Skin-core structure in mesophase pitch-based carbon fibers: causes and prevention Original Research Article

To prohibit skin-core structure from appearing in mesophase pitch based carbon fiber (CF) with a large diameter (30–50 μm), measures such as decreasing oxidation temperature, prolonging holding time and increasing the oxygen partial pressure in the oxidative atmosphere were taken. EPMA (electron probe X-ray micro-analyzer) was utilized to detect the oxygen content distribution along the diameter of oxidized pitch fiber (OF). The transverse structure of OFs and CFs was observed under a scanning electron microscope (SEM). It was found with certainty that the skin-core structure in CFs is caused by steep oxygen content gradient along the diameter of their OFs. The oxygen distribution in OFs was controlled by the oxidative stabilization conditions. In this work, the CF whose precursor fiber had been oxidized at 240°C in a flow of pure oxygen for 10 hours exhibits no skin-core structure and possesses a high tensile strength. The kinetics of stabilization was also studied. It can be concluded that those factors which increase oxygen diffusion or depress oxidative reaction are effective in overcoming skin-core structure in CFs.