Posted: Sep 16, 2010

First successful measurement of strength of boron nitride nanotubes

(Nanowerk News) A research group headed by Dr. Dmitri Golberg, a Principal Investigator in the International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS) succeeded for the first time in the world in nano-tensile strength measurements of boron nitride nanotubes (BNNTs) using a high performance transmission electron microscope. The group discovered that BNNT displays tensile strength of approximately 30 GPa (gigapascal), which is more than 15 times that of steel, and a large value of Young's modulus,4) ~900 GPa, which is comparable to that of diamond (~1,000 GPa).
BNNT consists of boron (B) and nitrogen (N) atoms and has a hollow structure similar to that of carbon nanotubes, but has attracted attention as a chemically more stable material than carbon nanotubes with high heat resistance, oxidation resistance, chemical resistance, and other properties. Although theoretical predictions indicated that BNNT possesses excellent mechanical properties similar to those of carbon nanotubes, the strength of BNNT had not been measured previously due to the technical difficulty of such measurements.
In this research, the MANA group succeeded in measuring the tensile strength of BNNT for the first time by installing a specially-designed nano-tensile strength testing device in a high performance transmission electron microscope (300 kV TEM; resolution: 0.17 nm). The BNNTs measured in this work were multi-walled nanotubes with diameters of only 10-50 nm and lengths of several hundreds nm. Using wax as an adhesive, the group succeeded in measuring the strength of a single BNNT by fixing the two ends of the nanotube to a force detection cantilever on one side and the metal wire of a piezo-motor drive on the other.
The tensile strength and Young's modulus of BNNT were calculated from measurements of the individual stress-strain curves of 14 BNNTs. Although the tensile strength of the BNNTs varied depending on differences in the shape of the tube (tube diameter and length), a maximum value of approximately 33 GPa was recorded. These tests also revealed that BNNT possesses an extremely large value of Young's modulus, ~900 GPa. This is comparable to the Young's modulus of diamond (~1,000 GPa).
Based on these outstanding mechanical properties, high expectations are placed on BNNT as a high strength electrically insulating filler material. Potential applications include various mechanically-reinforced materials such as polymer composites, ceramic composites, and metal composites, and key parts of nanomechanical systems.
Source: National Institute for Materials Science