Sciencemadness Discussion Board

Questions about AN Mixtures

Hurricoaster - 30-8-2016 at 11:29

Hello,

I read on Wikipedia that Ammonal is a mixture of Ammonium Nitrate and Aluminum. It said that AN is simply an oxidizer, but did not mention the actual chemical reaction with the Aluminum. I would assume that the final step is this:
Quote:

4Al + 3O2 -> 2Al2O3


Wolfram Alpha states that the enthalpy of this reaction is -3352 kJ/mol, which is exothermic. Wolfram Alpha also states that 3352kJ is roughly 0.8 times the amount of energy released by detonating 1kg of TNT, so assuming I am understanding this correctly, that much energy would be released when 1 mole of Al2O3 is formed by this reaction. 2 moles of Al are consumed for every 1 mole of Al2O3 produced, and the molar mass of Al is 26.9815386 g/mol, so that means that much energy would be produced from only 53.9630772g of aluminum reacting. Wow!

So, assuming this is actually the reaction that is taking place, this would mean I would need 2 moles of NH4NO3 for every 4 moles of Al, since each molecule of AN has 3 Oxygen atoms, so 2 moles of AN would produce 6 moles of atomic oxygen, which would combine into 3 moles of molecular oxygen. Right?

If so, this means I need 2 moles of Al per 1 mole of AN, or 53.9630772g of Al per 80.0434g of AN, which comes out to be 40.2690% Aluminum, by mass. This seems like far too much Aluminum; several videos I have seen of Ammonal explosions quote that their mixtures are 90% AN and 10% Al, by mass. Have I made any errors here, or are they just using non-stoichiometric mixtures?

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Lastly, I have seen a video here where a mixture of Ammonium Nitrate and sugar is detonated. The video links to this webpage in Russian, of which Google Translate does a spotty job of translating, at best. I'd like to know more about the actual reaction taking place here, as well as whether or not they mean sucrose by sugar, and lastly, all of the steps needed to prepare their mixture. I see at some point they mention mixing the sugar with Potassium Nitrate while being heated; is this what is then mixed in with the AN, or is that used for something else (I know that mixing KNO3 and sugar under heat creates the famous "Sugar Rocket" fuel, which can also be used to coat yarn in order to make homemade fuses, so maybe that's what they're using it for? I can't tell with the bad translation.) Has anyone tried this mixture? If so, what are all of the steps to prepare it? Or, can anyone who can read Russian tell me what that webpage says in order to prepare the mixture?

Metacelsus - 30-8-2016 at 11:57

Quote: Originally posted by Hurricoaster  

So, assuming this is actually the reaction that is taking place, this would mean I would need 2 moles of NH4NO3 for every 4 moles of Al, since each molecule of AN has 3 Oxygen atoms, so 2 moles of AN would produce 6 moles of atomic oxygen, which would combine into 3 moles of molecular oxygen. Right?

If so, this means I need 2 moles of Al per 1 mole of AN, or 53.9630772g of Al per 80.0434g of AN, which comes out to be 40.2690% Aluminum, by mass. This seems like far too much Aluminum; several videos I have seen of Ammonal explosions quote that their mixtures are 90% AN and 10% Al, by mass. Have I made any errors here, or are they just using non-stoichiometric mixtures?


Yes, you have made errors. The correctly balanced equation is:
2 Al + 3 NH4NO3 = Al2O3 + 3 N2 + 6 H2O

careysub - 30-8-2016 at 12:04

No.

The explosive decomposition reaction of ammonium nitrate is, more or less:
NH4NO3 ----> N2 + 2 H2O + 1/2 O2

So only one free oxygen is produced for each mole of ammonium nitrate.

So we get:

3 NH4NO3 ----> 3 N2 + 6 H2O + 1.5 O2

2 Al + 1.5 O2 -> Al2O3

or 2/3 moles of Al per mole NH4NO3, which knocks the stoichiometric ratio down to something like 13% by mass.

Hurricoaster - 30-8-2016 at 12:45

Okay, thank you to both Metacelsus and careysub for providing the correct formula for the explosive decomposition of Ammonium Nitrate. Using the correct formula, here are my calculations for the stoichiometric ratio of Aluminum to AN, by mass:

2 mol Al * 26.9815386 g/mol Al = 53.9630772 g Al
3 mol NH4NO3 * 80.0434 g/mol NH4NO3 = 240.1302 g NH4NO3

53.9630772 g Al / (53.9630772 g Al + 240.1302 g AN) * 100 = 18.3490% Al

18.3490% Aluminum is closer to the 10:90 ratio used in the video I saw, but still off by 8%, and not equal to the 13% ratio that careysub found. Where have I gone wrong this time?

