Growth Of Boron Nitride Nanotubes Research Articles

Surface Growth of Boron Nitride Nanotubes through Boron Source Design

AbstractBoron nitride nanotubes (BNNTs) are promising materials due to their unique physical and chemical properties. Fabrication technologies based on gas‐phase reactions reduce the control and collection efficiency of BNNTs due to reactant and product dispersion within the reaction vessel. A surface growth method that allows for controllable growth of BNNTs in certain regions using a preburied boron source is introduced. This work leverages the high solubility of boron in metals to create a boronized layer on the surface which serves as the boron source to confine the growth of BNNTs. Dense and uniform BNNTs are obtained after loading catalysts onto the boronized substrate and annealing under ammonia. Confirmatory experiments demonstrate that the boride layer provides boron for BNNTs growth. Furthermore, the patterned growth of BNNTs is realized by patterning the boronizing region, demonstrating the controllability of this method. In addition, the Ni substrate with BNNTs growth exhibits better performance in corrosion resistance and thermal conductivity than pure Ni. This study introduces an alternative strategy for the surface growth of BNNTs based on boron source design, which offers new possibilities for the controllable preparation of BNNTs for various applications.

Growth of boron nitride nanotubes from magnesium-based catalysts

Growth of boron nitride nanotubes from magnesium-based catalysts

Experimental and Computational Research on the Effect of Flow Distribution on the Growth of Boron Nitride Nanotubes by Chemical Vapor Deposition

The chemical vapor deposition (CVD) method offers a controlled and scalable approach for the large-scale production of boron nitride nanotubes (BNNTs). However, current research on BNNTs has been primarily focused on identifying precursors that can facilitate the efficient preparation of pure BNNTs. The collection of BNNTs remains a significant challenge due to the complex nature of the CVD reaction, which is influenced by the variable location of the floating aggregation of BNNTs generated from the gas phase reaction. To address this issue, we utilized B/MgO/Fe2O3, a well-established CVD precursor, to grow BNNTs in a horizontal furnace. Through experimental and computational fluid dynamics simulation analysis, we identified the impact of vortex generation and low flow rate on the floating height of BNNTs. Using the insights gained from these investigations, we designed a more efficient growth setup, laying the foundation for achieving larger-scale BNNT production in the future.

Spontaneous formation of boron nitride nanotube fibers by boron impurity reduction in laser ablation of ammonia borane

Highly crystalline and few-walled boron nitride nanotubes (BNNTs) had been synthesized by laser ablation using only ammonia borane as a precursor. As a molecular precursor, ammonia borane supplied both B and N atoms with a ratio of 1:1, and BNNTs were formed via the homogeneous nucleation of BN radicals, not the growth from boron nano-droplets, which is a generally accepted growth mechanism of the laser-grown BNNTs. Owing to the absence of amorphous boron impurities, the van der Waals interaction among BNNTs became effective and thus a BNNT fibers was formed spontaneously during the BNNT synthesis. The BNNT growth and the subsequent fiber formation are found to occur only at high pressures of a surrounding gas. The mechanism behind the critical role of pressure was elucidated from the perspective of reaction kinetics and thermal fluid behaviors. A polarized Raman study confirmed that the BNNT fiber formed exhibits a good alignment of BNNTs, which implies great potential for continuous production of high-quality BNNT fibers for various applications.

An effective growth of hierarchical BNNTs/SiC fibers with enhanced interfacial properties

Tailoring the SiC fiber-matrix interface in micron-sized fibers is crucial to attaining enhanced mechanical properties in ceramic reinforced composites. Herein, the authors report the growth of boron nitride nanotubes (BNNT) onto SiC fibers (SiCf), creating a fuzzy fiber architecture to promote the surface area for a defined load path of fiber to the matrix and improve the mechanical properties of these structures. Successful BNNT-growth is achieved by a boron oxide chemical vapor deposition method combined with growth vapor trapping with optimum parameters of 1200 °C and 1 h, comparatively low temperature to those reported in the literature. The strength loss of SiCf after exposure to 1200 °C was attributed to high process temperature, similar to what has been observed in the literature. Hence, BNNT growth does not lead to additional strength loss on these fibers measured by a single fiber tensile test. Moreover, through this direct growth method, grown BNNTs utilize a surface-anchored BNNTs/SiCf, creating a good matrix adhesion to prevent fiber-fiber sliding and pullout and increasing the interfacial shear strength (IFSS) with epoxy. Furthermore, microbond tests show that fuzzy BNNTs/SiCf architecture increased IFSS by at least 87.8% compared to as-received SiCf.

