Abstract:

Abstract:

Abstract:

Abstract:In recent years， molecular perovskite energetic materials have emerged as a kind of new-concept energetic materials， offering a new approach to design practicable single explosives for different applications by rational assembling diverse ionic components. Ammonium chlorate （NH₄ClO₃） is commonly used as an oxidizer benefiting from its high oxidizing ability， but its high hygroscopicity greatly limits its application. By mixing sodium chlorate， aqueous ammonia， and triethylenediamine （dabco）， then acidizing the aqueous solution， we have obtained a new molecular perovskite energetic material， （H₂dabco）（NH₄）（ClO₃）₃（DAC-4）. X-ray single-crystal diffraction analysis revealed that DAC-4 possesses an ABX₃-type perovskite structure belonging to the cubic space group Pmm with a crystallographic density of 1.86 g·cm^-3. DAC-4 exhibits exceptional theoretical detonation performances， with detonation heat， velocity， and pressure of 4.91 kJ·g^-1， 8.43 km·s^-1， and 32.6 GPa， respectively. DTA showed that DAC-4 has a decomposition peak temperature of 106 ℃， higher than that of ammonium chlorate （75 ℃）. Moisture absorption experiments demonstrate that DAC-4 remains nearly non-hygroscopic after being stored for near 2 month at relative humidity below 86%， the weight of DAC-4 only increases by 0.18%， much lower than that of ammonium chlorate （30%）.

Abstract:The octahedral cyclotrimethylenetrinitramine crystal （O-RDX） with an average particle size of 9.35 μm was prepared through the solvent-antisolvent method in the dimethylsulfoxide （DMSO） -ethylene glycol （EG） system using 1-ethyl-3-methylethimidazole acetate （EmimOAc） as an additive. The effects of crystallization parameters such as solvent system， solution concentration， crystallization temperature， additive and stirring speed on the growth behavior of RDX（cyclotrimethylenetrinitramine） crystals were systematically studied. It was observed that the main factor influencing the growth of RDX crystals was the supersaturation. With the gradual decrease of supersaturation， RDX crystals experienced the changes of rough growth， 2D growth and spiral growth， and the morphology of RDX crystals gradually evolved from dendritic to octahedral crystals. The results of analytical tests revealed that O-RDX crystals were in the α-form which was consistent with the raw RDX， showing high crystal density with few crystal internal defects and an increase of 5 ℃ in decomposition temperature. Moreover， compared to the raw RDX， the impact sensitivity and the friction sensitivity of O-RDX decreased by 60% and 50%， respectively. To further explore the formation mechanism of O-RDX， adhesion energy model and the molecular dynamics method were applied to simulate the crystal morphology of RDX in the presence of EmimOAc. The simulated results demonstrated that there were six main crystal faces of RDX： （1 1 1）， （2 0 0）， （1 0 2）， （0 2 0）， （2 1 0）， and （0 2 1）. The formation of the double-cone octahedral morphology originated from the uniform growth rates of the main crystal faces of RDX under the action of EmimOAc. The theoretical simulations generally agreed well with the experimental phenomena.

Abstract:In order to improve the energy release characteristics of Al powder in composite explosives， combining the advantages of microstructure design and surface modification of Al particles， hexanitrohexaazaisowurtzitane （CL-20）/Al@Co/nitrated bacterial cellulose （NBC） composite with 3D network structure was prepared. Firstly， Al@Co particles were synthesized by coating Al with Co via the replacement reaction. Then， Al@Co and CL-20 particles were deposited into the 3D network structure of NBC to form CL-20/Al@Co/NBC composite with 3D network structure. The transmission electron microscopy （TEM）， scanning electron microscope （SEM）， X-ray diffraction （XRD）， X-ray photoelectron spectroscopy （XPS） and Fourier transform infrared spectroscopy （FT-IR） were used to characterize the morphology and structure of the composites. The properties were analyzed by thermal analysis， sensitivity test and combustion test. The results show that the Al@Co particles are formed by coating Co on the Al surface with a thickness of about 32 nm. The CL-20/Al@Co/NBC composite has a 3D network structure. Compared with the NBC+CL-20+Al mixture and CL-20/Al/NBC composite， the higher thermal decomposition peak temperature of Al in CL-20/Al@Co/NBC composite is elevated by 123.7 ℃ and 99.5 ℃， and the heat release is increased by 5.93 kJ·g^-1 and 4.50 kJ·g^-1， respectively. Moreover， CL-20/Al@Co/NBC has a shorter ignition delay time， faster combustion rate， lower impact sensitivity （30 J） and friction sensitivity （192 N）.

