Sciencemadness Discussion Board

Confusion over power and velocity.

Deceitful_Frank - 5-11-2005 at 12:24

Hello all, I am posting this thread to try to make sence of the results gained from two of my most powerful detonations. Hoping that some knowledgable members can shed some light.

It concerns ANNMX charges and their effect on two sections of a concrete wall 3 feet high and 18 inches thick. I am STILL trying to perfect the mix and I wanted to compare two charges of approximately the same mass though of different densities and sizes, 1.0 and 1.1g/cm3.

The first charge was detonated a month ago, 280g ANNMX density 1.0g/cm3. The one I wanted to do last night would have been approximately the same mass (275g) in a 250ml pot at 1.1g/cm3 to see if the extra density gave more shattering power and for that matter, if it would still be sensitive enough to fire from the same 1 gram HMTD that I used previously.

All didnt go to plan. I activated, baked and ground my AN twice and added the sensitizer/fuel mix though due to clumsiness I added more NM and xylene than intended and this gave a mix of approximately 78% AN as apposed to the 81% needed for oxygen balance. This didnt bother me however as a slightly fuel rich mix would just give some CO and less red NOx gases... not a concern.

When it came to loading the cylindrical pot however, I got 265g evenly pressed in there but with 10 grams to go, it was becoming abit of a struggle using the back of a spoon to push the composition in. I decided to call it a day and go with a density of just over 1.05g/cm3. I cycled at midnight in the rain to my test sight and using an Al tube to extract a narrow core, inserted my waterproofed fused cap. Replaced the lid and sealed it all up with blu-tack. I then lit the fuse and retired to 30 metres.

The charge detonated some 15 seconds later with the usual yellow orange flash and thundered off across the estuary returning with the expected echoes and rumblings, I was on the phone to a freind who was listning outside his house some 2.25 miles away and he heard it faintly some 10 seconds later. The sound was low, clean and substantial but lacking in the high pitched "loudness" of the previous charge a month before. The blast was felt strongly but didnt leave me feeling shaken as did the previous charge and as I walked through the darkness and approached ground zero, I wasnt expecting to be bowled over by the damage to the wall!

This is when I was left feeling suprized, excited though a little confused. The damage to the wall was extensive. The blast had pounded a 7 inch+ wide hole 1.5 inches deep and left it filled with concrete debris and dust. Radial and concentric cracking was deep and extensive and a 16 X 5 X 3 inch section of the outside of the wall had fallen away onto thick grass but was found broken in two. Everything was warm to the touch.

This is where you guys come in...

Is it possible for an explosion to be more powerful yet quieter?
Is there really a (and if so what is the) relationship between the power and brisance of an explosion and the loudness and quality of the sound it makes?
Did the charge just SEEM quieter due to lack of high frequencies from a cleaner firing more evenly packed charge?
Was the charge just LESS powerful due to a fuel rich mix with less gas volume and loudness but more brisant and shattering than the first?
Should I shoot for more CO in my detonation products for extra brisance when I want to shatter very hard things but go for all CO2 and O2 balance for heaving or when I just want a REALLY LOUD bang?

Thanks in advance :)

[Edited on 5-11-2005 by Deceitful_Frank]

Attachment: Tests.txt (2kB)
This file has been downloaded 1031 times

12AX7 - 5-11-2005 at 12:43

FYI, you should shoot for CO, not CO2, since CO is lighter and takes up more space than CO2 = more pressure. The enthalpy of C --> CO is greater than CO --> CO2, also (IIRC).

Tim

Rosco Bodine - 5-11-2005 at 12:51

Quote:
Originally posted by Deceitful_Frank
Should I shoot for more CO in my detonation products for extra brisance


Only if you believe that the behavior of explosions and other chemical reactions are somewhat influenced by the laws of physics and a little thing called thermodynamics :D ......

otherwise go ahead and believe in the power of oxygen balance defined in terms of complete combustion to CO2 , as not being just an air quality standard for mining operations .


Quote:

when I want to shatter very hard things but go for all CO2 and O2 balance for heaving or when I just want a REALLY LOUD bang?

Thanks in advance :)


Just go for complete combustion when minimal smoke and air pollution is the goal . But when power density and intensity is the primary objective ,
then don't give a hoot and do pollute :D

a_bab - 5-11-2005 at 14:15

I'm assuming you can get some piuctures of the effect on the concrete wall. If you can, please get them and post here.

