| An improved floating catalyst method, with ferrocene as the precursor of catalyst and acetylene as a carbon source, was employed in the growth of vertically aligned carbon nanotubes (CNTs) on porousα-Al2O3 support. It was found that the growth of CNTs can be affected by many factors, so its appearance and structure are sensitive to the reaction conditions.The process parameters for the CNTs growth, such as reaction temperature, reaction time, flow rate of acetylene, deposition time of catalyst, distance between the catalyst precursor and the support, are examined. It was found that as the reaction temperature increased, carbon deposited on the support more uniformly, the carbon layer adhered on the support more tightly, but less carbon deposited. As the reaction time increased, the length of the CNTs increased, the uniformity of their orientation is better, however, with a long reaction time, the carbon layer may desquamate from the support. A moderate flow rate of acetylene is beneficial. If it is too small, CNTs grow slowly, while if it is too large, the carbon layer desquamates. It was also found that the distance between the catalyst precursor and the support has a strong effect on both the amount of carbon deposited and the adhesion of the layer on the support. A good condition for the growth of the aligned CNTs can be summarized as, reaction temperature is 800 oC, reaction time 10 min, acetylene flow rate 10 ml/min, deposition time of catalyst 1 min and the distance between the catalyst precursor and the support 28 cm. Furthermore, it was found that some other carbon structures were formed during the process described here.The gas permeability of the porousα-Al2O3 support and the composite of aligned CNTs with the support are examined. The process of gas flow through porousα-Al2O3 support was controlled mainly by viscous flow mechanism, while for the composite, the contribution of Knudsen diffusion increases, and the separate modulus of H2/N2 increases.
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