HREM observation of BN nanostructures produced from borides and boron/metal powder

Full text: Carbon nanocage structures, such as fullerene clusters, nanotube, nanocapsules, nanopolyhedra, cones, cubes and onions, have great potential for studying materials of low dimensions in an isolated environment. Recently, BN nanotubes and nanocapsules have also been synthesized by an arc-discharge method using boride materials such as HfB2. The properties of BN fullerene materials would be better than those of carbon fullerene materials, from the viewpoint of wide band gap and heating resistance in air. However, it is difficult to produce the BN fullerene materials with the ordinary arc-discharge method because of the difficulty in the control of arc conditions. Recently, BN nanotubes, nanocapsules and nanocages have been produced successfully by an arc-melting method from boron and metal powder compacts in a nitrogen/argon gas atmosphere. These materials are expected as gas storage materials, single-electron transistors and magnetic refrigeration. However, good catalyst metal has not been found out, and the all effects on reaction have not been understood yet. The purpose of the present work was to find out the catalyst metal by arc melting in nitrogen and argon gas atmosphere, and investigate the effects on reaction. In the present work, boron/Al powder compacts, TiB2, VB2 and MgB2 was selected to compare the catalytic effect. Since these have good conductivity, arc melting will be set off easier. TiB, VB2 and MgB2 were used as powder to increase surface area for nitridation of the boride materials, and to avoid preparation the boride-rods. To understand the formation mechanism of BN nanotubes, high-resolution electron microscopy (HREM) and electron dispersive X-ray spectroscopy (EDX) were carried out. For BN nanocapsules with TiN nanoparticles, magnetization measurement was carried out to investigate conductivity that is caused from quantity effect by using a SQUID magnetometer. These studies will give us a guideline to prepare BN nanocapsules- Nanoparticles of AlB10, TiN and VN encapsulated by BN layers were synthesized by an arc-melting method in N2/Ar mixture gas from boron/Al powder compacts, TiB2 and VB2, respectively. These structures were confirmed from HREM images, and formation mechanisms of nanocapsules were proposed. Magnetization of BN nanocapsules with TiN nanoparticles showed spin-glass-like behaviour. The present work indicates that Al, Ti and V can be key catalytic materials to produce BN nanocapsules. Copyright (2002) Australian Society for Electron Microscopy Inc