Conformational Changes and Decomposition Mechanisms of HMX-Based Cocrystal Explosives at High Temperatures

Abstract

The cocrystallization effect plays a prominent role in improving the performance of energetic materials. A combinational strategy based on density functional tight-binding molecular dynamics (DFTB-MD) simulations and density functional theory (DFT) was used to elucidate the decomposition mechanisms and reaction kinetics of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)-based cocrystal explosives [HMX/N,N-dimethylformamide (DMF) and HMX/bis­(2,4-dinitro-2,4-diazapentane) (DNDAP)] at high temperatures. The decomposition and reaction mechanisms of the two cocrystals showed great dependence on the temperature. In the HMX/DMF cocrystal, a conformational change of HMX at 2000 K and subsequent initial decomposition of HMX at 2500 K is involved. At 3000 K, the global decomposition and interaction of the HMX and cocrystal molecules occurred. There are two dominant competing reaction channels in the two cocrystals. The comparative results reveal that the HMX molecules have a larger reactivity with DNDAP at low temperatures but with DMF at high temperatures. The decomposition pathways of the HMX molecules based on DFT calculations were studied as a useful addition to the MD results. These findings provide a basic understanding of the thermal decomposition mechanisms and reaction kinetics of HMX-based cocrystal energetic materials at high temperatures.

The role of electric field on decomposition of CL‐20/HMX cocrystal: A reactive molecular dynamics study

“…The C N(2) and C N(3) bonds are still more sensitive to OEF than other bonds. However, it is found that EFs have almost no effect on the bond length of HMX as shown in Figure S6, which can be attributed to the stronger bonds of HMX than that of CL-20 in the cocrystal (about 42.6 45 $43.6 46 kcal/mol vs. 35.9 15 kcal/mol). To summarize, due to its molecular structure that is liable to deform under EF, CL-20 is more sensitive to EF than HMX.…”

“…Class-B reactions correspond to ring-opening reactions and intramolecular atom transferring reactions, which are difficult to be analyzed in RMD simulation, and often overlooked. 17,32,44,45 By using our new analytical method described in Section 2, we successfully identified such reactions in the simulations and summarized the ones with highest frequent in Table 3. In order to understand the initial decomposition mechanism of CL-20 comprehensively, we illustrate the identified main primary and These reactions are the dominant reason for the breakage of a large number of C N bonds within CL-20 before its decomposition into NO 2 , as shown in Figure 7.…”

Nitramine-Based Energetic Cocrystals with Improved Stability and Controlled Reactivity

“…Furthermore, the conformational change, decomposition mechanism, and reaction kinetics of different HMX/DMF and HMX/DNDAP cocrystals at high temperatures have been studied in recent work. The results indicate that the decomposition mechanisms of different HMX-based cocrystals show great dependence on the temperature.…”

Synthesis and Effects of Two Novel Rare-Earth Energetic Complexes on Thermal Decomposition of Cyclotetramethylene Tetranitramine (HMX)

“…Nitrate ester plasticized polyether (NEPE) propellant is a new type of crosslinked, high-energy, solid propellant which uses polyether polyurethane as a binder, nitrate esters as plasticizers, and is filled with a large amount of the high-energy oxidant, cyclotetramethylene tetranitramine (HMX) [1][2][3]. It also contains a combustion agent, stabilizer, and combustion promoter [4].…”

“…H: the heat release of HMX or a mixed system 2. ∆H: actual added heat value of the system with complexes 1 to 5 3. ∆T: the change in the HMX decomposition peak temperature after the addition of complex 1 to 5.…”