ABSTRACT
Temperature-induced morphological changes are one of the strategies for designing crystal shapes, but the role of temperature in enhancing or inhibiting crystal growth is not well understood yet. To meet the requirements of high density and low sensitivity, we need to control the crystal morphology of the energetic materials. We studied the crystal morphology of 1,1-diamino-2,2-dinitroethylene (FOX-7) in dimethyl sulfoxide/water mixed solvent by using the modified Hartman-Perdok theorem. Molecular dynamics simulations were used to determine the interaction of FOX-7 and solvents. The results showed that the crystal shape of FOX-7 is hexagonal, the (101) face is the largest exposed face and is adjacent to six crystal faces at 354 K. As the temperature goes down, the area of the (001) face is significantly reduced. The crystal morphology of FOX-7 at 324 K has a smaller aspect ratio of 4.72, and this temperature is suitable for tuning the morphology from slender hexagon into diamond. The prediction results are in remarkable agreement with the experiments. Moreover, we predicted the evolution path of FOX-7 morphology by Gibbs-Curie-Wulff theorem and explained the variation of crystal shape caused by different external conditions in the actual crystallization process.
ABSTRACT
The adsorption and decomposition of hexogen (RDX) molecule on the Mg(0001) surface were investigated by the generalized gradient approximation (GGA) of density functional theory (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 RDX's N - O bond breaking. Subsequently, the dissociated oxygen atoms and radical fragment of RDX oxidize the Mg surface. The largest adsorption energy is -2104.0 kJ mol(-1). We also investigated the decomposition mechanism of RDX molecule on the Mg(0001) surface. The activation energy for the dissociation step of configuration V4 is as small as 2.5 kJ mol(-1), while activation energies of other configurations are much larger, in the range of 964.9-1375.1 kJ mol(-1). Mg powder is more active than Al powder, and Mg powder performs better in increasing the combustion exothermicity of RDX as well.
ABSTRACT
The adsorption of hexogen (RDX) molecule on the Al(111) surface was investigated by the generalized gradient approximation (GGA) of density functional theory (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(-1). We also investigated the adsorption and decomposition mechanism of RDX molecule on the Al(111) surface. The activation energy for the dissociation steps of V4 configuration is as large as 353.1 kJ mol(-1), while activation energies of other configurations are much smaller, in the range of 70.5-202.9 kJ mol(-1). The N-O is even easier than the N-NO2 bond to decompose on the Al(111) surface.
