Search Results (374)

To meet the requirements of forest fire prevention, a water glass-based composite gel foam was developed by introducing hydroxypropyl methylcellulose (HPMC) and nanosilica sol into a sodium silicate/sodium bicarbonate matrix. The resulting water glass/HPMC/silica sol ternary system (SGF-HPMC-SOL) was designed to improve water retention, foam stability, substrate adhesion, and fire-barrier durability. The results indicate that HPMC and silica sol contributed to network reinforcement through hydrogen bonding, polymer-chain entanglement, nanoscale filling, and possible interfacial condensation. The optimized SGF-HPMC-SOL retained 20.4% of its initial mass after heating at 100 °C for 5 h, compared with 4.65% for SGF and 9.54% for SGF-HPMC; reached a carbonization time of 164 s under direct-flame exposure, versus 100 s for SGF and 137 s for SGF-HPMC; and maintained a residual mass of 76% at 800 °C in TGA, compared with 58.3% for SGF and 55.1% for SGF-HPMC. These improvements were associated with the formation of a denser silica-rich protective layer after combustion, which delayed heat transfer to the wood substrate. Under the adopted direct-flame screening conditions, SGF-HPMC-SOL exhibited enhanced flame-retardant performance compared with the reference gel foams, indicating its potential for enhanced flame-retardant performance under laboratory screening conditions for forest fire prevention. Full article

To address the erosion-induced failure of large-caliber gun barrels under extreme thermochemical coupling, this study systematically investigates the microstructural evolution of multi-layered gradient regions along the radial direction of 32CrNi3MoV steel under extreme thermochemical cycling. Leveraging SEM, EBSD, TKD, and double-beam aberration-corrected TEM, combined with JMatPro thermodynamic simulations, the phase transitions, crystallographic characteristics, and substructural evolution spanning from the bore surface to the matrix are elucidated. The results demonstrate that a three-layer gradient structure forms along the radial direction. The topmost layer is a chemically stabilized metastable austenite diffusion layer with a thickness of 1.5–4.0 μm. which is attributed to the suppression of martensitic transformation due to C/N interstitial diffusion lowering the MS temperature. The observed high-density dislocation tangles and stacking faults within this austenite diffusion layer result from thermal mismatch stresses during rapid thermal cycling. The subsurface region is a martensitic transformation layer with a thickness of 70–97 μm, exhibiting a substructural gradient from nanostructured high-density twinned martensite to refined lath martensite. Thermodynamic analysis indicates that rapid heating (≈10⁵ °C/s) facilitates significant austenite nucleation and growth during the reverse phase transformation, subsequently forming nanostructured martensitic grains via non-equilibrium transformation during rapid cooling. Adjacent to this is a matrix tempering layer extending approximately 160 μm. Nanoindentation hardness profiling reveals that the peak radial hardness (≈1000 HV) occurs within the fine-grained martensitic zone approximately 40 μm from the surface. In contrast, the tempered layer exhibits reduced hardness (≈400 HV) compared to the original matrix (≈500 HV). This is primarily attributed to transient high-temperature over-tempering effects, which induces carbide coarsening and the loss of solid solution strengthening, alongside the softening of prior austenite grain boundaries. This study clarifies the micro-to-nanoscale evolution of the barrel microstructure, providing critical theoretical insights for understanding erosion mechanisms and improving lifetime predictions. Full article

