Study On Preparation And Properties Of Coal-Based Needle Coke In Magnetic Field

Petroleum-based needle coke was first invented by American Great Lake Carbon Corporation in 1950. After the appearance of smelting technology used in ultra high power (UHP) electric furnace in 1969, the industrialized production of needle coke as the main raw material used for UHP electrode developed rapidly. Needle coke has the properties of obvious needle-like structure, fiber texture, low coefficient of thermal expansion (CTE), low porosity, low sulfur, low ash, low metal content, high conductivity and high graphitization degree. As a kind of high-quality raw material, it can be used to produce ultra-high power electrodes, special carbon materials, carbon fiber, carbon composite materials and other advanced carbon products. Coal-based needle coke, compared to petroleum-based needle coke, has a lower coefficient of thermal expansion (CTE) and higher real density. However, the CTE is the most important property of needle coke. Currently, coal-based needle coke can be produced only in Japan. The annual demand for needle coke is about 300～400 thousand ton in China and 80% to 90% is dependent on imports.This paper used medium temperature coal tar pitch with quinoline insoluble compounds removed as raw material to prepare coal-based needle coke in the form of changing preparation technology and adding catalysts through thermal condensation and high temperature calcination. The changes in the morphology and properties of needle coke prepared under the effect of magnetic field were investigated. The formation mechanism, structures and properties of different needle coke were further studied under the condition of ultrasound activation synthesis and catalytic synthesis. Sample analysis uses SEM, EDS, XRD, FT-IR, CV and EIS.The results show that:1. The effect of magnetic field on the preparation of needle coke was positive, which could effectively improve the ordered degree of needle coke and its pattern of fibrous tissue. And the degree of order was increasing with increased magnetic induction. The introduction of the magnetic field made the average crystallite size of needle coke decrease, graphite-based performances improve, density increase and transmittance reduce. When the magnetic induction of the magnetic field is 22mT, graphitization degree can be up to 45.35%.2. It is resulted that ultrasonic cavitation can effectively increase the order degree, graphitization degree and crystallinity of needle coke. Needle coke prepared with ultrasonic cavitation treatment and calcined at 1200℃formed larger planar molecules layers after planar molecules stack. And more scroll-like fibers appeared. 3. After adding ferric chloride (FeCl3), tosylate (PTSA) and hexamethylenetetramine (HMTA) to coal-tar pitch, needle coke with a large layer of fibrous was generated through polymerization and calcination. With the effect of magnetic field, plane macromolecules were oriented fatherly along the direction of magnetic field, which showed a better needle-like fiber structure.4. Peak current in cyclic voltammograms of needle coke prepared in magnetic field showed a declining trend. As magnetic induction of the magnetic field increased, the electrochemical capacitance arc radius of sample needle coke showed an increasing trend. And its transmission resistance increased.5. The oxidation peak in cyclic voltammograms of needle coke prepared through adding FeCl3 in magnetic field was the highest, whose current value increased by 78.6% in comparison with that of sample prepared without magnetic field or the catalyst. And its electrochemical transitivity is the best with minimum surface roughness and the lowest resistivity.6. It is illustrated from the cyclic voltammograms of needle coke prepared through adding PTSA and HMTA that electrostatic adsorption is the main form of electrode storage. After adding the magnetic field, the electrochemical activity of needle coke increased. Process of the electrode reaction changed from diffusion into the electrochemical control.