Pure Boron Research Articles

Comparison of ablators for the polar direct drive exploding pusher platform

We examine the performance of pure boron, boron carbide, high density carbon, and boron nitride ablators in the polar direct drive exploding pusher (PDXP) platform. The platform uses the polar direct drive configuration at the National Ignition Facility to drive high ion temperatures in a room temperature capsule and has potential applications for plasma physics studies and as a neutron source. The higher tensile strength of these materials compared to plastic enables a thinner ablator to support higher gas pressures, which could help optimize its performance for plasma physics experiments, while ablators containing boron enable the possibility of collecting additional data to constrain models of the platform. Applying recently developed and experimentally validated equation of state models for the boron materials, we examine the performance of these materials as ablators in 2D simulations, with particular focus on changes to the ablator and gas areal density, as well as the predicted symmetry of the inherently 2D implosion.

Chemical Vapor Deposition of Two-Dimensional Boron Sheets by Thermal Decomposition of Diborane.

Two-dimensional (2D) boron sheets (borophenes) are promising materials for the next generation of electronic devices because of their metallic conductivity. Molecular beam epitaxy has remained the main approach for the growth of borophene, which considerably restricts large-scale production of 2D boron sheets. The high melting point of boron and the growth of borophenes at moderate temperatures posed a significant challenge for the synthesis of borophenes. Employing diborane (B2H6) pyrolysis as a pure boron source, we report, for the first time, the growth of atomic-thickness borophene sheets by chemical vapor deposition (CVD). A methodical study on the effect of temperature, deposition rate, and pressure on the growth of 2D boron sheets is provided and detailed analyses about the morphology and crystalline phase of borophene sheets are presented. The CVD-borophene layers display an average thickness of 4.2 Å, χ3 crystalline structure, and metallic conductivity. We also present experimental evidence supporting the formation of stacked bilayer and trilayer borophene sheets. Our method paves the way for empirical investigations on borophenes.

Influence of Substrate Temperature on Electrical and Optical Properties of Hydrogenated Boron Carbide Thin Films Deposited by RF Sputtering

Amorphous hydrogenated boron carbide films were deposited on silicon and glass substrates using radio frequency sputtering. The substrate temperature was varied from room temperature to 300 °C. The substrate temperature during deposition was found to have significant effects on the electrical and optical properties of the deposited films. X-ray photoelectron spectroscopy (XPS) revealed an increase in sp2-bonded carbon in the films with increasing substrate temperature. Reflection electron energy loss spectroscopy (REELS) was performed in order to detect the presence of hydrogen in the films. Metal-insulator-metal (MIM) structure was developed using Al and hydrogenated boron carbide to measure dielectric value and resistivity. Deposited films exhibited lower dielectric values than pure boron carbide films. With higher substrate deposition temperature, a decreasing trend in dielectric value and resistivity of the films was observed. For different substrate temperatures, the dielectric value of films ranged from 6.5–3.5, and optical bandgap values were between 2.25–2.6 eV.

Modification of the Material Surface by Boron Ions Based on Vacuum Arc Discharge Systems and a Planar Magnetron

The principle of operation and the characteristics of the experimental equipment intended for the generation of boron ion plasma and beams are presented. The equipment comprises a vacuum arc source of boron ions with boron isotope separation in a magnetic field and a plasma generator for deposition of boron-containing coatings based on a planar magnetron sputter. Common to this equipment is the use of lanthanum hexaboride cathodes, but for planar magnetron, a pure boron cathode heated in the discharge is also used. It is shown that, when silicon wafer is implanted with beams of 10B+ and 11B+ boron isotope ions with doses of 1014–1016 ion/cm2, the isotopic effect of the diode properties of the implanted surface is observed. The results of studies of the properties of the obtained boron-containing coatings on model materials: stainless steel, crystal silicon, and E110 (Zr–1Nb) reactor alloy are presented.

