Chisholm
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Ammonium nitrate and zinc: Why so sensitive?
In Forensic Investigation of Explosives, 2nd Edition (2012), one finds this tidbit:
"Mixtures of ammonium nitrate and zinc have been known to detonate when heated well below the melting point of ammonium nitrate. Many fatal accidents
in the mining industry have been attributed to mixtures of AN and zinc. This is the only ammonium nitrate mixture the author knows of that is so
unstable."
While I haven't actually had a detonation, sub-gram-level experiments* I performed comparing powdered AN+ icing sugar in aluminium foil (cookoff
temperature: 180ºC) with powdered AN + zinc powder in aluminium foil revealed that the zinc mixture begins smoking with less heat, and produces more
copious vapor with less effort.
*Both used stoichiometric ratios of oxidizer to fuel.
Most fuels and/or additives that destabilize AN do so for well-explained reasons: chlorates and permanganates promote metathetical formation of
dangerously sensitive compounds; sulfur and icing sugar have low melting/decomposition points; copper powder forms an ammine complex in the presence
of trace moisture; and so on.
The fact that the author mentioned above is Dr. Kirk Yeager (chief explosives technician for the Federal Bureau of Investigation), and that even he
didn't have an explanation (at least, as of 2012), is curious.
If ammine complexes of zinc nitrate were primary explosives, you'd think they would be mentioned somewhere. Especially given that ammine complexation
is mentioned on the very same page as the reason for the sensitivity of AN+Cu mixtures.
So what is the precise reason for the sensitivity?
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PHILOU Zrealone
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I have typed a good reply to your request...but when pushing onto the "post reply" button...it is all gone lost into the electronic internet space...
I hate those SMF bugs :-(...
I don't feel the mood like retyping all now ...so maybe another day...
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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Fulmen
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I remember playing with AN/Zn/NH4Cl as a novelty as it will ignite from a drop of water. Even got a nasty burn when a freshly prepared mixture self
ignited within minutes and sprayed my hand with molten slag. So be careful, these mixtures have zero shelf life.
We're not banging rocks together here. We know how to put a man back together.
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clearly_not_atara
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Zn2+ is a Lewis acid so maybe it pisses off the nitrate anion once even a tiny bit forms
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PHILOU Zrealone
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Quote: Originally posted by Chisholm  | In Forensic Investigation of Explosives, 2nd Edition (2012), one finds this tidbit:
"Mixtures of ammonium nitrate and zinc have been known to detonate when heated well below the melting point of ammonium nitrate. Many fatal accidents
in the mining industry have been attributed to mixtures of AN and zinc. This is the only ammonium nitrate mixture the author knows of that is so
unstable."
While I haven't actually had a detonation, sub-gram-level experiments* I performed comparing powdered AN+ icing sugar in aluminium foil (cookoff
temperature: 180ºC) with powdered AN + zinc powder in aluminium foil revealed that the zinc mixture begins smoking with less heat, and produces more
copious vapor with less effort.
*Both used stoichiometric ratios of oxidizer to fuel.
Most fuels and/or additives that destabilize AN do so for well-explained reasons: chlorates and permanganates promote metathetical formation of
dangerously sensitive compounds; sulfur and icing sugar have low melting/decomposition points; copper powder forms an ammine complex in the presence
of trace moisture; and so on.
The fact that the author mentioned above is Dr. Kirk Yeager (chief explosives technician for the Federal Bureau of Investigation), and that even he
didn't have an explanation (at least, as of 2012), is curious.
If ammine complexes of zinc nitrate were primary explosives, you'd think they would be mentioned somewhere. Especially given that ammine complexation
is mentioned on the very same page as the reason for the sensitivity of AN+Cu mixtures.
So what is the precise reason for the sensitivity? |
There are a few known fact that may point out towards usual suspects working alone or as a team...
---------------------------------------------------
1°) It is known that NH4NO3/NH4Cl/Zn mix catches fire spontaneously when moist; a single water drop will start the reaction.
The NH4Cl is sufficiently acidic to be very corrosive towards the metallic Zn surface...
2 NH4Cl + Zn --> ZnCl2 + H2 + 2 NH3 + heat
ZnCl2 + 4 NH3 --> Zn(NH3)4Cl2 + heat
2°) NaCl may also sensitize the NH4NO3/Zn mix...