With the growing security requirements of sensor nodes in Internet of Things (IoT) systems, conventional silicon-circuit-based physical unclonable functions (PUFs) still face limitations in circuit overhead, design complexity, and system integration. To address these challenges, this paper proposes a lightweight gas sensor PUF (GS-PUF) design based on a Ni-doped SnO₂ nanoscale gas sensor array. The proposed method exploits both the unavoidable process randomness introduced during sensor fabrication and the device-to-device electrical response variations induced by gas–material interactions as entropy sources, thereby enabling high-quality PUF response generation. At the device level, Ni-SnO₂ nanomaterials are prepared by electrostatic spray deposition (ESD), and an indirectly heated gas sensor array is constructed to enhance the sensitivity and stability of the sensing response. At the algorithmic level, a random resistance balancing algorithm based on multi-sensor combinational comparison is proposed. By randomly comparing the summed resistances of multiple sensor clusters, a 128-bit multi-bit PUF response is generated, while the uniformity and independence of the output bits are effectively improved. Experimental results demonstrate that the proposed GS-PUF exhibits excellent randomness, uniqueness, and reliability: the information entropy of the PUF responses is greater than 0.99, approaching the ideal value; the probabilities of output bits “1” and “0” are 0.4988 and 0.5012, respectively, indicating a well-balanced distribution; the inter-device uniqueness reaches 49.8%, close to the ideal value of 50%; all items in the NIST randomness test suite are passed, with all p-values exceeding 0.01 and the minimum p-value being 0.0368, confirming a high level of statistical randomness confidence. In addition, long-term measurements under fixed laboratory conditions show that the PUF response reliability remains above 96%. Compared with other sensor-based PUFs, the proposed method provides a lightweight sensing-security integration approach for IoT sensor nodes by reusing intrinsic gas-sensor response variations and avoiding an additional dedicated silicon PUF circuit. Full article

Oxyresveratrol (Oxy) exhibits a diverse range of biological activities. However, its practical application is constrained by low aqueous solubility and chemical instability. In this work, Oxy-loaded zein (Z) nanoparticles (NPs) stabilized by a sodium alginate (Alg) coating (Oxy-Z/Alg NPs) were fabricated using an antisolvent precipitation method. The absence of crystalline peaks in X-ray diffraction analysis suggested that Oxy was dispersed as an amorphous phase in NPs, while the Fourier transform infrared spectra identified strong interfacial associations between the components. The stabilization of the NPs is attributed to the site-specific binding of Oxy with Z’s SER-162 and GLN-174 residues. Molecular docking, molecular dynamics simulations, and differential scanning calorimetry profiles evidenced the formation of intermolecular hydrogen bonds. Dynamic light scattering analysis showed that the nanocomplexes had a nano-scale dimension (243 ± 6 nm) and a zeta potential of −36 mV. SEM micrographs revealed that the NPs possessed a spherical morphology. The NPs exhibited colloidal stability against prolonged heating (80 °C for 75 min), ionic strengths (up to 100 mM NaCl), and pH range (2.0–10.0). Encapsulation within the Alg coating enhanced Oxy’s antioxidant capacity over its unprotected form by shielding its core bioactivity from degradation. The Oxy-Z/Alg nano-system shows significant promise for the encapsulation of Oxy, providing a practical basis for its integration into nutraceuticals and functional food fields. Full article

To meet the requirements for passive heat dissipation and self-cleaning of aluminum alloy enclosures used in 5G base-station active antenna units (AAUs), a scalable surface modification strategy involving sandblasting, NaOH etching, and PFTEOS grafting was developed for 6061 aluminum alloy. Microscale rough structures were first constructed by sandblasting, and hierarchical micro/nano structures composed of microscale pits and nanoscale plate-like/coral-like features were subsequently formed through NaOH etching and boiling-water treatment. Finally, a low-surface-energy PFTEOS layer was grafted onto the structured surface to achieve superhydrophobicity. The effects of sandblasting pressure and etching time on surface morphology, chemical composition, wettability, and infrared emissivity were systematically investigated. The results show that sandblasting enhanced infrared emissivity by increasing surface roughness and promoting optical trapping, while NaOH etching further improved emissivity through the formation of hierarchical micro/nano structures and infrared-active AlOOH/Al₂O₃ phases. After PFTEOS grafting, the surface wettability changed from hydrophilic to superhydrophobic, while the high infrared emissivity was maintained. Compared with the untreated aluminum alloy, the modified surface exhibited a remarkable increase in water contact angle from 80.10° to 153.63° and infrared emissivity from 0.0102 to 0.8951. Moreover, the water contact angle remained above 150° after continuous water-jet impact, indicating good preliminary resistance to hydraulic shear. This work provides a feasible surface-engineering route for integrating high infrared emissivity and self-cleaning capability on aluminum alloy surfaces for outdoor thermal management applications. Full article

