Microstructure of mesophase pitch-based carbon fiber and its control unt b 1二口 Fig. 2. Enlarged HR-SEM photographs of the transverse sections in F-A.(a) Micro-domain unit and loop shaped domain e region). (b) Micro-domain unit and linear shaped domain (outer region where less than 10% of fibers carried small cracks F-B also showed the radial orientation of the domains leveloped in the skin area. Radial alignment of in the outer area, whereas no alignment appeared in definitely appeared in the outer area of F-b the even if the degree was poorer than that of F-A. In HR-SEM of small magnification showed approxi- the core area, three isochromatic colors were observed mate radial orientation in the outer area of 1-2 um separately and randomly distributed. It is of value to deep from the surface, reflecting the shallow cracks mention that the blue color of the region, where the No definite orientation was observable in both middle racks were developed, was very strong and homogen- and eous. Although the shape and size of domains were HR-sem of larger magnification showed the size, again hardly distinguished, a SEM photograph of shapes and components of each domain. In the coreMicrostructure of mesophase pitch-based carbon fiber and its control 941 Fig. 2. Enlarged HR-SEM photographs of the transverse sections in F-A. (a) Micro-domain unit and loop shaped domain (core region). (b) Micro-domain unit and linear shaped domain (outer region). where less than 10% of fibers carried small cracks developed in the skin area. Radial alignment of domains definitely appeared in the outer area of F-B even if the degree was poorer than that of F-A. In the core area, three isochromatic colors were observed separately and randomly distributed. It is of value to mention that the blue color of the region, where the cracks were developed, was very strong and homogen￾eous. Although the shape and size of domains were again hardly distinguished, a SEM photograph of F-B also showed the radial orientation of the domains in the outer area, whereas no alignment appeared in the core area. HR-SEM of small magnification showed approxi￾mate radial orientation in the outer area of l-2 pm deep from the surface, reflecting the shallow cracks. No definite orientation was observable in both middle and core areas. HR-SEM of larger magnification showed the size, shapes and components of each domain. In the core