Sciencemadness Discussion Board

Stun grenade explosive : what ?

metalresearcher - 15-12-2014 at 13:26

During the Lindt Cafe raid in Sydney, the police used Stun Grenades to distract the hostagetaker Man Haron Monis (and finally kill him). On the video I saw lots of flashes of light.

On Wikipedia I read that NH4NO3 + Mg metal is used but does that detonate so quickly ?

hissingnoise - 15-12-2014 at 13:35

It doesn't detonate at all ─ the mix deflagrates quickly like most flash comps.

They are stun grenades, after all . . .

dermolotov - 15-12-2014 at 17:19

I'd assume that some sort of quick action thermite or metal oxidation is used.

If wikipedia says Ammonium Nitrate and Magnesium, I'd suppose some very fine powder is spread finely in the air. the magnesium makes a very bright light whereas the nitrate is just a simple explosive meant to make sound - not destruction.

IrC - 15-12-2014 at 18:00

I have read in the past they used Al dust and Potassium Perchlorate for Police flash bangs. True? Or not?

dermolotov - 15-12-2014 at 18:10

Quote: Originally posted by IrC  
I have read in the past they used Al dust and Potassium Perchlorate for Police flash bangs. True? Or not?

Very likely... Check out US patent 8161883
http://www.google.com/patents/US8161883

It consists of:
Quote:
a pyrotechnic mix of about 50 to about 55 wt. % strontium nitrate, about 35 to about 45 wt. % aluminum powder, about 3 to 6 wt. % sulfur, about 0.5 to about 1.5 wt. % boric acid, and about 0.5% anti-caking agent;

The oxidising agent doesn't matter too much. Nitrate, perchlorate, azides, etc etc etc.


Another one that references your specific Perchlorate/Aluminium cake is referenced in patent No. No. US7963227 titled "Multiple report stun grenade".
It mentions that US5654523 uses Aluminium powder / Perchlorate. But the patent itself gives no mention.


I did limited digging. Just referenced a few numbers that if you typed into google should provide you with the relevant information.

greenlight - 15-12-2014 at 18:35

All I have found without checking patents just military info is that the stun grenade composition could be Ammonium perchlorate/Magnesium 50:50.
Or another page I found says Potassium perchlorate, Aluminum powder and Barium nitrate but no amounts or ratios.
It seems the military keeps tight lipped about what the pyrotechnic composition in these grenades actually is.

The patent Dermolotov found states the filler being 8-10 grams,a lot less than I expected.


[Edited on 16-12-2014 by greenlight]

Bert - 15-12-2014 at 19:04

It is a flash powder mixture, there are MANY possible oxidizer and fuel combinations.

Most likely would be Potassium perchlorate and Aluminum powder. Least sensitivity and best storage life- The choice of industry for some time now. Minor variations in particle size, anti cakeing additives and % formulations only in my experience.

Magnesium powders oxidize from atmospheric Oxygen in storage, and thus Mg is avoided even in military use unless absolutely required. Nitrates and Aluminum are not extremely stable in humid environments unless protected by a mild acid. Chlorates and Aluminum are excessively shock and friction sensitive. Ammonium compounds are incompatible with Magnesium in the presence of moisture- A few amateurs I know of have used ammonium perchlorate/Magnesium flash mixtures. They are very high performance, releasing more energy and temporary gas output than nitroglycerin weight per weight. No commercial production of these AFAIK. These do not "keep" well, even with dichromate coating of the Magnesium powder.

There is a niche use of Magnesium powder or Magnesium/Aluminum alloys with nitrate oxidizers in theatrical flash powders, where it is desired that a substantial % of the metal fuel burn in the atmosphere as a vapor after ignition of the device, rather than within the device immediately on ignition. This is done with flash used in "concussion mortars" to ensure the steel mortar tube is not fragmented by the explosion, with the resulting splinters flying into the audience and cast.

No one uses ammonium nitrate for production of military or civil pyrotechnics as far as I know. It is, however, used for many high explosive mixtures-

hissingnoise - 16-12-2014 at 03:11

Quote:
They are very high performance, releasing more energy and temporary gas output than nitroglycerin weight per weight.

Weight for weight?

Come on Bert, that's a wild exaggeration ─ you know it's not true?


hissingnoise - 16-12-2014 at 03:30

Quote:
The oxidising agent doesn't matter too much. Nitrate, perchlorate, azides, etc etc etc .

It certainly does matter in the case of azides; they are flame and shock-sensitive primary explosives with high VOD!

careysub - 16-12-2014 at 09:42

Quote: Originally posted by greenlight  
All I have found without checking patents just military info is that the stun grenade composition could be Ammonium perchlorate/Magnesium 50:50.
Or another page I found says Potassium perchlorate, Aluminum powder and Barium nitrate but no amounts or ratios.
It seems the military keeps tight lipped about what the pyrotechnic composition in these grenades actually is.


