Does anyone understand the idea of pressure cooker bombs?
I don't quite get how the pressure cooker helps. If anything, a tight fitting pot would seem to dampen the blast. The homemade explosives aren't that powerful, are they? Just wondering if anyone else understands the "science" behind this. I don't really want to go searching around online for this. 
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the Anarchists Cookbook or Inspire Magazine? 
I think it has something to do with the fact that if you just used a normal metal container with a lid, then the blast would mostly go out the lid since that would be a weak spot. If you use something with a very strong lid (like a pressure cooker), then the blast would probably go equally in all directions.
Just spit-balling though, because I don't want the NSA to see my googling...
Ah, you are from the "pop belt".....
This is a "dry ice bomb". A piece of "dry ice" (solid CO2) is put into a plastic soda bottle (with some water to promote sublimation of the dry ice from solid to gas), and the cap screwed back onto the bottle:
Now, if you just take a piece of dry ice and put it in water, the dry ice turns back into gaseous CO2, and nothing happens other than some bubbling.
If you have something which is going to release gas slowly, then you don't get an "explosion" without a pressure vessel to contain that gas until the pressure builds up to the point where the pressure vessel fails dramatically.
If you just put a piece of dry ice into a soda bottle, and don't seal it up, the only thing that is going to happen is that you'll get some bubbles and some condensation (the white "smoky" like stuff you get from putting dry ice in water).
"High explosives" - substances like plastic explosive - are hard to obtain. "High explosives" will burn so fast (because at a molecular level they contain both the fuel and oxidizer in a single unit), that they create a pressure wave all on their own. Things like gunpowder and other less powerful substances are easy to obtain or make.
But if you take some gunpowder and light it on fire, it just burns really fast. It liberates a lot of gas, but doesn't "explode".
If you take that gunpowder and seal it into something that will hold a lot of pressure, then the gunpowder is going to burn, that gas pressure is going to build up, and the vessel will eventually fail violently.
Then, you can get creative with the vessel in order to create shrapnel - things which will fly out from the explosion in order to do more damage.
That's why one type of grenade looks like this:
When it fails, it will break along those seams, and send pieces of metal flying in all directions.
Last edited Thu Sep 22, 2016, 06:35 PM - Edit history (1)
This is simplified, but IMHO, the cool thing about explosives.
If you think about what it takes to make "something burn rapidly", you need two things: (a) the thing that burns, and (b) the thing that supplies oxygen to the thing that is burning.
In gunpowder, the "thing that burns" is carbon, and the the "thing that supplies oxygen" is potassium nitrate (KNO3). It turns out that at a convenient temperature, the potassium nitrate lets go of that oxygen very easily. So if you have a fine composition involving carbon (and some sulfur) and potassium nitrate, once you get it burning it sort of "burns by itself" since the heated nitrate will release oxygen to the carbon and sulfur, which will get hotter, and it goes very quickly.
The magic is in getting them mixed well in order to get a high speed of ignition and burn.
In "high explosives" you have molecules in which part of the molecule is the oxidizer and another part of the molecule is the fuel.
This is TNT:
Do you see that Carbon atom up there with the three hydrogen atoms? There are additional carbon atoms (not shown) at the corners of the ring. And do you see those Nitrogen atoms hanging onto those lovely big oxygen atoms?
Just like in gunpowder, you have a bunch of carbon sitting around, and some oxygen which is bound to nitrogen.
That Carbon would LOVE to get rid of those hydrogens, hook up with the oxygens, and make carbon monoxide. Meanwhile, the hydrogens would like to get together with a couple of oxygens of their own and make water.
The nitrogens, on the other hand, would prefer to just couple off on their own together.
It's like a miniature soap opera of unrequited love going in around that toluene ring (in which each of those corners of the ring is also a carbon atom).
All they need to do is to be given a little push for everyone to pick up the partner they want, and one part of the molecule supplies the fuel, while other parts of the molecule supply the oxygen.
It's the same thing that goes on in gunpowder, but unlike gunpowder, where you have various chemical components doing different parts of the work, high explosive molecules are tiny machines which reproduce that fuel/oxidizer concept at the molecular level. They are just itching to rip themselves apart, given the correct "push" to do so.
As you might imagine, an unstable molecule is going to rip itself apart faster than little bits of carbon will light on fire from nearby little bits of nitrate in the gunpowder. So when it goes, it goes at tremendous speed.
Honestly, as I said, they teach this to kids in Delaware, because the DuPont company played such an important role in the history of the state.
These are the old DuPont powder mills along the Brandywine River in Wilmington:
That's the mill race in the foreground, and the mills are powered by those wheels, to grind the powder. Notice that the mill houses are high stone in the back, and have a sloping wood roof facing toward the river (on the other side of the mill houses).
Here's another view:
They are built that way so that each one works a limited quantity. If one of them blows, speaking of pressure vessels, it explodes outward toward the river, and not toward the other mill houses or the rest of the plant (situated on the bank side across the mill race) - or, more importantly, toward E.I. DuPont's house, which is also situated just uphill from the plant.
But, seriously, groups of children in Delaware are regularly taken there and shown how to make and test blasting powder:
They have a small scale setup in one of the mill houses, and it's great to watch the kids jump when they set it off every half hour or so.
Sulfur has a low melting point and a lower ignition temperature than charcoal, so it brings down the ignition temperature of the mix.
You can make gunpowder without it, but it is a lot harder to light.
That is, making gun powder ( first "black powder," then modern nitro-cellulose propellant ("smokeless" powder). Approx. 215 years old.
The second oldest by this standard? Remington Arms, 200 years old this year.
One side of the structures DuPont made had very flimsy walls which were easy to replace when the "occasional" accident occurred and blew out the wall, along with the workers. 
Black powder, though less powerful than modern propellants, is far less stable, and sensitive to both heat and impact.
If I remember correctly, black powder explosions readily follow the path of least resistance, whereas TNT, etc. has an explosion which can radiate significantly in all directions. The Boston bomber's devices generally upwards, but left the sidewalk and its bed underneath with superficial damage. The great danger was shrapnel. Other immediate clues than the murderers used stripped away firecrackers were the "sulfurous" smell many reported, and the billowing white clouds.
Thank goodness the bombs were not fashioned with modern explosives.
You've got a moist material surrounded by a hot shell. Heat the popcorn kernel to a certain temperature and the moisture expands enough to overcome the resistance of the shell. Pop! The trick to manufacturing good popcorn is to develop a type of corn where all of the kernels have virtually the same shell strength. Orville Reddenbacker (sp??) has this down to a science -- there are rarely any unpopped kernels left.
