The role of interfacial phenomena in the structure of carbon deposits

Abstract

We have used a variety of experimental techniques, including controlled atmosphere electron microscopy, thermogravimetry, and electrical conductivity measurements to examine the structures of carbon filaments produced from the decomposition of hydrocarbons over copper-nickel and nickel catalysts. The structure of the carbon filaments formed at temperatures over the range 450 to 700°C were found to be extremely sensitive to the chemical nature of the catalyst particles. Alloy particles, particularly those rich in nickel, were found to produce much more ordered filament structures than those grown on nickel particles. This behavior is rationalized in terms of the differences in interfacial energy of the respective catalyst surfaces in contact with the carbon surface. It is speculated that metals that readily wet graphite will produce highly ordered carbon filament structures. There appears to be an upper temperature limit for filament growth from copper-nickel alloys, which is governed by the tendency of copper to preferentially segregate to the catalyst surface. Activity can be restored by subsequent reduction to the active temperature regime.