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Ammonium nitrate

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Ammonium nitrate
Structural formula
Ammonium nitrate crystal structure
Sample of white powder and spherules
Names
IUPAC name
Ammonium nitrate
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.026.680
EC Number
  • 229-347-8
RTECS number
  • BR9050000
UNII
UN number 0222with > 0.2% combustible substances
1942with ≤ 0.2% combustible substances
2067fertilizers
2426liquid
Properties
NH4NO3
Molar mass 80.043 g/mol
Appearance colorless
Density 1.725 g/cm3 (20 °C)
Melting point 169.6 °C (337.3 °F; 442.8 K)
Boiling point approx. 210 °C (410 °F; 483 K) decomposes
Endothermic
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]
-33.6·10−6 cm3/mol
Structure
trigonal
Explosive data
Shock sensitivity very low
Friction sensitivity very low
Detonation velocity 2500 m/s
Hazards
Main hazards Explosive, Oxidizer
GHS pictograms GHS07: Harmful GHS03: Oxidizing GHS01: Explosive
GHS Signal word Danger
H201, H271, H319
P220, P221, P271, P280, P264, P372
NFPA 704 (fire diamond)
Lethal dose or concentration (LD, LC):
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 otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Ammonium nitrate is a chemical compound with the chemical formula NH4NO3. It is a white crystalline solid consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is predominantly used in agriculture as a high-nitrogen fertilizer.[4] Global production was estimated at 21.6 million tonnes in 2017.

Its other major use is as a component of explosive mixtures used in mining, quarrying, and civil construction. It is the major constituent of ANFO, a popular industrial explosive which accounts for 80% of explosives used in North America; similar formulations have been used in improvised explosive devices.

Many countries are phasing out its use in consumer applications due to concerns over its potential for misuse.[5] Accidental ammonium nitrate explosions have killed thousands of people since the early 20th century.

Occurrence

Ammonium nitrate is found as the natural mineral gwihabaite – the ammonium analogue of saltpetre – in the driest regions of the Atacama Desert in Chile, often as a crust on the ground or in conjunction with other nitrate, iodate, and halide minerals. Ammonium nitrate was mined there in the past,[when?] but virtually 100% of the chemical now used is synthetic.

Production, reactions and crystalline phases

The industrial production of ammonium nitrate entails the acid-base reaction of ammonia with nitric acid:[6]

HNO3 + NH3 → NH4NO3

Ammonia is used in its anhydrous form (a gas) and the nitric acid is concentrated. The reaction is violent owing to its highly exothermic nature. 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 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 ammonia required for this process is obtained by the Haber process from nitrogen and hydrogen. Ammonia produced by the Haber process can be oxidized to nitric acid by the Ostwald process. Another production method is a variant of the nitrophosphate process:

Ca(NO3)2 + 2 NH3 + CO2 + H2O → 2 NH4NO3 + CaCO3

The products, calcium carbonate and ammonium nitrate, may be separately purified or sold combined as calcium ammonium nitrate.

Ammonium nitrate can also be made via metathesis reactions:

(NH4)2SO4 + Ba(NO3)2 → 2 NH4NO3 + BaSO4
NH4Cl + AgNO3 → NH4NO3 + AgCl

Reactions

As ammonium nitrate is a salt, both the cation, NH4+, and the anion, NO3, may take part in chemical reactions.

Solid ammonium nitrate decomposes on heating. At temperatures below around 300 °C, the decomposition mainly produces nitrous oxide and water:

NH4NO3 → N2O + 2H2O

At higher temperatures, the following reaction predominates.[7]

2NH4NO3 → 2N2 + O2 + 4H2O

Both decomposition reactions are exothermic and their products are gas. Under certain conditions, this can lead to a runaway reaction, with the decomposition process becoming explosive.[8] See § disasters for details. Many ammonium nitrate disasters, with loss of lives, have occurred.

The red–orange colour in an explosion cloud is due to nitrogen dioxide, a secondary reaction product.[8]

Crystalline phases

A number of crystalline phases of ammonium nitrate have been observed. The following occur under atmospheric pressure.

