Boron Nitride Samples Research Articles

Construction of MoS2/BN nanohybrids with enhanced photocatalytic performance for RhB and TC degradation

In this study, MoS2/boron nitride nanohybrids have been fabricated via a simple hydrothermal process. Highly efficient nanohybrids have been synthesized by adding boron nitride (BN) as interfacial charge carrier migrate mediators onto the MoS2. The MoS2/BN nanohybrids exhibit excellent photocatalytic efficiency for removing rhodamine B (RhB) and tetracycline (TC) pollutants. The MoS2/BN nanohybrids show the best rate constant of 0.07 min−1, which is 1.5 folds greater than MoS2. Besides, MoS2/BN nanohybrids exhibit excellent cycling stability. The conformable improved mechanism for MoS2/BN-10 % nanohybrids could be assigned to the useful interfacial charge carrier separation and transfer between MoS2 and BN. The investigative results exhibited that the heterostructures presented better photocatalytic performance than the bare MoS2, and a slight proportion of the BN sample was favorable for photoinduced electron-hole pairs separation, which can improve the photocatalytic efficiency of MoS2/BN nanohybrids. This study displayed a facile process for the reasonable design of photocatalysts by developing their heterostructure and application.

Neutron Irradiation Effects on Boron Nitride-Based Ceramics for Use in X-ray Detection.

X-ray detectors based on conventional semiconductors with large atomic numbers are suffering from the poor stability under a high dose rate of ionizing irradiation. In this work, we demonstrate that a wide band gap ceramic-boron nitride with small atomic numbers could be used for sensitive X-ray detection. Boron nitride samples showed excellent resistance to ionizing radiation, which have been systematically studied with the neutron- and electron-aging experiments. Then, we fully analyzed the influence of these aging effects on the fundamental properties of boron nitride. Interestingly, we found that the boron nitride samples could maintain relatively good charge transport properties even after large dose of neutron irradiation. The fabricated X-ray detectors showed decent performance metrics, and the neutron-aged boron nitride even showed improved operational stability under continuous X-ray irradiation, suggesting the great potential for real applications.

Dielectric property characterization at high temperature (RT to 1000 °C) of BN-based electromagnetic transparent materials for hypersonic applications

In this work, the dielectric properties of two dense, hot-pressed, commercial hexagonal boron nitride (h-BN, referred to as BN) samples and fabricated reinforced silicon carbonitride (SiCN) samples were evaluated from room temperature to 1000 °C across the Ka frequency band from 26.5 to 40 GHz in an air atmosphere. The two reinforcements in the fabricated samples are boron nitride nanotube (BNNT) and boron nitride nanobarb (BN-NanoBarb™). The ceramic matrix was prepared via the polymer-derived route. Each of the four types of samples was evaluated via free-space and waveguide methods. When the BNNT or BNNB loading was 10 wt%, the average permittivity of BNNT-SiCN and BNNB-SiCN were 2.52 and 3.42, with the loss tangent of 0.001 and 0.004, respectively. The porosity was detected to decrease from BN (31.14–41.61%) to BNNT - SiCN (28.11%) and BNNB - SiCN (23.28%) after the filler loading. The reduction of Van der Waals attraction by non-covalent functionalization ensures excellent dispersion between BNNT or BNNB and SiCN, as well as mechanical performance. This work aims to enhance the limited amount of dielectric data at high temperatures and across a high-frequency range. The results presented in the work establish the knowledge base for electromagnetic transparent materials in high-temperature and extreme environment applications.

Transition Metal-Doped Boron Nitride Atomic Sheets with an Engineered Bandgap and Magnetization

Controlled doping of flat atomic sheets of boron nitride (BN) can in principle break charge and spin symmetries. In contrast to graphene that oxidizes at >500 °C, due to its high melting point (ca. 2700 K) and the electrically insulating nature (Eg ∼ 5.5 eV), BN presents strong material candidature for flexible magnetic memory chips that are functional even under fire. Here, we report the transition metal (Fe and Cr) doping of BN by microwave and solvothermal methods. X-ray photoelectron spectroscopy reveals ∼17% doping by microwave (800 W) and <11% doping by the solvothermal method. Cr or Fe doping brings the bandgap down to ∼3.6 or ∼2.0 eV, respectively, for the doped BN samples. Cr doping by microwave results in intrinsic ferromagnetic ordering evident from the high Curie point (∼380 K) in contrast to orbital-mediated magnetic ordering in solvothermal Cr-doped BN systems. Fe doping raises magnetization values in particular. Spin-polarized DFT band structure calculations suggest vivid spin asymmetry caused by doping, supporting our experimental findings on doped BN samples.

