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Author: Subject: PETN-based Cast Explosives
Nitrojet
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[*] posted on 2-11-2006 at 13:23


I observed the same phenomenon when I tried to fuse a mixture of PETN-Dinitrodimethyloxamide 70/30 in a water bath. A 10gr sample of mechanically-mixed PETN-Dinitrodimethyloxamide was put in a test tube while the tube was externally heated by means of a water bath assembly. A sufficient quantity of Ammonium Nitrate then was added to water to increase its boiling point to 110’C. Constant stirring (10 RPM) was held throughout the test in water bath to insure a uniform heat flow to the sample. The mixture began to melt at 103’C and when the temperature reached 108’C the salted-water medium was boiling. Melting of the mixture continued and after an approximate time of 20 minutes (since the start of melting), no more change was observed in solid-liquid phases both quantitatively and qualitatively. In actuality, a considerable portion of PETN remained unchanged thus making a suspension together with the molten phase. I did not try to stir the suspension for getting more uniformity mostly because PETN in the liquid form can be extremely sensitive to any kind of mechanical stimuli. I removed the heat source and let the mixture solidify upon cooling. After 1hr I had a cast charge with a cylindrical geometry which was perfectly white in color. For this charge a density value of 1.41gr/cc was obtained through careful measurements. To overcome the non-uniformity of the resulting suspensions, I tried to have casts from a mixture previously co-precipitated from Acetone. The results were quite satisfactory. In this regard, I made an acetone solution of PETN-Dinitrodimethyloxamide in proper weight ratio and then precipitated the binary mixture by adding water to the solution. The crystals being obtained this way are of uniform distribution and upon casting they form a highly homogenous syrupy suspension which is optically translucent. Unlike the mechanical mixtures of the two explosives, the molten slurries from acetone-co precipitation contain no bulk of solid PETN crystals and the solid particles are of uniform distribution all throughout the molten phase. The densities, however, show no drastic change when practicing this technique while they merely exceed 1.50gr/cc.
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Rosco Bodine
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[*] posted on 2-11-2006 at 13:48


I suspect that if you take your translucent melt and add little by little to it twice its weight of crystalline PETN , you may be able to increase the density of the finished composition . You have to go slowly so as not to cool
the melt and you will probably have to " fold in " the
dry material portionwise to get it evenly wetted by the melt and freeing entrapped air . Keeping the mixture a bit above the melting point where it is thinner will
help the mixing , but it will still be about like trying to
wet granulated sugar with corn syrup or honey , and
getting the air out of it . Don't overstir it , once it is
fairly well mixed it should be like mixed epoxy which
is very viscous also , but if disturbed only slightly at
intervals the tiny bubbles will rise to the surface and
escape the thick slurry . If you stir it too much or too
vigorously it mixes air into the slurry instead of helping it to coalesce and escape . It is very much the same
as working with concrete where a vertical agitation
with a rod inserted and jiggled up and down a bit will settle the mix and bring any air to the surface , but any stirring which swirls the mixture only puts more air into it .
You might be able to gain a point or a point and a half on the density by special technique of loading the melt in this manner , unless of course the added solid PETN
disrupts the eutectic ....only an experiment will tell .
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Nitrojet
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[*] posted on 3-11-2006 at 11:33


PETN gives an Eutectic with Dinitrodimethyloxamide in 37% Wt. ratio. So you mean i should prepare the eutectic beforehand and after complete fusion i can go on adding the rest of PETN in small portions to the point that i get my favorite 70/30. occassional stirring is also needed to drive off all the entraped air bubbles from the PETN crystals.
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Rosco Bodine
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[*] posted on 3-11-2006 at 12:09


Yes . And it wouldn't hurt to make the initial Eutectic
a bit poor in PETN , by maybe 10-15% so that it must get the remainder from wetting the surface of the greater amount of PETN which you will be adding as a filler .
Doing this , and heating the initial melt which is not exactly eutectic above the temperature of the known eutectic enhances the wetability of the bulk filler PETN ,
and makes it easier to mix , and makes the thermodynamic more favorable for the mixing , because
even if the mixture is cooling a bit as the filler is added ,
the mixture is also forming the eutectic which resides
at a lower temperature than the initial non eutectic
" solvent " melt which is at a mildly higher temperature ,
if you follow the logic . The approach towards the eutectic tends to offset the cooling of the mixture from the added filler . Every little trick helps .

