TEM Observations of Surface Graphitization and Interior Microstructural Changes in a Furan-Resin-Derived Carbon
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TEM Observations of Surface Graphitization and Interior Microstructural Changes in a Furan-Resin-Derived Carbon Junji Yamanaka 1, Eiichi Yasuda 2, George C. Weatherly and Yasuhiro Tanabe 2 McMaster University, Dept of Materials Science and Engineering, Hamilton, ON, L8S 4M1 Canada. 1 Visiting from: Center for Crystal Science and Technology, Faculty of Engineering, Yamanashi University, Kofu 400-8511, Japan. 2 Center for Materials Design, Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan ABSTRACT Furan-resin-derived carbon structures have attracted interest as a component in carbon based composite materials. We have investigated the microstructures of furan-resin-derived carbon by transmission electron microscopy after high-temperature heat treatments. We observed that graphitization occurred at the surface even although furan-resin-derived carbon is believed to be a non-graphitizable carbon. On the other hand the interior of the specimens exhibited a cage-like structure. Specimens heat-treated at higher temperatures exhibited a well-developed cage structure, as evidenced by the number of stacked layers and their periodicity. Post-column type EELS was utilized to study the chemical state of the interior of the specimens. All of the EELS spectra had a characteristic edge structure showing the existence of π bonding. There were not significant differences between the spectra of early-stage and well-developed cage structures. INTRODUCTION The microstructure of the matrix and the interface of composites strongly affect their mechanical properties. Because of their engineering importance as high temperature composite materials, many studies of the carbon/carbon composite (C/C composite) have been reported. For example, the graphitization of non-graphitizable carbon at the interface of C/C composite has been reported [1-3]. Furan-resin-derived carbon is often used as the matrix of C/C composite. Hence fundamental studies of the microstructure of furan-resin-derived carbon are very important. Furan-resin-derived carbon is one of the typical non-graphitizable carbons. It was believed that furan-resin-derived carbon cannot transform into a rigid graphite structure, but displays the character of glasslike carbon even after high temperature heat treatment at temperatures up to 3273 K. Microstructural models of glasslike carbons, such as the Jenkins-Kawamura and Shiraishi models are well known [4, 5]. However there is as yet no widely accepted model. This may be because of the variety of glasslike carbons whose structures are influenced by the raw precursor materials. Furthermore, HR-TEM is the only method to observe atomic scale structure directly but it is quite difficult to derive three-dimensional structural information from this technique. Hence it is important to observe glasslike carbons individually by using HR-TEM and other techniques. Recently our knowledge of the microstructures of furan-resin-derived carbon has been improved remarkably. Hishiyama et al. reported free-surface
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