Preparation and application of long boron nitride nanotubes

Since the discovery of the carbon nanotubes (CNTs) in 1991 (Iijima 1991), a rapid development has been achieved in the fabrication and application of CNTs. In 2004, single-wall CNTs with a length of 4 cm were successfully synthesized at a high growth rate of 11 µm/s by a catalytic chemical vapor deposition approach (Zheng et al. 2004). Such long nanotubes have many advantages and enable many new applications (Baughman et al. 2002). For example, long CNTs can be spun into meter-long fibers of a high Young modulus (Jiang et al. 2002). Long metallic nanotubes can be readily assembled into a microelectromechanical system (MEMS) or nanoscale semiconductor devices (Zhu et al. 2002). Structurally similar to CNTs, boron nitride nanotubes (BNNTs) exhibit excellent mechanical (Chopra and Zettl 1998; Suryavanshi et al. 2004; Golberg et al. 2007) and thermal (Sanchez-Portal and Hernandez 2002; Popov 2003; Wirtz and Rubio 2003) properties comparable to CNTs. On the other hand, BNNTs are electrically insulating and exhibit better chemical stability and higher resistance to oxidation at high temperatures (Rubio et al. 1994; Chen et al. 2004) than CNTs. These unique properties make BNNTs very attractive for reinforcing composites and serving as insulator parts in 3D CNT-based MEMS. In this chapter, we brief the fabrication of over 1.0 mm long BNNTs through an optimized ball milling and annealing process, and demonstrate their potential applications in humidity-sensing unit, field-emission devices, and the treatment of oily wastewater.