Effect Of Graphene Size On Formation Of Mesophase Phase And Nucleation Mechanism

High-quality mesophase pitch is an indispensable precursor masterbatch for many high-performance carbon materials(such as high thermal conductivity carbon fiber,high thermal conductivity foam carbon,etc.),and is widely used in the aerospace industry,weapon equipment,high-end manufacturing,and other fields.Given the military application background of many mesophase pitches and their carbon materials,the United States,Japan,and other countries have imposed strict technology and product blockades on our country,which has severely restricted the development of our country’s high-end equipment industry.In recent years,some domestic units have also prepared mesophase pitch and high thermal conductivity carbon fibers,but their performance still lags far behind related foreign products.Part of the reason is that the key technologies and equipment are not up to standard,and there is little experience.In addition,some basic problems are not clear,such as the formation mechanism from aromatic hydrocarbons to mesophase.In this paper,the refined coal pitch with low ash content is used as the raw material,and graphene nanosheets of different sizes are used as nucleating agents.The role of mesophase pitch in the formation process,a two-step nucleation mechanism in the formation of mesophase pitch is proposed.Finally,the applicability of the obtained conclusions was explored again with petroleum pitch and methyl naphthalene pitch.First,by exploring the effects of reaction temperature,holding time,system pressure,and the amount of graphene nanosheets on the thermal polycondensation reaction of mesophase pitch,optimized basic reaction conditions were obtained.The results show that when the reaction temperature is 410 °C,the temperature is kept for 5 hours,and 0.01 wt% graphene nanosheets are added,and the system maintains the autogenous pressure,more mesophase structures can be obtained,which are more suitable for the next stage of exploration.Then,based on optimizing the reaction conditions,the size of graphene nanosheets was changed to explore the role of their size in the formation of mesophase pitch.The results show that with the decrease of the size of graphene nanosheets,the mesophase content of the obtained product gradually increases,and the microcrystalline structure also becomes more regular.In addition,data analysis shows that the crystallization nucleation of planar aromatic macromolecules is a two-step reaction nucleation process: during the nucleation of mesophase pitch,planar aromatic macromolecules first form clusters with high density but disordered internal molecular arrangements,and then The molecules in the cluster rearrange into regular nuclei,and then slowly grow into a continuous mesophase.Finally,considering the difference in the molecular structure of refined coal pitch,petroleum pitch,and naphthalene pitch,this experiment further used petroleum pitch and naphthalene pitch as raw materials to explore the effect of the size of graphene nanosheets The mechanism of action of phase formation.The results show that although there are certain differences in the molecular structures of the three pitches,the graphene nanosheets are more consistent in the process of promoting the transformation of pitch to mesophase,especially promoting nucleation,that is,as the size decreases,it is beneficial to the increase of the mesophase content of the product.In summary,graphene nanosheets have a positive effect on the thermal polycondensation of coal pitch,petroleum pitch,and naphthalene pitch to form mesophase pitch.The research in this paper will further reveal the formation mechanism of mesophase pitch,and make a little contribution to the development of mesophase pitch and its high-end carbon material industry.