Do you know what is ammonium nitrate? and why it is so dangerous?

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Ammonium nitrate


Introduction

Definition

    Ammonium nitrate is a crystalline white solid. Its made in large quantity industrially by the reaction of ammonia with concentrated nitric acid.

The industrial production of ammonium nitrate entails the acid-base reaction of ammonia with nitric acid. 


NH3 + HNO3  →  NH4NO3


Ammonia is used in its anhydrous form (a gas) and nitric acid is concentrated. After the solution is formed, typically at about 83% concentration, the excess water is evaporated off to leave an ammonium nitrate(AN) content of 95% to 99.9% concentration(AN melt), depending on grade. The AN melt is then made into “prills” or small beads in spray tower, or into granules by spraying and tumbling in a rotating drum. The prills or granules may be further dried, cooled, and then coated to prevent caking. These prills or granules are the typical AN products in commerce.


Applications


Ammonium nitrate is an important fertilizer with NPK rating 34-0-0 (34% nitrogen). It is less concentrated than urea (46-0-0), giving ammonium nitrate a slight transportation disadvantage. Ammonium nitrate's advantage over urea is that is more stable and does not rapidly lose nitrogen to the atmosphere.


Explosives


Ammonium nitrate is not an explosive in the form it is commonly sold. However, it readily forms explosive mixtures with varying properties when combined with primary explosives such as azides or with fuels such as aluminium powder or fuel oil.


Disasters


Ammonium nitrate decomposes, non-explosively, into the gases nitrous oxide and water vapor when heated. However, it can be induced to decomposes explosively by detonation. Large stockpiles of the material can also be a major fire risk due to their supporting oxidation, a situation that can easily escalate to detonation. Explosions are not uncommon: relatively minor incidents occur most years, and several large and devastating explosions have also occurred. Examples include the Oppau explosion of 1921(one of the largest artificial non-nuclear explosion), the Texas city disaster of 1947, the 2015 Tianjin explosions in China, and the 2020 Beirut explosions.


Safety, handling, and storage


Numerous safety guidelines are available for storing and handling ammonium nitrate. Health and safety data are shown on the safety data sheets available from suppliers and from various governments.


Pure ammonium nitrate does not burn but as a strong oxidizer, it supports and accelerates the combustion of organic (and some inorganic) material. It should not be stored near combustible substances.


While ammonium nitrate is stable at ambient temperature and pressure under many conditions, it may denote from a strong initiation charge. It should not be stored near high explosives or blasting agents.


Molten ammonium nitrate is very sensitive to shock and detonation, particularly if it becomes contaminated with incompatible materials such as combustibles, flammable liquids, acids, chlorates, chlorides, sulfur, metals, charcoal.


Contact with certain substances such as chlorates, mineral acids, and metal sulfides, can lead to vigorous or even violent decomposition capable of igniting nearby combustible material or detonating.


Ammonium nitrate begins decomposition after melting, releasing NOx, HNO3, NH3, and H2O. It should not be heated in a confined space. The resulting heat and pressure from decomposition increases the sensitivity to detonation and increase the speed of decomposition. Detonation may occur at 80 atmospheres. Contamination can reduce this to 20 atmospheres.


Ammonium nitrate has a critical relative humidity of 59.4%, above which it will absorb moisture from the atmosphere. Therefore, it is important to store ammonium nitrate in a tightly sealed container. otherwise, it can coalesce into a large, solid mass. Ammonium nitrate can absorb enough moisture to liquify. Blending ammonium nitrate with certain other fertilizers can lower the critical relative humidity.



 

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