For military use, the explosives could be toxic, they can produce noxious fumes etc. Who cares? They are supposed to kill people anyway. TNT for example makes a black smoke on explosion due to the non oxigen balanced formula, leaving some unburned carbon. Still, it is more brisant thus more effective for cutting steel then the TNT/AN mix, which could be perfectly balanced.

Civilian explosives should follow certain standards to be approved. Kinepak is one of them, hence the oxigen balance is close to the ideal in order to avoid the toxic effects of the byproducts.

Deceitful_Frank - 5-11-2005 at 15:13

Ok well here are three pictures of the damage that the previous 280g charge of oxygen balanced ANNMX made to the wall a month ago.
You can see the small deep hole and the cracking though the wall did stay intact.
I will try to get to the detonation sight to take photos in daylight of the results of my latest fuel-rich charge soon :)

280g_ANNMX_oxygen balanced for CO2.jpg - 483kB

12AX7 - 5-11-2005 at 16:58

Quote:
Originally posted by a_bab
Who cares? They are supposed to kill people anyway.


Well, the military engineering corps might have an issue with that statement..

Tim

a_bab - 5-11-2005 at 17:09

When dealing with military EVEYTHING is supposed to be dealig with killing. It is that simple. Defensively or offensively, "they" are supposed to inflict maximum of damage.

The explosives in army are the most powerfull, and they really don't pay attention to the price of it or the toxicity. Well; obviously they are not going to use methyl nitrate just because is very brisant (although they did it).

Chris The Great - 5-11-2005 at 18:59

See, I always thought that CO2, with an enthralpy of formation of -94kcal/mol, would give more energy release than CO, with -24kcal/mol.

Shattering effect is dependant more on the detonation shockwave than the amount of gas released. Also, higher molecular weight of the products means a higher Gurney energy, translating into better performance. (Gurney energy, as I understand it, is a measure of how much energy the detonation shockwave transfers to the surrounding material, however I am not 100% sure on this. I am sure a higher rating gives higher performance and heavier combustion products give a higher energy)

Your increased performance could be from a larger amount of NM and greater density. AN may give more energy output to the mixture but it certainly lowers the VoD.

Axt - 5-11-2005 at 20:45

Theres good reason for aiming for CO balance rather then CO2 if your oxidiser is less powerful then what your mixing it with, as Chris's last sentence suggests. Also with aluminized explosives where CO2 will be reduced to CO.

But generally, all other things being equal CO2 will hold more brisance & power then CO. Try comparing the nitramines MEDINA (CO2) with RDX (CO), even though MEDINA holds a lower density it has more brisance (in SC's) and not many things can compete with its power (bal. mortar/Pb block). EDNA is not quite CO balanced and falls considerably short of MEDINA in VOD, brisance & power.

One could argue that structure influences this, but OB is also going to influence structure, so its a null point as long as your comparing the same explosive groups.

The noise produced has no bearing on power or brisance, and has more to do with atmospheric conditions then anything else.

Lothrop, W & Handrick, G. "<a href="http://scimadpic.webtop100.net/banners/relationships-between-explosive-groups.pdf">The relationship between performace and constitution of pure organic explosive compounds</a>" Chem. Rev.; 1949; 44(3); 419-445.

Koch, A. "<a href="http://scimadpic.webtop100.net/banners/relation-vod-and-gurney.pdf">A Simple Relation between the Detonation Velocity of an Explosive and its Gurney Energy</a>" PEP 27, 365-368 (2002)

Rosco Bodine - 5-11-2005 at 23:09

Looks like its time for doing some damage tests on steel plates :D

Optimum brisance for non-homogenous mixtures of an explosive fuel with an explosive oxidizer is a whole different story from oxygen balance for molecular explosives .

For example , if you saturated nitromethane with picric acid in solution ,
it would be a homogenous mixture of
two explosive fuels having a very negative oxygen balance and would produce a lot of CO . However it would be extremely brisant , by itself likely more brisant than in mixture with any amount of NH4NO3 , which would likely be a diluent of its brisance , even though the
total energy output of all " combustion products " , tallied up for many microseconds following the peak detonation , would give a higher total
" heat value " for the alternative mixture with the nitrate .

