Search Results (102)

This study provides a comprehensive investigation into the growth behavior of boron nitride (BN) buffer layers on Silicon carbide (SiC) substrates and their influence on interfacial band alignment. BN layers were deposited on semi-insulating SiC by RF magnetron sputtering with deposition times of 2.5, 5, and 7.5 min (these deposition times are specific experimental parameters to adjust the thickness of the amorphous BN layer, not intrinsic material properties of BN). Atomic force microscopy revealed that the surface roughness of the BN layers initially decreased and then increased with thickness, indicating an evolution from nucleation to continuous film formation, followed by surface coarsening. Transmission electron microscopy confirmed the BN thicknesses of approximately 3.25, 4.91, and 7.57 nm, showing that the layers gradually became uniform and compact, thereby improving the structural integrity of the BN/SiC interface. Band alignment was analyzed using the Kraut method, yielding a valence band offset of ~0.36 eV and a conduction band offset of ~2.34 eV for the BN/SiC heterojunction. This alignment indicates that the BN buffer layer introduces a pronounced electron barrier, effectively suppressing leakage, while the relatively small VBO facilitates hole transport across the interface. These findings demonstrate that the BN buffer layer enhances interfacial bonding, reduces defect states, and enables band structure engineering, offering a promising strategy for improving the performance of wide-bandgap semiconductor devices. Full article

This study aimed to develop an industrially scalable coating route for enhancing the oxidation resistance of carbon fiber fabrics, a critical requirement for next-generation aerospace and high-temperature composite structures. To achieve this goal, synthesis of hexagonal boron nitride (h-BN) layers was achieved via a single wet step in which the fabric was impregnated with an ammonia–borane/THF solution and subsequently nitrided for 2 h at 1000–1500 °C in flowing nitrogen. Thermogravimetric analysis coupled with X-ray diffraction revealed that amorphous BN formed below ≈1200 °C and crystallized completely into (002)-textured h-BN (with lattice parameters a ≈ 2.50 Å and c ≈ 6.7 Å) once the dwell temperature reached ≥1300 °C. Complementary XPS, FTIR and Raman spectroscopy confirmed a near-stoichiometric B:N ≈ 1:1 composition and the elimination of O–H/N–H residues as crystallinity improved. Low-magnification SEM (100×) confirmed the uniform and large-area coverage of the BN layer on the carbon fiber tows, while high-magnification SEM revealed a progressive densification of the coating from discrete nanospheres to a continuous nanosheet barrier on the fibers. Oxidation tests in flowing air shifted the onset of mass loss from 685 °C for uncoated fibers to 828 °C for the coating produced at 1400 °C; concurrently, the peak oxidation rate moved ≈200 °C higher and declined by ~40%. Treatment at 1500 °C conferred no additional benefit, indicating that 1400 °C provides the optimal balance between full crystallinity and limited grain coarsening. The resulting dense h-BN film, aided by an in situ self-healing B₂O₃ glaze above ~800 °C, delayed carbon fiber oxidation by ≈140 °C. Overall, the process offers a cost-effective, large-area alternative to vapor-phase deposition techniques, positioning BN-coated carbon fiber fabrics for robust service in extreme oxidative environments. Full article

The use of molybdenum-based alloys as materials for components operating under high temperatures and significant mechanical loads is widely recognized due to their excellent mechanical properties. However, their low high-temperature resistance remains a critical limitation, which can be effectively mitigated by applying protective coatings. In this study, we investigate the influence of a two-step coating process on the properties and performance of the TZM molybdenum alloy. In the first step, pack cementation was performed. Simultaneous surface saturation with aluminum and silicon, a process known as aluminosiliconizing, was conducted at 1000 °C for 6 h. The saturating mixture comprised powders of aluminum, silicon, aluminum oxide, and ammonium chloride. The second step involved the application of a pre-ceramic coating based on polyhydrosiloxane modified with silicon and boron. This treatment effectively eliminated pores and cracks within the coating. Thermodynamic calculations were carried out to evaluate the likelihood of aluminizing and siliconizing reactions under the applied conditions. Aluminosiliconizing of the TZM alloy resulted in the formation of a protective layer 20–30 µm thick. The multiphase structure of this layer included intermetallics (Al₆₃Mo₃₇, MoAl₃), nitrides (Mo₂N, AlN, Si₃N₄), oxide (Al₂O₃), and a solid solution α-Mo(Al). Subsequent treatment with silicon- and boron-modified polyhydrosiloxane led to the development of a thicker surface layer, 130–160 µm in thickness, composed of crystalline Si, amorphous SiO₂, and likely amorphous boron. A transitional oxide layer ((Al,Si)₂O₃) 5–7 µm thick was also observed. The resulting coating demonstrated excellent structural integrity and chemical inertness in an argon atmosphere at temperatures up to 1100 °C. High-temperature stability at 800 °C was observed for both coating types: aluminosiliconizing, and aluminosiliconizing followed by the pre-ceramic coating. Moreover, additional oxide layers of SiO₂ and B₂O₃ formed on the two-step coated TZM alloy during heating at 800 °C for 24 h. These layers acted as an effective barrier, preventing the evaporation of the substrate material. Full article

