The Influence Of Magnetic Temperature And Coke Particles On The Structure And Properties Of Needle Coke During Carbonization

As a kind of new carbon material, needle coke has the properties of low resistivity, low thermal expansion coefficient, strong antioxidant properties, good thermal shock resistance and high strength, which is the important raw material manufacturing high power and ultra high power graphite electrode, and has great application prospect in the field of super capacitor and high-energy secondary batteries. The development of needle coke technology started late in China, and domestic needle coke has certain difference comparing with that imported. Due to the monopoly of foreign technology, the price was enslaved to them. Therefore, we should accelerate the study of needle coke production technology, and reverse the situation in the domestic and foreign needle coke market, which has great significance on the development of China’s metallurgical industry and heavy industry.This thesis used medium temperature coal-tar pitch with quinoline insoluble compounds removed as raw material to prepare needle coke by thermal polymerization and high-temperature calcination, and probed into the influence of magnetic temperature and coke particles during carbonization on the structure and properties of needle coke though magnetizing at different temperature and adding coke particles. The morphology and structure characteristics of needle coke were analyzed by scanning electron microscope (SEM), polarizing microscope and X-ray diffraction (XRD), and the chemical composition and electrochemical performance were tested by infrared spectroscopy analysis, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results show that:(1) The morphology and structures of needle coke prepared at different magnetic temperature had different degrees of difference. The orientation effect of magnetic field was more obvious when the magnetic temperature was close to420℃. And the sample prepared at420℃magnetic temperature had the densest crystal structure, the highest degree of crystallinity, the best order and orientation, and the graphitization degree getting greatly enhancement.(2) The needle coke prepared at420℃magnetic temperature had the largest capacitance, stronger energy storage performance, better electrochemical stability and discharge reversibility. The electrochemical impedance spectroscopy of sample approximated ideal capacitor. The electrode emerged higher electrochemical activity, better transitivity and smaller internal resistance. Meanwhile it exhibited better capacitor characteristics and power characteristics.(3) Coke particles could increase the needle coke microcrystalline layer spacing and promote the generation of the lamellar structure in a certain extent. At the same time the particles hindered the formation and merging of mesophase spherule, resulted in the needle-like fiber structure continuity poorer, and produced a number of microcrystalline fragments. Further more the crystallinity and graphitization degree of needle coke was reduced.(4) Mixing a small amount of coke particles in the asphalt raw material was not only conducive to enhancing the permeation of the electrolyte solution in the needle coke electrode, but also could promote the ability to charge mobile and transmission, enhance the capacitance of electrode and reduce its internal resistance. But if the coke ratio in the raw material is too high, it will seriously hamper the formation and growth of mesophase spherule, and restrict the electrochemical performance of needle coke.(5) The order and degree of crystallinity of needle coke which prepared with mixing coke in the asphalt raw material under magnetic field were markedly improved. But the microcrystalline layer spacing was increased because of coke, which gave rise to fibrous tissue structure loose arrangement of needle coke and leaded to ceramic fragments and crack increasing, and the strength of needle coke was decreased.