Ammonium Nitrate

Ammonium nitrate, NH₄NO₃, is prepared by neutralizing nitric acid with ammonia, or ammonium carbonate, or by double decomposition between potassium nitrate and ammonium sulfate. It can be obtained in three different crystalline forms, the transition points of which are 35°C, 83°C and 125°C. It is easily soluble in water, a considerable lowering of temperature taking place during the operation; on this account it is sometimes used in the preparation of freezing mixtures. On gentle heating, it is decomposed into water and nitrous oxide. P. E. M. Berthelot in 1883 showed that if ammonium nitrate is rapidly heated the following reaction takes place with explosive violence:--2NH₄NO₃ = 4H₂O + 2N₂ + O₂. In combination with gasoline or other liquid hydrocarbons it is a widely used industrial explosive, being particularly useful in open pit mining and is known as ANFO. The detonation rate is about 3000 feet per second (310 m/s); relatively slow compared to high explosives, which detonate at over 25,000 ft/s (7,600 m/s). This explosive combines the advantages of low cost and stability, requiring a high velocity explosive primer to begin detonation. It is sometimes used in small packets to break up snow cornices in avalanche control. Ammonium nitrate confined in large quantities (such as might be found in a ship's cargo hold) can detonate explosively if combined with hydrocarbons and heated sufficiently by a fire. A fire in a ship carrying ammonium nitrate waterproofed with wax was the cause of a devastating explosion resulting in the Texas City, Texas disaster.