Ammonium Nitrate Essay, Research Paper

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

PhaseVIVIIIIII

Crystal SystemOrthorhombicOrthorhombicOrthorhombicTetragonalCubic

Space groupPccnPmmnPnmaP4/mbmPm3m

Formular/UnitCell (Z)82421

Lattice Parametersa=7.943a=5.745a=7.7184a=5.7193a=4.366

b=7.972b=5.438b=5.8447

c=9.832c=4.942c=7.1624c=4.9326

Measured at (K)173295318355423

Reference: Herrmann, Michael, J., and Engel, Walter, Phase Transitions and Lattice Dynamics of Ammonium Nitrate, Propellants, Explosives, Pyrotechnics 22, 143-147 (1997).

More recent publications of AN Crystal Phase include

Boeyens at.al., S.Afr.Tydskr.Chem.,1991,Vol.44,No.2,pp.42-46 and

Ferg et.al.,Chemistry of Materials, 1993,Vol.5, pp.1293-1298.

An excellent article on Ammonium Nitrate corrosivity is “Corrosion of carbon Steel in Concentrated Solutions of Ammonium Nitrate by J. Bystriansky and P. Novak presented at the International Congress on Metallic Corrosion in Totonto, June 3-7, 1994.

If your interested in Ammonium Nitrate decomposition research, see the article by MacNeil, Zhang, Berseth and Trogler, “Catalytic Decomposition of Ammonium Nitrate in Superheated Aqueous Solutions,” in J. Am. Chem. Soc., 1997, vol. 119, pp. 9738-9744. Of course there are literally hundreds of articles available on Ammonium Nitrate decomposition and I will not try to list those here. I will however try to update this site with references to new articles as they may be published.

I would like to thank Dr. Paul Schields for providing the following updated volume and density data derived from XRD analysis. The PdV and dS are given for the polymorphic phase transformations. The phase transformation direction is 1to2, 2to3 and so forth. d=delta

Phase Dx V(cc/mol) V PdV dH(J.mol) dS(K/T mol)

1 1.5974 50.109 -1.519 -0.0154 -3.988 -10.02

2 1.6473 48.590 0.062 0.00628 -1.776 -4.97

3 1.6452 48.652 -2.159 -0.219 -1.672 -5.48

4 1.7216 46.493 0.675 0.0684 -0.536 -2.09

5 1.6970 47.168

Note these enthalpy values were published before 1932. Better values may be in the literature but I havent found them yet. Phase 1 is Cubic, 2 is tetragonal, 3 is orthorhombic, 4 is orthorhombic (some references call this phase pseudo-tetragonal or pseudo-trigonal), 5 is tetragonal. Phases 6 and 7 have not been sufficiently described to classify.

Dissociation Pressure, Free Energy and Entropy of Dissociation for Ammonium Nitrate

Dissociation Pressure, Free Energy and Entropy of Dissociation for Ammonium Nitrate

Temp., 0CDissoc.Press., mmDFdissoc. kcal/moleD Sdissoc. cal/0C,moleSNH4NO3 at Tcal/0C,moleSNH4NO3 at 250C cal/0C,mole

188.23.2511.2860.359.236.3

205.17.4510.1260.160.336.0

215.911.559.4959.7 61.135.9

223.115.809.0159.661.836.1

236.727.08.1559.362.735.9

249.141.07.4758.963.836.1

References: www.angelfire.com/ms/dthomaschemist/

ammonium nitrate

chemical compound, NH4NO3, that exists as colorless, rhombohedral crystals at room temperature but changes to monoclinic crystals when heated above 32?C. It is extremely soluble in water and soluble in alcohol and liquid ammonia. It is prepared commercially by reaction of nitric acid and ammonia. Major uses are in fertilizers and explosives. For fertilizers it is in the form of small clay-coated pellets. For explosives it is sometimes mixed with other substances, e.g., TNT, so that it is more easily detonated. It is also used in solid-fuel rocket propellants, in pyrotechnics, and in the production of nitrous oxide.

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