Theoretical Study On Mixed System Of Nano-AlH₃ And Nitro Compounds

Metal hydrides have excellent hydrogen storage capacity and high combustion heat value,and are expected to have good applications in the field of energetic materials.Research on the application of metal hydrides in high composite explosives was still limited up to now.Therefore,it is of great importance to study the interactions between metal hydrides and explosives.In present research,the surface properties of metal hydrides and their effects on the thermal decomposition properties of several common nitro compounds were studied theoretically.Firstly,based on the first principle of density functional theory,the surface energy and density of states of seven low-index surfaces of alpha-AlH₃,MgH₂ and LiH metal hydrides were calculated.The binding energy of aluminum hydride and magnesium hydride to the classic explosives RDX and TNT was studied by molecular dynamics simulation.The results show that the surface energy of AlH₃?010?surface is 0.72 J m^-2,with the largest energy gap and the best stability.Both RDX and TNT have the highest bonding strength with AlH₃?001?surface,more hydrogen bonds were formed by H atoms of AlH₃?001?surface and the nitro group on the explosive,which enhances the interactions between AlH₃ and explosives.Molecular dynamic simulation of a high explosive RDX mixed with AlH₃ nanoparticles were performed by a newly parameterized ReaxFF force field.Testing of the ReaxFF shows that the mean absolute error of the densities and bond lengths between calculated and experimental values are less than 7%and 3%,respectively.Using the ReaxFF,effects of AlH₃nanoparticles with different radii on the thermal decomposition of RDX were revealed.A new mechanism of the generation and the consumption of H₂ were discovered in the explosion.The H₂ was released by AlH₃ firstly and then it reacts with NO₂ and CO₂ from the decomposition of RDX,leading to the increase of H₂O,NO and CO.The number of produced H₂O and CO₂ molecules increase by 10.38%and 56.85%,respectively,when the radius of AlH₃ nanoparticles decreases from 1.10 to 0.68 nm.This showed that the RDX decomposes more completely with the smaller AlH₃ nanoparticles,which was further demonstrated by the analysis of reaction residues and the diffusion coefficients.Finally,the thermal decomposition of nano-AlH₃ and CL-20 composite systems at five different temperatures were studied by reactive molecular dynamics simulation.The evolution of structures and chemical species during thermal decomposition process was studied;the change of potential energy was analyzed;the mean square displacement and diffusion coefficient of different atoms in the system were calculated and analyzed.The results show that the interface between the nano-AlH₃ sphere and the CL-20 molecules exhibits a higher temperature due to the adsorption,while the CL-20 molecule that is not in contact with AlH₃at a long distance exhibits a relatively low temperature.In the initial heating stage,the formation of the R-NO₂-Al structure promotes the detachment of the nitro group from CL-20molecules.When temperature rising from 2000 K to 4000 K,the cracking time of all CL-20molecule is advance from 75 ps to 43 ps.In addition,the formation rate and final number of the main stable products N₂,CO₂ and CO increased with the rising of temperature.As the temperature increases,the potential energy decreases more rapidly,and the final potential energy decreases.It shows that the relatively high temperature promotes CL-20decomposition in a short time,and the explosives decompose more completely.