Design and implementation of a device based on an off-axis parabolic mirror to perform luminescence experiments in a scanning tunneling microscope.

We present the design, implementation, and illustrative results of a light collection/injection strategy based on an off-axis parabolic mirror collector for a low-temperature Scanning Tunneling Microscope (STM). This device allows us to perform STM induced Light Emission (STM-LE) and Cathodoluminescence (STM-CL) experiments and in situ Photoluminescence (PL) and Raman spectroscopy as complementary techniques. Considering the Étendue conservation and using an off-axis parabolic mirror, it is possible to design a light collection and injection system that displays 72% of collection efficiency (considering the hemisphere above the sample surface) while maintaining high spectral resolution and minimizing signal loss. The performance of the STM is tested by atomically resolved images and scanning tunneling spectroscopy results on standard sample surfaces. The capabilities of our system are demonstrated by performing STM-LE on metallic surfaces and two-dimensional semiconducting samples, observing both plasmonic and excitonic emissions. In addition, we carried out in situ PL measurements on semiconducting monolayers and quantum dots and in situ Raman on graphite and hexagonal boron nitride (h-BN) samples. Additionally, STM-CL and PL were obtained on monolayer h-BN gathering luminescence spectra that are typically associated with intragap states related to carbon defects. The results show that the flexible and efficient light injection and collection device based on an off-axis parabolic mirror is a powerful tool to study several types of nanostructures with multiple spectroscopic techniques in correlation with their morphology at the atomic scale and electronic structure.

Determination of the optical bandgap of the Bernal and rhombohedral boron nitride polymorphs

We report a study of polymorphic boron nitride (BN) samples. We interpret the photoluminescence (PL) line at $6.032\ifmmode\pm\else\textpm\fi{}0.005\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ that can be recorded at 8 K in $s{p}^{2}$-bonded BN as being the signature of the excitonic fundamental bandgap of the Bernal BN (bBN) [or graphitic BN (gBN)] polymorph. This is determined by advanced PL measurements combined with x-ray characterizations on pure hexagonal BN (hBN) and on polymorphic crystal samples, later compared with the theoretical predictions of Sponza et al., [Phys. Rev. B 98, 125206 (2018)]. The overall picture is consistent with a direct excitonic fundamental bandgap of the bBN (or gBN) polymorph. This value $d{X}_{b}=6.032\ifmmode\pm\else\textpm\fi{}0.005\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ is higher than the indirect bandgap of hBN $(i{X}_{h}=5.955\ifmmode\pm\else\textpm\fi{}0.005\phantom{\rule{0.16em}{0ex}}\mathrm{eV})$.

Rheological, thermal, and electrical characterization polyamide/polypropylene blend composites containing hybrid filler: Boron nitride and reduced graphene oxide

AbstractIn this study, the microstructural development and its effect on the thermal conductivity of polyamide6 (PA6)/polypropylene (PP) blends containing boron nitride (BN) and reduced graphene oxide (rGo) as hybrid fillers were investigated. Blend samples were prepared using the masterbatch method to localize BN and rGo in the matrix phase (PA6). Dynamic rheological results were consistent with selective localization of the fillers in PA6 as evidenced by nonterminal behavior (3D network) PP/PA‐BN at low frequencies. Compared with the case where the matrix phase (PA6) was only filled with BN particles, thermal conductivity measurements showed that replacing 10% and 15% BN particles with rGo nanoparticles yielded higher thermal conductivity. The hybrid fillers had a synergetic effect on the heat conductive network, forming a more efficient percolating network of BN and rGo in the matrix phase (PA6). A comparison between the BN‐filled PA6 blend and the BN‐rGo‐filled PA6 blend revealed higher thermal conductivity in the PP/PA6‐BN‐rGo sample with co‐continuous morphology than in the PP/PA6‐BN sample with matrix‐disperse morphology.

