Thermal Analysis of the Polymorphic Transformations of Ammonium Nitrate

Abstract

In order to prove that the four crystal phase transformations of ammonium nitrate proceed through various transition modifications simultaneous thermoanalytical, X-ray and DSC measurements were performed in different gas atmospheres. The presence of coexisting and transition phases were detected under different conditions. Cooling the crystals of phase I at a certain set of parameters phase II failed to appear, but a transformation occured through a non-crystalline phase to the crystalline phase III. The entalpies of V→IV, IV→II, IV→III and III→II transitions were 6.3 /± 10%/, 22.7 /±4%/ 18.4 /± 10% / and 17.8 /± 10%/ J/g, respectively.