Near-room temperature transesterification over bifunctional CunO-Bs/SBA-15 catalyst for biodiesel production

The transesterification of triglycerides is a critical step in biodiesel production. In this work, by loading boron-doped copper oxides onto SBA-15 mesoporous molecular sieve, an acid-base bifunctional catalyst (i.e., CunO-Bs/SBA-15) was prepared and applied to triglyceride transesterification. Compared with pure copper, sodium or boron oxides-based catalysts, CunO-Bs/SBA-15 enabled a higher biodiesel yield (>97.5%) at near room temperature (i.e., 40 °C) in 120 min. The characterization results showed that after B doping, the CunO-Bs/SBA-15 catalyst contained highly-dispersed acid-base sites without blocking the channels of porous SBA-15 support, which had good catalytic performance. Finally, in-situ DRIFTS was used to reveal the catalytic mechanism of the acid-base bifunctional groups of the as-prepared CunO-Bs/SBA-15 during transesterification.

Studying Adsorption and Cellular Toxicity of Boron Nitride Nanostructure versus Melphalan Anti-ovarian Cancer Drug.

Inclusion of anticancer drugs into biocompatible nanoparticulate carriers decreases the general toxicity and improves the efficacy of clinical treatments due to the reduction of soluble circulating free drugs. In addition, removal of emerging drug contaminants from wastewaters is a necessity that should be seriously attended. Boron nitride (BN) is a choice in drug delivery because of its many surprising properties. Here, boron nitride nanoparticles are prepared, characterized by Fourier-transform infrared spectroscopy (FT-IR) and x-ray diffraction (XRD) and used in the delivery of melphalan anti-cancer drug. Then, density functional theory (DFT) calculations are carried out to study the adsorption of this drug on the surface of pure boron nitride fullerene via familiar hybrid functionals B3LYP and B3PW91. In addition, the polarizable continuum model (PCM) calculations show that BN is stable in water. Finally, the in vitro cellular toxicity and viability of BN nanoparticles was examined on ES-2 cancer cells. The inhibitory dose IC50 of the material confirmed acceptable cytotoxicity and nanoparticles affected the average growth of the ES-2 cancer cells.

Investigation dissolution behaviours and kinetics parameters of ulexite in boric acid solution

Nowadays, boron and its derivatives are widely used in industrial and technological areas. Boron minerals are the main sources for obtaining pure boron chemicals in the usage of different applications such as the defense industry, health, industry, kitchen equipments, etc. In this paper, for the first time, it has been reported the dissolution behaviors and kinetics parameters of ulexite in the boric acid solution. To solve ulexite by boric acid is important, because boric acid as a solvent prevents the formation of impurities, and therfeore our study is a first in the literature. In this context, the dissolution of the ulexite has been investigated under various experimental parameters such as temperatures, acid concentration, solid/liquid ratio, particle size, dissolution rate, and stirring speed. The experimental findings shown that the dissolution kinetics of ulexite increase with an increase in temperature and acid concentration and a decrease in particle size, but decrease with mixing speed in the acid. Moreover, the dissolution of ulexite in boric acid and activation energy were evaluated. As a result, it was found that the dissolution kinetics were compatible with the chemical control model and the activation energy was 22.024 kJ mol-1.

PureB diode fabrication using physical or chemical vapor deposition methods for increased back-end-of-line accessibility

Several methods of depositing pure boron (PureB) layers on silicon are examined with respect to their potential for fabricating advanced PureB (photo)diodes with back-end-of-line (BEOL) CMOS compatibility. PureB devices were fabricated in two different batch furnace chemical-vapor deposition (CVD) systems or by electron-beam-assisted physical-vapor deposition (EBPVD), and their electrical characteristics were found to be comparable to those of devices previously fabricated using single-wafer CVD and molecular beam epitaxy (MBE) systems. For all methods, the material properties of the B-layers and the I-V characteristics of the PureB diodes follow the same temperature dependence over the range 50 °C–400 °C. This was also the case for the EBPVD layers which were deposited at 50 °C and then annealed at higher temperatures, instead of being deposited at these temperatures as for the other methods. At 400 °C, the ability to achieve an optimal suppression of the electron injection into the PureB anode regions, corresponding to an electron current density of ∼20 pA/cm2, was verified for all methods. The advantages and disadvantages of each deposition method is evaluated with respect to equipment availability, B-layer selectivity, conformality, and thickness control. The batch furnace systems could be attractive for high-volume production, but hardware improvements as discussed here would be needed to reduce the effects of gas depletion. On all points except conformality, EBPVD appears to be a very good option for fabricating nm-thin B-layers suitable for fabricating high-performance 400 °C PureB diodes.

