| 1,1-Diamino-2,2-dinitroethylene?FOX-7?is a new type of high-performance energetic material with a high crystal density(1.878g.cm-3),good chemical stability,benign heat resistance and having a good compatibility with TNT,RDX,and HMX.The energy level FOX-7 is similar to RDX,but is not as sensitive as RDX.In this work,the thermodynamics and crystallization behaviors of FOX-7 crystals were studied systematically,due to its crystal morphology and the particle size distribution was difficult to control in production applications.A more comprehensive solubility data of FOX-7 were obtained,the crystal with regular morphology and controllable particle size was prepared,which laid the foundation for the later application.Solubility of FOX-7 in different pure solvents and different binary mixed solvents was measured by turbidity method,and the modified Apelblat model,Yaws model,and ideal solution model were applied to correlate the experimental solubility data.The thermodynamic parameters such as dissolution enthalpy,dissolution entropy and Gibbs free energy of FOX-7 in the tested solvents were calculated.The metastable zone width of FOX-7 in the binary mixed solvent DMSO/H2O=2:1 was measured,and the effect of different crystallization conditions on metastable zone width was investigated.It was found that the solubility of FOX-7 in pure solvents decreases in an order of DMSO>NMP>DMF>DEF>?-butyrolactone>cyclohexanone>ethyl acetate>?1,4-dioxane,water?.The solubility of FOX-7 in binary mixed solvents DMSO/H2O and DMF/H2O increased with increasing temperature and increasing DMSO or DMF content in binary mixed solvents.The metastable zone width in the binary mixed solvent DMSO/H2O=2:1?volume ratio?narrows with the increase of temperature,decrease of cooling rate and increase of stirring rate.Recrystallization of FOX-7 in eight different solvents.The results showed that the type of solvent has a great influence on morphology of FOX-7.Recrystallization in different solvents can get crystal morphology such as rods,flakes,lumps,combs,and polycrystal.The crystal size also varies from tens to hundreds micron.Dimethyl sulfoxide and N,N-dimethylformamide are used as solvents can get bulk crystals,but their quality and particle size are difficult to control.Cooling crystallization in binary mixed solvent DMSO/H2O,and found that the crystal morphology and particle size of FOX-7 were significantly affected by the initial crystallization temperature and the cooling rate.In temperature range of 50-80?,and cooling rate is higher than 2?·min-1,the high quality FOX-7 crystals in the shape of cube can be obtained with controllable particle of 20-150?m.Performance analysis of FOX-7 crystals with different morphologies?rods,flakes,rhombuses,combs,prisms,blocks?.The results show that crystals with different morphologies have no transform in structure but have an influence on the crystal density,sensitivity and thermal stability.When FOX-7 have the same morphology?all are bulks?,however the particle size are different,it is found that the thermal stability of crystal increases correspondingly with increasing particle size. |
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