Abstract:Aluminum hydride （AlH₃） is a new energetic material with higher energy density than aluminum. A large amount of hydrogen produced in the combustion of AlH₃， which significantly reduced the average molecular weight of gas products. AlH₃ can be used as an energetic component of explosives. However， the crystal transformation process of AlH₃ is extremely dangerous and the unstable impurity phase is difficult to separate， thus it is challenge to obtain the pure stable phase α-AlH₃. The preparation of AlH₃ complexes can avoid the danger of crystal transformation of AlH₃， AlH₃ complexes retain the structural unit of AlH₃， avoid the dangerous crystal transformation process， and can be purified by recrystallization， which has a broad application prospect. This paper reviews the synthesis methods， coordination modes， types and applications of AlH₃ complexes， and focuses on the effects of different ligands， such as tertiary amine， tertiary phosphine， ether and carbene， and different coordination structures on the thermochemical properties of AlH₃ complexes. The future research direction of AlH₃ complexes is clarified.

Abstract:Electrically controlled solid propellant （ECSP） has the characteristics of multiple ignitions and controllable burning rate， and can be widely used in propulsion systems from micro to macro. The research on ECSP with ammonium nitrate， hydroxylamine nitrate and perchlorate as oxidants was summarized at home and abroad， especially the characteristics of ignition， combustion and extinction for ECSP based on hydroxylamine nitrate and perchlorate were emphatically reviewed. Meanwhile， the effects of voltage， pressure and metal additives on the burning rate adjustment of ECSP were analyzed， and the mechanism of electric energy in the ignition and combustion process of ECSP was discussed. Furthermore， some suggestions were put forward for further in-depth study on the ignition， combustion and extinction mechanism of ECSP： study the chemical reaction mechanism on the solid and gas phases of ECSP， establish the model and framework of the reaction mechanism for ignition， combustion and extinction； explore the effect of electrode arrangement and electrode configuration on the combustion efficiency of ECSP and the relationship between ECSP formula and electrical conductivity systematically， and seek the method to decrease the interface resistance between electrode and propellant. Finally， optimizing the formulation of high-performance ECSP， perfecting the combustion reaction mechanism and burning rate adjustment mechanism of ECSP， and raising the pressure threshold of ECSP are the keys to the design， application and performance regulation of electronically controlled solid rocket motor.

Abstract:In comparison with the plasticizer only with azido， the one bearing multiple energetic groups not only generally has a higher density and oxygen balance， but also possesses more energy content. It endows the propellant with an increasing specific impulse and a better combustion performance， which has become a hot research topic in the field of the energetic material. However， it is an essentially important factor that how to precisely control the quantities and distributions of microscopic energetic groups in the plasticizer′s structure. To design and synthesize the plasticizer with high energy density， high thermal stability， high oxygen balance， insensitivity as well as low glass transition temperature， above-mentioned factor should be payed considerable attentions. This study reviews the previously reported azido plasticizers， containing nitro， nitrate， nitramine， difluoroamino and/or furazan group， from the design， synthesis and characterization of molecules to propellant applications since the late 1970s. Some drawbacks are sorted out in this paper. What′s more， several valuable suggestions to synthesize azido plasticizers with outstanding properties are presented here. It is essential worth noting that organic azido compounds with nitro and/or nitramine group are the most promising plasticizers used in propellant in the future， and the properties and synthetic difficulties of these materials are simultaneously taken into consideration. Finally， some guidance for researchers being engaged in the investigation of energetic plasticizers are provided.

Abstract:In order to investigate the combustion stability of flake variable burning rate propellant under high and low temperature cycle preservation， based on the morphology of samples and the change of combustion performance， a 20 time thermal cycling treatment was carried out， in which samples were separately stored at 70 ℃ and -50 ℃ for 10 h as one cycle. The surface and section morphology of propellant was observed via optical microscope， and the combustion performance at 50 ℃， 20 ℃， -40 ℃ was tested by closed bomb. Microscopic observation shows that after thermal cycling treatment， the bubbles on the surface increase and the section of propellant becomes lumpy and uneven due to plastic deformation， while the interface between the inner and outer layers remains tight without visible cracks. The combustion performance basically unchanged after thermal cycling treatment， and the dynamic activity curves nearly overlap， for which the maximum ΔL_a is 2.57% at low temperature. After thermal cycling treatment， the temperature coefficient under high-pressure from normal to low temperature is significantly lower than that of the original under the same conditions， and the difference in pressure index of the flake variable burning rate propellant at high temperature and low temperature is smaller than that of the original under the same conditions. Attributed to bound interface and combustion consistency， flake variable burning rate propellant has good storage stability under different temperatures.

