Ammonium nitrate (\(\text{NH}_4\text{NO}_3\)) is a simple, white, highly water-soluble crystalline salt. It is produced through an acid-base reaction between ammonia and nitric acid. Although it occurs naturally, large-scale synthetic production began in the early 20th century. Manufacturing ramped up significantly in the 1940s for military applications, becoming widely available for commercial use after the Second World War.
Essential Nutrient for Agriculture
The single largest commercial application for ammonium nitrate is its use as a high-nitrogen fertilizer, fundamental to modern agriculture. It is highly valued because it provides nitrogen in two distinct forms readily utilized by plants. Commercial grade ammonium nitrate typically contains about 33.5 percent nitrogen, making it a concentrated source of this macronutrient.
The compound consists of two ions: the ammonium ion (\(\text{NH}_4^+\)) and the nitrate ion (\(\text{NO}_3^-\)). The nitrate portion is immediately soluble and is rapidly taken up by the plant’s roots, supporting quick vegetative growth. This fast-acting delivery addresses immediate nutritional needs during growth spurts.
The ammonium component provides a sustained, slower-release supply of nitrogen to the plant. The \(\text{NH}_4^+\) ions can be absorbed directly by the roots or gradually converted into the nitrate form by beneficial soil microorganisms. This dual mechanism ensures crops receive both an instantaneous boost and prolonged feeding necessary for high yields.
For agricultural use, ammonium nitrate is commonly manufactured into solid spherical shapes, such as granules or prills. Its high solubility makes it effective for various crops and allows for application through irrigation systems as a liquid solution. The widespread use of this fertilizer is a significant factor in increasing crop yields and supporting the global food supply chain.
Industrial Blasting and Mining Agent
Outside of agriculture, ammonium nitrate is a core component in the explosives industry, particularly for large-scale industrial operations. Its main use is as the oxidizing agent in Ammonium Nitrate Fuel Oil (ANFO), a mixture that revolutionized commercial blasting. ANFO is typically composed of approximately 94% porous ammonium nitrate prills and 6% fuel oil, such as diesel, by weight.
The ammonium nitrate supplies the necessary oxygen to react with the fuel oil during detonation. This reaction produces large volumes of nitrogen, carbon dioxide, and steam, creating the expansive force required for rock breakage. ANFO is classified as a blasting agent, meaning it is relatively insensitive and requires a separate, smaller explosive, known as a booster or primer, to initiate detonation.
This stability and low cost make it the preferred material for applications where massive amounts of rock or earth need to be displaced. ANFO is extensively employed in large-scale activities such as open-pit mining, quarrying, and civil construction projects. Its economic viability and ease of bulk handling have made it the most widely used industrial explosive globally.
Minor Commercial and Laboratory Roles
Ammonium nitrate also has several smaller, specialized applications across different sectors. One recognized use leverages its unique thermal property when dissolved in water. The process of dissolving the solid salt is endothermic, meaning it absorbs heat energy from its immediate surroundings.
This heat-absorbing property is the chemical basis for instant cold packs used in sports medicine and first aid. These packs contain solid ammonium nitrate crystals separated from a pouch of water. Squeezing the pack breaks the barrier, allowing the dissolution process to rapidly cool the contents.
In chemical manufacturing, ammonium nitrate serves as an intermediate compound in the production of other materials. Controlled heating of an ammonium nitrate solution can cause it to decompose, yielding water and nitrous oxide. It is also occasionally used in specialized metallurgical processes and as an oxidizing component in certain explosive mixtures.