Hydrogen energy offers high energy density and carbon-free combustion, making it a promising fuel for next-generation propulsion and power generation systems. Hydrogen offers approximately three times more energy per unit mass than natural gas, and its combustion yields only water as a byproduct, making it an exceptionally clean and efficient energy source. Materials used in hydrogen-fueled combustion engines must exhibit high thermal stability as well as resistance to corrosion caused by high-temperature water vapor. This study introduces a novel ceramic matrix composite (CMC) designed for such harsh environments. The composite is made of yttria-stabilized zirconia (YSZ) fiber-reinforced silicoboron carbonitride [Si(B)CN]. CMCs were fabricated via the polymer infiltration and pyrolysis (PIP) method. Multiple PIP cycles, which help to reduce the porosity of the composite and enhance its properties, were utilized for CMC fabrication. The Si(B)CN precursor formed an amorphous ceramic matrix, where the presence of boron effectively suppressed crystallization and enhanced oxidation resistance, offering superior performance than their counter part. Thermogravimetric analysis (TGA) confirmed negligible mass loss (≤3%) after 30 min at 1350 °C. The real-time ablation performance of the CMC sample was assessed using a hydrogen torch test. The material withstood a constant heat flux of 185 W/cm² for 10 min, resulting in a front-surface temperature of ~1400 °C and a rear-surface temperature near 700 °C. No delamination, burn-through, or erosion was observed. A temperature gradient of more than 700 °C between the front and back surfaces confirmed the material’s effective thermal insulation performance during the hydrogen torch test. Post-hydrogen torch test X-ray diffraction indicated enhanced crystallinity, suggesting a synergistic effect of the oxidation-resistant amorphous Si(B)CN matrix and the thermally stable crystalline YSZ fibers. These results highlight the potential of YSZ/Si(B)CN composites as high-performance materials for hydrogen combustion environments and aerospace thermal protection systems. Full article

Amorphous boron powder, as a high-energy fuel, is widely used in the energy sector. However, its ignition and combustion difficulties have long limited its performance in propellants, explosives, and pyrotechnics. In this study, Mg/Al-coated boron powder with enhanced combustion properties was synthesized using the electrical explosion method. To investigate the effect of Mg/Al coating on the ignition and combustion behavior of boron powder, four samples with different Mg/Al coating contents (4 wt.%, 6 wt.%, 8 wt.%, and 10 wt.%) were prepared. Compared with raw B95 boron powder, the coated powders showed a significant reduction in particle size (from 2.9 μm to 0.2–0.3 μm) and a marked increase in specific surface area (from 10.37 m²/g to over 20 m²/g). The Mg/Al coating formed a uniform layer on the boron surface, which reduced the ignition delay time from 143 ms to 40–50 ms and significantly improved the combustion rate, combustion pressure, and combustion calorific value. These results demonstrate that Mg/Al coating effectively promotes rapid ignition and sustained combustion of boron particles. Furthermore, with the increasing Mg/Al content, the ignition delay time decreased progressively, while the combustion rate, combustion pressure, and heat release increased accordingly, reaching optimal values at 8 wt.% Mg/Al. An analysis of the combustion residues revealed that both Mg and Al reacted with boron oxide to form new multicomponent compounds, which reduced the barrier effect of the oxide layer on oxygen diffusion into the boron core, thereby facilitating continuous combustion and high heat release. This work innovatively employs the electrical explosion method to prepare dual-metal-coated boron powders and, for the first time, reveals the synergistic promotion effect of Mg and Al coatings on the ignition and combustion performance of boron. The results provide both experimental data and theoretical support for the high-energy release and practical application of boron-based fuels. Full article