Also, out of curiosity, how did chemists come up with the formula NH4NO3 -> N2 + 2H2O + 1/2 O2? Can it be theoretically derived, or was it only found experimentally?

I would still like to know about the Ammonium Nitrate and Sugar mixture.

[Edited on 30-8-2016 by Hurricoaster]

careysub - 30-8-2016 at 13:08

I didn't do any calculation (I posted while juggling a phone call) - I just reduced the 40% mass you quoted, for 2 moles, by dividing by 3 for 2/3 moles. If your figure was in error (which is was), then so was my quick and dirty figure.

I just knew the NH4NO3 decomposition reaction off the top of my head.

This has to be determined experimentally as it is not the only possible decomposition process. In practice some minor nitric oxides are also produced.

Hurricoaster - 30-8-2016 at 13:11

Quote: Originally posted by careysub  
I didn't do any calculation (I posted while juggling a phone call) - I just reduced the 40% mass you quoted, for 2 moles, by dividing by 3 for 2/3 moles. If your figure was in error (which is was), then so was my quick and dirty figure.

I just knew the NH4NO3 decomposition reaction off the top of my head.

This has to be determined experimentally as it is not the only possible decomposition process. In practice some minor nitric oxides are also produced.


Alright, thanks for the assistance.

Microtek - 2-9-2016 at 07:55

Al will be oxidized before hydrogen, assuming sufficiently small particle size. Free hydrogen will be produced in this reaction.

MineMan - 2-9-2016 at 10:12

Microtek is correct that free hydrogen will be produced... although I thought that the H2O produced oxidized the Al....

Microtek - 2-9-2016 at 22:42

That is definitely possible. I was referring to the algorithm to determine the net reaction, where step one is to oxidize Al. Then comes C to CO, then H to H2O and finally CO to CO2, assuming there is any oxygen left.
There are variations on this algorithm, but they all have in common that Al to Al2O3 is the first (highest priority) step.

AN and Sugar Mixture?

Hurricoaster - 8-9-2016 at 17:48

Hello,

I have seen a video here where a mixture of Ammonium Nitrate and sugar is detonated. The video links to this webpage in Russian, of which Google Translate does a spotty job of translating, at best. I'd like to know more about the actual reaction taking place here, as well as whether or not they mean sucrose by sugar, and lastly, all of the steps needed to prepare their mixture. I see at some point they mention mixing the sugar with Potassium Nitrate while being heated; is this what is then mixed in with the AN, or is that used for something else (I know that mixing KNO3 and sugar under heat creates the famous "Sugar Rocket" fuel, which can also be used to coat yarn in order to make homemade fuses, so maybe that's what they're using it for? I can't tell with the bad translation.) Has anyone tried this mixture? If so, what are all of the steps to prepare it? Or, can anyone who can read Russian tell me what that webpage says in order to prepare the mixture?

Laboratory of Liptakov - 8-9-2016 at 23:56

Understand this webpage (process) is difficult even for experience deminers. Process preparation is described chaotic, confused. Forget on this pages. And you do it study world available patents. After reading 20 patents about ammonium nitrate and fuels, will be for you clear basic methode prepare AN - fuel. You have now a big eyes from video. In fact is broken the tree using huge 4 Kg ANFO very miserable and poor result. Usually is need on this diameter ( 25cm) tree about 400g EM.
Dr.
Next thing, is nonsense, that 4200 ANFO = 3500 TNT. Because detonation pressure is increase with square of VoD. And it is important for broken the tree. Well, all energy can be same for 4,2 and 3,5 but author is fool. You see on absolute primitive and dangerous detonator.

[Edited on 9-9-2016 by Laboratory of Liptakov]

NeonPulse - 9-9-2016 at 01:19

there are many things including sugar that can be used for fuel but after seeing the video i cant help but think that it was a poorly configured charge and probably not a complete detonation. the same thing can be done with 250- 300g ANNM and a little wet sand tamping. The guy that did it obviously has no commonsense either. You can hear him shuffling close to the camera which was pretty close to the charge. if that was me i would not want to be within min 65m of 4.2Kg of it and i certainly would use electric ignition.
But anyway each to their own. It is basically an oxidizer/fuel mixture which when exited enough will explode.
Sugar can be used as a fuel in a pinch, but there are better choices out there. It just needs to be ultra finely divided sugar and AN mixed very well and kept very dry, keeping in mind to work fast due to the hygroscopic nature of the AN.
setting it off with a booster will increase the performance which really counts with this stuff. and it is no where near an equivalent of 3.5 kg of TNT.

MineMan - 9-9-2016 at 10:10

LL, very well said!

