Search Results (12)

Trace elements such as boron (B) and zirconium (Zr) can increase creep resistance in nickel-based superalloys. This study investigates the change of microstructures on the grain boundary (GB) in phase-controlled nickel-based superalloys through the addition of trace elements. The basis alloy without B and Zr has distributed micrometer-sized (Nb, Ti)C and Cr₂₃C₆ carbides at the GBs. Zr is detected alongside Nb and Ti within certain (Nb, Ti)C carbides and its addition increases the fraction of (Nb, Ti)C or (Nb, Ti, Zr)C carbides. B affects the formation of precipitates constructed by nanometer-sized precipitates, which are Cr₂₃C₆ carbides, Cr₂₃(C, B)₆ boro-carbides, and Cr-rich borides, surrounded by γ’ phases. This film structure, which includes nanometer-sized precipitates surrounded by γ’ phases, forms more continuously with the addition of B and Zr. It is constructed with precipitates of (Nb, Ti)C carbides and Cr₂₃(C, B)₆ boro-carbides surrounded by γ’ phases. Numerous nanometer-sized precipitates (i.e., (Nb, Ti)C and Cr₂₃(C, B)₆) are distributed alternately within the film structure. The effect of the addition of B and Zr is such that nucleation sites of each precipitate are formed simultaneously and alternately along the GBs. The experimental results were discussed by correlating them with the predicted fraction of stable phases depending on the temperatures of these alloys, using the JMatPro program. Full article

The very high capture cross-section of (epi)thermal neutrons by the boron isotope ¹⁰B makes elemental boron and its compounds and composites prospective for serving as materials intensively interacting with neutron irradiation. In their nanostructured form, boron-rich materials reveal properties that improve their radiation-performance characteristics. In this regard, new technologies have been proposed for the synthesis of nanocomposites with matrices of boron carbide B₄C and hexagonal boron nitride h-BN. For the first time, boron carbide-tungsten and hexagonal boron nitride–(iron,magnetite) composites were obtained, respectively, in the form of layered/sandwich structures of components B₄C and W and h-BN nanopowders coated/intercalated with magnetic nanoclusters of iron Fe or magnetite Fe₃O₄. Studying of their chemical/phase composition, structure/morphology, and some other properties leads to the conclusion that the developed B₄C–W and h-BN–(Fe,Fe₃O₄) composites would be useful for solving important problems of boron-based neutron shielding and BNCT (Boron Neutron Capture Therapy), such as attenuating the gamma-radiation accompanying the absorption of neutrons by ¹⁰B nuclei and targeted delivery of ¹⁰B nuclei, as BNCT therapeutic agents, to tumor tissues using control by an external magnetic field, respectively. Full article

Boron carbide is one of the hardest materials in the world which can be synthesized by various methods. The most common one is a carbothermic or magnesiothermic reduction of B₂O₃ performed at high temperatures, where the obtained powder still requires grinding and purification. The goal of this research is to present the possibility of synthesizing B₄C nanoparticles from elements via vapor deposition and modifying the morphology of the obtained powders, particularly those synthesized at high temperatures. B₄C nanoparticles were synthesized in the process of direct synthesis from boron and carbon powders heated at the temperature of 1650 °C for 2 h under argon and characterized by using scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction analysis, and dynamic light scattering measurements. The physicochemical characteristics of B₄C nanoparticles were determined, including the diffusion coefficients, hydrodynamic diameter, electrophoretic mobilities, and zeta potentials. An evaluation of the obtained B₄C nanoparticles was performed on several human and mouse cell lines, showing the relation between the cytotoxicity effect and the size of the synthesized nanoparticles. Assessing the suitability of the synthesized B₄C for further modifications in terms of its applicability in boron neutron capture therapy was the overarching goal of this research. Full article

A boron-rich boron–carbide material (B_4+δC) was synthesized by spark plasma sintering of a ball-milled mixture of high-purity boron powder and graphitic carbon at a pressure of 7 MPa and a temperature of 1930 °C. This high-pressure, high-temperature synthesized material was recovered and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, Vickers hardness measurements, and thermal oxidation studies. The X-ray diffraction studies revealed a single-phase rhombohedral structure (space group R-3m) with lattice parameters in hexagonal representation as a = 5.609 ± 0.007 Å and c = 12.082 ± 0.02 Å. The experimental lattice parameters result in a value of δ = 0.55, or the composition of the synthesized compound as B_4.55C. The high-resolution scans of boron binding energy reveal the existence of a B-C bond at 188.5 eV. Raman spectroscopy reveals the existence of a 386 cm⁻¹ vibrational mode representative of C-B-B linear chain formation due to excess boron in the lattice. The measured Vickers microhardness at a load of 200 gf shows a high hardness value of 33.8 ± 2.3 GPa. Thermal gravimetric studies on B_4.55C were conducted at a temperature of 1300 °C in a compressed dry air environment, and its behavior is compared to other high-temperature ceramic materials such as high-entropy transition metal boride. The high neutron absorption cross section, high melting point, high mechanical strength, and thermal oxidation resistance make this material ideal for applications in extreme environments. Full article