Deep geological disposal is widely recognized as the most reliable strategy for the long-term isolation of high-level radioactive waste (HLW). In granitic host rocks, fractures in the near-field represent the primary pathways for groundwater flow and potential radionuclide migration. The self-sealing capacity of carbonate-filled fractures, along with its long-term effectiveness, plays a critical role in maintaining the integrity of the multi-barrier system and ensuring repository safety. Near-field fractures undergo complex thermo–hydro–mechanical–chemical (THMC) coupled evolution driven by excavation-induced disturbances, decay heat, groundwater saturation, and ongoing water–rock interactions. Within the confined fracture spaces, carbonate minerals may persistently undergo precipitation–dissolution cycling and micro- to nanoscale structural reorganization, resulting in progressive reductions in fracture connectivity and hydraulic transmissivity. However, existing studies have largely focused on short-term sealing effects, with limited systematic understanding of the long-term safety functions. In this context, this study comprehensively investigates carbonate-induced self-sealing in granitic fractures within the near-field of a repository under realistic THMC-coupled conditions. We elucidate the micro- and nanoscale heterogeneous precipitation characteristics governed by non-classical nucleation pathways, reveal how dynamic precipitation–dissolution equilibria facilitate ongoing reductions in fracture transmissivity, and propose a multi-dimensional framework for long-term hydraulic, mechanical, and chemical performance assessment. Our findings demonstrate that carbonate self-sealing operates as a dynamic, reorganizing, and multi-mineral cooperative mechanism rather than a static, one-directional process. Its core safety function lies in the sustained suppression of fracture transmissivity. The mechanistic insights and evaluation framework proposed in this study provide a foundation for integrating natural carbonate self-sealing with engineered barrier system design, thereby improving fracture control, advancing long-term safety assessment, and optimizing the design of HLW deep geological repositories. Full article

The present research article deals with the thermal degradation study of epoxy resins filled with hybrid nanostructured forms of carbon under oxidative conditions. In particular, the formulated polymer composites (denoted as HYB_0.1%_CNTs:GNs and HYB_0.5%_CNTs:GNs, respectively) consist of two kinds of fillers, namely multi-walled carbon nanotubes (CNTs) and graphene nanosheets (GNs), mixed together with two different total mass amounts: 0.1 and 0.5%. In both kinds of nanocomposites, three different CNT:GN mixing ratios were considered (5:1, 1:1, and 1:5, respectively), thus providing a total of six hybrid samples. The thermal behavior of these samples was studied by simultaneous thermogravimetry and differential thermal analysis (TG/DTA) under flowing air, and two processes took place in distinct temperature ranges. In each step, about 50% of mass loss is detected with an exothermic effect in the corresponding DTA curve, with the second one accompanied by an intense heat release. The kinetic analysis of the two-stage oxidative thermal degradation was investigated using a model-free isoconversional approach. A non-Arrhenian behavior of the temperature function k(T) was assumed, and lifetime prediction was estimated at temperatures close to those of the possible applications. Isoconversional analysis shows nearly constant activation energies for all composites except HYB_0.1%_5:1 (from 142 to 96 kJ·mol⁻¹), while lifetime predictions indicate that thermal stability increases with graphene content at 0.1% loading (HYB_0.1%_1:5) and with CNT content at 0.5% loading (HYB_0.5%_5:1), with uncertainties below 7%. Finally, because of the π–π bond interactions between the CNTs and the GNs dispersed in the epoxy resin matrix, an effective and remarkable electrical performance was found and a correlation with both electrical and morphological properties was established. In this regard, Tunneling Atomic Force Microscopy (TUNA) proved to be particularly powerful in allowing the simultaneous mapping of topography and localized conductive networks with exceptional sensitivity to nanofiller dispersion, such as CNTs and GNs. DC conductivity increased by up to nine orders of magnitude at 0.1 wt% hybrid loading (up to 3.73 × 10⁻⁴ S/m vs. 1.06 × 10⁻¹³ S/m for CNT-only), with nanoscale TUNA currents (−1.9 to 4.5 pA) mirroring macroscopic trends, while at 0.5 wt% all hybrids reached 10⁻² S/m, indicating reduced synergy once a fully developed conductive network is established. Full article

