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 bedazzle 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 size 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, and 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. Finally remember that in 2003, six deaths were linked to fireworks and hospital emergency departments treated 9,300 fireworks injuries so read these safety tips and enjoy the 4th."