Most of the research into nanotubes, man-made tubules with diameters of a few or a few tens of nanometres, has involved their growth using carbon. However, since ordered boron nitride also crystallizes in a graphite-like structure yet has electronic properties significantly different from graphite, considerable interest has developed in nanotubes with this composition.
John Fitz Gerald and Ying Chen, researchers at the Australian National University (ANU), have previously studied boron nitride nanotubes from reactive ball milled precursors and found that Fe contamination from the stainless steel ball mill had catalysed the nanotube growth. This year, new experiments have been conducted using boron milled in a nitrogen atmosphere in a tungsten-carbide ball mill.
Boron nitride nanotubes with high yield have been produced by annealing under carefully controlled furnace conditions. The microstructures of these intriguing materials have been carefully examined with scanning and analytical transmission electron microscopy to gain insight into formation processes. Boron nitride nanotubes have been observed growing from tungsten-metal particles. This process must occur by (surface?) diffusion in the solid state since annealing temperatures are low. These tubes with diameters about 20 nm have a nested, cup-like arrangement of the boron nitride layer planes. They are currently experimenting with the best conditions for producing the more ideal, parallel-walled boron nitride nanotubes.