Ammonium nitrate

Ammonium nitrate
IUPAC name Ammonium nitrate
Identifiers
CAS number	6484-52-2 Y
ChemSpider	21511 Y
UNII	T8YA51M7Y6 Y
UN number	0222 – with > 0.2% combustible substances 1942 – with <= 0.2% combustible substances 2067 – fertilizers 2426 – liquid
RTECS number	BR9050000
Jmol-3D images	Image 1
SMILES [O-][N+]([O-])=O.[NH4+]
InChI InChI=1S/NO3.H3N/c2-1(3)4;/h;1H3/q-1;/p+1 Y Key: DVARTQFDIMZBAA-UHFFFAOYSA-O Y InChI=1/NO3.H3N/c2-1(3)4;/h;1H3/q-1;/p+1 Key: DVARTQFDIMZBAA-IKLDFBCSAH
Properties
Molecular formula	(NH4)(NO3)
Molar mass	80.052 g/mol
Appearance	white solid
Density	1.725 g/cm3 (20 °C)
Melting point	169.6 °C
Boiling point	approx. 210 °C decomp.
Solubility in water	118 g/100 ml (0 °C) 150 g/100 ml (20 °C) 297 g/100 ml (40 °C) 410 g/100 ml (60 °C) 576 g/100 ml (80 °C) 1024 g/100 ml (100 °C)
Structure
Crystal structure	trigonal
Explosive data
Shock sensitivity	very low
Friction sensitivity	very low
Explosive velocity	5270 m/s
Hazards
MSDS	ICSC 0216
EU Index	not listed
Main hazards	Explosive
NFPA 704	0 2 3 OX
LD50	2085–5300 mg/kg (oral in rats, mice)
Related compounds
Other anions	Ammonium nitrite
Other cations	Sodium nitrate Potassium nitrate Hydroxylammonium nitrate
Related compounds	Ammonium perchlorate
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

The chemical compound ammonium nitrate, the nitrate of ammonia with the chemical formula NH₄NO₃, is a white crystalline solid 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. It is the main component of ANFO, a very popular explosive. It is used in instant cold packs, as hydrating the salt is an endothermic process.

Fertilizer

Ammonium nitrate is an important fertilizer with the NPK designation 34-0-0 (34% nitrogen). It is less concentrated than urea (45-0-0) giving ammonium nitrate a slight transportation disadvantage. Ammonium nitrate's advantage over urea is that it is more stable and does not lose nitrogen to the atmosphere. During warm weather urea should only be applied before imminent rain in order to minimize nitrogen loss.

Safe handling and storage

Health and safety data are shown on the material safety data sheets which are available from suppliers and can be found on the internet.

Heating or any ignition source may cause violent combustion or explosion. Ammonium nitrate reacts with combustible and reducing materials as it is a strong oxidant. Although it is mainly used for fertilizer it can be used for explosives. It was sometimes used to blast away earth to make farm ponds. Ammonium nitrates are also used to modify the detonation rate of other explosives. Example will be ammonia dynamites (Nitroglycerin).

Numerous safety guidelines are available for storing and handling ammonium nitrate. It should not be stored near combustible substances or certain fertilizers, especially urea.

Ammonium nitrate has a critical relative humidity of 59.4%, above which it will absorb moisture from the atmosphere.

The increased level of misuse by terrorists prompted the need to change how these substances should be dealt with. For example in Australia, the Dangerous Goods Regulations came into effect in August 2005 to enforce licensing in dealing with such substances. Licenses are granted only to applicants (industry) with appropriate security measures in place to prevent any misuse. Additional uses such as education and research purposes may also be considered but individual use will not. Employees of those with licenses to deal with the substance are still required to be supervised by authorized personnel and are required to pass a security and national police check before a license may be granted.

Production

The processes involved in the production of ammonium nitrate in industry, although chemically simple, are technologically challenging. The acid-base reaction of ammonia with nitric acid gives a solution of ammonium nitrate:

HNO₃(aq) + NH₃(l) → 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 Haber process combines nitrogen and hydrogen to produce ammonia, part of which can be oxidized to nitric acid and combined with the remaining ammonia to produce the nitrate. Another production method is used in the so-called Odda process.

Ammonium nitrate is also manufactured by amateur explosive enthusiasts by metathesis reactions:

(NH₄)₂SO₄ + 2 NaNO₃ → Na₂SO₄ + 2 NH₄NO₃

Ca(NO₃)₂ + (NH₄)₂SO₄ → 2 NH₄NO₃ + CaSO₄

Sodium sulfate is removed by lowering the temperature of the mixture. Since sodium sulfate is much less water-soluble than ammonium nitrate, it precipitates, and may be filtered off. For the reaction with calcium nitrate, the calcium sulfate generated is quite insoluble, even at room temperature.

