Praxichys
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Energetic Benefits of Co-crystallization
I recently stumbled across an interesting research paper and I have been reading into the subject of co-crystallization of energetic materials ever
since.
According to this presentation a mixture of 66% CL-20 by mass with the remainder TNT, co-crystallized from ethanol, was found to have 81% the energy density of the original CL-20.
Furthermore, the formed crystals had a density of 1.91, compared to TNT at 1.70 and 2.02 of the CL-20. If one works out the math, the additive average
crystal densities come out to 1.79. Co-crystallization through various intermolecular forces has "artificially" increased the density by 6.3%.
Lacking adequate predictive methods for crystal packing, modern science relies on trial and error to find packing orientation and density of most
heterogeneous crystal structures. I am certain many energetic compounds experience not only an affinity for one another but also a ratio at which that
affinity affords heterogeneous crystals of a maximum (and possibly greater) density than the sum of its parts.
The other interesting effect of co-crystallization is the blending of the original sensitivity properties of the original compounds. It may be
possible to co-crystallize highly unstable but extremely powerful energetic compounds (organic perchlorates perhaps) with both aromatic and aliphatic
energetic compounds. The paper asscociated with the presentation has more information on the nature of the intermolecular bonding forces suspected to be at play:
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With no available p–p stacking, this cocrystal forms based on a series of CH hydrogen bonds between nitro group oxygens and aliphatic hydrogens as
well as interactions between the electron-deficient ring of TNT and nitro groups of CL-20.
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Based on these findings, I believe it possible to co-crystalize a great deal of various energetic compounds for the mutual benefit of both. Suppose a
simple and small energetic compound could be locked into a crystal of some other energetic. It may very well become something like an interstitial alloy, some of which "fit" inside "holes" in the lattice of the other, essentially yielding a free density boost. Low proportions of
very brisant (but unstable) compounds could be co-crystallized with powerful and stable energetics to potentially increase VoD or and brisance.
Additionally, it may be possible to co-crystallize some energetics which have proven very powerful but impractical due to issues with their
susceptibility to atmospheric hydrolysis (particularly salts of nitro- and amino- derivatives of urea, guanidine, biguanidine, etc., several known of
which exceed the capabilities of RDX while remaining relatively insensitive.)
Food for thought.
PRAX
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franklyn
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More thought nutrition
The overall density of a double crystal is the average proportional to the
amount of each part The benefit sought from blending has long been
to enhance or inhibit properties of the selected ingredients and results
desired.
Practical results _
www.sciencemadness.org/talk/viewthread.php?tid=501
Speculative ideas _
www.sciencemadness.org/talk/viewthread.php?tid=9443#pid17013...
www.sciencemadness.org/talk/viewthread.php?tid=12452#pid1563...
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Rosco Bodine
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Binary and higher multiple mixtures, whether cocrystallized or not, and complex salts have long been identified which are peculiar in exhibiting some
synergistic property WRT performance, and if improved density is also observed then of course that is a bonus also. This technique of "compounding"
by the explosives chemist would have its parallel with the ancient art of compounding of medicines by pharmacists. A special composition which is
simply a mixture or is incorporated more or less intimately at a molecular level, can provide a formula especially well suited to a particular use, as
an engineered composite.
Melting point or solubility related properties might be the goal or a specific energy density or velocity for a composition might be intended to be
achieved. Often no single material used alone will have the desired properties, but a composition as simple as a binary mixture or a mixture of much
greater complexity will meet the design specification. Formulating such advanced composite materials is probably a mixture itself, or maybe a
cocrystallization, of art and science.
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Praxichys
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I disagree. According to the paper, the density is 6.3% higher than this calculation method would expect. I suppose it behaves like mixing water and
ethanol. The combined volume is of somewhat lesser volume (and thus higher density) than the average proportional density preditcs; in this case
through hydrogen bonding.
Ideal candidates will exhibit high intermolecular forces and achieve closer crystal packing than otherwise feasible with single compounds. I find the
clathrate thread particularly interesting as it demonstrates quite clearly that using basic lead picrate achieves greater performance, possibly due to
he hydroxyl group providing additional hydrogen bonding and perhaps increasing the overall packing density of the final material. I would be
interested in density measurements of each.
I have followed in Engager's footsteps with guanidine-based chemistry but I think co-crystallization products between substituted derivitives of urea
and smilar guanidine-based species could experimentally yield some very high density energetic compounds.
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franklyn
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Cocrystallization of Energetic Materials
http://deepblue.lib.umich.edu/bitstream/handle/2027.42/98068/kirlande_1.pdf
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