Formation of Rhombohedral Crystallite in Platelet Graphite Nanofibers

Graphite crystallizes in both hexagonal (2H) and rhombohedral (3R) systems. It is known that the 3R modification in graphite occurs locally by grinding of 2H crystal, and disappears by annealing at high temperature or decomposition of its intercalation compounds [Boehm 1955]. It was reported that the 3R phase content in artificial graphite, which was estimated from the integrated intensities of X-ray powder patterns, was increased by increasing the grinding time using ball-mill and saturated ca. 30% even at prolonged period [Inagaki 1973]. These observations suggest that the 3R stacking of carbon layers is meta-stable phase. Recently, the 3R modification in graphite has attracted attention as the cathode material for the Li-ion battery and as an intermediate for the cubic-diamond formation from graphite [Flandrois 1996, Guerin 1999, Yang 2001]. In this study, we found that the graphite nanofibers (GNFs) with high content of 3R phase could be synthesized by CVD method from CO/H2 mixture with Fe ultra fine particles as a catalyst. The stability of 3R phase in GNFs was also examined.