Scientists have predicted that carbon's immediate neighbors on the periodic chart, boron and nitrogen, may also form perfect nanotubes, since the advent of carbon nanotubes (CNTs) in 1991. First proposed then synthesized by researchers at UC Berkeley in the mid 1990's, the boron nitride nanotube (BNNT) has proven very difficult to make until now. Herein we provide an update on a catalyst-free method for synthesizing highly crystalline, small diameter BNNTs with a high aspect ratio using a high power laser under a high pressure and high temperature environment first discovered jointly by NASA/NIA/JSA. Progress in purification methods, dispersion studies, BNNT mat and composite formation, and modeling and diagnostics will also be presented. The white BNNTs offer extraordinary properties including neutron radiation shielding, piezoelectricity, thermal oxidative stability (> 800˚C in air), mechanical strength, and toughness. The characteristics of the novel BNNTs and BNNT polymer composites and their potential applications are discussed.
We present here the first fabrication of hollow cobalt oxide nanoparticles produced by a protein-regulated site-specific reconstitution process in aqueous solution and describe the metal growth mechanism in the ferritin interior.
Boron nitride nanotubes (BNNTs) are wide bandgap semiconducting materials with a quasiparticle energy gap larger than 6.0 eV. Since their first synthesis in 1995, there have been considerable attempts to develop novel BNNT-based applications in semiconductor science and technology. Inspired by carbon nanotube synthesis methods, many BNNT synthesis methods have been developed so far; however, it has been very challenging to produce BNNTs at a large scale with the structural quality high enough for exploring practical applications. Very recently there has been significant progress in the scalable manufacturing of high-quality BNNTs. In this article, we will review those particular breakthroughs and discuss their impact on semiconductor industries. Freestanding BNNT assemblies such as transparent thin films, yarns or buckypapers are highly advantageous in the development of novel BNNT-based semiconductor devices. The latest achievements in their manufacturing processes will be also presented along with their potential applications.
Boron nitride nanotubes (BNNT) are poised to fill an electrically insulating, high-temperature, highstrength niche. Despite significant progress over the past two decades, BNNTs are not yet synthesized in high enough quantity and quality to permit their use in engineering applications. The next necessary step to make BNNTs accessible for research and applications is to improve the availability of high-quality BNNTs. Here, we present a scalable bulk purification technique that yields high-purity BNNTs. Bulk synthesized material is introduced to a wet oxygen environment at elevated temperatures to remove elemental boron and hexagonal boron nitride impurities with a final yield of purified BNNTs near 10 wt %. This process shows full removal of impurities, as observed by scanning electron microscopy (SEM), cryogenic transmission electron microscopy (TEM), and high-resolution TEM. X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy show minimal BNNT functionalization, while high-resolution TEM shows damage to large-diameter BNNTs.
We report the thermal properties of boron nitride nanotube (BNNT) reinforced ceramic composites using the polymer derived ceramic (PDC) processing route. The nano‐composites had a BNNT loading of up to 35.4 vol.%. TGA results showed that nano‐composites have good thermal stability up to 900°C in air. BNNTs in nano‐composites survived in an oxidizing environment up to 900°C, revealing that nano‐composites can be used for high temperature applications. Thermal conductivity of PDC reinforced with 35.4 vol.% BNNT was measured as 4.123 W/(m·K) at room temperature, which is a 2100 % increase compared to that of pristine PDC. The thermal conductivity value increases with the increase of BNNT content. A thermal conductivity percolation phenomenon appeared when the BNNT content increased to 36 ± 5 vol.%. The results of this study showed that BNNTs could effectively improve the thermal conductivity of PDC materials. BNNT reinforced PDC could be used as thermal structural materials in a harsh environment at temperatures up to 900°C.
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