The incorporation of phase change materials in concrete is a practical strategy that holds great promise for enhancing the energy efficiency of buildings and reducing CO₂ emissions. However, the direct contact between phase change materials and cement interferes with the cement hydration reaction, leading to a significant reduction in the mechanical strength of cementitious composites. To encapsulate polyethylene glycol and prevent leakage, this study developed a shape-stabilized phase change aggregate via the cold-bonding method and the vacuum impregnation method. The nanoscale pore structure of the aggregate was regulated by adjusting the biochar content to enhance the phase-change material loading capacity. The phase change aggregate was characterized by indicators including crushing strength and water absorption. Meanwhile, its microstructure, the correlations between nano-sized hydration products, chemical compatibility, and phase change properties were analyzed. The fabricated phase change aggregate has a crushing strength of over 5 MPa, latent heat of 42.84 J/g, and phase change temperature of 29.17 °C while also exhibiting good mechanical properties and thermal energy storage performance. The compressive strength of phase change concrete can meet the strength requirements for structural building material. Moreover, phase change aggregate contributed to reduced CO₂ emissions during service, with favorable economic and low-carbon benefits over its service life, demonstrating good performance in both economic efficiency and CO₂ emission reduction. Full article

Massive pelagic Sargassum influxes along Caribbean coasts have created an urgent need for valorization routes for this biomass. Here, sodium alginate was extracted from Sargassum fluitans collected at Chuburná Beach, Yucatán, Mexico, using a multistep extraction involving 0.2% formaldehyde pretreatment at 4 °C and brief heating at 65–70 °C, and subsequently used to prepare calcium-crosslinked alginate nanoparticles by ionotropic gelation. To our knowledge, this is the first direct synthesis of alginate nanoparticles from non-commercial alginate extracted from pelagic S. fluitans. An extraction yield of 18.7 ± 0.05% (mean ± SD, n = 3) was obtained, and UV–Vis, FTIR, and NMR analyses confirmed the characteristic structural features of alginate. ¹H NMR revealed an M-rich composition (F_M = 0.61, F_G = 0.39; M/G = 1.54) with short guluronate blocks (N_G>1 = 2.42), whereas ¹³C NMR corroborated the presence of both β-D-mannuronic and α-L-guluronic acid residues. SEM images showed predominantly spherical-to-subspherical nanoparticles with representative dry diameters of 233–269 nm, whereas DLS measurements at 0, 24, and 72 h revealed a dominant volume-based nanoscale population with main peaks at 12.75–15.31 nm and PDI values of 0.229–0.291, indicating reasonable short-term colloidal stability at room temperature. These results demonstrate that pelagic S. fluitans can serve as a viable feedstock for the production of structurally preserved alginate and calcium-crosslinked alginate nanoparticles. The study supports converting recurrent Sargassum biomass into higher-value polysaccharide-based materials and provides a basis for future application-specific evaluation of these nanomaterials. Full article

