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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Additive manufacturing process for producing aluminum-boron carbide metal matrix composites

A method for additive manufacturing of a composite object containing a bonded network of boron carbide particles and aluminum occupying spaces between boron carbide particles, the method comprising: (i) producing a porous preform constructed of boron carbide by an additive manufacturing process in which particles of boron carbide are bonded together; and (ii) infiltrating molten aluminum, at a temperature of 1000-1400° C., into pores of said porous preform to produce said composite object constructed of boron carbide particles within an aluminum matrix, wherein the boron carbide is present in the composite object in an amount of 30-70 wt. %. The resulting composite material is also herein described.

Cramer, Corson L.↗
DOE OSTI2019

Reaction Mechanism and Kinetics of Boron Removal from Molten Silicon via CaO-SiO{sub 2}-CaCl{sub 2} Slag Treatment and Ammonia Injection

To improve the boron-removal efficiency of metallurgical-grade silicon by increasing the reaction rate, a combined method with the 30 mol pct CaO-23.3 mol pct SiO{sub 2}-46.7 mol pct CaCl{sub 2} slag treatment and ammonia injection at 1723 K to 1823 K was proposed. For 1 hour and at 1823 K, the maximum removal efficiency of boron was 98 pct, and the final boron concentration in silicon decreased to 1.5 ppmw by the present method without the introduction of the iron catalyst. A kinetic model was also established to clarify the reaction mechanism and rate-limiting steps of this complicated boron-removal process. In this model, the rate-limiting step is the mass transfer of boron oxide at the interface between the slag and silicon phase.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Effect of Boron and Zirconium on the Structure and Tensile Properties of the Cast Nickel-Based Superalloy ATI 718Plus

The effects of boron and zirconium on cast structure, hardness, and tensile properties of the nickel-based superalloy 718Plus were investigated. For this purpose, five alloys with different contents of boron and zirconium were cast via vacuum induction melting and then purified via vacuum arc remelting. Microstructural analysis by light-optical microscope and scanning electron microscope equipped with energy-dispersive x-ray spectroscopy and phase studies by x-ray diffraction analysis were performed. The results showed that boron and zirconium tend to significantly reduce dendritic arm spacing and increase the amount of Laves, Laves/gamma eutectic, and carbide phases. It was also found that boron led to the formation of B{sub 4}C and (Cr, Fe, Mo, Ni, Ti){sub 3}B{sub 2} phases and zirconium led to the formation of intermetallic phases and ZrC carbide. In the presence of boron and zirconium, the hardness and its difference between dendritic branches and inter-dendritic spaces increased by concentrating such phases as Laves in the inter-dendritic spaces. These elements had a negative effect on tensile properties of the alloy, including ductility and strength, mainly because of the increase in the Laves phase. It should be noted that the largest degradation of the tensile properties occurred in the alloys containing the maximum amount of zirconium.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Bottom up synthesis of boron-doped graphene for stable intermediate temperature fuel cell electrodes

The high surface area and electrical conductivity of few-layered graphene would make it an ideal catalyst support and electrode in fuel cells apart from its susceptibility to oxidative corrosion. Here we report the single-step, bottom-up synthesis of oxidation-resistant boron-doped graphene and show its increased stability in the aggressive electrochemical environment of intermediate temperature solid acid fuel cells (SAFCs). Boron was shown to alter the growth mode of single walled carbon nanohorns by laser vaporization to produce high yields of thin (<20 layer) boron-doped (2–3 at.%) crystalline flakes of turbostratic graphene (B-GLF). Alternatively, adding partial pressures of hydrogen less effectively shifted the growth mode of SWCNHs toward planar, turbostratic graphene-like flakes (GLFs). Thermogravimetric analysis indicates that boron-doping enhances the oxidation resistance of few-layer GLFs by >140 °C, with large fractions of multilayered B-GLFs surviving 10 °C/min ramps to 1000 °C. These B-GLFs provided a stable Pt catalyst support and electrode over 40 h operation in SAFCs with cesium dihydrogen phosphate electrolyte operating at 250 °C, as opposed to undoped GLFs or SWCNHs which were nearly completely consumed. Furthermore, the facile synthesis and oxidation-resistant properties of boron-doped GLF appear promising for graphene applications in oxidizing environments.