Abstract:Due to contacts with additives or changes of environmental conditions （temperature or pressure）， the polymorphism hexanitrohexaazaisowurtzitane （CL-20） is easy to transform into mixed crystal form in propellant system， which leads to structural damage and performance degradation of the propellant. In order to hinder the contact between the solvent and CL-20， then inhibit the crystal transformation of CL-20， the polyphenol amine （PCHA） film was prepared based on the oxidative self-polymerization of hexamethylenediamine （HMDA） and catechol （CCh）. The surface of CL-20 crystal was modified by water suspension method under mild conditions. The scanning electron microscopy （SEM）， Fourier transform infrared spectroscopy （FT-IR）， Raman spectroscopy （RAMAN）， X-ray diffraction （XRD） and X-ray photoelectron spectroscopy （XPS） were used to study the morphology， coating content， thermal properties， and stability in ethylene glycol solution for the composite particles. The results show that HMDA and CCh can modify the surface of CL-20 crystal under mild conditions and form a dense PCHA coating layer. The content of PCHA is about 1% measured by dissolution weighing method and high performance liquid chromatography （HPLC）. The PCHA coating layer increases the crystal transition and thermal decomposition temperature by 16 ℃ and 7 ℃， respectively. The thermal decomposition activation energy E_a at different heating rates was calculated by Kissinger method. The activation energy of CL-20@PCHA is about 8 kJ·mol^-1 higher than that of CL-20， and the thermal stability is greatly improved. The XRD test results indicate that the PCHA film can effectively prevent the contact between the solvent and CL-20， slow down the dissolution rate of CL-20 in the solvent， and effectively inhibit the crystal transformation of CL-20.

Abstract:To improve the reaction performance and reduce variations in the output pressure of Al/KClO₄ pyrotechnic compositions， in-situ replacement method was applied to replace the inert layer of micron-sized aluminum with TiO₂ layer. Scanning electron microscopy （SEM）， X-ray diffraction （XRD）， differential scanning calorimetry-thermogravimetry （TG-DSC） and thermal analysis were conducted to study the microstructure， composition， thermal and combustion properties of Al@TiO₂ particles. The consistency of output pressure was analyzed through ignition experiments. The results show that aluminum coated with TiO₂ layer is well prepared by in-situ replacement method. The explosives made with Al@TiO₂ have an 18% lower in activation energy （E_a） and a slightly lower enthalpy compared to ordinary Al. The standard deviation of output pressure decreased from 0.28 MPa to 0.13 MPa. The thermal behavior of aluminum and potassium perchlorate was enhanced by the TiO₂ layer， significantly improving the consistency of output pressure.

Abstract:In order to solve the problems of low density and effective oxygen content of the existing oxidant NH₄ClO₄ （AP） for mixed explosives， the oxidant KClO₄ （KP） with higher density and oxygen content was compounded with AP， and the optimal ratio of AP/KP composite oxidant was determined by Molecular Dynamics. The novel AP/KP composite oxidant with high density and high oxygen release was prepared by physical mixing and solvent evaporation method， respectively， and its elemental composition， morphology， structure， composition and thermal properties were characterized by inductively coupled plasma spectrum generator （ICP）， scanning electron microscope （SEM）， X-ray powder diffractometer （XRD） and thermal analyzer （DSC-TG）. The results show that element and particle size distribution of the AP/KP composite oxidant prepared by solvent evaporation method is reasonable and uniform. The crystal form has not changed， and the crystal form is relatively complete， as proved by XRD. The thermal decomposition peak temperature of AP and KP was decreased by 11.25 ℃ and 13.87 ℃， respectively， which was more conducive to the thermal decomposition process. In addition， the composite oxidants prepared by physical mixing and solvent evaporation method were introduced into typical metal combustible agent Al powder， the ignition and combustion properties of samples prepared by different methods with Al powder were compared and studied. The results show that when the AP/KP composite oxidant prepared by solvent evaporation was mixed with Al powder， the combustion calorific value reached 12.228 MJ·kg^-1， and the pressurization rate reached 5.21 MPa·s^-1. The laser ignition test shows that the shortcomings of slow AP combustion reaction rate and difficult KP ignition were greatly improved.

