Engineering the microstructure of organic energetic materials

Anatomies for the thermal decomposition behavior and product rule of 5,5′-dinitro-2H,2H′-3,3′-bi-1,2,4-triazole

High-performance energetic materials are mainly used in the military, aerospace industry and chemical fields. The ordinary technology of producing energetic materials cannot avoid the domination of its unique needs. At present, revealing the underlying mechanism of the formation of high-energy materials is of great significance for improving their quality characteristics. We pay special attention to the decomposition and reactive molecular dynamics (RMD) simulation of 5,5′-dinitro-2H,2H′-3,3′-bi-1,2,4-triazole (DNBT). Various forms were captured in the simulation, and the form is determined by the temperature of the initial reactant. By observing the heating pattern and morphological changes under the initial thermal equilibrium, interesting temperature jumps were found in 325 K and 350 K. Observation of continuous heating (simulated temperatures are 2600 K, 2900 K, 3200 K and 3500 K) shows that DNBT has the maximum heating rate at 3500 K. In addition, N₂ occupies this dominant position in the product, moreover, N₂ and NO₂ respectively dominate the gas phase products during the initial heating process. According to the transition state analysis results of the intermediates, we found 4 interesting intermediate products, which were determined by high frequency reaction under the 4 simulated temperatures and performed with transition state calculations. It shows that the selection of reactant temperature and its activity is the key to orderly decomposition of DNBT. It is expected that these findings will be widely used in comprehensive decomposition devices and to improve the concept of learning military and industrial technology.

The performance and behavior of DNBT under RMD simulation at high temperature (2600 K, 2900 K, 3200 K and 3500 K).

Nanoscale Homogeneous Energetic Copper Azides@Porous Carbon Hybrid with Reduced Sensitivity and High Ignition Ability

Research on green primary explosives with lead-free and excellent ignition performance is of significance for practical applications. In this work, we have developed a novel, green, and facile strategy for synthesizing copper azide@porous carbon hybrids (CA@PC) based on ionic cross-linked hydrogel with low-cost cellulose derivatives as the starting material, in which the CA nanoparticles are uniformly distributed in the porous carbon skeletons. The detailed characterizations and control experiments demonstrated that such an outstanding performance originates from the excellent electric conductivity of nanoscale carbon cages. With the favorable unique structures, the as-prepared hybrids can greatly benefit a new type of energetic materials, which exhibit a very low electrostatic sensitivity of 1.06 mJ. Interestingly, the hybrids possess a high ignition ability, and the flame sensitivity can even achieve 47 cm, superior to those well-developed CA-based materials reported previously. This work paves the way toward the design and development of next-generation highly efficient energetic materials.

Facile preparation of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane/glycidylazide polymer energetic nanocomposites with enhanced thermolysis activity and low impact sensitivity

HMX/GAP nanocomposites showed high thermal reactivity and low sensitivity, which could be a very promising ingredient in composite solid propellant.

Metal-Organic Framework Templated Synthesis of Copper Azide as the Primary Explosive with Low Electrostatic Sensitivity and Excellent Initiation Ability

A powerful yet safe primary explosive, embedded in a conductive carbon scaffold, is prepared by using a metal-organic framework as precursor. It simultaneously possesses low electrostatic sensitivity, good flame sensitivity, and excellent initiation ability. This method is simple, scalable, and provides a new platform for the development of energetic materials especially those employed in miniaturized explosive systems.

Small-scale, self-propagating combustion realized with on-chip porous silicon

For small-scale energy applications, energetic materials represent a high energy density source that, in certain cases, can be accessed with a very small amount of energy input. Recent advances in microprocessing techniques allow for the implementation of a porous silicon energetic material onto a crystalline silicon wafer at the microscale; however, combustion at a small length scale remains to be fully investigated, particularly with regards to the limitations of increased relative heat loss during combustion. The present study explores the critical dimensions of an on-chip porous silicon energetic material (porous silicon + sodium perchlorate (NaClO4)) required to propagate combustion. We etched ∼97 μm wide and ∼45 μm deep porous silicon channels that burned at a steady rate of 4.6 m/s, remaining steady across 90° changes in direction. In an effort to minimize the potential on-chip footprint for energetic porous silicon, we also explored the minimum spacing between porous silicon channels. We demonstrated independent burning of porous silicon channels at a spacing of <40 μm. Using this spacing, it was possible to have a flame path length of >0.5 m on a chip surface area of 1.65 cm(2). Smaller porous silicon channels of ∼28 μm wide and ∼14 μm deep were also utilized. These samples propagated combustion, but at times, did so unsteadily. This result may suggest that we are approaching a critical length scale for self-propagating combustion in a porous silicon energetic material.

Preparation of sub-micron nitrocellulose particles for improved combustion behavior

A novel method to prepare sub-micron nitrocellulose particles with spherical shape is demonstrated. The morphology of the nitrocellulose can be controlled by the solvent and the growth temperature. Using dimethylformamide (DMF) at a growth temperature is 5°C, reproducibly yielded spherical nitrocellulose particles. The final diameter of the prepared nitrocellulose particles can be further tuned by concentration. The smallest particles in this study were found to have diameters of 500nm at a concentration of 5-10mg/ml with 2 micron spheres formed at 30mg/ml. Furthermore, the thermal properties and the burn rates of the prepared materials are studied by differential scanning calorimetry and digital high-speed photography, respectively. In comparison to the bulk nitrocellulose material, the sub-micron nitrocellulose particles have lower decomposition activation energy, a 350% increase in burn rate, and a more complete combustion.

Measuring the activation energy of thiol desorption using lateral force microscopy

Thermal stability of self-assembled monolayers (SAMs) is important for applications in various surface science applications. As a model material, 16-mercaptohexadecanoic acid (MHA) on template stripped gold surfaces was investigated to determine the effect of temperature on the change of lateral force signal using atomic force microscopy (AFM). Friction force signals were obtained at various temperatures in order to determine whether it was possible to correlate the friction signal with desorption of the thiol molecule from the surface. Samples were heated for up to 10 h ranging from 40 to 80 °C in air and scanned every hour. A kinetic model was introduced to correlate the lateral force signal to the activation energy of desorption of the SAM from gold surface with heating. The activation energy of the detachment using this technique is 25.4 kcal/mol, which is consistent with other more complex techniques.