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By analogy with recent studies on the molecular behavior of concentrated aqueous nitrate salt solutions at high pressure and temperature, hydroxylammonium nitrate-based liquid propellants would be expected to contain relatively covalent, contact ion pairs the instant before chemical decomposition ensues at high temperature and pressure. This may accentuate the first step of the decomposition process which appears to be proton transfer.

A corresponding states correlation has been developed for the solubility of pure gases and mixtures in LGP 1846, a HAN based liquid propellant [1]. For nitrogen, methane, xenon, krypton, and argon, and their mixtures the correlation can be used to estimate gas solubilities for pressures upto 100 MPa in the temperature range 258 < T < 303 K. The correlation is in satisfactory agreement with all available experimental data for these systems. Dissolved gases are expected to significantly effect many physical and chemical properties of liquid propellant systems.

A cell for high pressure sound velocity measurements of liquids was designed and used in a Birch-Bridgman high pressure system with a liquid propellant specimen. The dependence of the sound velocity on pressure to 4.2 kbar (4200 atmospheres) was measured at room temperature and on temperature between 220 and 293 K at room pressure. These data, together with the temperature dependence of the specific heat which was also measured, and some thermodynamic arguments were used to obtain the full equation of state with temperature and the pressure dependence of the specific heat and of the volume expansivity at room temperature. We compare our results with data obtained by volumetric and other ultrasonic measurements.

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...