Owing to potential inaccuracies in the current stress–strain curve used for constructing the Johnson–Cook (JC) constitutive model of amorphous alloys, the parameters of the JC constitutive equation were derived using Oxley’s cutting theory, negative chamfer theoretical mechanics modelling, and the particle swarm optimisation algorithm. A two-dimensional finite element cutting model was subsequently established using AdvantEdge software. The optimised constitutive model was used to simulate the main cutting force (Fz) and the backward force (Fy), which resulted in average errors of 12.461% and 9.161%, respectively. Based on the optimised constitutive model in which the JC constitutive equation parameters were derived using Oxley’s method, the variations in temperature, strain rate, and stress in the deformation zone during the cutting process were analysed. The chip microstructures revealed the transformation of lamellar chips into serrated chips resulting from a combination of plastic deformation, adiabatic shear, and shear slip. Full article

Boron-modified ceramic materials derived from polymers (PDC) are the subject of this research. The primary objective is to compare the structure and microstructure of SiBOC materials obtained in varying pyrolysis conditions in comparison to base SiOC materials. The preparation involved a number of stages, staring with the hydrolytic polycondensation method, followed by the initial thermal treatment and the final stage—pyrolysis process in argon or argon/hydrogen atmospheres at different temperatures. Bulk SiOC and SiBOC glasses were thoroughly analyzed. Microstructure studies included Scanning Electron Microscopy and Mercury Intrusion Porosimetry. Moreover, to confirm the structure, the research consisted of Fourier-Transform Infrared spectroscopy, Raman spectroscopy, and X-ray diffraction. The conducted research confirmed boron incorporation into the material structure in all samples. A free carbon phase has also been observed in SiBOC glasses, which has been confirmed in Raman spectroscopy measurements. This research indicates that in particular conditions, it is possible to obtain amorphous materials with nanocrystalline inclusions. This paper proves that the introduction of boron increases the porosity of materials and enhances their thermal stability. Full article

In this study, a combination of theoretical calculations and experiments were carried out to analyze boron phosphide materials. Amorphous boron powder and amorphous red phosphorus were used as raw materials to directly synthesize the target samples in one step under high-pressure and high-temperature (HPHT) conditions. Theoretical calculations were then carried out based on the XRD spectra of boron phosphide at 4 GPa and 1200 °C. The experimental results show that the target samples can be successfully prepared at HPHT. The electrical properties of the samples were characterized, and it was found that their conductivity increased with the increase in temperature, and they have a semiconducting nature, which is consistent with the theoretical calculations. Its Seebeck coefficient is positive at different temperatures, indicating that the synthesized boron phosphide is a P-type semiconductor. The combination of theoretical calculations and experiments shows that high pressure can reduce the lattice constant of boron phosphide, thus reducing its forbidden bandwidth, which improves its electrical properties. EDS shows a homogeneous distribution of the elements in the samples. Successful synthesis of BP crystals will probably stimulate more research into its semiconductor properties. It may also provide some assistance in the application of BP in aero-engine high-temperature monitoring systems as well as thermally controlled coatings for deep-space probes. Full article

In this study, a novel and facile approach of catalytic graphitization was adopted for the preparation of graphitized polyacrylonitrile (PAN)-derived carbon. Pure PAN and boron-introduced PAN were derived from the monomer acrylonitrile using a polymerization technique. Iron nitrate nonahydrate at different concentrations (2.5%, 5%, and 10%) was added to the boronated PAN and carbonized at 1250 °C. The effect of iron and boron on the catalytic graphitization of PAN was comprehensively analyzed. The results showed that the boronated PAN containing a 5% Fe salt was more graphitized due to the optimized amount of the metallic iron, which promoted the rate of conversion of the amorphous carbon to graphitic carbon containing carbon nanotube (CNT) by rearranging the nearby carbon and reducing the energy barrier for the transformation. Furthermore, the in situ formed iron boron carbide within the graphitized carbon provided a nucleation site and stabilized the catalytic activity of the metallic iron at high temperature. This work presents a promising approach for obtaining a highly graphitic PAN-derived carbon by adopting a strategy of catalytic graphitization using the born and iron as catalytic agents. Full article

