Homogeneity of catalytically grown carbon nanofibers

Carbon nanofibers were synthesized via catalytic chemical vapor deposition (CCVD) similar to the process described by Rodriguez and Baker. The synthesis was performed in a quartz tube at 600 C using acetylene as a carbon source (5 ml/min), hydrogen as a carrier gas (25 ml/min) and nickel oxide powder as a catalyst. Our focus was to identify the key parameters for the production of nanofibers in terms of high yield and selectivity as well as structural homogeneity. In this paper, we investigated the influence of the amount of catalyst and the catalyst preparation, the catalyst position along the synthesis reactor tube axis, and the flow rates during the carbon deposition step. The carbon deposits were characterized by transmission electron microscopy and nitrogen sorption. With nickel as the catalyst and acetylene as the carbon source, the CCVD process predominantly results in carbon fibers with a characteristic morphology, so-called "segmented nanofibers". The yield and homogeneity of the deposit as well as the diameters of the nanofibers are found to strongly depend on the amount of catalyst, the catalyst concentration and preparation and the flow rates/conditions in the reactor tube. (Author)