Search Results (952)

This study investigates the thermodielectric properties of polyurethane-based microcomposites filled with hybrid microfiller systems based on combinations of wurtzite boron nitride (wBN), aluminium nitride (AlN), and aluminium hydroxide (Al(OH)${}_3$). The dielectric properties (${\epsilon }_r$, $tan\delta$) in the mHz–MHz frequency range and the effective thermal conductivity ($k_{\mathrm{eff}}$) were experimentally characterised for filler loadings up to 40 wt.%. The hybrid systems (wBN+AlN, wBN+Al(OH)${}_3$, and AlN+Al(OH)${}_3$) yielded thermal conductivities in the range of 0.40–0.50 W·m${}^{-1}$·K${}^{-1}$ at 40 wt.% total loading ($0.19\le \varphi \le 0.23$), showing modest synergistic enhancement and remaining within the quasi-linear regime of the Nan model. These results demonstrate that the overall thermal transport in the composites depends far more on the formation of particle percolation networks than on the intrinsic thermal conductivity of the individual fillers, even when accounting for Kapitza interfacial resistance, as confirmed by simulations. Importantly, even at high filler loadings, the electrical insulation properties remain suitable for highly energy-dense applications in electric aircraft. In particular, $tan\delta$ values are comparable to or better than those of unfilled polyurethane, while dielectric strength results lie within the industrially relevant range. Full article

Iron powder cores are widely used in cost-sensitive low- to medium-frequency applications because of their high saturation magnetisation, low cost and favourable formability. However, the low electrical resistivity of iron powders favours continuous conductive pathways between adjacent particles, leading to high-frequency eddy-current loss and heat accumulation. To combine electrical insulation, interfacial stability, magnetic-property retention and thermal diffusion in a single coating, a synergistic insulation/thermal-conduction coating based on thiol-functionalised boron nitride was designed for iron-based magnetic powder cores. Hexagonal boron nitride was surface-modified through ultrasonic activation followed by grafting with a mercaptosilane coupling agent, forming covalent linkages on the boron nitride surface. The resulting functionalised nanosheets were deposited onto water-atomised iron powders through interfacial interactions between nitrogen- and sulfur-containing functional groups and the iron surface. A coating content of 5 wt.% produced a relatively continuous and uniform interfacial layer with limited agglomeration, enabling the magnetic powder cores to combine interparticle insulation, loss reduction, magnetic-property retention and thermal transport. The optimised core exhibited a volume resistivity of 58.7 Ω·m and a total core loss of 81.2 kW/m³ at 10 mT and 100 kHz, corresponding to a 20.8% reduction relative to the pure iron core. The sample retained a saturation magnetisation of 201.4 emu/g and an effective permeability of 67.5 at 100 kHz, while achieving a thermal conductivity of 55.2 W/(m·K) and a thermal impedance of 0.215 K·m²/W. Loss-separation analysis indicates that the continuous insulating layer restricts interparticle induced-current pathways and suppresses high-frequency eddy-current loss, while the two-dimensional boron nitride framework promotes internal thermal diffusion. Full article

During the 9th NASA MISSE (Materials International Space Station Experiment) campaign, a multilayer LDPE-based shield was tested in a low Earth orbit (LEO) environment aboard the International Space Station for the first time, in the wake-facing orientation. The architecture of the multilayer flight sample, 1 inch in diameter, consisted of two external LDPE sheets and two inner layers filled with boron nitride and samarium–cobalt powders. The inner layers were manufactured using an original process based on compression molding of two superimposed LDPE sheets, with the functional filler deposited onto one of them by spray coating. Thanks to the partial filling of the inner layers and their relative positioning, four different shielding configurations were obtained. The sample was exposed to the space environment for approximately 200 days, experiencing the combined effects of vacuum, solar radiation, thermal cycling, and limited atomic oxygen exposure. The results show that the structural integrity of the shield was not affected by its prolonged residence in LEO. The most significant effect observed was the partial oxidation of the external surfaces of the individual layers, particularly the uppermost layer. Full article

