Microstructural control of pitch matrix carbon-carbon composite by iodine treatment
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Microstructural control of pitch matrix carbon-carbon composite by iodine treatment H. Kajiura,a) Y. Tanabe, and E. Yasuda Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226, Japan
A. Kaiho and I. Shiota Department of Chemical Engineering, Kogakuin University, Nakano, Hachioji, Tokyo 192, Japan
S. Yamada Faculty of Science and Engineering, Teikyo University of Science and Technology, Yatsuzawa, Uenohara, Kitatsuru-gun, Yamanashi 409, Japan (Received 9 October 1996; accepted 15 May 1997)
Matrix microstructure of a pitch-based carbon-carbon composite was controlled by an iodine treatment. Coal-tar pitch having the softening point of 101 ±C was used as a matrix precursor. The iodine treatment was carried out on a pitch-impregnated specimen at 90 ±C for 3–20 h. The specimen was carbonized at 800 ±C and graphitized at 2000–3000 ±C. The carbon yield increased from 73% to 93% by the iodine treatment. Microstructures of carbonized specimens changed from a flow type texture to a mosaic type one by the iodine treatment. The microstructural development to graphitic structure was suppressed by the iodine treatment.
I. INTRODUCTION
Because carbon fiber reinforced carbon composites (CyC composites) maintain their excellent mechanical properties at higher temperature in inert atmospheric conditions, the composites are expected to be used in an external situation.1 The CyC composites are usually prepared by impregnating a preform of carbon fibers with a matrix precursor, e.g., a thermoplastic or thermosetting resin. A pitch is a typical matrix precursor because of high carbon content and cost performance. Since the pitch converts into carbon through liquid phase, the pitch matrix precursor may flow out from the preform during the heat treatment and then carbon yield is limited. To overcome this matter, the pitch matrix CyC composites are often carbonized under pressure.2 This technique is effective for increasing carbon yield itself but not convenient for producing larger materials, and moreover it requires a lot of energy. Because the mechanical properties of the CyC composites are affected by their matrix microstructure,3 some treatments have been presented to improve pitch properties as a matrix precursor of the composites.4,5 A fine mosaic texture is preferable to a flow one.3 Barr et al. reported that the softening point of pitch increases by an oxidation treatment by the following equation6 : 2Ar–H 1
a)
1 O2 °! Ar–Ar 1 H2 O , 2
(1)
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II. EXPERIMENTAL PROCEDURE A. Specimen
Coal-tar pitch (Nippon Steel Chemical Co., Japan) with a 101 ±C of the softening point was used as a
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where Ar in Eq. (1) indicates an aromatic component. As shown in Eq. (1), polymerization reactions are accelerated by oxygen. White et al. performed an oxidation treatment to pitch-based CyC composites before carbonization.7 They showed that the oxidation treatment was e
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