Insight into the Thermodynamic Properties of Promising Energetic HNTO·AN Co-Crystal: Heat Capacity, Combustion Energy, and Formation Enthalpy

Abstract

A novel energetic co-crystal composed of hydrazinium 3-nitro-1,2,4-triazol-5-one (HNTO) and ammonium nitrate (AN), as a composite solid propellant oxidizer, was recently developed to substitute either pure ammonium perchlorate (AP) or nitrate. Unfortunately, the thermodynamic properties of this co-crystal or even the pure HNTO are not available in the open literature. Therefore, in this work, the low-temperature heat capacities of HNTO and HNTO·AN co-crystal were measured in the temperature range from 213.15 K to 378.15 K using differential scanning calorimetry. By fitting the heat capacity data, the thermodynamic functions ΔH298.15K, ΔG298.15K, and ΔS298.15K were derived. In addition, the standard molar energies of combustion ΔcU° of HNTO and HNTO·AN co-crystal were determined, and from the combustion results, the standard molar enthalpies of combustion ΔcHmo and formation ΔfHmo of these energetic compounds were derived at T = 298.15 K. The set of thermochemical data has been proposed in this work for the first time and will be undoubtedly indispensable information for the development of energetic materials based on HNTO and HNTO·AN co-crystal.