A perfectly contained explosion!

[YT2095]

Imagine a perfect steel cube in 2 halves with a tiny cavity in the center of it, enough to fit perfectly a quantity of explosive.

 

these steel halfves are then bolted together perfectly, and the explosive is of a quantity not large enough to rupture the steel container or allow any gasses out.

 

the products of detonation from this explosive X are Carbon Dioxide and Nitrogen, only.

 

what will happen when to explosive X when triggered (I`ll avoid the term detonate as I`m uncertain if it will).

 

I have many ideas in my head as to what will happen, ranging from detonation and liquification of the gasses, to compressing the inner cavity of the steel into a new substance (probably an isotope) to it only part detonating and refusing to go any futher leaving the explosive X still more or less in peice?

 

any ideas/theories ?

[VendingMenace]

interesting question...

 

i think first you have to decide whether anything will happen or not. So as far as that goes, here is my thoughts...

 

 

in a proccess in wich the right side of the equation has more mole of gas than the left side, increasing the pressure in reaction conditions will favor the left side of the equation. IN this case there is certainly more moles of gas in the products, so as the pressure increases the products will become more and more favored. In the begginning of the experiment we would be at standard temp and pressure (just for the sake of argument). As the reaction starts, it would proceed until a certain pressure was reached, and then it would stop.

 

Durring this time the temperature would also be rising. So, at the point when the reaction stops i feel that all prducts would remain gases. As the system starts to cool, you would observe condesation of the gases perhaps, due to the intesnely high pressures.

 

As the gas starts to condense, the pressure would drop and the reaction could again proceed in the forward direction, provided that there was enough heat left in the system for the reaction to occur.

 

This would continue to occur until there was not enough energy left in the system for the reaction to occur or until all the reactants were used up. (assuming that the reagents could "find" eachother in solution".

 

 

 

WEll, that is my thoughts for now. They are not ment to be 100 accurate or a definite timeline. Most likely, all of the prcesses would be occuring at different times, not just in the sequence that i have provided. Also, i am implicitely assumed that the liquid products take up less volume than the solid reagents.

 

Cool. Feel free to add to or corrrect errors or whatever

[YT2095]

I had in mind something simple like Nitro Glycerine, it`s at it max density and wouldn`t leave any air gaps, and it`s products are quite simple. you could use a large crystal of an explosive if you liked tho, the only condition is that it has no room to expand before being triggered, and is small enough not to rupture the container or buckle it.

and yes you`re right, there would be incredible heat generated, typicaly 7000k for NG.

[Skye]

I think the explosive would just rise in tempreture with the small amount of energy that normally triggers an explosion, as it is likely to be of much smaller volume than the products.

 

[Edited for confusing smaller with larger, doh]

[YT2095]

well lets for arguments sake use a hypothetical set of properties.

1 cm^3 of explosive X will liberate 2 liters of gas. those gasses are arbitrary in composition, but lets call the product Nitrogen, Carbon Dioxide and maybe some Water (sounds about right for most explosives).

it`s triggeres by an embeded wire (like a spark plug) that is insulated from the container by a fused ceramic (equaly unbreakable) we send a charge down the wire to trigger the reaction.

[YT2095]

has anyone got any other ideas at all???

[aman]

I don't know the bond strenth of the molecules in steel alloy but I would imagine the explosion would generate heat and pressure that might fracture some of the bonds and force the cube to be a little larger towards the center of each side with a larger volume void in the center of the cube.

Just aman

[YT2095]

would the carbon create diamonds?

could the Nitrogen and Hydrogen and Oxygen re combine to make Nitric acid ( a precursor of many explosives).

would that attack the iron and make more Hydrogen and NO2 to reform into Nirtic acid?

would any of it asctualy work under those kind of pressures?

these are the sort of things I wonder about

[JR]

Well, let's see if we can noodle some stuff out on this.

 

Detonation is a hydrodynamically mediated process, not chemically mediated. Essentially, this means that in a detonating medium, the sole 'process' that governs what is happening is the motion of the shock wave through the medium. Detonation is shock propagation.

 

So the question reduces to detonation or not? Well, that will solely depend on the initial impulse. If the initial impulse (the spark, for example) sufficiently compresses the explosive for shock propagation to occur, it will detonate. Otherwise, in these circumstances, probably not much will happen.