Abstract:The flame radiation characteristics of the single-base propellant and double-base propellant during combustion were explored for the guidance in the design of detectors for explosion suppression systems， by which the propellant flame spectroscopy experimental system was designed and constructed. The flame radiation spectra of typical single-base propellant and double-base propellant burning in air under different pressure conditions （-0.05， 0.00， 0.20 MPa） were collected and analyzed. Under atmospheric air， single-base propellant displays a weak continuous radiation only in the range of 550-650 nm. Due to the less interference of the continuous spectrum， the emission peaks of OH*， C₂*， CHO* and other emitting species can be identified in the combustion flame spectrum for the single-base propellant， and these active intermediates may be present in the flame zone during combustion. In contrast， the combustion flame radiation spectrum of double-base propellant shows the strong continuous radiation in the range of 200-1700 nm， which is attributed to that there are a large number of solid particles in its flame zone， that masks part of the emission peak information in the 200-1700 nm band. In the 1000-1700 nm band， the emission peaks of CN*， OH* and other groups were collected during the combustion of the double-base propellant. In addition， there are strong Na， K and Ca emission peaks in the flame spectra of the double-base propellant and single-base propellant， and Na， K and Ca species may come from the residual lignin in nitrocellulose. As the ambient pressure in the combustion chamber increases， the intensity of combustion radiation of both propellants is enhanced. The continuous radiation of double-base propellant in the initial stage of combustion is weak under low pressure conditions， and the characteristic peaks are similar to that of single-base propellant are collected. According to the test results， the detector for the single-base propellant should be designed based on the emission peaks of Na and K， while the detector for the double-base propellant should be designed in accordance to the peak wavelength of the continuous spectrum. The higher the ambient pressure， the lower the detector trigger threshold.

Abstract:In order to solve the problems of high energy consumption， difficulty in particle size control and serious pollution in the preparation of nano-aluminum powder. green and safe preparation of nano-aluminum powder is fulfilled by liquid chemical method through adding diisobutyl aluminum hydride （DIBAL） to aluminum chloride-1-ethyl-3-methylimidazole chloride（AlCl₃-EMIC） ionic liquid with the molar ratio of 2∶1. By means of X-ray diffraction （XRD）， nano-particle size detection， transmission electron microscopy （TEM）， scanning electron microscopy （SEM）， energy dispersive spectrum of X-ray （EDS） and linear scanning voltammetry （LSV）， the nano-aluminum powder was characterized and its growth process and reaction mechanism were explored The results show that when DIBAL concentration is 0.25 mol·L^-1 and reaction time is 0.5 min， the non-agglomerated aluminum powder with uniform particle size of 40-100 nm is obtained， which is more uniform than the one obtained by other liquid chemical methods. The abnormal growth of aluminum powder is observed at different DIBAL concentrations， which is related to the Ostwald ripening. In addition， the AlCl₃-EMIC ionic liquid is not only the reaction medium， but also the Al source of the nano-aluminum powder.

Abstract:Taking tetrahydrofuran copolyether （PET）-based high energy solid propellant as the research focus， the 3D printed propellant was designed and formulated with PET/nitrate（NG/BTTN） as the binder system modified by shaping agent（MS）， ammonium perchlorate（AP） as the solid filler and polyfunctional aliphatic isocyanate （N-100） as the curing agent. The shaping effect of MS at 25 ℃， its compatibility with each component， and its rheological properties at 25， 35， 45， 55 ℃ were studied. The reasonable range of the processing parameters for 3D printing such as temperature， nozzle diameter and pressure were determined preliminarily by simulation. The results show that MS has good compatibility with PET/NG/BTTN and AP in the propellant， and it also improves the safety performance of the propellant to a certain extent. The obtained slurry exhibits the temperature-sensitive characteristics， capable of achieving good setting effect at 25 ℃. By applying the determined printing parameters involving the temperature of 50 ℃， the nozzle diameter of 1.2 mm and the pressure of 11 kPa， the actual printing rate can be approached to 8 mm·s^-1， which is the first time that the 3D printing of PET based high-energy solid propellant to be realized.

