Sciencemadness Discussion Board - low order detonations

low order detonations

Ral123 - 1-6-2012 at 04:30

I'm posting this topic bacause I'm little confused. I was reading about nitro and stragnely different people made tests-liquid, maximum density in steel pipe 30-45mm and it says with blast cap No8 low velocity. With picric acid 8000+. With even more petn less then with picric acid. Supprisingly there is low velocity for egdn too. In this forum I've red about etn/petn cast going low order too. I haven't had low order problems, but I'm wondering about the pattern witch they folow. Does this happen only to the sensitive high power compositions? Most of us know that MeNO3 can be initiated by it's own vapours, but what happens with the det. vel. then? There is some difference if it's by a spark ot by hot wire or may be exotic platinum coated nail-ignition. Are only rdx/tnt and few more millitary explosives low order detonation proof? Will mixing the thing with inerts till sensetivity is lowered make it low order detonation proof?

dann2 - 1-6-2012 at 05:37

The exotic Platinum-coated-nail-ignition thing sounds interesting!

Simbani - 9-1-2013 at 18:37

MeNO3 detonates at nearly full velocity with the smallest available cap, it has the highest known sensitivity to initiation and will not go low order if it get´s going by whatever activation. I had a low velocity det once in a lightly confined (straw) detonator with highly pressed ETN. It was definately because back in the days I used SA DS(~150-250mg), therefore weak impulse. The one with 0,7g made a dent about 2-3x bigger and deeper than the low-order 1,0g ETN (on the same plate with same casing). So i can be sure it was a low-order detonation.

" I was reading about nitro and stragnely different people made tests-liquid, maximum density in steel pipe 30-45mm and it says with blast cap No8 low velocity. With picric acid 8000+. With even more petn less then with picric acid."
So there is it, different people made the tests. I bet that´s the reason that more PETN yields a lower VoD..

And it´s not only the high power compositions, look at AN/X (where X can be anything what can burn). A too weak shock gives a low-order det. only a big booster kindles the true power. The reasons for low order tendency are numerous, that´s for sure.

Ral123 - 10-1-2013 at 00:34

MeNO3 detonates more efficiently then NG with cap No1, according to one of the more popular books. With glass confinement both are much more prone to maximum velocity. In my opinion mixing the nitric esters with secondarys like tetryl and hexogen will greatly reduce the low order tendency. Did you know that 75% kizelghur/NG dynamite is said to detonate at maximum velocity(5000-6000) with No1 cap.

AndersHoveland - 10-1-2013 at 22:17

Tetrazene is very susceptible to low order detonation, if it is not adequately initiated. Its detonation velocity can vary between 1500 to more than 4000 m/s, depending on how it is initiated. For this reason, tetrazene was generally only suitable as a booster charge, not as a primary by itself. I also have read of composition using tetrazine with xylitol-pentanitrate, which is supposedly much more reliably initiated, and potentially suitable as a primary.

Dany - 28-8-2013 at 02:22

Almost all liquid explosive (e.g., NG, methyl nitrate, NG-EGDN) can undergo low velocity detonation (LVD). the explosive material is partially consumed in the detonation wave. the remainder of the material is scattered around. The 1-dimensional Chapman-Jouguet detonation theory don't predict this behavior of low order detonation, only high order detonation is proposed by this theory. Initiation of liquid explosive with a weak initiator can generate LVD. Also, LVD is seen in detonating liquid explosive in cylinder near their critical diameter. LVD can have velocity on the order of 2 km/s. It is important to say that both stable and unstable (pulsating non-steady detonation wave) LVD can occur. The confining material in the cylinder, is an important factor that determine unstable or stable LVD. It has been shown [1] that when the sound speed in the confining material is lower (e.g., lead) than the sound speed in the explosive, an unstable LVD is generated . detonation in aluminium or steel almost always produce stable LVD. The mechanism proposed for this observation is that precursor wave propagate in the confining material ahead of the detonation wave, creating cavities resulting from the cavitation of liquid explosive due to expansion (remember that a fluid cannot support tension wave, liquid will cavitate under tension wave) which play an important role (may be as a hotspot) in sustaining the delayed detonation wave. but as a general conclusion LVD is produced when liquid explosive are initiated with weak iniator at nearly critical diameter.

Reference:
[1] detonation in liquid explosives-the low velocity regime, R.W.Watson, C.R. Summers, F.C. Gibson, and R.W. Van dolah, 4th international symposium on detonation, page 117.

Dany.

[Edited on 28-8-2013 by Dany]

AndersHoveland - 28-8-2013 at 04:03

One strategy to make these compounds resistant to low order detonation is to mix in another explosive that is not vulnerable to undergoing a lower order detonation.

[Edited on 28-8-2013 by AndersHoveland]

dangerous amateur - 28-8-2013 at 08:54

Quote:

cap No1

Do you know what these numbers mean or what equivalent amount of what stuff they represent?