Also , disregard the eutectic ratio as applicable to the
total finished composition ....the eutectic is only the melt phase of what is a slurry of the melt liquid , loaded with an aggregate of additional crystalline PETN , until it is a consistency of a gritty sticky goo like wet concrete .
The eutectic portion is simply the glue that sticks the
solid PETN together .

[Edited on 3-11-2006 by Rosco Bodine]
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[*] posted on 3-11-2006 at 22:10


Hey Rosco,

I am just sitting here scratching my head trying to understand what exactly determines the final density in a melt.

I use the following example to try to illustrate my question:

Let's suppose you have an explosive with a crystal density of 1.5 and another explosive with a crystal density of 1.6
and what I mean by crystal density is supposing you had a large crystal of each explosive that just happens to measure 1 cubic centimeter each, but amounts to 1.5 and 1.6 grams respectivly. Now suppose these explosives had a melting point within a few degrees of each other and are in fact melted together and then solidified. From my basic understanding I would think that in order to estimate what the density will be you add 1.5 + 1.6 = 3.1 then 3.1 / 2 =1.55
Now, am I going in the wrong direction here, as far as my method of estimating what the density of the finished melt will be?

I've read in some literature that usually if a melt is cooled faster it retains a higher density than if it is cooled slowly.

What are the principles that dictate the finished density of a melt? Are ther non explosive materials that can be added to increase the density in a good way?

Is the best way to increase density in a melt to perhaps add materials that will modify the resulting crystals in a way that makes them more dense?
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Rosco Bodine
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[*] posted on 4-11-2006 at 00:16


I never really thought much about such matters ,
I suppose the same effects of volume compression
of melted mixtures are possible in some cases
as for when liquid solutions are mixed . Barium nitrate
has been used as a densifier for TNT mixtures ,
and I think lead nitrate also . I don't know of any
particular rules or principles in regards to such mixtures
other than to just make 'em and measure the density
to see what you have .
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[*] posted on 4-11-2006 at 06:44


The volume compression Rosco mentioned, if it does happen, will have a small effect on the final density, especially if you add over 50% crystals that don't dissolve. So as a first aproximation you can probably use the average of the TMDs as the TMD of the mix.

Note the "T", as in theoretical? Ever had a look at PETN, RDX etc under a 500x microscope? What we think are single crystals are often *agglomerates* of crystals with trapped air between. Due to the fine structures involved this air gets stirred into the melt, and does *not* rise to the surface like the air stirred in mechanically does. Hence the low density, which can be 25% under the theoretical. :(

Plus, for non-perfect HEs with either impurities, or low thermal stability, very small gas bubbles are generated on heating the melt. These don't escape either, lowering the density of the cast. As an example, if there is HDN in the melt/cast AN mix I described elsewhere, density goes from the theoretical 1.75+ to 1.50 and below. Before solidification, the cast was spongy, I could press it further into the casing and it 'sprang' back (read: expanded outwards slowly).

This property does not have to be a disadvantage. If the effect is not too pronounced, it can make initiation much easier, plus lower the critical dia quite a lot. 25% below TMD is too much though, that's also why I will stop adding HDN for future melt/cast-AN tests.

[Edited on 4-11-2006 by Boomer]
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[*] posted on 4-11-2006 at 11:59


It is so much better if we restrict ourselves within the realm of practicalities. In actuality the very primary purpose of casting an explosive compound or a mixture of explosives is to reach the highest possible density in favor of more brisance. Crystal density of a given explosive is the upper limit to which we can reach under ordinary conditions. In many applications, however, the charge needs not to be necessarily compressed to its crystal density to have effective functioning. A review of most military cast explosives reveals that the densities fluctuate between 1.55 to 1.75gr/cc depending on the nature of the explosive ingredients and their percentage. In other words manufacture of cast explosives essentially means not to drive off all the entrapped air bubbles and the micro-cavities inside. The left micro bubbles within the lattice can greatly facilitate the ease of detonation through their adiabatic compression. So as long as we can go on making cast charges within the mentioned density interval, our products will be brisant enough to be serviceable in many practices. Focusing on PETN itself as the base explosive for a pourable mixture, if the cast density exceeds 1.65gr/cc, the pertinent VOD will go beyond 8000m/s which makes the explosive highly brisant. I think such a density is attainable with ETN and Dinitrodimethyloxamide as the second ingredient for a binary mixture.

