Study On Spheroidization Crystallization Technology Of FOX-7

1,1-Diamino-2,2-dinitroethylene（FOX-7）is an elemental explosive with high crystal density,high energy,low sensitivity and excellent comprehensive properties.FOX-7 crystals prepared by existing techniques have various morphologies and irregular defects.Therefore,it is of great significance to study the spheroidization and crystallization of FOX-7 for improving its crystal morphology and improving its comprehensive properties.The vacuum crystal habit and morphologically important crystal planes of FOX-7 were calculated by the AE model;according to the interaction between the solvent and each crystal plane,the crystal habit of FOX-7 in 5 pure solvents and their mixed solvents with dimethyl sulfoxide（DMSO）was predicted;the interaction force between solvent molecules and FOX-7crystal planes was studied from the point of interface adsorption and diffusion,and the effects of solvent molecules on the conformation and growth of solute molecules were analyzed.The results show that the FOX-7 crystal is fusiform under vacuum,and there are 6 important growth crystal planes such as（0 1 1）and（1 0-1）;methyl ethyl ketone（MEK）,DMSO/methyl isobutyl ketone（MIBK）and DMSO/acetone（ACE）solvent systems are more favorable for the spheroidization of FOX-7;There are hydrogen bonds,van der Waals force and electrostatic force between the（0 1 1）crystal plane of FOX-7 and the three solvent molecules at the same time,among which van der Waals force dominates,inhibiting the growth of this crystal plane;compared with the molecules of the other two solvent systems,the DMSO/ACE solvent molecules diffused more easily to the FOX-7 crystal plane,and the interaction with the crystal plane was stronger.Using the laser dynamic method,the solubility of FOX-7 in 6 pure solvents and 5 mixed solvents composed of DMSO and other solvents were determined;correlating solubility data using the van’t Hoff equation,Modified Apelblat equation,Yaws equation and Jouyban-Acree equation;the thermodynamic parameters,solid-liquid surface tension and crystal surface entropy factor of the dissolution process of FOX-7 in various solvent systems were calculated.The results show that the solubility of FOX-7 in the solvent increases with the increase of temperature and DMSO content;the dissolution of FOX-7 in the chosen solvents are an"endothermic and non-spontaneous"process,and the enthalpy contributes more to the Gibbs free energy than entropy.The optimal solvent system for FOX-7 crystallization was screened from 6 pure solvents,and mixed solvents composed of DMSO and other solvents;in the optimized system,using cooling crystallization method and elution crystallization method,the optimal operation process for preparing spherical FOX-7 crystals with different particle sizes was studied;the crystal form and structure of the product crystallized under the optimal process conditions were characterized by XRD and FT-IR.The results show that the optimal solvent system for FOX-7crystallization is V_DMSO/V_ACE=2/1;cooling crystallization in the V_DMSO/V_ACE=2/1 system,the best cooling crystallization process is the additive（PEG600）dosage of 0.05%,the initial temperature of 60℃,the stirring rate of 400r/min,the cooling rate of 0.3℃/min,the obtained spherical crystals with a particle size of 300～350μm;elution crystallization in the V_DMSO/V_ACE=2/1（0.05%PEG600）system with ultrasound assisted.The best elution solvent was ethyl acetate.The optimal process parameters are the initial temperature of 25℃,the stirring rate of 500 r/min,the ethyl acetate dropping acceleration rate of 0.6 m L/min,the ultrasonic frequency of 50 KHz,the ultrasonic time of 2 h,the obtained spherical crystals with a particle size of 100～150μm;whether it is cooling crystallization or dissolution crystallization,neither the crystal form nor the structure of the spherical FOX-7 crystals produced by it has changed.The cooling crystallization kinetics of FOX-7 in V_DMSO/V_ACE=2/1 was studied.The kinetic experiment was carried out by the batch dynamic method,the process data was obtained,and the crystallization nucleation and growth rate model under the corresponding system was established;the effects of crystallization processes on crystal nucleation and growth rate were analyzed.The results show that the growth rate of FOX-7 in V_DMSO/V_ACE=2/1 is a particle size-independent mode;the supersaturation has a greater effect on the growth rate than the nucleation rate.For raw FOX-7 and spherical FOX-7 obtained by the optimal cooling crystallization process,TG-DSC,DSC and ARC were used to study their thermal decomposition behavior;impact sensitivity and friction sensitivity were measured according to the test methods specified in GJB 772A-97.The results show that the raw FOX-7 has two exothermic peaks（231.27℃and 297.95℃）,and the spherical FOX-7 has only one exothermic peak（238.53℃）.Compared with raw FOX-7,the thermal decomposition activation energy of spherical FOX-7 is increased by 64.14 k J·mol^-1,and the thermal explosion critical temperature is increased by 32.19 K,indicating that spherical FOX-7 has better thermal stability and faster energy release efficiency;the impact sensitivity of spherical FOX-7 is reduced by 4%,and the friction sensitivity is reduced by 8%,indicating that the mechanical sensitivity of spherical FOX-7 is lower.It can provide basic data and theoretical guidance for industrial production based on the research results of this paper.