 

Pressures in the shock wave for common explosives are in the megabar range, which likely far exceeds the pressure of gaseous components in the container volume. Therefore, if detonation occurs (and it will, provided a large enough impulse is given), all gaseous products will expand out of the shock wave. Lot's of detonation temperatures are very low (I believe ammonium nitrate, for example, detonates around 400-450 celsius), which is NOT the same thing as the shock temperature (which is generally thousands of kelvins). The result, therefore, would be the gases in the volume at some 'warm' temperature and elevated pressure.

Like all explosions, there would be some unexploded explosive remaining.

 

Does the resulting detonation shock have enough 'ummmff' to damage the container? Depends on the amount of explosive and detonation velocity (the property called brisance). Low brisance detonations (such as ammonium nitrate) tend to not have sufficient shattering power to fracture steel (except in very, very large quantities, where the shear 'weight' of the shock front can cause damage). I don't recall the precise number, but I THINK the threshhold for shattering steel is around 7000 or 7500 m/s detonation velocity (and a small amount of hi-ex would lack the power to do any noticeable damage - MAYBE some surface spalling, if that).

 

Finally, I think nitroglycerine is a liquid, so it would not be a perfect crystal in the cavity (under ordinary conditions).

 

These are just my opinions, based on what I THINK I understand about explosions.

[Radical Edward]

I think it would cause a rupture in the space time continuum and cause havoc with the laws of physics. This may involve armadilloes.

[YT2095]

lol @ Rad

 

JR, I understand exactly what you`re saying. I wasn`t thinking along the lines of AN, ANMN,ANFO ect... they`re just heaving charges, I was considering along the lines of a Primary, Fulminates, Azides, double salts, picrates etc...

and only in small quantities hence the use of a primaries as opposed to a secondary that require shockwave propagation. and only a gram or 2 at that

the DV`s actualy irrelevent as the object isn`t to break the steel container, but convert the explosive to gas (as they all do) but have that gas so under pressure, that it would be forced to do something? either liquify or make a solid due to the molecules not being able to be far enough appart to exist as a gas.

it`s basicly the Irrisistable force verses the imovable object, but on a practical scale and not quite literal

[JR]

lol @ Rad

 

JR, I understand exactly what you`re saying. I wasn`t thinking along the lines of AN, ANMN,ANFO ect... they`re just heaving charges, I was considering along the lines of a Primary, Fulminates, Azides, double salts, picrates etc...

and only in small quantities hence the use of a primaries as opposed to a secondary that require shockwave propagation. and only a gram or 2 at that

 

The physics of shock propagation are the same whether primary or secondary explosive. The only difference between primary and secondary is the ease with which the shock can get started. Primaries can go by thermal heating, secondaries require a detonation shock to sufficiently compress for propagating reaction to occur.

 

the DV`s actualy irrelevent as the object isn`t to break the steel container, but convert the explosive to gas (as they all do) but have that gas so under pressure, that it would be forced to do something? either liquify or make a solid due to the molecules not being able to be far enough appart to exist as a gas.

it`s basicly the Irrisistable force verses the imovable object, but on a practical scale and not quite literal

 

From what I understand the two thermodynamic states that have to be considered are: initial = conditions insides the shock wave, final = reaction products just after the shock wave passes. Inside the shock, the pressure is of the order of megabar and the temperature is say 4000 kelvin. After the shock passes, the pressure is related to moles of gas and volume of cavity (but Ideal Gas Law usually doesn't work here, of course) and temperature is say 1000 kelvin or less.

 

Therefore, compared to the initial state, the final products have expanded. You would have a spherical cavity with some reasonably high pressure gas, but it really would not be something super extraordinary.

 

Other than the size of the cavity, this is not so different from the controlled detonation trailers used by bomb squads. One EOD dude told me that after they let something go inside, the vent holes whistle for several days. Amazing. But compared to the 'gas state' in the shock itself (ie, after chemical reaction but before the shock passes), the cavity, though 'full' of explosive, is plenty of volume for the gaseous products.

 

In your 'back of the envelope' scenario, you had about 2 g of explosive in the cubic centimeter cavity; assume complete conversion to gases, and compute how many moles of gas there are using a temperature of about 1000 kelvin, or even 2000 kelvin (use IGL as a starting point). The pressure inside the cavity after the explosion again will be high, but not 'out of this world.'

 

Finally, if you use a primary explosive such as one of the inorganic salts (fulminate, azide, etc), your products will contain solids as well as gases (even secondary high explosives contain solid carbon products, that one of the things that makes numerical modeling of their detonation difficult), so your gas production is relatively smaller.