Phase Temperature (°C) Symmetry
(liquid) (above 169.6)
I 169.6 to 125.2 cubic
II 125.2 to 84.2 tetragonal
III 84.2 to 32.3 α-rhombic
IV 32.3 to −16.8 β-rhombic
V below −16.8 tetragonal[9]

Both the β-rhombic to α-rhombic forms are potentially present at ambient temperature in many parts of the world but have a 3.6% difference in density. As a result, this phase transition and attending change of volume, with the practical consequence that ammonium nitrate formed as solid rocket motor propellant develops cracks. For this reason, phase stabilized ammonium nitrate (PSAN) which incorporates metal halides as stabilisers has been investigated.[10]

Applications

Fertilizer

Ammonium nitrate is an important fertilizer with NPK rating 34-0-0 (34% nitrogen).[11] 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 rapidly lose nitrogen to the atmosphere.

Explosives

Ammonium nitrate is an ingredient in certain explosives. Examples of explosives containing ammonium nitrate include:

Mixture with fuel oil

ANFO is a mixture of 94% ammonium nitrate ("AN") and 6% fuel oil ("FO") widely used as a bulk industrial explosive.[12]: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.[12]:2

Terrorism

Ammonium nitrate-based explosives were used in the Sterling Hall bombing in Madison, Wisconsin, 1970, the Oklahoma City bombing in 1995, the 2011 Delhi bombings, the 2011 bombing in Oslo, and the 2013 Hyderabad blasts.

In November 2009, the government of the North West Frontier Province (NWFP) of Pakistan imposed a ban on ammonium sulfate, ammonium nitrate, and calcium ammonium nitrate fertilizers in the former Malakand Division – comprising the Upper Dir, Lower Dir, Swat, Chitral, and Malakand districts of the NWFP – following reports that those chemicals were used by militants to make explosives. Due to these bans, "Potassium chlorate – the stuff that makes safety matches catch fire – has surpassed fertilizer as the explosive of choice for insurgents."[13]

Niche uses

Ammonium nitrate is used in some instant cold packs, as its dissolution in water is highly endothermic. It also was used, in combination with independently explosive "fuels" such as guanidine nitrate,[14][15] as a cheaper (but less stable) alternative to 5-aminotetrazole in the inflators of airbags manufactured by Takata Corporation, which were recalled as unsafe after killing 14 people.[16]

A solution of ammonium nitrate with nitric acid called Cavea-b showed promise for use in spacecraft as a more energetic alternative to the common monopropellant hydrazine. A number of trials were carried out in the 1960s but the substance was not adopted by NASA.

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.[17][18][19]

Pure ammonium nitrate does not burn, but as a strong oxidizer, it supports and accelerates the combustion of organic (and some inorganic) material.[17][20][21] It should not be stored near combustible substances.

While ammonium nitrate is stable at ambient temperature and pressure under many conditions, it may detonate 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 and sawdust.[22][17]

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.[23][24]

Ammonium nitrate begins decomposition after melting, releasing NO
x
, HNO3, NH
3
and H2O. It should not be heated in a confined space.[17] The resulting heat and pressure from decomposition increases the sensitivity to detonation and increases the speed of decomposition. Detonation may occur at 80 atmospheres. Contamination can reduce this to 20 atmospheres.[22]

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. Blending ammonium nitrate with certain other fertilizers can lower the critical relative humidity.[25]

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.[26] Licenses are granted only to applicants (industry) with appropriate security measures in place to prevent any misuse.[27] 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.

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.[28]

Ammonium nitrate is not hazardous to health and is usually used in fertilizer products.[28][29][30]

Ammonium nitrate has an LD50 of 2217 mg/kg,[31] which for comparison is about two-thirds that of table salt.

