Abstract:As a typical representative of the third generation energetic materials， 2，4，6，8，10，12-hexanitro-2，4，6，8，10，12-hexaazaisowurtzitane （CL-20） is currently the most powerful energetic compound that has already been commercially available. The important research directions are， at present， the optimum synthesis of CL-20 and the preparation of CL-20-based high energy and low sensitivity energetic compounds in the development of energetic materials. The development status of the intermediates in the preparation of CL-20 was analyzed and summarized. The solutions and prospects of the intermediates were also proposed. In addition， the research progress， structural characteristics and main properties of CL-20 crystal products were also discussed. Through sorting out the synthesis and crystals of CL-20， it is concluded that low-cost， high yield， high purity and environmental friendliness are the future development direction of the synthesis process of CL-20.

Abstract:To research the influence of the additives such as RDX， Al， AP and polymer PBNMO on the moulding and mechanical characteristics of DNAN， the crystallization process of different intermixtures and the initial solidification temperature were observed mainly by photic microscope. The solidification rate was calculated by measuring the solidification time and the distance change. The effects of additives on the molding process were studied by testing the relative density of the Φ20 mm samples. The effects of additives on the mechanical properties were studied by testing the tensile strength and the compressive strength. Results show that those additives could improve the crystallization process， increase the relative density and decrease the solidification rate of DNAN. The mechanical properties such as the tensile strength，compressive strength and the anisotropy of the DNAN were improved by adding polymer PBNMO. The tensile strength was over 6 MPa. The results showed that， DNAN based explosives with fine crystals， less defects and better mechanical properties could be got by the synergistic effects of RDX， Al， AP and PBNMO.

Abstract:The HNIW/FOX-7-based PBX has been aged 7， 14， 21 d and 28 d at 71 ℃ according to GJB736.8-90 initiators and pyrotechnics test method， respectively. And the morphology and thermal decomposition properties of PBX molding powder before and after aging were characterized. The PBX molding powder was tested by FTIR and XRD. The variations of size， mass and mechanical properties of the PBX columns have been measured before and after aging tests. Results show that the mass and size change rate are both within 1%， which meets the evaluation standard of MIL-STD-1751， indicating that PBX columns are still at an acceptable level after aging tests. The surface morphology of PBX molding powders has changed in varying degrees. There are more surface cracks and the surface morphology are more uneven with the increase of aging time. Moreover， FTIR and XRD results indicate that the molecular structure and crystal form of HNIW/FOX-based PBX have not changed after aging tests. Besides， the analyses of thermal decomposition performance show that the thermal decomposition activation energy of PBX molding powders have decreased after aging tests with the decreases of -5.23%， -5.88%， -7.00% and -8.23%， respectively， which demonstrates that PBX still has good thermal stability after aging tests. The results of mechanical properties show that the compressive strength of HNIW/FOX-7-based PBX increases by 3.18， 3.40， 3.67 MPa and 3.79 MPa， respectively， and the modulus increases by 0.65， 0.79， 0.91 GPa and 0.96 GPa respectively after aging for 7， 14， 21 d and 28 d. Therefore， the change rate of compressive strength and elastic modulus of PBX columns are positively correlated with the aging time， indicating that the compressive strength of PBX columns increases after aging test.

Abstract:A pair of pressed combined CL-20-based and JO-8（HMX-based）explosives are selected to investigate the improvements in the explosion driving performance by using more powerful explosive. This paper presents the test results of detonation velocity， detonation pressure and Gurney coefficient from devices loaded by CL-20-based explosive and JO-8， respectively. Enhanced warhead performance has been demonstrated in static experiments of prefabricated fragment warhead and shaped charge. The results show that the fragment velocity （kinetic energy） driven by CL-20-based explosive is 5.1%-7.3% （10.5%-15.1%） higher than that driven by JO-8. The penetration of shaped charge loaded by CL-20-based explosive is 3.2%-12.6% larger than that loaded by JO-8.

Abstract:In order to analyze high temperature phase transformation of hexanitrohexaazaisowurtzitane （CL-20）， phase transformation temperatures and coefficients of thermal expansion of ε-， β-， and γ-CL-20 were studied via ReaxFF-lg reactive force field molecular dynamics， with modified valence potential intercept. To validate the applicability of selected force field，the density， cell constant， lattice energy， and sublimation enthalpy for three types of CL-20 at room temperature were calculated. The third order Birch-Murnaghan equation of state was used to fit the p-V curve of ε-CL-20， with pressure ranging from 0 to 280 GPa. And the variation of bulk modulus （B₀） and its partial derivative to pressure （B′₀） with the increase of pressure is analyzed. High temperature phase transformation analysis shows that ε-and γ-CL-20 change phases at 398-423 K， of which the ε→γ phase transition occurs at atmospheric pressure， while the γ→ε phase transition needs 0.5 GPa or higher pressure； β-CL-20 transforms to ε crystal form at 448 K. The thermal expansion coefficient analysis shows that there is no obvious anisotropy in the high temperature thermal expansion process of ε-CL-20， while β- and γ-CL-20 show anisotropy in c direction and b direction， respectively. Results show that the modified ReaxFF-lg reactive force field is suitable for the study of phase transition of ε-， β-， and γ-CL-20 at high temperature and high pressure， while the accuracy of thermal expansion of β- and γ-CL-20 needs to be further improved.

