Hexanitrohexaazaisowurtzitane (CL-20) has a high detonation velocity and pressure, but its sensitivity is also high, which somewhat limits its applications. Therefore, it is important to understand the mechanism and characteristics of thermal decomposition of CL-20. In this study, a ε-CL-20 supercell was constructed and ReaxFF-lg reactive molecular dynamics simulations were performed to investigate thermal decomposition of ε-CL-20 at various temperatures (2000, 2500, 2750, 3000, 3250, and 3500 K). The mechanism of thermal decomposition of CL-20 was analyzed from the aspects of potential energy evolution, the primary reactions, and the intermediate and final product species. The effect of temperature on thermal decomposition of CL-20 is also discussed. The initial reaction path of thermal decomposition of CL-20 is N-NO2 cleavage to form NO2, followed by C-N cleavage, leading to the destruction of the cage structure. A small number of clusters appear in the early reactions and disappear at the end of the reactions. The initial reaction path of CL-20 decomposition is the same at different temperatures. However, as the temperature increases, the decomposition rate of CL-20 increases and the cage structure is destroyed earlier. The temperature greatly affects the rate constants of H2O and N2, but it has little effect on the rate constants of CO2 and H2.
Using VISAR interferometer techniques, the free-surface velocity of the copper plate is measured. The phenomenon of spallation in a copper plate is observed during the copper plate acceleration experiments. Numerical simulation of spallation in a copper plate due to explosive loading is studied by a nonlinear finite element method. The calculation results accords with the experimental data.
The explosive detonation reaction occurs when explosives are compressed by different shock strengths, and the degree of compression affects the chemical reaction of the detonation process. The thermal decomposition mechanism of explosives under different compression densities has thus attracted significant research interest, and a better understanding of this mechanism would be helpful for determining the mechanism of the detonation reaction of explosives. In this study, a ε-CL-20 supercell was constructed, and the thermal decomposition was calculated at different compression densities and temperatures using molecular dynamics simulations based on the ReaxFF-lg reactive force field. We analyzed the effect of density on the main elementary reaction, which consists of the initial reaction and the formation of final products. In addition, we studied the effect of density on the generation of clusters and the reaction kinetics of the thermal decomposition. The results indicate that the initial reaction pathway of the CL-20 molecule is the cleavage of the N-NO2 bond at different densities and that the frequency of N-NO2 bond breakage decreases at high density. As the density increases, clusters easily form and are resistant to decomposition at the later stage of thermal decomposition, which eventually leads to a decrease in the number of final products. Increasing the initial density of CL-20 significantly increases the reaction rate of the initial decomposition but hardly changes the activation energy of the decomposition.
The n-decane/air (C10H22/air) combustion reaction kinetics has attracted much research attention because of its potential application in the aerospace field. In this work, C10H22 oxidation in O2 under high temperature and pressure is simulated based on the first-principles molecular dynamics method for the first time. Our results show that C-C bond breaking and H-abstraction are the two main initial reactions in the oxidation process of C10H22. However, there exists an obvious difference under high and atmospheric pressures. Under high pressure, C-C bond dissociation reactions of hydrocarbon molecules are the main reaction types, while H-abstraction reactions are the main reaction types under atmospheric pressure. The radicals (HO2, OH, O, etc.) play key roles in promoting the oxidation of hydrocarbon molecules. A detailed chemical kinetic model (76 species and 435 elementary reactions), the FP-C10H22 model, of C10H22/air mixture combustion is constructed and verified. The predicted values of FP-C10H22 model on the ignition delay time, laminar flame speed and species concentration of jet stirred reactor (JSR) species concentration are in good agreement with the experimental data.
The electrochemical behavior of samarium ions was investigated in LiCl-KCl melt at molybdenum and aluminium electrodes using different electrochemical techniques such as cyclic voltammetry, square wave voltammetries, chronopotentiometry and open circuit chronopotentiometry. On Mo electrode the electroreduction process of Sm(III) to Sm(II) is reversible within the electroactive window. The reduction of Sm(II) is not observed in cyclic voltammogram, but it can be reduced on Al electrode by forming Al-Sm alloy. It is an effective approach to extract Sm from spent nuclear fuel.
The millimeter-wave (mm-wave) single-pole double-throw (SPDT) switch designed in bulk CMOS technology has limited power-handling capability in terms of 1-dB compression point (P1dB) inherently. This is mainly due to the low threshold voltage of the switching transistors used for shunt-connected configuration. To solve this issue, an innovative approach is presented in this work, which utilizes a unique passive ring structure. It allows a relatively strong RF signal passing through the TX branch, while the switching transistors are turned on. Thus, the fundamental limitation for P1dB due to reduced threshold voltage is overcome. To prove the presented approach is feasible in practice, a 90-GHz asymmetrical SPDT switch is designed in a standard 55-nm bulk CMOS technology. The design has achieved an insertion loss of 3.2 dB and 3.6 dB in TX and RX mode, respectively. Moreover, more than 20 dB isolation is obtained in both modes. Because of using the proposed passive ring structure, a remarkable P1dB is achieved. No gain compression is observed at all, while a 19.5 dBm input power is injected into the TX branch of the designed SPDT switch. The die area of this design is only 0.26 mm 2 .
Abstract The effects of aluminum mass content and particle size in CL‐20‐based aluminized explosives were investigated with a small‐scale confined plate push test. The confinement strength of the detonation products was enhanced to twice that of cylinder tests to accelerate the aluminum particle reaction. An all‐fiber displacement interferometer system for any reflector was used to continuously measure the plate velocity over time. A series of aluminized explosives containing various aluminum particle masses and sizes were tested, as well as explosives containing LiF instead of aluminum. Numerical simulations of explosive detonation and metal plate acceleration were performed, where parameters for the equation of state of the detonation products were calibrated by comparing the results with experiment. The results indicated that most of the aluminum particles (including 200‐nm diameter particles) reacted with the detonation products after the Chapman‐Jouguet point. Moreover, the released energy from the reaction could further accelerate the metal plate and increase the acceleration time, although the initial plate velocity was reduced. The start reaction times of small particles were earlier than that of larger particles. Specifically, 2‐50‐μm aluminum particles start to react when the volume of detonation products expanded to 1.24 times the initial volume, while the 200‐nm particles start to react at 1.07 times the initial volume, with a significantly higher reaction rate. The reaction rates decreased with increasing mass fraction of reacted aluminum and a decrease in pressure.
The cover picture shows a shock initiation test on explosively driven flyer-initiated heated explosive to investigate the effect of temperature on shock initiation of RDX-based aluminized explosives. The pressure histories at different depths inside the explosives were measured by using manganin pressure gauges. The ignition and growth reaction model, some parameters of which rely on temperature, was used to simulate the shock-initiation processes. The relationship between the model parameters and the temperature were obtained from the experimental results, and the reaction degree of the explosives were determined. The results indicated that binder softening and the increasing sensitivity of RDX are the two main reasons that change the shock sensitivity of RDX-based aluminized explosives. For 25 °C–110 °C, the shock sensitivity decreases with an increase in temperature, mainly because of binder softening. However, for 110 °C–170 °C, the shock sensitivity increases with an increase in temperature, which depends on the increasing sensitivity of RDX. Details are discussed in the paper titled "Effect of Temperature on Shock Initiation of RDX-Based Aluminized Explosives" by Pin Zhao et al. on page 1562 ff.
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