Boron nitride nanotube precursor formation during high-temperature synthesis: kinetic and thermodynamic modelling

We performed integrated modelling of the chemical pathways of formation for boron nitride nanotube (BNNT) precursors during high-temperature synthesis in a B/N2 mixture. Integrated modelling includes quantum chemistry, Quantum–classical molecular dynamics, thermodynamic modelling, and kinetic approaches. We demonstrate that BN compounds are formed via the interaction of molecular nitrogen with small boron clusters, rather than through interactions with less reactive liquid boron. (This process can also be described as N2 molecule fixation.) Liquid boron evaporates to produce these boron clusters (B m with m ≤ 5), which are subsequently converted into B m N n chains. The production of such chains is crucial to the growth of BNNTs because these chains form the building blocks of bigger and longer BN chains and rings, which are in turn the building blocks of fullborenes and BNNTs. Additionally, kinetic modelling revealed that B4N4 and B5N4 species in particular play a major role in the N2 molecule fixation process. The formation of these species via reactions with B4 and B5 clusters is not adequately described under the assumption of thermodynamic equilibrium, as is demonstrated in our kinetic modelling. Thus, the accumulation of both B4N4 and B5N4 depends on the background gas pressure and the gas cooling rate. Long BN chains and rings, which are precursors of the fullborene and BNNT growth, form via self-assembly of components B4N4 and B5N4. Our modelling results—particularly the increased densities of B4N4 and B5N4 species at higher gas pressures—explain the experimentally observed effect of gas pressure on the yield of high-quality BNNTs. The catalytic role of hydrogen was also studied; it is shown that HBNH molecules can be the main precursor of BNNT synthesis in the presence of hydrogen.

Synthesis of Boron Nitride Nanotubes Using Plasma-Assisted CVD Catalyzed by Cu Nanoparticles and Oxygen.

We found that oxidized Cu nanoparticles can catalyze the growth of boron nitride nanotubes from borazine via plasma-assisted chemical vapor deposition. The Raman spectra suggest that the formation of thin-walled nanotubes show a radial breathing mode vibration. The presence of oxygen in the plasma environment was necessary for the growth of the nanotubes, and a part of the nanotubes had a core shell structure with a cupper species inside it. In atomic resolution transmission electron microscope (TEM) images, Cu2O was found at the interface between the Cu-core and turbostratic BN-shell. The growth mechanism seemed different from that of carbon nanotube core-shell structures. Therefore, we pointed out the important role of the dynamic morphological change in the Cu2O-Cu system.

Synthesis of boron nitride nanotubes using triple DC thermal plasma reactor with hydrogen injection

Highly crystalline boron nitride nanotubes (BNNTs) having multi-walls (≤5 walls) and a small diameter (~7 nm) were synthesized using a triple DC thermal plasma reactor with hydrogen injection. Triple torch configuration not only generates larger high temperature regions than single torch but also allow precursors to directly penetrate the core of the plasma flame, the hottest area in the reactor. A triple torch increases the productivity of BNNT synthesis by preventing the flow of precursors into the rim of plasma flame, a problem that occurs with single torch due to the high velocity and viscosity of the central flame. The role of hydrogen in the growth of BNNTs was analyzed by thermodynamic equilibrium reaction calculations and numerical analysis of thermal flow in the system. The reaction calculations revealed that hydrogen facilitates the formation of NH, NH2, and N2H2 molecules by inhibiting N from recombining into N2 in the high temperature region. Hydrogen influences the formation of scattered high temperature and enthalpy regions due to its thermal properties and expands the vortex region, leading to longer residence times for B-N-H intermediates in the reactive region. As a result, 12.6 g of BNNTs are produced with 21.4 kW of input power. A comparison with other methods shows that this yield is superior and provides an economic perspective for the proposed pilot synthesis of BNNTs.

Enhanced In-Plane Thermal Conductance of Thin Films Composed of Coaxially Combined Single-Walled Carbon Nanotubes and Boron Nitride Nanotubes.

Carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs) are one-dimensional materials with high thermal conductivity and similar crystal structures. Additionally, BNNTs feature higher thermal stability in air than CNTs. In this work, a single-walled carbon nanotube (SWCNT) film was used as a template to synthesize a BNNT coating by the chemical vapor deposition (CVD) method to form a coaxial heterostructure. Then, a contact-free steady-state infrared (IR) method was adopted to measure the in-plane sheet thermal conductance of the as-synthesized film. The heterostructured SWCNT-BNNT film demonstrates an enhanced sheet thermal conductance compared with the bare SWCNT film. The increase in sheet thermal conductance shows a reverse relationship with SWCNT film transparency. An enhancement of over 80% (from ∼3.6 to ∼6.4 μW·K-1·sq-1) is attained when the BNNT coating is applied to an SWCNT film with a transparency of 87%. This increase is achieved by BNNTs serving as an additional thermal conducting path. The relationship between the thermal conductance increase and transparency of the SWCNT film is studied by a structured modeling of the SWCNT film. We also discuss the effect of annealing on the thermal conductance of SWCNTs before BNNT growth. Along with the preservation of high electrical conductance, the enhanced thermal conductance of the heterostructured SWCNT-BNNT films makes them a promising building block for thermal and optoelectronic applications.