Abstract:In order to improve the ignition and combustion performance of boron powder， four kinds of micro- and nano B-Fe-Bi₂O₃@AP/PVDF composite were prepared by high-energy ball milling combined with spray drying method. According to their high calorific value and high combustion efficiency， four composite were named as μBHH_c， μBHC_e， nBHH_c， and nBHC_e. Their morphology， thermal reactivity， ignition delay time， mass burning rate and condensed phase combustion products were characterized and analyzed. The results show that the maximum calorific value of μBHH_c and μBHC_e composite in argon is 9.7 kJ·g^-1， and the maximum combustion efficiency in argon is 66.2 %. The maximum calorific value in oxygen is 14.6 kJ·g^-1， the maximum combustion efficiency in oxygen is 93.3%， and the oxidation peak temperature is between 750 ℃ and 760 ℃. The maximum calorific value of nBHH_c and nBHC_e composite in argon is 9.9 kJ·g^-1， and the maximum combustion efficiency in argon is 68.9%. The maximum calorific value in oxygen is 14.8 kJ·g^-1， the maximum combustion efficiency in oxygen is 97.2%， and the oxidation peak temperature is between 595 ℃ and 600 ℃. The highest combustion temperature of all kinds of composite is between 1954 ℃ and 2011 ℃. The ignition delay time of nBHH_c composite is the shortest （26 ms）， while the mass burning rate is the highest （1.84 g·s^-1）. The μBHC_e composite has the longest ignition delay time （39 ms） and the lowest mass burning rate （0.80 g·s^-1）. The condensed phase combustion products of various composites are mainly composed of B₂O₃， B₄C and a small amount of incompletely burned boron. The morphology of condensed phase combustion products includes 5-10 μm spheres and 10-20 μm flakes.

Abstract:In order to study the effect of high pressure from screw pumping and medium deep hole charging on the microstructure and thermal stability of the on-site mixed emulsion explosive matrix， the microstructure， particle size distribution， crystallization content， thermal decomposition process， thermal decomposition reaction activation energy， thermal decomposition mechanism function and rate equation of the matrix under atmospheric and high pressures were studied by optical microscope， laser particle size analyzer， water solubility experiment， thermogravimetry and derivative thermogravimetry （TG-DTG） couple method， Kissinger method and Ozawa method， Coats-Redfern method and Šatava method. The results show that from atmospheric pressure to high pressure， polymerization， demulsification and crystallization of the intra-matrix phase droplets appeared， the particle size increased from 3.717 μm to 4.474 μm， the precipitation amount of ammonium nitrate crystals increased from 0.0530 g to 0.0640 g， and the uniformity of the emulsion system was weakened. The average thermal decomposition onset temperature of the matrix T_onset increased from 157.4 ℃ to 184.0 ℃， the average first-order derivative thermogravimetric peak temperature T_p increased from 262.6 ℃ to 281.8 ℃， the average mass loss rate increased from 0.1454 %·s^-1 to 0.1476 %·s^-1， and the reaction activation energy decreased from 108.49 kJ·mol^-1 to 84.74 kJ·mol^-1. The free water released by evaporative demulsification under high pressure might cause the rise of T_onset and T_p， and the thermal decomposition reaction was more likely to occur. The activation energy calculated by the Ozawa method had a different trend with the increase of conversion rate， and the thermal decomposition reaction mechanism function changed from Valensi equation to inverse Jinder equation and the rate equation also changed. The high pressure promotes the process of droplet polymerization， demulsification and crystallization of the intra-matrix phase， reduces the activation energy of the thermal decomposition reaction， and weakens the homogeneity and thermal stability of the system.

