Abstract:

Abstract:A cyclo-pentazolate anion-based energetic cocrystal （NH₃OH⁺N₅^-）₂·NH₃OH⁺Cl^-·H₂O was designed and synthesized by AgN₅ （or NH₃OH⁺N₅^-） and hydroxylamine hydrochloride（NH₃OH⁺Cl^-） as raw materials. The structure of the compound was characterized by X-ray single crystal diffraction， infrared spectroscopy and elemental analysis. The structure belongs to the monoclinic crystal system，the P2₁/n space group， a=3.8390（6）Å， b=14.665（2）Å， c=21.975（3）Å， V=1236.4（3）ų， α=γ=90°， β=92.034（3）°， Z=1， D_c=1.589 g·cm^-3. In addition， the thermal stability of （NH₃OH⁺N₅^-）₂·NH₃OH⁺Cl^-·H₂O was studied using DSC and TG， and the results showed that its initial decomposition temperature was about 95.6 ℃. Its detonation velocity and detonation pressure were calculated by EXPLO5 to be 8260 m·s^-1 and 23.79 GPa. （NH₃OH⁺N₅^-）₂·NH₃OH⁺Cl^-·H₂O has low impact and friction sensitivities （IS>40 J； FS>360 N）， as the cocrystal of hydroxylamine hydrochloride can greatly reduce the mechanical sensitivity of NH₃OH⁺N₅^-.

Abstract:Herein， two energetic salts， 3，4-diamino-5-（3，4-diamino-1，2，4-triazol-5-yl）-1，2，4-triazolium perchlorate （2） and 3，4-diamino-5-（3，4-diamino-1，2，4-triazole-5-yl）-1，2，4-triazolium nitrate （3）， were prepared by neutralization reaction of 3，4-diamino-5-（3，4-diamino-1，2，4-triazol-5-yl）-1，2，4-triazole （1） with perchloric acid and nitric acid， respectively. The suitable single crystals of 2 and 3 were obtained and the crystal structures were measured by single crystal X-ray diffraction analysis. In the crystal structure of 2， each cation interacted with 12 adjacent perchlorates anions through hydrogen bonding. Layer structures were formed by the cations of protonated 1. Perchlorate anions were embedded into two nearby layers. In the crystal structure of 3， each cation interacted with 10 nearby nitrates through hydrogen bonding. Layer structures were built by the cations and nitrates. The thermal stabilities of 2 and 3 were measured by differential scanning calorimeter （DSC） and thermogravimetric analyzer （TG）. Compounds 2 and 3 had ultra-high thermal stabilities， and their thermal decomposition temperatures were 338.3 ℃ and 289.8 ℃， respectively. In addition， the calculated detonation velocity and specific impulse of 2 were 8308 m·s^-1 and 250.3 s， respectively， indicating 3 shows excellent energetic properties. Compound 3 had excellent mechanical sensitivity. The values of impact sensitivity and friction sensitivity were higher than 20 J and 360 N， respectively.

