Introduction

Introduction

Between room temperature and its melting point (169°C), ammonium nitrate exhibits four stable forms, designated IV, III, II, and I, respectively (Brown and McLaren, 1962). For the temperature ranges over which each of these forms are stable at atmospheric pressure, see the accompanying plot of specific volume as a function of temperature (Fig. 1). The sample configurations are shown in Figure 2 and Figure 3.

Figure 1. Phase Diagram – Specific Volume vs. temperature characteristics of the phases I, II, III and IV. Note the volume changes in the range ca. 1 % to 5 % at the first-order transitions. Transformations are labeled as being either displacive (D) or reconstructive (R).

Figure 2. Experimental set-up for system with no external stresses applied.

Figure 3. Experimental set-up for system with a constant stress applied.

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