| Needle coke, with low coefficient of thermal expansion (CTE), low sulfur, low ash, low metal content, high conductivity, high oxidation resistance, high surface area and a series of excellent quality, is one of the most important carbon materials, which has been developing greatly since the1950s. This new carbon material is being widely applied to following fields:energy source, industrial, national defense, environment protection and so on. Until now, only a small number of nations such as United States, England and Japan are able to produce the needle coke that could be used as the graphite anode for ultra high power electric furnace. However, their manufacturing techniques are all highly confidential, which lead to the trading market in concentration. In the late1970s, we began to research the techniques of making needle coke independently because of the UHP had presented a higher request to its aggregate. We have been studying this technique for more than forty years, but can not learn about the precursor clearly and there is no real product. The needle coke used for making electrode in domestic steel mills could only rely on import, which restricted our Electric furnace steelmaking technology developing to a larger scale. Therefore, how to produce the needle coke of high quality under the restricted condition is still a meaningful topic.In this paper, the medium temperature coal tar pitch with quinoline insoluble compounds removed was used as raw material to preparing coal-based needle coke in a home-made pressure vessel. In the process of preparation, changed the temperature and pressure or mixed different additives or applied magnetic field to the whole system, to discuss the structure and properties of needle coke. The samples were characterized by SEM (Scanning Electron Microscope), XRD (X-Ray Diffraction), Polarizing Microscope, FT-IR, CV (Cyclic Voltammetry) and EIS (Electrochemical Impedance Spectroscopy) analysis.The conclusions are drawn as follows:The coal-tar pitch needle coke prepared at appropriate pressure condition will obtain the better performance. In this study, it has shown that the pressure of0.4MPa is more favorable for the growth and fusion of the mesophase. Whether the pressure is too low or high, it is not conductive to the extension of the graphite along with the X-Y plane and the formation of the needle-like fibrous structure.The maximum temperature of520℃is the best. At this condition, the system temperature is high enough for the thermal polymerization. The mesophase molecules achieve its required size along with a large number of gas escapes from the system. When the mesophase pitch in the definition phase, there is enough shear force effect on it, which make the needle-like structure much more tightening. In a word, this is the synergy of temperature and pressure. Both the results of EIS and CV have illustrated that the needle coke had the best electrochemical properties when the maximum pressure is0.4MPa and the maximum temperature was520℃.Blended conductive black or nature flake graphite into the raw material did not have a positive impact on generating orderly structure as expected. Mixing this kind of additive hindered the formation and growing of mesophase to some extent, affected the order of needle coke and made the electrochemical reversibility eventually.The magnetic field and additive worked on the carbonization system simultaneously could improve the order of needle coke efficiently. In this condition, the needle coke prepared was much better than the one that prepared by the coal tar pitch only or by the mixture of coal tar pitch and additive. Under the effect of magnetic, the mesophase molecules were oriented further along the direction of magnetic field and showed a better needle-like fiber structure. |
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