Abstract:In order to decrease the acidity of insensitive explosive 3-nitro-1，2，4-triazol-5-one （NTO）， NTO·（3，5-DATr） energetic ionic salt （Ⅰ） and NTO/IMZ energetic co-crystal （Ⅱ） were prepared by the reactions of NTO with 3，5-diamino-1，2，4-triazole （3，5-DATr） and imidazole（IMZ）. The single crystals were obtained by solvent volatilization， and the crystal structures were measured by single crystal X-ray diffraction. Crystal Ⅰ belongs to monoclinic crystal system， space group P2₁/c， with M_r=229.19，a=3.5687（7） Å，b=17.245（3） Å，c=14.655（3） Å，β=93.79（3）°，V=899.9（3） ų，Z=4，D_c=1.692 g·cm^-3；Crystal Ⅱ belongs to orthorhombic crystal system，space group Pbcn，with M_r=207.17，a=16.9398（16） Å，b=5.6802（5） Å，c=17.9111（19） Å， V=1723.4（3） ų， Z=8， D_c=1.597 g·cm^-3. Differential scanning calorimetry （DSC） and thermal weight loss method （TG） were used to test their thermal decomposition properties， and the results show that both Ⅰ and Ⅱ have good thermal stability. The Gaussian 09 program was used to optimize the molecular structures and calculate their enthalpy of formation. Software EXPLO 5 was used to calculate the detonation velocity and pressure of Ⅰ（D=7662.3 m·s^-1，p=21.0 GPa） and Ⅱ（D=6490.2 m·s^-1，p=14.6 GPa）. The mechanical sensitivity was tested by the BAM method. Results show that both of them are insensitive towards impact and friction （IS > 40 J， FS > 360 N）. The pH value of standard samples were measured by pH meter. The pH values of NTO， Ⅰ， and Ⅱ in 0.01 mol·L^-1 standard solution are 2.92 （22.8 ℃）， 4.10 （22.7 ℃）， and 4.98 （22.8 ℃）， respectively， indicating that the formation of salt and co-crystal significantly decrease the acidity of NTO.

Abstract:The thermites with different morphologies performed differently. To explore the influence of different MoO₃ morphologies on the thermal properties and combustion behavior of Al/MoO₃ thermite， Al/rod-MoO₃ and Al/ribbon-MoO₃ thermite were prepared. Field emission scanning electron microscope （FE-SEM）， X-ray diffractometer （XRD） and differential scanning calorimetry （DSC） were used to characterize their morphology and thermal properties. The DSC results showed that the Al/ribbon-MoO₃ thermite had a heat release about 1702 J·g^-1， while the Al/rod-MoO₃ thermite released 432 J·g^-1. The initial reaction temperature of Al/ribbon-MoO₃ thermite was 401.95 ℃， which was 102.92 ℃ earlier than the 504.87 ℃ of Al/rod-MoO₃ thermite. Non-isothermal thermodynamic analysis showed that the activation energy （E_a） of the two thermites was not significantly different， but the Al/rod-MoO₃ thermite presented a higher thermal explosion critical temperature （T_b）， indicating that the Al/rod-MoO₃ thermite exhibited higher safety. In the open combustion experiment， there was little difference in the combustion behavior of the two thermites. When the thermite burnt out， the Al/ribbon-MoO₃ thermite splashed sparks. The closed-tube combustion experiment showed that the combustion wave velocity of Al/rod-MoO₃ thermite increased primely then decreased， and the maximum wave velocity reached 1037 m·s^-1. The combustion wave velocity of Al/ribbon-MoO₃ thermite was on the rise， and the maximum velocity was 2710 m·s^-1. Al/ribbon-MoO₃ thermite is superior to Al/rod-MoO₃ thermite in heat release and combustion performance， but the Al/rod-MoO₃ thermite is much safer.

Abstract:This study probed the influence of compounds containing NH_n （n=0-4） groups such as ammonium perchlorate （AP）， guanidine nitrate （GN）， nitroguanidine （NQ）， N-methyl-4-nitroaniline （MNA） and cyclotetramethylene-tetranitramine （HMX） on the solidification process and solidification temperature of 2，4-dinitroanisole （DNAN）. The effects of the type of additives and AP content on the solidification temperature of DNAN were disclosed by a DSC and an optical microscope technique. Furthermore， as-calculated solidification linear velocity and the characteristics of dynamic crystallization process were analyzed based on the solidification process of addictive-containing DNAN in thin layer observed by microscope. The influence of the additives on the formability of the DNAN was studied by cross-section images of a Φ20 mm test pieces. In addition， relationships between solidification enthalpy and corresponding temperature of DNAN was studied based on crystallization thermodynamics. Besides， the mechanisms towards the influences of NH_n compounds on DNAN solidification was analyzed and verified. The results showed that an remarkable-increased solidification temperature of DNAN was achieved by the AP， while being slightly influenced by the AP content and other compounds like GN， NQ， MNA and HMX. The lowest solidification line rate of AP containing object with dendrite-like crystallization could be attributed to the elevated solidification temperature. Influenced by crystallization latent heat during the bulk-growth of DNAN， the microstructure of pure DNAN could be demonstrated as columnar blocks while additive-containing counterparts were disclosed as tiny crystallization. Solidified thermodynamic analysis showed that the DNAN solidification enthalpy was positively correlated with the solidification temperature， which is also affected by heterogeneous additive particles on heterogeneous nucleation. The mechanism and verification of the solidification temperature of DNAN in the present paper demonstrated that the additives with NH₄⁺ can significantly improve the solidification temperature of DNAN.