The halide anion is a corrosion catalyst for metals
Discretely NH4Cl is formed...
NaCl + NH4NO3 <==> NaNO3 + NH4Cl
3°) Zn/S is used for some rocket propellant...due to reaction heat the Zn and S both melt and turn into a gas and burn blue into the outlet.
S melt arround 115°C and Zn arround 420°C.
S boils arround 445°C while Zn arround 907°C.
So into the NH4NO3/Zn mix the Zn will vapourise into the hot burning mix and turn the mix to be even more intimately mixed.
4°) Zn is a strong reductor while NO3(-) is an oxydizer...
Depending onto the pH one may get Zn(2+) and...
NO2(-)
N2
NH2OH
NH3
5°) NH4NO3 is also quite acidic and reactive towards some reductive metals when moist (Al, Mg, Zn, ...)...but less so than NH4Cl...; so even if
chloride anion is absent (as NaCl or NH4Cl), the heating will take care of the activation energy barrier and allow for the speeding up of the
surfacial oxydoredox
---------------------------------------------------
From the above points 1°) to 5°) one may conclude that into a mix of Zn/NH4NO3...one may find the following explosive compounds:
*Zn(NH3)4(NO3)2 (moderate sensitivity and stable)
*Zn(NH3)4(NO2)2 (probably sensitive and unstable - decomposing on its own)
*Zn(NH2OH)4(NO3)2 (or Zn(NH2OH)2(NO3)2) (probably sensitive and stable)
Two or four NH2OH into the complex depending if NH2-OH complexate like NH3 or like NH2-NH2 thus as monodentate or bidentate ligand...
*Zn(NH2OH)4(NO2)2 (or Zn(NH2OH)2(NO2)2) (probably sensitive and unstable - decomposing on its own)
*NH4NO2 (sensitive and unstable - decomposing on its own)
*HONH3NO3 (sensitive and stable)
*HONH3NO2 (probably sensitive and unstable -decomposing on its own)
Many of the above compounds are powerful HE (high explosives) with VOD (velocity of detonations) ranking from 4 to 8 km/s...and some decompose on
their own generating heat and moisture...
This explains that a single drop of water is able to start a vigorous reaction when NH4Cl is present...and propagate it very fast...because the
reaction releases even more water and heat...the reaction is thus auto-catalytic...
HONH3NO2 --> N2 + 2 H2O + 1/2 O2
NH4NO3 --> N2 + 2 H2O + 1/2 O2
NH4NO2 --> N2 + 2 H2O
In the absence of NH4Cl or Cl(-), the heating afwords some moisture migration and micro-melting zones where the reactions starts...even if the overal
mass is not macroscopically melting.
The above speculations would need further study to confirm what is effectively happening...but the truth must not be far from the depicted story...
[Edited on 12-7-2017 by PHILOU Zrealone]
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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Chisholm
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| Quote: Originally posted by PHILOU Zrealone | | Quote: Originally posted by Chisholm | In Forensic Investigation of Explosives, 2nd Edition (2012), one finds this tidbit:
"Mixtures of ammonium nitrate and zinc have been known to detonate when heated well below the melting point of ammonium nitrate. Many fatal accidents
in the mining industry have been attributed to mixtures of AN and zinc. This is the only ammonium nitrate mixture the author knows of that is so
unstable."
While I haven't actually had a detonation, sub-gram-level experiments* I performed comparing powdered AN+ icing sugar in aluminium foil (cookoff
temperature: 180ºC) with powdered AN + zinc powder in aluminium foil revealed that the zinc mixture begins smoking with less heat, and produces more
copious vapor with less effort.
*Both used stoichiometric ratios of oxidizer to fuel.
Most fuels and/or additives that destabilize AN do so for well-explained reasons: chlorates and permanganates promote metathetical formation of
dangerously sensitive compounds; sulfur and icing sugar have low melting/decomposition points; copper powder forms an ammine complex in the presence
of trace moisture; and so on.
The fact that the author mentioned above is Dr. Kirk Yeager (chief explosives technician for the Federal Bureau of Investigation), and that even he
didn't have an explanation (at least, as of 2012), is curious.
