Atomic scale investigations of catalyst and catalytic graphitization in a silicon and titanium doped graphite

The catalysts and catalytic graphitization mechanisms in the graphite blocks doped by silicon (Si) and titanium (Ti) have been systematically investigated at the atomic scale by high-resolution transmission electron microscopy. Few silicon carbide (SiC) crystallites would be residual and coexisted with titanium carbide (TiC) crystallites with two forms due to the low-energy interface between them, inhibiting the escape of the SiC. Three kinds of residual TiC coexisted with the graphite, which correspond to two distinct catalytic mechanisms. Besides the well-acknowledged dissolution-precipitation mechanism for TiC catalytic graphitization, the TiC formation-decomposition mechanism has been experimentally validated for the first time. Extensive investigations on the interfaces between TiC and graphite crystallites reveal that the orientation of the (1 1 1) planes of TiC relative to the interface essentially influence the growth modes and basal plane stacking sequence of graphite, and the related model has been proposed to decode the precipitation mechanism of hexagonal and rhombohedral graphite.