Crystal Growth Theory Study For Nitroamine Explosives

Recently, various studies about the crystal growth of explosive are mainlyrelying on the experimental methods. That is, in order to get an explosive withhigh density insensitive, it always needs to constantly adjust experimentalconditions and optimize crystallization process. However, the crystallizationprocess referred the most fundamental problem of crystal formation andevolution mechanism is still lack of investigations. While the computersimulation can track crystal growth process at the molecular or atomic scale, andexplore the explosive molecular crystal nucleation and growth process. Moreover,it can explain the main factors influencing the nucleation and crystal growth, andobtain the interaction force between solvent, solute, and crystal. Thus moleculardynamic simulation is very important for investigating the growth mechanism ofnitroamine explosives, providing theoretical support for the development ofexplosive crystallization technology with high quality. In this dissertation, wefocus on cyclotetramethylene tetranitramine (HMX) as a prototypical nitroamineexplosive and design two models for studying their nucleation and growthprocess using molecular dynamic simulation based on crystal growth theory. Inaddition, we study the Li-Al intermetallics by using density functional theory.The outline of this dissertation is as follows:1. The crystallization of HMX from solution in dimethylsulfoxide (DMSO)has been investigated by using molecular dynamics simulation at278,298,318,338,358, and378K. Firstly, an amorphous solution was built by Materials Studio3.0, in which there are20HMX and100DMSO molecules. After energyminimization, dynamics simulations were performed using Forcite module. Thediffusion coefficients of DMSO and HMX, and binding energy between HMXand DMSO were calculated at six different temperatures over the278-378K. Theresults demonstrated that the diffusion coefficient of HMX is largest and the bind energy between HMX and DMSO is smallest at358K, thus the optimaltemperature for nuclei formation was358K. The interaction force between HMXand DMSO was ascribed to the van der Waals’ force and electrostatic interaction.2. The growth of HMX from acetone and DMSO solutions on (100) face ofthe HMX crystal has been studied with three system model using moleculardynamics simulations at room temperature. The diffusion coefficients of acetone,DMSO, and HMX in two different solutions were calculated. The results showthat the diffusion coefficient of acetone is smaller than that of DMSO, and thediffusion coefficient of HMX in acetone solution is larger than that in DMSO.These results demonstrated that HMX molecule is more easily growth in acetonesolution. According to investigating the binding energy between (100) face andacetone molecule, DMSO molecule and HMX molecule, it was found that theinteraction force between HMX and (100) face is40kcal/mol, and the interactionforce between DMSO, acetone and (100) face is2kcal/mol and3kcal/mol,respectively. Thus HMX molecules will grow along the crystal face in thesolution. Finally, the growth processes of HMX on (100) face in differentsimulation time analysis showed that HMX molecule growth on (100) face can bemostly accomplished in a layer-by-layer manner in acetone and DMSO solution.3. The structural properties, heats of formation, elastic properties, andelectronic structures of four compositions of binary Al-Li intermetallics, Al3Li,AlLi, Al2Li3, and Al4Li9, are analyzed here in detail by using density functionaltheory.