The effect of the oxygen concentration of stabilization atmosphere on the radial structure of polyacrylonitrile (PAN) stabilized fibers and the resulting carbon fibers (CFs) was investigated quantitatively by means of X-ray energy dispersive spectrometer

infrared spectrum analysis

microscopic laser Raman spectrometer and electron spin resonance.Results reveal that with the increase of the volume concentration of oxygen(Vo)

radial structure of PAN stabilized fibers tends to be more homogeneous as a consequence of the stronger transferring of oxygen into fiber interior.When Vo increases from 20.38% to 21.15%

an obvious decrease in the radial skin-core structure and a rapid increase in the cyclization degree of PAN stabilized fibers are observed; meanwhile

the porosity of the resulting CFs is decreased and the tensile strength is increased.This condition is demonstrated to be beneficial to form turbostratic graphite structure in the skin region of CFs during the carbonization.In the case of Vo is greater than 21.34%

the radial shin-core structure is almost disappeared in the PAN stabilized fibers

however

the increase of the cyclization degree turns into much slower

which impedes the formation of turbostratic graphite structure in the skin region of the resulting CFs and gives rise to the increase of the porosity and decrease of the tensile strength.When Vo is dominated between 21.15% and 21.34%

the cyclization and the homogenization of radial structure of PAN stabilized fibers are both facilitated.Meanwhile

the turbostratic graphite structure is increasing in the core and is keeping at a much higher degree in the skin of CFs

enabling a 12.22% increase in tensile strength of the resulting CFs compared to the one obtained from regular air atmosphere.