25 ENERGY STORAGE↗
DOE OSTI2013

Evidence for boron diffusion into sub-stoichiometric MgO (001) barriers in CoFeB/MgO-based magnetic tunnel junctions

Evidence of boron diffusion into the MgO barrier of a CoFeB/MgO based magnetic tunnel junction has been identified using analytical scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy. Structures were deposited by DC/RF-magnetron sputtering, where defective, sub-stoichiometric MgO barriers degrading device performance have been previously mitigated against by deposition of thin Mg layers prior to MgO deposition. We show that despite the protection offered by the Mg layer, disorder in the MgO barrier is still evident by STEM analysis and is a consequence of the oxidation of the Co{sub 40}Fe{sub 40}B{sub 20} surface during MgO deposition. Evidence of boron diffusion from CoFeB into the MgO barrier in the as-deposited and annealed structure is also presented, which in the as-deposited case we suggest results from the defective structures at the barrier interfaces. Annealing at 375 Degree-Sign C results in the presence of B in the trigonal coordination of [BO{sub 3}]{sup 3-} in the MgO barrier and partial crystallization of the top electrode (we presume there is also some boron diffusion into the Ta capping layer). The bottom electrode, however, fails to crystallize and much of the boron is retained in this thicker electrode. A higher annealing temperature or lower initial boron content is required to crystallize the bottom electrode.

36 MATERIALS SCIENCE↗
DOE OSTI2021

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

In this work, we performed integrated modelling of the chemical pathways of formation for boron nitride nanotube (BNNT) precursors during high-temperature synthesis in a B/N 2 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 N 2 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 B 4 N 4 and B 5 N 4 species in particular play a major role in the N 2 molecule fixation process. Furthermore, the formation of these species via reactions with B 4 and B 5 clusters is not adequately described under the assumption of thermodynamic equilibrium, as is demonstrated in our kinetic modelling. Thus, the accumulation of both B 4 N 4 and B 5 N 4 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 B 4 N 4 and B 5 N 4 . Our modelling results—particularly the increased densities of B 4 N 4 and B 5 N 4 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.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Boron Carbide Synthesis in Low-Voltage DC Electric Arc Initiated in Open Air

We describe a method of obtaining ultrafine boron carbide (B{sub 13}C{sub 2}) powder using the effect of a dc electric arc on a mixture of initial reactants containing carbon and boron. A peculiarity of the proposed method is that it can be implemented using arc discharge operating in open air without any vacuum equipment and protective inert gas atmosphere. X-ray diffraction data showed that the synthesized product in the general case contained three crystalline phases: boron carbide (B{sub 13}C{sub 2}), graphite (C), and boron oxide (B{sub 2}O{sub 3}). Electron-microscopic examination showed that the average size of boron carbide particles ranged from ~50 nm to ~2 μm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The Impact of High Pressure, Doping and the Size of Crystalline Boron Grains on Creation of High-Field Pinning Centers in In Situ MgB{sub 2} Wires