Abstract:Composite solid propellant contains more solid particles， so it is difficult to accurately simulate the extrusion process of the propellant in twin-screw extruder with traditional finite element analysis method. Whereas， the coupling of discrete element method （DEM） and computational fluid dynamics （CFD） is an effective method for simulation the production process of composite solid propellant， but it is very difficult to implement. In this paper， based on the calibrated contact model parameters， the simulation of solid particles in solid propellant with aluminum powder and ammonium perchlorate as main components in twin-screw extrusion process was realized with DEM， and then the DEM-CFD coupling calculation of the solid propellant solid particles and the liquid phase was realized. The results show that the transportation of solid propellant particles in twin-screw calculated by DEM is consistent with the experimental law. Comparing the results between DEM-CFD coupled simulation and DEM for solid particles， it can be seen that the fluidity of materials was significantly improved by adding the liquid phase The filling rate of materials in the screw conveying section increases from 20% to 40%， and the average conveying speed of solid particles increases by 150%， but the stress of screw does not change much.

Abstract:To study the mechanical properties of Hydroxyl-Terminated Polybutadience （HTPB） propellant/liner bonding interface for solid rocket motor at different temperatures accurately， the model-Ⅰ fracture properties of the interface were studied with experimental method and simulation. Firstly， the load-displacement curves of the test samples at different temperatures were obtained through uniaxial tensile tests and the failure process of the samples were also recorded with the high-speed cameras. It was found that the failure form of HTPB propellant/liner interface was cohesive failure of HTPB propellant， which indicated that the strength of bonding interface was higher than that of the propellant. From -40 ℃ to 60 ℃， the critical displacement first increased and then decreased， indicating that the effect of temperature on this parameter is obvious. And then a cohesion model with polynomial damage variable was developed， based on the bilinear cohesion law. According to the simulation data， the effects of the interface parameters on the predicted results of the interface properties at different temperatures were analyzed. Moreover， the load-displacement curves of the bonding interface at different temperatures were predicted with the critical displacement as a known parameter. It found that the predicted results by simulation were in agreement with the experimental results， which indicates that the developed interface model can more accurately reflect the temperature-dependent behavior of model-Ⅰfracture of the debonding interface for solid rocket motor than the bilinear cohesion model.

Abstract:Slow cook-off test is one of the key tests of low vulnerability assessment for solid rocket motor. In order to study the influence of the charge size of HTPB composite propellant on the slow cook-off characteristics， slow cook-off tests and numerical simulation were carried out to compare and analyze the ignition growth laws of solid rocket motor under slow cook-off tests， with charge dimensions of Φ100 mm × 200 mm， Φ160 mm × 400 mm and Φ522 mm × 887 mm. Their corresponding ignition temperatures， ignition positions and response levels were determined. Results show that the ignition temperature of specimens of Ф100 mm×200 mm， Ф160 mm×400 mm and Ф522 mm×887 mm of solid rocket motors are 244 ℃， 172 ℃ and 155 ℃， respectively. Taking test data as inputs， the calculated ignition temperature is 250， 269， 154℃， and their corresponding calculation errors and response levelsare 2.88%， 1.17%， 0.64%， and explosion， explosion and deflagration. The calculated cloud diagram shows that the ignition position of medium and small test pieces is located in the center of charge cylinders， and the ignition position of full-scale solid motor is in the center of meat thickness of solid propellant front-end， which is a ring shape area.

