Ammonium Nitrate - Things You Should Know

February 2021

Ammonium nitrate (AN), NH 4 + NO 3 - is the ammonium salt of nitric acid. It is the main component of many fertilizers (e.g., "blue grain"). Earlier, it was also used in airbags as a gas-generating component since it is inexpensive and safe to handle and produces good yields of non-toxic gases (mainly H 2 O, N 2, and O 2). Today it is no longer used in airbags because it is hygroscopic (water-drawing) and shows several phase transitions near room temperature (i.e., the Ammonium nitrate exists in different crystal forms with different densities).

It is used in the reaction with dicyandiamide, (H 2 N) 2C = N-CN, with intermediate formation of guanidinium nitrate, C (NH 2) 3 + NO 3 -, for the production of nitroguanidine, (H 2 N) 2 C = N-NO 2 (component inhomogeneous, from different substances built-up, propellant charge powders). Due to its positive oxygen balance (+20%), it is also used as a component in (mostly civil) explosives (e.g., emulsion explosives, suspended droplets of an aqueous Ammonium nitrate solution in oil). The explosion of pure Ammonium nitrate follows the following equation:

NH 4 + NO 3 - (solid) ➝ 2 H 2 O (gas) + N 2 (gas) + ½ O 2 (gas)

Problem with Ammonium Nitrate

Although Ammonium nitrate is considered fire-promoting and decomposes when heated from a melting point of 170 ° C to 210 ° C, it does not belong to the explosive substances in the sense of the Explosives Act. However, this decomposition can occur explosively, especially if the storage of large quantities (tons) leads to (self-) damming and if oxidizable impurities (oil, gasoline, sawdust, grain, flour) are added. ("Damming" means that an explosive is enclosed in a solid envelope, which generally increases the detonation effect compared to the more harmless burning of the substance.) There have been many severe accidents with Ammonium nitrate in history, including Oppau (1921, 400 t ASN, 559 dead), Texas City (1947, approx. 500 dead), and most recently, Beirut (2020, 2,750 t, approx. 140 dead).

Ammonium Nitrate: Explosive under Certain Circumstances

Ammonium nitrate is a colorless, crystalline substance. It is a salt that can be made from ammonia and nitric acid relatively cheaply.

If it is not mixed, ammonium nitrate is harmless; it can only explode and become fatal under certain circumstances, for example, if huge quantities are close together. Then ammonium nitrate behaves like a bio bin or a compost heap; it heats up. If the amount is significant enough, it catches fire. In turn, oxygen is released, and the fire spreads.

Ammonium nitrate in chemistry: - Ammonium nitrate melts at just under 170 degrees Celsius. At this temperature, it also breaks down into water and nitrous oxide.

- At temperatures above 300 degrees Celsius or a vital initial ignition, ammonium nitrate detonates.

- Ammonium nitrate is a medium-strength explosive: it detonates around four times more strongly than black powder. However, TNT detonates around two and half times more than ammonium nitrate.

- The burning rate during the detonation of ammonium nitrate is 2,500 m / s.

The ammonium nitrate melts, whereby a hard layer can form on the outside while the quantity continues to burn on the inside. Like a volcanic eruption, gases are created inside the crowd that generates high pressure and breakthrough at some point and thus trigger an explosion.

Final Words

Ammonium nitrate is a salt made from ammonia and nitric acid. Ammonia and ammonium salts are essential nutrients that promote plant growth enormously. But it is also used to manufacture explosives. Ammonium nitrate is considered oxidizing and can explode when heated.

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