Desensitizing Effect of Graphene Oxide on Thermolysis Mechanisms of 4,4′-Azo-1,2,4-triazole Studied by Reactive Molecular Dynamics Simulations

Abstract

Graphene oxide (GO) has obvious desensitizing effect on the thermal decomposition of energetic materials such as HMX, CL-20, etc. 4,4′-Azo-1,2,4-triazole (ATRZ) is known as a new type of energetic material with high N content; the underlying thermal decomposition mechanism of graphene oxide−ATRZ (GO−ATRZ) complex with low sensitivity has not been studied. The present work studies the thermal decomposition mechanisms of GO, ATRZ,and the GO−ATRZ complex (the number of carboxyl groups on GO:ATRZ = 2:1) by the ReaxFF molecular reactive dynamic simulations and kinetics calculations. As a result, it has been found that the main decomposition pathway of GO is the exfoliation of hydroxyl and carboxyl groups on the graphene sheet, whereas ATRZ breaks its fivemembered ring as the main decomposition path, and the ring further decomposes into small molecules, such as CHN, N 2 , HN 2 , H 2 N 2 , etc. The major effect of GO on ATRZ is probably derived from the stable graphene sheet, which has a space effect on ATRZ, and the strong oxidizing hydroxyl groups produced during GO decomposition, which results in the formation of CON and CHON. By calculating the activation energy of N 2 generation in the reactions, it can be concluded that the addition of GO can increase the decomposition activation energy of ATRZ (41.1 kJ•mol −1 ) in comparison with that of its pure substance (25.0 kJ•mol −1 ). Therefore, GO can be combined with ATRZ as a desensitizer where GO can improve the molecular stability of ATRZ.

Interaction Mechanisms of Insensitive Explosive FOX-7 and Graphene Oxides from Ab Initio Calculations

“…The lattice parameters of the hybrid system were adopted the GO values, since the lattice mismatch was only 4% and 5% in the x and y directions, respectively. Note that as a compromise between computational cost and accuracy, this computational scheme has been proven to be reliable in handling composite systems of energetic materials [19,20,21].…”

“…Among them, molecular and crystal structures, including chemical composition, crystal packing, crystal morphology, size, shape, purity, and defects, are strongly related to the intrinsic qualities of the materials. Until now, various strategies, such as recrystallization, energetic co-crystals, adding and coating of the inert materials including with organic wax [7], high polymers [8], stearic acid [9], and carbon materials (CMs) [10,11,12,13,14,15,16,17,18,19,20,21,22], have been proposed to reduce the sensitivity and improve the performance of EMs.…”

“…First-principles calculation suggested that in carbon nanostructures and graphene layers, the energetic molecules of FOX-7 (1,1-Diamino-2,2-dinitroethylene), RDX (hexahydro-1,3,5-trinitro-striazine), and HMX can be stabilized, thereby reducing the sensitivity [19]. Recent molecular dynamic simulations and kinetics calculations using ReaxFF have also indicated that as an efficient desensitizer or additive, GO could increase the molecular stability and decomposition activation energy of ATRZ (4,4′-Azo-1,2,4-triazole, a new stable high-nitrogen compound) [20]. Ab initio molecular dynamics simulations by Liu et al showed that functionalized graphene with a carbon vacancy defect could greatly accelerate the thermal decomposition of nitromethane and its derivatives [21].…”

The Effects of Metal Complexes of Nano-Graphene Oxide to Thermal Decomposition of FOX-7

“…Compared to 40 °C, the ratio of peaks According to the MS result of nGO (Figure 8b,c), the decomposition products can be investigated. The initial decomposition process of nGO mainly undergoes decomposition of oxygen-containing functional groups, including detachment of hydroxyl groups, decomposition of carboxyl groups into hydroxyl radicals, and carbon monoxide, and the radical reaction of hydroxyl radicals with hydroxyl groups and carboxyl groups on nGO [57]. Therefore, its main decomposition products include water, carbon monoxide, carbon dioxide, etc.…”

“…Compared to 40 • C, the ratio of peaks m/z = 18 to m/z = 32 increases, indicating that nGO has water formation at the time of decomposition. According to reference [57], the product represented by m/z = 28 may contain carbon monoxide at 179 • C.…”