Significant strengthening of copper-based composites using boron nitride nanotubes

Nanotubes, such as boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs), exhibit excellent mechanical properties. In this work, high-quality BNNTs were synthesized by ball milling and annealing. Subsequently, well-dispersed 3vol%BNNTs/Cu and 3vol%CNTs/Cu composites were successfully prepared using ball milling, spark plasma sintering, and followed by hot-rolling. Moreover, the mechanical properties and strengthening mechanisms of BNNTs/Cu and CNTs/Cu composites were compared and discussed in details. At 293 K,both BNNTs/Cu and CNTs/Cu composites exhibited similar ultimate tensile strength (UTS) of~404 MPa, which is approximately 170%higher than pure Cu. However, at 873 K, the UTS and yield strength of BNNTs/Cu are 27%and 29%higher than those of CNTs/Cu, respectively.This difference can be attributed to the stronger inter-walls shear resistance, higher thermomechanical stability of BNNTs, and stronger bonding at the BNNTs/Cu interface as compared to the CNTs/Cu interface. These findings provide valuable insights into the potential of BNNTs as an excellent reinforcement for metal matrix composites, particularly at high temperature.

Adsorption of Fe(CO)_4 on the Sidewall of Boron Nitride Nanotubes:A Periodic DFT Study

The adsorption of Fe（CO）4 on various types of boron nitride nanotubes （BNNTs） areinvestigated by employing density functional theory. Our results indicate that Fe（CO）4 prefers to adsorb on the top of nitrogen atom via Fe atom, and the electronic property analysis indicates that the adsorption of Fe（CO）4 can reduce the band-gap of BNNTs.

Preferable Orientations of Interacting C_(60) Molecules inside Single Wall Boron Nitride Nanotubes

This work focuses on the preferable orientation analysis of the hybrid system where the C60 molecules are encap- sulated inside the boron nitride nanotubes by using the two-molecule model. The low-energy state can be acquired in the contour map, which provides the visual information of the systematical van der Waals interaction potential for the C60 molecules adopting different orientations. Our results show that the C60 molecules exhibit the pre- ferred pentagon and hexagon orientations with the tube＇s diameter smaller and larger than 13.55A, respectively. The preferred two-bond orientation obtained in the single-molecule model is absent in this study, indicating that the intermolecular interaction of adjacent C60 molecules plays an important role in the orientational behaviors of this peapod structure.

A density functional theory study on parameters fitting of ultra long armchair(n,n) single walled boron nitride nanotubes

Armchair （n, n） single walled boron nitride nanotubes with n = 2-17 are studied by the density functional theory at the B3LYP/3-21G（d） level combined with the periodic boundary conditions for simulating the ultra long model. The results show that the structure parameters and the formation energies bear a strong relationship to n. The fitted analytical equations are developed with correlation coefficients larger than 0.999. The energy gaps of （2, 2） and （3, 3） tubes are indirect gaps, and the larger tubes （n = 4-17） have direct energy gaps. Results show that the armchair boron nitride nanotubes （n = 2-17） are insulators with wide energy gaps of between 5.93 eV and 6.23 eV.

Mechanosynthesis of Boron Nitride Nanotubes

Boron nitride nanotubes （BN-NTs） with pure hexagonal BN phase have been synthesized by heating ball-milled boron powders in flowing ammonia gas at a temperature of 1200℃. The as-synthesized products were characterized by X-ray powder diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and electron energy loss spectroscopy （EELS）. The diameters of nanotubes are in the rage of 40-120nm and the lengths are more than 10μm. EELS result identifies that the ratio of boron and nitrogen is almost 1：1 The growth temperature is a crucial growth parameter in controlling the structure and crystalline of BN-NTs. The nanotubes grown at 1100℃ possesses of a bamboo-like structure, while as the temperature increased to 1200℃, most of the nanotubes exhibited a cylindrical structure. In addition, changing the heating time can control the size of the nanotubes. The gas atmosphere has influence on the yield of BN-NTs during heating process. When heating atmosphere was replaced by nitrogen, the yield of nanotubes was remarkably decreased.

Boron Nitride Nanotubes as Novel Vectors for Drug Delivery of Amino Acids：A First Principles Simulation

The first principles calculations based on density functional theory（DFT） were performed for investigating the interaction of amino acids with（5, 5） armchair and（8, 0） zigzag boron nitride nanotubes（BNNTs）. Findings showed that the adsorption and solvation energies were negative for（5, 5）/（8,0） BNNTs-amino acid complexes, implying the thermodynamic favorability and spontaneous interactions of amino acids with BNNTs sidewall. Based on calculated results, the BNNTs are expected to be a potential efficient adsorbent as well as a suitable drug delivery vehicle for the adsorption of amino acids within biological systems.

