Influence of copper on the structural characteristics of carbon nanofibers produced from the cobalt-catalyzed decomposition of ethylene

We have used a combination of techniques to examine modifications in the structural characteristics of carbon nanofibers produced from the interaction of cobalt and copper-cobalt powders with ethylene at temperatures over the range 425 to 700 degrees C. The nanofibers generated from the interaction of cobalt with ethylene at 600 degrees C were found to be highly crystalline in nature. Incorporation of as little as 2% copper into the cobalt created a major modification in the conformation of the solid carbon deposit, which was composed of multiple nanofiber limbs emanating from a single catalyst particle, and in this state the carbon structures tended to be disordered. As the composition of the bimetallic was progressively changed to the point where copper became the major component, there was a significant increase in the degree of crystalline perfection of the nanofibers even though they maintained their multidirectional form. The transformation in structural characteristics of the carbon nanofibers is rationalized, according to a concept wherein the crystalline order of the deposit is related to the wetting properties of the bimetallic particles with graphite.