Abstract:Aiming at the development and problems of high-strength energetic structural materials （ESMs）， the characteristics， static mechanical behaviors and dynamic mechanical behaviors of high-entropy alloys （HEAs） were summarized and analyzed. The assumptions， potential and challenges of HEAs as high-strength ESMs were proposed and verified from the perspective of both theoretical and experimental aspects. It was found that HEAs had the basic features of “free composition design”， “simple crystal structure with strong lattice distortion” and “high strength and hardness”. At the same time， both static and dynamic mechanical behaviors of HEAs could be adjusted in a wide range by means of process adjustment and composition design. All the above features indicated that HEAs had the potential advantages to be used as high-strength ESMs in terms of workability， high strength， and rapid oxidation to release energy. Existing experimental results also confirmed the application potential of HEAs ESMs. Finally， the challenges faced by the research of high-entropy alloy ESMs and the priorities of future research， such as high-throughput experiments and simulations， researches on dynamic mechanical behaviors and preparation for large-scale samples， were raised based on the intrinsic features of HEAs and previous experimental results.

Abstract:To investigate the influence of fluororubber coating on the combustion properties of micro-sized aluminum powder （μ-Al）， several methods such as laser ignition，constant volume burning and thermal analysis were employed to study the combustion and thermal performance of 5 μm and 50 μm aluminum powder coated by different content of fluororubber. Ignition delay time， burning speed， state of combustion， combustion heat and thermal reaction properties of these samples were presented. It showed that un-coated μ-Al cannot be ignited by laser in a 0.1 MPa oxygen atmosphere. For the coated 5 μm aluminum powder （5μ-Al@n%FP）， ignition delay time can be reduced from 91 ms to 31 ms， burning speed can also be increased from 3.08 mm·s^-1 to 364.96 mm·s^-1， and combustion heat can reach up to 27.61 kJ·g^-1 by varying the content of fluororubber in the composite particles. Similarly， for the coated 50 μm aluminum powder （50μ-Al@n%FP）， ignition delay time can be reduced from 130 ms to 40 ms， burning speed can also be increased from 1.80 mm·s^-1 to 43.78 mm·s^-1， and combustion heat can reach up to 26.08 kJ·g^-1. Based on thermal analysis （TG）， the reaction depth of fluororubber and the thickness of Al₂O₃ were calculated. It revealed that the reaction between fluororubber and μ-Al occurred merely on the surface of aluminum particles. Under the same reaction condition， the thickness of Al₂O₃ had no correspondence with the size of μ-Al.

Abstract:In order to improve the reactivity of submicron aluminum powder， Al-Cu composite metal powder was prepared by means of electric explosion composite wires. The preparation parameters were determined by monitoring the waveform with oscilloscope in the electric explosion process. The structure and morphology of the composite was characterized by X-ray powder diffraction（XRD）， scanning electron microscope（SEM）， transmission electron microscope mapping（TEM-MAPPING） and X-ray fluorescence spectroscopy（XPS）. The Al-Cu composites powder was consisted of CuAl₂ and Al. The morphology of the material was sphere with an average size 150 nm. The forming mechanism of the morphology of the as-prepared composite particles was analyzed. Both DSC and aluminum-vapor methods were employed to evaluate the reactivity of the material. The first oxidation peak temperature of Al-Cu composite metal powder was 550 ℃， as shown in its DSC curve. This parameter was decreased by 50 ℃ comparing with Al prepared with the same parameters. This results indicated that as-prepared composite particles had better reactivity. The first oxidation process of Al-Cu composite metal powder lasted from 500 ℃ to 600 ℃ within 5 mins， while the counterpart lasted from 500 ℃ to 650 ℃ within 7.5 min. Comparing with Al， the heat release rate of Al-Cu composite metal powder was increased by 33% during the first oxidation process. The reaction completeness of the as-prepared composite particles was 0.88 tested by aluminum-water reaction method， but it was only 0.73 for the counterpart. During the first 10 mins of aluminum-vapor reaction， the reaction completeness of Al-Cu composite powder was 0.36 which was as much as ten times that of the counterpart. The result suggested that the reactivity of the composite was improved a lot.

