ammonium nitrate

 

chemical compound, NH₄NO₃, that exists as colorless, rhombohedral crystals at room temperature but changes to monoclinic crystals when heated above 32°C. It is extremely soluble in water and soluble in alcohol and liquid ammonia. It is prepared commercially by reaction of nitric acid and ammonia. Major uses are in fertilizers and explosives. For fertilizers it is in the form of small clay-coated pellets. For explosives it is sometimes mixed with other substances, e.g., TNT, so that it is more easily detonated. It is also used in solid-fuel rocket propellants, in pyrotechnics, and in the production of nitrous oxide.

Ammonium nitrate
IUPAC name	Ammonium nitrate
Identifiers
CAS number	6484-52-2
RTECS number	BR9050000
Properties
Molecular formula	NH4NO3
Molar mass	80.04336 g/mol
Appearance	white solid
Density	1.123 g/cm³, solid
Melting point	191 °C
Boiling point	approx. 210 °C decomp
Solubility in water	119 g/100 ml (0 °C) 190 g/100 ml (20 °C) 286 g/100 ml (40 °C) 421 g/100 ml (60 °C) 630 g/100 ml (80 °C) 1024 g/100 ml (100 °C)
Explosive data
Explosive velocity	5,270 m/s
Hazards
EU classification	not listed
NFPA 704	0 2 3 OX
Related Compounds
Other anions	Ammonium nitrite; ammonium perchlorate
Other cations	Sodium nitrate; potassium nitrate; hydroxylammonium nitrate
Related compounds	Nitrous oxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

The chemical compound ammonium nitrate, the nitrate of ammonia with the chemical formula NH₄NO₃, is a white powder at room temperature and standard pressure. It is commonly used in agriculture as a high-nitrogen fertilizer, and it has also been used as an oxidizing agent in explosives, including improvised explosive devices.

Use

Use in Industry

Ammonium Nitrate is used for zeolite modification. In ion-exhanges, UZM zeolites have their sodium ions exhanged with the proton in NH₄⁺ in ammonium nitrate. This forms zeolite catalysts which have many uses in various fields, including petroleum.

Use in fertilizer

The highly water soluble salt is the preferred nitrogen source of fertilizers. Most of the produced ammonium nitrate ends therefore in the production of fertilizers. However, the runoff of excess ammonium nitrate is a leading source of environmental waste.

Use in explosives

As a strong oxidizing agent, ammonium nitrate makes an explosive mixture when combined with a fuel such as a hydrocarbon, usually diesel fuel (oil), or sometimes kerosene. ANFO mixtures have reportedly been used for bombs in terrorist acts such as the Oklahoma City Bombing, because ammonium nitrate and fuel oil (ANFO) are readily available in bulk.

Ammonium nitrate is used in military explosives such as the daisy cutter bomb, and as a component of amatol. Military mixtures are often spiked with ~20% aluminium powder as well, increasing the blast power, but with some loss of brisance. One example of this is Ammonal, which contains ammonium nitrate, TNT & aluminium. Aluminised mixtures are very effective under confinement, as in underwater demolition, torpedoes, and rock blasting. Very cheap water-based blasting slurries tap the power of an aluminium-water reaction with enough ammonium nitrate added to burn off the resulting hydrogen.

Ammonium nitrate is also an explosive in its purest form although it is an unusually insensitive one. Explosive properties become much more evident at elevated temperatures. When ammonium nitrate is fused and "boiled" to generate nitrous oxide, it has been claimed to be as sensitive as dynamite at the ~240 °C operating temperature.

This exothermic reaction can run away and reach detonation velocities (without proper temperature controls). The extent of this possibility has been demonstrated several times, most notably at the Ohio Chemical plant in Montreal in 1966. Millions of pounds of relatively pure ammonium nitrate have been (accidentally) detonated when subjected to severe heat and/or shocks; see "Disasters" below. Ammonium nitrate has also found use as a solid rocket propellant, but for a while ammonium perchlorate was frequently considered preferable due to higher performance and faster burn rates. Lately, favor has been swinging back towards ammonium nitrate in rocketry, as it delivers almost as much thrust without producing an exhaust jet full of gaseous hydrochloric acid (HCl) and without the extra expense and sensitivity hazards. Fertiliser-grade ammonium nitrate (FGAN) is manufactured in more compact form, with much lower porosity, in order to achieve more stability and less sensitivity to detonation, whereas technical grade ammonium nitrate (TGAN) prills are made to be porous for better absorption of fuel and higher reactivity.