Assessment of Physico-Chemical and Toxicological Properties of Commercial 2D Boron Nitride Nanopowder and Nanoplatelets.

Boron nitride (BN) nanomaterials have been increasingly explored for potential applications in chemistry and biology fields (e.g., biomedical, pharmaceutical, and energy industries) due to their unique physico-chemical properties. However, their safe utilization requires a profound knowledge on their potential toxicological and environmental impact. To date, BN nanoparticles have been considered to have a high biocompatibility degree, but in some cases, contradictory results on their potential toxicity have been reported. Therefore, in the present study, we assessed two commercial 2D BN samples, namely BN-nanopowder (BN-PW) and BN-nanoplatelet (BN-PL), with the objective to identify whether distinct physico-chemical features may have an influence on the biological responses of exposed cellular models. Morphological, structural, and composition analyses showed that the most remarkable difference between both commercial samples was the diameter of their disk-like shape, which was of 200–300 nm for BN-PL and 100–150 nm for BN-PW. Their potential toxicity was investigated using adenocarcinomic human alveolar basal epithelial cells (A549 cells) and the unicellular fungus Saccharomyces cerevisiae, as human and environmental eukaryotic models respectively, employing in vitro assays. In both cases, cellular viability assays and reactive oxygen species (ROS) determinations where performed. The impact of the selected nanomaterials in the viability of both unicellular models was very low, with only a slight reduction of S. cerevisiae colony forming units being observed after a long exposure period (24 h) to high concentrations (800 mg/L) of both nanomaterials. Similarly, BN-PW and BN-PL showed a low capacity to induce the formation of reactive oxygen species in the studied conditions. Even at the highest concentration and exposure times, no major cytotoxicity indicators were observed in human cells and yeast. The results obtained in the present study provide novel insights into the safety of 2D BN nanomaterials, indicating no significant differences in the toxicological potential of similar commercial products with a distinct lateral size, which showed to be safe products in the concentrations and exposure conditions tested.

Heat transfer of hexagonal boron nitride (h-BN) compound up to 1 MeV neutron energy: Kinetics of the release of wigner energy

In the present work, hexagonal boron nitride (h-BN) samples were irradiated by using high fluxes neutron irradiation. The neutron irradiation of the samples was carried out at the room temperature up to 1015 n/cm2 neutron flux with up to 1 MeV neutron energy at the IBR-2 M pulsed reactor in the Joint Institute for Nuclear Research, Dubna, Russia. The hexagonal boron nitride (h-BN) heat transfers changes with a differential mechanism under high flux neutron irradiation. The heat transfer depends on the transfer energy of the neutron. In the DSC curves for unirradiated and irradiated hexagonal boron nitride samples are seen phase transitions at the high temperature. However, the mechanism of the heat transfer flow rate functions for hexagonal boron nitride is more complex at the 300 ≤ T ≤ 1400 K temperature range. On the other hand, the Wigner energy of irradiated boron nitride samples was calculated for each of the irradiation fluxes. The Wigner energy increased up to 373 J/g with increasing neutron flux. The results have revealed that it has been observed a change in the rate of release of Wigner energy from 400 K to 1300 K. The surface morphology of hexagonal boron nitride under different fast neutron irradiation doses is investigated. The swelling was observed in the surface dynamics of the materials with an increased dose of irradiation.

Granularity-induced plastic deformation mechanism of pure polycrystalline cubic boron nitride

Combined X-ray diffraction(XRD) profile analysis and HRTEM observation, a method for exploration of plastic deformation in pure polycrystalline cubic boron nitride (PcBN) samples with sizes of primary cBN powders was developed. XRD profile results showed that the coarse-grained PcBN exhibited a larger micro-strain ε, a greater deformation stacking faults probability fD, which was an order of magnitude larger than that of fine-grained PcBN, but a smaller twin stacking faults probability fT. It was deduced that the plastic deformation of the coarse-grained PcBN was dominated by stacking faults and mechanical twins mode, which would result in strain strengthening and then recrystallization. While the manner of growth twins was the mainly modes of fine-grained PcBN by phase transform, especially utilized the curled SP2 structure as a basis for a cubic structure nucleation. Fundamental plastic deformation principles of the ultrafine polycrystalline cBN was crucial for the field of high-precision cutting tools.