The utilization of silicomanganese slag (SiMnS) as a precursor for alkali-activated materials (AAMs) is considered as an efficient approach for sustainable and eco-friendly large-scale resource utilization. However, sodium silicate solutions account for more than 50% of the production costs and carbon emissions of AAMs. In this study, AAM activators were prepared by silica-containing waste (acid leaching residue of boron mud, BM-AR) and NaOH as raw materials, and were successfully substituted for commercial sodium silicate-NaOH activators. Results indicated that the NaOH dosage had a great effect on the concentration and modulus of the activator. With the appropriate dosage of NaOH (NaOH: BM-AR = 0.4–0.7), suitable moduli of AAM activators can be produced at a wide range of solid/liquid ratios (L/S = 3–4.5) under mild conditions (80–100 °C). The compressive strength of the SiMnS AAM specimens prepared by this activator can reach 68.58 MPa, and its hydration products were mainly hydrated calcium silicate and amorphous silica–alumina gel, indicating the successful preparation of AAM. Calculation showed that the carbon emission of the AAMs prepared in this study was 12.4% and 37.6% of that of OPC and commercial water glass/NaOH-activated AAMs, and the cost was only 67.14% and 60.78% of them. The process achieves the use of waste materials to replace commercial activators, and is expected to be extended to a variety of AAMs raw materials and silica-containing waste. This makes it a highly promising alternative method for the production of AAMs, particularly the ‘just add water’ AAMs. Full article

Thermoplastic polyimides have garnered significant interest in the electronic and electrical industries owing to their performance characteristics. However, their relatively low thermal conductivity coefficients pose a challenge. To address this issue, this study focused on the properties of nanocomposites comprising two thermoplastic semicrystalline polyimides R-BAPB and BPDA-P3, one amorphous polyimide ULTEM^TM, and hexagonal nanoparticles. Polyimide R-BAPB was synthesized based on 1,3-bis-(3′,4-dicarboxyphenoxy)benzene (dianhydride R) and 4,4′-bis-(4′-aminophenoxy)biphenyl (BAPB diamine); polyimide BPDA-P3 was synthesized based on 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and diamine 1,4-bis[4-(4-aminophenoxy)phenoxy]benzene (P3); and amorphous polyimide ULTEM^TM was commercially produced by Sabic Innovative Plastics. Using microsecond-scale all-atom molecular dynamics simulations, the effects of incorporating hexagonal nanoparticles with enhanced thermal conductivity, such as graphene, graphene oxide, and boron nitride, on the structural and thermophysical characteristics of these materials were examined. The formation of stacked aggregates was found for graphene and hexagonal boron nitride nanoparticles. It was observed that graphene oxide nanoparticles exhibited a dispersion in polyimide binders that was higher than those in graphene and hexagonal boron nitride nanoparticles, leading to reduced translational mobility of polymer chains. Consequently, the decrease in polyimide chain mobility correlated with an increase in the glass transition temperature of the nanocomposites. Aggregates of nanoparticles formed a pathway for phonon transport, resulting in improved thermal conductivity in polyimide nanocomposites. An increase in the thermal conductivity coefficient of polyimide nanocomposites was observed when the concentration of graphene, graphene oxide, and hexagonal boron nitride nanofillers increased. The enhancement in thermal conductivity was found to be strongest when graphene nanoparticles were added. Full article

This article considers the prospects of using heat-resistant polyimide boron-containing composites to protect astronauts of manned orbital stations from secondary neutron radiation. Variant calculations are performed regarding neutron and gamma-quanta flux distributions in a polyimide composite material with different boron content used to reduce capture radiation. The dependences of spatial distributions of thermal neutron flux density and the gamma-quanta dose rate in a polyimide composite layer with a boron content of 0 to 5% are obtained. An experimental assessment of the energy distribution of neutron and gamma radiation behind the protective polyimide composite is carried out. The introduction of boron atoms in an amount of 3.0 wt.% shows the absence of bursts of secondary gamma radiation energy in the composite, which is due to the high cross-section of thermal neutron absorption by boron atoms. As a result, with a material layer thickness of 3–10 cm, the gamma-quanta dose rate decreases by 2–3 times. The differential thermal analysis method showed that the upper limit of the working temperature of the polyimide composite is 500 °C. The polyimide matrix filled with boron atoms can find effective application in the development of new radiation-protective polymer materials used in manned orbital stations. Full article