Effective thermal management is critical for ensuring the reliability of modern high-power electronic devices, where thermal interface materials (TIMs) play key roles in minimizing contact resistance and improving heat dissipation. Boron nitride (BN) is widely used as a thermally conductive filler due to its high in-plane thermal conductivity and electrical insulation. However, achieving BN-based polymer composites that simultaneously offer high filler loading, flexibility, and high thermal conductivity (κ) remains a significant challenge. In this work, we introduce a novel two-step fabrication strategy to overcome this limitation. First, continuous BN fibers with high aspect ratios are assembled into BN fiber papers with enhanced fiber alignment. These papers are then cut and integrated into a silicone matrix to form well-oriented thermal conductive channels. This approach enables a significantly higher filler mass fraction of 70%, resulting in a thermal pad with a high κ of 19.23 W/(m·K), low thermal resistance of 1.61 cm²·K/W, and excellent electrical insulation and flexibility. Application tests further demonstrate superior heat dissipation performance and operational stability compared to commercial silicone pads. This work not only highlights the potential of BN fiber-based TIMs but also offers a feasible process for their large-scale manufacturing. Full article

Silicon nitride ceramics exhibit excellent structural strength and electromagnetic wave transmission performance, yet demonstrate significant thermal shock instability under extreme conditions. Boron nitride (BN), on the other hand, possesses outstanding thermal shock resistance and electromagnetic wave transmission properties but exhibits relatively lower structural strength. Compositing these two materials holds promise for developing an integrated material that combines high-temperature load-bearing capacity with wave transmission capability. This study employed spark plasma sintering (SPS) technology to systematically investigate how varying BN content affects the sintering densification process and microstructural evolution of Si₃N₄/BN composite ceramics. Furthermore, we elucidated the mechanisms by which material composition and processing parameters influence key mechanical properties, dielectric characteristics, and other multifunctional attributes of the composites, providing a theoretical foundation for synergistic optimization design. The results indicate that BN incorporation suppresses both the phase transition from α-Si₃N₄ to β-Si₃N₄ during sintering and the growth of elongated β-Si₃N₄ crystals: the former hinders densification while the latter promotes it, resulting in a dual competitive mechanism that initially increases followed by decreases in sintered density. The effects of BN content on elastic modulus and fracture toughness align with trends in sintering density, whereas hardness, flexural strength, dielectric constant, and dielectric loss all show a monotonically decreasing trend with increasing BN content. Full article

The rapid growth of electric vehicles and electrified systems has increased the risk of bearing failures due to combined mechanical and electrical stresses. This study investigated the performance of hexagonal boron nitride nanoparticle-enhanced lithium grease under electrified conditions. Experiments based on a Taguchi L9 orthogonal array were conducted on deep groove ball bearings using a full-scale test rig at 1200 rpm with varying loads (100–300 N), currents (6–10 A), and hBN concentrations (0.1–1 wt.%). The tribo-electrical performance of nano-enhanced grease was compared with the base grease and commercial grease. It was observed that the base grease exhibited superior performance with a lower current flow, reduced vibration, and minimal surface degradation. In contrast, the hBN-enhanced grease exhibited inferior tribo-performance, with high vibrations and surface damage in electrified conditions. The surface analysis revealed features morphologically similar to white etching areas and micro-pitting. The FTIR results indicated grease degradation, while ICP-OES confirmed higher wear debris generation in the commercial and hBN-added greases. The present work indicates that additives like hBN nanoparticles do not necessarily improve performance under electrified conditions, making it important to consider the type of additives to be added during lubricant formulation. Thus, the findings emphasize the importance of lubricant formulation for controlling electrically induced bearing failures and provide insights for developing advanced greases for electric machinery applications. Full article