Abstract:To study the energy output law of the suspended AlH₃ dust in explosion and release process， a modified 20 L ball explosion test system was used to study the explosion pressure and flame propagation law in closed and venting conditions alternately. The results showed that the lower explosion limit concentration of suspended AlH₃ in a closed system decreased from 40 g·m^-3 to 30 g·m^-3 comparing with aluminum powder， indicating that the hydrogen released by the burning AlH₃ accelerated the entire chemical reaction process. In addition， both the maximum explosion pressure and explosion pressure rise rate of AlH₃ dust explosion in a closed system were higher than that of the aluminum powder. The maximum explosion pressure rose from 1.02 MPa to 1.15 MPa， indicating that a combustible gas-dust composite system was formed due to the release of hydrogen to exacerbate the violence of the explosion energy release process. Under venting conditions， when the concentration of AlH₃ dust was 500 g·m^-3， the explosion pressure （p） and pressure rise rate （dp/dt） decreased the most， reaching 43% and 30% respectively， indicating explosion venting can effectively reduce explosion damage. Moreover， it was concluded that the length and speed of the explosion vent flame reached the peak values when the concentration of AlH₃ was 750 g·m^-3， meanwhile the probability and frequency of multiple flames presented a positive correlation with the concentration.

Abstract:In order to study the influence of modification technology on the ignition and explosion characteristics of the composite hydrogen storage materials， the combustion heat of Al， MgH₂， Hydrogen storage material CM and hydrogen storage material CM-H coated with hydroxyl terminated polybutadiene （HTPB） was measured by an oxygen bomb calorimeter， and the mass change of the four samples within 48 h was test as well. Results show that CM-H has the highest combustion heat for 30.5633 MJ·kg^-1. Meanwhile its mass gained within 48 h in air is the least for 0.46%. Result show that the modification can effectively prevent the performance degradation of the materials so that they can maintain a high combustion heat. The minimum ignition energy， flame propagation characteristics and explosion pressure of the four samples were studied by an 1.2 L Hartmann tube， a high-speed camera and a 20 L ball explosion test device respectively. Results show that the minimum ignition energy of CM is 50-60 mJ， which was only a half of the critical ignition energy of aluminum powder （100-150 mJ）. It indicated that the addition of MgH₂ into metal materials can effectively reduce the ignition energy. The minimum ignition energy of CM-H dramatically increased to 700-750 mJ after coating. The test results of flame propagation speed， explosion pressure and explosion index presented the performance order of MgH₂ > CM > CM-H > Al. Results indicat that the modified composite hydrogen storage material has lower electric spark sensitivity， higher safety and better explosion performance.

Abstract:A 20 L explosion device was used to study the explosion characteristics of fuel-air explosive containing micro/nano-aluminum powder. Results indicated that when adding 5% and 10% nano-aluminum to micro-aluminum， the maximum pressure of mixed powder increased by 24.2% and 58.5%， respectively. The maximum rate of pressure rise increased by 80.6% and 103.4%. The nano-aluminum would not have any contribution to the explosion effect while its content was more than 10%. For the fuel with a solid/liquid ratio of 30/70， while the ignition energy increased from 11.83 J to 28 J， the explosion pressure consequently increased from 0.28 MPa to 0.52 MPa， meanwhile the explosion temperature increased from 834 ℃ to 1118 ℃，indicating that the explosion parameters of FAE could be improved by increasing the ignition energy. Increasing the content of micro/nano aluminum powders could effectively increase the explosion pressure and temperature of FAE.