 

Two Cents Worth, if that much....

[YT2095]

no not at all, all input is welcome

 

I understand about the shock propogation and therfore didn`t want to mess about with secondaries, a primary is just fine for this scenario, NG would be have been just as good if not better due to the fact that`s already as max density whereas with some primaries you risk "dead pressing" and you`ll never get max density per Cm^3, a liquid is ideal, so if we work around NG for example, it`s not the easiest to detonate (despite what the TV would have you beleive) but it would be easy enough for this instance.

and so, the NG starts detonation reaction, it obviously can not become a gas as that requires more room for molecular freedom.

it`s DV is significantly high enough to propogate throughout the rest of the liquid as it`s critical diameter is quite small (a few mm).

the temp is roughly 7000K (well above the vaporisation point of Tungsten), and the products are all gaseous.

so in YOUR esstimation, what may (maynot) happen?

[JR]

and so, the NG starts detonation reaction, it obviously can not become a gas as that requires more room for molecular freedom.

 

Well, that's my point. There is PLENTY of room in the cavity for the gaseous products. 2 g or so of NG will not produce THAT much gas. The gaseous products are expanding from the highly compressed explosive (NG or whatever) in the shock, that's where the super high pressure is.

 

the temp is roughly 7000K (well above the vaporisation point of Tungsten), and the products are all gaseous.

 

The temp is only that high IN the shock wave itself, which does not last for a very long time at any given point in space. The net heating of the bulk material is actually quite small. ANFO detonates at relatively low temp (not because it is 'heaving' or low brisance), and other high ex's like RDX are similar, though admittedly higher final temp than ANFO. I don't have my book of such data within reach at the moment, or I'd give some numbers.

 

so in YOUR esstimation, what may (maynot) happen?

 

I think you will detonate the hi-ex and have a cavity containing compressed (but not extraordinarily so) gas. If the material can withstand the conditions of the detonation itself (megabar shock wave), than it certainly will withstand the expanded product gases. I don't think the products will condense (these gases get compressed in cylinders several hundred atmospheres and don't condense, they are not polar and van der Waals forces are not so great).

 

[YT2095]

with respect to RDX, PETN or the like, I wished to avoid them, nitrated Hexamethylene or polysachride based explosives require det caps, and that lets in room for expansion as the compression cannot be 100%, whereas a liquid would be better, so we`ll stick with NG for now, it`ll keep the maths simple

 

NG starts as a liquid, and therefore if not allowed to expand, the resultant products after reaction must also therefore be a liquid

however some of these liquid may re-combine to form acids or even solids (it`s under extreme pressure remember).

 

lets stick to NG for the model, and we`ll assume no air gaps in the cavity either.

[JR]

NG starts as a liquid, and therefore if not allowed to expand, the resultant products after reaction must also therefore be a liquid

 

I don't think that's true at all. It is a liquid because (a) compared to the size of the molecular products, the reactant liquid molecules are quite large and (b) the reactant molecules interact with other quite strongly.

 

After decomposition, if the products are considered to be mostly N2 and CO2, the intermolecular interactions (which determine gas, liquid or solid) are relatively weak; these are gases.

 

The liquid is initially filling the cavity, but it is not under pressure. After reaction, the chemical composition of the material inside the cavity is different. It is perfectly reasonable for the liquid to occupy 'all available' space in the cavity, but the reaction products to be a gas.

 

'All available' space in the cavity is a relative term, too. The reacting medium molecules exclude considerable space that are not formally occupied by mass. To visualize this (I know NG does not have phenyl rings, this is just for illustration), consider for a second liquid benzene. There is a lot of space inside the ring (and above and below it) that is excluded from being occupied by other benzene molecules. However, if the benzene were to decompose to C and H2, the excluded space is MUCH less, so the 'effective' available volume to the products is much greater.

 

When we numerically model detonations, one of the parameters needed is the 'covolume' of the products ... that is, the volume occupied by the molecules rotating in three dimensions. This defines the excluded volume, which in turn when subtracted from total volume, defines the available product volume. It is a tricky modeling problem, since volume is variable, along with temperature and pressure and moles of products (hey, that's all the gas law parameters that can vary!) depending on how much of which product is produced.

 

however some of these liquid may re-combine to form acids or even solids (it`s under extreme pressure remember).

 

Well, I am asserting that the pressure is not THAT high after the shock wave passes, which it does quickly. The wave hits the steel, then dissipates. The final thermodynamic state inside the cavity is just not that extreme.