Quote:

It was definately because back in the days I used SA DS(~150-250mg), therefore weak impulse

I find that very much for ETN...
What do the experts say, how many DS would you put in your caps for best reliability?

Dany - 28-8-2013 at 09:33

numeration of blasting cap indicate it's strength. there are 8 strength ranging from No 1 (weakest) to No 8 (strongest). Indeed as the strength increase so dose the quantity of priming charge. No 6 blasting cap contain 1 gr of 80/20 mercury fulminate/KClO3 while No 8 blasting cap contain 1.6 gr Hg(OCN)2 and 0.4 g KCLO3. we can notice that this quantity is not small, because these blasting cap are called single component cap. the primary explosive can be reduced to few hundred of milligrams (e.g, 200 mg of lead azide) coupled with 0.5 g of secondary explosive (e.g., PETN). these are called compound blasting cap and are much stronger than single component cap (because of the presence of secondary explosive acting as a base charge).

ETN has been used in old compound detonator. for making such detonator see the attachement below. for more information on blasting cap see Encyclopedia of Explosive and related items, Vol.2, page B-185.

Dany.

Attachment: detonator.pdf (79kB)
This file has been downloaded 609 times

[Edited on 28-8-2013 by Dany]

Fantasma4500 - 28-8-2013 at 09:47

i know a 'No 8' cap would be approx 3g in total of 10:90 lead styphnate

ETN (fluffy, pressed or cast?)
we had a visit from an explosives expert but in my country im not sure how much you can take for word, he didnt mention total amount although, but i have heard several places (nope, cant remember sources) that its about 3g in total

he showed where a blasting cap was set off in a metal can (steel?) and the sure pattern of the aluminium fragments could be seen, very interesting, nearly artistic.. although something makes me wonder... wouldnt at least 2.5g PETN be enough to remove a such can? can had diameter of appox 15cm

Ral123 - 28-8-2013 at 11:15

I guess you need a booster for almost every maximum density/high density material. TNT, TNP, RDX-PBX, OCTOL, Trtytol. The nitric esters don't need that much. Few grams crystaline RDX and they are UP.

Dany - 28-8-2013 at 11:33

initiating high explosive charge is a complex topic and depend on many factors not only on the iniator. The sensitivity of an explosive material is a chemical and physical problem. Every one knows that nitroglycerine is sensitive, but this feature is not of chemical nature only (e.g, presence of weak -O-NO₂ bond in nitric ester). in fact, one of the experiment done on nitroglycerine shows that removing microscopic bubble gas from the liquid, decreases the sensitivity of the explosive. Of course, explosive at theoretical maximum density (TMD) are harder to initiate due to the lack of active site that form hotspot after the passage of detonation/shock wave. In some cases, it is advisable to add solid material to increase sensitivity. for example, pure nitromethane is very hard to initiate (even with an intermediate booster charge) but adding glass micro-balloon (GMB) to the solution increase the sensitivity of liquid nitromethane. 3% Poly(methyl methacrylate) (PMMA) are added to prevent the GMB's from settling-out. Some time nitromethane can be sensitized by chemical mean (e.g., adding amine or acids). The physical state of the material (fine or coarse) will affect the sensitivity of explosive. The type of confining material, temperature...all affect the pressure threshold for the initiation of high explosive.

Dany.

Ral123 - 28-8-2013 at 11:42

I've heard that if you confine your stuff with maximum density, hard material like glass, the high velocity is easier to obtain. Do you know how kizelghur makes NG to be set off reliably with weak initiators?

Dany - 28-8-2013 at 12:04

adding fine glass or fine sand will increase sensitivity/lower the critical pressure of initiation. compared to pure material, the addition of sand or glass will serve to attain maximum velocity in shorter time or decreasing what we call run-up distance. suppose a stable detonation wave (constant detonation velocity) is achieved after 10 microseconds of the entering of the shock wave into pure explosive, the time will be for example 1 microsecond for explosive mixed sand/glass material. Indeed the inert solid is added in small proportion because after a certain limit you loose explosive energy because you are diluting you explosive charge with inert stuff. Remember that in order to increase sensitivity of explosive by mean of inert solids, the latter should have a melting point above of that of the explosive material. if the melting point of the added inert solid is low, it will melt after the passage of the shock wave. Melting will consume energy from shock wave and then the latter will fade to a point were chances of initiation is almost impossible. However, high melting solids tend to concentrate the energy from shock wave around them, and hence rising the temperature well above the remainder of the explosive charge. the chemical reaction start at this point (called hotspots) forming many waves. these waves will coalesce forming a detonation wave. this is the heterogeneous mode of initiation in detonation theory. pure liquids and single crystals explosive obeys the homogenous mode of initiation.

Dany.

dangerous amateur - 30-8-2013 at 05:47

I meant especially the No.1 Cap.

