Carbon Cones - a Structure with Unique Properties
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Carbon Cones - a Structure with Unique Properties Geir Helgesen1,2, Kenneth D. Knudsen1,3, Jean Patrick Pinheiro1, Arne T. Skjeltorp1,2, Eldrid Svåsand1,2, Henning Heiberg-Andersen1, Arnljot Elgsaeter3, Torgunn Garberg3, Stine Nalum Naess3, Steinar Raaen3, Merete F. Tverdal3, Xiaofeng Yu3, and Thor Bernt Melø3 1 Physics Department, Institute for Energy Technology, Kjeller, NO-2027, Norway 2 Department of Physics, University of Oslo, Oslo, NO-0316, Norway 3 Department of Physics, Norwegian University of Science and Technology, Trondheim, NO7491, Norway ABSTRACT Large-scale production of perfect conical carbon nanostructures that are fundamentally different from the other nanocarbon materials, such as buckyballs and nanotubes, can be made using the so-called Kvaerner Carbon Black & Hydrogen Process. This involves pyrolysis of hydrocarbons using a torch plasma process. The carbon cones that occur appear in five distinctly different forms. In addition, disk-shaped particles may be produced. Here we report about the current status for the experimental research and theoretical modeling of these particles, which have properties different from the other known forms of carbon. INTRODUCTION Prior to 1985 carbon was only known in two crystalline forms, i.e. graphite and diamond. The third carbon form, namely fullerenes or buckyballs, was then discovered. In 1991 elongated fullerene analogues, the carbon nanotubes (CNT) which are the fourth form, appeared [1]. Carbon cones (CC) are the fifth form of carbon, fundamentally different from all the so far known carbon structures, and were accidentally discovered [2] in 1997 in the so-called Kvaerner Carbon Black & Hydrogen Process (CB&H) [3]. This emission-free process decomposes hydrocarbons directly into carbon and H2, based on a specially designed plasma torch. Under well-defined conditions, CB&H produces a carbon material composed of microstructures, which are flat carbon discs (70%) and cones (20%). However, minute quantities of fullerene cones were first produced in 1994 [4]. At the same time, the first theoretical studies of such structures were reported [5,6]. These cones are distinctly different from the naturally occurring helically wound graphitic cones [7] and from carbon nanohorns [8]. A review of the current knowledge of carbon cones and related conical carbon particles can be found in [9]. The carbon cones consist of curved graphite sheets formed as open cones with one to five carbon pentagons at the tip with successively smaller and discrete cone angles, respectively. The physics of carbon cones has been relatively little explored until now. These carbon cones may be imagined formed from graphene sheets by cutting out sectors of n x 60o from the flat sheet and then connecting the cuts. The strain at the cone tip will give rise to the formation of (6–n) pentagons near the tip and cone angles of 112.9o, 83.6o, 60.0o, 38.9o, and 19.2o for 1, 2, 3, 4, and 5 pentagons, respectively. The carbon cone particles formed in the Kvaerner Carbon Black & Hydrogen Pro
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