Sol–gel processing provides an unusually controllable route to nanoporous solids, making silica aerogels the leading reference systems for extremely low thermal conductivity due to their high porosity, nanoscale pore sizes, and tunable solid frameworks. Under near-ambient conditions, thermal transport is multi-scale and multiphase, arising primarily from coupled solid conduction through the skeletal network and gas conduction within the pore space. Accordingly, aerogel design has emphasized suppressing solid-phase transport by reducing network connectivity, increasing tortuosity, and enhancing boundary scattering, while also limiting gaseous conduction through the control of pore size and gas pressure. This critical review provides an integrated overview of these mechanisms and the theory-to-experiment toolbox used to quantify the separate and combined contributions of the solid and gas phases to the effective thermal conductivity. We link key structural and environmental parameters (porosity, pore size distribution, density, backbone morphology, and pressure) to dominant transport regimes and the assumptions embedded in common models. Classical approaches, including effective-medium and percolation-based models, are assessed alongside phonon-scaling descriptions that incorporate characteristic length scales. Particular attention is given to the Knudsen effect and pressure-sensitive gas-conduction models, which are central to interpreting performance at atmospheric conditions and under vacuum or low-pressure operation. This review highlights inconsistencies across datasets and modeling practices, identifies persistent knowledge gaps, and outlines practical directions toward processable structure–property guidelines for manufacturing aerogels with targeted thermal performance, with regard to conduction-dominated heat transport mechanisms. Full article

The precipitation of nanoscale HfO₂ plays a critical role in the high-temperature creep properties of Fe-Cr-Al electrical heating alloys. However, the atomic-scale initial nucleation and growth mechanisms remain unclear, hindering the precise design of precipitates based on Hf microalloying. In this study, classical molecular dynamics simulations implemented in LAMMPS were employed to investigate the formation and evolution of Hf-O clusters at 1773 K, 1873 K, and 2000 K. The Fe-Cr-Al-Hf-O system was described by hybrid potential functions, whose reliability was verified by lattice-parameter calculations in good agreement with literature values. The simulation results demonstrate that Hf atoms and O atoms attract each other, forming stable Hf-O clusters. At higher temperatures, the diffusion capabilities of Hf and O atoms are enhanced, the number of Hf-O bonds grows, and the size of the largest cluster expands, indicating that elevated temperatures promote cluster growth. The calculated diffusion activation energy of Hf and O atoms indicates that increasing temperature promotes O atom diffusion more significantly. Analysis of the cluster radius of pair gyration and average atomic energy reveals that Hf-O clusters formed at 1873 K exhibit more compact and stable structural characteristics. Radial distribution function analysis further revealed that the atomic arrangement of neighboring atoms in Hf-O clusters closely resembles the relaxed HfO₂ crystal structure at the same temperature, indicating that Hf-O clusters serve as critical nucleation cores promoting the precipitation of HfO₂ crystals. This study elucidates the dynamic formation mechanism and structural evolution of Hf-O clusters in Fe-Cr-Al alloys at the atomic scale, providing valuable guidance for the optimized design of precise control over HfO₂ nanoprecipitates. Full article

Aluminum–silicon (Al-Si) alloys are widely used in aerospace, automotive manufacturing, power electronics, marine engineering and other fields due to their excellent physical properties. However, their corrosion resistance is insufficient in harsh service environments. In this study, a variety of characterization methods were adopted, including scanning electron microscopy (SEM), X-ray diffraction (XRD), electrochemical measurements (electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization), immersion corrosion tests, and scanning vibrating electrode technique (SVET). The results show that the appropriate heat treatment regime can significantly enhance the corrosion resistance of the alloy, while improper aging parameters will aggravate the corrosion tendency. The optimal heat treatment regime is solution treatment at 500 °C for 4 h followed by aging at 200 °C for 48 h. Under this condition, the corrosion current density (i_corr) is as low as 79.30 μA/cm², and the low-frequency impedance modulus and phase angle in EIS tests are optimal. The as-extruded alloy exhibits severe localized corrosion, while the heat-treated alloy transforms into mild and uniform corrosion. The underlying mechanism is that heat treatment induces the formation of uniformly distributed nanoscale Mg₂Si and Al₃(Sc,Zr) precipitates, which synergistically improve the corrosion resistance of the alloy by weakening micro-galvanic coupling and facilitating the formation of a stable passive film. Full article

