|
|
Chemistry of Pyrotechnics
| Incandescence is light produced from heat. Heat causes a substance to become hot and glow, initially emitting infrared, then red, orange, yellow, and white light as it becomes increasingly hotter. When the temperature of a firework is controlled, the glow of components, such as charcoal, can be manipulated to be the desired color (temperature) at the proper time. Metals, such as aluminum, magnesium, and titanium, burn very brightly and are useful for increasing the temperature of the firework. |
 |
Just about everyone in the United States has some personal experience with fireworks, either from Fourth of July or New Year's Eve celebrations. For example, you have probably seen both sparklers and firecrackers. It turns out that if you understand these two pyrotechnic devices, then you are well on your way to understanding aerial fireworks! The sparkler demonstrates how to get bright, sparkling light from a firework, and the firecracker shows how to create an explosion.
 |
There are three primary fields of application for these effects: propellants, explosives and pyrotechnics. Propellants create a high gas pressure for driving projectiles or rockets and for similar uses. Explosives create a disruption of solid or liquid bodies, as in construction, mining or warfare. Pyrotechnics have effects that are mainly sound and light, but include many other varied applications, mainly on a small scale. Fireworks is an application that is entertainment--a show of light, noise and motion. |
"Fireworks" is an almost exact translation of the Greek roots of "pyrotechnics." Perhaps "pyrotechnics" should be reserved for the serious applications and "fireworks" used for the entertainment side.
The chemical reactions we shall consider are reactions between an oxidizer that supplies oxygen or receives electrons, and a fuel that combines with the oxygen or releases electrons, and is a reducing agent. These two functions may reside in the same molecule, or in different molecules. Some constituents, such as sulphur, may serve as either a fuel or an oxidizer. In any case, both functions are present in every explosive (a general term for all three kinds of applications), and the oxygen of the atmosphere plays no role as an oxidizer, as it does in combustion or respiration, two other chemical sources of energy. For rapid reaction, the oxidizer and the fuel must be intimately mixed before the reaction occurs. In some cases, atmospheric oxidation may play a minor role.
Firecrackers have been around for hundreds of years. They consist of either black powder (also known as gunpowder) or flash powder in a tight paper tube with a fuse to light the powder. Black powder, discussed briefly in How Rocket Engines Work, contains charcoal, sulfur and potassium nitrate. A composition used in a firecracker might have aluminum instead of or in addition to charcoal in order to brighten the explosion.
|
|
|
|