The charge with the terrible oxygen balance would be better for cutting steel ,
or for shattering rock or concrete , but for heaving tons of earth the mixture with the nitrate would show the greater total energy , only spread out over a longer duration of time at a lower intensity of
detonation plus combustion pressure .

Its something like the difference between
an instantaneous very rapid spike of intense energy , compared with a slower
and much longer duration fireball having greater total energy but much lower of
any " instant average " intensity microsecond by microsecond from the
time of detonation . For brisance the velocity , the rapidity of the detonation
with an increased intensity of pressure is what does the damage , even though the
process of detonation is finished more quickly leaving incompletely burned fuel .

So which composition does more and better work on the target , depends entirely on the sort of work you are intending it to do .

But for molecular explosives or homogenous mixtures , then you will more likely see a benefit to the brisance at oxygen balance for CO2 where the more rapid formation of the CO2 is possible in the core detonation reactions ,
not as a secondary reaction .

Axt - 6-11-2005 at 00:33

I'm a believer in oxygen balance :D

Yes, I see the point thats being made picric acid is going to be more brisant then PA/AN, simular case with ANNM but here it has other issues where a certain percentage of AN has to be used for sensitivity reasons.

BUT when using two explosives of simular properties I think its advantageous to use CO2 calculations. It would be more suitable to look at the difference between NG & NC/NG or more rightly between sprengel explosives where both individual constituents are explosively inert. For example mix HNO3/nitrobenzene to CO & CO2 and perform plate dent tests, I've never seen an example of such a comparison but I'll place my money on CO2 :D

Bringing discussion back to the original post, your constructing the detonators thus differences in initiation and the difference in confinement and charge geometry are having a much more significant effect then trying to relate the difference to a couple % of NM.

[Edited on 6-11-2005 by Axt]

Rosco Bodine - 6-11-2005 at 05:23

As a general rule I think oxygen balance is overemphasized in importance in terms of achieving optimum brisance , even though the generality would hold true for total power output economy . There are many exceptions which will be found where brisance and oxygen balance are not optimized even in the same direction .
Mixing sulfur in small percentage with TNT is one of the exceptions which immediately comes to mind , and TNX is another modifier which also increases brisance for TNT ....both of which worsen the oxygen balance which is already bad ,
but increase the brisance of TNT even though the oxygen balance is worsened .

I believe that there are so many exceptions in both the negative and the positive direction for oxygen balance in relation to brisance , that the relationship is uncertain to be any sort of widely general rule , but only applies in limited and special circumstances .

It may only apply as a small benefit in peculiar compositions where the explosive properties are about equal for both the explosive fuel and the explosive oxidizer , mixed in proportions where the
added energy from achieving an oxygen balance results in a synergistic mixture .

So one might realize the increase from an oxygen balanced mixture of ETN and RDX , each of which are closely matched in
brisance when independent of each other , while the synergy derived from an
oxygen balanced mixture of ETN and nitronaphthalene would likely reduce the brisance below ETN used alone , even though the total heat output would be increased over ETN used alone .

So , while the quest for oxygen balance has some merit , it is a highly qualified and idealized circumstance where oxygen balance will determine the mixture for achieving maximum brisance . More often
oxygen balance will likely not be the one factor which determines maximum brisance , but it will often be found instead to only be the determinant for total heat output irrespective of brisance .

There are other factors to be considered beyond what are the stoichiometric proportions for achieving an oxygen balance . There is probably a slope which could be graphed for various mixtures , similarly as can be done for mixtures used as initiators , where the peak brisance for the mixture is achieved , and that point on the slope will very likely be at a different point from where is the oxygen balanced mixture , simply to confound the formulator .

Deceitful_Frank - 6-11-2005 at 15:42

Well I've been back to the test site, albeit under cover of darkness and have surveyed the damage and taken some pictures. I attatched them to this post so you can peruse at your leisure.

Well guys... you've certainly given me alot of info to take in and I have drawn a few conclusions. Firstly I dont believe that an extra 2% of fuel in the mixture really would have made that much of a difference to the power and brisance of the charge, all things being equal though there were several other small differing factors which may have added to each other and caused the increase in damage to the wall over the previous charge.

The second charge was much more homogenous due to two cycles of activation and grinding, the baked AN was noticibly finer and I spent more time mixing and incorporating the NM and xylene.

