Preparation Of Nano-FOX-7 By Ultra-low Temperature Recrystallization Method

1,1-diamino-2,2-dinitroethylene(FOX-7)is a new type of simple explosive with excellent comprehensive properties,which was first synthesized and disclosed in 1998.Its energy is similar to that of the most widely used single explosive 1,3,5-trinitro-1,3,5-triazacyclohexane(RDX)with the best comprehensive performance and "high efficiency damage" performance,but has lower mechanical sensitivity than RDX.The sensitivity of FOX-7 is similar to that of1,3,5-triamino-1,3,5-trinitrobenzene(TATB),which has the lowest mechanical sensitivity,and it has good compatibility with RDX and 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane(HMX)and good potential application value in the field of high energy and insensitivity explosives.The properties of explosive could be improved by its nanocrystallization,and the nano explosives in thermodynamic metastable state are easier to be obtained at low crystallization temperature,and the low temperature is helpful to keep the particle size at a small level without growing up.In this paper,FOX-7 was selected as the research target,liquid nitrogen was used as the ultra-low temperature medium,and nano FOX-7 was prepared by ultra-low temperature recrystallization method under different conditions.Effects of surfactants and solvents on the properties of the prepared nano-FOX-7 were discussed in detail.The primary contents in the paper are as follows:(1)Using N,N-dimethylformamide(DMF),N,N-Dimethylacetamide(DMAC),acetone and N-methylpyrrolidone(NMP)as solvents,FOX-7 nano particles were prepared by ultra-low temperature recrystallization method in liquid nitrogen.The average grain sizes of the prepared nano FOX-7 are about 30 nm,and their particle sizes are mainly between 100?200nm,and less than 300 nm.The temperature range between the high and low temperature decomposition exothermic peaks of the prepared nano FOX-7 becomes narrow,the energy release efficiency and decomposition exothermic enthalpy are greatly improved,and the impact sensitivity and friction sensitivity are significantly reduced.When the solvent is NMP,the minimum particle size of the prepared nano FOX-7 is 40 nm,and its initial decomposition peak temperature,decomposition enthalpy and impact sensitivity of nano FOX-7 increase by 11.8 ?,19% and 58.5%,respectively.(2)Using NMP as solvent,nano-FOX-7 nano particles were prepared under different kinds of surfactants.The average grain sizes of prepared nano-FOX-7 are between 25 nm and 40 nm.When Tween-80 and op-50 were added,the prepared FOX-7 was spherical,and there was only one exothermic peak in their thermal decomposition process,which was different from the two-step heat release of the raw material,the prepared sample shows the characteristic of one-step heat release.The Kissinger model was used to calculate the one-step exothermic samples.It was found that the apparent activation energy of the samples decreased by 22.4% and 31.0% compared with the raw materials,respectively.Moreover,the initial thermal decomposition peak temperature and enthalpy of decomposition of prepared FOX-7 increase and the impact sensitivity also greatly reduce.