 

Let's play with some numbers, just to get 'an idea (for this back of envelope calculation, I am ignoring sig figs):'

 

(1) assume NG decomposes to H2O, CO2, N2 and O2

 

4 C3H5N3O9 --> 10 H2O + 12 CO2 + 6 N2 + O2

 

or 4 moles of solid produces 29 moles of gas.

 

(2) the density of NG is 1.59 g/cm^3, so to fit 2g, we'll need a cavity of 1.26 cm^3 = 0.00126 L.

 

(3) let's say product state temperature is 1000 kelvin. NG detonates at 3470 kelvin, but that is T INSIDE shock.

 

(4) let's assume Ideal Gas Law, just for simplicity.

 

These assumptions, except for the temperature one, will give us an UPPER limit of pressure inside the cavity.

 

Molar Mass NG = 227 g/mol

 

2g NG = 0.0088 mol

 

0.0088 mol solid reactant = 0.06 mol gaseous products

 

p = nRT/V

 

p = (0.06 mol)(0.08206 L atm/mol K)(1000 K)/(0.00126 L)

 

p = 3908 atm, which is about 55,000 psi.

 

55,000 psi is about what is present inside a high powered rifle (such as 30-06 Springfield) chamber when the gun is fired. This activity is done all the time without producing outlandish products and results, or even condensation of the product gases.

 

You may get a higher than this, sure, but I maintain my hypothesis that you won't get so high to produce the kinds of effects being considered.

 

But hey, that's the fun the thing about hypotheses..they are, after all, just guesses!!

 

[wolfson]

3908 atm = 57,431.737 psi, good estimate.

[YT2095]

"1) assume NG decomposes to H2O, CO2, N2 and O2

 

4 C3H5N3O9 --> 10 H2O + 12 CO2 + 6 N2 + O2

 

or 4 moles of solid produces 29 moles of gas."

 

H20 being a liquid would for sure, become just that.

under those pressures and heat the N and O would combine that`s a given, the CO2 is easily solidified at those pressures too (think CO2 gas bottles).

at those heats however, I`m more that sure the H and O would disassociate into H and O at 1`st, I`de anticipate a few secondary reactions closely followed by a few side reactions, and NON of those materials could be sustained as a gas either, not at that mass in that tiny volume of space.

 

we need to know the Exact volune of gas (and compostion) liberated by 1cc of NG at standard RTP before we even begin to work out exactly what may happen.

it is ONLY a hypothetical question anyway, a "WHAT IF" scenario, a bit of fun really

[JR]

Well, one of my company's services is numerical modeling of detonation phenomena

 

I'm pretty tied up with some other work right now, but maybe a bit later, I can set up this calculation and see what the numerical models 'say.'

[YT2095]

most splendid!

 

Be sure, I shall be looking forwards to it, and thnx for your help

[JR]

One point I thought of a little bit ago ... all the species were are considering at 1000 kelvin and 55,000 psi would be supercritical, so not really gas or liquid. (We were both right!!! )

 

Critical Temp - H2O: 374 C

Critical Press - H2O: 3212 psi

 

Critical Temp - CO2: 31.1 C

Critical Press - CO2: 1072 psi

 

Critical Temp - N2: -146 C

Critical Press - N2: 485 psi

 

Critical Temp - O2: -118 C

Critical Press - O2: 735 psi

 

So, I don't really know what the phase diagrams for these compounds look like at 55,000 psi. I do know that water does some really weird stuff at high pressure.

[YT2095]

all I know about water under pressure is that it can be heated more than high enough to melt lead and still remain a liquid, of course when it`s free to move it boils of at 273k RTP, and considerably above that as a gas it may freely disassociate from the H-O-H bonds.

[JR]

FYI, I bounced this off a colleague of mine who knows a lot more about detonation than I do. His reply to the question "what would the products look like?" was:

 

"A ball of mush." Whatever is in there lies in parts of the phase diagrams probably not well understood, and certainly a lot of dissociated species (H, OH, etc. etc) as YT mentioned.

 

He also said that he saw this very thing in a book that was written in the 1950's. I don't have the name of the book; heck, it's probably out of print anyway.

 

[YT2095]

" A ball of mush"

I like it LOL!

[budullewraagh]

this idea is interesting, but raises the question: how would one detonate the explosive?

 

if you use a fuse, the contents will explode and release gas in the direction of the hole created to hold the fuse. if you try to heat it in another way, the outside container most likely will be melted or will be less effective in containing the blast.