Ammonium perchlorate

Ammonium perchlorate (AP) is a chemical compound with the formula NH4ClO4. It is the salt of ammonia and perchloric acid. Like other perchlorates, it is a powerful oxidizer.

It is produced by reaction between ammonia and perchloric acid, or by double decomposition between an ammonium salt and sodium perchlorate.

It crystallises in colorless rhombohedra with a relative density of 1.95. Like most ammonium salts, it decomposes before melting. Mild heating results in chlorine, nitrogen, oxygen and water, while strong heating may lead to explosions.

The combustion of such compound is quite complex and is widely studied in literature. Ammonium perchlorate crystals decompose before melting, even though a thin liquid layer has been observed on crystal surface during high pressure combustion processes.

The gaseous decomposition products are in general ammonia- and chlorine-based and can react together generating a thin premixed flame very close to the crystal surface. Pure crystals cannot sustain a flame below the pressure of 20 bar (2 MPa). Nevertheless, the material is considered hazardous if ground under 15 micrometres. When AP is mixed with a fuel (like a metal powder or mixed with a polymeric binder) it can generate self-sustained combustion also far under atmospheric pressure.

It is an important oxidizer used in solid rocket propellants known as Ammonium perchlorate composite propellants (APCP). Uses include the Space Shuttle Solid Rocket Boosters, as well as many other solid rockets including some fireworks, amateur and hobby high powered rockets, and larger rockets used for space launch and military purposes.

The PEPCON disaster happened at an ammonium perchlorate manufacturing plant. The resulting explosions measured 3.5 on the Richter scale some 600 miles (1000 km) away. Over 400 people were injured, but only 2 died in the monstrous blast.