Structure and phase composition of a catalyst for carbon nanofiber formation

Novel carbon nanofibers (CNFs) consisting of graphite layers crossed by two systems of stripes are formed on an iron catalyst using the chemical vapor deposition method under conditions close to the phase equilibrium of the iron carbides Fe3C and Fe5C2. The formation of these CNFs is explained by the deformation caused by the decay of the carbides. It is shown that the catalyst particle, often twinned, consists of Fe3C, Fe5C2 or both. The crystallographic peculiarities of α-Fe → Fe3C → Fe5C2 transformation are discussed.