Ko Tse-Hao er al / New Carbon Materials, 2006, 21(4): 297-301 Atomic force microscopy(AFM)was used to further ob- time was 40 min, as shown in Fig. 2(b) and(c). The modified serve the microsurface structure, which indicated the depo- carbon fibers that were produced when the CVd time was tion of a different kind of carbon film on carbon fibers 40 min exhibit rough and densely distributed even islands Fig 2 shows AFM images of the surfaces of the as-received with pellets of approximately 0. 1 um XO.1 um dimensions carbon fibers and the modified ones. Surface morphologies It is proved that the original surfaces of carbon fibers are of as-received fibers are smooth and filled with several strip completely and evenly covered by deposited carbon film, grooves in the direction of the fiber axis in Fig. 2(a). The which, with the increase of deposition time, forms agglom modified carbon fibers that were produced when the Cvd erate on the surface of carbon fibers time was 20 min show nonuniform surface and larger pellets than the unmodified ones that were produced when the CVD Fig2 AFM images of the surfaces of as received carbon fiber and their modified forms (a)as-received carbon fiber, (b)modified carbon fiber C, (c)modified carbon fiber E 3.2 Stacking size and Raman spectra analysis tization. Carbon layer planes are packed side by side to form a basic structure unit(BSU)of graphite fiber 12], and Table 1 summarizes the crystalline parameters of the such structure augments fiber density. In contrast, anothe as-received carbon fibers and their modified forms after factor decreases the density because of the formation of being graphitized at 2700C defects and voids during graphitization Tuinsta and Koenig [13] proposed the first-order Raman Table 1 Crystalline parameters of as-received carbon fibers and spectrum of a graphite single crystal. This spectrum exhib- their modified forms after being graphitize ited a single characteristic line at 1575 cm- that was desig doone Lc /nm La/mR/·l1 nated as G(graphite)band. A second band at 1360 cm was As-received 0.3509 designated as D(defect) band, which becomes equivalent or 0.3449 .76 22.44 even more intense than g band for more disordered solid 0.3480 0.205 The degree of structural order or degree of graphitization(R) with respect to graphite structure is evaluated according to 0.3489 13.26 20.00 0.220 the ratio of integrated intensities of d to G bands (14yThe 0.3511 21.61 0.205 degree of structural order(R)drops, and this drop indicates the pattern of increase of graphitization in carbon materials Microstructural parameters of carbon fibers during heat The degree of structural order of a fiber declines as the eatment were studied by X-ray diffraction and Raman temperature of heat treatment rises[15, 16] spectrum. Scherrer equation was used to calculate the It is now generally accepted that R value shows depend stacking height of graphite planes(Lc, value stacking size) ence on microcrystalline planar size(stack width, La)ac from the 002 diffraction microstructural changes arise from cording to La= 44/R. The stacking width of fiber rapidly microfibril crystallites, showing elongated ribbons at a increases with graphitization temperature, as summarized in graphitization temperature range of 1500-2800C [11. The Table l size of sharp-edged voids among the complex During heat treatment at 2700C, noncrystalline layers three-dimensional interlinked layer planes also increases gradually stack onto a crystalline region. Compared with the with graphitization temperature. The above two factors af- as-received carbon fibers(Lc: 8 nm, La: 23 nm, and R: 0.53) fect the changes in density of graphite fibers during graph their modified forms provide a larger crystalline structureKo Tse-Hao et al. / New Carbon Materials, 2006, 21(4): 297–301 Atomic force microscopy (AFM) was used to further ob￾serve the microsurface structure, which indicated the depo￾sition of a different kind of carbon film on carbon fibers. Fig.2 shows AFM images of the surfaces of the as-received carbon fibers and the modified ones. Surface morphologies of as-received fibers are smooth and filled with several strip grooves in the direction of the fiber axis in Fig.2(a). The modified carbon fibers that were produced when the CVD time was 20 min show nonuniform surface and larger pellets than the unmodified ones that were produced when the CVD time was 40 min, as shown in Fig.2(b) and (c). The modified carbon fibers that were produced when the CVD time was 40 min exhibit rough and densely distributed even islands with pellets of approximately 0.1 µm×0.1 µm dimensions. It is proved that the original surfaces of carbon fibers are completely and evenly covered by deposited carbon film, which, with the increase of deposition time, forms agglom￾erate on the surface of carbon fibers. Fig.2 AFM images of the surfaces of as-received carbon fiber and their modified forms (a) as-received carbon fiber, (b) modified carbon fiber C, (c) modified carbon fiber E 3.2 Stacking size and Raman spectra analysis Table 1 summarizes the crystalline parameters of the as-received carbon fibers and their modified forms after being graphitized at 2700℃. Table 1 Crystalline parameters of as-received carbon fibers and their modified forms after being graphitized. No. d002/ nm Lc /nm La /nm R /ID·IG –1 As-received 0.3509 8.07 8.10 0.538 A 0.3449 12.76 22.44 0.190 B 0.3480 12.18 21.66 0.205 C 0.3479 13.57 21.80 0.205 D 0.3489 13.26 20.00 0.220 E 0.3511 12.64 21.61 0.205 Microstructural parameters of carbon fibers during heat treatment were studied by X-ray diffraction and Raman spectrum. Scherrer equation was used to calculate the stacking height of graphite planes (Lc, value stacking size) from the 002 diffraction. Microstructural changes arise from microfibril crystallites, showing elongated ribbons at a graphitization temperature range of 1500–2800℃ [11]. The size of sharp-edged voids among the complex three-dimensional interlinked layer planes also increases with graphitization temperature. The above two factors af￾fect the changes in density of graphite fibers during graph￾itization. Carbon layer planes are packed side by side to form a basic structure unit (BSU) of graphite fiber [12], and such structure augments fiber density. In contrast, another factor decreases the density because of the formation of defects and voids during graphitization. Tuinsta and Koenig [13] proposed the first-order Raman spectrum of a graphite single crystal. This spectrum exhib￾ited a single characteristic line at 1575 cm–1 that was desig￾nated as G (graphite) band. A second band at 1360 cm–1 was designated as D (defect) band, which becomes equivalent or even more intense than G band for more disordered solid. The degree of structural order or degree of graphitization (R) with respect to graphite structure is evaluated according to the ratio of integrated intensities of D to G bands [14]. The degree of structural order (R) drops, and this drop indicates the pattern of increase of graphitization in carbon materials. The degree of structural order of a fiber declines as the temperature of heat treatment rises [15,16]. It is now generally accepted that R value shows depend￾ence on microcrystalline planar size (stack width, La) ac￾cording to La = 44/R. The stacking width of fiber rapidly increases with graphitization temperature, as summarized in Table 1. During heat treatment at 2700℃, noncrystalline layers gradually stack onto a crystalline region. Compared with the as-received carbon fibers (Lc: 8 nm, La: 23 nm, and R: 0.53), their modified forms provide a larger crystalline structure