Preparation And Theoretical Investigation Of HMX Cocrystal Explosives

Explosives are widely used for military and civil purposes. However, most of currently used explosives cannot meet the requirements of insensitive high explosives (IHEs), where IHEs must be thermally stable, powerful, and insensitive towards external stimuli. Therefore, it is urgent to explore novel IHEs. Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is a well-known powerful explosive. But its application is limited, due to its high mechanic sensitivity. Recently, cocrystallization is emerging as an attractive strategy to improve the performance of existing explosives. Indeed, that HMX cocrystallizes with IHEs is a promising approach to decrease its sensitivity and maintain its powerful detonation performance. To date, many fundamental problems of HMX cocrystals are not well understood, such as their assembling mechanisms and detonation performance. Further researches are still essential to characterize them both experimentally and theoretically.This dissertation is devoted to the assembling mechanisms, detonation performance, sensitivity and thermal stability of HMX cocrystals. The important results achieved in this dissertation are listed as follows:1. Solubilities of HMX in dimethyl formamide (DMF),1,4-butyrolactone, and cyclohexanone were measured by using dynamic method, with process analysis technology (PAT) including focused beam reflectance measurement (FBRM) and Labmax automatic reactor system. The measured data are quite close to those derived from references, indicating that FBRM can determine the solubility accurately and quickly. In addition, the experimental solubilities were correlated by Apelblat model and polynomial empirical equation. The relative derivations for Apelblat model are less than1%, suggesting that the solubilites of HMX are well-fitted in the Apelblat model.2. HMX/N-methyl-2-pyrrolidone (NMP), HMX/1,3-dimethyl-2-imidazolidinone (DMI), HMX/pyridine-N-oxide (PNO) cocrystals were synthesized by solution evaporation method, and their crystal structures were characterized by using X-ray single crystal diffraction. The crystal structure analysis together with density functional theory (DFT) calculations reveals the assembling mechanism of HMX cocrystals that methylene groups of HMX molecules possessing high chemical reactivity can easily form hydrogen bondings with electron withdrawing groups, and nitro groups can also form various interactions with electron donating groups. 3. Geometrical structures of HMX/DMI and HMX/2-picoline-N-oxide (HMX/MPNO) cocrystals under the hydrostatic pressure of0-100GPa were systematically investigated on the GGA/PBE/G06level. And it is found that HMX molecules in cocrystals are becoming more seriously distorted with the increment of hydrostatic pressure. Consequently, their crystal densities increase significantly, indicating that the increment of external pressure is a promising approach to improve their detonation performance.4. The band gap of HMX/DMI cocrystal decreases as the hydrostatic pressure increases. As a result, its sensitivity increases. For the HMX/MPNO cocrystal, its band gap decreases under the hydrostatic pressure of0-70GPa, and suddenly increases at the70GPa. Then, its band gap decreases ranging from70to100GPa. It implies that HMX/MPNO cocrystal may exhibit good detonation performance and insensitivity at the70GPa.5. Thermodynamic properties of HMX/DMI and HMX/MPNO cocrystals were studied by using the phonon density of states calculation. The results show that they are easily formed in the high temperature and low pressure.6. Binding energies, thermodynamic properties, natural bond orbital (NBO), and atoms in molecule (AIM) of HMX/imidazole derivatives, HMX/2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105), HMX/3-nitro-1,2,4-triazol-5-one (NTO) cocrystals were investigated on the ωB97XD/6-311G(d,p) level. Large host-guest interactions in cocrystals are observed, and are mainly contributed from CH...O, NH...O, N...O,o...O interactions. The assembling reaction is an exothermic process. Low temperature promotes their formations. Furthermore, most of HMX cocrystals’ densities are much larger than that of HMX, and it indicates that cocrystallization can tailor crystal density without changing their chemical structures. Detonation performance and sensitivity calculation results show that cocrystallization can indeed decrease their sensitivities and maintain their energy. These exciting conclusions provide some novel insights to explore IHEs.