Adsorption and Decomposition Mechanism of 1,1-Diamino-2,2-dinitroethylene on Al(111) Surface by Periodic DFT Calculations

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.

Density functional theory studies of methanol adsorption and decomposition mechanism on Al13 clusters

The adsorption and decomposition of the CH3OH molecule on Al13 clusters were investigated by generalized gradient approximation of the density functional theory. The strong attractive forces between the CH3OH molecule and aluminum atoms induce the breaking of the H–O and C–O bonds of CH3OH. Subsequently, the dissociated CH3O and OH radical fragments oxidize the aluminum clusters. The largest adsorption energy is –205.4 kJ/mol. We also investigated five reaction pathways of the CH3OH molecule on the Al13 clusters. The activation energies are in the range of 10.3−113.1 kJ/mol. Compared with the bond dissociation energies of the C–O and O–H bonds in the isolated methanol, Al13 performs very well in decreasing the bond break barrier of CH3OH. In addition, although the C–O bond is slightly weaker than the O−H bond, the O−H bond is even easier to decompose on the Al13 surface. The rate constants of five adsorption paths over the temperature range 300−700 K are presented.

Density functional theory studies on adsorption and decomposition mechanism of FOX-7 on Al13 clusters

The adsorption and decomposition of the FOX-7 molecule on Al13 clusters were investigated by generalized gradient approximation of the density functional theory. The strong attractive forces between the FOX-7 molecule and aluminum atoms induce the N−O bond breaking of FOX-7. Subsequently, the dissociated oxygen atoms and radical fragment of FOX-7 oxidize the aluminum clusters. The largest adsorption energy is −1020.4 kJ/mol. We also investigated three adsorption reaction paths of the FOX-7 molecule on the Al13 clusters in the A configuration. The activation energy for the adsorption steps are 0.2, 11.4, and 10.2 kJ/mol, respectively, and Al13 is more active than the Al(111) surface and the Al13 cluster performs better in decreasing the adsorption barrier of FOX-7 on the aluminum surface as well. The rate constants of three adsorption paths increase as temperature increases over the temperature range 275–500 K.