Highly efficient synthesis of boron nitride nanotubes by catalytic chemical vapor deposition of boron/nickel containing precursors

High-purity and high-yield boron nitride nanotubes with large aspect ratio were prepared by a facile two-step process, including the synthesis of boron/nickel containing precursors by precipitation reactions and subsequent thermally catalytic chemical vapor deposition reactions. The influence of catalyst content and annealing temperature on the phase composition and microstructure of the products were investigated. The results show that it is difficult to exert the catalytic effect of nickel-based catalyst at low temperatures (<1 400 °C). At appropriate temperatures (1 400–1 500 °C), highly crystalline boron nitride nanotubes with a length of more than 50 μm and a diameter of 50 nm are formed. The content of catalyst in the precursor mainly affects the morphology of the boron nitride product. If the content is too low, it is easy to form boron nitride particles; while high catalyst content can easily lead to catalyst aggregation and form a submicron one-dimensional boron nitride with unregular structure. Based on microstructural evolutions, phase changes, and thermodynamic analysis, the vapor-liquid-solid (V-L-S) growth mechanism of the tip growth mode dominates the formation of boron nitride nanotubes has also been verified.