A Structural Study of the Oxidized High Modulus Pitch Based Carbon Fibers by Oxidation in Carbon Dioxide

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A Structural Study of the Oxidized High Modulus Pitch Based Carbon Fibers by Oxidation in Carbon Dioxide

Jae-Seung Roh

NN

Department of Materials Engineering, Chungnam National University, Daejeon 305-764, Korea

(Received October 5, 2003; Accepted October 28, 2003)

Abstract

Structural changes of high modulus carbon fiber by oxidation in carbon dioxide gas using SEM, TEM, and XRD have been observed. It was shown that the originally high modulus carbon fiber is composed of highly ordered gra- phitic crystalline area and non-crystalline area. It was observed that the La increases during the whole oxidation pro- cess. It was shown that the oxidation of high modulus carbon fiber initiates at the non-crystalline area and at the ends of fiber. The large pores developed in fiber by direction of fiber length at high temperature (1,100°C), and the small pores developed on the fiber surface at low temperature (900°C). In conclusion, it is found that the oxidation of the carbon fiber was progressed through the imperfection.

Keywords: high modulus carbon fiber, oxidation, SEM, TEM, XRD

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Table 3. Structural parameters of high modulus carbon fibers as a function of burn-offs

Burn-off (%)

d002

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d100

(Å)

Lc (Å)

La

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Fig. 10. SEM photographs of oxidized fiber in carbon dioxide gas at 900°C. The degree of burn-off is 51%: (a) cross-section and (b) fiber surface.

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References

[1] Marsh, H.; Rodriguez-Reinoso, F. Science of Carbon Materials, Universidad de Alicante, Alfredo Candela, 2000, 8.

[2] Endo, M.; Kim, C.; Kasai, T.; Mathews, M. J.; Brown, S.

D. M.; Dresselhaus, M. S.; Tamaki, T.; Nishimura, Y. Car- bon 1998, 36, 1633.

[3] Hong, S. H.; Korai, Y.; Mochida, I. Carbon 2000, 38, 805.

[4] Montes-Moran, M. A.; Young, R. J. Carbon 2002, 40, 845.

[5] Donnet, J. B.; Bansal, R. C. Carbon Fibers, 2nd ed., Mar- cel Decker, inc., 1990, 8.

[6] Donnet, J. B.; Bansal, R. C. Carbon Fibers, 2nd ed., Mar- cel Decker, inc., 1990, 128.

[7] Sharma, A.; Kyotani, T.; Tomita, A. Carbon 2000, 38, 1977.

[8] Kovalevski, V. V.; Buseck, P. R.; Cowley, J. M. Carbon 2001, 39, 243.

[9] Senneca, O.; Salatino, P.; Masi, S. Fuel 1998, 77, 1483.

[10] Busyin, R. M.; Rouzaud, J. N.; Ross, J. V. Carbon 1995, 33, 679.

[11] Marsh, H.; Reinoso, F. R. Science of Carbon Materials,

Universidad de Alicante, Alfredo Candela, 2000, 379.

[12] Mattson, J. S.; Mark, H. B. Jr. Activated Carbon, Marcel Decker, New York, 1971, 20.

[13] Yoshizawa, N.; Maruyama, K.; Yamada, Y.; Zielinska-Bla- jet, M. Fuel 2000, 79, 1461.

[14] Ryu, Z.; Rong, H.; Zheng, J.; Wang, M.; Zhang, B. Car- bon 2002, 40, 1131.

[15] Chang, Q.; Liu, T.; Cal, X. In Proceeding 22nd Biennial Conference in Carbon, 1995, 514.

[16] Yoshizawa, N.; Yamada, Y.; Shiraishi, M. J. Mater. Sci.

1998, 33, 199.

[17] Huttepain, M.; Oberlin, A. Carbon 1990, 28, 103.

[18] Sha, X. Z.; Kyotani, T.; Tomita, A. Fuel 1990, 69, 1564.

[19] Biscoe, J.; Warren, B. E. J. of Applied Physics 1942, 13, 364.

[20] Kercher, A. K.; N. Dennis, C. Carbon 2003, 41, 15.

[21] Schukin, L. I.; Kornievich, M. V.; Vartapetjan, R. S.;

Beznisko, S. I. Carbon 2002, 40, 2021.

[22] Lu, S.; Blanco, C.; Rand, B. Carbon 2002, 40.

[23] Hong, S. H.; Korai, Y.; Mochida, I. Carbon 1996, 34, 86.

[24] Dobb, M. G.; Guo, H.; Johnson, D. J.; Park, C. R. Carbon 1995, 38, 1553.