I beleive that the second charge had more efficient geometry as it was wider and shorter being 1.5 times as tall as it was thick. The first charge was twice as tall as it was thick.

The second charge was slightly denser but more importantly it was an even density throughout due to the ease of packing a regular cylinder compared with forcing ANNMX into the narrow neck of a plastic bottle.

As for the on going issue of oxygen balance, I see both sides of the argument but having spent considerable time working out a good ratio of AN, NM and xylene that balances, mixes easily to a dry sensitive powder that fires reliably I think I will stick to what I know for now. maybe I could increase brisnce slightly by making the mix more fuel rich but NM and Xylene are very expensive for me and my 24:5:1 ratio works just fine. I'll be concentrating on making and firing the most homogenous and dence explosive I can using this mix.

As for the lower perceived sound level and blast felt... well, think I'll just put that down to a freak of nature! I know that atmospheric conditions have a huge influence. Think that the wall tells me all I really need to know :)


Any more thoughts and ideas would obviously be gratefully received. Thanks for all your help :)

[Edited on 6-11-2005 by Deceitful_Frank]

[Edited on 6-11-2005 by Deceitful_Frank]

[Edited on 7-11-2005 by Deceitful_Frank]

265g ANNMX fuel rich for CO, density 1.05.jpg - 422kB

simply RED - 12-11-2005 at 05:28

The optimal explosive will have CO2 balance. It is absolutely false that CO formation gives more energy than CO2.

CO - 110 kJ/mol
CO2 - 393 kJ/mol

Formation of:
100g CO - 393 kJ
100g CO2 - 893 kJ

With 32g O2 (1 mol) and 2 mol C - 2 mol CO - 220 kJ
With 32g O2 and 1 mol C - 1mol CO2 - 393kJ

The OB is importaint! Certain explosive to be effctive - should have "unreacted" oxigen (-NO2, (CLO4(-)...). (Not C=O, C-O, R-O-H)
The energy released for certain explosive is also influenced by the heat of formation of its molecule. With other words - more cyclic stressed molecule will be more energetic.

When we use ammonium nitrate explosives, the upper statements shoud not be interpreted directly. For example ANFO - 3% liq.CH2 fuel gives the highest sensitivity, and we - seeking more sensitive product could sacrifice % of the energy released....

Brizance is not fully dependent on energy output, so no conclusions should be made for it, having only this data.

[Edited on 12-11-2005 by simply RED]

Rosco Bodine - 12-11-2005 at 06:13

Quote:
Originally posted by simply RED
The optimal explosive will have CO2 balance.


That very much depends on what you define as being " optimal " about the explosive and what is the nature of its composition . Is your optimal explosive
needed to be optimized for brisance only , or for total heat and gaseous products without regards to velocity ? What is optimal depends on the intended purpose . Oxygen balance is often part of a three or four dimensional system describing performance suited to a task which can vary considerably , such as the difference between certain mostly straight TNT compositions in comparison with oxygen balanced ammonals .
Quote:

It is absolutely false that CO formation gives more energy than CO2.


True statement , but it is equally true that total energy has zero to do with brisance ,
which is all about the rapidity of rise time to a higher average detonation pressure
during a brief time window .
Quote:

CO - 110 kJ/mol
CO2 - 393 kJ/mol

Formation of:
100g CO - 393 kJ
100g CO2 - 893 kJ

With 32g O2 (1 mol) and 2 mol C - 2 mol CO - 220 kJ
With 32g O2 and 1 mol C - 1mol CO2 - 393kJ

The OB is importaint! Certain explosive to be effctive - should have "unreacted" oxigen (-NO2, (CLO4(-)...). (Not C=O, C-O, R-O-H)
The energy released for certain explosive is also influenced by the heat of formation of its molecule. With other words - more cyclic stressed molecule will be more energetic.

When we use ammonium nitrate explosives, the upper statements shoud not be interpreted directly. For example ANFO - 3% liq.CH2 fuel gives the highest sensitivity, and we - seeking more sensitive product could sacrifice % of the energy released....


Ammonium nitrate explosives are not the only exception . The entire generalization about oxygen balance governing optimization of an explosive is like arguing which is better , apples or oranges , which raises the question better for what ? What are you going to do with them ?

Counting calories is relevant to total energy released over a longer duration of time , such as would describe the total
work possible to be done by an explosive
heaving earth from a crater , but a lower count of calories for a more oxygen poor composition may well better decsribe a
variation of the same composition more suited for cutting steel than for heaving earth .

