THE CHEMISTRY OF FIREWORKS I’m John Conkling, I’m an adjunct professor of chemistry at Washington College in Chestertown Maryland. I wrote a textbook, “The Chemistry of
Pyrotechnics: Basic Principles and Theory.” Everything you see in a fireworks display is chemistry in action. How the colors are all produced by very specific chemical mixtures that produce beautiful color flames. The sparks are small pieces of fuel that continue to burn in air. Without chemistry, you couldn’t have the burning mixtures. Without the burning mixtures, we wouldn’t have the fireworks. LETS TALK CHEMICALS Every pyrotechnic composition has at least one chemical that’s oxygen-rich an oxidizer: Potassium nitrate used to make black powder. Potassium perchlorate used in a lot of color compositions. Strontium nitrate is an oxygen-rich chemical, but the strontium being in there also produces a red flame color. Then you need a fuel that’s gonna combined with the oxidizer to produce heat. The fuels are things like sulfur, charcoal, aluminum powder, magnesium powder, you vary your fuel to get a specific heat output. Specific burning rate to try and get the exact behavior you looking for in your chemical reaction. Most people when they think a fireworks think of the sky…EXPLODING! AERIAL SHELLS This is an aerial shell, this is what people go to watch a fireworks display at sea. It’s a cardboard casing. The bottom has a little pocket of black powder, granular black powder propellant. There’s a very important time fuse that goes from the propellant into the center of the casing. That determines when the shells going to burst up in the air. The inside of the sphere itself has a black powder bursting charge, and then a number of little green pea marble sized pellets of chemical mixture, that will produce different colors different visual effects when the shell burst open. So this device is placed in a mortar tube, a fuse or it’s gonna be electrically fired a wire and extends out into mortar tube. At exact time you wanna fire it, the signals is given, the button’s pushed the propellant ignites and throws this device up into the air. At the same time this little delay fuse, which is running from the propellant up into the center the shells burning. And then 3,4,5 seconds later, depending on how high you wanted to go burns into the center in the shell, light that gunpowder bursting charge, and – BOOM! – blows the shell open up in the sky and you see the beautiful colors, the sparks, all the effects, the patterns that have been engineered into the device. We produce colors by using the fact that different chemical elements, heated to high temperature, get rid of this energy by emitting very specific wavelengths of light. You know this is the stock room where we keep a broad assortment of chemicals. Copper oxide is a chemical element that will produce a very, very nice blue flame color for us. For a red you’d look for a strontium compound, here’s strontium chloride. Sodium of course will produce the yellow orange, sodium silicate. Calcium makes a nice yellow orange here’s a calcium nitrate or the calcium carbonate. If we want a grain color we need some kind of a barium compound, this is barium acetate. You look for chemicals that don’t strongly pick up water, that are not hydroscopic. SAFTEY FIRST! Anytime we have students in the lab or I’m doing demos, everybody has to have their safety glasses on. Now the glasses I’m wearing are polycarbonate lenses, which are shatter resistant, but when I’m around energetic chemicals I always wear the extra protection of goggles or side shades. DEMO TIME! I mean, to produce color you start with a burning mixture, you need an oxidizer and a fuel and then you add the other ingredients, the color producing ingredients to it. This is a mixture of potassium
perchlorate and red gum. (INSTANT REPLAY ) (DRAMATIZATION) Now instead of red, now we want to produce green, so we’ve added some barium carbonate. Blue is the hardest color to
produce pyrotechnically. You need perfect chemistry. This is copper oxide this is a red flame composition, from strontium nitrate. It’s a very bright flame because it has magnalium, a magnesium aluminum alloy in the composition that raises the flame temperature. Now I’ve taken my base mixture and added moderately coarse magnesium. This should produce a nice white sparkle effect. When I’m not sure exactly what’s going to happen when I test something, I’ll use a little piece of fuse and I light the fuse and it gives me the time to step back just a short distance. There goes the fuse. AWESOME! Fireworks make people happy. There’s something about watching that night sky explode in color and sparks and noise that I think really gets deep in the human soul and seeing the night sky exploding in fire, still brings chills to a lot of people.