Ammonium nitrate (uh-MOH-ni-um NYE-trate) is a white crystalline substance first made artificially in 1659 by the German chemist Johann Rudolf Glauber (1604–1670). The compound does not occur in nature because it is so soluble that it is washed out of the soil by rain and surface water. Ammonium nitrate is stable at lower temperatures, but tends to decompose explosively when heated to temperatures above 200°C (390°F). Its two most important uses today are in fertilizers and explosives. In 2004, it ranked fourteenth among all chemicals manufactured in the United States. Just over six million metric tons (6.6 million short tons) of the compound were produced in 2004.
German saltpeter; Norway saltpeter; nitric acid, ammonium salt
Nitrogen, hydrogen, oxygen
211°C (412°F); decomposes at its boiling point
Very soluble in water, soluble in alcohol and acetone
HOW IT IS MADE
Ammonium nitrate is made commercially by passing ammonia gas (NH3) and a water solution of nitric acid (HNO3) through a pipe. The ammonia combines with the nitric acid to form ammonium nitrate. The formula for this reaction can be written as NH3 + HNO3 → NH4NO3.
Large amounts of heat are released during the reaction, so the pipe and supporting equipment must be very strong. The solution of ammonium nitrate in water is allowed to evaporate, leaving behind pure white crystals of the compound.
COMMON USES AND POTENTIAL HAZARDS
The primary use of ammonium nitrate is the manufacture of fertilizers. In 2005, about 2 million metric tons (2.2 million short tons) of ammonium nitrate fertilizer was used in the United States. The compound is added to soil to provide the nitrogen that plants need to grow. It may be used by itself or in combination with another nitrogen-rich compound, urea, in a mixture known as UAN.
Ammonium nitrate is also an important component of some explosives. It provides the oxygen needed to cause some other material to catch fire and burn very rapidly, producing an explosion. One common type of explosive is made of ammonium nitrate mixed with fuel oil and called ANFO (Ammonium Nitrate Fuel Oil). When the mixture is heated, ammonium nitrate breaks down to release oxygen, which causes the rapid combustion (explosion) of the fuel oil.
- Glauber named the compound he discovered in 1659 nitrum flammans, Latin for "flaming nitre." He chose the name because of the compound's tendency to explode when exposed to heat.
- An ammonium nitrate explosion in Texas City, Texas, on April 16, 1947, was responsible for the worst industrial accident in U.S. history. While being loaded into two ships at the Texas City harbor, more than 7.5 million kilograms (17 million pounds) of the ammonium nitrate was exposed to flames and exploded. The force of the explosion was so great that it could be felt more than 400 kilometers (250 miles) away in Louisiana. Officials estimate the death toll at 581 people, with more than 5,000 more injured.
- Two American men, Timothy McVeigh and Terry Nichols, used a truckload of ammonium nitrate and other materials to blow up the Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma, on April 19, 1995. The event was one of the worst terrorist incidents ever on American soil.
Some other uses of ammonium nitrate include the following:
- In fireworks, where it provides the oxygen needed to ignite other chemicals;
- In the manufacture of nitrous oxide (N2O), commonly known as laughing gas;
- In rocket engines, where it provides oxygen needed to burn the rocket fuel;
- In the manufacture of safety matches, where the compound supplies oxygen to substances that catch fire when the match is struck; and
- As a nutrient in commercial processing for growing yeasts and antibiotics.
FOR FURTHER INFORMATION
"Chemical Profile for Ammonium Nitrate." Scorecard: The Pollution Information Site. http://www.scorecard.org/chemical-profiles/summary.tcl?edf_substance_id=6484-52-2. (accessed on September 13, 2005).
Gorman, Christine. "The Bomb Lurking in the Garden Shed." Time (May 1, 1995): 54.
Olafson, Steve. "The Explosion: 50 Years Later Texas City Remembers." The Houston Chronicle (April 14, 1997): A1. Also available online at http://www.chron.com/content/chronicle/metropolitan/txcity/main.html. (accessed on September 13, 2005).