Fulmen - 9-9-2016 at 13:30

Could it be co-crystallized to generate a more intimate mixture?

Metacelsus - 9-9-2016 at 16:40

It's very unlikely that they would form a cocrystal, because the crystal structures are quite different. You'd just end up with a mixture of ammonium nitrate crystals and sucrose crystals, which might as well be obtained by mixing them dry.

Laboratory of Liptakov - 10-9-2016 at 00:50

Yesterday was tested AN 85 sacharose 15. Detail prepare: 8,5g AN + 1,5g sugar + 20g water. Dissolved and evaporate at 120 C. After 5 minute is material very similar motor oil, consistency and color. Stopped heated in this point and cooling on 80 C. Arises solid orange - brown material. Crushing on the sieve on agglomerate 1x1 mm. Drying process by 1 Hour at 100C . Filling the charge of 10g on density 1,0g/cm3. Berta kick equivalent No.8. The charge only smell, minimal partially detonation. Behind same conditions for example ammotropin (AN 91/ HMTA 9) gives fully a strong detonation at 10g. Always.
Dr.

Fulmen - 10-9-2016 at 02:11

I was merely speculating on what was done in the video. I know it probably wouldn't form proper co-crystals.

It could also have been melted, although I'm not sure if it's entirely safe. Molten AN is quite reactive, IIRC experiments with this tends to form porous grains due to gas formation. But that could also increase sensitivity...

dillee1 - 12-9-2016 at 01:40

In CJ model, brisance/CJ pressure is directly proportional to VOLUMETRIC energy density; that is how much engery you can shove inside a given cubic centimeter.
Complete combustion usually results in higher SPECIFIC energy density; ala energy/gram.
Having higher specific energy do not equals to higher volumetric energy density. If the fuel/oxidizer you add has low density it might actually lowers brisance because of this.
In case of aluminium+AN. Density and specific energy both increase if all water are combusted to hydrogen and alumina. Sweet spot of the mix should be at somewhere deeply negative OB.

MineMan - 12-9-2016 at 19:43

Dillee. Can you expand on why t should be deeply OB negative...

I know a postage OB. 5perecent Al has the smallest critical dia.

Laboratory of Liptakov - 13-9-2016 at 10:28

Melting dry ammonium nitrate + sugar is practically impossible. At 150 C it all started burning, smelling, smoking. Against this, total dry AN + dry hexamine is possible melting at 145 C. Without any changes after 5 minute. Some compounds is possible melting with An and some not. For example, the flour 15 + AN 85 started burning very early. And even impossible stopped. Only getaway. Dr.

Fulmen - 13-9-2016 at 13:07

Sounds reasonable, all things considered. Sugar caramelizes at fairly modest temperatures, and that can be enough to initiate the mixture. Perhaps some of the low-melting sugars and sugar alcohols would work better?

dillee1 - 13-9-2016 at 22:43

@MineMan
Thats because:
(1) this release 818.3KJ/mol
2Al + 3(H20) -> Al203 + 3(H2)

(2) Aluminium density 2.70 g/cm3
AN density 1.725 g/cm3

So high aluminium content increase both specific energy and density of the charge.
Since aluminium react (relatively) slowly, so at very high Al content most energy will be release far behind the detonation wave, unable to pump up the CJ pressure. It does maintain the pressure for longer though.
What percentage of Al generates highest CJ pressure depends on burn speed, which in turn depends on particle size, oxide layer thickness and many other factor, which cannot be estimate by simple CJ model alone. However one can be assure that the sweet spot is not at 100% hydrogen, nor 100% water as product, because of reasons above.


[Edited on 14-9-2016 by dillee1]

[Edited on 14-9-2016 by dillee1]

Laboratory of Liptakov - 13-9-2016 at 23:51

From sugar alcohols worked erythritol and sorbitol. However, for both substances, the same applies. Is impossible melting without water. Always is necessary stopped heating at changes of colour to red - brown. And at this point is in mix always still some % of water. Therefore is need this mixes cooling on 40C and crushing. On agglomerate for example 1x1 mm. After this operation is possible next drying process. At temperature 80 - 100C. By a few hours. Same prosess is for ascorbic acid (E300) and sodium ascorbate (E301) All mixtures worked, but his power, respectively VoD is low. Dr.

[Edited on 14-9-2016 by Laboratory of Liptakov]

Laboratory of Liptakov - 17-9-2016 at 08:38

Yet, that aluminium burning behind shock wave, allows start and hold detonation. In much mixes. However, should be it all conversely. Aluminium reactive as first with AN. And after will be running ammonium nitrate + some fuel. Dr.