There is nothing secret about compositions like this, in fact there may be more than one composition in use depending on supplier.

Here is the original procurement request by the DOD:
http://www.fbodaily.com/cbd/archive/1995/06(June)/02-Jun-1995/Asol008.htm

It defines performance requirements, and it is up the manufacturer to offer something that satisfies them. The military does not like to sole source an item so it likely accepted bids from more than one company.

The M84 and XM84 stun grenades are commercially available to law enforcement.

All credible citations indicate it is a magnesium/perchlorate composition, it may be that both ammonium and potassium perchlorate have been used.

Bert, above, is correct about stability issues with magnesium/perchlorate - as mixed by pyro amateurs - but the military is probably using polymer coatings/binders that address this.

Here is a report from 1991 (four years before the CBD RFP) that states that such coating were under development:
http://www.dtic.mil/dtic/tr/fulltext/u2/a238923.pdf
Quote:
The patent Dermolotov found states the filler being 8-10 grams,a lot less than I expected.


It contains 4.3 grams of composition:
http://www.parttarget.com/1330-01-459-8141_1330014598141_129...


[Edited on 16-12-2014 by careysub]

Bert - 16-12-2014 at 10:38

Quote: Originally posted by hissingnoise  
Quote:
They are very high performance, releasing more energy and temporary gas output than nitroglycerin weight per weight.

Weight for weight?

Come on Bert, that's a wild exaggeration ─ you know it's not true?




Please do the math. And don't confuse the speed at which energy is released or the destructive capabilities of the two very different explosives against a target with the total amount of energy released per weight-

Look at the boiling points of Magnesium chloride and oxide. They are gasses at typical reaction temperatures, unlike Aluminum oxide.

This whole question was worked over exhaustively on amateur pyrotechnic forums & news groups over 10 years back- After a few people started using ammonium perchlorate/Magnesium flash powders at PGI convention in an attempt to get the absolute biggest bang possible under size limits then imposed on the ground bomb range.

[Edited on 16-12-2014 by Bert]

hissingnoise - 16-12-2014 at 10:44

Quote:
All credible citations indicate it is a magnesium/perchlorate composition, it may be that both ammonium and potassium perchlorate have been used.

It's likely that ammonium perchlorate comps. cannot be used in stun grenades which may be used in enclosed spaces as its decomp. produces HCl!

Bert - 16-12-2014 at 11:14

Additional searching finds claims of ammonium NITRATE as the oxidizer. That's an engineering challenge- hygroscopic, reactive oxidizer with highly reactive fine metal powder. Use of Mg in storage stable mixtures calls for coatings as careysub noted. My text books are not to hand, recollection is that polymer coatings have been used- but dichromate coating was more effective.

Military pyrotechnic design considerations are... Different from civil pyrotechnics. I primarily work with civil.

careysub - 16-12-2014 at 11:15

Quote: Originally posted by hissingnoise  
Quote:
All credible citations indicate it is a magnesium/perchlorate composition, it may be that both ammonium and potassium perchlorate have been used.

It's likely that ammonium perchlorate comps. cannot be used in stun grenades which may be used in enclosed spaces as its decomp. produces HCl!


I doubt this is an issue.

The grenades aren't decomposing ammonium perchlorate, they are using it to oxidize magnesium to the chloride and oxide.

In ammonium perchlorate rocket fuel there are substantial HCl emissions due to the carbonaceous fuel that is present (and producing lots of gas is the objective). Flash/bang compositions don't have a hydrocarbon fuel. I'm sure there is some HCl released (reaction equilibria, etc.) , but most the chlorine in going to be in the form of magnesium chloride.

hissingnoise - 16-12-2014 at 11:29

Quote:
. . . in an attempt to get the absolute biggest bang possible under size limits then imposed on the ground bomb range.

'Biggest bang', Bert? What are you talking about?

Cl contributes very little to reaction energy and its high atomic mass is a limiting factor!

No maths required . . . :D

Bert - 16-12-2014 at 11:50

Quote: Originally posted by hissingnoise  


No maths required . . . :D



No math = ungrounded assumption ;)

hissingnoise - 16-12-2014 at 12:43

Quote:
The grenades aren't decomposing ammonium perchlorate, they are using it to oxidize magnesium to the chloride and oxide.

The oxygen supplied is an NH4ClO4 decomp. product ─ but yes you're correct, MgCl2 is but a minor irritant and wouldn't preclude its use in these comps..

hissingnoise - 16-12-2014 at 12:48

Quote:
No math = ungrounded assumption.

Assumptions have been made, certainly, but I stand by my original assertion!