Thermophysical behavior of boron nitride and boron trioxide ceramics compounds with high energy electron fluence and swift heavy ion irradiated

We report differential scanning calorimetry (DSC) studies of boron nitride and boron trioxide compounds under different irradiation conditions. In the present work, boron nitride (h-BN) (purity of 99.8% and density of 2.29 g/cm3) and boron trioxide (B2O3) (purity of 99.5% and density of 3.10 g/cm3) samples were irradiated by using high intense electron beam and swift heavy ions irradiation. Electron beam irradiation of the samples was carried out at the different electron fluence of 4.16 × 1016, 1.20 × 1017 and 1.03 × 1018 cm−2 with energy of 2.5 MeV. Whereas the swift heavy ion irradiation of the samples was carried out using 132Xe ions with energy of 167 MeV/u at the different fluence of 5 × 1012, 5 × 1013 and 3.83 × 1014 ion/cm2. The thermal parameter changes with a differential mechanism under different irradiation conditions were investigated. In the DSC curves at the low temperature for initial and irradiation samples do not undergo phase transitions. However, at the 100 ≤ T ≤ 300 K temperature range widely changed the mechanism of the heat flow rate, specific heat capacity and thermodynamic functions in the boron nitride and boron trioxide samples is a more completed. In addition, for each of irradiation fluences, the calculated thermodynamic functions and specific heat capacity was found to increase from 0.002 J/g‧K to 0.08 J/g‧K as the irradiation electron fluence increased. For swift heavy ion irradiation, the specific heat capacity was found to increase from 0.005 J/g‧K to 0.06 J/g‧K. The results have revealed that there was a thermodynamic change.

Self-bonding mechanism of pure polycrystalline cubic boron nitride under high pressure and temperature

Cubic boron nitride (cBN) powders with different grain size were used as a starting material, and the pure polycrystalline cubic boron nitride (PcBN) samples were sintered under the same conditions at 7GPa, 1700 °C, 270 s. Abrasion resistance and compressive strength of sintered pure PcBN samples were tested, and the microstructure was observed and analyzed by SEM, HRTEM, XRD and Raman spectrum. The results show that the particle size of cBN has not only a great influence on microstructure and property of the sintered pure PcBN un-der the same conditions but also influence on the bonding mechanism of the cBN particles. The inner stress of the pure PcBN sintered with the cBN particle size of 10 μm during the high pressure sintering process is about 199–222% higher than that of the sample with the cBN size of 1 μm. The wear ratio and the compressive strength of PcBN samples sintered with 10 μm cBN was increased by 47.7% and 39.7% than that of the sintered sample with 1 μm cBN respectively. The coarser-grained PcBN contains serious deformation and crushing, which can be attributed to the twin boundary and the stacking faults in the samples. As a consequence, the abrasion ratio and compressive strength of the pure PcBN are dramatically increased. It is assumed that self-bonding mechanism generated from plasticity deformation, which is a main bonding mechanism for the high pressure sintering of pure cubic boron nitride.

Nonreversible Transition from the Hexagonal to Wurtzite Phase of Boron Nitride under High Pressure: Optical Properties of the Wurtzite Phase

We present an infrared reflectance and transmission study of a pressure-induced phase transition of boron nitride from the hexagonal layered structure to the wurtzitic phase. The transition is completed at about 13 GPa. The phase transition is nonreversible and the optical features of the metastable wurtzitic phase are retained after a pressure cycle from 20.5 GPa down to ambient pressure. This allows the infrared-active optical phonons and the dielectric properties of the cold-pressed wurtzitic boron nitride sample to be studied over the whole range of pressures. Experimental permittivity values of e0 = 6.65 ± 0.03 and e∞ = 4.50 ± 0.05 are determined from fits to the reflectance spectra at ambient pressure. Accurate values of the refractive index in the mid-infrared and visible–ultraviolet regions are evaluated from the interference patterns. Contrary to the h-BN case, the refractive index of w-BN decreases slightly with pressure, on account of the much lower compressibility of the close-packed structure. The pressure coefficients for the longitudinal optical and transverse optical modes are determined, and an overall good agreement with ab initio calculations is found.

