Molecular Dynamics Study On Microstructure Of Pingyao Coke

Coke is an essential raw material for the traditional ironmaking process.Its strength plays an irreplaceable role as a burden support in the blast furnace.A microstructure model for Pingyao coke is established by experimental characterizations combined with the molecular dynamics method based on reactive force field（Reax FF）,and its compression process in the blast furnace environment is also simulated.By analyzing the microstructural changes and the cause during the compression process of the model,the molecular basis of coke strength characteristics is explained.Firstly,the molecular formula C₆₀₄₆₈H₂₁₉₃O₅₂₇N₄₆₈S₄₉ of Pingyao coke obtained by elemental analysis.Then,X-ray photoelectron spectroscopy（XPS）characterization results determined that there are three forms of carbon elements in coke,such as graphitized carbon,aliphatic carbon and linear carbon,as well as their relative proportions.The average stacking number of carbon layers is 7.6 and the average width 58.2 ? are determined by X-ray diffraction（XRD）characterization.Finally,the simulated annealing algorithm is used to obtain the optimized geometry of coke model.The structure of the model is basically consistent with the results of XPS and XRD data.From the model,it can be intuitively observed that the carbon matrix in coke is composed of wrinkled carbon layers.Local structures,non-graphited carbon and stacking-fault structure result in the bending of carbon layer and the increase of carbon layer spacing.To investigate the molecular basis for coke strength,Reax FF simulations are performed for coke compression at 300 K and 3500 K.Results show that the stackingfault structure of wrinkled carbon layers is the main microscopic cause of coke strength.Wrinkled carbon layers can disperse the external force and the stacking-fault structure could effectively restrain interface slippage of carbon layers.Moreover,high temperatures serve the reconstruction process of coke matrix,and then prompt the formation of large and planar carbon layers.The method developed may provide new ideas for further studies in coke structure and its thermal reaction mechanism.Figure 37;Table 4;Reference 70...