Multiwalled carbon nanotube monoliths prepared by spark plasma sintering (SPS) and their mechanical properties

Three types of multiwalled carbon nanotube (MWCNT) monoliths without any binders were obtained by spark plasma sintering (SPS) treatment at 2000°C under 80 MPa sintering pressure. Three MWCNTs with different diameters: thin (∅20–30 nm, CNT Co., Ltd., Korea), thick (∅100 nm, Nano Carbon Technologies Co., Ltd., Japan) and spherical thin (∅20–30 nm, granulated diameter = 1–3 μm, Shimizu Corporation, Japan) were employed for SPS. SEM observation confirmed that these materials maintained the nanosized tube microstructure of raw CNT powder after SPS treatment. The densest monolith was prepared with the spherical MWCNTs. The mechanical properties of this material were estimated by the dynamic hardness test. The elastic modulus of the monolith did not depend on the difference of MWCNTs, but the hardness of spherical MWCNTs was higher than that of thick MWCNTs. The high density and hardness of the spherical MWCNTs were caused by the high packing density during the SPS process because of its spherical granulation. Thus, the spherical MWCNTs were most useful for the MWCNT monolith preparation with the SPS process and its application as a bone substitute material and a bone tissue engineering scaffold material was suggested.