Reactions

Ammonium nitrate reacts with metal hydroxides, releasing ammonia and forming alkali metal nitrate:

NH₄NO₃ + NaOH → NH₃ + H₂O + NaNO₃

NH₄NO₃ + KOH → NH₃ + H₂O + KNO₃

Ammonium nitrate gives ammonium chloride and nitric acid upon reaction with hydrochloric acid:

NH₄NO₃ + HCl → NH₄Cl + HNO₃

Ammonium nitrate leaves no residue when heated:

NH₄NO₃ Δ→ N₂O + 2H₂O

Ammonium nitrate is also formed in the atmosphere from emissions of NO, SO₂ and NH₃ and is a secondary component of PM10.

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	125.2 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 is a quasi-cubic form which is related to caesium 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.

Health hazards

Health and safety data are shown on the material safety data sheets which are available from suppliers and can be found on the internet.

Ammonium nitrate is not an extremely hazardous chemical and is usually used in fertilizer products. Thus, the chances of direct personal exposure to the chemical are very low, because the fetilization of the soil by use of ammonium nitrate is done at early stages of plant growth and usually does not remain detectable on the harvested plants or when the plants reach the consumer.^{[citation needed]}

Ammonium nitrate has an LD₅₀ of 2217 mg/kg, which for comparison is about two-thirds that of table salt.

Acute health effects

Short-term exposure to ammonium nitrate can cause symptoms ranging from minor irritation to nausea, vomiting, gastric irritation, headaches, dizziness and hypertension.

Area of exposure	Hazard level
Ingestion	Moderately hazardous
Skin contact	Moderately hazardous (irritant)
Eye contact	Moderately hazardous
Inhalation	Moderately hazardous

Long-term health effects

The toxicity of nitrates when ingested is due to in vivo conversion to nitrites. The material safety data sheet considers chronic ingestion of more than 5 mg/kg/day unacceptable. The primary overdose effects of chronic exposure are orthostatic hypotension and methemoglobinemia. Other common effects include: faintness, fatigue, weakness, depression, mental impairment, dizziness, shortness of breath, and reflex tachycardia; headache, nausea, vomiting, and nephritis may also occur.

Types of effect	Effect level
Carcinogenic effects	Though no ammonium-nitrate-specific studies are available, nitrates can be reduced to nitrites in the body, and the formed nitrites can subsequently react with amines to form suspect carcinogens N-nitrosamine.
Mutagenic effects	In general, nitrates and nitrites are genotoxic.
Teratogenic effects	None
Developmental toxicity	Though not specific to ammonium nitrate, some studies have shown a link between birth defects (particularly neural tube defects) and nitrate-contaminated well water.
Prolonged exposure	Causes damage to lungs and mucous membranes and may also cause damage to blood and gastrointestinal tract. Chronic ingestion may also cause nephritis.

Disasters

Main article: Ammonium nitrate disasters

Ammonium nitrate decomposes into the gases nitrous oxide and water vapor 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 and Tessenderlo.

• 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 "deflagration-to-detonation transition", or DDT). Pure, compact AN is stable and very difficult to ignite, and there are numerous cases when even impure AN did not explode in a fire.

Ammonium-nitrate-based explosives were used in the Oklahoma City bombing and in the 2011 Delhi bombing and the bombing in Oslo 2011.

Ammonium nitrate decomposes in temperatures normally well above 200°C. However the presence of impurities (organic and/or inorganic) will often reduce the temperature point when heat is being generated. Once the AN has started to decompose, then a runaway reaction will normally occur as the heat of decomposition is very large. AN evolves so much heat that this runaway reaction is normally impossible to stop. This is a well-known hazard with some types of N-P-K Fertilizers, and it is responsible for the loss of several cargo ships.

Under normal handling conditions, ammonium nitrate is not harmful. However, inhalation of high concentrations of ammonium nitrate dust can cause respiratory tract irritation. Symptoms may include: coughing, sore throat, shortness of breath, or even suffocation. When swallowed in high concentrations, ammonium nitrate may cause headache, dizziness, abdominal pain, vomiting, bloody diarrhea, weakness, a tingling sensation, heart and circulation irregularities, convulsions, collapse, and suffocation. Ammonium nitrate forms a mild acid when mixed with water. This acid can cause irritation to the eyes, nose, and skin.

In November 2009, a ban on ammonium sulfate, ammonium nitrate, and calcium ammonium nitrate fertilizers was imposed in the former Malakand Division—comprising the Upper Dir, Lower Dir, Swat, Chitral, and Malakand districts of the North West Frontier Province (NWFP) of Pakistan—by the NWFP government, following reports that those chemicals were used by militants to make explosives. In January 2010, these substances were also banned in Afghanistan for the same reason. After several cases, AN has now been legalised due to the pakistani forces of NWFP.

Main article: ANFO

References

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

External links

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