What Is Ammonium Nitrate?
Ammonium nitrate, the ammonium salt of nitric acid, is a colorless crystalline substance. It is produced both naturally and synthetically, with an annual global production of approximately 20 million tons. Due to its involvement in several catastrophic explosions, many countries are reconsidering its consumer use due to safety concerns.
Uses of Ammonium Nitrate
Primarily used as a nitrogen fertilizer, ammonium nitrate is not recommended for paddy fields due to denitrification risks. Its other applications include the manufacture of explosives, gunpowder, fireworks, herbicides, insecticides, and propellants for rocket engines. The well-known ANFO explosives, combining 94% ammonium nitrate with 6% fuel oil, are widely used in mining and construction.
Properties of Ammonium Nitrate
With the chemical formula NH4NO3 and a molar mass of 80.04, ammonium nitrate has a density of 1.7 g/mL. It melts at 170°C and decomposes at 210°C. Although hygroscopic, it does not form hydrates and is soluble in water and ethanol. Ammonium nitrate is stable under normal conditions but can explode if mixed with flammable materials or exposed to heat, shock, or friction in confinement.
Other Information on Ammonium Nitrate
1. Synthesis of Ammonium Nitrate
Produced through the acid-base reaction between nitric acid and ammonia, this exothermic process involves concentrating nitric acid using anhydrous ammonia. The resulting solution is evaporated to obtain a high concentration of ammonium nitrate, typically around 83%, which can be further concentrated to 95%-99.9%. The melt is processed into prills or granules, which are often coated to prevent caking.
2. Raw Materials and Products in the Synthesis of Ammonium Nitrate
Ammonia, used in the synthesis, is derived from hydrogen and nitrogen via the Haber-Bosch process and then oxidized to nitric acid by the Ostwald process. Calcium carbonate, a byproduct, is purified and sold separately as calcium ammonium nitrate.
3. Reaction of Ammonium Nitrate
When heated, ammonium nitrate decomposes into ammonia and dinitrogen monoxide above its melting point. Under confinement, it explosively decomposes into nitrogen, oxygen, and water. This decomposition can be harnessed in explosive formulations. Additionally, its dissolution in water is endothermic, making it useful in instant cooling packs.