Initial Formation Process Of Pyrolytic Carbon And Its Micro Mechanical Properties

Pyrolytic carbon is the name of carbon material deposited on a substrate from the pyrolysis of volatile hydrocarbon at high temperature,which has many important applications in nuclear materials and aerospace industry.However,due to the high temperature,multiple influencing factors and complex reaction pathways during the preparation process,the prepared pyrolytic carbon materials show great dispersion in structure and mechanical properties.Meanwhile,it is difficult to obtain comprehensive and reliable mechanical parameters of pyrolysis carbon through experimental methods directly due to the difficulty of producing pyrolytic carbon in large bulk form,which leads to the inconveniences for the composites'design and investigation.Therefore,it is necessary to study the relationship among its preparation process,micro-structure and mechanical properties,which is crucial for the control of its microstructure and macro performance,as well as the subsequent composites design.In this thesis,the initial deposition process of pyrolytic carbon and effect of interlayer connections on its micro-mechanical properties were studied respectively.Firstly,molecular dynamics simulations with ReaxFF potential were performed to reveal the initial formation process of pyrolytic carbon and analyze the impacts of temperature,gas density and surface defects.Three-layer carbon structure formed during the simulation using propylene as precursor gas,and showed features similar to those of real pyrolytic carbon.At the same time,from some statistical values and the change of carbon rings,we gained a quantified description of the process and discovered two deposition modes.Then,the potential relations between the formed carbon structures in our simulations and the typical pyrolytic carbon structures(SL,RL and ISO)were discussed.Further,based on the formed structure,we created simplified atomic models of pyrolytic carbon which only considered interlayer connection.Subsequently,their mechanical properties were calculated using MD simulations with AIREBO potential.We also discussed the impacts of the number of interlayer connections on the modulus and strength of pyrolytic carbon,and analyzed the deformation modes of different loading orientations.This thesis provided a molecular insight into the specific pyrolysis and deposition process of pyrolytic carbon,and investigated the influence of interlayer connections on the mechanical properties of pyrolytic carbon,which can help us learn more about its formation process and the correlations between its micro-structure and mechanical properties.Meanwhile,the parameters like modulus,strength provided in this thesis would become a reference for the following studies about pyrolytic carbon using methods such as finite element under a larger scale.