The influence of BN particle size on lithium grease performance was systematically compared among a base grease (Li), a micro-BN (3 µm, 0.1 wt%) modified grease (Li + 0.1% mBN), and a nano-BN (50 nm, 0.1 wt%) modified grease (Li + 0.1% nBN). SEM shows that addition nano-BN leads to a more compact soap fiber networks, whereas micro-BN tends to agglomerate and provides limited reinforcement, leaving the base grease with a loose, porous network. Consequently, Li + 0.1% nBN outperforms both Li and Li + 0.1% mBN in dropping point (199.5 °C vs. 194.9 °C and 198.6 °C), oil separation (0.39% vs. 0.64% and 0.44%), and flow point (49% vs. 45% and 47%). Its plateau modulus is significantly higher, reflecting stronger network entanglement. However, Li + 0.1% nBN shows lower structural recovery (61.0%) than Li (65.8%) and Li + 0.1% mBN (67.2%) due to rigid particle–fiber junctions. Notably, Li + 0.1% mBN exhibits a unique frequency-dependent viscoelasticity: higher tanδ at low frequencies but lower tanδ at high frequencies relative to Li. Tribologically, Li + 0.1% nBN reduces friction coefficient by 35% and wear scar diameter by 12.7% compared with Li, outperforming Li + 0.1% mBN. XPS confirms a protective hybrid tribofilm (BN + organic nitrogen species + iron oxides) on the nano-BN lubricated surface. Particle size critically governs BN–fiber interactions and the resulting rheological and tribological performance. Full article

Hydrogen is a clean and renewable energy carrier, but its reversible storage near ambient conditions remains a major challenge. Here, density functional theory (DFT) combined with ab initio molecular dynamics (AIMD) is employed to assess the newly predicted 2D orthorhombic diboron dinitride (o-B₂N₂) monolayer, in pristine and Li-functionalized forms, as a hydrogen storage medium. On the pristine surface, H₂ physisorbs with binding energies of −0.158 to −0.174 eV. Li atoms anchor strongly at the hexagonal hollow sites ($E_{\mathrm{bind}}$ from −0.979 to −1.321 eV, strongest at the B-rich H1 site), donate 0.65–0.84 $\left|e\right|$ to the substrate, and render the semiconducting monolayer metallic. A positive cluster formation energy ($+0.171$ eV per Li pair) and a 5 ps AIMD simulation at 400 K confirm that the Li adatoms remain dispersed, without clustering. Each ${\mathrm{Li}}^{+}$ center polarizes and binds up to five H₂ molecules, with average adsorption energies of −0.207 to −0.336 eV/H₂, within the optimal window for room-temperature reversible storage. The 4Li@o-B₂N₂(20H₂) system attains a theoretical gravimetric capacity of 15.12 wt% and a practical capacity of 10.99 wt% under realistic operating conditions (charging at 30 atm/25 °C; release at 3 atm/100 °C). These results establish Li-functionalized o-B₂N₂ as a promising hydrogen storage material that merits experimental exploration. Full article

Superhydrophobic materials offer promising prospects for utilization in energy, environmental, and related fields. However, their long-term stability in natural environments is constrained by factors such as mechanical wear and aging, which compromise their practical effectiveness and service life. While notable experimental results have been obtained worldwide, scalable application remains limited by the complexity of the requisite fabrication processes. In this study, a durable superhydrophobic coating was developed through a facile one-step process, utilizing a polyaspartic ester (PAE) matrix reinforced with a composite of self-synthesized fluorinated silica (F-SiO₂) and hexagonal boron nitride (h-BN) micro-/nano-structures. This strategy effectively enhanced filler dispersion within the resin matrix and promoted hydrophobicity, yielding a stable superhydrophobic surface. The resulting coating exhibits significant potential for scalable application. The optimized coating demonstrated a water contact angle of 161.2° and a roll-off angle of 7.6°, showing excellent repellency to water, corrosive liquids, and fluids across a wide pH range, along with remarkable self-cleaning performance. Benefiting from the synergistic enhancement of h-BN and F-SiO₂, the coating also exhibits superior mechanical durability, maintaining a contact angle of 144.4° after 1000 abrasion cycles. Furthermore, in low-temperature anti-icing tests, the coating significantly delayed ice formation on its surface. Notably, after 1000 h of UV aging tests, the F-SiO₂@BN/PAE coating retained its intact superhydrophobic structure, with the water contact angle only slightly decreasing from 159.6° to 152.8°, still within an excellent superhydrophobic state, demonstrating outstanding weather resistance. By integrating surface functionalization with mechanical reliability through a facile one-step fabrication process, this study provides significant insights for the large-scale application of hydrophobic materials in the energy and transportation sectors. Full article

