I MOcHIDA et al SK Fig. 7. Enlarged HR-SEM image of the longitudinal section in F-C assemble to form the clusters under 10 nm in their able in the viscous How through the nozzle, ma crystalline height and length, as revealed by X-ray define the micro-domains from which domain assem [23]. Such clusters may gather to form the micro- bles. So far, micro-domains and domain units are not of mSuch micro-domains also observable in the mesophase pitch before the spin- gather to form above 100 nm, as also found ning. The optical unit assessed by an optical micro- uch units have never been scope appears to be too large to define such micro obtains a fiber form in the spinning nozzle pitch structural units entified in the pitch. When the mesophase At the outlet of the nozzle hole, the extrudate is structural units are deformed in their shapes and wound up into a fiber form in the atmosphere during according to the flow patler articular distribution the spinning. The stable alignment of aromatic plane sizes, and rearranged rns of clusters in the may differ in contact with either nozzle wall or atmo iscous flow under the interaction with the nozzle sphere, and their rearrangement may take place after all. Table 4 summarizes the changes of microstruc- the outlet (defined as die- swelling) while the fiber is tural and crystallographic units due to final heat deformable [25]. During such a rearrangement, the treatment temperature structural units of the mesophase pitch may change The size of clusters formed either increases or their alignment probably maintaining their dimensions decreases during spinning according to the mesophase Thus, the basic alignment is introduced at the pitch precursors. MNP showed a small decrease in spinning step. The stabilization fixes such an align s valuc of Lc(002), whcrcas NP showed a small ment. Carbonization and graphitization promote increase after the spinning. The extent of change is layer stacking of the carbon planes in terms of their ery dependent upon the shear stress(pressure in stacking height, reduce the interlayer spacing and xtruding ). The mNP pitch fiber extruded at 1.3 atm enlarges the plane width, allowing the development showed a la (002)values of 6.0-6.7 nm than of the graphitic structure. Such a crystalline growth the 4.0-4.5 nm of that extruded at 12.0 atm. the affects the size and shape of clusters in the micro- reduction of the apparent viscosity by increasing the domains, though the shrinkage due to the graphitiza- shear rate [24]is further evidence for the deformation tion which happens with the evolution of volatile of the cluster. It is not clarified yet whether the micro- matter and the microscopic densification may also domain units present in the mesophase deform, or influence them. Oberlin et al. reported that the anso y clusters assemble to form micro-domains of particular of the graphitic grain (cluster) boundary change shape and size according to the nature of the meso- from around 90-120 after the graphitization phase pitch and spinning conditions, including the carbonized fiber at 2700C [8]. Thus, during graphit nozzle material and dimension. The size, shape, flow ization the clusters grow and coalesce to form a large rate and direction of the cluster, which are all change- crystal within the micro-durmainl, even if the clusteRs952 1. MOCHIDA et al. Fig. 7. Enlarged HR-SEM image of the longitudinal section in F-C. assemble to form the clusters under 10 nm in their crystalline height and length, as revealed by X-ray [23]. Such clusters may gather to form the micro￾domains of ca. l-200 nm. Such micro-domains also gather to form domains above 100 nm, as also found in the fiber, although such units have never been identified in the pitch. When the mesophase pitch obtains a fiber form in the spinning nozzle, such structural units are deformed in their shapes and sizes, and rearranged in a particular distribution according to the flow patterns of clusters in the viscous flow under the interaction with the nozzle wall. Table 4 summarizes the changes of microstruc￾tural and crystallographic units due to final heat treatment temperature. The size of clusters formed either increases or decreases during spinning according to the mesophase pitch precursors. MNP showed a small decrease in its value of Lc(OO2), whereas NP showed a small increase after the spinning. The extent of change is very dependent upon the shear stress (pressure in extruding). The MNP pitch fiber extruded at 1.3 atm showed a larger Lc(OO2) values of 6.0-6.7 nm than the 4.0-4.5 nm of that extruded at 12.0 atm. The reduction of the apparent viscosity by increasing the shear rate [24] is further evidence for the deformation of the cluster. It is not clarified yet whether the micro￾domain units present in the mesophase deform, or clusters assemble to form micro-domains of particular shape and size according to the nature of the meso￾phase pitch and spinning conditions, including the nozzle material and dimension. The size, shape, flow rate and direction of the cluster, which are all change￾able in the viscous flow through the nozzle, may define the micro-domains from which domain assem￾bles. So far, micro-domains and domain units are not observable in the mesophase pitch before the spin￾ning. The optical unit assessed by an optical micro￾scope appears to be too large to define such micro structural units. At the outlet of the nozzle hole, the extrudate is wound up into a fiber form in the atmosphere during the spinning. The stable alignment of aromatic plane may differ in contact with either nozzle wall or atmo￾sphere, and their rearrangement may take place after the outlet (defined as die-swelling) while the fiber is deformable [25]. During such a rearrangement, the structural units of the mesophase pitch may change their alignment, probably maintaining their dimensions. Thus, the basic alignment is introduced at the spinning step. The stabilization fixes such an align￾ment. Carbonization and graphitization promote layer stacking of the carbon planes in terms of their stacking height, reduce the interlayer spacing and enlarges the plane width, allowing the development of the graphitic structure. Such a crystalline growth affects the size and shape of clusters in the micro￾domains, though the shrinkage due to the graphitiza￾tion which happens with the evolution of volatile matter and the microscopic densification may also influence them. Oberlin et al. reported that the angle of the graphitic grain (cluster) boundary changed from around 90-120” after the graphitization of carbonized fiber at 2700°C [S]. Thus, during graphit￾ization the clusters grow and coalesce to form a large crystal within the micro-domain, even if the clusters