MICROSTRUCTURE OF MESOPHASE PITCH-BASED CARBON-FIBER AND ITS CONTROL

The macro as well as microscopic structure of four mesophase pitch-bas ed carbon fibers of typical textures is observed using optical, scanni ng electron, transmission electron, and scanning tunneling microscopes . The four fibers had transverse textures of radial, radial-skin/rando m-core, random and quasi-onion. High resolution SEM clarified the doma ins to have typical shapes of linear, bent, multi-fold bent and loop. The shapes and alignment of the domains depended upon the spinning con ditions and mesophase pitch properties, which defined the texture in a rather complex manner, varying in the transverse locations of the fib ers of any overall textures. Each domain appeared to possess micro-dom ains which were arranged to define the size and shape of the domain. T he shape of the micro-domains was basically unchanged by carbonization and graphitization, while the carbon plane cluster, or graphitic unit grew during carbonization and graphitization within the micro-domain. Such crystal growth brings about shrinkage of the micro-domain to cha nge the size of the domains, strongly influencing overall structure an d the properties of the carbon and graphitized fibers. The unique plea t shaped structural units, which are aligned in a zig-zag manner in th e longitudinal section of the carbon and graphitized fibers, were foun d by high resolution SEM and STM. Such structures were formed in the s pinning step with the fiber of liquid crystal polymers and mesophase p itch-based carbon fiber. Neither PAN, isotropic pitch-based fibers nor needle coke exhibited such a structure. The size and alignment in the pleat-like structure were also dependent upon the nature of mesophase pitch and spinning conditions, although the formation mechanism is no t clarified yet. Such overall structure is briefly compared to the pro perties of the carbon fiber to find guidelines for the preparation of carbon fibers with better performances. Copyright (C) 1996 Elsevier Sc ience Ltd