Solid + liquid phase equilibria in the hydroxylammonium nitrate + water system

Abstract The binary solid + liquid phase diagram has been measured for the water + hydroxylammonium nitrate (HAN) system. The phase diagram is a simple eutectic type with the eutectic at 231.5 K (41.7°C) and a mole fraction HAN of 0.281 (wt fraction HAN - 0.676). The enthalpy of fusion of the HAN was determined from the solid + liquid results to be 11 ± 2 kJ·mol−1. The HAN was obtained from Southwestern Analytical Chemicals, Inc. as an approximately 2.8 molar solution. The water was removed by vacuum drying over a three month time period, but the sample still contained some impurity. The impurity level calculated from the change in melting temperature with fraction melted is 0.040 mole fraction. Chemical analysis indicates the sample contains 0.005 mole fraction HNO3 and 0.007 mole fraction NH4NO3, with N2H5NO3 absent. The remainder of the impurity could be water, but this is not known for sure. We obtained a melting temperature for the impure sample of HAN of 315.9 K (42.7°C). The melting point corrected to zero impurity is 317.7 ± 1 K (44.5°C).