The production, properties and applications of vapor-grown carbon fibers (VGCF) and carbon filaments were reviewed in the course of a previous NATO ASI [1]. It is generally accepted that the growth of carbon fibers from gaseous hydrocarbons in the presence of a catalyst (VGCF) occurs as a result of the initial formation of carbon filaments or nanofibers, by a mechanism involving the dissolution and diffusion of carbon at the exposed surface of the catalyst particles and precipitation at the metal/support interfaces. In this way, the catalyst particles are carried out on top of the growing filaments [2,3]. This lengthening stage stops when the catalyst particles become covered with a carbon layer; thereafter, thickening occurs by chemical vapour deposition of pyrolytic carbon, leading to the production of VGCF exhibiting the well known "tree-trunk" structure of concentric carbon layers [4-6]. Originally, a Vapor-Solid process (V-S) was invoked, as the catalyst particles were considered to be in the solid state [7]. However, it was later recognised that, in order to account for the observed rates of fiber growth, a Vapour-Liquid-Solid (V-L-S) mechanism must be involved in the production of VGCF. Indeed, Benissad et al. [8] proposed that the catalyst particles can be molten, according to their sizes, in the temperature range where fiber lengthening occurs (1050-1100°C). More recently, Tibbetts and Balogh [9] showed that only molten particles are effective in catalyzing fiber growth. Two different methods have been developed to produce VGCF: The substrate seeding method and the floating catalyst, or fluidization seeding method [10,11]. The latter has the advantage of being a continuous process, but it produces shorter fibers (some micrometers) with smaller diameters (hundreds of nanometers) when compared to the first method (which leads to fibers several centimeters long and some micrometers in diameter).
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