Ammonium nitrate

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Ammonium nitrate
Structural formula
Ammonium nitrate crystal structure
Sample of white powder
Identifiers
CAS number 6484-52-2 YesY
ChemSpider 21511 YesY
UNII T8YA51M7Y6 YesY
UN number 0222with > 0.2% combustible substances
1942with <= 0.2% combustible substances
2067fertilizers
2426liquid
RTECS number BR9050000
Jmol-3D images Image 1
Properties
Molecular formula (NH4)(NO3)
Molar mass 80.052 g/mol
Appearance white/grey 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)1
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
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g., fluorine Special hazard OX: Oxidizer. E.g., potassium perchlorateNFPA 704 four-colored diamond
LD50 2085–5300 mg/kg (oral in rats, mice)2
Related compounds
Other anions Ammonium nitrite
Other cations Sodium nitrate
Potassium nitrate
Hydroxylammonium nitrate
Related compounds Ammonium perchlorate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
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 popular explosive, which accounts for 80% explosives used in North America. It is used in instant cold packs, as hydrating the salt is an endothermic process.

Ammonium nitrate is found as a natural mineral (ammonia nitre—the ammonium analogue of saltpetre and other nitre minerals like sodium nitrate) in the driest regions of the Atacama Desert in Chile, often as a crust on the ground and/or in conjunction with other nitrate, chlorate, iodate, and halide minerals. Ammonium nitrate was mined there in the past, but virtually 100% of the chemical now used is synthetic.

Fertilizer

Ammonium nitrate is an important fertilizer with the NPK rating 34-0-0 (34% nitrogen).3 It is less concentrated than urea (46-0-0) 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.45

Safety, handling and storage

Health and safety data are shown on the material safety data sheets available from suppliers and found on the internet.6

Heating or any ignition source may cause violent combustion or explosion.7 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.89 Ammonium nitrate is also used to modify the detonation rate of other explosives, such as ammonia-based dynamites, for example nitroglycerin.citation needed

Numerous safety guidelines are available for storing and handling ammonium nitrate.10 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. 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 liquefy.

The potential for use of the material as an explosive has prompted regulatory measures. For example in Australia, the Dangerous Goods Regulations came into effect in August 2005 to enforce licensing in dealing with such substances.11 Licenses are granted only to applicants (industry) with appropriate security measures in place to prevent any misuse.12 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:13

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 can also be made via metathesis reactions:

(NH4)2SO4 + 2 NaNO3 → 2 NH4NO3 + Na2SO4
(NH4)2SO4 + Ca(NO3)2 → 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 PM10.14

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.15

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.6

Ammonium nitrate is not an extremely hazardous chemical6unreliable source? and is usually used in fertilizer products.1617 The chances of direct personal exposure to the chemical are very low, because the fertilization 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,6 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.18

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.6

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.6
Mutagenic effects In general, nitrates and nitrites are genotoxic.6
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.6

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, Oakdaledisambiguation needed), 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, 2013 Hyderabad blasts 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.19

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.

Ammonium nitrate was suspected as the explosive responsible for the fertilizer plant explosion in West, Texas on April 17, 2013. Investigators said they believe it exploded following a fire that began in the plant's office.20

Mixture with fuel oil

ANFO is a mixture of 94% ammonium nitrate and 6% fuel oil (ANFO) widely used as a bulk industrial explosive.21:1 It is used in coal mining, quarrying, metal mining, and civil construction in undemanding applications where the advantages of ANFO's low cost and ease of use matter more than the benefits offered by conventional industrial explosives, such as water resistance, oxygen balance, high detonation velocity, and performance in small diameters.21:2

References

  1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
  2. ^ Martel, B.; Cassidy, K. (2004). Chemical Risk Analysis: A Practical Handbook. Butterworth–Heinemann. p. 362. ISBN 1-903996-65-1. 
  3. ^ Nutrient Content of Fertilizer Materials
  4. ^ [1]
  5. ^ [2]
  6. ^ a b c d e f g h Ammonium nitrate MSDS
  7. ^ Pradyot Patnaik (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 0-07-049439-8. 
  8. ^ Pothole pond
  9. ^ Progressive Farmer Magazine
  10. ^ Storing and handling ammonium nitrate
  11. ^ Dangerous Goods (HCDG) Regulations
  12. ^ Ammonium Nitrate-Regulating its use, Balancing Access & Protection from "Worksafe Victoria". 
  13. ^ http://www.google.com/patents/pdf/Process_of_producing_concentrated_soluti.pdf?id=XronAAAAEBAJ&output=pdf&sig=ACfU3U0iYFRDUxltKLaVind-3wwP_JYPxg
  14. ^ Int Panis, LLR (2008). "The Effect of Changing Background Emissions on External Cost Estimates for Secondary Particulates". Open Environmental Sciences 2: 47–53. 
  15. ^ Choi, C. S.; Prask, H. J. (1983). "The structure of ND4NO3 phase V by neutron powder diffraction". Acta Crystallographica B 39 (4): 414–420. doi:10.1107/S0108768183002669. 
  16. ^ "Chemicalland21 – Ammonium Nitrate". 
  17. ^ "Ammonium Nitrate". Paton Fertilizers Pty Ltd. 2005. 
  18. ^ Martel, B.; Cassidy, K. (2004). Chemical Risk Analysis: A Practical Handbook. Butterworth–Heinemann. ISBN 1-903996-65-1. 
  19. ^ The Hazards and Dangers of Ammonium Nitrate [Ammonium Nitrate Dangers | http://www.nortechlabs.com/hazards-ammonium-nitrate.html
  20. ^ http://www.dallasnews.com/news/west-explosion/headlines/20130506-investigators-blame-ammonium-nitrate-in-massive-west-explosion.ece Investigators blame ammonium nitrate in massive West explosion
  21. ^ a b Cook, Melvin A. (1974). The Science of Industrial Explosives. IRECO Chemicals. p. 1. ASIN B0000EGDJT. 
  • Properties: UNIDO and International Fertilizer Development Center (1998), Fertilizer Manual, Kluwer Academic Publishers, ISBN 0-7923-5032-4.

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