Skin-core structure in mesophase pitch-based carbon fibers: Causes and prevention

To prohibit skin-core structure from appearing in mesophase pitch based car bon fiber (CF) with a large diameter (30-50 mu m), measures such as decreas ing oxidation temperature, prolonging holding time and increasing the oxyge n partial pressure in the oxidative atmosphere were taken. EPMA (electron p robe X-ray micro-analyzer) was utilized to detect the oxygen content distri bution along the diameter of oxidized pitch fiber (OF). The transverse stru cture 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 cause d by steep oxygen content gradient along the diameter of their OFs. The oxy gen distribution in OFs was controlled by the oxidative stabilization condi tions. In this work, the CF whose precursor fiber had been oxidized at 240 degrees C in a flow of pure oxygen for 10 hours exhibits no skin-core struc ture and possesses a high tensile strength. The kinetics of stabilization w as also studied. It can be concluded that those factors which increase oxyg en diffusion or depress oxidative reaction are effective in overcoming skin -core structure in CFs. (C) 1998 Elsevier Science Ltd. All rights reserved.