Fabrication of microspherical Hexanitrostilbene (HNS) with droplet microfluidic technology

Self-Template Evolution Toward Hierarchically Hollow Spherulites of Energetic Materials for Safety Control and Combustion Enhancement

The hierarchical hollow structure can endow functional materials with concerning performances, whereas its rational design remains challenging, especially for organic molecules. Herein, a novel strategy of self-template evolution is presented to construct hollow spherulites (HSs) for energetic organic materials with controllable safety and enhanced combustion, utilizing the mechanism of pseudomorphic replacement coupled with Ostwald ripening. Specifically, the spherulites of thermodynamically metastable β-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (β-CL-20) as the self-template spontaneously evolves into the HSs of CL-20-based inclusion compounds in solution, during which the dissolution of β-CL-20 and the crystallization of CL-20-based inclusion compounds are spatiotemporally correlated, enabling pseudomorphic replacement preserving the spherulitic structure, and cavities are formed inside via Ostwald ripening. Moreover, the conversion rates and the mediating solvent cause different locations of cavities, with two cases exhibited. The hollow-core spherulites of CL-20-formic acid exhibit controllable safety through manipulating micro-/nanostructures, and the hollow-spoke spherulites of CL-20-CO2 can be the efficient carrier to composite with oxidants, enhancing combustion with increases of 23.2% in pressure duration effect, 9.8% in peak pressure, and 3.3% in pressurization rate. This work offers a novel route to construct hierarchical hollow energetic crystals with enhanced performance and puts insight into the design of hierarchical hollow crystals for broad material systems.

Research Progress on the Modification of B and Al High-Energy Fuels for Powder Fuel Ramjet Applications

Metal powder fuels are widely used in various fields such as aerospace, pyrotechnics, damage, and renewable energy. Recently, ramjets have gained significant attention due to their beneficial characteristics, including simple design, light weight, and high thrust-to-weight ratio. These features make them well-suited for aircraft, missiles, and unmanned aerial vehicles. However, there is a conspicuous lack of comprehensive research on modification methods and applicability into the metal powder fuels for ramjets, which creates an obstacle to further and widespread application. Therefore, this paper focuses on modifying metal fuels suitable for powder fuel ramjets. First, the effects of metal features, such as crystallinity, microscopic morphology, and particle size, on the ignition and combustion performance of fuel, flowability, and density are summarized. Second, the research discusses the modified materials and techniques of metal fuels, especially those that can be adapted to powder fuel ramjets, and systematically exhibits the properties of these modified metal fuels in terms of oxidation, ignition, and combustion. Third, the present challenges and prospects of powder fuels ramjets are discussed in detail. The paper serves as a comprehensive reference and guidance for the research on powder fuel ramjets.

Preparation of μ-HMX/C-Based Composite Energy Composite Microspheres by Microdroplet Technology

Taking μ-HMX particles as the main research subject, a set of microdroplet sphericalization coating technology platforms was designed and constructed to realize the preparation of composite microspheres by sphericalization coating of μ-HMX. The suspension stability of μ-HMX particles and the mechanism of droplet formation were investigated, and the application effect of nanocarbon materials was also analyzed. The results showed that the prepared sample microspheres all showed a better spherical morphology, as well as good dispersibility; the samples with micron-sized particles for spherical coating had a lower thermal decomposition temperature, a higher energy release efficiency, lower mechanical sensibility, and better combustion performance; the incorporation of CNFs changed the combustion mode of the system, which resulted in the microsphere system of μ-HMX having a good safety performance. The stability and feasibility of uniform spheronization when the dispersed phase is a low-concentration particle suspension system in the spheronization encapsulation process by microdroplet technology were verified.

Facile Recrystallization Process for Tuning the Crystal Morphology and Thermal Safety of Industrial Grade PYX

In this study, the crystal appearance of industrial grade 2,6-diamino-3,5-dinitropyridine (PYX) was mostly needle-shaped or rod-shaped with an average aspect ratio of 3.47 and roundness of 0.47. According to national military standards, the explosion percentage of impact sensitivity s about 40% and friction sensitivity is about 60%. To improve loading density and pressing safety, the solvent-antisolvent method was used to optimize the crystal morphology, i.e., to reduce the aspect ratio and increase the roundness value. Firstly, the solubility of PYX in DMSO, DMF, and NMP was measured by the static differential weight method, and the solubility model was established. The results showed that the Apelblat equation and Van't Hoff equation could be used to clarify the temperature dependence of PYX solubility in a single solvent. Scanning electron microscopy (SEM) was used to characterize the morphology of the recrystallized samples. After recrystallization, the aspect ratio of the samples decreased from 3.47 to 1.19, and roundness increased from 0.47 to 0.86. The morphology was greatly improved, and the particle size decreased. The structures before and after recrystallization were characterized by infrared spectroscopy (IR). The results showed that no chemical structure changes occurred during recrystallization, and the chemical purity was improved by 0.7%. According to the GJB-772A-97 explosion probability method, the mechanical sensitivity of explosives was characterized. After recrystallization, the impact sensitivity of explosives was significantly reduced from 40% to 12%. A differential scanning calorimeter (DSC) was used to study the thermal decomposition. The thermal decomposition temperature peak of the sample after recrystallization was 5 °C higher than that of the raw PYX. The thermal decomposition kinetic parameters of the samples were calculated by AKTS software, and the thermal decomposition process under isothermal conditions was predicted. The results showed that the activation energy (E) of the samples after recrystallization was higher by 37.9~527.6 kJ/mol than raw PYX, so the thermal stability and safety of the recrystallized samples were improved.