Study on the properties and fracture mode of pure polycrystalline cubic boron nitride with different particle sizes

In this paper, pure polycrystalline cubic boron nitride (cBN) without additives was synthesized by a direct sintering method at 7.3 GPa and 2100 °C using industrial cBN powders with different particle sizes. High-pressure experiments without heating verified that the actual pressure of the cBN particles in the cavity was lower than that of the fine-grained samples during the sintering of coarse-grained samples. The best hardness (4900 HV2) and density (3.342 g/cm2) of sintered bodies were obtained when using fine-grained (2–4 μm) particles. The fracture modes of fine-grained and coarse-grained sintered bodies were investigated using scanning electron microscopy, and the microstructures of intra-grain and grain boundaries were systematically studied using high-resolution transmission electron microscopy. It was concluded that the main fracture mode of the fine-grained sample was transgranular fracture, while that of the coarse-grained sample was intergranular fracture. Moreover, a large number of dislocations and high-density twins were generated in the cBN grains under high temperature and high pressure, which improved the hardness of samples and caused transgranular fracture in fine-grained (2–4 μm) samples. This study of the fracture mode of industrial pure polycrystalline cBN is important to enable its use as a high-precision machining tool material.

Effect of different tungsten compound reinforcements on the electromagnetic radiation shielding properties of neopentyl glycol polyester

In this study, isophtalic neopentyl glycol polyester (NPG-PES) based composites with different loading ratios of pure tungsten metal (W), tungsten (VI) oxide (WO3), tungsten boron (WB) and tungsten carbide (WC) composites were prepared as alternative shielding materials for ionizing electromagnetic radiation (IEMR) shielding. Structural characterizations of the composites were done. Gamma spectrometric analysis of composites for 80–2000 keV energy range was performed and their usability as IEMR shielding was discussed. As a result, the produced composites showed a shielding performance of 60–100% of the lead (the most widely used IEMR shielding material) depending on the reinforcement material, reinforcement loading rate and experimental conditions. Thus, it was reported that produced composites could be an alternative to lead shieldings that have several disadvantages as toxic properties, difficulty of processing and inelasticity.

Adsorption behavior of melphalan anti-ovarian cancer drug onto boron nitride nanostructures. Studying MTT assay: in vitro cellular toxicity and viability

Ovarian cancer is believed as one of the most fatal reproductive cancers and melphalan has been known to treat this cancer as an intraperitoneal chemotherapeutic agent. Fortunately, nanotechnology enabled us to explore new approaches like nano vectors as drug nanocarriers to avoid or to diminish the collateral and secondary effects of anticancer drugs. Herein, boron nitride (BN) is disclosed as an effective nanocarrier for the delivery of melphalan anti-cancer drug. The performed density functional theory (DFT) studies showed good adsorption of melphalan on the surface of pure and Ge-doped boron nitride. In addition, the in vitro cellular toxicity and viability of boron nitride nanoparticles were examined on SKOV3 cancer cells. The inhibitory dose ID50 of BN nanoparticles confirmed that this material can be achieved as an acceptable vehicle for delivery of melphalan. Moreover, the effect of boron nitride nanoparticles (2 μg/mL) on the average growth curves of SKOV3 cancer cells showed a decrease of the MTT signal compared to the untreated cells and BN can reduce the metabolic activity of the performed cancer cells. Therefore, this fullerene can be regarded as a suitable sensor for detection of melphalan anti-cancer drug in biological systems. This study showed that BN nanoparticles have a clear inhibitory effect on the proliferation of SKOV3 ovarian cancer cells.

