Thermal Or Aluminum/Magnesium Catalyzed Decompositions Of Several Energetic Materials

Recent years, high energetic density materials (HEDM) have been received much attention. In this paper, the Quantum Mechanics (QM) and Molecular Dynamics (MD) were used to investigate the HEDMs. The initial reactions of DTTO, BCHMX, MTO and MTO3N were probed by the Density Functional Theory (DFT) molecular dynamics simulations (DFT-MD) The results suggest that a variety of initial decomposition reactions are favorable for DTTO, BCHMX, MTO and MT03N, depending on temperature, pressure, and crystal packing. Then we studied the decomposition and adsorption of FOX-7 and RDX on the Al or Mg surfaces. The adsorption and reaction mechanism of FOX-7 and RDX on the surface of the active metal were analysed. The main research contents are as follows:1. Initial reaction mechanism of DTTODensity Functional Theory (DFT) molecular dynamics simulations (DFT-MD) is used to investigate the DTTO crystal for the two most stable monomers. For c1 isomer, the DFT-MD studies find that the initial reaction at lower pressure is unimolecular decomposition to form two N2O molecules (barrier 192.1 kJ/mol), while at higher pressure it is intermolecular oxygen-transfer with a barrier of 167.9 kJ/mol. For the c2 isomer (less stable by 5.0 kJ/mol) the initial reaction involves two DTTO molecules reacting to form a dimer which then releases N2 as a direct product (barrier 201.3 kJ/mol), a unique initial reaction among EMs. These results suggest that DTTO may have a higher thermal stability (barrier>29.3 kJ/mol higher) than RDX, HMX, and CL-20.2. Initial reaction mechanism of BCHMXDFT-MD simulations is used to investigate the initial chemical reactions of BCHMX:For the non-compressed BCHMX, the nitro-aci isomerization reaction occurs earlier than the NO2 releasing reaction, while for compressed BCHMX intermolecular hydrogen-transfer and bimolecular NO2 releasing reactions occur earlier than the HONO releasing reaction. At high-pressures, the initial reaction involves intermolecular hydrogen-transfer rather than intramolecular hydrogen-transfer and the intermolecular hydrogen-transfer decreases the reaction barrier for release of NO2, by ～29.3 kJ/mol. Thus the HONO releasing reaction is take place more easily in compressed BCHMX. We find that this reaction barrier is 41.9 kJ/mol lower than the unimolecular NO2 release and ～12.6 kJ/mol lower than the bimolecular NO2 release. This rationalizes the origin of the higher sensitivity of BCHMX compared to RDX and HMX. We suggest changes in BCHMX that might help improve the sensitivity by avoiding the intermolecular hydrogen-transfer and HONO releasing reaction.3. Initial reaction mechanism of MTO and MT03NDFT-MD simulations is used to investigate the initial chemical reactions of MTO and MT03N:Our DFT-MD studies find that the first step in the decomposition of MTO is intermolecular hydrogen-transfer reaction (barrier 12.5 kJ/mol) which is followed quickly by H2O and NO release. In contrast for MT03N (P2(1)/c predicted space group), we find that the first steps are a bimolecular decomposition to release NO2 (barrier 184.3 kJ/mol) simultaneous with unimolecular NO2 cleavage (barrier 250.4 kJ/mol) a unique initial reaction among EMs. These results suggest that MTO3N would be significantly more thermally stabile (barrier> 25.1 kJ/mol higher) than RDX and HMX, making it an excellent candidate to be insensitive new green energetic materials. However we find that MTO leads to very favorable hydrogen transfer reactions that may complicate synthesis and crystallization, making MTO3N the more promising system.4. Adsorption and dissociation of FOX-7 on Al13 clustersThe adsorption and decomposition of FOX-7 molecule on Al13 clusters were investigated by generalized gradient approximation (GGA) of density functional theory (DFT). The strong attractive forces between FOX-7 molecule and aluminum atoms induce the N-I bond breaking of the FOX-7. Subsequently, the dissociated oxygen atoms and radical fragment of FOX-7 oxidize the Al clusters. The largest adsorption energy is-1020.4 kJ/mol. We also investigated three adsorption reaction paths of FOX-7 molecule on the Al13 clusters. The activation energy for the adsorption steps are 0.2 kJ/mol,11.4 kJ/mol and 10.2 kJ/mol, respectively. And Al13 is more active than Al(111) surface and Al13 cluster performs better in decreasing the adsorption barrier of FOX-7 on Al surface as well. The rate constants of three adsorption paths increase as temperature increases over the temperature range 275-500 K.5. Adsorption and dissociation of FOX-7 on Al(111) surfaceThe adsorption of 1,1-diamino-2,2-dinitroethylene (FOX-7) molecule on the Al(111) surface were investigated by GGA of DFT. The calculations employ a supercell (4×4×2) slab model and three-dimensional periodic boundary conditions. The strong attractive forces between oxygen and aluminum atoms induce the N-0 bond breaking of the FOX-7. Subsequently, the dissociated oxygen atoms and radical fragment of FOX-7 oxidize the Al surface. The largest adsorption energy is -940.5 kJ/mol. The most of charge transfer is 3.31 e from the Al surface to the fragment of FOX-7 molecule. We also investigated the adsorption and decomposition mechanism of FOX-7 molecule on the Al(111) surface. The largest activation energy for the dissociation steps is 483.8 kJ/mol, while activation energies of other paths are much smaller, in range of 2.4 to 147.7 kJ/mol.6. Adsorption and dissociation of RDX on Al(111) surfaceThe adsorption of RDX molecule on the Al(111) surface was investigated by GGA of DFT. The calculations employ a supercell (4×4×3) slab model and three-dimensional periodic boundary conditions. The strong attractive forces between RDX molecule and aluminum atoms induce the N-O and N-N bond breaking of the RDX. Subsequently, the dissociated oxygen atoms, NO2 group and radical fragment of RDX oxidize the Al surface. The largest adsorption energy is -835.7 kJ/mol. We also investigated the adsorption and decomposition mechanism of RDX molecule on the Al(111) surface. The largest activation energy is 353.1 kJ/mol, while activation energies of other paths are much smaller, in range of 70.5 to 202.9 kJ/mol.7. Adsorption and dissociation of RDX on Mg(0001) surfaceThe adsorption and decomposition of RDX molecule on the Mg(0001) surface were investigated by the GGA of DFT. The calculations employed a supercell (4×4×4) slab model and three-dimensional periodic boundary conditions. The strong attractive forces between RDX molecule and magnesium atoms induce the N-O bond breaking of the RDX. Subsequently, the dissociated oxygen atoms and radical fragment of RDX oxidize the Mg surface. The largest adsorption energy is -2104.0 kJ/mol. We also investigated the decomposition mechanism of RDX molecule on the Mg(0001) surface. The lowest activation energy is 2.5 kJ/mol, while activation energies of other configurations are much larger, in the range of 964.9 to 1375.1 kJ/mol. Mg powder is more active than Al powder and Mg powder performs better in increasing the combustion exothermicity of RDX as well.