Carbon/inorganic hybrid composites have evolved from filler-reinforced materials into design platforms for coupled electromagnetic, thermal, sensing, environmental, protective and energy-related functions. Their distinctive value lies in the possibility of combining a conductive, polarizable or porous carbon phase with an inorganic phase that contributes dielectric, magnetic, catalytic, ionic, thermally conductive or barrier behavior. This review examines carbon/inorganic hybrid multifunctional composites from the viewpoint of structure–property relationships, with emphasis on interfacial design, percolation, anisotropy, hierarchical architecture, processing and metrology. Selected graphitic composite studies are discussed as case studies for broadband dielectric spectroscopy, microwave shielding, high-frequency contact metrology, thermal diffusivity analysis and impedance-monitored graphene filters; these case studies are integrated with the broader international literature on CNT and graphene polymer composites, MXene films and foams, graphene/metal oxide photocatalysts, boron nitride/carbon thermal networks, biochar–graphene adsorbents, smart coatings, sensors, supercapacitors and water remediation systems. The central argument is that credible multifunctionality requires more than measuring several properties on the same material. It requires simultaneous or service-relevant co-optimization under constraints of thickness, density, processability, aging, humidity, corrosive media, regeneration, toxicity, economic feasibility and scalable fabrication. The review concludes with design rules and reporting recommendations intended to help move the field from impressive property demonstrations toward application-ready hybrid material systems. Full article

To meet the growing demand for materials combing high thermal conductivity and electrical insulation, we developed epoxy (EP) composites filled with zero-dimensional (0D) silver nanoparticles (AgNPs) and two-dimensional (2D) boron nitride nanosheets (BNNSs). This hybrid filler system synergistically enhances both thermal conductivity and dielectric properties, while retaining excellent electrical insulation. With only 1 wt% AgNPs and 15 wt% BNNSs, the composite achieved a dielectric constant of 4.17 at 100 Hz, outperforming pure EP. At 30 wt% BNNSs and the same AgNP loading, the in-plane and out-of-plane thermal conductivities reached 3.02 and 0.41 W·m⁻¹·K⁻¹, respectively, along with improved thermal stability. Moreover, the composite exhibited an electrical conductivity below 10⁻⁹ S/cm at 1000 Hz, confirming that the minimal metal filler content negligibly affects insulation. Thus, this work offers a feasible strategy for designing next-generation high-performance composites using 0D/2D hybrid fillers, highlighting their promising potential for advanced electronic packaging. Full article

Accurate measurement of the temperature in the cutting zone is essential for closed-loop machining. However, it remains difficult due to the small size of the tool–chip contact area, its partial concealment by chips and the steep thermal gradients present. This study presents an integrated framework that combines a thin-film thermocouple (TFTC) on the rake face of a polycrystalline cubic boron nitride (PCBN) tool with a thermo-mechanical wear-coupled simulation in order to monitor cutting temperature and predict tool wear. The three-dimensional finite-element turning model includes a moving heat source that represents plastic and frictional heat at the tool–chip interface, as well as an Archard-type wear law that is enhanced by a temperature correction factor. The TFTC is fabricated by magnetron sputtering NiCr and NiSi films onto an insulating layer, after which it is embedded in the tool as a minimally intrusive in situ sensor. Turning experiments on AISI 1045 steel were performed at spindle speeds of 1000–3000 rpm, feeds of 0.05–0.20 mm/rev and depths of cut ranging from 0.3 to 1.0 mm under dry, wet (emulsion) and cryogenic (liquid nitrogen) cooling conditions. Simulated temperature fields reveal strong localisation at the tool–chip contact and a nonlinear increase in peak rake-face temperature with spindle speed, which fits a quadratic regression with R² = 0.99. The TFTC shows a response time of around 0.3 s with less than 5% overshoot, and its thermoelectric voltage is almost perfectly linear with temperature (R² = 1), with a sensitivity of approximately 12 µV/°C. During cutting, TFTC readings agree with infrared measurements within ±3 °C and demonstrate improved robustness in occluded zones. The coupled wear model replicates the observed wear growth trend with the compact expression VB = 0.0001·t^0.8. Sensitivity tests indicate that thermo-mechanical coupling increases wear rates compared to single-factor models, and that cooling reduces thermal loads by approximately 15% (wet) and 25% (cryogenic). Full article

