Mechanical properties of single-walled carbon nanotube solids prepared by spark plasma sintering

In this paper, a spark plasma sintering (SPS) method was employed to solidify single-walled carbon nanotubes (SWCNTs) only, and the effect of sintering conditions on the mechenical properties of the SWCNT solids were examined using a small punch (SP) testing method. The sintering temperature used in the range of 600-1400°C, and the sintering pressure used 40 MPa and 120 MPa. It was demonstrated that the SPS method allowed SWCNTs to be solidified, without any additives. The experimental results showed that the purification of raw soot was critically importance. The SWCNT solid prepared from purified raw soot showed significant non-linear deformation response, producing quasi-ductile fracture behavior. In contrast, unpurified raw soot produced brittle SWCNT solids. The Young's modulus, fracture strength and work of fracture increased with increasing sintering temperature and pressure. The Raman scattering and SEM observations showed that the amount of the graphite-like materials were observed to increase with the increasing temperature and pressure, which indicate that the structure of the SWCNTs was changed partially into the graphite-like materials. The formation of graphite-like materials increased tendency of brittle fracture in the SWCNT solids. TEM observations revealed that the fracture surfaces of SWCNT solids were characterized by pull out of SWCNT bundles. This observation suggests that it may be possible to improve the mechanical properties of SWCNT solids by increasing the cohesion between SWCNTs.