Disasters

Ammonium nitrate decomposes, non-explosively, into the gases nitrous oxide and water vapor when heated. However, it can be induced to decompose explosively by detonation.[32] Large stockpiles of the material can also be a major fire risk due to their supporting oxidation, a situation which 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 explosions), the Texas City disaster of 1947, the 2015 Tianjin explosions in China, and the 2020 Beirut explosions.[33]

Ammonium nitrate can explode through two mechanisms:

See also

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. ^ "Archived copy". Archived from the original on 17 February 2015. Retrieved 13 March 2015.CS1 maint: archived copy as title (link)
  4. ^ Karl-Heinz Zapp "Ammonium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2012, Wiley-VCH, Weinheim. doi:10.1002/14356007.a02_243
  5. ^ Ammonium nitrate sold by ton as U.S. regulation is stymied. Archived 28 February 2018 at the Wayback MachineThe Dallas Morning News
  6. ^ "Archived copy" (PDF). Archived from the original (PDF) on 23 January 2012. Retrieved 11 November 2008.CS1 maint: archived copy as title (link)
  7. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 469. ISBN 978-0-08-037941-8.
  8. ^ a b "The chemistry behind the Beirut explosion".
  9. ^ 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.
  10. ^ Kumar, Pratim (December 2019). "Advances in phase stabilization techniques of AN using KDN and other chemical compounds for preparing green oxidizers". Defence Technology. 15 (6): 949–957. doi:10.1016/j.dt.2019.03.002.open access
  11. ^ "Nutrient Content of Fertilizer Materials" (PDF). Archived from the original (PDF) on 24 December 2012. Retrieved 27 June 2012.
  12. ^ a b Cook, Melvin A. (1974). The Science of Industrial Explosives. IRECO Chemicals. p. 1. ASIN B0000EGDJT.
  13. ^ Brook, Tom Vanden. "Afghan bomb makers shifting to new explosives for IEDs". USA TODAY.
  14. ^ US 5531941 
  15. ^ Airbag Compound Has Vexed Takata for YearsThe New York Times
  16. ^ A Cheaper Airbag, and Takata's Road to a Deadly Crisis.The New York Times
  17. ^ a b c d Chemical Advisory: Safe Storage, Handling, and Management of Ammonium Nitrate United States Environmental Protection Agency
  18. ^ "Storing and handling ammonium nitrate" (PDF). Archived (PDF) from the original on 4 July 2011. Retrieved 22 March 2006.
  19. ^ "Ammonium nitrate MSDS".
  20. ^ Pradyot Patnaik (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN 0-07-049439-8.
  21. ^ "Ammonium nitrate". PubChem. Retrieved 6 August 2020.
  22. ^ a b "Report for Kooragang Island Update PHA MOD1 Report". Orica Mining Services. 1 April 2012. Retrieved 6 August 2020.
  23. ^ "Chemical Engineering Transactions" (PDF). Archived from the original (PDF) on 14 April 2016.
  24. ^ "Ammonium Nitrate". webwiser.nlm.nih.gov. Retrieved 6 August 2020.
  25. ^ Fertilizers Europe (2006). "Guidance for Compatibility of Fertilizer Blending Materials" (PDF).
  26. ^ "Dangerous Goods (HCDG) Regulations" (PDF).
  27. ^ Ammonium Nitrate-Regulating its use, Balancing Access & Protection from "Worksafe Victoria". Archived from the original on 11 March 2011.
  28. ^ a b CF Industries. "Ammonium nitrate MSDS" (PDF). Archived from the original (PDF) on 27 March 2014.
  29. ^ "Chemicalland21 – Ammonium Nitrate". Archived from the original on 10 January 2012.
  30. ^ "Ammonium Nitrate". Paton Fertilizers Pty Ltd. 2005.
  31. ^ "Material Safety Data Sheet, Ammonium nitrate MSDS".
  32. ^ Chaturvedi, Shalini; Dave, Pragnesh N. (January 2013). "Review on Thermal Decomposition of Ammonium Nitrate". Journal of Energetic Materials. 31 (1): 1–26. doi:10.1080/07370652.2011.573523.
  33. ^ "Lebanon's president calls for two-week state of emergency in Beirut after blast". Beirut. Reuters. 4 August 2020. Retrieved 4 August 2020. Aoun, in remarks published on the Presidency Twitter account, said it was “unacceptable” that 2,750 tonnes of ammonium nitrate was stored in a warehouse for six years without safety measures and vowed that those responsible would face the “harshest punishments”.

Sources

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

External links