Abstract:In order to study the energy output characteristics of three composite explosives containing Mg-based hydrogen storage materials， Ti-based hydrogen storage materials and ZrH₂ hydrogen storage materials respectively， a constant temperature detonation heat calorimeter and an underwater explosion system were used to study the detonation heat and underwater energy characteristics of the explosives. The results illustrated an order of the detonation heat in terms of a thermobaric formulation of RDX/hydrogen storage material/AP/others， which was Mg-based sample>Ti-based sample≫ZrH₂-based sample. Accordingly， the detonation heat for the three explosives were 7587.0606 kJ·kg^-1， 6416.4741 kJ·kg^-1 and 3950.6279 kJ·kg^-1. It was indicated that the detonation heat of the explosives containing hydrogen storage materials was positively correlated with the chemical potential of each hydrogen storage material. In underwater explosions， the explosion parameters including peak pressure， impulse， energy flow density and shock wave energy of the composite explosives presented a similar order， that the Mg-based sample was the best and the ZrH₂-based sample was the worst. Accordingly， the shock wave energy was 1.41 times， 1.26 times and 0.97 times of TNT equivalent for each formula. It was showed that hydrogen storage materials with much higher activity and potential energy could be beneficial for the shock wave in underwater explosion. The contribution to the energy released in underwater explosion of hydrogen storage materials was mainly in the form of bubble pulsation. The bubble energy of the composite explosives containing Mg-based， Ti-based and ZrH₂ hydrogen storage materials were 2.17 times， 1.78 times， and 0.86 times of TNT equivalent respectively， indicating that Mg-based hydrogen storage material had the best energy releasing performance in the secondary reaction， followed by Ti-based hydrogen storage material and ZrH₂was the worst The trends of the explosion parameters of the composite explosives in detonation heat test and underwater explosion test were consistent. The overall energy level of the explosives was in the order of Mg-based sample>Ti-based sample>ZrH₂-based sample. The explosive containing Mg-based hydrogen storage material had the largest energy in underwater explosion， reaching up to 2.02 times of TNT equivalent. The applicability of the ZrH₂ in thermobaric formulation was not strong for both of the energy tested in detonation heat and underwater explosion was lower than TNT.

Abstract:In order to explore the detonation law of α-AlH₃ in condensed phase explosive， the safety features of α-AlH₃ were characterized. The results indicated that α-AlH₃ had poor thermal stability due to its sensitivity to temperature and humidity. The operational condition for α-AlH₃ samples should not exceed 30 ℃ RT and 60% RH. HMX was selected as the main high explosive to develop a formulation containing α-AlH₃ with a self-designed technology namely direct method of step temperature control and cooling. The safety， detonation performance， work capacity and explosion reaction process of the explosive were studied. The molding powder had low mechanical sensitivity and good moldability. When the α-AlH₃ content exceeded 10%， the relative density of the grain decreased with increasing content of α-AlH₃. The characteristic detonation velocity of α-AlH₃ was 6078 m·s^-1. Compared with an HMX based explosive formulation containing aluminum， the counterpart with α-AlH₃ had an equivalent work capacity. But its work capacity was poor at the high and medium pressure stage of the detonation products. The hydrogen element in α-AlH₃ mainly existed in the form of hydrogen in the detonation products.

Abstract:How to improve the explosion energy and power ability of explosive by applying reactive metal particles effectively is the key problem for the design of metalized explosive. To explore the application of the micro-B/Al composite powder in enhance blast explosive （EBX） and thermobaric explosive （TBX）， three HMX-based explosives containing B/Al particles were designed and prepared. The energy output characteristics of the samples with a dimension Φ100 mm×105 mm was studied by air blast and underwater explosion tests， meanwhile the power abilities were evaluated by a Φ50 mm cylinder test. The effect of the content of micro-metal on energy output process and power ability of metalized explosives was discussed. Results show that in the air blast and underwater explosion tests， initiated by the detonation of HMX， the combustion of micro-Al can promote the afterburning effect of micro-Boron resulting in releasing a great amount of combustion heat to generate expansible products with high temperature and high pressure， finally increase the sustained duration of fireball and total energy in underwater explosion. In the cylinder test， there was not enough oxygen to react with micro-B before the cooper cylinder burst， accordingly the advantage of combustion energy of micro-boron in explosives containing B/Al could not present. However， after the cooper cylinder burst， the oxygen in the air can oxide B/Al composite powder to release a large amount of combustion heat， which can enhance the power ability of aftereffect.

Abstract:To explore the effect of solid boron hydrogen fuel on the burning mechanism of aluminum powder， the simultaneous thermal analysis-infrared mass spectrometry technology and the pyrolysis in-situ cell-Fourier transform infrared spectroscopy technology were employed. Combining with the numerical model of the effect of BHN-12 on the burning reaction of aluminum powder in the explosion flow filed， the mentioned experiment was introduced to study the reaction time， dispersion characteristics and combustion-supporting effect of boron-hydrogen fuel. Results show that the thermal decomposition process of BHN-12 started from 314 ℃， and ended at 360 ℃. There are three exothermic peaks and two endothermic peaks during the decomposition process with a total mass loss 32.3%-33.9%. The decomposition process obeyed the law of power series （Mampel power）， and the dynamic mechanism function is . The gaseous products of the thermal decomposition are mainly H₂， C₂H_4， C₂H₆ and NH₃， and the solid products are simple substances of amorphous C and B. The component transportation model was introduced to simulate the after- burning process of the Al/BHN-12 system. During the process， the dispersion speed of Al fuel was slower than that of BHN-12 particles. At the time of 20 ms， the dispersion radius of Al fuel was about 2.5 m， but it was 3m for BHN-12. In the first 2 ms of the reaction， there was no gaseous product produced， until 4m the gaseous products came out with a temperature 1800 ℃ in the middle of the fire ball. BHN-12 could increase the after-burning temperature of the entire system by about 300 ℃.

