Abstract: A mechanism for the catalytically growth of vapor grown fibrous carbon (VGFC)preparing from the floating catalyst method has been proposed, in which liquid diffusion-determined diffusion of carbon atoms through catalyst particles is described mathematically, and the physical and chemical properties of the catalyst particles during the growth process are taken into account. From the model the growth rate and grown length of VGFC are calculated theoretically which coincides with the experimental data; and the necessity of reducing gas such as hydrogen in preparing VGFC is explained as to reduce Fe3C, which acts as intermediate catalyst shown by the model. Fe3C formed on the surface of γ-Fe will stop the growth of carbon fiber if they can not be reduced at once. Additionally, the growth temperature and diameter of VGFC are also discussed in the paper.

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