Three-dimensional vapor growth mechanism of carbon microcoils
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Three-dimensional vapor growth mechanism of carbon microcoils Xiuqin Chen Department of Chemical Engineering, Huaqiao University, Fujian 362011, People’s Republic of China
T. Saito and M. Kusunoki Japan Fine Ceramics Center, 2-4-1 Mutsuno, Atsuta-ku, Nagoya 456-8587, Japan
S. Motojimaa) Department of Applied Chemistry, Faculty of Engineering, Gifu University, Gifu 501-1193, Japan (Received 16 April 1999; accepted 4 August 1999)
Carbon microcoils were grown by the Ni-catalyzed pyrolysis of acetylene. The growth patterns and the tip morphologies of the carbon coils are examined in detail, and a growth mechanism is proposed. Basically, six thin fibers grew from a Ni catalyst grain during the initial growth stage immediately followed by the coalescence of the four fibers to form two fibers and then forming double-helixed carbon coils. A small amount of S and O, as well as C and Ni, was observed on the periphery of the cross section of the Ni catalyst grain. On the other hand, S and O were not observed in the central part. The driving force of the coiling of the straight fibers to form carbon coils is considered to be the strong anisotropy of the carbon deposition between different crystal faces.
I. INTRODUCTION
Many researchers have been trying to prepare materials with a 3D-helical/spiral structure. Some researchers have reported the growth of coiled fibers of carbon,1–9 SiC,10–12 and Si3N413–16 from the vapor phase. However, the growth of these coiled fibers is extremely accidental and the reproducibility is very poor. We have prepared regularly microcoiled carbon fibers by the catalytic pyrolysis of acetylene containing a small amount of sulfur or phosphorus impurity, and reported the preparation conditions, morphologies, and some properties of the products.17–26 The microcoiled carbon fibers (referred to as “carbon coils” hereafter) have a 3D-helical/spiral structure, which is the fundamental structure in nature: DNA, proteins, electric waves, growth of vine plants, screw dislocation in solids, etc. The carbon coils may be the candidates for novel electromagnetic wave absorbers, tunable microdevices, absorbers of hydrogen, etc. Furthermore, the growth mechanism of carbon coils is very interesting based on the similarity of the fundamental structure of all objects. Amelinckx et al. proposed a formation mechanism for a catalytically grown helix-shaped graphite nanotube.28 We postulated the 2D and 3D growth mechanism of car-
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e-mail: [email protected] J. Mater. Res., Vol. 14, No. 11, Nov 1999
http://journals.cambridge.org
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bon coils based on the anisotropy of carbon deposition among catalyst crystal faces.26,27,29 However, the growth process and growth mechanism of the carbon coils has not been known in detail until now. In this paper, we propose a 3D growth mechanism of the carbon microcoils based on the growth patterns and morphologies of the coils from the vapor phase, and also show some of its properties.
II. EXPERIMENTAL
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