title: Boron-assisted transformation to rod-like graphitic carbons from multi-walled carbon nanotubes in boron-mixed multi-walled carbon nanotube solids.
abstract: We produced boron-mixed multi-walled carbon nanotube solids (B-mixed MWCNT solids) by heating and pressing the powder of purified MWCNTs mixed with 1, 5, and 10 wt % boron in the temperature range 1400-1800 °C every 200 °C under a constant pressure of 20 MPa in vacuo, and investigated the influence of boron addition on nanotube structure and the mechanical and electrical properties of the resulting B-mixed MWCNT solids. The structure of the prepared material was characterized by scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy-electron energy loss spectroscopy, Raman scattering spectroscopy, and X-ray diffraction, and their mechanical properties and conductivity were measured using a mechanical and Vickers indentation tester and an electric resistor, respectively. It is notable that part of the nanotubes in the B-mixed MWCNT solids solidified at 1800 °C had dramatically changed into rod-like graphitic carbons (RLGCs). The occupancy distribution of RLGCs increased with increasing boron contents. However, boron was not detected in the energy-loss near-edge structure spectrum of RLGCs. Furthermore, RLGCs were not observed in the boron-unmixed sample treated with the same solidified condition, indicating that adding boron causes a remarkable ability to transform the phase of MWCNT. Transformation from MWCNTs to RLGCs resulted in increased specific bending strength and modulus, Vickers hardness, and electrical conductivity of B-mixed MWCNT solids with increasing boron content and solidified temperature.
authors.affiliation: Graduate School of Environmental Studies, Tohoku University, Aoba 6-6-20, Aramaki, Aoba-ku, Sendai 980-8579, Japan. hige@bucky1.kankyou.tohoku.ac.jp
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Sato
authors.forename: Hikaru
authors.initials: H
authors.lastname: Nishizaka
authors.forename: Kenichi
authors.initials: K
authors.lastname: Motomiya
authors.forename: Go
authors.initials: G
authors.lastname: Yamamoto
authors.forename: Akira
authors.initials: A
authors.lastname: Okubo
authors.forename: Hisamichi
authors.initials: H
authors.lastname: Kimura
authors.forename: Mikio
authors.initials: M
authors.lastname: Ishikuro
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Wagatsuma
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Hashida
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Tohji