PURIFICATION OF INDONESIAN NATURAL GRAPHITE AS CANDIDATE FOR NUCLEAR FUEL MATRIX BY ACID LEACHING METHOD: CHEMICAL CHARACTERIZATION

PURIFICATION OF INDONESIAN NATURAL GRAPHITE AS CANDIDATE FOR NUCLEAR FUEL MATRIX BY ACID LEACHING METHOD: CHEMICAL CHARACTERIZATION. Graphite matrix in Pebble Bed Reactor (PBR) – High Temperature Gas Cooled Reactor (HTGR) has an important role as heat transfer medium, neutron moderator and structural material to protect fuel. Thus, graphite matrix must fulfill chemical and physical characteristics for PBR-HTGR fuel. Indonesia has graphite sources in several regions that can potentially be purified. This research aimed to purify Indonesian natural graphite by several variation of acids and to perform chemical characterizations. Natural graphite from flotation process was purified by several variations of acid, i. e., hydrofluoric acid (HF), sulphuric acid + nitric acid (H2SO4 + HNO3) and hydrofluoric acid + hydrochloric acid + sulphuric acid (HF + HCl + H2SO4) and subsequently followed by chemical characterizations such as purity level, ash content, and boron quivalent. The highest purity was obtained in the purification process by HF with carbon content up to 99.52%; this purity level fulfills the specification of nuclear graphite (>99%). Ash content analysis shows a value in compliance with the specification requirement, i.e., < 100 ppm, and boron equivalent value also fulfills the specification value of < 1 ppm. It can be concluded from this study that the graphite purified by acid leaching with HF can be used as fuel matrix candidate but is qualified as low quality. Futher research is required to produce high quality nuclear graphite, particularly research in the minimization of the impurity by evaporation at temperatures over 950 oC to by far lower the ash content.Keywords: Indonesian natural graphite, purification, nuclear fuel matrix, acid leaching, chemical characterization.

Structural and electronic transitions in few layers of isotopically pure hexagonal boron nitride

Hexagonal boron nitride (hBN) is attracting tremendous interest as an essential component in van der Waals heterostructures due to its ability to provide weakly interacting interfaces and because of its large bandgap. Although most of theoretical calculations yield the standard AA′ stacking for few-layer hBN, the exact determination of its structural and electronic properties remains unrevealed to date. Here, we provide the direct observation of structural and electronic transitions in few layers of isotopically pure exfoliated h11BN flakes. Our nanoscopic angle-resolved photoemission spectroscopy measurements combined with density-functional theory calculations indicate that the stacking and the band structure can be strongly affected by the thickness of h11BN. Hence, we show that hBN presents an AA′ stacking in its bulk form and another more exotic stacking for three and four layers. Our findings open perspectives in understanding and controlling the stackings in hBN, which could be of great interest for optoelectronic applications.

Outstanding Thermal Conductivity of Single Atomic Layer Isotope-Modified Boron Nitride.

Materials with high thermal conductivities (κ) are valuable to solve the challenge of waste heat dissipation in highly integrated and miniaturized modern devices. Herein, we report the first synthesis of atomically thin isotopically pure hexagonal boron nitride (BN) and its one of the highest κ among all semiconductors and electric insulators. Single atomic layer (1L) BN enriched with ^{11}B has a κ up to 1009 W/mK at room temperature. We find that the isotope engineering mainly suppresses the out-of-plane optical (ZO) phonon scatterings in BN, which subsequently reduces acoustic-optical scatterings between ZO and transverse acoustic (TA) and longitudinal acoustic phonons. On the other hand, reducing the thickness to a single atomic layer diminishes the interlayer interactions and hence umklapp scatterings of the out-of-plane acoustic (ZA) phonons, though this thickness-induced κ enhancement is not as dramatic as that in naturally occurring BN. With many of its unique properties, atomically thin monoisotopic BN is promising on heat management in van der Waals devices and future flexible electronics. The isotope engineering of atomically thin BN may also open up other appealing applications and opportunities in 2D materials yet to be explored.

