A fundamental understanding of the thermal behavior of reinforcement materials is crucial to fully exploit their properties in composites. Boron nitride nanotubes (BNNTs), structural analogues to carbon nanotubes, are a strong candidate for nanofillers in high-temperature composites due to their high thermal stability, oxidation resistance, excellent mechanical properties, and high thermal conductivity. In this paper, samples of high-quality, high-purity BNNTs were tested to thermal failure in an inert atmosphere for the first time up to 2500 °C. A significant fraction of the BNNTs survived temperatures as high as 2200°, and the BNNT samples were completely undamaged at temperatures as high as 1800 °C. Boron nitride (BN) nanopowders were tested identically to perform a comparative study, as hexagonal BN is commonly found in purified BNNT samples. Observed color darkening, significant weight loss, an increased boron atomic level, significant weight gain upon oxidation, the presence of boron oxide compounds in an oxidized sample, and the observed boron clusters at the nanoscale indicate dissociation of B-N bonds in the BNNT sample at 2200 °C. The stability of BNNT structures was observed up to 2000 °C, with local/partial wall dissociation or unzipping, and complete survivability of highly crystalline BNNTs is demonstrated up to 1800 °C. This paper presents the first-ever study on extreme temperature thermal stability of purified BNNTs in an inert atmosphere analogous to manufacturing processes for high-temperature nanocomposites.

Boron nitride nanotubes (BNNTs) possess extraordinary properties on the molecular level; hence, it is of particular interest to use them for the assembly of macroscopic materials. However, difficulties in BNNT synthesis and purification hinder their processing into such objects. Only recently, a large-scale production of high-quality BNNTs has been explored. Here, we study by advanced electron microscopy techniques BNNTs synthesized by the high temperature–pressure (HTP) method and compare BNNTs after different purification processes. We document many different defects and demonstrate that these do not prevent nematic alignment of BNNTs at high concentrations. In fact, we show that small-ordered domains form at lower concentrations for BNNTs of higher purity. Cryogenic electron microscopy provides direct-imaging evidence of the BNNT liquid crystalline phase, indicating the potential for the fabrication of highly ordered BNNT-based macroscopic assemblies by liquid-phase processing.

Boron nitride nanotubes (BNNTs) have attracted attention for their predicted extraordinary properties; yet, challenges in synthesis and processing have stifled progress on macroscopic materials. Recent advances have led to the production of highly pure BNNTs. Here we report that neat BNNTs dissolve in chlorosulfonic acid (CSA) and form birefringent liquid crystal domains at concentrations above 170 ppmw. These tactoidal domains merge into millimeter-sized regions upon light sonication in capillaries. Cryogenic electron microscopy directly shows nematic alignment of BNNTs in solution. BNNT liquid crystals can be processed into aligned films and extruded into neat BNNT fibers. This study of nematic liquid crystals of BNNTs demonstrates their ability to form macroscopic materials to be used in high-performance applications.

With the rapid development of electromagnetic (EM) wave circuit devices, high-performance wave-transparent materials with various functions have attracted great attention. Ceramic material is a promising candidate to be applied in harsh environments because of its chemical and corrosion resistance. In this work, a polymer-derived route was adopted to synthesize ceramic composite at room temperature. The composite is made of perhydropolysilazane-derived SiON ceramic and reinforced with boron nitride nanotubes (BNNTs) sheets. With the addition of SiON ceramic materials, the resultant sample showed an excellent hydrophobicity with a contact angle of 135–146.9°. More importantly, superior thermal stability at 1600 °C in the oxygen-containing atmosphere was observed for the fabricated SiON/BNNTs sample, without any shape change. The electromagnetic transparency of the SiON/BNNTs was studied through the waveguide method. The prepared SiON/BNNTs sample has an average real permittivity between 1.52 and 1.55 and an average loss tangent value in the range of 0.0074–0.0266, at the frequency range of 26.5–40 GHz. The effect of thickness on the wave transparency of SiON/BNNTs samples is also discussed. To summarize the aforementioned superior characterization and measurement results, the presented SiON/BNNTs material system has a great potential to be used as EM transparent materials in harsh conditions.

Boron nitride nanotubes (BNNTs) will be one of the most important materials of this century. Recent synthetic advances have made BNNTs viable candidates for advanced multifunctional materials. Like carbon nanotubes and graphene, BNNTs and h-BN have extraordinary physical properties. Unlike CNTs, BNNTs have a wideband gap; they are piezoelectric, have neutron radiation shielding capability, and can withstand degradation up to 1000 °C. BNNTs could be the next big leap for nanocomposite advanced applications; however, significant scientific challenges must be addressed. Predominantly, large-scale synthesis techniques are immature. Production products require careful characterization, analysis, and purification. Impurities such as boron, amorphous BN, and h-BN lead to difficulty studying chemical modification and translation of BNNT properties. This review synthesizes relevant literature and state-of-the-art techniques regarding purification methods of BNNTs, classified as physical, chemical, and multi-step techniques and their applications. The review also discusses BNNT synthesis methods and future research directions.

Rice University researchers produce images and movies of a single molecule of BNNT undergoing Brownian motion, the jitterbug-like action of a very small particle frequently encountered in the studies of microbes and other small objects. This fundamental work gives researches a glimpse into the behavior of isolated BNNTs, an important step in understanding their physics and potential applications.

Kyung Hee University scientists film BNNTs at work as sensors on a robotic arm. Nano-sensors can greatly reduce the weight and complexity of the control and actuation systems in prosthetics and other bio-engineering devices.