Abstract:In order to study the influence of aluminum powder on the mechanical property， interface， combustion， safety， energy， density and other performance of propellants， the glycidyl azide polymer （GAP） propellants with 5%， 10%， 15% and 18% aluminum powder were evaluated by tensile testing machine， dynamic thermomechanical analysis （DMA）， calculation program and etc. Results show that， with the replacement of 320 μm AP with 30 μm aluminum powder and the increase of aluminum powder contents， the propellant has increasing maximal tensile strength and maximal elongation， and improving interface performance. The burning rates change scarcely but the pressure indexes drop down from 0.43 to 0.40 under the pressure of 3-9 MPa. The hazard grades of propellants with 5% and 18% aluminum powder are 1.3 both. The impact and friction sensitivities of propellant with 18% aluminum powder are 0% and 44%， respectively， which are lower than the formulation with 5% aluminum powder （4% and 48%， respectively）. At last， the calculation result shows that with the increase of aluminum powder， the energy and density of propellants grow up， but the standard specific impulse levels off to moderate pace of growth.

Abstract:In order to obtain the metal alloy composite fuel with pressurization effect， Al/Mo/PMF composite powder was prepared by a combination of vacuum suspension smelting， ultra-high temperature gas atomization and mechanical alloying. The phase， morphology and thermal properties of the composite powder were analyzed by XRD， SEM， TG/DTA. The combustion enthalpy and pressurization properties of the composite powder was measured by oxygen bomb calorimeter and constant volume isothermic combustion experiments. Results show that PMF distributes homogeneously in the composite particles after mechanical ball milling， which is helpful to improve the thermal reactivity of the powder and advance the initial reaction temperature. The extra pressurization effect was obvious due to the production of AlF₃ and MoO₃ with low boiling point. The extra pressurization generated by the combustion of Al/Mo/PMF 64/16/20 composite powder was 4.49% higher than that of pure Al powder. With the increase of PMF in the composite， the combustion enthalpy and combustion completeness of the composite powder decreased. The measured combustion enthalpy of Al/Mo/PMF 76/19/5 composite powder was 22541.8 J∙g^-1， while the measured combustion enthalpy of Al/Mo/PMF 64/16/20 composite powder was 16788.5 J∙g^-1. When the PMF content was 5%， the composite can burn completely， meanwhile the extra pressurization can be presented effectively. The corresponding maximum pressure was 3.430 MPa. In addition， the oxidation process and the mechanism of Al/Mo/PMF 76/19/5 composite powder were also studied.

Abstract:The dispersion characteristics of metal additives in binders might tremendously affect the processing properties of propellants and explosives. Rheological properties of the two metastable intermolecular composites （QAlPV and PAlPV） mixed with hydroxyl-terminated polybutadiene （HTPB）， glycidyl azide polymer （GAP） or poly （ethyleneoxide-co-teterafuran） （PET） separately were investigated by RS-300 rheometer respectively. Results show that all the six sorts of suspensions exhibited pseudoplastic fluid characteristics， and their apparent viscosity decreases with the increase of temperature between 20 ℃ and 60 ℃. In the systems containing GAP and PET， the flow activation energy of the suspensions with PALPV is greater than those containing QALPV. The results present that the suspensions filled with the lamellar aluminum-based composite exhibites more rigidity， meanwhile their apparent viscosity are more sensitive to temperature. Therefore， the dispersion of PALPV in binders could be improved by increasing the temperature. The dispersion and homogeneity of the suspensionsformed by QALPV， GAP or PET separately could be improved by accelerating the shear rate.

