Preparation And Combustion Decomposition Properties Of Tungsten-containing Composite Fuels

As a high-energy fuel,metal powders are used in a wide range of research in the field of energy-bearing materials,and the enormous energy released by their redox reaction helps to increase the destructive power of munitions.Among the many metallic fuels,tungsten has good thermal stability,is suitable for high temperature environments and has an important role in defence and military fields.Research into energy-containing materials is now moving towards high energy densities,of which the incorporation of some high-energy metal particles,either through direct application or in energy-containing materials,is an important research direction.As a new class of energy-containing materials,molecular perovskite energetic materials have the advantages of strong oxidation,high heat resistance,convenient synthesis methods and excellent blast performance,and have broad application prospects in the field of energy-containing materials;ammonium perchlorate（AP）is currently the best overall performance of the oxidizer;hexanitrohexaazoisowuzane（CL-20）has excellent blast performance and energy levels,and is a representative of high explosive military slam explosives.Therefore,DAP-4（（H₂dabco）[NH₄（Cl O₄）₃]）,a typical representative of molecular perovskite energetic materials,and AP and CL-20,three widely used energetic materials,were used to prepare composite materials and polymer bonded explosive（PBXs）with metallic fuel nano-tungsten powder,respectively,and the structure and combustion thermal decomposition properties of the composite materials were investigated experimentally.The main content of this paper are listed as follow:（1）Structural characterization and performance study of DAP-4 raw material.The X-ray diffraction（XRD）pattern indicates the successful preparation of the DAP-4 raw material.Scanning electron microscopy（SEM）morphological characterization of the DAP-4 material showed a regular cubic structure with a particle size of approximately 30μm.The DAP-4/W composite materials were prepared by physical mixing method;the DAP-4/W polymer bonded explosive（PBXs）were prepared by adding fluororubber F2602 binder,and the composite materials were subjected to basic structural characterization and thermal decomposition performance tests.SEM images show the compact structure of the prepared composite materials.The XRD pattern shows that the composite materials are structurally stable and no spurious peaks are present.The results of the TG-DSC experiments show that the exothermic peak of DAP-4 is located at 380.8°C,while the exothermic peak temperature of the composite materials decreases with increasing the proportion of nano-tungsten powder.The mass loss curve of DAP-4 has a sharply decreasing phase,corresponding to a rapid heat release phase.With the addition of nano-tungsten powder,the weight loss of the composite materials became significantly lower,indicating that the oxygen content provided by DAP-4was not sufficient to support the complete combustion of the composite materials,resulting in a significant reduction in the mass loss of the composite materials.（2）Characterization tests on the appearance and thermal decomposition properties of AP/W composite materials.The X-ray diffraction（XRD）results illustrate that the addition of the nano-tungsten powder did not change the crystalline shape of the AP for the composite materials.Differential Scanning Calorimeter（DSC）showed a reduction in the peak exothermic temperature of the AP/W composite materials,which was more pronounced at the heat release peak.AP/W polymer bonded explosive（PBXs）show a new exothermic peak near350°C,suggesting that the PBXs are more compact in their structural arrangement,releasing heat and promoting decomposition during the warming process.The DSC curves of the CL-20/W composite materials show that the decomposition temperatures of the composite materials are all earlier than those of the CL-20 raw material.The results indicate that the thermal stability of the composite materials is reduced compared to the CL-20 raw material,which promotes the decomposition of CL-20.（3）Combined with high speed photography,the combustion performance of DAP-4/W composite materials is investigated using electrical ignition.The experimental results showed that the DAP-4 raw material burned faster,burning violently within 60ms-90ms and showing an explosive yellow flame.With the addition of nano-tungsten powder,the combustion time of the DAP-4/W composite materials became longer and the flame was a slender flame,indicating that the combustion of the W powder consumed the oxygen in the composite materials,resulting in a less violent combustion and an increase in the duration of the composite materials.The combustion behaviour of DAP-4/W polymer bonded explosive（PBXs）was analyzed using gun ignition.The results show that the combustion duration of PBXs decreases with increasing nano-tungsten powder content and suggest a combustion mechanism for DAP-4/W composite materials.（4）The combustion experimental test results of CL-20/W composite materials showed that the combustion time of CL-20/W composite materials was prolonged compared to that of CL-20 raw material and the intensity of the combustion flame was reduced,indicating that the combustion of W powder consumed the oxygen in the composite materials,resulting in a less intense and longer duration of combustion of the composite materials.The combustion rate of CL-20/W polymer bonded explosive（PBXs）was analyzed and showed a decreasing trend with the addition of nano-tungsten powder,indicating that the combustion rate of CL-20/W polymer bonded explosive（PBXs）decreases with increasing nano-tungsten powder content.Therefore,the combustion mechanism of the CL-20/W composite fuel is analysed based on the experimental results.As the decomposition and combustion threshold of CL-20 is lower than that of W powder fuel,CL-20 decomposes first and releases heat under ignition conditions,and then triggers the combustion reaction of W powder when the flame temperature reaches the ignition temperature of W powder,and the exothermic reaction generates a large amount of heat and acts on the composite fuel system.The burning time of the composite fuel is significantly longer than that of the CL-20 material.