Spray Evaporated Microcrystalline Explosives

[nbk2000]

Grinding into fine powders strongly affects the properties of explosives. Even those characteristics which are usually considered to be constant can change, such as a decrease in melting point. At the same time the chemical reactivity increases, because fine particles have high specific surfaces and therefore have excess energy.

These changes in chemical and physical properties are especially interesting in so-called energetic substances. For example, the ancient Chinese knew that gunpowder acted better when finely ground. But it is impossible to pulverize an explosive such as hexogen mechanically, it would simply explode.

Thus, the idea of spray evaporation. This is used in the medical field for preparing inhalable forms of drugs that would be destroyed by mechanical reduction.

In principle, a supersaturated solution of the desired drug is held (under pressure) at a temperature over it's normal boiling point. It is then sprayed out through a nozzle under high pressure into a collection chamber at normal temp/pressure, where the solvent instantly vaporizes, leaving the solvate to crystallize into micron sized powders.

In our application, this could be used to produce a microfine crystalline powder of say...AP mixed with AN, without any dangerous mechanical reduction needed.

Simply find a solvent, or solvent system, in which both explosives are soluble in. Supersaturated the solution by heating above its normal boiling point under pressure (like a pressure cooker), then spray the solution through an electrically heated mist nozzle (to prevent crystallization in the nozzle) into a large cardboard box lined with plastic sheeting to collect the fine powder that falls out.

The powder can then be collected and pressed into blocks or such for use.

The russians have developed nano-sized particle explosives using vacuum evaporation and collection on a liquid nitrogen cooled plate, mixing HMX with AN.

[Anthony]

Could be a good way to reduce that sack of FGAN to a nice small, easily initiated power!

[NoltaiR]

And you could make the densities of certain explosives far greater than the old 'mortar and pestle' method (which would detonate friction sensitive explosives). The question is exactly how large would your collection chamber have to be for the particles to be able to cool off enough to recrystallize (if needed) and evaporate all the solvent while still airborne in the chamber.

[Helos]

BTW I have a little block of TNP (around 20g) that have recrystalized in one piece. Can I grind this with a mortar and pestle or do I need to this chemically :)

[mr.evil]

well, TNP isn't really sensitive... I had tried detonate a 100gram TNP charge once, with 2 grams of AP and it didn't detonate...

But be carefull, if your chemicals weren't that pure or you used metal spoons etc. there may be some dangerous metal picrates in your TNP, witch can detonate easily.

edit: Typo's

[xoo1246]

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<small>[ December 28, 2002, 12:07 PM: Message edited by: xoo1246 ]</small>

[THErAPIST]

im somewhat experienced with explosives but i have no idea what FGAN is. anyone mind tellin me? it seem familiar but i cant place anything other than the AN.

+++++++++++++++++++++++++++++++++++++++++++++++

Fertilizer Grade Ammonium Nitrate

NBK

<small>[ October 09, 2002, 08:47 PM: Message edited by: nbk2000 ]</small>

[nbk2000]

Well, you have to have a constant supply of non-solvated air to ensure rapid evaporation. The chamber might have to be fairly large, like a refrigerator sized box, to allow for evaporation and settling of the dust fine powder.

I wonder if a negative ion generator could be used to cause rapid precipitation of the air float? Or might it create a static charge and BOOM! ?

[Al Koholic]

If you had a constant supply of clean air entering (which you would have to have to prevent condensation of the solvent) there would also have to be an air outlet and a way to keep the micron sized particles from just floating out with the air current. I would expect them to take a bit of time to settle out. By positioning the air inlet and outlet far from the spray nozzle this could probably be done. Maybe you could even use extremely fine particle filters on the outlet to catch any stray explosive and then either shake them out of the filter or dip it in a solvent bath for the next batch to get the good stuff out and reduce inefficiency. I think the temp of the cooling chamber would also be very important. Would a more or less cool (ie, cooler than the mist) internal chamber temperature be ideal?

[nbk2000]

If the collection chamber was long enough, then the powder would settle out. Perhaps a large diameter pipe of PVC several meters long? HEPA filters would definately get it, but they'd likely choke up after only a few grams were collected.

If it wasn't for the product being explosive, electrostatic precipitation would be best.

