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Microscopic Mechanisms of Femtosecond Laser Ablation of HMX from Reactive Molecular Dynamics Simulations
摘要： With ultrashort duration and ultrahigh energy, femtosecond laser (fs-laser) pulses are very promising for the precision machining of energetic materials. Compared with the mechanical machining methods of energetic materials, fs-laser machining technology has the advantages of high safety, high precision and absence of pollution. A deep understanding of the mechanisms between fs-lasers and energetic materials is the basis for the development of fs-laser machining technology. In this paper, the method of reactive molecular dynamics (ReaxFF-MD) was adopted to calculate the fs-laser ablation process of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX, a high explosive compound), and the ablation mechanisms of HMX under different fs-laser energies were studied. The results show that the fs-laser ablation mechanisms of HMX are related to the laser power density. When the laser power density is high enough (3.4×1014 W/cm2, 1.0 mJ/pulse), HMX undergoes ionization or decomposition reactions at the picosecond level (~7.65 ps) and produces a high temperature and pressure plasma. Many N, H and O single atoms and their ionic products occurs along with some small molecular fragments of NO2, H2O, CO2, N2, H2, NH, NH2, CO, OH, CNO2 and very few toxic products of NO and HNO2. In this case, the removal process of HMX occurs via a phase explosion mechanism. As the laser energy decreases, the ionization degree of ablation products decreases, in which the number of monoatomic and ionic products decreases, while the number of toxic small molecules (such as NO, HNO2, and HNO) increases. When the laser power density is relatively low (0.34×1014 W/cm2, 0.1 mJ/pulse), the removal process of HMX occurs via a photomechanical mechanism, and the compound escapes as intact initial HMX molecules. When the laser power density is close to the ablation threshold of the explosive, the HMX molecules only undergo a melting state to some extent without escaping from the surface of the crystal. Therefore, the fs-laser can be used in the precise machining of explosives and preparation of high-purity energetic nanomaterials by a reasonable selection of fs-laser energy.
关键词： energetic materials,ReaxFF-MD,femtosecond laser,HMX,ablation mechanisms
更新于2025-09-23 15:21:01
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Enhanced RDX Detection Studies on Various Types of Substrates via Tunable Quantum Cascade Laser Spectrometer Coupled with Grazing Angle Probe
摘要： Owing to scientific advances in the field of materials sciences and engineering, researchers have developed new energy sources used for spectroscopic applications and measurements of properties resulting from the interaction of matter and electromagnetic radiation in the mid-infrared (MIR) region. MIR lasers, such as quantum cascade lasers (QCLs), used for spectroscopy have quickly found numerous applications in a wide cadre of IR techniques. This provides the opportunity to study properties of highly energetic materials (HEM), among many other applications. MIR laser spectroscopy based detection experiments of HEMs were carried out using a QCL optically coupled to compact grazing angle probe mount (QCL-GAP) enabling reflection-absorption infrared spectroscopy (RAIRS) measurements of thin films of HEMs. A saturated solution of RDX in acetone was prepared, and aliquots of subsequent dilutions of the stock solutions were transferred to test surfaces for QCL-GAP back-reflectance measurements. RDX reflectance signals were monitored as function as the decreasing surface concentration until the signal/noise was ~ 3. Stainless steel (SS) plates were used as reflective substrates, and anodized aluminum (AN-Al), cardboard, and Teflon were used as non-reflective (matte) substrates. Using generated calibration curves a low limit of detection (LOD) of 1.7 ng/cm2 for RDX/SS and 95 μg/cm2 for RDX/AN-Al were found. Based on the area of laser spot (0.3 cm2) we conclude the minimum masses detected were 490 pg (RDX/SS) and 28 μg (RDX/AN-Al).
关键词： Quantum Cascade Laser,RDX detection,Grazing Angle Probe,Highly Energetic Materials,Mid-Infrared Spectroscopy
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - New Type Metal-Azides for Low Threshold Laser Initiation
摘要： The exploration and mining of minerals on extraterrestrial bodies in the solar system: planets, moons, planetoids, asteroids and comets requires the development of fundamentally new primary explosives that are not subject to spontaneous detonation during vibration and static discharges when launched from the ground. Available detonators do not fully meet these requirements and pose a danger to future space missions, therefore, are considered undesirable as payload on board. Therefore, the synthesis, research and testing of new energetic materials sensitive exclusively to the selected wavelength, duration and energy of the exciting laser pulses is of particular relevance. Laser radiation is delivered to the detonator by means of an optical fiber, which imposes an upper limit on the energy of the pulses. In addition, lasers for space missions should be quite miniature, consume little power and do not require cooling. Therefore, it is necessary to pay special attention to lowering the threshold for laser initiation of energetic materials. In this work, we synthesized and investigated energetic materials based on both nontrivial and well-known azides with the ultimate goal of reducing the laser initiation threshold.
关键词： metal-azides,energetic materials,laser initiation,space missions,primary explosives
更新于2025-09-12 10:27:22
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Optimizing the oxygen balance by changing the A-site cations in molecular perovskite high-energetic materials
摘要： We presented two new members of molecular perovskite high-energetic materials, (H2pz)[Na(ClO4)3] (PAP-1) and (H2dabco-O)[K(ClO4)3] (DAP-O2), in which H2pz2+ (piperazine-1,4-diium) and H2dabco-O2+ (1-hydroxy-1,4-diazabicyclo[2.2.2]octane-1,4-diium) act as A-site fuel cations, respectively. Compared with their H2dabco2+ analogues, (H2dabco)[M(ClO4)3] (M = Na+ for DAP-1 and K+ for DAP-2, respectively), PAP-1 and DAP-O2 exhibit optimized oxygen balance by employing two strategies to change the A-site cations, i.e., “trimming the C and H atoms” of H2dabco2+ by using H2pz2+ to form PAP-1 and adding an O atom into H2dabco2+ by using H2dabco-O2+ to form DAP-O2, respectively. As suggested by DFT calculations and the K–J equation, the smaller H2pz2+ cation in PAP-1 gives a significantly-optimized oxygen balance from ?22.0% to ?3.9% and an increased crystal density from 2.02 to 2.07 g cm?3, resulting in a better detonation performance for PAP-1. Meanwhile the larger H2dabco-O2+ cation gives a slightly-optimized oxygen balance from ?21.3% to ?17.1% but a decreased crystal density from 2.04 to 1.98 g cm?3, leading to a decreased detonation performance from DAP-2 to DAP-O2. This study demonstrated how to rationally choose the A-site cations in a perovskite structure for modulating the properties of molecular perovskite high-energetic materials, providing important clues for designing more advanced energetic materials for practical use.
关键词： high-energetic materials,oxygen balance,molecular perovskite,detonation performance,A-site cations
更新于2025-09-04 15:30:14