Other Use

Ammonium nitrate is also used in instant cold packs.^[1] In this use, ammonium nitrate is mixed with water in an endothermic reaction, which absorbs 26.2 kilojoules of heat per mole of reactant.

Products of ammonium nitrate reactions are used in airbags. When sodium azide (NaN₃) is used in airbags, it decomposes to Na (s) and N₂ (g), the sodium forms a fine dust composed of sodium salts, which is not preferred by the airbag producers.

Ammonium nitrate is used in the treatment of some titanium ores.

Ammonium nitrate is used in the preparation of nitrous oxide (N₂O):

NH₄NO_3(aq) -> N₂O_(g) + 2H₂O_(l)

Ammonium nitrate is used in survival kits mixed with zinc dust and ammonium chloride because it will ignite on contact with water.

Ammonium nitrate can be used to make anhydrous ammonia, a chemical often used in the production of methamphetamine.

Production

Industrial production is chemically quite simple, although technologically challenging. The acid-base reaction of ammonia with nitric acid gives a solution of ammonium nitrate: HNO₃(aq) + NH₃(g) → NH₄NO₃(aq). For industrial production, this is done using anhydrous ammonia gas and concentrated nitric acid. This reaction is violent and very exothermic. After the solution is formed, typically at about 83% concentration, the excess water is evaporated to 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 a 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. The processes involved are simple in principle, but certainly not easy.

The Haber process combines nitrogen and hydrogen to produce ammonia, part of which can be oxidised to nitric acid and combined with the remaining ammonia to produce the nitrate. Another production method is used in the so-called Odda process.

Crystalline phases

Transformations of the crystal states due to changing conditions (temperature, pressure) affect the physical properties of ammonium nitrate. The following crystalline states have been identified:

System	Temperature (°C)	State	Volume Change (%)
-	>169.6	liquid	-
I	169.6 to 125.2	cubic	+2.1
II	125.5 to 84.2	tetragonal	-1.3
III	84.2 to 32.3	α-rhombic	+3.6
IV	32.3 to −16.8	β-rhombic	−2.9
V	−16.8	tetragonal	-

The type V crystal form was reported by M. Herrmann, W. Engel, J. Schneider and H. Goebel, Materials Science Forum, 1994, 166, 489. This is a quasi-cubic form which is related to cesium chloride, the nitrogens of the nitrates and the ammoniums are at the sites in a cubic array where Cs and Cl would be in the CsCl lattice. See C.S. Choi and H.J. Prask, Acta Crystallographica B, 1983, 39, 414-420.

Disasters

Main article: Ammonium nitrate disasters

Ammonium nitrate decomposes into gases including oxygen when heated (non-explosive reaction); however, ammonium nitrate can be induced to decompose explosively by detonation. Large stockpiles of the material can be a major fire risk due to their supporting oxidation, and may also detonate, as happened in the Texas City disaster of 1947, which led to major changes in the regulations for storage and handling.

There are two major classes of incidents resulting in explosions:

• In the first case, the explosion happens by the mechanism of shock to detonation transition. The initiation happens by an explosive charge going off in the mass, by the detonation of a shell thrown into the mass, or by detonation of an explosive mixture in contact with the mass. The examples are Kriewald, Morgan (present-day Sayreville, New Jersey) Oppau, Tessenderlo and Traskwood.
• In the second case, the explosion results from a fire that spreads into the ammonium nitrate itself (Texas City, Brest, Oakdale), or from a mixture of ammonium nitrate with a combustible material during the fire (Repauno, Cherokee, Nadadores). The fire must be confined at least to a degree for successful transition from a fire to an explosion (a phenomenon known as "transition from a decomposition or deflagration", or DDT). Pure, compact AN is stable and very difficult to initiate. However, there are numerous cases when even impure AN did not explode in a fire.

Ammonium nitrate decomposes in temperatures above 210 °C. Pure AN is stable and will stop decomposing once the heat source is removed, but when catalysts are present (combustible materials, acids, metal ions, chlorides. ..) the reaction can become self-sustaining (known as self-sustaining decomposition, SSD). This is a well-known hazard with some types of NPK fertilisers, and is responsible for the loss of several cargo ships.

References

• Properties: UNIDO and International Fertilizer Development Center (1998), Fertilizer Manual, Kluwer Academic Publishers, ISBN 0-7923-5032-4.

1. ^ Marshall Brain. Cold Packs. How Refrigerators Work. Howstuffworks.com.

External links

• International Chemical Safety Card 0216
• "Storing and Handling Ammonium Nitrate", UK Health and Safety Executive publication INDG230 (1986)

This information was useful to me. Useful:1 (please add) Didn't Help: (please add)

Donate to Wikimedia