Abstract:To improve the stability of aluminum hydride （AlH₃）， three kinds of embedded-coated AlH₃@Al@xAP（AHAPs） energetic composite particles were prepared by the combination of using acoustic resonance and spray drying technology. The mass ratios of AlH₃@Al and AP were 9∶1（AHAPs-10%）， 7∶3（AHAPs-30%）， and 1∶1（AHAPs-50%）， respectively. The morphologies and structures of the AHAPs and their condensed combustion products were characterized by SEM， EDS， and XRD. The thermal reactivity and stability of the prepared samples were comparatively studied by TG-DSC analysis and vacuum stability tester （VST）. Results show that AHAPs energetic composite particles could not only improve the stability of AlH₃ but also promote the decomposition of AP. With the increase of AP content， the initial decomposition temperatures of AlH₃ are increased by 8.5-11 ℃， and the peak temperature at high-temperature decomposition stage of AP is decreased by about 80 ℃. Compared with the total decomposition time of pure AlH₃（1006 min）， the decomposition time of AHAPs-50% composite particles extend to 1518 min， which corresponds to a 50.9% increment. In addition， the reaction heat of embedded-coated composite particles AlH₃@Al/63.5% AP reaches 9125.6 J·g^-1， which is 1054.1 J·g^-1 higher than that of mechanically mixed samples， and the particle sizes of the condensed combustion products appear to be finer， indicating that their combustion become more complete and the combustion efficiency is greatly enhanced.

Abstract:In order to explore the droplet ignition characteristics of a new type of hydroxylamine nitrate（HAN）-based liquid propellant EMP-01， a droplet electric ignition experimental platform was built by placing the droplet in a hemispherical groove and inserting the electrode. The electrical ignition characteristics of EMP-01 droplets under the conditions of droplet diameter of 6.5 mm， electrode spacing of 0.5 mm and voltage loading rate of 86.31 V·s^-1 were studied， and the ignition delay time under this condition was determined. At the same time， the variation law of droplet ignition delay time and combustion process was also studied within 34.20-246.37 V·s^-1 under the condition of constant droplet diameter and electrode spacing. The results show that the droplet separation of EMP-01 undergoes three stages： heating， thermal decomposition and combustion， and there is a periodic expansion and contraction process in the thermal decomposition stage. When the voltage loading rate is 34.20 V·s^-1， the EMP-01 droplet cannot be successfully ignited； When the voltage loading rate is 49.49-246.37 V·s^-1， the ignition delay time decreases gradually with the increase of voltage loading rate， but with the increase of voltage loading rate， the decrease rate of ignition delay time gradually slows down.

Abstract:A series of ionic liquids based on N，N-（dimethylcyclopropyl）cyclopropylamines as cations and dicyandiamide/cyanoborohydride as anions were synthesized by using the three-member carbocyclic ring as the tension energy structural unit. The structures of ionic liquids were confirmed with the characterizations such as nuclear magnetic （NMR）， infrared spectroscopy （IR） and high-resolution mass spectrometry （HRMS）. Their physicochemical properties （e.g.， melting point， thermal decomposition temperature， density， viscosity， heat of formation， specific impulse， and ignition delay time） were measured and/or calculated in detail. The results demonstrate that all ten synthesized ionic liquids show hypergolicity with white fuming nitric acid （WFNA）， and the cyanoborohydride based ionic liquids have the shorter ignition delay times than the corresponding dicyandiamide ionic liquids. More strained ring groups lead to the higher heats of formation （0.87-1.96 kJ·g^-1）， and the compact stacking of small ring structures makes an increase in the densities （1.01-1.18 g·cm^-3） of the ionic liquids. Therefore， the strained ring-based hypergolic ionic liquids exhibit the higher density-specific impulse （436.7-454.4 s·g·cm^-3）. The introduction of high-energy strained ring groups in the molecular structures provides a way to improve the energy densities of hypergolic ionic liquids.

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