Concerning mercury fulminate - have you compared this to DS?
DS seems to be the perfect stuff if it wasn't so static sensitive.

That they are both weak does not bother me. I want the "safest" stuff. I don't care to spend 400mg or more to initiate ETN boosters.

Ral123 - 10-9-2013 at 09:15

Quote: Originally posted by Dany

adding fine glass or fine sand will increase sensitivity/lower the critical pressure of initiation. compared to pure material, the addition of sand or glass will serve to attain maximum velocity in shorter time or decreasing what we call run-up distance. suppose a stable detonation wave (constant detonation velocity) is achieved after 10 microseconds of the entering of the shock wave into pure explosive, the time will be for example 1 microsecond for explosive mixed sand/glass material. Indeed the inert solid is added in small proportion because after a certain limit you loose explosive energy because you are diluting you explosive charge with inert stuff. Remember that in order to increase sensitivity of explosive by mean of inert solids, the latter should have a melting point above of that of the explosive material. if the melting point of the added inert solid is low, it will melt after the passage of the shock wave. Melting will consume energy from shock wave and then the latter will fade to a point were chances of initiation is almost impossible. However, high melting solids tend to concentrate the energy from shock wave around them, and hence rising the temperature well above the remainder of the explosive charge. the chemical reaction start at this point (called hotspots) forming many waves. these waves will coalesce forming a detonation wave. this is the heterogeneous mode of initiation in detonation theory. pure liquids and single crystals explosive obeys the homogenous mode of initiation.

Dany.

Thanks, for your scientific answers.
Would you suggest lead confinement, when it's desired to have a reliable product, that would force great pressures at the opposite end of the initiation?

Dany - 10-9-2013 at 09:56

Ral123,

i don't recommend lead, because it has low yield and tensile strength compared to steel. so the resistant of steel is better than that of lead.

Dany.

Ral123 - 10-9-2013 at 10:04

I agree on that when it comes to deflagrations, for example FP confinement or NG at low diameters/speeds. But when it comes to HE's I didn't think the tensile strength will matter, specially at 200+k.bars of liquid/cast nitro ester.
http://www.youtube.com/watch?v=6rRg7ksNaZs
Here the tough steel container became dust, that did nothing to the fragile objects, and that's Tetryl, it's not even ETN.

Dany - 10-9-2013 at 10:35

Ral123,

the idea of steel being totally pulverized or vaporized is not true. Detonation wave don't have the energy or the time to vaporize or completely pulverize metals. if this was the case (vaporization and pulverizing) explosive will become useless in artillery shell because only tiny fragment will be produced which have little penetration ability and looses energy in an exponential manner with distance to the target (P.S. velocity of large fragment also decay in an exponential manner). A normal cylinder like the one in the video, will undergo a natural fragmentation generating large, medium, small and very small fragment. the distribution of fragment size can be predicted based on Mott equation or other relationships [1]. first the video on youtube is filmed in the dark (which is the worst situation for analyzing an explosive event).
The conclusion at the final of the video is wrong because if he didn't find fragment in the items (bottle, wood...) around the explosive charge after detonation this doesn't mean that fragment are not produced. first the arrangement of the test is wrong, the item should completely surround the explosive charge (like plywood panel) and the explosive charge should be in a vertical position so the fragment are sent radially. when you lie the explosive charge on one side, the fragment tend to enter the earth and some will go upward. don't forget that there is a probability hit when a fragment is intended to engage a target. I'm sure that if he repeat test in the right condition, he will find a distribution of fragment size.

[1] Tactical Missile Warheads (Progress in Astronautics and Aeronautics) J. Carleone.

i recommend you to read the book of reference [1]. this book is an important book on warhead and fragmentation phenomena. you can download the book from here.

http://libgen.net/view.php?id=918393

photos of professional detonation test arena:

also, a nice video from oregon ballistic lab showing the explosion of car bomb loaded with ANFO. at slow speed and @12-13 second one can see how the fragment surpass the shock wave in air, the shock wave looses energy faster than the fragments, so the fragment at certain point will be faster and surpass the shock wave in air.

http://www.youtube.com/watch?v=UPSz62a-C44&feature=c4-ov...

Dany.

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[Edited on 10-9-2013 by Dany]

Ral123 - 10-9-2013 at 11:51

I thought warheads are with metal cases so that the same volume will generate more mass, flying around, and secondary are the fragments. My impression so far is that in larger diameter charge, no matter how powerful the material is, there will be significant fragments( http://www.youtube.com/watch?v=w0Xk-TgGcDE ). Also, thicker container, doesn't mean bigger fragments, till a certain point.
This test in a brittle arrowtube gave high velocity micro particles( http://www.youtube.com/watch?v=luj3NdyBisA ) I'm not sure if the brisanse was low, or fragments were genereted because the material was pressed and micro hollow spots were created, preventing even pulverisation.