Driving Force of an Iron Particle’s Movement in Solid-Phase Graphitization

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Solid-phase graphitization, and thus solid-phase nanotube growth, was induced by the movement of iron particles into an amorphous carbon matrix at a certain temperature around 600 °C. We analyzed this iron particle movement in an amorphous carbon wall by in situ monitoring by scanning transmitted electron microscopy (STEM). Isotropic diffusion of iron particles with a diffusion constant of approximately 0.06 nm2/min at 680 °C during furnace heating was observed. In contrast, during anisotropic heating, which was realized by heating a wall-shaped specimen on a fine tungsten filament, the Gaussian distribution of the iron particles shifted toward lower temperature. Iron particles in solid-phase graphitization preferred to move to a lower temperature region, where an exothermic reaction can catalyze amorphous carbon into graphite.
2007-09-30