Theoretical Modeling of Single-Walled Boron Nitride Nanotube Growth in CVD

Growth mechanism of single-walled boron nitride nanotube (BNNT) in chemical vapor deposition method is presented based on investigation of role of phonon oscillations in the system. The theoretical analysis shows that thicker produced BNNT has shorter length. Also, depending on the type of catalyst, there is a furnace temperature which optimizes the growth of BNNT. Moreover, when the ambient gas pressure is increased, the nanotube growth rate is increased.

The MgB2-catalyzed growth of boron nitride nanotubes using B/MgO as a boron containing precursor.

With the development of preparation technology, obtaining boron nitride nanotubes (BNNTs) is no longer difficult, but it is still not easy to balance the quality and purity of the obtained products using existing methods. In this work, we investigated a previously reported MgB2 catalyst to explore the synthesis of BNNTs at a higher temperature in a conventional chemical vapor deposition (CVD) system from a classic B/MgO precursor. Various characterization methods showed the high activity of MgB2 at 1400 °C and the superiority of the as-grown BNNTs in terms of purity and quality. Further reference experiments and element characterization measurements were also performed to verify the role of MgB2 in the growth of the BNNTs, finding that B/MgO/MgB2 is a simple and efficient precursor.

Ammonium-tungstate-promoted growth of boron nitride nanotubes

Ammonium tungstate ((NH4)10W12O41 · xH2O) is a kind of oxygen-containing ammonium salt. The following study proves that it can be successfully used as a metal oxide alternative to produce boron oxide (B2O2) by oxidizing boron (B) in a traditional boron oxide chemical vapor deposition (BOCVD) process. This special oxidant promotes the simplistic fabrication of boron nitride nanotubes (BNNTs) in a conventional horizontal tube furnace, an outcome which may have resulted from its strong oxidizability. The experimental results demonstrate that the mole ratio of B and (NH4)10W12O41 · xH2O is a key parameter in determining the formation, quality and quantity of BNNTs when stainless steel is employed as a catalyst. We also found that Mg(NO3)2 and MgO nanoparticles (NPs) can be used as catalysts to grow BNNTs with the same precursor. The BNNTs obtained from the Mg(NO3)2 catalyst were straighter than those obtained from the MgO NP catalyst. This could have been due to the different physical forms of the catalysts that were used.

Highly Efficient Growth of Boron Nitride Nanotubes and the Thermal Conductivity of Their Polymer Composites

We developed a novel strategy for the gram-scale fabrication of boron nitride nanotubes (BNNTs). Li3N was used as the promoter: it not only catalyzes the BNNTs growth but also serves as the nitrogen source. BNNT/thermoplastic polyurethane (TPU) are flexible, transparent, and thermally conductive composite films that were also fabricated with an in-plane thermal conductivity of 14.5 W m–1 K–1 at 1.0 wt % BNNTs. This is an improvement of more than 400% over neat TPU. This study will enable BNNTs to be used in heat dissipation materials, high temperature components, and thermal protection systems.

Role of Hydrogen in High-Yield Growth of Boron Nitride Nanotubes at Atmospheric Pressure by Induction Thermal Plasma.

We recently demonstrated scalable manufacturing of boron nitride nanotubes (BNNTs) directly from hexagonal BN (hBN) powder by using induction thermal plasma, with a high-yield rate approaching 20 g/h. The main finding was that the presence of hydrogen is crucial for the high-yield growth of BNNTs. Here we investigate the detailed role of hydrogen by numerical modeling and in situ optical emission spectroscopy (OES) and reveal that both the thermofluidic fields and chemical pathways are significantly altered by hydrogen in favor of rapid growth of BNNTs. The numerical simulation indicated improved particle heating and quenching rates (∼105 K/s) due to the high thermal conductivity of hydrogen over the temperature range of 3500-4000 K. These are crucial for the complete vaporization of the hBN feedstock and rapid formation of nanosized B droplets for the subsequent BNNT growth. Hydrogen is also found to extend the active BNNT growth zone toward the reactor downstream, maintaining the gas temperature above the B solidification limit (∼2300 K) by releasing the recombination heat of H atoms, which starts at 3800 K. The OES study revealed that H radicals also stabilize B or N radicals from dissociation of the feedstock as BH and NH radicals while suppressing the formation of N2 or N2+ species. Our density functional theory calculations showed that such radicals can provide faster chemical pathways for the formation of BN compared with relatively inert N2.