The paper presents the results of the study of the processes of self-propagating high-temperature synthesis of Zr-1%B alloy and its refining by electron beam melting. Experiments on the influence of boron’s amorphous and crystalline modifications on the safety parameters of the synthesis process of Zr-1%B alloy necessitated the conversion of amorphous boron into crystalline form by electron beam melting, with an increase in its purity from 94% to 99.9%. High efficiency of vacuum induction and electron beam equipment was demonstrated, which provided a high purity of the Zr-1%B alloy of at least 99.9%. The alloy ingots had a uniform distribution of the alloying element (boron) all over the volume. The obtained alloy is suitable for the production of materials with thermal neutron capture cross-sections of up to 40 barns for neutron protection. Full article

In the present work, the evolution of the microstructure in additively manufactured 17-4PH stainless steel, which was subjected to laser surface alloying with amorphous boron and nitrogen at the varying process parameters, was studied. The main aim was to improve surface hardness and hence potential wear resistance of the steel. Scanning electron microscopy, wavelength-dispersive X-ray spectroscopy (WDS), and Auger electron spectroscopy (AES) were used. It was shown that the final microstructure developed in the laser-melted zone (LMZ) is dependent on a variety of processing parameters (1 and 1.5 mm laser beam spot diameters; 200, 400, and 600 mm/min laser scan speeds), which primarily influence the morphology and orientation of the eutectic dendrites in the LMZ. It was metallographically proven that a fully eutectic microstructure, except for one sample containing 60 ± 4.2% of the eutectic, was revealed in the LMZ in the studied samples. The results of WDS and AES also confirmed alloying the LMZ with nitrogen. The formation of the boron eutectic and the supersaturation of the α-iron solid solution with boron and nitrogen (as a part of the eutectic mixture) led to enhanced microhardness, which was significantly higher compared with that of the heat-treated substrate (545.8 ± 12.59–804.7 ± 19.4 vs. 276.8 ± 10.1–312.7 ± 11.7 HV0.1). Full article

Glass properties play crucial roles in ensuring the safety and reliability of electronic packaging. However, challenges, such as thermal expansion and resistance to acid corrosion, pose long-term service difficulties. This study investigated the impact of the microstructure on acid resistance by adjusting the glass composition. A glass material with excellent acid resistance was obtained by achieving a similar coefficient of thermal expansion to tantalum; it exhibited a weight loss rate of less than 0.03% when submerged in 38% sulfuric acid at 85 °C for 200 h. Theoretically, this glass can be used to seal wet Ta electrolytic capacitors. Differential scanning calorimetry (DSC) was used to analyze the glass transition temperature and thermal stability of borosilicate glasses. X-ray diffractometry (XRD), scanning electron microscopy (SEM), and Raman spectroscopy were used to study the microstructure of the amorphous phase of the borosilicate glass, which revealed a close relationship between the degree of network phase separation in the borosilicate glass and the degree of polymerization (isomorphic polyhedron value, IP) of the glass matrix. The IP value decreased from 3.82 to 1.98 with an increasing degree of phase separation. Boron transitions from [BO₄] to [BO₃] within the glass network structure with increasing boron oxide content, which diminishes the availability of free oxygen provided by alkaline oxide, resulting in a lower acid resistance. Notably, the glass exhibited optimal acid resistance at boron trioxide and mixed alkaline oxide contents of 15% and 6%, respectively. Raman experiments revealed how the distributions of various bridging oxygen atoms (Q_n) affect the structural phase separation of the glass network. Additionally, Raman spectroscopy revealed the depolymerization of Q₄ into Q₃, thereby promoting high-temperature phase separation and highlighting the unique advantages of Raman spectroscopy for phase recognition. Full article