Inorganic nanoparticles of boron-rich compounds represent an attractive alternative to boron-containing molecules, such as boronophenylalanine or boranes, for BNCT applications. This work describes the synthesis and biological activity of multifunctional boron carbide nanoparticles stabilized with polyacrylic acid (PAA) and a gadolinium (Gd)-rich solid phase. A fluorophore (DiI) was included in the PAA functionalization, allowing the confocal microscopy imaging of the nanoparticles. Analysis of the interaction and activity of these fluorescent Gd-containing B₄C nanoparticles (FGdBNPs) with cultured cells was appraised using an innovative correlative microscopy approach combining intracellular neutron autoradiography, confocal, and SEM imaging. This new approach allows visualizing the cells, the FGdBNP, and the events deriving from the nuclear process in the same image. Quantification of ¹⁰B by neutron autoradiography in cells treated with FGdBNPs confirmed a significant accumulation of NPs with low levels of cellular toxicity. These results suggest that these NPs might represent a valuable tool for achieving a high boron concentration in tumoral cells. Full article

This work aims to research the influence of boron and quenching temperature on the microstructures and performances of boron-bearing high-speed alloy steel. The results showed that the hardness and wear resistance of boron-bearing high-speed alloy steel were improved after increasing the boron content. The volume fraction of boron-rich carbide gradually decreased, and the hardness increased significantly with the rise in quenching temperature. The highest comprehensive mechanical properties were obtained for samples quenched at 1040 °C. The TEM results showed the boron-rich carbide was M₇(C, B)₃ with an HCP structure, and the precipitated particles were M₂₃(C, B)₆ with an FCC structure after tempering. This work may help improve the wear resistance of materials in the field of surface coatings. Full article

Polymers have an excellent effect in terms of moderating fast neutrons with rich hydrogen and carbon, which plays an indispensable role in shielding devices. As the shielding of neutrons is typically accompanied by the generation of γ-rays, shielding materials are developed from monomers to multi-component composites, multi-layer structures, and even complex structures. In this paper, based on the typical multilayer structure, the integrated design of the shield component structure and the preparation and performance evaluation of the materials is carried out based on the design sample of the heat-resistant lightweight polymer-based interlayer. Through calculation, the component structure of the polymer-based materials and the three-layer thickness of the shield are obtained. The mass fraction of boron carbide accounts for 11% of the polymer-based material. Since the polymer-based material is the weak link of heat resistance of the multilayer shield, in terms of material selection and modification, the B₄C/TiO₂/polyimide molded plate was prepared by the hot-pressing method, and characterization analysis was conducted for its structure and properties. The results show that the ball milling method can mix the materials well and realize the uniform dispersion of B₄C and TiO₂ in the polyimide matrices. Boron carbide particles are evenly distributed in the material. Except for Ti, the other elemental content of the selected areas for mapping is in good agreement with the theoretical values of the elemental content of the system. The prepared B₄C/TiO₂/polyimide molded plate presents excellent thermal properties, and its glass transition temperature and initial thermal decomposition temperature are as high as 363.6 °C and 572.8 °C, respectively. In addition, the molded plate has good toughness performs well in compression resistance, shock resistance, and thermal aging resistance, which allows it to be used for a long time under 300 °C. Finally, the prepared materials are tested experimentally on an americium beryllium neutron source. The experimental results match the simulation results well. Full article

