Study On Crystal Morphology And Crystallization Kinetics Of FOX-7

1,1-Diamino-2,2-dinitroethylene(FOX-7)is a commonly used high-energy low-sensitivity explosive,with excellent detonation performance and stable safety performance.At the same time,it is widely used in insensitive explosives and solid propellants.In order to improve the physical and chemical properties and application performance of FOX-7,a large number of studies have been conducted on the crystal modification of FOX-7 at home and abroad,but there are few studies on the kinetic mechanism of crystal nucleation and growth.In this thesis,the crystallization process of FOX-7 has been studied through theoretical calculations combined with experiments.At the same time,the nucleation and growth kinetics during the cooling crystallization process were explored,and the influence of the crystallization parameter change law on the crystal nucleation and growth was obtained,and the corresponding dynamic model was established.These provide theoretical guidance for the research of FOX-7 crystallization technology and the control of crystal particle size and crystal quality.In the study of FOX-7 crystal morphology,the attachment energy(AE)model was used to predict the crystal morphology of FOX-7 in vacuum and eight different solvents,and the aspect ratio of the simulated crystal form was obtained.The natural cooling method of saturated solution was used to recrystallize FOX-7 to verify the applicability of the AE model to the simulated crystal form of FOX-7.The results show that:FOX-7 crystal has six important crystal planes:(1 0-1),(1 0 1),(0 1 1),(0 0 2),(1 1 0),(1 1-1).The order of aspect ratio under the influence of solvent was:DMSO<DMSO/H₂O(V/V=2/1)<acetone<methanol<NMP<DMAC<ethylacetate<H₂O.The theoretical prediction results are in good agreement with the experimental FOX-7 crystal morphology.In the FOX-7 crystallization kinetics study,multi-channel crystallizer and turbidimetric method were selected to measure the nucleation induction time of FOX-7 in the DMSO/H₂O binary solvent in the primary nucleation part.We can get the nucleation kinetics parameters and determine the nucleation mechanism and growth mode.In the secondary nucleation and growth part,the batch dynamic method was used to sample and measure the kinetic data of the cooling and crystallization process of FOX-7 in DMSO/H₂O binary solvent in real time.Then the nucleation rate equation and the growth rate equation are established to discuss the effects of supersaturation,suspension density,temperature,and stirring rate on the crystallization process.The results show that the induction time decreases with the increase of supersaturation and temperature.Homogeneous nucleation dominates when S>1.27 and heterogeneous nucleation dominates when S<1.25.The FOX-7 crystal growth method is continuous growth.Increasing the crystallization temperature and reducing the degree of supersaturation are conducive to crystal growth.The particle size independent growth model is suitable for the FOX-7 crystal growth process.In the study of FOX-7 crystal size control,the cooling method was used to study the effects of crystallization temperature,stirring rate,cooling rate,whether seed crystals were added,and the amount of seed crystals added on FOX-7 crystal size and distribution.The results show that the average crystal size increases with the increase of the initial crystallization temperature and the decrease of the cooling rate.The particle size tends to decrease when the stirring rate increases.The addition of seed crystals increases the grain size of FOX-7crystals.With the increase in the amount of seed crystals,the average crystal grain size gradually becomes smaller.