Perchlorates are the salts derived from perchloric acid (HClO4). They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders. They are also used as an oxidizer in rocket fuel and can be found in airbags, fireworks, and Chilean fertilizers. Both potassium perchlorate (KClO4) and ammonium perchlorate (NH4ClO4) are used extensively within the pyrotechnics industry, whereas ammonium perchlorate is a component of solid rocket fuel. Lithium perchlorate, which decomposes exothermically to give oxygen, is used in oxygen "candles" on spacecraft, submarines and in other esoteric situations where a reliable backup or supplementary oxygen supply is needed. Most perchlorate salts are soluble in water.
Ammonium perchlorate (AP) is a chemical compound with the formula NH4ClO4. It is the salt of ammonia and perchloric acid. Like other perchlorate, 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 crystallizes 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 micrometers. 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.
As an oxidizer, KClO4 reacts with a wide variety of fuels. A common example is glucose, C6H12O6.
3 KClO4 + C6H12O6 ? 6 H2O + 6 CO2 + 3 KCl
When mixed with cane sugar, it can be used as a low explosive, if the necessary confinement is provided. Otherwise the mixture will simply deflagrate with an intense purple flame indicative of potassium salts. Flash compositions used in firecrackers usually consist of fine aluminium powder mixed with potassium perchlorate.
Potassium perchlorate can be used safely in the presence of sulfur; however, potassium chlorate cannot. The common explanation for this is that the sulfur will, given time, produce minute quantities of sulfurous acid and sulfuric acid. These will, in turn, react with potassium chlorate to produce chloric acid, which is highly unstable and can lead to premature ignition of the composition. The corresponding acid of potassium perchlorate, perchloric acid, is stable enough as to prevent spontaneous ignition.
Sodium perchlorate is a perchlorate of sodium and has the formula NaClO4. Sodium perchlorate melts with decomposition at 480 °C. Its heat of formation is -382.75 kj mol-1. It is a white crystalline solid. It is hygroscopic. It is soluble in water and in alcohol. It usually comes as the mono hydrate, which has a rhombic crystal structure.