Structure and properties of T300 and T700 carbon fibers

The microstructures of T300 and T700 carbon fibers were investigated by scanning electron microscopy, elemental analysis, X-ray diffraction and Raman spectroscopy. Results showed that the surface of T700 was smooth, whereas ridge-like prominences and grooves were much more obvious on the surface of the T300 fibers, indicating that the former were produced by dry-jet wet spinning and the latter by wet spinning. Grain-like features were seen in the cross section areas of both fibers. T700 fibers had a higher carbon content and less nitrogen than did T300 fibers. The difference in microstructure parameters, such as d(002) L-a and L-c, showed that the heat treatment temperature of T700 during manufacture was higher than that of T300. Compared with T300, the preferred orientation parameter Z of T700 fibers was 2.3 degrees lower, the density 2.27% higher and the microvoid volume 7.54% less. Thus it is the densification that produces the higher tensile strength for T700 fibers.