STABILIZATION AND CARBONIZATION OF PAN-BASED CARBON-FIBERS AS RELATED TO MECHANICAL-PROPERTIES

Fibers studied in this paper underwent two types of carbonizations: slow pyrolyses at 4-degrees-C/min and "pilot" rapid carbonizations under tension. These products were characterized by elemental analysis, transmission electron microscopy, X-ray diffraction and tensile mechanical properties. A classification of stabilized precursors is sought, directly through X-ray diffraction data, and indirectly through microtexture and mechanical properties of fibers heat-treated at 1000-degrees-C (4-degrees-C/min). For classifying "pilot" carbonized fibers, not only their transversal and longitudinal close-packing degree are to be taken into account, but also the degree of organization of carbonaceous layers. Studying precursors at various stages of carbonization enhances the role of elemental composition of the fiber at the moment local molecular orientation (LMO) settles. From this moment microtexture is virtually fixed and only minor reorganizations are likely to occur. In particular, the amount of nitrogen remaining available at LMO is of utmost importance. As (N/C) atomic ratio is found to be related to (H/C)at, it is thought that an equilibrium should be found: LMO should occur at a temperature such as a high amount of nitrogen remains available, and the flexibility of the carbon skeleton be kept as late as possible during carbonization. This excludes any too early formation of this skeleton.