Anti-hygroscopic Study Of Ammonium Dinitramide Based On The Regulation Of Crystal Surface Properties

Ammonium dinitramide(ADN)is a new type of oxidizer without halogen,carbon,high energy density and low characteristic signal,which has great application potential in the fields of propellants and explosives.However,the strong hygroscopicity of ADN under high humidity conditions greatly limits its application.In this paper,through the combination of theoretical calculation and experimental research,the problem of moisture absorption of ADN is solved based on the regulation of crystal surface properties such as cocrystal and additive effects.By calculating the binding energy between host and guest molecules with different molar ratios,the stoichiometric ratio of host and guest molecules with the most stable structure was obtained.Then,the radial distribution function is used to analyze the type of intermolecular force,and the formation of hydrogen bonds is used to determine whether there is a driving force for cocrystal formation.Finally,the electrostatic potential under the optimal structure of the host and guest molecules is calculated by quantum mechanical method,and whether cocrystal crystals can be formed at a specific ratio can be determined by interacting site pairing,and a theoretical calculation method for ADN-based cocrystal formation and molar ratio is created.By comparing with the experimental results reported in the literature,it is shown that the proposed theoretical calculation method is feasible.The cocrystal ligand 3,4-Diaminofura(DAF)was screened,a new 1:1ADN/DAF energetic cocrystal was successfully synthesized by experiments,and the formation of cocrystal was verified by PXRD,DSC,SEM,FT-IR and Raman.The structure,PXRD,crystal morphology and hygroscopicity of ADN/DAF cocrystal were predicted by molecular simulation.The results show that the simulation results are in good agreement with the experimental results,the newly formed ADN/DAF cocrystal surface adsorbed a smaller number of water molecules,the water sorption capacity is lower than that of pure ADN,and the water sorption capacity is reduced from 15.35% to 7.90%,which can effectively reduce the hygroscopicity of ADN crystals.A method for micro-doping additives to regulate the surface properties of ADN crystals to improve hygroscopicity is proposed.Based on the modified adhesion energy theory,a three-layer model of crystal surface-solvent +additive-vacuum was constructed to calculate the corrected adhesion energy and the water sorption capacity of each crystal face of ADN under the action of different solvents and additives,explore the influence of additives on the crystal growth and morphology of ADN under the action of different solvents,and analyze the interaction between different solvents and crystal planes,and the adhesion energy formula is modified.The results showed that the additive HMX had a great influence on the crystal morphology,crystal plane proportion and growth rate of ADN under different solvent environments,and the anti-moisture absorption effect of additive HMX on ADN was better in the dichloromethane solvent environment.The regulation of the surface properties of ADN crystals based on cocrystal method and additive effect to improve hygroscopicity has theoretical guiding significance for the research and development of ADN crystal anti-moisture absorption methods.