j_smith
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RDX crystal size question
Are RDX crystals the size of coarse table salt too big to plasticize?
It seems like the crystals should be a much smaller for an even distribution in the plasticizer.
Is there an optimum size? If I need to make the crystals smaller, what's the best way to do that?
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h0lx
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crashing would make the xals smaller. Never had contact with RDX so I can't help you with the other aspect. Large crystal size would make the
plastique more sensitive to detonation and possibly more brisant tho.
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hinz
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I would dissolve them in acetone and quickly add water, so the crystalls will be quite small. Milling, crashing orany other mechanical method is a
bad idea, because even with RDX you'll never be sure if the friction or shock will be enough for detonation.
BTW this reminds me to this thread:http://www.sciencemadness.org/talk/viewthread.php?tid=3769 
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j_smith
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Ball milling RDX...makes you wonder how some people have managed to survive for as long as they have...LOL
I read where one guy said he "gently crushed" the crystals...that doesn't sound like very good advice, either.
It sounds like warm acetone/cold water is the way to go.
How critical is the size of the crystals? Should I even bother with this?
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Boomer
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Remember that RDX based PBX are *machined* to size. So mechanically reducing crystal size is an option, though mortar/pestle is a no-no. You can
either
- rub *gently* between boards of wood, in small amounts. Wetting is a good idea.
- scrape with a knife over paper, like when cutting/homogenizing coke (that's what I do with small batches - not the cutting duh).
- run through a food blender with lots of water, like 10 times by weight. This even works for TATP, at one spoon per liter though. Start with the
water already in!
- dissolve in hot acetone, then cool quickly. This gives not-too-small xtals.
- dissolve in hot acetone, then stirr into water. This give very fine xtals.
Mixing the result of the last two methods results in a bi-modal crystal mix, which allows higher solid-loading. Ever wondered why C-4 stays together
without crumbling at just 9% binder?
[Edited on 15-11-2006 by Boomer]
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j_smith
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Thanks for the insight, everyone. I plan on concluding the experiment this weekend.
I'll post back with the results.
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nitro-genes
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Table salt size is too big to plasticize, and will give plastique that is not mouldable and has a large failure diameter...
Crystals from a blender (been there) are too small to give really high densities. Although they exhibit excellent mouldability and detonate in small
diameter, densities of more than 1.55 are difficult to achieve with these very fine crystals because of their larger surface area...
Underwater milling of crystals about 8-10 mm long and about half a mm thick gave the best results for PETN. Densities of 1.67-1.70 were reached
multiple times, though the plastique behaved incredibly stiff and fairly brittle. For RDX though you might want to experiment a bit with the different
procedures described in "Crystallization and Characterization of RDX HMX and CL-20.pdf" present on page 16 in the "Unconventional shaped charge
tread". It describes crystalizations from different solvents and condition for RDX...
Another thing I've been experimenting with is the sphericalization procedure mentioned in the same article or, in more detail, in US patent 4065529.
The pdf is available from -->http://www.freepatentsonline.com/4065529.html The results are reasonable, though not as good as I had hoped. I suspect
the smaller crystal fraction from the milling procedure is dissolved first, compromising the eroding effect on the larger crystals...
[Edited on 16-11-2006 by nitro-genes]
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h0lx
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| Quote: | Originally posted by hinz
Milling, crashing orany other mechanical method is a bad idea
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Crashing is the practice dissolving a material in one solvent and ppting by adding another. Just what you described.
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nitro-genes
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| Quote: | Originally posted by hinz
Milling, crashing orany other mechanical method is a bad idea
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Hehe, I think most people here agree that the destilation of methylnitrate without any vacume is even more suicidal! 
Large crystals of RDX will be fairly insensitive, more so at least than RDX in a fine powder form. The resulting crystals are very brittle, and there
is not much force needed at all to break them apart. Gentle pressure, while milling under lots of water, is absolutely no problem...
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