Abstract:In order to study the interface structure of aluminum core/oxide layer intuitively， the slicing method of aluminum powders （2-8 µm） were successfully established based on FIB micro and nano processing technology. The slices were obtained by combining FIB direct cutting with profile thinning. The interface structure of the prepared slice samples was clear and intact， and the oxide layers were not damaged. The microstructure， crystallinity and element distribution of “Al core/oxide layer” under different ageing conditions were obtained were characterized by SEM， HRTEM and EDS. The stoichiometric ratio of Al and O elements in the oxide layer of aluminum particles deviated from the standard Al₂O₃， showing a gradient distribution. The positive correlation between the oxide layer thickness of aluminum particles and the aging temperature has been quantitatively obtained. The oxide layer thickness of the samples without thermal aging was ~5.4 nm， and the oxide layer thickness of the samples aged at 75 ℃ and 95 ℃ increased to （34.1±2.1） nm and （51.3±2.2） nm， respectively.

Abstract:Aluminum powder was widely used to improve the energy characteristics of explosives and solid propellants due to its excellent properties， such as high activity， high density， high combustion enthalpy and low oxygen consumption. The transition metal Cu had a good catalytic effect on the combustion of aluminum powder and could make the aluminum powder burn more completely. As a binder component of solid propellant， hydroxy-terminated polybutadiene （HTPB） was beneficial to prevent the oxidation and agglomeration of aluminum particles， accordingly in favor of the press-packing and curing while uniformly coating on the surface of aluminum particles. Using the copper acetylacetonate as copper source， formaldehyde and hydrazine as reducing agent， HTPB/Cu/μAl composite particles were prepared by one-pot liquid phase reduction. The structure and morphology of the samples were characterized by IR， XRD， SEM and EDS. Meanwhile， the catalytic performance of HTPB/Cu/μAl on the decomposition of AP was studied. The results showed that the reduced Cu particles were scattered on the surface of aluminum particles， and HTPB was evenly coating on the surface of Cu/μAl. In the DSC curve of HTPB/Cu/μAl， the oxidation exothermic peak of transition metal Cu and the decomposition exothermic peak of HTPB appeared simultaneously between 150-350 ℃. However， the coating had almost no effect on the oxidation exothermic peak of micron aluminum powder at 550 ℃. The average activation energy of HTPB/Cu/μAl was 287.2 kJ·mol^-1， which was 36.35 kJ·mol^-1 lower than that of μAl （323.55 kJ·mol^-1）. Both of the decomposition peaks of AP at high temperature and low temperature had changes when HTPB/Cu/μAl composites were added. Compared with pure AP， the exothermic decomposition peak at high temperature of HTPB/Cu/μAl/AP was reduced by 127 ℃， indicating that the HTPB/Cu/μAl composites could promote the thermal decomposition behavior of AP.

Abstract:To investigate the effect of Mg content on the properties of centrifugal atomized aluminum-magnesium （Al-Mg） alloy powders， Al-Mg alloy powders with different mass ratios （70∶30， 50∶50， 30∶70） were prepared by centrifugal atomization. The particle size， morphology， physical phase， and kinetics parameters of the samples were characterized via the particle size distribution meter， scanning electron microscope （SEM）， X-ray powder diffractometer （XRD） and TG-DSC. The effect of different Mg content on the activity of the alloy was also studied by thermal oxidation at 71 ℃. Results showed that all Al-Mg alloy powders had a good size distribution， regular morphology and high sphericity. The metallographic structure demonstrated that Al-Mg30 and Al-Mg50 had a dendritic structure， and Al-Mg70 was composed of α-solid solution and dendritic precipitates. The main phase of the alloy was α-Al， β-Al₃Mg₂ and γ-Al₁₂Mg₁₇. The β-Al₃Mg₂ phase gradually decreased and the γ-Al₁₂Mg₁₇ phase increased with the increasement of Mg content. Moreover， the deactivation rate of Al-Mg alloy powders was found to increase with the increasement of Mg content. The activity of alloy powders remained basically constant after 48 h. The TG-DSC results indicated that both the initial exothermic temperature and the activation energy of the alloys were gradually reduced as the Mg content increased， but the reactive speed was accelerated. The increasement ratio of weight of all Al-Mg alloys was greater than that of micron Mg （53.06%） and Al （8.63%）. The results of Laser ignition showed that the ignition delay of Al-Mg alloy was much shorter than monolithic aluminum， as well as the combustion duration. The microburst phenomenon was observed in the test.

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