In this work, we investigated the influence of isostatic pressure (of 0.1 MPa and 1.1 GPa) during heat treatment, doping, size and shape of crystalline boron grains, and annealing time at low annealing temperature (570 °C) on the formation of high-field pinning centers in MgB{sub 2} wires. The results indicate that high isostatic pressure (1.1 GPa) at low annealing temperature (570 ° C) and annealing time of 120 min significantly increases the density of high-field pinning centers in MgB{sub 2} wires with small and large boron grains. Transport measurements show that an increase of annealing time from 120 to 210 min at 1.1 GPa slightly decreases the critical current density (J{sub c}) and irreversibility field (B{sub irr}) in MgB{sub 2} wires with large boron grains, suggesting that longer annealing time weakly affects the density of high-field pinning centers. On the other hand, for MgB{sub 2} wires with small boron grains, the annealing time of 210 min significantly reduces J{sub c} and B{sub irr}. This indicates that the longer annealing time at 1.1 GPa significantly reduces the density of high-field pinning centers. Our studies indicate that dislocations created by the hot isostatic pressure process significantly increase B{sub irr} in the temperature range from 5 to 12 K. On the other hand, strains due to the shrinkage of MgB{sub 2} material increase B{sub irr} in the temperature range from 12 to 34 K. The results show that small grains of crystalline boron and high isostatic pressure lead to a high density of dislocations and strains during transformation to the MgB{sub 2} phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Synthesis and pharmacological activity of a silicon—zinc—boron-containing glycerohydrogel

A new pharmacologically active nanostructured silicon—zinc—boron-containing glycerohydrogel was synthesized by the sol—gel method using silicon, zinc, and boron glycerolates as biocompatible precursors. The hydrogel composition and structural features were investigated by transmission electron microscopy, powder X-ray diffraction, IR spectroscopy, atomic emission spectrometry, and elemental analysis; a structural model was proposed. It was found that the 3D framework of the gel is formed by the products of hydrolysis and subsequent (co)condensation of silicon- and boron-containing precursors. Meanwhile, the major part of zinc monoglycerolate does not undergo hydrolytic transformations during gelation, being present in the 3D framework cells as amorphous nano-sized particles. The dispersion medium of the gel is an aqueous glycerol solution of silicon and boron glycerolates, products of their hydrolytic transformations, and water-soluble products of hydrolytic transformations of zinc monoglycerolate. The silicon—zinc—boron gel is nontoxic and possesses wound-healing and antimicrobial activities; it can be considered as a nanostructured dispersed system promising for biomedical applications, which is prepared in a simple and cost-effective way without using catalysts or toxic organic solvents.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Effect of Boron Content on Hot Ductility and Hot Cracking Susceptibility in 316L Austenitic Stainless Steel for Welding Components

Liquation cracking may occur in the heat-affected zone during welding. Two factors influence this phenomenon: the tensile stresses generated during welding and the potential loss of ductility due to the presence of a liquid film at grain boundaries depending on their chemical composition. Gleeble hot ductility tests have been used to study the combined effect of boron content and holding time on ductility drop in the liquation temperature range of a 316L type austenitic stainless steel. It is shown that high boron contents and short holding times promote the loss of ductility in this temperature range. Secondary ion mass spectrometry has been used to correlate mechanical results to boron distribution either at grain boundaries or in the bulk. Other welding tests have been performed to confirm the influence of boron content on hot cracking sensitivity of AISI 316L stainless steels. Results indicate that cracks appear on all specimens but at different strain levels. The higher the boron content is, the more the specimen exhibits tendency to hot cracking.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Predicting boron coordination in multicomponent borate and borosilicate glasses using analytical models and machine learning

Accurate prediction of boron coordination in multicomponent glasses is critical in glass science and technology as it strongly affects the properties of borate and borosilicate glasses. We have collected a dataset containing 657 glasses from literature with boron coordination values and developed models using analytical functions based on the well accepted Dell, Xiao and Bray model. Good prediction of boron coordination with a R 2 value higher than 0.8 was obtained. The large variation of boron coordination from experiments, originated from sample preparations and characterizations, led to difficulties in obtaining models with better prediction performance. Various machine learning (ML) algorithms were evaluated and slightly better prediction performance was observed; however, interpretation of the ML models is less straight forward. In conclusion, this study developed various models capable of providing quantitative boron coordination predictions, providing insights into its structural roles in multi-component glasses, and suggesting fruitful areas for future research.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Studies of lithiumization and boronization of ATJ graphite PFCs in NSTX-U

