Radio Frequency Plasma Synthesis of Boron Nitride Nanotubes (BNNTs) for Structural Applications: Part III

The emergence of commercial quantities of BNNTs facilitates the exploration of structural
material applications. BNNT-reinforced composites must exhibit extraordinary mechanical
properties in order to justify the cost premium. Prevailing theory indicates that suitable BNNTs
must possess an aspect ratio (AR= length/diameter) approaching 10,000 to provide effective
discontinuous reinforcement under tensile loading. A survey of commercial products shows that although the quantities are sufficient, lots of uniform morphology are unavailable. Therefore, the opportunity exists to supplement procedures either during synthesis operations or post-synthesis processing in order to deliver homogeneous batches of high AR BNNTs.
An assessment of relevant technologies reveals established methods compatible with sorting of BNNTs by physical dimensions, i.e., size and/or shape. Electrostatic fractionation emerges as the leading candidate, with the potential to isolate high-purity, low-defect, high AR product. The adaptation of existing equipment to the handling of fibrous particulate on the nanoscale will be paramount to success. Although currently focused on BNNTs, the concepts outlined may be applied to nanotubes synthesized from any organic or inorganic compounds. This survey sets the stage for delivering reproducible lots of BNNTs that satisfy the dimensional requirements for use in acreage structural materials.