P.S I think a good account of ETN is available in “Nitroglycerin and Nitroglycerine explosives” by Naoum. Does anybody have any kind of access to this book??
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Rosco Bodine
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[*] posted on 5-11-2006 at 13:01


The same special crystallization techniques which have
been worked out as industrial methods for producing
clean well formed high density crystals of complementary
mesh sizes for having a high volumetric density as aggregates , are equally applicable to casts as to plastiques for which such methods were developed .

If the process starts with low volumetric density material , then that is what you end up with , unless
is exhaustively milled , extruded , rollered repetitiously
to squeeze all of the entrapped air out , which will be done anyway . But if the starting materials are optimum
then it greatly reduces the manipulation , particularly for a melt . At a certain particle size , the occluded air will
coalesce and rise to the surface , and the density of the
composition will approach more closely the theoretical
maximum .
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[*] posted on 6-11-2006 at 08:39


Just noting, the max density for most HEs is achieved by pressing, not by casting.

And FYI, it is a common misconception that *adiabatic compression* plays a role in detonation transfer. It may play a role in starting a LVD in liquid explosives, but detonation transfer works through *voids* not necessarily gas bubbles. Quoting Jerry once again:

"LE uses interstitial space (which is usually filled with air on earth)
as room in which to spurt hot gases to neighboring surfaces. HE, on
the other hand, uses these voids as volumes through which pressure
can be readily exerted such that PV work can be expended and turned
into heat (hot spots). Some people like to think of this process as
the adiabatic compression of entrained gas because they know that
gases get hot when compressed.

In reality, the HE does not care if there is gas present to compress
or not. Even an empty void acts as a place where heat can be generated
by impact with the same end effect as if gas had been present.

Insensitive HE tends to benefit most from dispersed void. Your ANFO (...)
TNT is another example of an explosive that needs a teeny bit of space.
The cast material will not shoot with a 50 gram primer, but the ground
and pressed material shoots fine with a cap even if it is pressed to
*near* its crystal density (...)

Nearly all commercial explosives rely heavily on entrained gas (void)
for sensitivity and will not shoot without its presence. It sometimes
happens that hydrostatic pressure in boreholes is great enough to
compress the voids to the point where the material loses its primer
or cap sensitivity. For such situations there are many formulations
which rely on microballoons of glass or plastic to preserve void volume.
At least in the case of the glass material the void is a pretty good vacuum."/ end quote

Note the last sentence about micro balloons! And:

"Void volume is the operative phrase. Solids
and liquids are not very compressible and therefore do not readily
allow the conversion of PV energy into heat under the influence of
even very high pressures. Add some well distributed void and the
pressure can now do work on the porous mass and reappear as heat
energy within that mass. This enabling of compression explains
the sensitization of detonating explosives by voids. Note however
that this has nothing to do with the adiabatic compression of
any gas in those voids. If there is gas in the voids, it can reach
astronomical temperatures, but in condensed explosives it makes
relatively little difference.

Please be aware that many books refer to the "adiabatic
compression of air" or "gas" in dealing with bubbles in high
explosives such as NG. I base my statements on this matter on my
own experiments in sensitizing both solid and liquid explosive
formulations. I first used the term "void volume" in a patent I
wrote 25 years ago." / end quote

He's advertising kinepack again..... but seriously, I have thought about this myself too, and came to the same conclusion: If it was adiabatic compression of gas, it would start a *burn* reaction at the bubble wall. This then had to make DDT. A material that has to make DDT layer-wise, again and again for every sub-millimeter, will not shoot even near it's normal VoD. Convinced?
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[*] posted on 7-11-2006 at 00:35


Quote:
Originally posted by Nitrojet
P.S I think a good account of ETN is available in “Nitroglycerin and Nitroglycerine explosives” by Naoum. Does anybody have any kind of access to this book??


