High energy density with low mechanical sensitivity: A novel energetic cocrystal composed of CL-20 and FOX-7 obtained by electrostatic spray method

Abstract

Cocrystallization technique is an effective strategy to tune performances of materials and it has been proved to be a novel and promising approach to decrease mechanical sensitivity and improve physicochemical properties of energetic compounds. In this work, based on the high energy density compound 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12- hexaazaisowurtzitane (CL-20) and insensitive energetic compound 1,1-diamino-2,2-dinitroethylene (FOX-7), a novel CL-20/FOX-7 cocrystal (molar ratio 1:1) was prepared by electrostatic spray method and the crystal structure, thermal behavior, mechanical sensitivity and energetic property were characterized and the intermolecular interaction was analyzed. Scanning electron microscopy (SEM) reveals that the cocrystal has smooth crystal surface, the particle size is within 1 μm∼5 μm, and the crystal morphology is different from CL-20 and FOX-7. Powder X-ray diffraction (PXRD) indicates that a new substance is formed between CL-20 and FOX-7. Fourier transform infrared spectroscopy (FT-IR) illustrates that the absorption peaks in cocrystal is shifted from 5 cm⁻¹ to 10 cm⁻¹, meaning that intermolecular interaction is formed. Differential scanning calorimetry (DSC) results declares that the melting point of cocrystal is 7.5 °C higher than FOX-7, while the thermal decomposition temperature is decreased by 7.0 °C. The mechanical sensitivity indicates that compared with raw CL-20, the impact sensitivity of CL-20/FOX-7 cocrystal is decreased by 64 %, drop height is increased by 31 cm and friction sensitivity is decreased by 68 %. The predicted crystal density, and detonation parameters of CL-20/FOX-7 energetic cocrystal are 1.928 g/cm³, 9178 m/s, 40.44 GPa, these parameters are higher than HMX, implying that this cocrystal has high energy density. The intermolecular interactions in CL-20/FOX-7 cocrystal mainly include hydrogen bonding and van der Waals (vdW) forces. Therefore, the CL-20/FOX-7 cocrystal is a novel energetic material with high energy density and low mechanical sensitivity, and it has wide application prospect in the near future.