We have investigated the formation of graphite nanofibers from the catalytic decomposition of CO/H 2 mixtures over a series of powdered Fe-Cu catalysts at temperatures ranging from 500 to 700 °C. The physical and structural characteristics of the nanofibers have been established from examination of the materials by a variety of techniques including transmission electron microscopy, temperature-programmed oxidation, nitrogen surface area measurements, and X-ray diffraction. It was found that the addition of Cu to Fe did not exert a significant influence on the amount of solid carbon product formed in the reaction. On the other hand, examination of the nanofibers by high-resolution TEM revealed that the materials generated from Fe-rich Cu bimetallics were notably more graphitic in nature than those grown from pure Fe. As the reaction temperature was increased from 600 to 700 °C, the structure of the graphite nanofibers underwent a dramatic change from a "platelet" to "tubular" configuration. It is suggested that this transformation is directly associated with the R-Fe to γ-Fe phase change over this temperature range.
Comparison of early-and late-growth crystal morphologies of several water-soluble ionic materials suggests that early rapid growth is accompanied by a speci®c type of morphological distortion. This distortion, involving a change in the relative growth rate of just one growth direction, is consistent with our previously proposed mechanism for the transition from normal, polyhedral crystal growth to dendritic growth. Interpretation of this morphological distortion was aided by morphology prediction methods based on computed attachment energies.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.