Potassium perchlorate is an oxidizer used in ammunition, fireworks, flash grenades and explosives primers. It can be used as a rocket propellant, but has been replaced by ammonium perchlorate in most modern rocketry applications. Potassium perchlorate also has limited medical use.
Potassium perchlorate works by enhancing the combustion of other substances; it does this by transferring oxygen to the combusting substance. It is not flammable or explosive on its own. In carbon-based substances such as sugars, this produces carbon dioxide and causes an explosion. Materials that do not explode burn with a purple flame. This flame is colored by the potassium.
Firecrackers and small fireworks mix aluminum with potassium perchlorate to produce their characteristic flashes and bangs. Larger pyrotechnics displays use sulfur or magnesium to produce brighter flashes and more smoke. Other compounds, such as antimony sulfide and barium nitrate, are added to change the color of the flash and increase the volume of the sound produced.
Potassium perchlorate can be used as a treatment for an overactive thyroid gland. This is due to the chemical similarities between the perchlorate ion and the idodide ion the thyroid gland utilizes. When it is used, potassium perchlorate is combined with other thyroid medications.