Electromechanical coupling effect on electronic properties of double-walled boron nitride nanotubes

We report on a first-principles study of a novel band modulation in zigzag double-walled boron nitride nan- otubes （DBNNTs） by applying radial strain and coupled ex- ternal electric field. We show that the band alignment be- tween the inner and outer walls of the DBNNTs can be tuned from type I to type II with increasing radial strain, accompa- nied with a direct to indirect band gap transition and a sub- stantial gap reduction. The band gap can be further signifi- cantly reduced by applying a transverse electric field. The coupling of electric field with the radial strain makes the field-induced gap reduction being anisotropic and more re- markable than that in undeformed DBNNTs. In particular, the gap variation induced by electric field perpendicular to the radial strain is the most remarkable among all the modu-lations. These tunable properties by electromechanical cou- pling in DBNNTs will greatly enrich their versatile applica- tions in future nanoelectronics.

The Buckling Behavior of Boron Nitride Nanotubes under Bending： An Atomistic Study

In this paper, the buckling behavior of zigzag BN （Boron Nitride） nanotubes under bending is studied through molecular dynamics finite element method with Tersoff potential. The tube with namely （15, 0） BN zigzag tube is investigated. The critical bending buckling angle, moment and curvature are studied and examined with respect to the tube length-diameter ratios from 5 to 30. Effects of a SW （Stone-Wales） defect in the middle tube on the bending behavior are also discussed. The results show that the tube length affects significantly the bending behavior of these tubes. All tubes exhibit brittle fracture under bending. The buckling takes place at the middle in the compressive side of these tubes. These results are important information on the buckling behaviors of pristine and Stone-Wales BN nanotubes, which will be useful for their future applications.

An Efficient Boron Source Activation Strategy for the Low‑Temperature Synthesis of Boron Nitride Nanotubes

Lowering the synthesis temperature of boron nitride nanotubes(BNNTs)is crucial for their development.The primary reason for adopting a high temperature is to enable the effective activation of highmelting-point solid boron.In this study,we developed a novel approach for efficiently activating boron by introducing alkali metal compounds into the conventional MgO–B system.This approach can be adopted to form various low-melting-point AM–Mg–B–O growth systems.These growth systems have improved catalytic capability and reactivity even under low-temperature conditions,facilitating the synthesis of BNNTs at temperatures as low as 850℃.In addition,molecular dynamics simulations based on density functional theory theoretically demonstrate that the systems maintain a liquid state at low temperatures and interact with N atoms to form BN chains.These findings offer novel insights into the design of boron activation and are expected to facilitate research on the low-temperature synthesis of BNNTs.

Growth of boron nitride nanotubes from magnesium-based catalysts

This study reports an efficient method for growing high-quality boron nitride nanotubes(BNNTs)via chemical vapor deposition of low-melting-point precursors—magnesium diboride(MgB_(2)),magnesium nitride(Mg_(3)N_(2)),and diboron trioxide(B_(2)O)at a growth temperature of 1000–1300℃.The strong oxygen-capturing ability of Mg_(3)N_(2)inhibits the formation of high-melting-point Mg_(3)B_(2)O_(6),which helps MgB_(2)to maintain an efficient and stable catalytic capacity,thereby enhancing its growth efficiency and utilization of the boron source.Moreover,polydimethylsiloxane(PDMS)composites formed from these BNNTs demonstrated much greater thermal conductivities than pure PDMS.Thus,this novel strategy for preparing BNNTs is efficient,and they have great potential for application as thermal interface materials.

Highly efficient synthesis of boron nitride nanotubes by catalytic chemical vapor deposition of boron/nickel containing precursors

High-purity and high-yield boron nitride nanotubes with large aspect ratio were prepared by a facile two-step process,including the synthesis of boron/nickel containing precursors by precipitation reactions and subsequent thermally catalytic chemical vapor deposition reactions.The influence of catalyst content and annealing temperature on the phase composition and microstructure of the products were investigated.The results show that it is difficult to exert the catalytic effect of nickel-based catalyst at low temperatures(<1400℃).At appropriate temperatures(1400-1500℃),highly crystalline boron nitride nanotubes with a length of more than 50 mm and a diameter of 50 nm are formed.The content of catalyst in the precursor mainly affects the morphology of the boron nitride product.If the content is too low,it is easy to form boron nitride particles;while high catalyst content can easily lead to catalyst aggregation and form a submicron one-dimensional boron nitride with unregular structure.Based on microstructural evolutions,phase changes,and thermodynamic analysis,the vapor-liquid-solid(V-L-S)growth mechanism of the tip growth mode dominates the formation of boron nitride nanotubes has also been verified.

