The Chemistry of Firework Displays

Ponca City, We love you writes "David Ropeik writes at MSNBC that there's a lot more to making a basic firework display than putting a fuel source and an oxidizer together. Pyrotechnic chemists, who are trying to create bedazzlement instead of bang, don't want their work to explode, but to burn for a bit, so it gives a good visual show. To achieve the desired effect, the sizes of the particles of each ingredient have to be just right, and the ingredients have to be blended together just right. To slow down the burning, chemists use big grains of chemicals, in the range of 250 to 300 microns, and they don't blend the ingredients together very well, making it harder for the fuel and oxidizer to combine and burn, thus producing a longer and brighter effect. Surprisingly few emitters are used in pyrotechnics, and there are no commercially useful emitters in blue-green to emerald green in the 490-520 nm region. Energy from the fire in the basic fuel is transferred to the atoms of the colorant chemicals, exciting the electrons in those chemicals into a higher energy state. As they cool down, they move back to a lower state of energy, emitting light. So, you actually see the colors in fireworks as they're cooling down. To get the really tricky shapes, like stars or hearts, the colorant pellets are pasted on a piece of paper in the desired pattern. That paper is put in the middle of the shell with explosive charges above it, and below. When those charges go off, they burn up the paper, and send the ignited colorant pellets out in the same pattern they were in on the sheet of paper, spreading wider apart as they fly."

Comments

Pellet pattern?

[michaelmalak]

the colorant pellets are pasted on a piece of paper in the desired pattern

Not being an explosives expert, but wouldn't the pellets be pasted on in the inverse of the pattern -- i.e. 1/r in polar coordinates or some such?

On a barely-related note, I was surprised to learn after having moved to Denver that not only are 100% of consumer fireworks banned, but there are also no free professional fireworks displays either (though there are several where you pay for admission). You have to either go on July 3 (missed it) to a park or go to an adjacent city (Aurora, Westminster, Boulder, etc.).

Re:Pellet pattern?

[Overzeetop]

I've been present for a 5 gallon bucket full of flash powered being ignited, about 1000-1500' away*. That's about the equivalent of a 12" salute, I believe. It was an awesome "holy shit" moment. Unfortunately, some of the crowd were not aware of that part of the display, and there were gasps and not a few people sobbing immediately thereafter, fearing that something had gone wrong. Even at that distance, the fireball warmed your face and body, and the thump was felt to your toes.

*The Pyrotechnics Guild International 1994(?) convention in Pennsylvania - all licensed and legal. It may have been a bit further, and my memory has it "just across the lake."

Powder Game or Powder Toy - Fireworks-like program

[borbetomagus]

Someone might enjoy these two programs which allow fireworks-like effects: http://dan-ball.jp/en/javagame/dust/ http://powder.unaligned.org/ http://www.youtube.com/watch?v=MESkoRgSeJo http://www.youtube.com/watch?v=Jdf2JSKHWe0

Re:Forget the pretty colors ...

[jonadab]

> explain the chemistry behind the ones that make the big bangs

As a general rule, I think the main active chemical ingredient in those is plain old smokeless powder (which you can easily look up on Wikipedia if you're curious, so I won't duplicate all the details here).

What's more interesting to me is the physics behind the boom. It's very similar to the physics behind thunder. Sudden temperature changes cause a rapid change in volume (Charles' Law in action). The resulting movement creates a sound wave.