Unfortunately, you r belief is wrong: ETN accounts for a mere half a page in Naoùm's work, and teaches nothing you don't know yet...
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[*] posted on 7-11-2006 at 05:07


On occation I really look for information on specific materials and ETN is a shallow pool. Aside from some patents and short (one page or muich less) blurbs in some popular older works, the most material is actually in the boards on the internet (kitchen chemisrty mostly). As you can imagine I am quite familiar with Naoum's work. What's more there is alot more then just "Nitroglycerin & Nitroglycerine Explosives” but he was involved with nitric esters more than anything else. At least that was what he published. At that time in histrory eurythritol was very tough to get....it was very exotic. They nitrated everything and it's dog but those things that got the most study were that which had some commercial future are far as the scientific community was concerned. Exotic materials were mostly left as lab curiosities.



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Nitrojet
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[*] posted on 28-11-2006 at 02:14


I obtained Erythritol in the form of pressed tablets directly from a pharmacy. I’m not sure about the purity or the possible presence of any other additives in my tablets but I observed that the whole material went into solution when treated with strong Nitric acid. With the temperature being kept below 2’C, I got a totally colorless solution with no trace of insoluble material. Crystalline ETN after precipitation from acid was dissolved in 95% Ethanol and then recrystallized in the form of very thin flakes. Before trying to fuse the explosive with Nitropenta, I made some sensitivity tests to evaluate the possible dangers involved with this particular type of the Nitric esters family. To test the behavior of the material to heat, small quantities of ETN was dropped onto a hot plate previously heated to 300’C. In all the tests carried out this way, ETN deflagrated as soon as it came into contact with the plate. But no detonation observed at all. The test continued for the weights as high as 0.4gr but the mere result was a rapid deflagration with a very luminous flame. Impact sensitivity tests was rendered with wrapping 0.35gr of the material in thin Aluminum foils and the small packages made so, was glued against the very smooth surface of a piece of marble. The whole assembly was set perpendicular to the floor and then shot with leaden pellets from a 0.22 air-rifle (Diana 48-52). A distance of 10ft was kept off the target. Of the total 10 tests performed this way, ETN detonated 8 times with a very loud report causing the Aluminum sheath to be shattered into hundreds of pieces. In the remaining two tests ETN actually did not detonate but made yellowish flames resembling that of Mercury Fulminate when fired in open. Considering the fact that the mechanical conditions under which such tests were carried out, were too strong for evaluating the impact sensitivity of a sensitive explosive like ETN, I made several ball drop tests in a simple apparatus which I made myself. It consists of a steel-made cylindrical anvil with a very smooth top to minimize the effects of friction on triggering the charges under test. This anvil is of the height of 1 in and a cross-section area of 0.08 square inch. It is filmy fixed on a heavy steel plate (pin and box connection), steel balls of various sizes so can be let drop on the charges being emplaced on top of the anvil from different heights. In my tests with such a ramshackle apparatus ETN sensitiveness to impact was found to be comparable to that of Mercury fulminate, certainly I did not follow the Military standards for testing of explosives, but Fulminate of mercury gives the same account of impact sensitivity when being tested in the same apparatus. It did not, however, stop me to proceed more and try to make the highly controversial cast-melt of ETN-PETN. Yet I have not managed to get my favorite results with such mixtures as firstly the highest attainable density was 1.58gr/cc and I am about to go as far as 1.65+. Secondly the sensitivity of molten ETN is a big difficulty on my way to Adobe Charges. Once I read somewhere that molten TNT is as sensitive as MF. Based on this piece of fact, what can we say about molten ETN? Anyway, anybody can confirm/Discredit this claim that molten TNT is about as sensitive as Fulminate of mercury?
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[*] posted on 28-11-2006 at 03:53


Drop test apparatus with 2 kg weight, 50% explosion:

TNT at 22 deg. C. --> 60 cm

TNT at 110 deg. C. --> 6.5 cm
TNT at 130 deg. C. --> 4.5 cm

I think the idea that explosives become more sensitive with higher temperature is without exceptions indeed. Don't know exactly for ETN, since it would also depend on the purity and size of the sample. All in all, I do think with ETN @ 80 deg. C you have good reason to be VERY carefull IMHO...:)

[Edited on 28-11-2006 by nitro-genes]
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[*] posted on 28-11-2006 at 07:55


