What is Needle Coke?
Needle coke is derived from premium-quality residual oil that are low in sulfur and ash, while rich in aromatics and low in resins and asphaltenes. Its surface displays distinct striations, and the internal structure features elongated, oval-shaped pores arranged in a uniform orientation. When fractured, the material breaks into slender, needle-like particles. After graphitization, needle coke demonstrates exceptionally low coefficients of thermal expansion and electrical resistivity, making it an indispensable raw material for the production of high-power (HP) and ultra-high-power (UHP) graphite electrodes.
Classification of Needle Coke
There are two types of needle coke. One is petroleum-based needle coke produced using petroleum residual oil as the raw material, and the other is pitch-based needle coke (also known as coal-based needle coke) produced with refined coal tar pitch.
Structure of Needle Coke
In appearance, needle coke exhibits distinct fibrous textures. Under a polarizing microscope, sections cut parallel to the fibrous orientation reveal predominantly anisotropic fibrous structures, along with some highly anisotropic lamellar textures. In contrast, sections cut perpendicular to the fiber direction display anisotropic mosaic structures (see Figures as follows).
Micrograph of Needle Coke Microstructure (Parallel Section)
As a result, needle coke demonstrates pronounced anisotropy in its physical and mechanical properties. Along the longitudinal axis of the particles, it possesses excellent electrical and thermal conductivity, as well as a relatively low coefficient of thermal expansion. During extrusion molding, most particle long axes are oriented along the extrusion direction.