Boron carbide is one of the most important non-metallic materials. Amorphous BC_x films were synthesized at room temperature by single- and dual-target magnetron sputtering processes. A B₄C target and C target were operated using an RF signal and a DC signal, respectively. The effect of using single- and dual-target deposition and process parameters on the chemical bonding and composition of the films as well as their functional properties were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray energy dispersive analysis, X-ray diffraction, ellipsometry, and spectrophotometry. It was found that the film properties depend on the sputtering power and the used targets. EDX data show that the composition of the samples varied from B₂C to practically BC₂ in the case of using an additional C target. According to the XPS data, it corresponds to the different chemical states of the boron atom. A nanoindentation study showed that the film with a composition close to B₂C deposited with the highest B₄C target power reached a hardness of 25 GPa and Young’s modulus of 230 GPa. The optical properties of the films also depend on the composition, so the band gap (E_g) of the BC_x film varied in the range of 2.1–2.8 eV, while the E_g of the carbon-rich films decreased to 1.1 eV. Full article

The aim of the work was to study the interaction between boron-rich boron carbide nanoparticles and selected tumor and immune phagocytic cells. Experiments were performed to investigate the feasibility of the application of boron carbide nanoparticles as a boron carrier in boron neutron capture therapy. Boron carbide powder was prepared by the direct reaction between boron and soot using the transport of reagents through the gas phase. The powder was ground, and a population of nanoparticles with an average particle size about 80 nm was selected by centrifugation. The aqueous suspension of the nanoparticles was functionalized with human immunoglobulins or FITC-labeled human immunoglobulins and was then added to the MC38 murine colon carcinoma and to the RAW 264.7 cell line of mouse macrophages. Flow cytometry analysis was used to determine interactions between the functionalized boron carbide nanoparticles and respective cells. It was shown that B₄C–IgG nanoconjugates may bind to phagocytic cells to be internalized by them, at least partially, whereas such nanoconjugates can only slightly interact with molecules on the cancer cells’ surface. Full article

A novel approach is demonstrated for the synthesis of the high entropy transition metal boride (Ta, Mo, Hf, Zr, Ti)B₂ using a single heating step enabled by microwave-induced plasma. The argon-rich plasma allows rapid boro-carbothermal reduction of a consolidated powder mixture containing the five metal oxides, blended with graphite and boron carbide (B₄C) as reducing agents. For plasma exposure as low as 1800 °C for 1 h, a single-phase hexagonal AlB₂-type structure forms, with an average particle size of 165 nm and with uniform distribution of the five metal cations in the microstructure. In contrast to primarily convection-based (e.g., vacuum furnace) methods that typically require a thermal reduction step followed by conversion to the single high-entropy phase at elevated temperature, the microwave approach enables rapid heating rates and reduced processing time in a single heating step. The high-entropy phase purity improves significantly with the increasing of the ball milling time of the oxide precursors from two to eight hours. However, further improvement in phase purity was not observed as a result of increasing the microwave processing temperature from 1800 to 2000 °C (for fixed ball milling time). The benefits of microwave plasma heating, in terms of allowing the combination of boro-carbothermal reduction and high entropy single-phase formation in a single heating step, are expected to accelerate progress in the field of high entropy ceramic materials. Full article

Superhard boron-rich boron carbide coatings were deposited on silicon substrates by microwave plasma chemical vapor deposition (MPCVD) under controlled conditions, which led to either a disordered or crystalline structure, as measured by X-ray diffraction. The control of either disordered or crystalline structures was achieved solely by the choice of the sample being placed either directly on top of the sample holder or within an inset of the sample holder, respectively. The carbon content in the B-C bonded disordered and crystalline coatings was 6.1 at.% and 4.5 at.%, respectively, as measured by X-ray photoelectron spectroscopy. X-ray diffraction analysis of the crystalline coating provided a good match with a B₅₀C₂-type structure in which two carbon atoms replaced boron in the α-tetragonal B₅₂ structure, or in which the carbon atoms occupied different interstitial sites. Density functional theory predictions were used to evaluate the dynamical stability of the potential B₅₀C₂ structural forms and were consistent with the measurements. The measured nanoindentation hardness of the coatings was as high as 64 GPa, well above the 40 GPa threshold for superhardness. Full article

Boron carbide is an extremely hard and lightweight material used in armor systems. Upon impact above the Hugoniot elastic limit (HEL), boron carbide loses strength and suddenly fails. Atomistic models suggest that boron-rich boron carbides could mitigate amorphization. Such samples were processed, and indentation-induced amorphous zones were created throughout the boron-rich samples of varying degrees and were mapped with Raman spectroscopy to assess changes in the amorphization intensity. Boron-rich samples with a B/C ratio of 6.3 showed a large reduction in amorphization intensity compared to commonly used stoichiometric B₄ C, in agreement with recent TEM results. Additionally, hardness trends were also noted as boron content is varied. This offers another pathway in which doping boron carbide can reduce amorphization. Full article