Irshad Hussain Wazir et al. /New Carbon Materials, 2009, 24(1): 83-88 b 1 Fig 2 Polarized light microphotographs of(a) precursor pitch showing the mesophase sphere formation, (b) the longitudinal surface of spun fiber, and(c)the cross section of spun fiber Fig 3 SEM microphotographs of (a) stabilized fiber, (b) carbonized fiber at 1000C and(c)cross sectional area of carbonized fiber with high magnification The isotropic pitch is composed mainly of polyaromatic and the H/C ratio decrease abruptly and C content increase by hydrocarbons along with many aliphatic side-chains. The dis- carbonization. The existence of relatively high concentration ordered phase of the isotropic pitch become more and more of low molecular weight components of alkyl groups can be ordered because of the removal of low weight volatile com- derived from the fact that a high uptake of oxygen(16.5 %) onents during heat treatment. The texture of the graphitizable was found during stabilization tion into liquid crystalline state. The nucleation, growth, and 3.1.2 Melt spinning texturing of the mesophase pitch are strongly dependent upon High performance pitch fibers are preparation method, rheological properties of the precursors, mesophase pitch having liquid-crystal characteristics. The and heat treatment temperaturell6l liquid crystalline in the pitch can be readily oriented to pro- It is considered that mesophase pitch having high mo- duce highly oriented texture of fibers during melt spinning lecular weight components without any side groups or small The resulting fibers in their as-spun and stabilized state show molecular components is difficult to be melt-spun. Therefore, highly oriented X-ray reflections, which are similar to the a mesophase pitch containing a small amount of low molecu-(002)reflection of graphite crystalls). Fig. 2(b)and(c)shows lar weight side groups that cause disordering texture is easier respectively, the as-spun fiber and its cross section under the to be melt-spun to form fibers!7. polarized light microscope. Fig 3(a)and(b) show, respectively, The polished section on glass slide of precursor pitch the cross sections of the stabilized fiber and carbon fiber. The shows the mesophase sphere formation as shown by the carbon fiber showed a typical radial core structure-12, 19). The larized light microscope in the Fig. 2 (a). The precursor pitch transverse texture of the cross-sectional area of the carbon was found to be composed of 75% mass fraction mesophase, fiber under a high magnification is also shown in Fig 3(c), which was successfully melt-spun into fibers. The elemental indicating a typical radial core structure with linear and bent analysis results of samples in the process of carbon fiber for- type anisotropic texture. This structure is also considered to be mation are listed in Table 2. It can be found that C, H, and the dependent upon the spinning conditions and the properties of H/C ratio decreases, whereas N and O increase gradually with the precursor pitch processing before carbonization. The contents of H, N, and O,Arshad Hussain Wazir et al. / New Carbon Materials, 2009, 24(1): 83–88 Fig.2 Polarized light microphotographs of (a) precursor pitch showing the mesophase sphere formation, (b) the longitudinal surface of spun fiber, and (c) the cross section of spun fiber Fig.3 SEM microphotographs of (a) stabilized fiber, (b) carbonized fiber at 1000 o C and (c) cross sectional area of carbonized fiber with high magnification The isotropic pitch is composed mainly of polyaromatic hydrocarbons along with many aliphatic side-chains. The dis￾ordered phase of the isotropic pitch become more and more ordered because of the removal of low weight volatile com￾ponents during heat treatment. The texture of the graphitizable carbon depends upon the material structure during transforma￾tion into liquid crystalline state. The nucleation, growth, and texturing of the mesophase pitch are strongly dependent upon preparation method, rheological properties of the precursors, and heat treatment temperature[16]. It is considered that mesophase pitch having high mo￾lecular weight components without any side groups or small molecular components is difficult to be melt-spun. Therefore, a mesophase pitch containing a small amount of low molecu￾lar weight side groups that cause disordering texture is easier to be melt-spun to form fibers[17]. The polished section on glass slide of precursor pitch shows the mesophase sphere formation as shown by the po￾larized light microscope in the Fig.2(a). The precursor pitch was found to be composed of 75% mass fraction mesophase, which was successfully melt-spun into fibers. The elemental analysis results of samples in the process of carbon fiber for￾mation are listed in Table 2. It can be found that C, H, and the H/C ratio decreases, whereas N and O increase gradually with processing before carbonization. The contents of H, N, and O, and the H/C ratio decrease abruptly and C content increase by carbonization. The existence of relatively high concentration of low molecular weight components of alkyl groups can be derived from the fact that a high uptake of oxygen (16.5 %) was found during stabilization. 3.1.2 Melt spinning High performance pitch fibers are prepared from mesophase pitch having liquid-crystal characteristics. The liquid crystalline in the pitch can be readily oriented to pro￾duce highly oriented texture of fibers during melt spinning. The resulting fibers in their as-spun and stabilized state show highly oriented X-ray reflections, which are similar to the (002) reflection of graphite crystal[18]. Fig.2(b) and (c) shows, respectively, the as-spun fiber and its cross section under the polarized light microscope. Fig.3(a) and (b) show, respectively, the cross sections of the stabilized fiber and carbon fiber. The carbon fiber showed a typical radial core structure[11-12, 19]. The transverse texture of the cross-sectional area of the carbon fiber under a high magnification is also shown in Fig.3(c), indicating a typical radial core structure with linear and bent type anisotropic texture. This structure is also considered to be dependent upon the spinning conditions and the properties of the precursor pitch[20]