Rapid Fabrication of Boron Nitride Fine Fibers

Polymer derived ceramics (PDCs) refers to ceramic materials formed through the pyrolysis of a pre-ceramic polymer. The use of the PDC process enables the fabrication of complex, lightweight, mechanically robust shapes that are too difficult to machine otherwise. The PDC process also allows for granular control over the chemistry, resulting in better fiber homogeneity and allowing for application-specific tailoring. NASA’s PDC process to rapidly fabricate multifunctional h-BN nanofibers entails the following steps. First a liquid-based polymer precursor solution containing boron and nitrogen is made. Next, the precursor undergoes a forcespinning process, which causes the solvent to evaporate, leaving behind only polymeric nanofiber preforms. These preforms are then cured via UV exposure or other means to link the polymer chains to one another. Finally, the crosslinked polymers are heat treated under specific conditions to convert the polymer fibers into ceramics. This NASA innovation offers the ability to make low-cost, layered h-BN fiber mats or weaved fabrics of flexible h-BN from spun yarns at scale. The size of the fibers (> 200 nm) makes them easier to handle and disperse relative to nanotubes or nanosheets and mitigates respiratory hazards. The process offers high yields relative to alternative fabrication processes such as electrospinning. The resulting h-BN nanofibers have a broad range of potential applications and are poised to enable the development of new, multifunctional materials. Hexagonal boron nitride (h-BN) nanofibers have become an area of significant interest to industry given their combination of unique characteristics including excellent thermal conductivity, high electrical resistivity, chemical inertness, light weight, and mechanical strength. Potential applications for h-BN nanofibers include their use as an additive to polymers and other composites to improve material properties, high voltage cable insulation, re-entry shielding, radiation shielding, electric vehicle thermal dissipation, and much more. However, manufacturing of h-BN nanofibers is costly, difficult at scale, and could pose respiratory hazards resulting from their small scale (< 100nm). This has limited the commercial availability of h-BN nanofibers. High-cost BN nanosheets are available, but their use is limited as the form factor is already established and they are difficult to disperse. h-BN nanofibers could be a critical technology enabling the development of advanced multifunctional materials not just for space systems, but also for a variety of terrestrial applications. So, innovators at NASA’s Glenn Research Center (GRC) developed a polymer derived ceramic (PDC) process utilizing forcespinning technology that enables the rapid, low-cost fabrication of h-BN fibers. Fibers generated using the process have larger diameters (= 200nm), mitigating respiratory hazard risk.