Chris The Great - 12-11-2005 at 15:03

Quote:
Originally posted by Deceitful_Frank
The second charge was much more homogenous due to two cycles of activation and grinding, the baked AN was noticibly finer and I spent more time mixing and incorporating the NM and xylene.

I beleive that the second charge had more efficient geometry as it was wider and shorter being 1.5 times as tall as it was thick. The first charge was twice as tall as it was thick.

The second charge was slightly denser but more importantly it was an even density throughout due to the ease of packing a regular cylinder compared with forcing ANNMX into the narrow neck of a plastic bottle.


Well that would certainly explain the difference! You have more explosive in contact, so of course more area will be hit with the detonation shockwave. The explosive is better mixed and of equal density, which will produce a good detonation compared to varying densities and poor mixing.
Those factors would make far more difference to the explosion than a few % difference of the AN/Fuek ratio.

simply RED - 13-11-2005 at 08:23

"it is equally true that total energy has zero to do with brisance "

Brizance could well be described by the pressure created by the detonation front, when travelling through the explosive (Pcj). This exact pressure acts on the target when there is a contact between it and the explosive.

Pcj depends from :
1. Density of the explosive.
2. Volume (and other physycochemical characterystics of gasses produced by weight part .
3. Total energy output (per weight)....

Rosco Bodine - 13-11-2005 at 09:08

Brisance is purely a function of kinetic energy delivered to the target and it is
* very much * a time dependant , velocity related effect .

The " rise time " and peak intensity for the initial pressure pulse are definitive factors for brisance , but are irrelevant to total energy which is released over longer time .

Again brisance has nothing to do with
" total energy " .

Brisance is an effect manifested during a brief time window of microseconds , while
" total energy " is an effect manifested over tens of milliseconds or even more . Total energy isn't realized until all the rocks stop falling , but brisance is what cracks the rock into " how many and how small fragments " before they are moved a millimeter .

Don't you understand the difference ?

You can believe the myth there is a non-time dependant relationship between total energy and brisance if you like ,
and recite math to describe irrelevant
" total energy " calculations ad infinitum ,
but that won't change the reality of what brisance is , and that it is independant
of " total energy " .

vulture - 13-11-2005 at 12:45

I'm with Rosco here. Unless you are detonating something in a limited confined space, where explosion heat also contributes to the total overal pressure, optimum brisance will not be achieved by aiming for CO2.

There are also many complex equilibrium reactions in the detonation front like the Boudouard (sp?) equilibrium, etc.

Rosco Bodine - 13-11-2005 at 14:20

IIRC there is an underwater test which can be used to quantify the
" bubble energy " of explosives and display on an oscilloscope the pressure
gradient sensed by a piezoelectric transducer in the test tank , with the trace
following a very small time interval which
can be captured by the oscilloscope .
Other sensors can detect the volume increase for the water in the tank which is being displaced by the bubble of gases from the detonating explosive . By studying the data from the sensors , the
rapidity and intensity of the pressure rise
can be quantified and the brisance of the explosive can be measured , according to the rapidity of the rising pressure during the first few microseconds after detonation , while the *average * of * all * the readings across the duration of the entire trace describes the
total " bubble energy " or " total energy "
for the explosive .

Another test of brisance is the solid lead block test and it is not unusual for many explosives having much higher total energy , to have much lower brisance than other explosives having much lower total energy , but never the less showing the higher brisance . While it is not an absolute rule that it is always the case
that oxygen balance has no bearing on the brisance , it is often the case that the
oxygen balance is irrelevant . There is a school of thought that most of the more instantaneous energetic properties of many explosives is associated with the nitrogens of the molecule , but that view
has its exceptions also depending upon the particular energetic material , some of which may still be explosive yet contain no nitrogen and perhaps no oxygen either .

Kinepak Astrolite Hydrazine Ooh My

franklyn - 3-7-2006 at 13:18

An very interesting usenet I found , with sample threads _

http://yarchive.net/explosives/index.html

http://yarchive.net/explosives/astrolite.html

http://yarchive.net/explosives/hydrazine.html

http://yarchive.net/explosives/aluminum_powder.html

http://yarchive.net/explosives/kinepak.html

.

[Edited on 3-7-2006 by franklyn]