Electrostabilized homogeneous dispersion of boron nitride nanotubes in wide-range of solvents achieved by surface polarity modulation through pyridine attachment

Boron nitride nanotubes(BNNTs)show exceptional physical properties including high mechanical strength and thermal conductivity;however,their applications have been restricted due to limited dispersibility in processing solvents.Here,a novel BNNT dispersion method with exceptional dispersibility in a wide range of solvents has been demonstrated by surtace polarity modulation through short-molecule pyridine attachment.Nitrogen atoms in pyridine are selectively bonded to electron-deficient boron atoms of the BNNT surface through Lewis acid-base reaction,which changes the surface polarity of BNNTs from neutral to negative.Re-dispersing pyridine-attached BNNTs(Py-BNNTs)create a thick and stable electronic double layer(EDL),resulting in uniform dispersion of BNNTs in solvents with an exceptional solubility parameter range of 18.5-48 MPa^1/2.The uniform dispersion of BNNTs is maintained even after the mixing with diverse polymers.Finally,composites incorporating uniformly-distributed BNNTs have been realized,and extraordinary property enhancements have been observed.The thermal conductivity of 20 wt.%Py-BNNT/epoxy composite has been significantly improved by 69.6%and the tensile strength of 2 wt.%Py-BNNT/PVA has been dramatically improved by 75.3%.Our work demonstrates a simple and facile route to dispersing BNNTs in diverse solvents,consequently leading to selective utlization of BNNT dispersed solvents in various application fields.

A New Target for Synthesis: Theoretical Prediction for the Reaction between Boron Nitride Nanotube and Dichlorocarbene

Understanding the chemistry of BNNT is a crucial step toward their ultimate practical use. A comparative study of Reactions A （ASWCNT （5,5） and CCl2） and B （ASWBNNT （5,5） and CCl2） have been performed by using ONIOM （B3LYP/6-31G＊： AM1） method in Gaussian03 program package. The results show that （1） the two reactions are both exothermic; （2） the mechanism of Reaction B is a two-step mechanism; （3） the difference in energy barriers suggests that the reaction of CCl2 with BNNT is easier than with CNT; （4） in reaction B, CCl2 prefers to attack the boron atom of BNNT first.

Length dependence of linear and nonlinear optical properties of finite-length BN（5,0） nanotube

In this paper, we investigate the length dependence of linear and nonlinear optical properties of finite-length BN nanotubes. The recently predicted smallest BN（5,0） nanotube with configuration stabilization is selected as an example. The energy gap and optical gap show the obvious length dependence with the increase of nanotube length. When the length reaches about 24 /~, the energy gap will saturate at about 3.2 eV, which agrees well with the corrected quasi- particle energy gap. The third-order polarizabilities increase with the increase of tube length. Two-photon allowed excited states have significant contributions to the third-order polarizabilities of BN（5,0） nanotube.

Electronic structures of an(8,0)boron nitride/carbon nanotube heterojunction

The electronic structure of the heterojunction is the foundation of the study on its working mechanism. Models of the heterojunctions formed by an （8, 0） boron nitride nanotube and an （8, 0） carbon nanotube with C-B or C-N interface have been established. The structures of the above heterojunctions were optimized with first-principle calculations based on density functional theory. The rearrangements of the heterojunctions concentrate mainly on their interfaces. The highest occupied molecular orbital and the lowest unoccupied molecular orbital of the heterojunctions distribute in the carbon nanotube section. As the band offsets of the above heterojunctions are achieved with the average bond energy method, the band structure is plotted.

Nanotubes in a Gradient Electric Field as Revealed by STM TEM Technique

We have investigated the behavior of two nanotube systems,carbon and boron nitride,under controlled applied voltages in a high-resolution transmission electron microscope(TEM)equipped with a scanning tunneling microscope(STM)unit.Individual nanotubes(or thin bundles)were positioned between a piezo-movable gold electrode and a biased(up to±140 V)STM tip inside the pole-piece of the microscope.The structures studied include double-and multi-walled carbon nanotubes(the latter having diverse morphologies due to the various synthetic procedures utilized),few-layered boron nitride nanotube bundles and multi-walled boron nitride nanotubes(with or without functionalized surfaces).The electrical breakdown,physical failure,and electrostatic interactions are documented for each system.