Ammonium nitrate: Difference between revisions
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The most common use of ammonium nitrate is in [[fertiliser]]s. This is due to its high Nitrogen content (a desirable feature of fertilisers) and easy (and therefore inexpensive) industrial manufacture. <!-- This wants more text. --> |
The most common use of ammonium nitrate is in [[fertiliser]]s. This is due to its high Nitrogen content (a desirable feature of fertilisers) and easy (and therefore inexpensive) industrial manufacture. <!-- This wants more text. --> |
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Ammonium nitrate is also used in instant cold packs. In this use, ammonium nitrate is mixed with [[water]] in an [[Exothermic_reaction|endothermic reaction]], which absorbs 26.2 [[joule|kilojoules]] of [[heat]] per [[mole (unit)|mole]] of reactant. |
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Due to its low temperature and non-toxic decomposition products, it finds use in gas generator applications such as [[airbag]]s. |
Due to its low temperature and non-toxic decomposition products, it finds use in gas generator applications such as [[airbag]]s. |
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Revision as of 15:51, 27 March 2006
| Ammonium nitrate | |
|---|---|
| Ammonium nitrate | |
| General | |
| Systematic name | Ammonium nitrate |
| Molecular formula | NH4NO3 |
| Molar mass | 80.04 g/mol |
| Appearance | white solid |
| CAS number | [6484-52-2] |
| Properties | |
| Density and phase | 1.73 g/cm3, solid |
| 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) |
| Melting point | 169 °C |
| Boiling point | approx. 210 °C decomp |
| Explosive velocity | 5,270 m/s |
| Critical relative humidity | 78% (0°C) 65% (20°C) 58.5% (30°C) 52.5% (40°C) 46.5% (50°C) 41% (60°C) |
| Nitrogen content | 34.5 %N |
| Structure | |
| Coordination geometry |
? |
| Crystal structure | trigonal |
| Hazards | |
| MSDS | External MSDS |
| EU classification | not listed |
| NFPA 704 | Template:Nfpa |
| RTECS number | BR9050000 |
| Supplementary data page | |
| Structure and properties |
n, εr, etc. |
| Thermodynamic data |
Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| 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 chemical formula NH4NO3, is commonly used in agriculture as a high-nitrogen fertiliser.
Use in explosives
Ammonium nitrate has found many uses as a strong oxidiser component of explosives. Most commonly, it is mixed with a hydrocarbon, usually Diesel fuel (oil) or, sometimes, kerosene. Because of the ready availability in bulk of the raw materials, ammonium nitrate/fuel oil (ANFO) mixtures have occasionally been used for improvised bombs, for example by the Provisional IRA and in the Oklahoma City bombing by Timothy McVeigh and Terry Nichols. However the greater bulk of material use in the OKC bombing was an improvised "kinepak" mixture of ammonium nitrate and nitromethane and this is considerably more destructive than ANFO, at least when unconfined. (Both components can detonate as pure compounds.) True Kinepak and Kinestiks were marketed by Gerald Hurst's company and were binary mixtures that were mixed directly before use on construction sites, and other small scale civilian uses. According to Nichols' later testimony, McVeigh was trying to put together an even more powerful explosive mixture made from the reaction products of anyhdrous hydrazine and ammonium nitrate, in essence this would have been "Astrolite-G". Apparently this effort failed largely because McVeigh could not afford the extremely high cost of such a large amount of hydrazine. Astrolite is said to rival the destructive power of miltary explosives and exceed most commercial ones, according to promotions in the early seventies.
Ammonium nitrate is used in military explosives such as the daisy cutter bomb, and as a component of amatol. Military mixture 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 slurrys tap the power of a aluminium-water reaction with enough ammonium nitrate added to burn off the resulting hydrogen. Ammonium nitrate is 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.
How badly this exothermic reaction can run away and reach detonation velocities (without proper temperature controls) 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 subject 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, while technical grade ammonium nitrate (TGAN) prills are made to be porous for better absorption of fuel and higher reactivity.
Other uses
The most common use of ammonium nitrate is in fertilisers. This is due to its high Nitrogen content (a desirable feature of fertilisers) and easy (and therefore inexpensive) industrial manufacture.
Ammonium nitrate is also used in instant cold packs. In this use, ammonium nitrate is mixed with water in an endothermic reaction, which absorbs 26.2 kilojoules of heat per mole of reactant.
Due to its low temperature and non-toxic decomposition products, it finds use in gas generator applications such as airbags.
Ammonium is used in the treatment of titanium ores.
Aluminum nitrate fertiliser is used in the synthesis of methamphetamine.
Aluminum nitrate is used in the preparation of nitrous oxide (N2O)
Aluminum nitrate is used in survival kits mixed with zinc dust and ammonium chloride because it will ignite on contact with water.
Ammonium nitrate is used as an oxidiser in some solid rockets, primarily used with a magnesium fuel. Ammonium nitrate is not a preferred propelant due to its slow burn rate. However, it is good for rockets that are intended to burn longer with less thrust. It is, however, gaining some favor over ammonium perchlorate due to lower toxicity (no hydrochloric acid in the exhaust). It is often used with burn rate catalysts such as ammonium dichromate to improve the burn rate.
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. It should never be attempted by amateurs or in improvised equipment using such concentrated materials, though with plenty of dilution by water, it could be considered easy. 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 States of Ammonium Nitrate
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: | - | I | II | III | IV | V |
|---|---|---|---|---|---|---|
| Temperature (°C): | >169.6 | 169.6 – 125.2 | 125.5 – 84.2 | 84.2 – 32.3 | 32.3 – (-16.8) | (-16.8) |
| State: | liquid | cubic | tetragonal | α-rhombic | β-rhombic | tetragonal |
| Volume Change (%): | - | +2.1 | -1.3 | +3.6 | -2.9 | - |
The phase transformation IV to III at 32.3 °C is notorious for fertilizer producers, since the change in specific volume may cause fertilizer particles to degrade during storage and handling. This is especially important in subtropical countries, where the stored ammonium nitrate can cycle back and forth leading to disintegration of prills and granules, which in turn leads to caking, excessive dust-formation and safety risks (detonation).
