Transformation mechanism from carbon nanotubes to n-diamond
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Tingju Lib) Laboratory of Special Processing of Raw Materials, Dalian University of Technology, Dalian 116023, People’s Republic of China
Chuang Dong Department of Materials Engineering, Dalian University of Technology, Dalian 116023, People’s Republic of China
Junze Jin Laboratory of Special Processing of Raw Materials, Dalian University of Technology, Dalian 116023, People’s Republic of China (Received 23 December 2004; accepted 3 March 2005)
Nanocrystal n-diamond particles were synthesized after a pyrogenation of carbon nanotubes and colloidal Fe(OH)3 at atmospheric pressure. The product was investigated with x-ray diffraction, transmission electron microscopy, thermal gravimetric analysis, and differential thermal analysis. The results indicate that the n-diamond can be synthesized with the carbon nanotubes as carbon source. The formation mechanism of the n-diamond is suggested in this paper. With the increase of temperature and hence the carbon diffusion in iron, the phase sequence is from Fe(OH)3 into Fe2O3, ␣–Fe, ␥–Fe, and then liquid iron. When carbon in the liquid iron is saturated, graphite separated out of the liquid iron. With the decrease of temperature, the carbon in ␥–Fe is separated out, and the n-diamond nuclei form and grow. I. INTRODUCTION
Diamond, graphite, and carbyne are three kinds of well-known carbon allotropes, and they are distinguished by the type of electron hybridization.1 In 2001, ndiamond, a new kind of carbon allotrope was validated by Konyashin, Jarkov, and their co-workers. The ndiamond has a metallic form of carbon with facecentered-cubic (fcc) structure, and its lattice constant is 0.3563 nm.1,2 Different techniques have been applied to produce the n-diamond: radio frequency plasma aided decomposition of hydrocarbon,3 plasma-assisted chemical vapor deposition using diluted hydrocarbons, 4 transformation of graphite under shock-compression,5 transformation of C60 films under shock-compression,6 transformation of graphite at high pressure and temperature,7 plasma-chemical synthesis with the aid of a carbon plasma jet,2 treatment of diamond surface in hydrogen plasma,1 and annealing of silica wafer embedded by carbon atom.8–10 In 2003, we discovered that n-diamond could also be synthesized by the method of catalyzed
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2005.0205 J. Mater. Res., Vol. 20, No. 6, Jun 2005
carbon black at atmospheric pressure and at temperature of 1100 °C.11,12 Carbon black has been an important engineering material for decades. Due to its numerous applications, the structure of the carbon black has been studied extensively. Carbon black is a type of soot, which is a class of solid carbons that can be described as closed manylayer carbon particles. Along with other soot and fullerenes, carbon black is composed of fragments of carbon network, either single layers (bent, curved, or flat) or small, assembled packs.13,14 Before the discovery of fullerenes,15 the idea that graphene sheet
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