Surface graphitization and mechanical properties of hot-pressed bulk carbon nanotubes compacted by spark plasma sintering

The carbon nanotube bulk material was prepared by the spark plasma sintering of multi-walled carbon nanotubes. When the surface of the bulk material was polished unexpected graphitization happened and the surface became covered by interlocked graphene layers. A similar phenomenon was observed in polishing raw multi-walled carbon nanotubes, indicating that a sheer stress caused graphene layers to peel away from the multi-walled carbon nanotubes. Nanoindentation and scratch techniques were used to evaluate the mechanical properties of this material. It was suggested that the easy sliding between graphene layers in a multi-walled carbon nanotube played a major role in determining its mechanical behavior.