Needle Coke The Main Raw Material of Graphite Electrode Research
Needle coke is an important raw material for the preparation of high-power graphite electrodes (HP), ultra-high-power graphite electrodes (UHP) and other carbon products. It has the obvious advantages of low sulfur, low ash content, high density, good electrical conductivity, easy graphitization and low thermal expansion coefficient. The significant advantage is that with the deepening of needle coke research, it has been found that the nature of the raw material has an important impact on the quality of needle coke, especially the formation, growth and melting of the mesophase. Therefore, the research of raw materials of needle coke has gradually become the focus of the research of needle coke. Stock and so on proposed that the raw materials of high-quality needle coke should at least meet the following requirements: Density≥1.02 g/cm3; Ash content≤0.05%; Sulfur content<0.5%; Insoluble matter QI<0.1%; organic content<50 mg/kg; shackle content<50 mg/kg; aromatic compounding degree (BMCI)>120. Therefore, we fully understand the influence of raw material properties on mesophase formation and needle coke structure, It has important guiding significance for the preparation of high-quality needle coke.
1 Mesophase formation mechanism
In the process of preparing needle coke, the formation, growth and fusion of the mesophase are very important. Brooks and Taylor first proposed the concept of mesophase. In 1985, the International Committee on Carbon Characterization and Terminology officially named the mesophase formed in the carbonization system. It is the carbonaceous mesophase (carbonaceous mesophase). A large number of scholars have supplemented and perfected the formation mechanism of the carbonaceous mesophase in the liquid phase carbonization theory, and laid the foundation for different mesophase principles.
In the liquid phase carbonization theory, the formation mechanism of the mesophase is described as: As the temperature rises, the materials in the raw materials undergo reactions such as dehydrogenation condensation, cyclization, and aromatic ring formation to gradually form a large molecular weight aromatic ring fused-ring planar molecular structure. Under the action of thermal motion, plane molecules are stacked in the vertical direction due to VDW(Van der Waals' force) and intermolecular dipole moment to form colloidal particles. Under the action of surface tension, a new phase of anisotropic, flowing, spherical liquid crystal is formed. — Mesophase ball (as shown in the figure 1), the small ball continuously absorbs the aromatic molecules in the isotropic matrix from the pitch and gradually grows up. When the grown spheres contact each other, the flat molecules of each sphere insert and fuse each other to form a larger sphere (reballing), and form an intermediate phase after repeated fusion and collision.
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