Abstract:In order to analyze the mechanism of shock sensitivity of CL-20/HMX cocrystal close to that of HMX， ReaxFF molecular dynamics simulation was used to investigate the mechanical-thermal structural changes and subsequent initial chemical reactions in CL-20/HMX cocrystals with or without voids. The structural deformation and subsequent chemical reaction process are effectively analyzed by using the momentum mirror model combined with shock-front absorbing boundary condition. When shocks subjected to CL-20， HMX， and CL-20/HMX， it is found that the decomposition speed of CL-20 is faster than that of HMX， while CL-20/HMX"s decomposition speed is very close to HMX"s. Besides， the decomposition speed of CL-20/HMX ［100］ shocks is faster than ［111］ shocks. This phenomenon is related to alternative arrangement of CL-20 and HMX molecular layers and the relative slip amount. When CL-20/HMX with 20 nm diameter void is shocked along the ［100］ direction at particle velocity of 2 km·s^-1， hydrodynamic jet collapse does not occur instead of viscoplastic pore collapse. It largely promotes the rapid decomposition of CL-20 and HMX molecules in the high temperature and high pressure conditions formed by pore collapse and the viscoplastic deformation of crystal structure. A new hot spot formation from the void collapse further enhances the shock loading process.

Abstract:In order to get the phase diagrams of 3，4-dinitropyrazole （DNP）/3，4-bis（3-nitrofurazan-4-yl） furoxan （DNTF） binary mixture system and understand the eutectic melting process， DSC was used to investigate the liquefaction and melting process of DNP/DNTF mixed system with different proportions. The T-x phase diagram and H-x phase diagram were established， and the effects of different heating rates and additives on melting process of eutectic were studied. Finally， the kinetic parameters E_a and A of eutectic melting process were calculated by Kissinger equation and Šatava-Šestak equation. Results show that the mass percentage of DNP/ DNTF eutectic is 70.38/29.62 and the eutectic temperature is 76.38 ℃ based on T-x phase diagram， which is good consistent with that from H-x phase diagram as 70.57/29.43. With the increase of heating rate， the initial temperature and peak temperature of melting process are delayed correspondingly. After the addition of Octogen （HMX） and nitroguanidine （NQ）， the melting point of the low eutectic is significantly delayed， while ammonium perchlorate （AP） has little effect on the melting point. The melting kinetic parameters E_a and A of DNP/DNTF eutectic are 19.13 kJ·mol^-1 and 10^9.74 s^-1 respectively， and the integral form of the most probable mechanism function is： G（α）=（1-α）^-1-1.

Abstract:Fluororubber/glycidyl azide polymer/hexanitrohexaazaisowurtzitane （F₂₆₀₂/GAP/CL-20） composite fibers were prepared through electrospinning process， and the effects of solution concentration， binder ratio， spinning voltage and injection rate on the morphology were explored. Scanning electron microscope （SEM） was used to observe the morphology of composite fibers prepared under different conditions. It is found that when the solution concentration is 20%， the binder F₂₆₀₂/GAP content is 10%， the spinning voltage is 14 kV， and the injection rate is 5×10^-3 L·h^-1， the F₂₆₀₂/GAP/CL-20 composite fiber exhibits a three-dimensional network structure and its surface is uniform and smooth. X-ray diffraction （XRD）， infrared spectroscopy （IR）， differential scanning calorimeter （DSC） and mechanical sensitivity tests were performed on the F₂₆₀₂/GAP/CL-20 composite fiber and raw CL-20. The results show that the crystal form of CL-20 in the composite fiber changes from ε to β after electrospinning. There is no chemical reaction between CL-20 and F₂₆₀₂/GAP during the electrospinning process. After electrospinning， the apparent activation energy of F₂₆₀₂/GAP/CL-20 increases from 178 kJ·mol^-1 of the raw CL-20 to 374.3 kJ·mol^-1， indicating that the composite possesses better thermal stability. The impact sensitivity H₅₀ increases from 21.2 cm to 62.6 cm， and the friction sensitivity decreases from 84% to 52%. Therefore， the effect of sensitivity reduction is significant.