ETN is unique in it's sensitivity in that depending upon how it is re-crystalized, one may increase it's sensitivity to impact. IF the crystals are dense enough the reaction is suprising. The use of methanol for re-crystalization is possible. Acetone is too strong a solvant leaving behind leaflettes and lessing the solid granular crystals that respond well to impact. testing. Ethanol appears to be best suited for large granular crystals. (Bring to boiling, desolve at satuaration level, re-crystalize over ice = large multi-facited crystals; hexagonal shapes predominate)
However if the alcohol is not used at temp extremes the leafletts may appear but they can be shaved / crushed to a point wherein the density level (powder) could be achieved through moderate compression. Quality ETN will yield a marvelous report at 1-1.5 mg level in a small fold of Al foil struck with a hammer upon a steel surface (eye protection is sufficient at that weight - it's only noise). It may be an interesting experiment to clean out a primer cap; use ETN-cast and determine if the blow of a firing pin is sufficient for detonation. & if so would this impart a useful train effect on a cartridge via SBSP or DBSP.




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[*] posted on 30-11-2006 at 13:40


Anybody if he is of the slightest idea of the great power of ETN/PETN mixtures, will definitely think twice about it. a 20gr sample of the cast explosive @ density of 1.58gr/cc shattered a thick conceret block into atoms. The charge was simply put on the concrete block ( 2ft * 1.8ft * 0.4ft) without any confinement and primed with a blasting cap containing 3gr of pressed Mercury Fulminate. Parts of a wooden box which roomed the charge and the concerete block were blown off as far as 200 yards away. Shattering power of the test sample was DISTINCTLY more than those of other HEs in my previous experiments. Now i'm more encouraged towards fining some effective ways of curbing the too downright dangerous sensitiveness of ETN, thus It becomes feasible to have highly brisnat charges for demolition purposes. I have always kept in my mind that premature detonations of even small quantities of ETN can be fatal. as reported in "Encyclopedia of explosives" a British pharmacist experienced his divine existance when he tried to pulverize the material in a mortar! anyway, on my next step I will focus on ETN crystallization for getting crystals of less sensitivity. Methods recommended by quicksilver look promising and worth considering to be tried out in lab.
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[*] posted on 30-11-2006 at 22:09


I don't see what the trouble is!

Just add a few percent of a desensitizer. Parrafin wax works well for this purpose and generally has a melting point of around 50-57 degrees celsius. Davis reports that adding parrafin wax to high explosive, compressed or cast, causes it to become 'distinctly less sensitive to mechanical shock", but still "responds satisfactory to the impulse of a detonator."

Since ETN is oxygen positive just calculate in the additional fuel to the melt.

A few percent of desensitizer may decrease the density and VoD a bit, but will result in more gas release upon detonation, not to mention a much safer explosive.

The addition of a few percent wax to military explosives is a well established practice and has many benefits, incuding low cost.
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[*] posted on 1-12-2006 at 01:15


Phlegmatization is definitely a widely practiced method for desensitizing high explosives. It renders the explosive suitable for press loading while here we are not talking about pressing. The potential danger involved with ETN/PETN cast melts, is the prolonged heating of a highly sensitive explosive which sometimes needs occasional stirring for effective removing of the entrapped air. We can have some crystals of less sensitiveness by either waxing them or controlled crystallization. It is however true that upon heating, such methods can not satisfactorily eliminate the hazards. Molten ETN as stated before can be extremely sensitive to any kind of stimuli. Melting ETN/PETN can be safely practiced for making small charges for detonator fillings but what about a half a pound of a brick demolition charge?! If it was not because of the great power of such mixtures I would easily put this discussion aside trying to enjoy my waxed PETN which is about as powerful as C-4.
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[*] posted on 1-12-2006 at 01:44


Quote:
Originally posted by Nitrojet
I made several ball drop tests in a simple apparatus which I made myself.........


Posted this before but I too done some drop tests on ETN using the rig in the attachment. It regularly detonated with a drop of 30-35cm, PETN was used as a standard for comparison which detonated at a drop of 40-45cm. This was for bicarb washed ETN, not recrystalised. Acetone peroxide for example required only a drop of 0-5cm (it has 5cm increments).

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Boomer
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[*] posted on 1-12-2006 at 03:04


I can understand his worries. If molten TNT is an order of magnitude more sensitive than solid TNT, molten ETN could end up more sensitive than NG or MF. Not a nice thought if working with a pound.

