Application Of Molecular Dynamics In The Study Of Physical And Chemical Properties Of Carbon Materials

Carbon is the most widely distributed and most abundant element on Earth.Because of its diverse electronic orbital characteristics(SP,SP2,and SP3 hybrids),carbon materials have almost all the properties of the earth.Because of its high hardness and strength,diamond is an important grinding material in industry.However,the unclear mechanism of deformation and damage at the nano scale limits its application in ultra precision machining.Carbon nanotubes,which are also excellent in performance,cannot be produced on a large scale because the conversion mechanism is complicated and difficult to control.In this paper,molecular dynamics method is used to study the microstructure evolution mechanism of diamonds after pressure and the mechanism of hydrocarbon pyrolysis to generate carbon nanotubes,and provide theoretical guidance for product performance analysis and safety and reliability evaluation.Firstly,molecular dynamics simulations of nanoindentation on the(010)planes of single crystal diamond was studied using tersoff potential.Load-controlled indentations were performed using a rigid indenter and constant-temperature.The apparent plastic deformation occurred on the specimen(010)surface,the load-depth curve on the(010)plane is shown that no obvious "pop in" phenomenon can be seen and the calculated value Er of diamnd for the(010)plane is 1127.55Gpa.We applied computed tomography(CT)to analysis the micro structure details of the simulation model at the max indentation depth.The deformation after unloading was still remained and the spread orientation of the mismatching atoms,looks like the number key "#" from the vertical view.The relative displacement between the translation region and the lattice distortion region generating a shear force on their interface,and the C-C bond was pulled off,crack emergedThen,we simulates the pyrolysis of C2H4 and C2H6 at temperature of 3500 K and density of 0.1 g/cm3 by molecular reactive force field(ReaxFF),and compared with the simulation data of methane and acetylene.The formations of final product are dependent on number of nucleation centers which were generated at stage I and cyclization model of nucleation centers.The formation of C2H6,C2H4,C2H2 and CH4 undergoes the following stages,that is,hydrocarbon decay,chain elongation and branching,cyclization and polymerization,and condensation and curling.The final product of the four hydrocarbons are different from each other.The decomposition pathways of C2H6,C2H4,C2H2 and CH4 are mainly two kinds of intermolecular collisions and direct decomposition,that is,the CH4 and C2H2 decay dominated by intermolecular collision instead of direct decomposition,the C2H6 decay dominated by direct decomposition,and there is no major reaction to C2H4 decomposition.Besides,the polyyne are found to be stable at our simulation,suggesting that the pyrolysis of hydrocarbons may be a feasible method of producing carbine.