Room temperature electroless Ni-coating on boron particles: Physicochemical and oxidation-resistance properties

Ni nanoparticles were coated on irregularly shaped micron sized boron particles by facile electroless Ni-deposition method. Four kinds of Ni-coated boron particles were prepared using four different simple paths during the electroless deposition process: no rinsing and no drying (Path A), only drying (Path B), both rinsing and drying (Path C), and only rinsing (Path D). Surface morphology confirmed the Ni-nanoparticles coating on the surface of boron particles. The size of the Ni nanoparticles varied between 10 and 120nm with respect to the chosen paths used for preparation. The Ni nanoparticle's size was also studied using TEM and found to be consistent with the surface morphology results. XRD measurement of the Ni-coated boron particles showed the formation of crystalline Ni nanoparticles. EDAX and XPS results showed the presence of the primary B and Ni elements in the obtained samples. Thermogravimetric analysis conducted in air atmosphere found the boron particles had enhanced oxidation resistance after the coating of Ni nanoparticles. The Ni-coated boron particles showed a shift in exothermic peak to a lower temperature and higher heat evolution than the pure boron, recommending the use of Ni-coated boron particles in solid fuel in missile/rocket engines, and high temperature applications.

Boron efficiency in increasing olive (cv. Frantoio) fruit productivity and oil yield and quality

This study was conducted for two successive seasons, 2017 and 2018, using 20-yr old olive trees (cv. Frantio). The trees are grown in sandy soil under drip irrigation system at the Nuclear Research Center Experimental Farm, Inshas, El-Qaliubiya Governorate, Egypt. Treatments included six pure boron concentrations (0.0, 100, 200, 300, 400, 500 mg.L−1) applied on 1st January (before bloom). Boron was applied as foliar spray boric acid. The objective of this study was to investigate the effect of boron foliar application on olive (OleaeuropeaL.) fruit productivity, oil yield and quality. Boron treatments increased olive fruit productivity and oil yield relative to the control. The maximum fruit yield and oil yield was observed at 200 mg.L−1 boron treatment. This treatment has increased fruit yield by 275% and oil yield by 318% (average of two seasons). The acid value range was from 1.173 to 1.667 (mg KOH/g oil) in the first season and from 1.323 to 1.800 (mg KOH/g oil) in the second season. The acid value significantly decreased as the boron application rate increased. The peroxide value range was from 0.0026 to 0.0067 in the first season and from 0.0032 to 0.0078 in the second season. The peroxide value decreased as the boron application rate increased. A non-significant reduction in the iodine values was observed as the boron application rate increased. The iodine value range was (from 77.20 to 77.40 g/100 g of oil) for the first season and (from 77.67 to 78.23 g/100 g of oil) for the second season. The saponification value range is (from 191.4 to 193.3 mg KOH/g oil) for the first season and (from 192.5 to 193.8 mg KOH/g oil) for the second season. The saponification value significantly decreased as the boron application rate increased. Boron has improved oil quality by decreasing the acid value, the peroxide value and the saponification value, while maintained the iodine value almost similar to the control. Boron treatment has increased olive fruit productivity and oil yield and it improved oil quality characteristics.

Characterization of Freeze-Dried Boron Nanopowders and Parameter Optimization in Ex Situ MgB2 Wire Production

This article reports a study to identify optimal synthesis parameters for a pure boron precursor prepared following a patented process developed at CNR-SPIN laboratories, performed in the framework of a collaboration between CNR-SPIN and CERN. Boron is a precursor that plays a crucial role in the MgB2 wire manufacturing, as a consequence, the synthesis parameters of the superconducting phase have been investigated. In this article, we report results for MgB2 samples synthesized at 870 °C for 17nbsp;h under Ar/5% H2 flow and 760 °C for 0.2 h. Magnesiothermic amorphous nanoboron (MANB) and commercial boron nanopowders (purchased from Pavezyum) have been compared in terms of morphological features. MgB2 derived from both sources has been characterized and the superconductive properties in the wire form have been compared. Results demonstrate that the MANB performance is comparable with the nanoboron obtained via gas synthesis.