Another thing is Tc (critical temperature). Even PETN will self-heat catastrophically below 100C given enough material. ETN's figure will be below that, possible below 80C (it's melting point). The PETN figure was for a 1m sphere, but still....

Edit:

"... enjoy my waxed PETN which is about as powerful as C-4"

Have you tested both? :P

I mean he's right, density has the biggest impact on brisance. Brisance (det pressure): P ~ d*VoD^2, with VoD being roughly proportional to density *too*, making P~d^3 , i.e brisance goes with the *third* power of the density!

[Edited on 1-12-2006 by Boomer]
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nitro-genes
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[*] posted on 1-12-2006 at 05:19


Quote:
Originally posted by Nitrojet
Melting ETN/PETN can be safely practiced for making small charges for detonator fillings but what about a half a pound of a brick demolition charge?! If it was not because of the great power of such mixtures I would easily put this discussion aside trying to enjoy my waxed PETN which is about as powerful as C-4.


The original idea of Rosco was use of the PETN/ETN meltcast for detonators and small booster charges IIRC, personally I would never cast more than 25 grams at most...:)

With properly recrystallized PETN or RDX you can reach densities of 1.7 g/cc with about 5-6% of inert plasticizer. To fill up the same volume with ETN you would need twice as much. (Even more because rolling the plastique reduces sharp edges on the crystals, further decreasing intercrystalular space). That is why the PETN/ETN meltcast uses as much as 30% ETN. You should further consider that ETN is not as brisant as PETN. Sure, if it comes to total poweroutput, the SLIGHTLY better oxygenbalance would be in favor of the PETN/ETN meltcast. But if it comes to shear brisance, I would place my money on the PETN with 5% inerts...:D

[Edited on 1-12-2006 by nitro-genes]
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[*] posted on 4-12-2006 at 19:03


Sorry to come in with a question at this point, but can anyone comment on what is commonly used as inert binder to produce formable PETN putty mixtures? What about energetic binders that could yield a formable plastique, are there any suitable which exist?

My real question is, are these putty mixtures at a Vod sacrifice in comparison with cast melts such as ETN/PETN where 100% of the mixture is energetic?

As was said above, PETN with 5% inerts may have comparabe brisance against the ETN/PETN melt, but I would assume a formable putty uses a higher percentage of inert binder than 5%...maybe I'm wrong however.

[Edited on 5-12-2006 by AlbertV]
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[*] posted on 5-12-2006 at 02:27


VoD does suffer from inerts, but less than one would think. The 9% inert binder/plasticiser in C-4 do not lower VoD by 9%. Semtex has up to 30% inert crap (rubber, oil, ...) btw, but is not slowed down 30%. Instead, all materials have a "characteristic velocity" which enters the calculation of the resulting velocity of the mix. Air (voids, empty space between crystals) has 1.5 km/s, most inerts used as binder are around 4-5 km/s. This does not mean they speed up slow HEs which are below that speed if pure :P

Also look here: http://www.sciencemadness.org/talk/viewthread.php?tid=5469#p...

And no, I won't say what is used. Search for yourself!
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[*] posted on 5-12-2006 at 03:22


Quote:
Originally posted by AlbertV
I would assume a formable putty uses a higher percentage of inert binder than 5%...maybe I'm wrong however.
[Edited on 5-12-2006 by AlbertV]


With 5% binder it behaves incredibly stiff, but can be kneeded with some force without losing coherency. When kneeded too long the density will decrease slowly, just like with C4 and it will become more spongy due too entrapped air. The same crystal fraction with 10% binder is much more mouldable and can be shaped easily, though density is somewhat lower than the theoretically attainable 1.68 g/cc... (usually around 1.6 g/cc instead)

An ordinary crashing in water yields crystals that need about 30% binder to fill all voids, just like the cheaply produced semtex uses...
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Microtek
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[*] posted on 7-12-2006 at 05:20


Nitrojet, on the first page of this thread you mentioned using hexamine, HCl and oxalic acid to synthesize dimethyloxamide. Could you elaborate on this please?
I have experimented a bit with the same dinitrodimethyloxamide/PETN compound and ran into the same problems with much lower density than expected, but due to the difficulty of producing ethyloxalate from esterification of oxalic acid with ethanol, I never got far.
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