Adsorption and decomposition of HMX and CL-20 on Al(111) surface by DFT investigation

Adsorption mechanisms of decomposition species of CHON-containing explosives on aluminum surfaces

Aluminum (Al) possesses high combustion enthalpy and is thus extensively used as the fuel additive in explosives to form aluminized explosives with excellent energy performance. In the energy release process of aluminized explosives, the adsorption of Al surfaces plays an important role in catalyzing the explosive decomposition and triggering the oxidation of themselves. However, it still remains elusive owing to the multiplicity of adsorbed substances. Herein, the adsorption mechanism of decomposition species of CHON-containing explosives on Al surfaces is studied synoptically by combining reactive molecular dynamics simulations with density functional theory calculations. The results indicate that the Al surface structure and the activity of adsorbed molecules both have an impact on adsorption. The cluster surface generally outperforms the slab one in adsorptivity due to the lower coordination number of Al atoms. Meanwhile, the more active adsorbed molecules lead to chemisorption or even dissociative adsorption, beneficial to the subsequent Al oxidation. Besides, electrons will transfer from the Al surface to the adsorbed molecules as chemisorption occurs; while the density of states of the Al surface and molecules are altered, especially for carbon oxides with significant electronic delocalization. This work is expected to deepen insights into the energy release of aluminized explosives and help provide a proposal for enhancing energy release efficiency.

Comparing the Catalytic Effect of Metals for Energetic Materials: Machine Learning Prediction of Adsorption Energies on Metals

Energetic materials (EMs) and metals are the important components of solid propellants, and a strong catalysis of metals on EMs could further enhance the combustion performance of solid propellants. Accordingly, the study on the adsorption of EMs such as octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and ammonium dinitramide (ADN) on metals (Ti, Zr, Fe, Ni, Cu, and Al) was carried out by density functional theory (DFT) to reveal the catalytic effect of metals. The deep dissociation of EMs on Ti and Zr represents a stronger interaction and corresponds to the rapid thermal decomposition behavior of the EMs/metal composite in the experiment. It is expected that DFT calculation can be selected instead of experiments to compare the catalytic effect of metals and preliminarily screen out potential high-performance metals. Based on the data set of the calculated adsorption energy, further machine learning (ML) was used to predict the adsorption energy of EMs on metals for a convenient comparison of the catalytic effect of metals, since a quite high adsorption energy value represents a more thorough dissociation. The kernel ridge regression (KRR) method shows the best performance on predicting adsorption energy and helps to choose the metals for efficiently catalyzing ammonium nitrate (AN) and hexanitrohexaazaisowurtzitane (CL-20). Such adsorption computation and ML not only reveal the decomposition mechanism of EMs on metals but also provide a simple underlying method to predict the catalytic effect of metals.

Reactive molecular dynamics simulation of thermal decomposition for nitromethane/nano-aluminum composites

The thermal decomposition of pure nitromethane (NM) and NM/nano-aluminum (Al) composites was simulated by reactive molecular dynamics with ReaxFF-lg corrected force field parameters. The initial decomposition pathway of NM molecules in pure NM is C-N bond rupture. However, NM is decomposed early by the initial pathway of N-O bond rupture when it mixes with nano-Al because of the strong attraction of Al to O. The decomposition process of NM/nano-Al can be divided into three stages: adsorption, slow decomposition, and rapid decomposition. The addition of nano-Al particles decreases the energy barrier in decomposition, increases the released energy, and reduces the decomposition temperature of NM. Adding 3% Al to the explosive can make the detonation pressure 3.083% higher than that of pure system. Compared with pure NM, the energy barrier of 16% Al composite is 25.63 kcal/mol lower and the energy released is 22.99 kcal/mol more. There is an optimal amount of Al contents being added to the NM composite by which the largest total numbers of gaseous products (N₂, H₂O, and CO₂) are released. The effect of Al additives on CO₂ production is the most obvious. The maximum detonation pressure can be achieved by adding an appropriate amount of nano-Al, which is similar to the experimental results. Graphical abstract.

Investigation on Adsorption and Decomposition Properties of CL-20/FOX-7 Molecules on MgH2(110) Surface by First-Principles

Metal hydrides are regarded as promising hydrogen-supplying fuel for energetic materials while CL-20 (Hexanitrohexaazaisowurtzitane) and FOX-7 (1,1-Diamino-2,2-dinitroethylene) are typical principal components commonly used in energetic materials. Hence, it is interesting to explore the interactions between them for development of new energetic systems. In this paper, the adsorption and decomposition of CL-20 or FOX-7 molecules on the MgH2 (110) crystal surface were investigated by employing the First-Principles. In total, 18 adsorption configurations for CL-20/MgH2 (110) and 12 adsorption configurations for FOX-7/MgH2 (110) were considered. The geometric parameters for the configurations, adsorption energies, charge transfer, density of states, and decomposition mechanism were obtained and analyzed. In most of the configurations, chemical adsorption will occur. Moreover, the orientation of the nitro-group in CL-20 or FOX-7 with regard to the MgH2 (110) surface plays an important role on whether and how the energetic molecule decomposes. The adsorption and decomposition of CL-20 or FOX-7 on MgH2 could be attributed to the strong charge transfer between Mg atoms in the first layer of MgH2 (110) surface and oxygen as well as nitrogen atoms in the nitro-group of CL-20 or FOX-7 molecules.