This work examines the effect of boron and lithium conditioned ATJ graphite surface bombarded by low-energy deuterium atoms on the deuterium retention and chemical sputtering. We use atomistic simulations and compare them with experimental in situ studies with x-ray photoelectron spectroscopy (XPS), to understand the effects of deuterium irradiation on the chemistry in lithiated, boronized and oxidized amorphous carbon surfaces. Our results are validated qualitatively by comparison with experiments and with quantum classical molecular dynamic simulations. We explain the important role of oxygen in D retention for lithiated surfaces and the suppression of oxygen role by boron in boronized surfaces. The calculated increase of the oxygen role in deuterium uptake after D accumulation in B–C–O surface configuration is discussed. The sputtering yield per low energy D impact is significantly smaller in boronized than in lithiated surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2026

CO (2) Electroreduction on Borated Copper Surfaces: Boron Active Sites, Not Copper

Boron-doped copper has recently emerged as an active and stable catalyst for the electrochemical reduction of CO 2 to value-added C 2 products. Here, in this work, we develop a realistic model of CO electroreduction on surface borides of copper under operational conditions, taking into account the effects of electrode potential, electrolyte environment, and pH. We study the possible reconstruction of the electrocatalyst surface using grand canonical DFT and global optimization to obtain a potential-dependent grand canonical ensemble description of metastable, hydrogen-covered catalyst surfaces. Two key surface configurations, low H coverage (LC, −0.6 V SHE ) and high H coverage (HC, −0.8 V SHE ), dominate this ensemble, with the former being kinetically persistent and C 2 selective under strongly reducing conditions. Nonmetallic boron sites on the surface copper boride are found to bind CO more strongly than copper sites, and mechanistic investigation of CO electroreduction pathways presents a surprisingly unconventional case of boron-centered reactivity in contrast to typical copper-centered reactivity. Neighboring boron sites present along boron chains on the surface copper boride are found to facilitate C−C coupling, thereby driving the high C 2 selectivity of this electrocatalyst.

boron-doped copper↗
DOE OSTI2014

Enhanced diffusion of oxygen depending on Fermi level position in heavily boron-doped silicon

The enhanced diffusivity of oxygen in heavily boron doped silicon was obtained by analyzing oxygen out-diffusion profile changes found at the interface between a lightly boron-doped silicon epitaxial layer and a heavily boron-doped silicon substrate by secondary ion mass spectrometry. It was found that the diffusivity is proportional to the square root of boron concentration in the range of 10{sup 18 }cm{sup −3}–10{sup 19 }cm{sup −3} at temperatures from 750 °C to 950 °C. The model based on the diffusion of oxygen dimers in double positive charge state could explain the enhanced diffusion. We have concluded that oxygen diffusion enhanced in heavily boron-doped silicon is attributed to oxygen dimers ionized depending on Fermi level position.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

B{sub 27}{sup −}: Appearance of the smallest planar boron cluster containing a hexagonal vacancy

Photoelectron spectroscopy and ab initio calculations have been carried out to probe the structures and chemical bonding of the B{sub 27}{sup −} cluster. Comparison between the experimental spectrum and the theoretical results reveals a two-dimensional (2D) global minimum with a triangular lattice containing a tetragonal defect (I) and two low-lying 2D isomers (II and III), each with a hexagonal vacancy. All three 2D isomers have 16 peripheral boron atoms and 11 inner boron atoms. Isomer I is shown to be mainly responsible for the observed photoelectron spectrum with isomers II and III as minor contributors. Chemical bonding analyses of these three isomers show that they all feature 16 localized peripheral B–B σ-bonds. Additionally, isomer I possesses 16 delocalized σ bonds and nine delocalized π bonds, while isomers II and III each contain 17 delocalized σ bonds and eight delocalized π bonds. It is found that the hexagonal vacancy is associated generally with an increase of delocalized σ bonds at the expense of delocalized π bonds in 2D boron clusters. The hexagonal vacancy, characteristic of borophenes, is found to be a general structural feature for mid-sized boron clusters. The current study shows that B{sub 27}{sup −} is the first boron cluster, where a hexagonal vacancy appears among the low-lying isomers accessible experimentally.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

