first charge 100gr RDX eq detonator
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[*] posted on 24-10-2009 at 21:01


US military thermobaric rounds include ammonium perchlorate as an oxidizer to assist in the combustion of the aluminum surrounding the HE.
It was found thru testing that if the aluminum powder around the HE charge was more than 35% the weight of the HE, a lot of aluminum powder was wasted due to incomplete combustion. Oxidizers are added to complete combustion in low-oxygen environments (like caves)- whether the oxygen is taken from the environment or an added oxidizer doesn't matter- it is whether the resulting heat that is produced enhances the pressure over time curve- keeping the pressure on the target for longer is the actual goal- not depleting oxygen.
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hiperion42
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[*] posted on 7-11-2009 at 13:04


i'm looking for a way to incorporate teflon/fluorine into the mix. I read the teflon that is coated on the aluminum would interact with the aluminum and auminum-oxide in such a way that the ignition temperature is reduced from 2050 K to about 1150 K.
It has been suggested teflon tape could be inserted as-is
into the thermobaric mixture as the heat and pressure of the explosion would be sufficient to break the reflon molecule and releasethe fluorine element. I have not tested this yet but i have been looking for and found a pure PTFE 'grease' spray to treat the aluminum with. As i have no access to teflon powder i think the spray could sensitise the aluminum nicely.
Has someone here produced and tested a composition with
the aluminum/teflon element?

[Edited on 7-11-2009 by hiperion42]

[Edited on 7-11-2009 by hiperion42]
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argyrium
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[*] posted on 7-11-2009 at 14:08


Regarding PTFE, I doubt there is enough in a spray-able "grease" to bother with. Many other fluorinated hydrocarbons are "good" oxidizers with metals. Please be aware that combustion products will be toxic. Depending on particle size of both the PTFE and metal - you may have some unexpected sensitivity issues (personal experiences).


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