Abstract:In order to study the influence of explosive crystal particle size on mechanical properties and interfacial enhancement of polymer bonded explosive （PBX）， HMX-based PBXs were prepared by using four kinds of HMX with different particle sizes （160 µm，60 µm，25 µm and 150 nm） as main explosive. The fluorine resin and neutral polymeric bonding agent were used as binder and interface enhancement agent， respectively. The compressive stress-strain test and Brazilian test were performed to obtain the compressive and tensile mechanical properties of 8 types of PBXs at room temperature （20 ℃） and high temperature （60 ℃）， respectively. The storage modulus and mechanical loss factor were obtained using the three-point bending mode of dynamic mechanical analysis. The cross-sections of PBXs were characterized by scanning electron microscopy. Results show that both the compressive and tensile mechanical strength of explosive increase with the decreasing of HMX particle size， in which the nano-HMX based PBX （PBX-nano） shows the highest strength. The compressive strength and tensile strength of PBX-nano are 61.3 MPa and 5.7 MPa， increasing by 73.1% and 63.5% from PBX-L， respectively. By adding the bonding agent， the compressive mechanical strength and tensile mechanical strength for all the PBXs are significantly improved， especially the PBX-nano. The tensile strength of PBX-nano-M at 20 ℃ and 60 ℃ are up to 10.4 MPa and 5.8 MPa， which are 82.6% and 101.4% higher than that of PBX-nano， respectively. When the average particle size of HMX decreases from 100 µm to 100 nm， the greater the fracture energy required for interface debonding/damage and even fracture of explosive， the greater the increase in tensile mechanical strength.

Abstract:This study presents a method for rapidly estimating energy density based on the energy difference of chemical bonds， along with a technique for promptly evaluating cage structural stability by integrating Laplacian bond order and the bond dissociation energy of molecular fragments. By exhaustively constructing all nitrogen-rich frameworks derived from Noradamantane and its 435 nitro derivatives， the study applied the aforementioned computational methods to screen molecular structures with high energy density and stability. The reliability of the screening results was confirmed through quantum chemical energy calculations and transition state reaction barrier calculations. Two nitro compounds exhibiting both high energy density and structural stability were identified， with theoretical maximum values of detonation heat， detonation velocity， detonation pressure， and metal acceleration capability reaching 7.77 kJ·g^-1， 10.1 km·s^-1， 47 GPa， and 1.14 times the metal acceleration capability of HMX， respectively， and with structural decomposition reaction barriers ≥96 kJ·mol^-1. The rapid screening method for energy density and stability of energetic molecules established in this study can provide theoretical guidance for the future design of high-energy stable energetic molecules.

Abstract:In order to study the combustion characteristics of aluminum powder in the detonation environment， based on the combustion model of aluminum powder in the detonation environment， the non-isothermal combustion model of aluminum powder in the detonation environment was established by comprehensively considering the effects of gas components of the detonation products and the temperature of the detonation environment system on the combustion and energy release process of aluminum powder. The non-isothermal combustion control equations of aluminum powder in the detonation environment， including the combustion process of aluminum powder， the gas components of the detonation products and the temperature of the detonation environment system， were proposed. And it was verified by laser induced breakdown spectroscopy experiments. The results show that the deviation between the calculated values of the non-isothermal combustion model control equation of aluminum powder and the experimental values of laser induced breakdown spectroscopy is within 12%， which verifies the accuracy of the theoretical model calculation. The laws of the influence of aluminum powder particle size and aluminum-oxygen ratio on the combustion characteristics of aluminum powder in explosives were obtained.

Abstract:Ammonium perchlorate （AP） is an important oxidant in solid propellants， and its thermal decomposition performance directly affects the combustion characteristics of solid propellants. The use of combustion catalysts can lower the decomposition temperature and increase the decomposition rate of AP. Different methods for microstructure control of nano-combustion catalysts for AP thermal decomposition were studied and summarized. The effects of microstructure control methods such as crystal planes， defects， and composite interfaces on the catalytic activity and catalytic mechanism of combustion catalysts for AP thermal decomposition reaction were analyzed. Besides， the characteristics of catalysts that can achieve optimal catalytic performance were explored. The results indicate that the catalytic activity of nanometal oxide combustion catalysts can be improved by adjusting the exposed crystal faces， element doping and constructing a composite interface structure. Among them， transition metal oxide nano-catalysts can enhance catalytic activity by exposing designated crystal planes， and element doping enhances catalytic activity by generating defects， while constructing a composite interface structure utilizes interface effects to regulate the activity of catalytic sites， thereby enhancing catalytic activity. Transition metal oxide nano-catalysts showed good catalytic activity in improving the thermal decomposition performance of AP.