Microstructure and mechanical properties of bulk carbon nanotubes compacted by spark plasma sintering

Multi-walled carbon nanotube bulk materials were prepared by spark plasma sintering at 1700–2000 °C. The effect of the sintering temperature on the microstructure and mechanical properties of the bulk materials were investigated. The results indicated that with increasing sintering temperatures, the density, electrical conductivity, bending strength and fracture toughness of the compacts all increase. However, when the sintering temperature exceeds 1900 °C, the density slowly increases, resulting in a slow increase in bending strength. The multi-walled carbon nanotube bulk material sintered at 2000 °C exhibits the highest density of 1.56×103 Kg/m3 with an electrical conductivity of 5.23×105 S/m, bending strength of 77.9 MPa and fracture toughness of 4.06 MPa m1/2. The formation of the graphene nanosheets is the main factor that greatly improves the electrical conductivity of the bulk materials. In addition, graphitization was observed and the surface of the bulk material became covered by the interlocked graphene layers when the surface was polished.