I'd think avoidance of cold would be best to prevent condensation of the solvent back into the powder, which would get it wet and cause formation of larger crystals, the very thing you're spray evaporating to prevent happening in the first place.

[Al Koholic]

Ok heres what Im thinking...if you have a nice long chamber the particles will settle out. To aid the process of capturing the particles I think all you will have to do is place barriers along the length of the box. Lets say you have a long square box. Maybe 1 foot square in area and 10 feet long or something. At regular or variable intervals place a 1/4 inch plastic board that is 12 inches by 11 inches so you leave a 1 inch gap at the top of the box. That way the particles of explosive will collect like snow will in a drift. This would enable you to move the vapor current fairly rapidly and would result in a good efficient collection. At the end you can place a HEPA if you want to catch any strays. This would be like the gold dust collectors used in the 1800's I think.
Al

[Boob Raider]

I don't think HMX and RDX are sensitive to electrical charge, so I think static charge ppt should be ok. For something like AP ..... you all know whats going to happen. Just be sure to use very low current, something like 0.0? uA. I have a 5kV, 0.05 uA unit which runs of 24V DC salvaged from a photocopier. I think all thermally and moderately shock insensitive explosives should be fine. AN, TNT, Picric acid, Tetryl, I can't be too sure about RDX.

[Al Koholic]

I know this isnt a high explosive...but it fits under the topic.

What about using this technique to get ultra-intimate mixtures of fuels and oxidizers....like KNO3 and Sucrose? KNO3 and Ascorbic Acid also comes to mind.

Al

lol....been reading this shit since like 1998 or something....finally I am an amateur!!!

<small>[ October 16, 2002, 06:20 PM: Message edited by: Al Koholic ]</small>

[nbk2000]

I don't know if mixtures of disparate compounds is possible. It might happen that the two chemicals would crystaliize at different rates, forming different crystals sizes, rather than uniformly sized crystals. This could affect the burning characteristics.

But it wouldn't hurt to try it, though.

[Phoenix]

i would first try to find information about nano sized explosives because if it dont increase thier properties in a positiv way this discussion is nonsense
and i cant imagine fine rdx could be better then plastisized
i would rather try to make hm lets say 100 g cristalls to get the maximum density (if possible)
does anyone know of rdx in huge kristals is more sensitiv then pulverized rdx??
like lead azid???

[nbk2000]

My original post is partially a reworded copy of an article about nanoparticulate explosive, so your post is moot. :p

Very small particles of explosive have increased energy because the particles have an extremely high ratio of area to volume, making them "burn" extremely fast, much faster than unitary explosive charges of the same composition.

When powdered explosives are pressed into blocks under multi-tons of pressure, there's always microscopic air bubbles entrained in the block that act as canals for the propagation front to spread more rapidly than it could by normal shockwave propagation.

<small>[ October 19, 2002, 07:22 AM: Message edited by: nbk2000 ]</small>

[cutefix]

</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">quote:</font><hr /><font size="2" face="Verdana, Arial, Helvetica"> and i cant imagine fine rdx could be better then plastisized
i would rather try to make hm lets say 100 g cristalls to get the maximum density (if possible)
does anyone know of rdx in huge kristals is more sensitiv then pulverized rdx??
</font><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">In military explosives they still employ different grades of explosives according to particle size.The example is well known C-4 is a blend of fine and coarse particle RDX.
Look at previous post about C-4.
Meanwhile these nanoparticle high explosives such TATB,HMX,TNAZ,HNS etc are useful for special applications.
Indeed coarser particle size RDX is sligthly more sensitive than the fine particle grade.

[Al Koholic]

We can probably expect to find that RDX made by the nanoparticulate method would make more sensitive charges then. Lower VOD but far more sensitive. Good if you need something that can be detonated very very easily. Kind of like custom-fit manufacturing....just by varying the size of particle.

Cutefix...you think the larger particle size would be more sensitive? I dont know if thats the case as by having more and smaller particles you increase the number of "air spaces" in the final charge. The most miniscule size pockets are all that is necessary for a huge increase in the sensitivity.

