Structure–property relationships in thermally-annealed multi-walled carbon nanotubes

• Published in: Carbon (New York) 2014-01, Vol.66, p.219-226
• Main Authors: Yamamoto, Go, Shirasu, Keiichi, Nozaka, Yo, Sato, Yoshinori, Takagi, Toshiyuki, Hashida, Toshiyuki
• Format: Article
• Language: English
• Subjects: Annealing; Catalysts; Chemical vapor deposition; Cold working, work hardening; annealing, quenching, tempering, recovery, and recrystallization; textures; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; Materials science; Nanoscale materials and structures: fabrication and characterization; Nanostructure; Nanotubes; Physics; Planes; Scanning electron microscopy; Specific materials; Strength; Treatment of materials and its effects on microstructure and properties; Waviness
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2013.08.061

The mechanical properties of individual multi-walled carbon nanotubes (MWCNTs) synthesized by a catalytic chemical vapor deposition (CVD) method followed by a series of high temperature annealing steps at 1200, 1800, 2200 and 2600°C are investigated by a manipulator tool operated inside a scanning electron microscope. To investigate the relationship between the MWCNT structure and mechanical properties, such MWCNTs with a significantly different nanostructure are separately tested in tension, and subsequently observed their nanostructure and fracture morphology by a transmission electron microscope. The results show that the thermal annealing is effective for improving both the strength and modulus of the catalytic CVD-grown MWCNTs. The MWCNTs annealed at 1800, 2200 and 2600°C display enhancements to their strengths by factors of ∼5.4, ∼5.1 and ∼15.6, and moduli by factors of ∼5.9, ∼13.2 and ∼18.9, respectively, compared to the MWCNTs annealed at 1200°C. This effect is associated with the degree of waviness of the graphitic planes along the nanotube axis as well as the degree of crystallinity of the MWCNTs: the strength and modulus of the MWCNTs increases with a higher degree of orientation of the 002 graphitic planes and with a lower degree of defect concentration in the MWCNT structure.