If ammine complexes of zinc nitrate were primary explosives, you'd think they would be mentioned somewhere. Especially given that ammine complexation
is mentioned on the very same page as the reason for the sensitivity of AN+Cu mixtures.
So what is the precise reason for the sensitivity? |
There are a few known fact that may point out towards usual suspects working alone or as a team...
---------------------------------------------------
1°) It is known that NH4NO3/NH4Cl/Zn mix catches fire spontaneously when moist; a single water drop will start the reaction.
The NH4Cl is sufficiently acidic to be very corrosive towards the metallic Zn surface...
2 NH4Cl + Zn --> ZnCl2 + H2 + 2 NH3 + heat
ZnCl2 + 4 NH3 --> Zn(NH3)4Cl2 + heat
2°) NaCl may also sensitize the NH4NO3/Zn mix...
The halide anion is a corrosion catalyst for metals
Discretely NH4Cl is formed...
NaCl + NH4NO3 <==> NaNO3 + NH4Cl
3°) Zn/S is used for some rocket propellant...due to reaction heat the Zn and S both melt and turn into a gas and burn blue into the outlet.
S melt arround 115°C and Zn arround 420°C.
S boils arround 445°C while Zn arround 907°C.
So into the NH4NO3/Zn mix the Zn will vapourise into the hot burning mix and turn the mix to be even more intimately mixed.
4°) Zn is a strong reductor while NO3(-) is an oxydizer...
Depending onto the pH one may get Zn(2+) and...
NO2(-)
N2
NH2OH
NH3
5°) NH4NO3 is also quite acidic and reactive towards some reductive metals when moist (Al, Mg, Zn, ...)...but less so than NH4Cl...; so even if
chloride anion is absent (as NaCl or NH4Cl), the heating will take care of the activation energy barrier and allow for the speeding up of the
surfacial oxydoredox
---------------------------------------------------
From the above points 1°) to 5°) one may conclude that into a mix of Zn/NH4NO3...one may find the following explosive compounds:
*Zn(NH3)4(NO3)2 (moderate sensitivity and stable)
*Zn(NH3)4(NO2)2 (probably sensitive and unstable - decomposing on its own)
*Zn(NH2OH)4(NO3)2 (or Zn(NH2OH)2(NO3)2) (probably sensitive and stable)
Two or four NH2OH into the complex depending if NH2-OH complexate like NH3 or like NH2-NH2 thus as monodentate or bidentate ligand...
*Zn(NH2OH)4(NO2)2 (or Zn(NH2OH)2(NO2)2) (probably sensitive and unstable - decomposing on its own)
*NH4NO2 (sensitive and unstable - decomposing on its own)
*HONH3NO3 (sensitive and stable)
*HONH3NO2 (probably sensitive and unstable -decomposing on its own)
Many of the above compounds are powerful HE (high explosives) with VOD (velocity of detonations) ranking from 4 to 8 km/s...and some decompose on
their own generating heat and moisture...
This explains that a single drop of water is able to start a vigorous reaction when NH4Cl is present...and propagate it very fast...because the
reaction releases even more water and heat...the reaction is thus auto-catalytic...
HONH3NO2 --> N2 + 2 H2O + 1/2 O2
NH4NO3 --> N2 + 2 H2O + 1/2 O2
NH4NO2 --> N2 + 2 H2O
In the absence of NH4Cl or Cl(-), the heating afwords some moisture migration and micro-melting zones where the reactions starts...even if the overal
mass is not macroscopically melting.
The above speculations would need further study to confirm what is effectively happening...but the truth must not be far from the depicted story...
[Edited on 12-7-2017 by PHILOU Zrealone] |
So ammine complexation almost certainly plays some role, as I suspected. That would fit the overall picture, where other reducing metals such as
magnesium and aluminium—while sensitizing the AN and producing mixtures that can be detonated by strong shock—produce mixtures less prone to
detonating from heat, and which require the AN to begin melting (app. 169.6ºC) before such a reaction occurs.
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Melgar
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Location: Connecticut
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| Quote: Originally posted by PHILOU Zrealone | I have typed a good reply to your request...but when pushing onto the "post reply" button...it is all gone lost into the electronic internet space...
I hate those SMF bugs :-(...