<small>[ October 19, 2002, 10:24 PM: Message edited by: Al Koholic ]</small>

[nbk2000]

Another benefit is the fact that pressed powered PETN or RDX has the consistancy and appearance of ceramic. Thus, one could press a mug out of RDX, attach a handle, paint, and walk through a metal detector with "coffee" mug in hand, sipping your morning brew on your way to blowing up something. <img border="0" title="" alt="[Wink]" src="wink.gif" />

Perhaps mail in some "ceramic" plaques or some such that'll bypass any explosive detectors, and pick them up from the inside once you've passed through security.

Also, extremely fine particles like this can be initiated by impact forces, with no need for a detonator. I've read that a 20 joule impact will set off RDX like this. A ball peen hammer against concrete can easily generate such impact force.

[mongo blongo]

When you talk about small pockets of air in pressed explosives, do you mean "air" or just voids? I thought explosives were pressed under a vacuum. Are there cases where this is not so? Maybe sometimes they just don't bother.

[nbk2000]

Well, unless you use a vacuum to remove the air, there's going to be some inside.

Now, you try replacing air with some other gas like argon to potentially increase its flash. Helium is an excellent conductor of heat and has the second fastest mach number of any gas, and thus might increase velocity by conducting the shockwave faster than it would with air in the voids.(just an idea)

[Al Koholic]

Basically I mean voids. Air is one thing that can fill the spaces, but in a plasticized charge the plastic is just a more viscous filler than air is. Im sure there are details I am leaving out but the concept is the same. Just like adding little hollow glass spheres to AN emulsions to make them cap sensitive...or as with NBKs thoughts, enough air spaces and you can make impact sensitive explosives. Im not positive about this but...based on my experience making cap sensitive AN explosive I believe it is possible to make flame/impact sensitive AN charges as well. Most people dont think of it being that sensitive but if you lower the density of the charge enough (with inorganic microspheres) you continue to increase the sensitivity....I believe to being impact sensitive.

Forgot to mention it....but i like the idea with the mug NBK. Actually...that pretty much rules.
Theres got to be so many things you could do that with and go totally unnoticed.

<small>[ October 20, 2002, 03:53 PM: Message edited by: Al Koholic ]</small>

[cutefix]

</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">quote:</font><hr /><font size="2" face="Verdana, Arial, Helvetica">" you think the larger particle size would be more sensitive? I dont know if thats the case as by having more and smaller particles you increase the number of "air spaces" in the final charge. The most miniscule size pockets are all that is necessary for a huge increase in the sensitivity."

</font><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">The presence of a combination of different particle size enables the succesful intiation to be done effective and reliably in the field conditions.As even if the composite explosive like C-4;the explosive particles though bonded with a polymer the resulting explosive surface exposes more varied surface area as points for effective detonation wave shock transfer from the detonator.
Unless the explosive is very sensitive a uniform particle size composition will require a stronger booster to set it off properly.

[Al Koholic]

However by having the smaller particles you are exposing more total surface area. Plus, if I'm not mistaken in making this leap, the microparticles will not be of say, spherical nature either. They will probably be irregularly shaped to some extent, increasing the surface area like you describe with the bigger particles.
Al

[nbk2000]

While doing further research on FOX-7, I ran across an energetic materials conference topic listing. In there was mentioned production of nanoexplosive using the "sol-gel" method.

Naturally I had to look this up. I found this page ( <a href="http://www.llnl.gov/str/RSimpson.html" target="_blank">http://www.llnl.gov/str/RSimpson.html</a> )which explains the basic concept behind it.

Further google searching reveals a wealth of information that could be expanded on to make this technique applicable to our field of study.

Here's a citation on spray evaporation of particles less than 10nanometers.

<a href="http://www.aist.go.jp/NIMC/publication/annual96/16/16_24.html" target="_blank">http://www.aist.go.jp/NIMC/publication/annual96/16/16_24.html</a>

<small>[ December 26, 2002, 07:01 PM: Message edited by: nbk2000 ]</small>

[xoo1246]

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<small>[ December 28, 2002, 12:07 PM: Message edited by: xoo1246 ]</small>

[THe_rEaL_dEaL]

This is the same evaporation technique that they use to make atomised Al isnt it? Except for the solvent part.

Sorry if the answer to this question is extremely obvious butI have a feeling that there are minor technicalities which make it different to the method being discussed here.

Cheers

[xoo1246]

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<small>[ December 28, 2002, 12:08 PM: Message edited by: xoo1246 ]</small>