Abstract:To facilitate the crystallization of spherical FOX-7, a laser dynamic method was performed to determine the solubility of FOX-7 in the solvent mixtures of DMSO-EAC with different volume ratio in the temperature range of 298.15~333.15 K. The solubility equation was established and the crystallization thermodynamic parameters were estimated. The cooling crystallization experiment was carried out in DMSO-EAC mixed solvent. The results show that the solubility of FOX-7 in mixed solvents increases with increasing temperature and DMSO content. All models fit well with experimental data, of which the CNIBS/R-K model has the best correlation. The crystals of FOX-7 obtained by cooling crystallization in V_DMSO∶V_EAC=1∶3 system are regular, ellipsoidal and uniform in particle size.

Abstract:The three-dimensional nanostructured and degradable polyhemiaminal aerogel (PHA) was used as template to induce the in situ crystallization of 1,1-diamino-2,2-dinitroethylene (FOX-7) by evaporation crystallization method. The FOX-7 with three-dimensional nanostructure (nano-FOX-7) was prepared after the degradation of the PHA in dilute sulfuric acid (10%). The purity of nano-FOX-7 was determined to be 99% by high performance liquid chromatography (HPLC), indicating that the template was almost completely removed. The morphology, phase, structure and thermal properties of the samples were characterized. Detemplated nano-FOX-7 preserved three-dimensional nano structure of PHA. The average size of nano-FOX-7 crystal particle was 83.68 nm. Owing to the special micro-nano structure, the peak temperature of phase transition and first thermal decomposition temperature for nano-FOX-7 was delayed by 11.3 °C and 21.3 °C, respectively. Compared with raw FOX-7, the thermal decomposition of nano-FOX-7 almost completely took at exothermal profile with peak of 291.0 °C. The enthalpy of the thermal decomposition increased from 1309 J·g^-1 (raw FOX-7) to 1421 J·g^-1 (nano-FOX-7), together with 31.6% increase of the apparent activation energy (from 408.80 kJ·mol^-1 to 537.42 kJ·mol^-1), which explained the remarkable improvement of the energy release efficiency and thermal stability for the nanostructure FOX-7.

Abstract:In order to solve the problems of irregular crystal morphology and uneven particle size distribution of 1,1-diamino-2,2-dinitroethylene (FOX-7) obtained by direct synthesis. Solubility, supersolubility and cooling crystallization kinetics of FOX-7 in V(N,N-dimethylformamide)∶V(water)=7∶3 binary system were determined by laser dynamic method and intermittent dynamic method respectively.Results show that the solubility equation of FOX-7 in the above system is . There is a granularity-independent growth model during cooling crystallization.In the nucleation rate and growth rate equation, the supersaturation ratio S index are respectively 0.61 and 0.45, the suspension density M_T index is 2.30, and the stirring strength ω_r index is 0.22.

Abstract:The effects of mass fraction and particle size of 1,1-diamino-2,2-dinitroethylene(FOX-7),different composite combustion catalysts with lead, copper and carbon on the combustion performance of nitrocellulose (NC)/trimethylotethane reinitiate(TMETN） low-insensitive and smokeless composite modified double base(CMDB) propellant with screw extrusion process were investigated by means of strand burner method. The results shown that the burning rate of CMDB propellant is first rise and then descend with the addition of FOX-7. When the FOX-7 content is 25%,the burning rate of CMDB propellant rised from 5.87 mm·s^-1 to 14.90 mm·s^-1 at 10 MPa, and when the content of FOX-7 increases from 25% to 30%, the burning rate decreased from 14.90 mm·s^-1 to 12.78 mm·s^-1 at 10 MPa. The pressure exponent of burning rate between 6-16 MPa decrease from 0.97 to 0.60 as the mass fraction of FOX-7 in the formulation increased from 5 % to 30 %. When the FOX-7 be replaced by finer particles FOX-7 with the same mass, the burning rate decreased 1.16 mm·s^-1 at 10 MPa, while the pressure exponent of burning rate between 6-14 MPa increased. The burning rate of propellant with addition of β-Pb/β-Cu/CB combustion catalyst increases from 14.90 mm·s^-1 to 18.65 mm·s^-1 at 10 MPa, while the pressure exponent of burning rate between 6-16 MPa decrease from 0.63 to 0.35, which compared with the referenced formulation (no combustion catalyst).

Abstract:Deuterated nitroguanidine （NQ-d₄） and deuterated 1，1-diamino-2，2-dinitroethylene （FOX-7-d₄） were synthesized via H/D exchange starting from nitroguanidine （NQ） and 1，1-diamino-2，2-dinitroethylene （FOX-7）. The target products were characterized by IR， NMR （¹H and ¹³C）， HPLC， TG-DTG， DSC and neutron diffraction. DSC/TG data show that the decomposition temperatures of NQ-d₄ and FOX-7-d₄ were 2.5 ℃ and 2.6 ℃ higher than those of NQ and FOX-7， respectively. The deuteration rates of NQ-d₄ and FOX-7-d₄ are respectively 95.27% and 98.87% as measured by neutron diffraction. The purities of NQ-d₄ and FOX-7-d₄ are respectively 99.51% and 99.28% obtained by HPLC via area normalization method.