Synthesis of Boron Nitride Nanotubes and Boron Nitride Nanoflakes with Potential Application in Bioimaging

Hexagonal boron nitride (BN) is structural analogues to graphitic structure of carbon. Similar to graphene and carbon nanotubes, BN also has nanosheets structure, also known as white graphene and nanotubes structure. These BN nanostructures show excellent properties, such as high stability, mechanical strength and resistant to chemicals. Synthesis of BN nanosheets is easier as compared to synthesis of its 1D nanostructure due its hexagonal layered structure, in which stacks are attached with each other by weak Van der Waals forces. In the present work, synthesis and applications of 1D and 2D nanostructures are discussed. Growth of BN nanotubes on tungsten substrate was performed by using copper as catalyst with a simple and easy method. Synthesis of fluorescent BN nanoflakes was performed using solid precursor, boric oxide and urea for boron and nitrogen, in a high-temperature furnace under argon atmosphere. The product was ultrasonicated in water to get completely stable dispersion of fluorescent nanoflakes as final product. Both The product was then characterized by FESEM, TEM, FTIR. The fluorescence behaviour of BN nanoflakes was also measure and applied for bioimaging of breast cancer cells (MCF-7).

Bimetallic catalytic growth of boron nitride nanotubes.

Boron nitride nanotubes (BNNTs) have outstanding properties and potential applications. However, the fundamental issue regarding the growth mechanism remains an open question. Herein, we design a bimetallic catalyst that dissolves B and N simultaneously, which has been proved to be key for BNNT growth.

Glass fabrics self-cracking catalytic growth of boron nitride nanotubes

Glass fabrics were used to fabricate boron nitride nanotubes (BNNTs) with a broad diameter range through a combined chemical vapor deposition and self-propagation high-temperature synthesis (CVD-SHS) method at different holding times (0min, 30min, 90min, 180min and 360min). SEM characterization has been employed to investigate the macro and micro structure/morphology changes of the glass fabrics and BNNTs in detail. SEM image analysis has provided direct experimental evidences for the rationality of the optimized self-cracking catalyst VLS growth mechanism, including the transformation situations of the glass fabrics and the BNNTs growth processes respectively. This paper was the further research and compensation for the theory and experiment deficiencies in the new preparation method of BNNTs reported in our previous work. In addition, it is likely that the distinctive self-cracking catalyst VLS growth mechanism could provide a new idea to preparation of other inorganic functional nano-materials using similar one-dimensional raw materials as growth templates and catalysts.

Remote catalyzation for growth of boron nitride nanotubes by low pressure chemical vapor deposition

Direct deposition of high purity and quality boron nitride nanotubes (BNNTs) on Si substrate were obtained using low pressure chemical vapor deposition (LPCVD). We find Fe–Mg–O species may act as catalysts for growing BNNTs. This synthesis process conforms to vapor–liquid–solid (VLS) growth mechanism. As-grown BNNTs also show a large optical energy band gap of 6.12eV, approaching to hexagonal phase BN single crystals. Meanwhile, as-grown BNNTs exhibit an intense UV-emission band located at 345nm and a weak deep band at 237nm. Their optoelectronic properties make them have promising for future nanoscale deep-UV light emitting devices.

Boron nitride nanotube growth via boron oxide assisted chemical vapor transport-deposition process using LiNO3 as a promoter

High-purity straight and discrete multiwalled boron nitride nanotubes (BNNTs) were grown via a boron oxide vapor reaction with ammonia using LiNO3 as a promoter. Only a trace amount of boron oxide was detected as an impurity in the BNNTs by energy-dispersive X-ray (EDX) and Raman spectroscopies. Boron oxide vapor was generated from a mixture of B, FeO, and MgO powders heated to 1,150 °C, and it was transported to the reaction zone by flowing ammonia. Lithium nitrate was applied to the upper side of a BN bar from a water solution. The bar was placed along a temperature gradient zone in a horizontal tubular furnace. BNNTs with average diameters of 30–50 nm were mostly observed in a temperature range of 1,280–1,320 °C. At higher temperatures, curled polycrystalline BN fibers appeared. Above 1,320 °C, the number of BNNTs drastically decreased, whereas the quantity and diameter of the fibers increased. The mechanism of BNNT and fiber growth is proposed and discussed.

Effective Synthesis of Vertically Aligned Boron Nitride Nanotubes via a Simple CCVD

A simple catalytic chemical vapor deposition technique based on the combined logic of previously synthesized vertically aligned carbon nanotubes and pattern growth of boron nitride nanotubes (BNNTs) along with a few simple modifications in the experimental setup is successfully used for the synthesis of vertically aligned BNNTs. Field emission scanning electron microscope images show the top and side view of the as grown pure BNNTs. High-resolution transmission electron microscope images confirm the tubular structure as well as the highly crystalline nature of the tubes. X-ray photon spectroscopy and Raman spectroscopy indicate h-BN as a main constituent of BNNTs synthesized in the present work.