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, 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 to a mixture of an ammonium nitrate with a combustible material during the fire (Repauno, Cherokee). 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.
Morgan, New Jersey, 1918
On 1918-10-04, a fire in a munitions factory led to many artilliary shells being launched into the air, some of which landed on a neighbouring warehouse where 4000 tonnes of ammonium nitrate were stored in barrels. One of the shells caused a large explosion, but the majority of the ammonium nitrate did not detonate.
On 1921-07-26 in this railway town (now in Poland) workers tried to dislodge 30 tonnes of ammonium nitrate which had aggregated in two wagons. When mining explosives were used on solid mass the wagons exploded killing nineteen people.
Another attempt at disagregation of a fertiliser mix with industrial explosives caused the death of 450 people and the destruction of 700 houses on 1921-09-21. The fertiliser was a 50:50 mixture of ammonium nitrate and ammonium sulfate and the factory had used this method of disagregation over 20,000 times without incident. It is thought that, on this occasion, poor mixing had led to certain parts of the mass to contain more ammonium nitrate than others. Only 450 tonnes exploded, out of 4500 tonnes of fertiliser stored in the warehouse.
See also: Oppau explosion
Nixon, New Jersey, 1924
A fire and several large explosions destroyed a warehouse containing ammonium nitrate on 1924-03-01. The explosivity of the product was perhaps enhanced, as it had been prepared using nitric acid which had previously been used for the production of TNT.
Muscle Shoals, Alabama, 1925
In 1925, April 4 and May 3, two carloads, each containing 220 barrels of ammonium nitrate, were dispatched from Muscle Shoals, Alabama and caught fire in transportation. The barrels had been stored in a warehouse with varying humidity for 6 years, so it is believed that they were ignited by friction with their nitrate-impregnated manilla paper lining. Other shipments were reportedly more successful.
During a bombing raid on 1940-06-05, a bomb exploded in a warehouse containing ammonium nitrate: the fertiliser was dispersed around the crater, but did not explode.
1940-08-05: 240 tonnes of ammonium nitrate in sacks exploded after being hit by a shell from a nearby fire in a munitions train.
Tessenderlo, Belgium, 1942
Another attempt to disagregate a pile of 150 tonnes of ammonium nitrate with industrial explosives ended tragically on 1942-04-29: several hundred people were killed.
Texas City, United States, 1947
The cargo ship Grandcamp was being loaded on 1947-04-16 when a fire was detected in the hold: at this point, 2600 tonnes of ammonium nitrate in sacks was already aboard. The captain responded by closing the hold and pumping in pressurised steam. One hour later, the ship exploded, killing several hundred people and setting fire to another vessel, the High Flyer, which was moored 250 metres away and which contained 1050 tonnes of sulfur and 960&tonnes of ammonium nitrate. The High Flyer exploded the next day, after having burned for sixteen hours. 500 tonnes of ammonium nitrate on the quayside also burned, but without exploding, probably due to the fact that it was less tightly packed.
See also: Texas City disaster
The cargo ship Ocean Liberty was loaded with 3300 tonnes of ammonium nitrate and various inflammable products when it caught fire at 12:30 1947-07-28. The captain ordered the hold to be sealed and pressurised steam was pumped in. As this did not stop the fire, the vessel was towed out of the harbour at 14:00, and exploded at 17:00. The explosion caused 29 deaths and serious damage to the port of Brest.
Red Sea, 1954
A fire was detected on the cargo ship Tirrenia on 1954-01-23, while it was carrying 4000 tonnes of ammonium nitrate. Attempts to extinguish the fire with steam were unsuccessful, and the ship was abandoned before it exploded later in the night.
In September 21, 2001, at 10:15 AM, in the AZF (Azote de France) fertiliser factory in Toulouse, France, an explosion occurred in a warehouse where the off-specification granular AN was stored flat, separated by partitions. About 200-300 tons is said to be involved in the explosion, resulting in 31 people dead and 2,442 injured, 34 of them seriously. The blast wave shattered windows up to 3 kilometres away and the resulting crater was 10 metres deep and 50 metres wide. The exact cause remains unknown. The material damage was estimated at 2.3 billion euros. [1]
A lorry carrying 25 tonnes of ammonium nitrate fertiliser exploded half an hour after a traffic accident on 2004-03-09, killing two people and injuring three others. The explosion, which could be heard at a distance of 10 km (6 miles) caused a crater five metres deep.
Ryongchon, North Korea, 2004
A freight train carrying ammonium nitrate exploded in this important railway town near the Chinese border on 2004-04-22, killing 161 people and injuring over 3000 others. The station was destroyed, as were most building within 500 metres, and nearly 8000 homes were destroyed or damaged. Two craters of about ten metres in depth were seen at the site of the explosion. The authorities blamed "human error" for the explosion, although rumours persist that it was in fact an attempt to assassinate the Korean leader Kim Jong-Il, who was due to be passing through the station at the time.
See also: Ryongchon disaster
Mihailesti, Romania, 2004
A lorry carrying 20 tonnes of ammonium nitrate in sacks exploded an hour after a traffic accident on 2004-05-24, killing eighteen people, seriously injuring ten others and causing a crater ten metres deep.
External links
- International Chemical Safety Card 0216
- "Storing and Handling Ammonium Nitrate", UK Health and Safety Executive publication INDG230 (1996)