Precipitation of carbon nanoparticles encapsulating silicon carbide from molten oxide
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Precipitation of carbon nanoparticles encapsulating silicon carbide from molten oxide Mamoru Mitomoa) National Institute for Research in Inorganic Materials, Tsukuba-shi, Ibaraki 305, Japan
Chong-Min Wang Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania 18015
Hideyuki Emoto Research Center, Denki Kagaku Kogyo K. K., Machida, Tokyo 194, Japan (Received 17 December 1997; accepted 14 March 1998)
A kind of fullerenes, carbon nanoparticle encapsulating b –SiC grain, was precipitated during cooling Al2 O3 –Y2 O3 –CaO oxide melt containing SiC and C from 2023 K. The SiC grains with a diameter of 5–20 nm were covered with 2–4 graphitic carbon layers with the spacing of 0.34 nm as revealed by high resolution transmission electron microscopy. The result provides a new preparation method of carbon nanoparticles through a ceramic process, which contrasts with previous physical methods applying electric arc discharge or electron irradiation in vacuum.
Since the discovery of fullerene (C60 ),1 many attempts have been carried out to prepare various types of their derivatives.2–11 Multilayered carbon nanomaterials are particularly interesting in their wide variety of structures and compositions. They are mainly classified into two groups, nanoparticles2–8 or nanotubes.9–11 Metal encapsulating carbon nanoparticles are found during catalytic decomposition of carbon-containing gas.2 Later, it was reported that spherical or polyhedral carbon nanoparticles, which consist of concentric graphitic layers, are prepared more effectively under severe conditions like electric discharge between carbon electrodes3,4 or electron beam irradiation of carbon particles.5 Encapsulation of transition metals or their carbides in carbon nanoparticle was also reported previously.6–8 They were prepared by electric arc discharge between carbon electrodes containing metal oxides. We have observed the formation of carbon nanoparticles encapsulating silicon carbide in liquid-phase sintered silicon carbide with Al2 O3 , Y2 O3 , and CaO as sintering additives. The sintered materials are composed of fine b –SiC grains and showed superplastic deformation at 1973 K.12 During densification, the solution of small SiC grains and the precipitation on larger SiC grains takes place. A larger number of nanoparticles have been found in intergranular glassy phase of superplastically deformed materials than in those before deformation. The conditions for nanoparticle formation are not clearly met if it is simply due to the precipitation
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 13, No. 8, Aug 1998
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from oxide melt, or due to superplastic deformation, because of the small volume fraction of the liquid phases (which solidify as glassy or a crystalline phase upon cooling) in sintered materials. In this communication, we report the precipitation of carbon nanoparticles incorporat
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