Study On The Properties Of Oxidant ADN And The Interaction Between Components Of Hybrid System

In the field of energetic materials,ammonium dinitramide(ADN)as an ideal oxidant for propellants has the characteristics of high energy density,low toxicity and no halogen elements.It can improve the ideal specific impulse of the propellant and meet the requirements of environmental friendliness and low characteristic signal.However,its high moisture absorption rate seriously affects the process and mechanical properties of the propellant.Studies have found that ADN can form a cocrystal with 18-Crown-6 or pyrazine-1,4-dioxide(PDO).Not only the moisture absorption rate is significantly reduced,but also the ideal state of 0 oxygen balance can be achieved.Therefore,the oxidant cocrystal is expected to replace ADN in solid propellants.This paper uses molecular simulation technology,density functional theory and molecular dynamics theory to study ADN and its cocrystal ADN/18-Crown-6,ADN/PDO.It provides ideas and theoretical guidance for in-depth understanding of the crystal structure and properties of ADN,the preparation of ADN-containing cocrystal and its application in solid propellants.The specific research content of this paper is as follows:(1)Based on density functional theory,the ADN unit cell is geometrically optimized.Based on this,the energy band structure,density of state,charge density,elastic constant and dielectric function are calculated and analyzed,and the electronic structure,mechanical properties and dielectric functions of ADN are deeply studied.Analysis shows that ADN is a direct band gap material.O and H atoms have higher activity in the crystal.The strength of the H-N bond in NH₄⁺is weak,and the H atom is easily hydrolyzed with water molecules in the air,which makes the surface of ADN hydroxylate,causing ADN to absorb moisture and agglomerate.The elastic constant meets the criteria for determining the elastic stability of monoclinic system materials.The ratio of bulk modulus K to shear modulus G exceeds 1.75,and ADN has better ductility.The static dielectric function of ADN?(0)=3.59,the static refractive index n(0)=1.89,the reflectivity reaches the maximum value of 0.31 at 5.09 eV,and the absorption coefficient reaches the maximum value of 1×105 cm^-1 at an energy of 4.75 eV.(2)During the preparation process of the oxidant cocrystal,the solvent can change the crystal morphology,leading to changes in the properties of the oxidant cocrystal,and ultimately affect its application in propellants.Based on molecular dynamics theory,an interface adsorption model of oxidant cocrystal ADN/18-Crown-6 with ethanol solvent was constructed.The interaction between ethanol solvent and ADN/18-Crown-6 cocrystal and the influence of ethanol solvent on the crystal morphology of ADN/18-Crown-6 were deeply studied.The results show that ADN/18-Crown-6 cocrystal has four main growth surfaces in vacuum:(1 1 0),(2 0 0),(0 0 2),(2 0-2).At low temperatures,ADN/18-Crown-6 has a more stable cocrystal mode.Ethanol molecules are more likely to adhere to the cocrystal growth surface.There is a hydrogen bond interaction between ADN/18-Crown-6 and ethanol solvent.The strength of the hydrogen bond interaction between the two increases as the temperature decreases.Ethanol solvents have larger diffusion coefficients on the(2 0 0)and(0 0 2)faces.The morphology of the ADN/18-Crown-6 cocrystal at 303 K predicted by the modified adhesion energy model is consistent with the experimental results.The morphology at 293 K is close to spherical.Therefore,it is speculated that the ADN/18-Crown-6 cocrystal prepared at 293 K is more suitable to be used in propellants,so that the propellants can obtain better performance.(3)ADN/18-Crown-6 is expected to replace ADN in propellants because of its low moisture absorption rate.Molecular dynamics simulation methods are used to study the compatibility of ADN/18-Crown-6 with common propellant binders.Explore the application of ADN/18-Crown-6 in propellants.At the same time,the compatibility of the oxidant cocrystal ADN/PDO and the binder has also been extensively studied.Construct two oxidant cocrystal and HTPB,PEG and GAP binder blend system models respectively,simulate and calculate the solubility parameters,binding energy,radial distribution function and mechanical properties of the above pure substances and blend systems,analyze and advance Compatibility between the components of the agent.According to the calculation of the difference in solubility,the oxidant cocrystal is compatible with the binder HTPB and incompatible with PEG,ADN/18-Crown-6 is incompatible with GAP,and ADN/PDO is compatible with GAP.The calculation results of binding energy show that the two oxidant cocrystal has better compatibility with HTPB,and can form a stable propellant system.The intermolecular interaction is larger and the mode of action is hydrogen bond interaction.The mixed system composed of ADN/18-Crown-6 and binder HTPB has better ductility.