Abstract:In order to improve the safety performance of cyclotetramethylenetetranitramine (HMX) based cast polymer bonded explosive (PBX), a certain amount of 1,1-diamino-2,2-dinitroethylene (FOX-7) was substituted for HMX in the formulation. The influence of FOX-7 on the thermal stability, mechanical sensitivity, shock wave sensitivity and electrostatic spark sensitivity of the formulation was studied. The friction sensitivity of the formulation GOXL-A was lower than that of the HMX based cast PBX formulation GO-1 after the introduction of FOX-7. The response time in the fast cook-off and slow cook-off tests was delayed by 58.8% and 18.5%, respectively. The formulation had passed the EIS slow cook-off test with a heating rate of 3.3 ℃·h^-1. The shock wave sensitivity was significantly reduced. The separator thickness (L₅₀) was reduced by 15.7% compared with GO-1, and the 50% critical detonation pressure (p₅₀) was increased by 9.5%. Its static spark sensitivity is significantly reduced. The 50% ignition voltage (V₅₀) and 50% ignition energy (E₅₀) increased by 65.3% and 187.5%, respectively.

Abstract:Nano-1,1-diamino-2,2-dinitroethylene(FOX-7) was prepared by the solvent-non-solvent method using N,N-dimethylacetamide(DMAC), N-methylpyrrolidone (NMP) and a mixture of the two as solvents. The morphology, phase, structure and thermal performances of the prepared nano-FOX-7 were characterized by field emission scanning electron microscope (FE-SEM), X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FT-IR), differential scanning calorimetry(DSC) and thermogravimetric analysis(TG) method and its sensitivities were tested. On this basis, the effects of solvents and surfactants on the performances of nano-FOX-7 were investigated The results show that the average grain size of the prepared nano-FOX-7 is less than 30 nm. The addition of surfactant is helpful to reduce the grain size and particle size of the prepared nano-FOX-7, enhance its uniformity of particle size distribution and improve its dispersity. Compared with the raw material, the initial decomposition temperatures of the prepared nano-FOX-7 increase, the temperature ranges between their two decomposition exothermic peaks become narrow, their energy release efficiency and decomposition enthalpy greatly increase and the impact and friction sensitivities significantly reduce. When using the mixed solvents and adding the surfactants OP-10 and Tween 20, the initial decomposition temperatures of the prepared nano-FOX-7 increase nearly by 15 ℃, the enthalpies of decomposition increase by 4.97% and 4.65% respectively. And the friction sensitivities decrease by 66.7% and 50.0% respectively.

Abstract:To improve the safety performance of hexanitrohexaazaisowurtzitane (CL-20) and maintain its higher energy, three kinds of CL-20/FOX-7 polymer bonded explosives(PBXs) with different formulation proportions were prepared by water suspension coating method using polyurethane polymer Estane as coating agent and 1,1-diamino-2,2-dinitroethene(FOX-7) as energetic sensitivity-reducing component. The morphology structure, crystal form, thermal decomposition characteristic and impact and friction sensitivity of samples were tested and analyzed by scanning electron microscopy (SEM), X-ray diffractometer (XRD), differential scanning calorimeter (DSC), impact sensitivity tester and friction sensitivity tester. The detonation velocity of three kinds of PBXs was tested by an electrical measurement method. The results show that the explosive particles based on CL-20/FOX-7 have better coating effect, and neither CL-20 nor FOX-7 has crystal transformation. The apparent activation energy of three kinds of PBXs are increased by 17.12, 32.87 and 40.24 kJ·mol^-1 compared with refined CL-20. The enthalpies of activation (ΔH) of PBX samples are also significantly improved compared with CL-20. The characteristic drop height increases from 27.5 cm of refine CL-20 to 58.3, 56.5 cm and 54.2 cm， respectively, compared with CL-20. The actual detonation velocities of three kinds of PBXs with different formulation proportions are 8474, 8503 m·s^-1 and 8577 m·s^-1 ，respectively, which is equivalent to the detonation velocity of PBXN-5, but the characteristic drop height increases by more than 48.5% compared with PBXN-5, the safety performance of explosives is significantly improved.