Abstract:In order to improve the efficiency of charging and molding of the explosive network， as well as the energy performance， high-energy azide binder 3，3-diazide methyl oxetane-tetrahydrofuran copolymer （PBT）， ultraviolet （UV） curing acrylate and hexanitrohexaazaisowurtzitane （CL-20） were selected as bonding system and main explosive respectively， an ultraviolet assisted curing CL-20-based energetic ink was designed， and using a 3D printing device to write. Rheometer， scanning electron microscope （SEM）， X-ray diffractometer （XRD）， and shore durometer were employed to characterize and test the rheological properties， microstructure， crystal form and hardness of the molded composite. Results show that the ink system is stable when the content of CL-20 is 82%. The curing efficiency of ink is fast with UV assisting， and the surface of molded sample is smooth. The hardness is 70 HA. The special height of impact sensitivity of the composite is 20 cm higher than the raw material； the test of detonation performance shows that the detonation wave can transfer 90° corner， and the critical detonation size reaches 0.387 mm when the line width of charge is 1.2 mm.

Abstract:It was proved that the sensitivity， safety and density of explosive compound were extremely affected by its morphology and particle size. The influence factor of hexanitrohexaazaisowurtzitane （CL-20） particle size was studied in the recrystallization process with the ultrasonic-assisted recrystallization method， the anti-solvent method and the optimization of agitator type， respectively . The effects of continuous and intermittent ultrasonic with different ultrasonic frequencies （20-40 kHz） were also investigated in order to obtain the small particle size product. In the recrystallization process with anti-solvent method， ethyl acetate and chloroform were applied as solvent and anti-solvent respectively. The dropping acceleration of chloroform （20， 50， 100 mL·h^-1）， the ratio chloroform and ethyl acetate （1∶1， 1∶2， 1∶3）， the recrystallization time （24， 48， 72 h） and temperature （30， 40， 50 ℃） were optimized by orthogonal experiments. In addition， three types of agitator including four straight-blade open turbine， six straight-blade turbine and double-layer dispersing discs were performed in the CL-20 product morphology study together with their stirring speed effect. It was concluded that the assistance of intermittent ultrasonic could considerably reduce CL-20 crystal size. Particle size of 14 μm CL-20 could be obtained by ultrasonic assistant method while the frequency was controlled at 40 kHz with every 30 minutes vibration after 5 minutes stop. Moreover， L9（3⁴）orthogonal experiments were designed and particle size of 140 μm CL-20 could be achieved when the crystallization time， temperature， the chloroform dropping rate， and the dropping amount was 72 h， 30 ℃， 20 mL·h^-1 and 150 mL， respectively. Furthermore， three kinds of agitators were employed in the recrystallization process which obviously effected CL-20 morphology and particle size. A controllable particle size between 40-100 μm CL-20 crystals with spherical shape， a smooth and uniform surface were prepared with the double-layer dispersion disc. Comparing with the four straight blades open turbine type and the six straight blades turbine type agitator， it is proved that the product with desired impact sensitivity and friction sensitivity could be prepared by the double-layer dispersion disc method， which characteristic drop height and the explosion probability were 23.5 cm and 44%， respectively.

Abstract:A new high-energy compound 3，4-bis（（4-chloro-3，5-dinitro-1H-pyrazol-1-yl）methyl）-furoxan was synthesized by using 4-chloropyrazole as raw material， and its single crystal was obtained by solvent evaporation. The structures of this compound and its intermediates were characterized by ¹H and ¹³C NMR， FT-IR， DSC and TG， and the crystal structure of the product was characterized by X-ray single crystal diffraction. Results show that the compound belongs to the orthorhombic space group Pbca， a=10.1817（7） Å， b=16.1917（11） Å， c=21.7300（16） Å， V=3582.4（4） ų， α=90°， β=90°， γ=90°， Z=8， D_c=1.836 g·cm^-1. The Kamlet-Jacobs semi-empirical equation was used to predict the explosion velocity of 8304 m·s^-1 and the explosion pressure of 30.5 GPa. The sensitivities of this compound were measured by the BAM standard method， and the measured impact sensitivity is 9 J and the friction sensitivity is 180 N.

Abstract:Using nitromethane， tert-butylamine and formaldehyde as raw materials， a novel melt-casting explosive 5-methylnitrate-1，5-dinitrooxazine （TNOP） was synthesized via condensation and nitration reactions with the total yield of 46.2%. FT-IR， ¹H NMR， ¹³C NMR， elemental analysis and single-crystal testing approaches were conducted to obtain the structure of TNOP， disclosing an orthorhombic crystal structure with a space group of Pbca and the density of 1.722 g·cm^-3. The melting point and thermal decomposition temperature were examined to 110.8 ℃ and 203.5 ℃ using DSC technique， respectively. Furthermore， the detonation velocity and the detonation pressure are predicted to be 8112 m·s^-1 and 29.23 GPa based on calculated enthalpy of solid phase formation （-346.6 kJ·mol^-1）. In addition， an impact sensitivity of 50 J could be obtained for TNOP. By coordinating the energetic groups N—NO₂， C—NO₂ and —ONO₂ and facile synthesis process， TNOP was revealed with high energy， low melting point and low sensitivity， implying that it can be used as potential melt-casting explosive in weapons.

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