No abstract

Metallic additives, Al nanoparticles in particular, have extensively been used in energetic materials (EMs), of which thermal decomposition is one of the most basic properties. Nevertheless, the underlying mechanism for the highly active Al nanoparticles and their oxidized counterparts, the Al2O3 nanoparticles, influencing the thermal decay of aluminized EMs has not fully been understood. Herein, we explore the influence of Al and Al2O3 nanoparticles on the thermal decomposition of 1,3,5trinitro-1,3,5-triazinane (RDX), one of the most common EMs, based on large-scale reactive force field molecular dynamics simulations within three heating schemes (constant-temperature, programmed and adiabatic heating). The presence of Al nanoparticles significantly reduces the induction time and energy required to activate the RDX decay, and greatly increases energy release. The fundamental reason for these results is that Al changes the primary decay pathway from the unimolecular N-NO2 scission of RDX to bimolecular barrier-free or low-barrier Al-involved reactions, and possesses a strong O-extraction capability and a moderate one to react with C/H/N. It is also responsible for the growth of the Al-contained clusters. And Al2O3 nanoparticles can also demonstrate such catalysis capability but contribute less to the enhancement of energy release. Moreover, the detailed evolutions of key thermodynamic properties, intermediate and final gaseous products, and Al-contained products are also presented. Besides, under the programmed heating and adiabatic heating conditions the catalysis of the Al and Al2O3 nanoparticles becomes more distinct. Thereby, many properties of aluminized EMs are expected to well be understood by our simulation results.

It has become increasingly important to add Al nanoparticles (ANPs) into energetic materials (EMs) to overcome the issue of Al particles aggregation and promote the efficiency of heat release. Nevertheless, the underlying mechanism for the role of ANPs in EMs still remains limited. By means of reactive molecular dynamics simulations with the ReaxFF potential, the present work focuses upon the evolution of ANPs in a hot EM of 2,4,6-trinitro-1,3,5-triaminobenzene (TATB), which features very high insensitivity and O-lack. As a whole, adding ANPs unexceptionally increases heat release, and the morphological evolution of ANPs significantly depends on their sizes and contents, as the smaller size and the smaller content facilitate microexplosion. Moreover, a cracking of the core–shell structured Al@Al2O3 is observed in the hot TATB, as in oxygen. Besides Al–O bonds, Al–C and Al–N bonds are formed owing to the O-poor character of TATB. In addition, fusion of four ANPs in a model is observed as the reaction proceeds. A hollow alumina sphere is formed when adding an Al@Al2O3 particle to hot TATB, and it is found that there is an inward O transport and more O atoms concentrated around the center of an ANP with a relatively large size and high content. This work is expected to deepen insight into the complex reaction mechanism of ANPs-containing EMs.

Exploring and designing two-dimensional (2D) nanomaterials for armor-piercing protection has become a research focus. Here, by molecular dynamics simulation, we revealed that the ultralight monolayer covalent organic framework (COF), one kind of novel 2D crystalline polymer, possesses superior impactresistant capability under high-velocity impact. The calculated specific penetration energy is much higher than that of other traditional impact-resistant materials, such as steel, poly(methyl methacrylate), Kevlar, etc. It was found that the hexagonal nanopores integrated by polymer chains have large deformation compatibility resulting from flexible torsion and stretching, which can remarkably contribute to the energy dissipation. In addition, the deformable nanopores can effectively restrain the crack propagation, enable COF to resist multiple impacts. This work uncovers the extreme dynamic responses of COF under highvelocity impact and provides theoretical guidance for designing superstrong 2D polymer-based crystalline nanomaterials.

Poly(p-phenylene benzobisoxazole) (PBO) fiber shows fascinating properties including excellent mechanical performance, high crystallinity, and fairly good heat resistance as a kind of polymer fiber. Its properties make it a possible candidate as a precursor of carbon fiber. This paper mainly investigates the possibility of yielding carbon fiber from PBO by direct carbonization using a continuous process and multiple properties of yielded fiber treated under different heat treatment temperature (HTT). The results show that PBO fiber was able to sustain an HTT as high as 1400 °C under the inert atmosphere and that the shape of fiber was still preserved without failure. Using thermal gravimetric analysis (TGA) and TGA coupled with mass spectroscopy (TGA-MS), it was found that a significant mass loss procedure happened around 723.3 °C, along with the emission of various small molecules. The mechanical performance first suffered a decrease due to the rupture of the PBO structure and then slightly increased because of the generating of graphite crystallite based on the broken structure of PBO. It was observed that PBO’s microstructure transformed gradually to that of carbonaceous material, which could be the reason why the change of mechanical performance happened.

The results of this article show that 2D-CNN has great potential in the field of soil recognition and classification combine with LIBS, and provides a new and reliable data processing method for LIBS to classify materials with similar chemical properties.

No abstract

No abstract