Nano boron nitride/polyurethane adhesives in flexible laminated food packaging: Peeling resistance and permeability properties

Polymeric multilayer films are widely used in food packaging due to their versatility. However, there are still some properties that might be improved, such as gas and vapor barrier behaviors. The incorporation of boron nitride into polymer matrixes is emerging as a potential method for the improvement of barrier properties due to its lamellar structure. In this context, our work investigates the addition of boron nitride into a bicomponent reactive polyurethane (PU), which could be used as an adhesive and improve the barrier layer. This material could be used as an alternative to aluminum foil in food packaging. Different concentrations of two different sizes of boron nitride (BN) particles were added to the PU adhesive: micro-structured boron nitride (BNm) and nano-structured boron nitride (BNn). The aim was to investigate the influence on the barrier properties against moisture and the peeling resistance. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) were performed to characterize the boron nitride samples. The effect of BNm or BNn addition on the glass transition of the nanocomposites was investigated by differential scanning calorimetry (DSC). Barrier properties were measured by a water vapor permeation test and the practical adhesion of laminates with BN/PU adhesives was characterized using peeling tests. The nanocomposites achieved reduction in water vapor permeance of up to 50% and a 37% increase in mechanical adhesion properties compared to the PU adhesive. The results revealed the high potential of boron nitride/PU adhesives for food packaging applications.

The effect of boron oxide on the physical and mechanical properties of nanostructured boron nitride by spark plasma sintering

Hexagonal boron nitride is a substance with unique properties that has attracted a remarkable amount of interest in last decades. In this work, hexagonal boron nitride samples were prepared by Spark Plasma Sintering at 1600 °C with 1.7, 2.4 and 3 wt% B2O3 as an additive. Physical and mechanical properties of the sintered samples were investigated. The result showed that the increase of the additive can effectively promote the samples features especially density. The best sample containing 3 wt% B2O3 had the highest relative density of 99%, hardness of 1.67 GPa, bending strength of 85 MPa and dielectric constant of 6.2.

The influence of ultrasonic exposure on polytetrafluoroethylene structure modified with boron nitride

The purpose of study is to state influence patterns of ultrasonic exposure on the density and porosity change of the synthesized polymer composite material based on polytetrafluoroethylene, modified with boron nitride. The density of 5 % boron nitride samples manufactured by ultrasonic pressing is 9% higher than the similar samples manufactured by cold pressing have and this confirms the structure defectiveness results received by electron microscopy. As the result of carried studies it was stated that polymer composite material pressing with ultrasonic vibration is an active technology increasing efficiency of matrix structure modification and affecting significantly the structure formation processes in it.

Coupled elastoplasticity and plastic strain-induced phase transformation under high pressure and large strains: Formulation and application to BN sample compressed in a diamond anvil cell

In order to study high-pressure phase transformations (PTs), high static pressure is produced by compressing a thin sample within a high strength gasket in a diamond anvil cell (DAC). However, since a PT occurs during plastic flow, it is classified and treated here as a plastic strain-induced PT. A thermodynamically consistent system of equations for combined plastic flow and plastic strain-induced PTs is formulated for large elastic, plastic, and transformation strains. The Murnaghan elasticity law, pressure-dependent J2 plasticity (both dependent of the concentration of a high-pressure phase), and plastic strain-induced and pressure-dependent PT kinetics are utilized. A computational algorithm within finite element method (FEM) is presented and implemented in a user material subroutine (UMAT) in the FEM code ABAQUS. Combined plastic flow and strain-induced PT from the highly-disordered hexagonal boron nitride (hBN) sample to a superhard wurtzitic wBN is simulated within the rhenium gasket for pressures up to 50 GPa. The evolution of the fields of stresses and plastic strains, as well as the concentration of phases in a sample is obtained and discussed in detail. Stress-strain fields in a gasket and diamond are presented as well. An unexpected shape of the deformed sample with almost complete PT in the external part of the sample that penetrated the gasket was found. Obtained results demonstrated the difference between material and system behavior which are often confused by experimentalists. Thus, while plastic strain-induced PT may start (and end) at plastic straining slightly above 6.7 GPa, it is not visible below 12 GPa. It becomes detectable at 21 GPa and is not completed everywhere in a sample even at a maximum pressure of 50 GPa. Due to a strong gasket the gradient of pressure is much smaller than the gradient of plastic strain, and therefore the distribution of the high pressure phase is mostly determined by the plastic strain field instead of the pressure field. Possible misinterpretation of the experimental data and characterization of the PT is discussed. The developed model will allow computational design of experiments for synthesis of high-pressure phases.

