Ammonium Nitrate

Ammonium Nitrate

Ammonium Nitrate
Ammonium Nitrate (AN), NH4NO3, has a molecular weight of 80.05. It does not occur in nature. This white crystalline solid was first described in 1659 by Gauber who called it Nitram flammens because it produced a yellow flame when burned due to traces of sodium in his samples. Today, AN is the most widely produced ammonium compound in the world. According to the International Fertilizer Development Center, the current production of AN exceeds 4.5 Million Tons per year in North America. It is primarily used as a Nitrogen fertilizer (as High Density Ammonium Nitrate Granules or Prills) and as a component in Blasting Agent formulations (as Low density prills or in emulsions).
AN is very hygroscopic, absorbing moisture from the atmosphere at relative humidities above 59% in the pure form and as one would also expect is very water soluble. AN can form a 65% solution inwater at 20C. The solid can exist in as many as seven different crystalline modifications or phases depending on temperature, pressure and moisture content of the solid. The pure solid melts at 169 C.
Chemically, AN is a salt, the result of an acid-base reaction of ammonia and nitric acid. The reaction is highly exothermic with a heat of neutraliztion of 280 BTU/ld in dilute solution. The solid has a negative heat of solution (-142 BTU/lb).
A classic article describing Ammonium Nitrate is the Miller and Saeman article published in "Industrial and Engineering Chemistry, Vol.40, No.1, Jan 1948, pp.154-160.

Crystallographic Data for Ammonium Nitrate Crystal Systems
Phase V IV III II I
Crystal System Orthorhombic Orthorhombic Orthorhombic Tetragonal Cubic
Space group Pccn Pmmn Pnma P4/mbm Pm3m
Formular/UnitCell (Z) 8 2 4 2 1
Lattice Parameters a=7.943 a=5.745 a=7.7184 a=5.7193 a=4.366
b=7.972 b=5.438 b=5.8447
c=9.832 c=4.942 c=7.1624 c=4.9326
Measured at (K) 173 295 318 355 423

Reference: Herrmann, Michael, J., and Engel, Walter, Phase Transitions and Lattice...