Abstract:By-product dinitromethane in the manufacturing process of 1, 1-diamino-2, 2-dinitroethylene(FOX-7) from 4, 6-dihydroxy-2-methylpyrimidine(MPO) was recovered, the long needle dinitromethane potassium salt(KDNM) crystal with stable property was prepared via neutralization using aqueous potassium hydroxide solution, 1, 3-dibutyl -5, 5-dinitrohexahydropyrimidine was prepared via Mannich condensation reaction using KDNM, formaldehyde and tert-butylamine as raw materials, and 1, 3, 5, 5-tetranitrohexahydropyrimidine(DNNC) was prepared via the nitrolysis of 1, 3-dibutyl -5, 5-dinitrohexahydropyrimidine with mixed acid system of concentrated sulfuric acid and concentrated nitric acid with total yield of 78.9%(Calculated by KDNM). The structure of DNNC and intermediate were characterized by ¹H NMR, IR, MS. The effect of pH value, solvents and temperature on Mannich condensation reaction, and the effect of selection of nitration system on the nitating reaction were studied. The optimal conditions of Mannich condensation reaction were determined as: the molar ratio of KDNM, formaldehyde and tert-butylamine is 1.0:3.5:2.0, 10% aqueous methanol solution is used as solvent and hydrochloric acid is used to adjust pH value to 8 at room temperature; and then temperature rises up to 50 ℃ subsequently with reaction for 3 hours, and the yield reaches 85.3%. Using mixed acid composed of 20 mL 98% H₂SO₄ and 10 mL HNO₃By as nitrolysis system, the yield reaches 92.5%.

Abstract:To accurately understand the effect of solvent and temperature on crystal morphology of energetic materials, molecular dynamics simulations were employed to investigate the crystal morphologies of 1, 1-diamino-2, 2-dinitroethene (FOX-7) under H₂O/dimethylacetamide (DMF) condition. By calculating the interaction energies of solvent and crystal surfaces, the attachment energies in vacuum were modified and the crystal shapes in different ratio of solvents with different temperatures were obtained. The intermolecular interactions of solvent molecules and crystal surfaces were also discussed. Results show that the morphologically dominant faces of FOX-7 in vacuum are (0 1 1), (1 0 -1), (1 0 1), (1 1 -1), (0 0 2) and (1 1 0), the crystal morphologies of FOX-7 in H₂O/DMF solutions are variable in different temperatures, the crystal shape is similar to block in different ratio of solutions in 298 K, and the predicted crystal morphology was in agreement with the experimental result from the reference.

Abstract:Four kinds of gas clusters of 1, 1-diamino-2, 2-dinitroethene (FOX-7) were obtained by using RI-B2PLYP-D3 and PW6B95-D3 methods with dispersion correction density functional theory. On this account, the existing state of FOX-7 molecules in the crystal structures was simulated. The electron density difference of the neighboring molecules in the process of cluster formation was plotted, and the formation and origin of intermolecular interactions were explained from the point of view of electron density change. The effect of intermolecular interaction of condensed phase FOX-7 on the dissociation mechanism of FOX-7 was investigated. Results show that the intermolecular interactions are due to the partial intermolecular sharing of electrons formed by electron offsets in the FOX-7 clusters. The formation of intermolecular interactions also weakens the chemical bonds in some molecules, resulting in a change in the cleavage channel of FOX-7. Compared with the unimolecule state, the intermolecular interaction makes the cleavage activation energy of C—NO₂ bond in FOX-7 clusters reduce generally when PW6B95-D3 theory is used. Because of different angles of molecular interaction in different clusters, the process of nitro isomer has changed, compared with the unimolecule, the activation energy of nitro isomer channels of cluster Ⅱ decreases by 210.9 kJ·mol^-1, and the activation energy of nitro nitro isomer channel of cluster Ⅳ increases by 39.4 kJ·mol^-1.

Abstract:To obtain the influence rule of different crystallization conditions on the quality and morphology of 1, 1-diamino-2, 2-dinitroethylene(FOX-7)crystals and realize the control of its crystal morphology, the solubility of FOX-7 in dimethyl sulfox- ide(DMSO), water(H₂O)and its binary mixed solvent in the range of 20-95 ℃ and the metastable zone width of binary sol- vent mixtures DMSO / H₂O=2:1(in volume ratio) were measured by turbidimetric method using a CrystalSCAN multi-channel crystallizer. The crystal morphology of FOX-7 under various crystallization conditions was investigated by cooling method, and the mechanical sensitivity and thermal performance of FOX-7 were tested. Results show that the solubility of FOX-7 increases with the increase of temperature and DMSO content in binary mixed solvent. The width of metastable zone becomes narrower with the increase of temperature, decrease of cooling rate and increase of stirring rate. In the process of cooling crystallization, the crystal morphology of FOX-7 is significantly affected by solvent ratio, starting temperature and cooling rate of crystallization. In the range of 50-80 ℃, at the cooling rate of higher than 2 ℃ ·min^-1, the cube-like high-quality FOX-7 crystal with almost the same aspect ratio and regular morphology can be obtained, and particle size is controllable in the range of 20-150 μm. At the same time, the better crystal quality of FOX-7, the higher crystal density and the higher thermal decomposition temperature. The impact sensitivity of FOX-7 is lower and small affected by the crystal morphology, but the friction sensitivity is greatly affected by parti- cle morphology, the frictional sensitivity value of columnar-like crystals is the smallest and that of plate-like crystals is the largest.