Editing Ammonium nitrate (section)

==Production, reactions and crystalline phases==
The industrial production of ammonium nitrate entails the [[acid-base reaction theories|acid-base reaction]] of [[ammonia]] with [[nitric acid]]:<ref>{{cite patent |country=US|number=4927617|title=Process of producing concentrated solutions of ammonium nitrate|pubdate=1990-05-22|inventor1-last=Villard|inventor2-first=Yves|inventor2-last=Cotonea|inventor1-first=Alexandre|assign= Societe Chimique des Charbonnages S.A.}}</ref>
:HNO<sub>3</sub> + NH<sub>3</sub> → NH<sub>4</sub>NO<sub>3</sub>
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]]. 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.

Another production method is a variant of the [[nitrophosphate process]]:

:[[calcium nitrate|Ca(NO<sub>3</sub>)<sub>2</sub>]] +  [[ammonia|2 NH<sub>3</sub>]] + [[carbon dioxide|CO<sub>2</sub>]] + H<sub>2</sub>O → 2 NH<sub>4</sub>NO<sub>3</sub> + CaCO<sub>3</sub>

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 [[Salt metathesis reaction|metathesis reaction]]s:
:[[ammonium sulfate|(NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>]] + [[barium nitrate|Ba(NO<sub>3</sub>)<sub>2</sub>]] → 2 NH<sub>4</sub>NO<sub>3</sub> + [[barium sulfate|BaSO<sub>4</sub>]]
:[[Ammonium sulfate|(NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>]] + [[Calcium nitrate|Ca(NO<sub>3</sub>)<sub>2</sub>]] → 2 NH<sub>4</sub>NO<sub>3</sub> + [[Calcium sulfate|CaSO<sub>4</sub>]]
:[[ammonium chloride|NH<sub>4</sub>Cl]] + [[silver nitrate|AgNO<sub>3</sub>]] → NH<sub>4</sub>NO<sub>3</sub> + [[silver chloride|AgCl]]
===Reactions===
As ammonium nitrate is a [[salt (chemistry)|salt]], both the cation, {{chem2|NH4+}}, and the anion, {{chem2|NO3-}}, may take part in chemical reactions. 

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

: NH<sub>4</sub>NO<sub>3</sub> → N<sub>2</sub>O + 2 H<sub>2</sub>O

At higher temperatures, the following reaction predominates.<ref>{{Greenwood&Earnshaw2nd|page=469}}</ref>

: 2 NH<sub>4</sub>NO<sub>3</sub> → 2 N<sub>2</sub> + O<sub>2</sub> + 4 H<sub>2</sub>O

Both decomposition reactions are [[exothermic]] and their products are gases. Under certain conditions, this can lead to a [[runaway reaction]], with the decomposition process becoming explosive.<ref name="CEN"/> See {{section link||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.<ref name="CEN">{{Cite web|url=https://cen.acs.org/safety/industrial-safety/chemistry-behind-Beirut-explosion/98/web/2020/08|title=The chemistry behind the Beirut explosion|website=Chemical & Engineering News}}</ref>

===Crystalline phases===
Several crystalline phases of ammonium nitrate have been observed. The following occur under atmospheric pressure. 

:{| class="wikitable"
|-
! Phase
! Temperature (°C)
! Symmetry
|-
| (liquid)
| (above 169.6) 
| 
|-
| I
| 169.6 to 125.2
| [[Cubic crystal system|cubic]]
|-
| II
| 125.2 to 84.2
| [[Tetragonal crystal system|tetragonal]]
|-
| III
| 84.2 to 32.3
| α-[[Orthorhombic crystal system|rhombic]]
|-
| IV
| 32.3 to −16.8
| β-[[Orthorhombic crystal system|rhombic]]
|-
| V
| below −16.8
| [[Tetragonal crystal system|tetragonal]]<ref>{{cite journal |first1=C. S. |last1=Choi |first2=H. J. |last2=Prask |title=The structure of ND<sub>4</sub>NO<sub>3</sub> phase V by neutron powder diffraction |journal=Acta Crystallographica B |year=1983 |volume=39 |issue=4 |pages=414–420 |doi=10.1107/S0108768183002669 |doi-access=free |bibcode=1983AcCrB..39..414C }}</ref>
|}
The transition between β-rhombic to α-rhombic forms (at 32.3&nbsp;°C) occurs at ambient temperature in many parts of the world. These forms have a 3.6% difference in density and hence transition between them causes a change in volume. One practical consequence of this is that ammonium nitrate cannot be used as a [[solid rocket motor]] propellant, as it develops cracks. Stabilized ammonium nitrate (PSAN) was developed as a solution to this and incorporates metal halides stabilisers, which prevent density fluctuations.<ref>{{cite journal |last1=Kumar |first1=Pratim |title=Advances in phase stabilization techniques of AN using KDN and other chemical compounds for preparing green oxidizers |journal=Defence Technology |date=December 2019 |volume=15 |issue=6 |pages=949–957 |doi=10.1016/j.dt.2019.03.002|doi-access=free |bibcode=2019DeTe...15..949K }}</ref>