Foundation Reasearch On Anti-Hygroscopicity Of High Energy Oxidant Ammounium Dinitramide

As one of the typical representatives of the third generation of energetic materials,ammonium dinitramide(ADN)has the characteristics of high oxygen balance,high energy performance,and clean combustion products.When ammonium dinitramide is used as a solid propellant oxidant to replace the traditional oxidant ammonium perchlorate,the energy of the solid propellant is significantly increased,the characteristic signal of the solid propellant is significantly reduced,and the combustion products are environmentally friendly,which has good application prospects.However,the ammonium dinitramide has the defect of strong hygroscopicity,which decreases the stability of the propellant,seriously affect the performance of the propellant,and limit the application and development of ammonium dinitramide in solid propellants.Therefore,the anti-hygroscopicity technology of ammonium dinitramide is a key technology to break through its application bottleneck.In this thesis,to reduce the hygroscopicity of ammonium dinitramide,the simulation calculation of ADN crystal properties and crystal habit discipline,theoretical simulation screening of ADN co-crystal coformers,and foundation research on the screening and preparation of ADN coated prills have been carried out.It also verified the accuracy of the theoretical calculation method,and provided theoretical support and technical guidance for reducing ADN water sorption capacity.Firstly,this thesis simulates and studies the crystal properties and crystal habits of ammonium dinitramide.Through the calculation of solubility parameters and cohesive energy,it was found that the main intermolecular force of ADN is electrostatic interaction.Therefore,ADN is easily soluble in polar solvents or solvents containing hydrogen bond interaction.Through molecular dynamics and binding energy calculations,the water sorption process of ADN and the role of anions and cation were revealed.This thesis established the ADN water sorption capacity computational model,and predicts the water sorption capacity of the crystal plane at 35 ?,50% relative humidity.This thesis bulid the ADN crystal nucleation and growth model,and the nucleation rate of ADN crystals under different solvent environments was calculated theoretically,and the influence of solvents,impurities,and temperature factors on the crystal growth rate was revealed.The sorption energy of anions on the kink and flat positions on the crystal surface was calculated and it was found the control step is at the kink position.According to the three models of BFDH,AE and EM,the main crystal faces of ADN were determined.Based on the crystal morphology,this thesis found the relationship between hygroscopicity,sensitivity and crystal morphology.Based on the water sorption capacity,crystal morphology,modified atttachment energy model,this thesis revealed the influence of solvation on the hygroscopicity of ADN crystals theoretically.This work provides theoretical guidance and important reference for the optimization of ADN crystallization technology and crystal control technology.Then,this thesis established a calculation method of screening ADN cocrystal coformers for reducing hygroscopicity.Hexanitrohexaazaisopentetane(CL-20),benzofuroxan(BTF),cyclotetramethylenetetranitramine(HMX),trinitrotoluene(TNT),Tetranitrobutane(ETN),cyclotrimethylene trinitroamine(RDX),1,3,5-trinitrobenzene(TNB),2,4,6-trinitrobenzylamine(MATNB),Trinitroazetidine(TNAZ)nine energetic materials and experimentally verified18-crown-6 ether are the co-crystal co-formers,and the feasibility of co-crystal coformer,energy performance,water sorption performance factors were comprehensively studied to screen co-crystal coformers.The suitable co-crystal coformers were selected by molecular frontier orbit analysis,molecular electrostatic potential analysis,co-crystal structure prediction,water sorption capacity.For exploring the anti-hygroscopic mechanism of the co-crystal,the surface free energy,the interaction energy of water molecules and the anion and cation surface exposure analysis technology were investigated.It was found that CL-20 and HMX are co-crystal co-formers that are likely to form co-crystal with ADN and can reduce the water sorption capacity of ADN with good propellant application prospects.This work provides a set of basic simulation calculation methods for the screening of ADN co-crystal co-formers,and provides a theoretical basis for the ammonium dinitramide co-crystal technology for reducing water sorption capacity.Finally,this thesis selected ADN coating materials though better compatibility from 12 coating materials,and calculated the binding energy of the coating materials and ADN clusters to judge the compatibility of the coating materials.It was found that the water sorption capacity of coated ADN with better compatibility coating materials was greatly reduced.Then,this thesis carried out the coated product preparation experiments,the preparation conditions optimization.After testing at the condition of 20 ? and 40%relative humidity,the water sorption capacity of ammonium dinitramide was reduced from 2.68% to 0.39%.