Differential scanning calorimetric and Raman studies of phase transition V ⇌ IV of ammonium nitrate

Abstract

Differential scanning calorimetry, alone and in conjunction with Raman spectrophotometry for simultaneous calorimetric and spectral measurements, was used to study the solid state phase transitions of ammonium nitrate between − 50 and 100 °C. On heating, two transition paths were observed between − 40 and 0 °C: one showing two separate peaks in DSC and the other showing a single peak. The latter path became dominant when samples were thermally cycled. The double transition was followed by transition IV →II at 51 °C and the single transition by transitions IV → III → II at about 50 and 87 °C. Raman spectra showed that there were two phases present between the two DSC peaks at low temperature. The first peak was attributed to a transition from the phase here designated as V to phase IV, and the second peak to a transition from V to IV. The single peak under 0 °C was the transition V → IV.