2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is a widely used high-energy explosive for the application of energetic materials. However, the phase transformation from ε-CL-20 to γ-CL-20 restrains its further application in polymer bonded explosives (PBXs) and propellants. To inhibit the phase transition of CL-20, dopamine was first used in an efficient and facile method of in situ polymerization to passivate CL-20 crystals. The core-shell microcapsule particles were obtained, and the morphological characterization demonstrates the formation of a dense core-shell structure. The differential scanning calorimetry (DSC) and in situ X-ray diffraction (XRD) test results show that the compact and dense coating delays the ε-CL-20 crystal transformation temperature by about 30 °C, which enhances thermal stability. In addition, with the coating via polymers, the friction sensitivity of ε-CL-20 crystals decreases significantly. The findings indicate a successful application of dopamine chemistry in high-energy explosives, which provides an attractive method to modify the properties of CL-20 crystals.

Nano-boron, as a potential high-energy additive due to its high calorific value, is widely studied in propellants, explosives, and thermites. However, the unexpected agglomeration of surface oxidation hinders its further application, especially in the casting of energetic materials. The fluorine-modified nano-boron nB@F2603 and nB@F2603@CL-20 preagglomerated microspheres were prepared by electrospray to improve the ignition and combustion reactions and the rheological properties of boron-containing casting systems. Sphericity microspheres could be obtained by controlling the voltage and propulsion rate. The morphology and elemental distribution of the microspheres were characterized by the scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffractometer (XRD). Results showed that the particle size of the microspheres ranged from 4 to 14 µm. Boron, fluorine and nitrogen were uniformly distributed on the surface of the microspheres. XRD results showed that CL-20 in nB@F2603@CL-20 microspheres was β-crystal. The thermal reaction properties were studied by differential scanning calorimetry, thermogravimetry and mass spectrometry (TG-DSC-MS), oxygen bomb calorimeter, laser ignition, and volume combustion cell test. Results showed that F2603 could significantly promote the ignition and combustion of nano-boron, causing higher energy release and pressurization rates, and lower ignition temperature. Adding CL-20 to the microspheres could also greatly promote the reaction rates and energy release. The hydrophobicity and corrosion resistance of the structures were also studied, and results showed that the preagglomerated microspheres had good stabilities. Therefore, fluorine-containing nB@F2603 and nB@F2603@CL-20 microspheres might be used in composite energetic materials, replacing nano-boron.

In order to reduce the mechanical sensitivity of ε-CL-20, wax and fluororubber polymers were used as coating materials and desensitizers to coat ε-CL-20 by the water suspension method. Through molecular dynamics calculations, fluorine rubber F₂₃₁₁, which had a good combination with ε-CL-20, was selected as the coating material and then ε-CL-20-based composite particles with double-layer structure were prepared. The contact angles of water, glycerin and diiodomethane as the testing liquids on the surface of F₂₃₁₁ and wax were measured by a contact angle measuring instrument, and the thermodynamic parameters of ε-CL-20/F₂₃₁₁ and the ε-CL-20/wax interface were calculated. ε-CL-20 before and after coating was characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and the mechanical sensitivity analytical method. The results showed that F₂₃₁₁/wax had uniformly passivated on the surface of ε-CL-20, forming a dense and uniform protective film, and the CL-20 crystal form did not change after coating. The double-layer composite structure effectively reduces the sensitivity of ε-CL-20 and improves the thermal stability of ε-CL-20.