Preparation And Properties Of Energetic Ammonium Cocrystals

Energetic ammonium salt is an important part of the field of energetic materials.Ammonium perchlorate（AP）is used as an oxidant in propellants;The decomposition products contain acid gas HCl and corrosion of flying devices;however,ammonium dinitramide（ADN）has the following advantages:high energy density,low characteristic signal,halogen-free,it can be considered as a candidate to replace AP,but ADN has serious hygroscopicity,which limits its widespread application;another ammonium salt Ammonium nitrophenolate（NH₄）（PA）also has the drawback of hygroscopicity.The ammonium ion in the ammonium salt molecular structure easily combines with the water molecule to form a hydrogen bond,resulting in its hygroscopicity,which severely limits its widespread use.In order to reduce the hygroscopicity of these three ammonium salts,cocrystallization technology is applied in this paper.Combining the three ammonium salts with the cyclic compound 18-crown-6（18C6）at the molecular level,These obtained co-crystals can fundamentally reduce the hygroscopicity.Further providing a new idea for the future modification of energetic ammonium salts.The main work of the thesis is as follows:（1）Adopting hydrogen bond design method and analog design method as cocrystal design methods,18C6 was selected as the co-former molecule and cocrystallized with three kinds of energetic ammonium salts.Using anhydrous ethanol as the solvent,three kinds of ammonium salt cocrystals ADN/18C6,AP/18C6 and（NH₄）（PA）/18C6 were prepared by solvent evaporation.（2）The structures of three energetic ammonium salt cocrystals were determined by single crystal X-ray diffraction.The molar ratio of the three cocrystals was 1:1.The cocrystal ADN/18C6 and AP/18C6 belong to the monoclinic system,but the（NH₄）（PA）/18C6 cocrystal belongs to the triclinic system.These crystal density all exceeds 1.33 g/cm³,and formation of the three cocrystals is mainly contributed to the medium strong hydrogen bond between the H atom in the ammonium ion and the O atom in the crown ether ring.The cocrystals of ADN and AP is connected to a 3D network by C-H???O type weak hydrogen bond,whileπstacking only exists in the（NH₄）（PA）cocrystal,and finally a layered structure is formed.（3）The thermal analysis of ammonium salt cocrystals show that melting point of ADN/18C6 and（NH₄）（PA）/18C6 cocrystals are 151.5°C and 221.4°C,respectively,which are higher than their raw components.However,the melting point of AP/18C6 cocrystal is141.7℃,which is between the two components.The decomposition temperatures of ammonium salts also changed.The ADN/18C6 cocrystal has a reversibility of solid-liquid phase.In other word the cocrystal does not deteriorate after melting.（4）Quantitative analysis of hygroscopicity for cocrystals.The co-crystallization of ADN with 18C6 reduced the moisture absorption rate of ADN from 18%to 1.2%,and the hygroscopicity was significantly reduced.The formation of the cocrystalstructure of ADN effectively prevents the binding of water molecules in the air with ammonium ions,reduces the probability of ADN binding to H₂O molecules,and essentially reduces the hygroscopicity of ADN.The other two cocrystals have little effect on reducing moisture absorption.（5）By referring to and summarizing the preparation method of cocrystalc,according to the idea of cocrystal ternary phase diagram,The high-purity ADN/18C6 cocrystal was rapidly prepared by solution concentration.It is faster and easier than traditional methods,and provides new ideas for the engineering preparation of energetic eutectic.