Low-temperature heat capacities, standard molar enthalpies of formation and detonation performance of two CL-20 cocrystal energetic materials

Abstract

Two cocrystals of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) with 2,4,6-trinitrotoluene (TNT) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) were prepared by a solvent/non-solvent (acetonitrile/distilled water) method at room temperature. The low-temperature heat capacities of CL-20∙TNT cocrystal and 2CL-20·HMX cocrystal were measured in the temperature range from 1.9 to 300 K using the heat capacity option of a Quantum Design Physical Property Measurement System (PPMS). By fitting the heat capacity data to a series of theoretical and empirical models, the thermodynamic functions were derived. In addition, the standard molar heat capacities, entropies and enthalpies of cocrystal samples at 298.15 K and 0.1 MPa were also obtained. The standard molar energies of combustion of CL-20, TNT, HMX, CL-20∙TNT cocrystal, and 2CL-20·HMX cocrystal were determined. From the combustion results, the standard molar enthalpies of combustion and formation for the compounds at T = 298.15 K were derived. The detonation velocity (D) and detonation pressure (P) were obtained by Kamlet-Jacobs equations. 2CL-20·HMX cocrystal shows superior detonation velocity and detonation pressure, which are higher than those of CL-20∙TNT cocrystal.