The boron-tailing myth in hydrogenated amorphous silicon solar cells

The boron-tailing effect in hydrogenated amorphous silicon (a-Si:H) solar cells describes the reduced charge collection specifically in the blue part of the spectrum for absorber layers deposited above a critical temperature. This effect limits the device performance of state-of-the art solar cells: For enhanced current density (reduced bandgap), the deposition temperature should be as high as possible, but boron tailing gets detrimental above 200 °C. To investigate this limitation and to show potential paths to overcome it, we deposited high-efficiency a-Si:H solar cells, varying the deposition temperatures of the p-type and the intrinsic absorber (i) layers between 150 and 250 °C. Using secondary ion mass spectroscopy, we study dedicated stacks of i-p-i layers deposited at different temperatures. This allows us to track boron diffusion at the p-i and i-p interfaces as they occur in the p-i-n and n-i-p configurations of a-Si:H solar cells for different deposition conditions. Finally, we prove step-by-step that the common explanation for boron tailing—boron diffusion from the p layer into the i layer leading to enhanced recombination—is not generally true and propose an alternative explanation for the experimentally observed drop in the external quantum efficiency at short wavelengths.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Boron–oxygen complex yields n-type surface layer in semiconducting diamond

Diamond is a wide-bandgap semiconductor possessing exceptional physical and chemical properties with the potential to miniaturize high-power electronics. Whereas boron-doped diamond (BDD) is a well-known p-type semiconductor, fabrication of practical diamond-based electronic devices awaits development of an effective n-type dopant with satisfactory electrical properties. Here we report the synthesis of n-type diamond, containing boron (B) and oxygen (O) complex defects. We obtain high carrier concentration (~0.778 × 10 21 cm -3 ) several orders of magnitude greater than previously obtained with sulfur or phosphorous, accompanied by high electrical conductivity. In high-pressure high-temperature (HPHT) boron-doped diamond single crystal we formed a boron-rich layer ~1–1.5 μm thick in the {111} surface containing up to 1.4 atomic % B. We show that under certain HPHT conditions the boron dopants combine with oxygen defects to form B–O complexes that can be tuned by controlling the experimental parameters for diamond crystallization, thus giving rise to n-type conduction. First-principles calculations indicate that B 3 O and B 4 O complexes with low formation energies exhibit shallow donor levels, elucidating the mechanism of the n-type semiconducting behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Impact of toroidal magnetic field direction on integrated ELM-stable operation and divertor power exhaust via boron powder injection in EAST

We report the first in-depth comparison of the impact of toroidal magnetic field direction on solid boron injection used for Edge-Localized Mode (ELM) control, power exhaust, and core high-Z impurity control in the Experimental Advanced Superconducting Tokamak. With favorable ion ∇B drift towards the upper X-point in an upper-single-null configuration, boron injection effectively suppresses ELMs, produces a detachment of the inner divertor target, and leads to improved energy confinement. ELM suppression in this configuration is accompanied by the excitation of an Edge Harmonic Mode. In contrast, with unfavorable ion ∇B drift away from the upper X-point, boron injection also suppresses ELMs but leads to a more symmetric detachment state of both the inner and outer divertor targets, while plasma energy confinement is slightly degraded despite similar boron injection levels; a different low-frequency coherent mode without multiple harmonics is observed. Measurements from toroidally separated views show that the divertor response to boron injection is essentially toroidally symmetric, supporting the use of two-dimensional SOLPS-ITER modeling with a toroidally uniform impurity source. These experimental observations are qualitatively consistent with SOLPS-ITER simulations, which highlight the critical role of E × B drift effects in setting the Bt-dependent in–out asymmetry of detachment and in asymmetrically transporting particles and injected impurities within the scrape-off layer and private-flux region. These findings underscore the importance of drift physics and real-time wall conditioning in controlling low-Z impurity transport and optimizing edge solutions for integrated, ELM-stable, high-performance tokamak operation.

E × B drift↗