Review Articles

On the Mechanical Behavior of Boron Nitride Nanotubes

[+] Author and Article Information
H. M. Ghassemi

Department of Mechanical Engineering-Engineering Mechanics, Michigan Technological University, Houghton, MI 49931smirshah@mtu.edu

R. S. Yassar

Department of Mechanical Engineering-Engineering Mechanics, Michigan Technological University, Houghton, MI 49931reza@mtu.edu

Appl. Mech. Rev 63(2), 020804 (Feb 24, 2010) (7 pages) doi:10.1115/1.4001117 History: Received January 28, 2009; Revised January 19, 2010; Published February 24, 2010; Online February 24, 2010

Boron nitride (BN) nanotubes have structural and mechanical properties similar to carbon nanotubes and are known to be the strongest insulators. Great interest has been focused on understanding the mechanical properties of BN nanotubes as a function of their structural and physical properties. Yet, the published data have not been reviewed and systematically compared. In this paper, we critically review the mechanical properties of BN nanotubes from both experimental and simulation perspectives. The experimental reports include thermal vibrations, electric induced resonance method, and in situ force measurements inside transmission electron microscopy. The modeling and simulation efforts encompass tight bonding methods and molecular dynamics. Replacing the covalent sp2 bond (C–C) by ionic bond (B–N) results in differences in the mechanical properties of BN nanotubes in comparison to carbon nanotubes. The experimental and computational simulations indicate that BN nanotubes are highly flexible. High necking angles in BN nanotubes are assumed to be correlated with unfavorable bonding in B–B and N–N atoms.

Copyright © 2010 by American Society of Mechanical Engineers
Topics: Nanotubes
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Figure 1

Schematic of a single-wall BN nanotube

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Figure 2

Thermal vibration can be used to estimate the elastic properties of a BN nanotube. TEM image of BN nanotube at 300 K, the black arrows identify the supported base and tip of a long cantilevered nanotube; the tip region is markedly blurred due to thermally induced vibrations of the nanotube. The white arrow identifies another BN nanotube whose thermally induced vibration amplitude is too small to be resolved (10).

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Figure 3

RMS amplitude of oscillation as a function of the position from the base of the BN determined from the line scans. The solid line shows the best fit using the normal modes of a thermally excited cantilever (10).

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Figure 4

Electric field induced resonance method was used to measure the elastic properties of a BN nanotube. TEM images showing (a) a cantilevered BN nanotube with an outer diameter of 43 nm, an inner diameter of 12 nm, and a length of 9.75 mm, (b) the first mode harmonic resonance of the BN nanotube, and (c) the second mode harmonic resonance of the BN nanotube. The dotted lines in (b) and (c) are the analytical fit to the corresponding deflection contour of the resonances. The lines are offset from the nanotube so that the true resonance contours of the nanotubes are not masked (11).

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Figure 5

Experimental setup for multicycle bending of BN nanotubes performed inside a HRTEM. The inset shows a TEM view of the setup (12).

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Figure 6

The multicycle bending experiments on BN nanotubes inside a TEM. Severe distortion of the tubular layers in the vicinity of the dark-contrast (filled) nanotube fragment occurs ((a) and (c)), but the original shape is again fully restored after reloading ((b) and (d)) (12).

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Figure 7

Schematic of the AFM-TEM holder used to measure the mechanical properties of the BN nanotubes. The inset on the right shows a TEM view of the framed area, where an individual multiwalled BN nanotube stretches between a sample wire and a silicon cantilever. The position of the tube against the cantilever may be precisely adjusted through piezo-driven displacements of the sample wire (15).

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Figure 8

Forcepiezo-displacement curves obtained using an AFM-TEM holder show the data (a) for a thick BN nanotube and (b) for thin BN nanotubes. The left and right insets on each curve display the appearance of the starting and bent nanotube morphologies. The intentional directions of piezo-driven moves of an Al wire with the attached nanotube during the deformation are pointed out (15).

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Figure 9

The energy difference ΔE versus the tensile strain ε for the (5, 5) armchair and (10, 0) zigzag BN nanotubes. Here ΔE=E−Eperfect is the difference between the energy for systems with and without Stone–Wales transformation. SW formation occurs at tensile strains of 11.47% and 14.23% for the (5, 5) armchair and (10, 0) zigzag BN nanotubes, respectively (17).

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Figure 10

Variation in the Young’s modulus with radius of the BN and carbon nanotubes. The Young’s modulus decreases when the diameter of BN nanotubes increases from 7 Å for the armchair nanotube and 10 Å for zigzag nanotube (19).

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Figure 11

Young’s modulus as a function of the tube diameter for carbon, BN calculated from the tight-binding simulations. Results obtained for (n, n) nanotubes (filled symbols), (n, 0) nanotubes (empty symbols). The Young’s modulus increases as the diameter increases (20).

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Figure 12

Young’s modulus of BN nanotubes versus the nanotube diameter for the (a) armchair and (b) zigzag BN nanotubes. The Young’s modulus is independent of the diameter as it exceeds 2 nm (21).

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Figure 13

Energy change relative to the initial geometry as a function of (a) bending Δθ and (b) twisting Δφ angles for (1) armchair (5,5) carbon nanotubes, and (2) zigzag (17,0) BN nanotubes. Results show that the required energy increases by increasing the bending angles, and at breaking point due to neck/crack formation, the required energy decreases (23).



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