I don't feel the mood like retyping all now ...so maybe another day... |
Get the "Lazarus" extension if you use either Chrome or Firefox. It saves all the data you ever type into text boxes, so you can bring it back from
the dead when a web page craps out on you.
The first step in the process of learning something is admitting that you don't know it already.
I'm givin' the spam shields max power at full warp, but they just dinna have the power! We're gonna have to evacuate to new forum software!
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PHILOU Zrealone
International Hazard
Posts: 2893
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Location: Brussel
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| Quote: Originally posted by Melgar | | Quote: Originally posted by PHILOU Zrealone | I have typed a good reply to your request...but when pushing onto the "post reply" button...it is all gone lost into the electronic internet space...
I hate those SMF bugs :-(...
I don't feel the mood like retyping all now ...so maybe another day... |
Get the "Lazarus" extension if you use either Chrome or Firefox. It saves all the data you ever type into text boxes, so you can bring it back from
the dead when a web page craps out on you. |
Thank you Melgar for that valuable information    ...
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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woelen
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There are more mixes with the property that adding a little water sets of the mix. The water is essential for setting off, by dissolving the soluble
reactant and allowing the concentrated solution to react with the metal in the mix. This reaction produces sufficient heat to have the remaining solid
mix reacting as well, with fire and smoke.
Some other examples:
- Mix of finely ground AgNO3 plus Mg-powder. The dry mix is stable, but even adding a tiny amount of water leads to ignition and a bright white flash
of fire, with molten silver droplets spraying around. If you want to try this, do not use more than a few tenths of a gram of this mix.
- Mix of crushed I2 and Mg powder. Adding a small drop of water leads to puffs of violet iodine vapor and if you use a somewhat larger pile of the mix
(a few grams), you may get ignition of the mix.
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AJKOER
Radically Dubious
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Here is my take on the possible reaction mechanics.
First, as occurs in the case of the metal Aluminum (see, for example, equation (3.7) in a doctoral thesis from 2008, "Alkaline dissolution of
aluminum: surface chemistry and subsurface interfacial phenomena", by Saikat Adhikari, link: https://www.google.com/url?sa=t&source=web&rct=j&...), I would argue similarly with zinc, the creation of the metal hydroxide directly
from the metal, proceeds with the release of electrons per the reaction:
Zn + 2 OH- → Zn(OH)2 + 2 e-
Note, the reaction is charged balanced. Based on the above reaction, if we introduce a source of H+ from say:
NH4+ = NH3 + H+
Upon adding H+ to each side, in neutral to acidic conditions:
Zn + 2 H2O → Zn(OH)2 + 2 (H+ + e-)
H+ + e- → •H
•H + •H → H2
And also, a further possible reaction in the presence of nitrate, with either prehydrated or totally solvated electrons, being reported as readily
scavenged by nitrate:
e(p)-/e(aq)- + NO3- + H2O -> NO2 + 2OH- (Source: see eq. (5) in JAERI-Conf 95-003, "5. 6 Radiolysis of Concentrated Nitric Acid Solutions R.
Nagaishi" by P.Y. Jiang, et al, link: https://www.google.com/url?sa=t&source=web&rct=j&... )
Or, one could rewrite the above reaction upon adding H+ to both sides as:
(H+ + e(p)-/e(aq)-) + NO3- + H2O → OH- + •NO2 + H2O
Or, equivalently, after eliminating water, one could expressed the above in the form of a radical based charge transfer/oxygen extraction reaction
(since H+ + e- = •H):
•H + NO3- → OH- + •NO2
(and, I suspect similarly the process continues with say any created nitrite from a water interaction with NO2, then forming correspondingly nitric
oxide:
•H + NO2- → OH- + •NO )
Finally, the creation of the very unstable ammonium nitrite :
2NO2 + 2(NH3•H2O) → NH4NO2 + NH4NO3 + H2O (Source: https://chemiday.com/en/reaction/3-1-0-8045)
Or, a gas phase reaction with NH3, NO, NO2 and water vapor at RT, creating a dry ammonium nitrite powder:
2 NO2 + 2 NO + 4 NH3 --> 2 NH4NO2 + 2 H2O + 2 N2 (Source: see http://www.sciencemadness.org/talk/viewthread.php?tid=23807&...)
which in the presence of zinc powder and heat likely detonates.
[Edited on 28-9-2017 by AJKOER]
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