Molecular Dynamics Insight into the Evolution of Al Nanoparticles in the Thermal Decomposition of Energetic Materials

Abstract

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.

Crack Mechanism of Al@Al2O3 Nanoparticles in Hot Energetic Materials

“…In comparison, in L-ANP, the disintegration is not obvious, and the Al cluster formed first has not been dispersed, with a void generated only. Such a void has been found in a recent MD simulation of ANPs in another hot EM of TATB at 3000 K. 33 The morphologic evolution of an Al@Al 2 O 3 nanoparticle in the O-ANP model is shown in Figure 4c. In the oxygen environment, the ANP adsorbs a small amount of O 2 on the surface at 20 ps, and subsequently the nanoparticle appears as an obvious deformation, and its oxide shell is collapsed at 3000 K (Figure 4c).…”

“…The reactions occur readily because they are energy barrierfree. 33,36,37,40,41 A more remarkable reduction in the potential energy of L-ANP is observed and has a relation on a higher content of the Al@Al 2 O 3 nanoparticle, compared with H-ANP. It agrees with a previous experimental research, as a high content of Al largely facilitates to increase the heat release.…”

Fabrication and Characterization of Viton@FOX-7@Al Spherical Composite with Improved Thermal Decomposition Property and Safety Performance

“…Aluminum powder is used as a fuel additive to increase the energy of the air blast wave, the bubble energy in underwater explosions, and the duration of combustion action in aluminized composite explosives [ 4 , 5 , 6 ]. Compared to micrometer-sized particles, nano-sized aluminum (nAl) particles own high special surface areas and enhanced contact areas with explosives, so as to achieve more complete and faster oxidation [ 4 , 7 ].…”

Pushing the Limits of Energy Performance in Micron-Sized Thermite: Core–Shell Assembled Liquid Metal-Modified Al@Fe2O3 Thermites

“… The former method focuses on the meticulous architecture design of the thermite system, realizing a variety of structural forms, for instance multilayered, ,− 3D macroporous, − and core–shell − structures. Among these shapes, the core–shell structure has received extensive attention because of its unique properties, including highly specific surface area, controllable pore size, uniform distribution, excellent exothermicity as well as compatibility with MEMS systems. ,, The latter method focuses on accelerating the participation of Al in the reaction, such as reducing the fuel size, − multimetal fuels, , annealing and quenching aluminum, ,, and decomposing the alumina layer. , Among these methods of modifying fuels, reducing the aluminum size could bring many advantages, including fast reaction rate and low initial redox reaction temperature . However, aluminum naturally develops a 3–5 nm alumina shell upon exposure to oxygen, which leads to reduced active aluminum content at smaller particle sizes, presenting a barrier to the interaction of aluminum with the oxidizer .…”