Oxidation, ignition and combustion behaviors of differently prepared boron-magnesium composites

Effect of magnesium on ignition and combustion characteristics of boron was explored for three materials containing ca. 23 wt% of magnesium. Boron was sintered with elemental Mg, leading to the formation of MgB2. This material showed the most homogeneous distribution of Mg. Boron was also mechanically milled with elemental Mg, as well as with commercial MgB2, respectively. The presence of Mg delayed the oxidation of boron in all materials. The delay was nearly the same for both milled powders and it was somewhat greater for the sintered material. The observed oxidation rate of all materials, however, was greater than for pure boron. All materials could be ignited by a heated wire at nearly the same temperature, although boron could not. Particles of all materials, including elemental boron, could be ignited by a CO2 laser with the lowest power required for the sintered material. The addition of Mg had a weak effect on particle burn times. Boron milled with elemental Mg showed distinct two-stage combustion patterns interpreted as delayed, and separate, Mg combustion. A small increase in the maximum pressure and rate of pressure rise is observed for the Mg-bearing powders in constant volume explosion experiments.

Thermodynamical evaluation, microstructural characterization and mechanical properties of B4C–TiB2 nanocomposite produced by in-situ reaction of Nano-TiO2

This work discusses the pressureless sintering of a boron carbide-titanium diboride (B4C– TiB2) nanocomposite via in-situ reaction of the boron carbide/titanium dioxide/carbon system. Attempting to sinter pure boron carbide leads to poor mechanical properties. In this work, the effect of adding TiO2 to B4C on mechanical properties of the boron carbide was investigated. Thermodynamic simulations were performed with HSC chemistry software to determine the phases which were most likely to form during the sintering process. The reaction thermodynamics suggested that during the sintering process, formation of TiB2 occurs preferentially over formation of TiC. For examination of the microstructural evolution of the samples, Scanning Electron Microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were utilized. The density, porosity, Young's modulus, microhardness and fracture toughness of the specimens were compared. Optimum properties were achieved by adding 10 wt% TiO2. In the sample possessing 10 wt% TiO2, the relative density, Young's modulus, hardness and fracture toughness were 94.26%, 428 GPa, 23.04 GPa and 5.19 MPa m0.5, respectively, and the porosity was decreased to 5.73%. Furthermore, phase analysis via XRD confirmed that the final product was free of unreacted TiO2 or carbon.

Comparison of the Microstructure Evolution and Wear Resistance of Ti6Al4V Composite Coatings Reinforced by Hard Pure or Ni-plated Cubic Boron Nitride Particles Prepared with Laser Cladding on a Ti6Al4V Substrate

Titanium alloy is a major structural material with excellent high specific strength in aerospace applications. Cubic boron nitride (cBN) is a synthetic wear-resistant material with high hardness, similar to that of diamond, that is used in mechanical cutting and grinding. In addition, the thermal stability of cubic boron nitride particles is much better than that of diamond. In order to further enhance the wear resistance of the Ti6Al4V alloy, the laser cladding (LC) technology characteristics of metallurgical bonding were used to prepare cubic boron nitride/Ti6Al4V and Ni-plated cubic boron nitride/Ti6Al4V composite coatings on Ti6Al4V substrates in this paper. However, in the laser molten pool, it is difficult to retain the raw properties of cubic boron nitride particles under laser radiation. Both composite coatings were analyzed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The microstructures and interface bonding between cubic boron nitride particles and the Ti6Al4V matrix were examined using SEM, and the wear resistance and the worn track morphology of the composite coatings were evaluated using the ball-on-disc wear test and step profiler (WTM-2E). The results indicated that the Ni-plated cubic boron nitride/Ti6Al4V composite coating showed fewer thermal defects in comparison with the cubic boron nitride/Ti6Al4V coating. The Ni plating on the surface of cubic boron nitride particles was able to avoid the generation of thermal cracking of the cubic boron nitride particles in the composite coating. The TiN reaction layer was formed between the cubic boron nitride particles and Ti6Al4V matrix, which effectively prevented the further decomposition of the cubic boron nitride particles. The XRD and XPS results confirmed that the TiN reaction layer formed between the cubic boron nitride particles and Ti6Al4V. The Ni plating on the surface of the cubic boron nitride particles was also beneficial for increasing the wear resistance of the composite coating.