Preparation and characterization of an ultrafine HMX/NQ co-crystal by vacuum freeze drying method

Abstract

In this paper a new energetic co-crystal consisting of 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX) and nitroguanidine (NQ) was prepared using a vacuum freeze drying method. Scanning electron microscopy (SEM) revealed that the particle size was under 500 nm and the morphology was spherical. Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy suggest that hydrogen bonds exist between HMX and NQ molecules. Powder X-ray diffraction spectra (PXRD) indicated the product was different from the single components and their mechanical mixture. Thermal gravimetric analysis and differential scanning calorimetry (TGA/DSC) were employed to characterize the thermal behavior of the co-crystal and then the related thermodynamic parameters were calculated, which indicated that after co-crystallization the molecule of the co-crystal needed more energy to activate. The result of an impact sensitivity test indicated that the sensitivity was effectively reduced compared to neat HMX and the mechanical mixture. The density of the product was found to be 1.80 g cm⁻³ and the storage performance was also investigated.