Abstract:In order to realize the non-destructive measurement when predicting the storage life of nitrate ester plasticized polyether （NEPE） propellant， the high temperature accelerated aging， gas content monitoring and uniaxial tensile mechanical property experiment were carried out on NEPE propellant with 10% constant compression strain . The non-destructive storage life prediction model based on characteristic gas contents was proposed through correlation analysis and remaining life prediction model. The results show that during the storage and aging processes， the total amount of CO gas is the largest， reaching more than 1300 mg at different temperatures. The generating rates of NO and CO are growing slowly in the early aging period， and growing faster in the late period. The generating rate of HCl increases rapidly during the eraly and late aging period and slowly in the middle. Maximum tensile strength σ_m and maximum elongation ε_m increase slightly in the early aging period， the former oscillates slightly and the latter gradually increases in the middle period， and both of them decrease sharply in the late period. The correlation between the contents of CO and the maximum tensile strength is largest and there is a single correlation between them at different temperatures. The maximum correlation value reaches about 0.93-0.95. Four life prediction methods of NEPE propellant are established based on traditional and improved aging life prediction model， tensile strength and CO content. The maximum correlation coefficient and estimation results show that the improved prediction model based on the content of CO gas release is most effective.

Abstract:The thermal decomposition characteristics and thermal safety of methylhydrazine （MMH） were studied by means of differential scanning calorimetry （DSC）. The kinetics， thermodynamics and thermal safety parameters of MMH were calculated， respectively. The thermal explosion delay period of MMH of ball shaped with radius of 1 m at different supercritical ambient temperatures were also obtained. Based on the isoconversion rate method， the adiabatic induction period and self-accelerating decomposition temperature of MMH were further evaluated by using AKTS software. The results show that the thermal decomposition process of MMH has only one strong exothermic peak. The apparent activation energy values of MMH calculated by Kissinger and Ozawa methods are 159.13 kJ·mol^-1 and 158.89 kJ·mol^-1， respectively. The values of T_bp0 of MMH is 469.55 K. The values of entropy of activation （ΔS≠）， enthalpy of activation （ΔH≠）， and free energy of activation （ΔG≠） are 73.93 J·mol^-1， 155.32 kJ·mol^-1 and 121.46 kJ·mol^-1， respectively. The corresponding temperatures for adiabatic induction period at 8， 24 h and 168 h are 429.55， 424.05 K and 414.95 K， respectively. When the packing mass was 5， 25， 50 kg and 100 kg， the self-accelerating decomposition temperatures of MMH are 415.15， 414.15， 413.15 K and 412.15 K in turn. The results provide the necessary theoretical basis for evaluating the thermal safety of MMH in the processes of production， storage， transportation and use.

Abstract:Caged energetic compounds are the hotspots in the research field of energetic materials due to their high energy and density levels， and the clarification of their thermal decomposition mechanisms is significant to the in-depth study of their detonation mechanisms and the improvement of their thermal stabilities. Herein， the thermal decompositions of energetic adamantanes， cubanes and isowurtzitanes are reviewed according to the clue of their caged skeletons， and the thermal decomposition mechanisms of these three caged compounds are also summarized. The thermal decomposition of energetic adamantanes initiated from the substituents and possessed Bridgehead Carbon Effect. In contrast， the thermal decomposition of energetic cubanes and polynitroisowutzitanes usually started from the C—C bond in the cage skeleton and the removal of nitro groups， respectively. Future research should further enrich the types of caged energetic compounds and carry out systematic study on thermal decompositions of caged compounds， especially the thermal decomposition mechanisms of the caged skeletons.