New hexagonal boron nitride polytypes with triple-layer periodicity

Regular hexagonal boron nitride (h-BN) samples present a few of intrinsic stacking faults, which result in a long-standing controversy about their electronic properties. To resolve this controversy, we designed eight possible BN polytypes with triple-layer periodicity. Under ambient pressure, the energies of all the proposed polytypes are between those of observed AA and Aa (h-BN) structures. Two proposed polytypes with direct bandgaps might be responsible for the direct bandgap observed in the h-BN samples. A model was proposed to show how the proposed structures might exist in the h-BN samples by analyzing the stacking characteristics and the previous experimental micrographs of h-BN samples.

Nanoporous Boron Nitride as Exceptionally Thermally Stable Adsorbent: Role in Efficient Separation of Light Hydrocarbons.

In this work, nanoporous boron nitride sample was synthesized with a Brunauer-Emmett-Teller (BET) surface area of 1360 m2/g and particle size 5-7 μm. The boron nitride was characterized with X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electron microscopy (TEM and SEM). Thermogravimetric analysis (TGA) under nitrogen and air and subsequent analysis with XPS and XRD suggested that its structure is stable in air up to 800 °C and in nitrogen up to 1050 °C, which is higher than most of the common adsorbents reported so far. Nitrogen and hydrocarbon adsorption at 298 K and pressure up to 1 bar suggested that all hydrocarbon adsorption amounts were higher than that of nitrogen and the adsorbed amount of hydrocarbon increases with an increase in its molecular weight. The kinetics of adsorption data suggested that adsorption becomes slower with the increase in molecular weight of hydrocarbons. The equilibrium data suggested that that boron nitride is selective to paraffins in a paraffin-olefin mixture and hence may act as an "olefin generator". The ideal adsorbed solution theory (IAST)-based selectivity for CH4/N2, C2H6/CH4, and C3H8/C3H6 was very high and probably higher than the majority of adsorbents reported in the literature. IAST-based calculations were also employed to simulate the binary mixture adsorption data for the gas pairs of CH4/N2, C2H6/CH4, C2H6/C2H4, and C3H8/C3H6. Finally, a simple mathematical model was employed to simulate the breakthrough behavior of the above-mentioned four gas pairs in a dynamic column experiment. The overall results suggest that nanoporous boron nitride can be used as a potential adsorbent for light hydrocarbon separation.

Few-layer boron nitride nanosheets: Preparation, characterization and application in epoxy resin

Large-scale exfoliated boron nitride nanosheets were achieved via a liquid exfoliation sonication method by using sodium fluoride and ammonium hydroxide as Lewis base compounds. The crystal structure, surface functional groups, morphology and thickness of the as-prepared samples were characterized by X-ray diffraction, fourier transform infrared spectroscopy, transmission electron microscopy and atomic force microscopy, respectively. The as-prepared samples were introduced into epoxy resin to fabricate the polymer-based composites. Experimental results showed that the layer thickness of the as-prepared nanosheets was in the range of 1 to 3 layers. Moreover, it could improve the tensile properties of the matrix. When the loading of the as-prepared nanoparticles was 0.4wt%, the tensile strength and elongation at break of the composites reached to their maximum values 65.6MPa and 25.9%, which were increased by 118% and 192% more than that of pure resin. In addition, the as-prepared boron nitride samples could improve the thermostability and promote the curing of the matrix.