Structure of Mesophase-Pitch Carbon Fibers

Cross Section. The cross-section structure of mesophase-pitch carbon fibers is one of the four types shown in Fig. 8.12 and is determined by the spinning method, the temperature of stabilization, and the partial pressure of oxygen.The formation of a skin-core structure or skin effect is often observed. This structure is similar to that of the PAN-based carbon fiber shown In Fig. 8.8 above. 

Radial Onion-Skin Onion-Skin Onion-Skin 

Interiayer Spacing and Crystallite Size. The increase of the apparent crystaliite size of mesophase-pitch fibers as a function of heat-treatment is shown in Fig. 8.7, and the decrease of the interlayer spacing (c spacing) in Fig.8.9.I The spacing of the heat-treated fiber is relatively close to that of the ideal graphite crystal ( 0.340 nm vs. 0.3355 nm), indicating a decreased turbostratic stacking of the basal planes and a well-ordered structure. In this respect, the difference between these fibers and the PAN-based fibers is pronounced. 

However, this high degree of crystallinity also results in low shear and compressive strengths. In addition, these carbon fibers tend to have flaws such as pits, scratches, striations, and flutes. These flaws are detrimental to tensile properties but do not essentially affect the modulus and the thermal conductivity.  

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