The work investigated the formation mechanisms, structure, and properties of the modified layer obtained during electrolytic-plasma nitroboriding of Steel 20 in the temperature range of 650–850 °C. A comprehensive approach, including numerical modeling and experimental methods, was applied to analyze diffusion processes, phase formation, and performance characteristics. A one-dimensional diffusion model was developed, taking into account the coupled transport of boron, nitrogen, and carbon, as well as the movement of phase boundaries. It was shown that a gradient layer is formed, characterized by boron enrichment in the near-surface zone, deeper nitrogen penetration, and carbon redistribution. The calculated layer thickness at 850 °C (~70–75 μm) is in good agreement with the SEM data (~73.4 μm, taking into account the transition zone). SEM and EDS analysis confirmed the formation of a multilayer structure with a pronounced transition region. A significant increase in microhardness up to ~950–1000 HV at 850 °C was established, with a gradual decrease to the matrix level (~200–250 HV) at a depth of 70–90 μm. Tribological tests showed a decrease in the coefficient of friction and an increase in wear resistance, with the best characteristics achieved at 850 °C. Full article

UV-curable polymer composites are attractive for fabricating complex components by digital light processing (DLP), but improving thermal transport while preserving printability remains challenging at high filler loadings. In this work, solvent-free UV-curable formulations filled with hexagonal boron nitride (h-BN) and h-BN/graphite hybrids were developed for DLP 3D printing using commercially available equipment. The effects of filler composition on viscosity, printability, microstructure, through-thickness thermal conductivity, electrical conductivity, and tensile behavior were investigated. Viscosity increased markedly with filler loading, yet reliable DLP printing was achieved up to 40 wt% h-BN through composition-dependent adjustment of build parameters. Thermal analysis supported negligible macroscopic sedimentation during printing, while optical and FE-SEM observations revealed generally uniform platelet dispersion, visible 50 μm layer stratification, and limited phase segregation in the hybrid systems. The through-thickness thermal conductivity increased from ~0.25 W/mK for the neat resin to ~1.95 W/mK at 40 wt% h-BN. At a fixed 20 wt% h-BN, graphite addition led to a smaller increase in thermal conductivity, up to ~1.16 W/mK, while increasing electrical conductivity and reducing mechanical performance. A phenomenological percolation-type model captured the thermal-conductivity trend of the h-BN series. Overall, h-BN-rich formulations provided the most effective route to enhance thermal conductivity while preserving electrical insulation. Full article

This study investigates the mechanical performance, high-temperature resistance, and microstructural characteristics of ground granulated blast furnace slag (GGBFS)-based geopolymer composites reinforced with boron nitride (BN)-modified hemp nanofibers. BN-modified hemp nanofibers (PVA-mBN/Hemp) were produced via electrospinning and incorporated into geopolymer mixtures at varying ratios ranging from 0 to 4 wt%. The effects of nanofiber content on composite properties were evaluated through mechanical testing, ultrasonic pulse velocity (UPV) measurements, and exposure to elevated temperatures (300–1200 °C), supported by SEM-EDS, FTIR, and XRD analyses. The results indicate that low nanofiber additions (0.5–1 wt%) improve flexural strength by up to 15%, although compressive strength is slightly reduced due to increased porosity. UPV measurements confirm the changes in internal structure. At elevated temperatures, nanofiber-reinforced samples exhibit enhanced residual strength compared to the control specimens, particularly at moderate temperatures, whereas significant degradation occurs above 900 °C. Microstructural analyses reveal improved fiber-matrix interaction, reduced crack propagation, and enhanced thermal stability attributed to BN modification. Overall, the incorporation of 0.5–1 wt% BN-modified hemp nanofibers provides an effective balance between mechanical performance and high-temperature resistance, highlighting their potential for use in sustainable and fire-resistant construction materials. This study contributes to the United Nations Sustainable Development Goals (SDGs), particularly SDG 9 (Industry, Innovation, and Infrastructure), SDG 11 (Sustainable Cities and Communities), and SDG 12 (Responsible Consumption and Production). Full article