Improving the quality of welded joints, as well as the advancement of equipment and materials, inevitably requires deep theoretical knowledge of the physical phenomena occurring in the arc column and in the cathode and anode regions. Achievements in the field of controlling metal transfer at the micro- and nanoscale through the regulation of current and voltage in welding power sources have encountered the problem of the formation of cathode and anode spots, which affect the stability of welding arcs and the quality of the weld. Under short current pulses and pauses, the stability of the arc discharge depends on the ability to form a cathode spot, melt the wire metal, and transfer it through the arc column. In this article, based on the generalization of known experimental facts and studies performed using a high-speed camera, it is shown that the current-carrying channel of the electric arc has a discrete structure consisting of a multitude of thin channels through which the main discharge current flows. The cathode spot of the arc discharge represents a highly heated and brightly luminous region on the cathode surface. Electron emission sustaining the discharge and the removal of cathode material occur from this region. A new method is proposed for investigating the reverse side of the cathode spot, which makes it possible to identify a structure consisting of individual cells or fragments of the cathode spot. For the first time, anode spots recorded with a high-speed camera are presented. An analysis of the spot structure is carried out. The parameters influencing the mobility of cathode and anode spots are determined. Based on the obtained experimental facts, a hypothesis is proposed regarding the non-uniform structure of cathode and anode spots in the arc discharge. Full article

The study investigates the microstructure evolution in the stir zone produced by the friction stir processing (FSP) of a heat-treated microalloyed Al-Mn-Cu alloy in the area subjected to the highest temperature, strain, and strain rate. The samples were studied using electron microscopy and atom probe tomography (APT) to obtain structural and chemical information from the macro to the nano scale. FSP refines the dendritic Al-rich solid solution grains through dynamic recrystallisation in the range of a few micrometres. The primary intermetallic phases were dispersed to the particles in the 0.5–3 µm range and transformed mainly into a more stable τ₁-Al₂₉Mn₆Cu₄ phase. The fraction of dispersed particles after FSP increased due to the precipitation from the solid solution during cooling. The nanoscale quasicrystalline precipitates in the matrix, formed upon heat treatment, dissolved entirely during FSP, while the strong coarsening of the L1₂ precipitates occurred due to high temperatures in the stir zone. After FSP, the hardness of the stir zone was nearly identical for specimens in the as-cast and heat-treated conditions. Full article

In this study, the Nd:YAG laser process was employed with preselected welding parameters and varying initial welding temperatures (including room temperature, 10 °C, and 0 °C) for spot welding of (Zr₅₃Al₁₇Co₂₉)Nb₁ bulk metallic glass. Following welding, the microstructure—including the parent material, heat-affected zone (HAZ), and weld fusion zone (WFZ)—as well as the microhardness, thermal properties, and corrosion resistance of the welds, were systematically investigated. Owing to the low glass-forming ability of the alloy, a small amount of Zr₆CoAl₂ phase was observed within the amorphous matrix at the center of the bulk metallic glass cast plate. After the laser welding, sub-micron or nanoscale Zr(Al_xCo_1−x)₂ phases have formed in the HAZ of all welded samples, which significantly influenced the microhardness, thermal properties, and corrosion resistance in this region. As the initial welding temperature decreased, both the volume fraction and the density of the Zr(Al_xCo_1−x)₂ phase were reduced. Notably, for the weld performed at the lowest initial temperature of 0 °C, small crystalline phases were detected only at approximately 70 μm below the surface of the HAZ. To clarify the effect of IWTs on corrosion resistance, welded samples were immersed in 6 M HCl at 35 °C for 72–120 h. Surface morphologies after corrosion were examined by SEM in the PM, HAZ, and WFZ. No evident pitting was detected after 72 h of immersion. After 120 h, pitting corrosion was observed on the HAZ surfaces of welds subjected to RT and 10 °C IWTs, whereas no obvious pitting was found at an IWT of 0 °C. The pit size and density in the HAZ increased with increasing IWT. In contrast, no pitting was observed in the WFZ under any IWT condition. Full article