Molecular Design Of Two Types Of Energetic Systems And Their Structure And Properties

Combining experimental and theoretical methods is one of the most important trends in the development of energetic materials. Theoretical methods for the design and development of advanced energetic materials are very important. The present work is some problems and solutions in theoretical design of energetic materials. The whole work can be divided into two parts:1) design of tetrazole energetic metal complexes;2) design of eutectic system based on MeNQ.Energetic metal complexes (EMCs) are a class of complexes with strong explosive. Tetrazoles usually perform high nitrogen content, low hydrocarbon content, high heat of formations (HOFs). What is more, lone pair of electrons of nitrogen in the ring of tetrazoles provide the necessary conditions for the center metal ions to form coordination bonds, which indicates Tetrazoles to be smart energetic ligands. Nowadays, only a few research groups at home and abroad have done some preliminary research on EMCs, and they mainly focus on the preparation and characterization of substituted tetrazoles. The energy and safety performances of tetrazole energetic metal complexes (TEMCs) are closely related to their structures. Therefore, the design of TEMCs is of significance importance for the novel primary explosives. The main contents of this section including:1) Exploring calculation routes and methods. The molecular structures, electronic structures and crystal structures of several existing tetrazole alkali metal salts and complexe BNCP were studied. Accordingly, a variety of theoretical methods such as quantum chemistry, coordination chemistry et al. were carried out to calclulate the frontier orbital, charge distribution, band structure, density of states and other basic properties.2) Study on the TEMCs we designed. Theoretical methods including quantum chemistry, molecular dynamics were used to calculate the density, enthalpy of formations, band structures, density of states, and so on. In this paper, series of complexes were designed using1,5-diamino-tetrazole (DAT) and nitro tetrazole (NT) as ligands, respectively. The microscopic structures such as charge distribution and bond order of the designed complexes and ligands were studied. The coordination manners and coordination sites of ligands were also analyzed. According to a comprehensive survey on HOFs and crystal densities, complexes Zn(DAT)2Cl2and MNFeP were recognized as candidates for high energetic materials. 3) Study on thermal decomposition of the TEMCs. Quantum chemistry and chemical kinetics were combined to investigate the thermal decomposition of the studied TEMCs. For the designed TEMCs, we found their initial decomposition steps and the controlling steps of decomposition (thermal decomposition of the ligands). Moreover, a combination of thermodynamic and kinetic methods was utilized to study the mechanism of thermal decomposition ligands DAT and NT in detail.Poor mechanical properties, solidification shrinkage and charging defects are the bottlenecks of the security and operational effectiveness of traditional B explosives. In order to retain the advantages of casting charge process and meet the technical requirements of IM, so toughening and elasticizing study on the melt-cast explosives must be carried out. At home and abroad, the work on modifying the melt-cast explosives mainly including:1) developing substitutes for TNT;2) adding polymer and organic plasticizers.Currently, methyl nitroguanidine (MeNQ) based eutectics have been proposed as the most promising alternatives for TNT. On the basis of the four components formulation reported by the United States, we developed a novel five MeNQ-based eutectic (MAHNA—methyl nitroguanidine (MeNQ):ammonium nitrate (AN):hydrazine nitrate (HN):nitroguanidine (NQ):ammonium perchlorate (AP)=37.8%:31.3%:3.1%:9.1%:8.7%). The properties of which is much better than that of Michael. For example, the melt point decreases to86℃, which is applicable to the present vapour melt-cast technology. However, hygroscopic is still a difficult for us to account for. It is known that phase transformation is one of the most important facts for hygroscopic of system containing AN. Transforming the components of the eutectic system to cocrystals may be of great help to restrain phase transformation. Then, study on the phase diagrams of components in MeNQ-based eutectic system must be carried out. Meanwhile, some other aspects, such as the complex components, staged crystallization during the re-crystallization after melting and the mechanism of melting point decrease by adding the HN, are also need to be studied. This paper investigated the relationship between the various components in MAHNA by theoretical methods, aiming to optimize the formulation of MAHNA and reduce the melting point while improving moisture absorption. On the other hand, there is no effective method to choose toughening and elasticizing polymers that are compatible with mobile phase in melt-cast explosives. Therefore, the main contents of this section are as following:1) Through theoretical studying on the energetic cocrystals reported, we confirmed that the structures of energetic-energetic cocrystals can be governed by non-hydrogen bonded non-covalent interactions. The local conformation and the intricate non-covalent interactions were effectively mapped and analyzed from the electron density (p) and its derivatives. In addition, several smart cocrystal precursors were found by ESPs, HSPs and LUMO analysis.2) According to the phase diagram, we found that eutectics with at least two eutectic points are the prerequisite for the formation of cocrystals. The equations describing phase diagram with two eutectic points and a novel stable compound (cocrystal) were derived on the basis of Van’t HofF’s equation. By the modified equations, we draw the binary T-X phase diagram of two eutectic points containing MeNQ/AN system, the result agreed very well with that reported in a patent. What is more, using the phase diagram we explained why Michael chose those distribution ratios, that is, between the eutectic point and the molar ratio of co-crystal.3) The electron structure, intermolecular interactions of the designed MeNQ and NQ-based dimers and copolymers based on MeNQ-based eutectic system. Combing with the results of the reported cocrystals, we suggested that NQ/HN、NQ/AN and MeNQ/AN can form cocrystals, on the other hand, MeNQ/HN cannot form cocrystal, which were confirmed by drawing the corresponding phase diagrams.4) The interactions between HTPB-MDI (HTPB:Hydroxyl-terminated polybutadiene; MDI:4,4’-diphenylmethane diisocyanate) and crystal surface of2,4,6-trinitrotoluene (TNT)(or cyclotrimethylenetrinitramine (RDX)) were studied by using molecular dynamics. Comparing the isotropic elastic coefficient and mechanical properties of substance TNT with TNT (or RDX)/HTPB-MDI, we found that the addition of HTPB-MDI effected the ductility of TNT and RDX plane not obviously. However, it can improve toughness and flexibility of both TNT and RDX to some extent indeed.