Computational Study On Atomic Packing Changes Of Mg Nano-particles Under Temperature And Uniaxial Compression

Low dimensional nanoscale materials have different structures and properties than bulk materials,in heterogeneous chemical reactions,the high surface area/volume ratio and the change of atomic packing structure with temperature and pressure must be taken into account in the use of nanoscale powders.Magnesium has attracted much attention for its advantages of light weight and abundant reserves.Because of its excellent properties,magnesium nano-particles can be widely used in the energy industry and energetic system In order to their application to meet the actual demand,it is very important to study the influence of temperature,particle size,and external force on the change of atomic packing structures in Mg nano-particles.In this paper,molecular dynamics simulations are performed to study the atom packing structures of these Mg nano-particles having different particle diameters on heating at the atomic scale;At room temperature,two Mg nano-particles containing different atomic numbers are subjected to uniaxial compression,and the atomic packing structures under loading and unloading are simulated.By calculating the average energy,the pair distribution function(PDF),mean square displacement(MSD),atomic packing,and pair analysis for these particles,the results are obtained as the following:1.As the temperature increases,the diffusion and mis-arrangements among these atoms on the particles’ surface gradually extend into the interior of these particles,accompanied by the formation of defects including vacancies and interstitial atoms.The atomic packing becomes disordered.Mg nano-particles with larger particle size have higher transition temperature,and they present higher thermodynamic stability.During the process of continuously heating,the shapes of these Mg nanoparticles change from quasi-sphere to irregular polyhedron.2.When applied external force is small,the changes in these Mg nano-particles only occur near the top and bottom layers being subjected to the force.As the force increases,the atoms in the top and bottom surface layers are pressed into sub-surfaces regions.At unloading the force,the atoms that are pressed into the subsurface regions can back to the original atomic layer.In these processes,the atoms being far away from the surface of these particles are still hold their close-packed hexagonal packing structures.When the force is large,these Mg nano-particles are obviously deformed,and the stacking faults are observed.There exists the structural transition from HCP to FCC in some atoms.The deformation is significantly affected by the loaded force.When the larger external force is unloaded,most the atoms still hold the packing patterns at loading.For these nanoparticles containing more atoms,the external force resulting in the obvious deformation is higher than that applied on these small size particles.