Search Results (413)

This study presents the fabrication of a Cr₃C₂-25NiCr/NiCr coating on Co₃W₃ steel utilizing high-velocity oxygen fuel (HVOF) spraying. The effects of the vacuum heat treatment process on the microstructures, mechanical properties, and wear mechanisms of the coating were systematically analyzed. The results indicated that the microstructure became denser following heat treatment. During the spraying procedure, decarburization resulted in transformation of the metastable phase structure into a stable one. In comparison to the sprayed coating, there was a 93.8% reduction in porosity. The precipitation of nano-secondary carbides shifted the mechanism of solid-solution strengthening to precipitation strengthening, resulting in a 29.1% increase in microhardness. Meanwhile, the thermal softening effect led to a 114.3% increase in fracture toughness. Wear experiments demonstrated that the friction-induced amorphous structure effectively mitigated stress concentration and inhibited crack initiation. The polycrystalline interface transition region between the nano-secondary carbides and the matrix facilitated the shedding of nano-secondary carbides, forming abrasive particles that generated a rolling effect, which significantly reduced the coefficient of friction. The semi-coherent interface between secondary carbides and NiCr decreased the interfacial energy and enhanced the bonding strength, effectively preventing the shedding of carbides during the wear process. Consequently, a dense microstructure, the type of interface, and high hardness and toughness were critical factors in enhancing its wear resistance. Full article

High-entropy alloys, due to their excellent mechanical properties and service stability, hold broad application prospects under extreme working conditions. However, their high strength and complex multi-component characteristics also pose significant processing challenges. This study investigates the nanoscale material removal mechanisms of single-crystal and polycrystalline FeCrNiCoCu high-entropy alloys (HEAs) under abrasive scratching using molecular dynamics simulations. In single-crystal HEAs, dislocations preferentially nucleate along <110> directions, with significant lattice self-healing and elastic recovery. Crystallographic orientation strongly affects dislocation density, phase transformation, and residual plastic deformation, with the (100) plane exhibiting the most favorable machining performance. For polycrystalline HEAs, subsurface deformation is dominated by dislocation migration, grain boundary rupture, and dislocation entanglement, leading to higher dislocation density, larger residual plastic deformation, and increased phase transformation compared with single crystals. Elemental composition significantly modulates these behaviors: higher Cu and Cr contents suppress dislocation motion and reduce subsurface defects, improving surface quality, whereas higher Fe content slightly increases plastic deformation but mitigates phase transformation and amorphization. Grain size effects are also pronounced, with smaller grains showing higher dislocation density and residual deformation. These findings provide atomic-scale insights into the combined effects of crystallography, grain size, and elemental composition on the machining response of FeCrNiCoCu HEAs, offering guidance for precision machining and alloy design. Full article

Metallic glasses can be transformed into nanocrystalline–amorphous alloys via controlled crystallisation with fast nucleation and slow grain growth. This can be achieved either through appropriate chemical composition of amorphous precursors or by applying ultra-rapid annealing (URA). Typically, heating between preheated copper blocks is used to ensure the URA conditions. In this work, ribbons were heated by an electric current flowing along their length, and the temperature was monitored using pyrometers. The investigated alloys were Fe_86-xNi_xB₁₄ (at. %), where x = 4, 6 or 10. Properly adjusted isothermal annealing at 380–410 °C for 1–20 s induced crystallisation, with the nanocrystalline bcc-Fe(Ni) phase occupying 0–55% of the volume. With increasing annealing time, the coercive field increased from 9 A/m in the amorphous state to 25 A/m and 17 A/m for x = 4 and x = 10, respectively. Transmission electron microscopy confirmed that samples annealed at higher temperatures for shorter times exhibited smaller grain sizes compared to those annealed at lower temperatures for longer times, which resulted in improved magnetic softness. An increase in nickel content reduced coercivity, improved ductility, and offered a wider window for the choice of annealing temperature. Full article

The solidification behavior and microstructural evolution of Al–Ge microparticles were investigated on Si, SiO₂, Al₂O₃, amorphous carbon, and ZrO₂ substrates. Micrometer-sized particles with a hypereutectic composition were produced by melting and resolidifying 40 nm thick Al–Ge films. Their size, wetting angle, crystal structure, and internal morphology were characterized by SEM and TEM techniques. We demonstrate that Al–Ge particles exhibited strongly substrate-dependent wetting, with contact angles ranging from 46° on SiO₂ to 123° on ZrO₂. Nevertheless, all particles developed a similar internal microstructure consisting of a fully interconnected, irregular Ge network within an Al matrix, indicating complete phase separation during solidification. The eutectic network was quantified by its ligament thickness. No correlation was found between ligament thickness and substrate type or contact angle, indicating that the coral-like internal Ge network forms independently of particle wetting. Instead, the ligament thickness increased with particle size and during post-solidification annealing. The network gradually coarsened up to 310 °C, followed by its complete breakdown and transformation into an equilibrium Janus morphology at 370 °C. These findings provide new insight into the solidification of irregular eutectic systems and suggest a route for tailoring three-dimensional internal microstructures in eutectic microparticles. Full article

Pulsed laser-induced phase change in silicon underpins applications from photonic device trimming to stealth dicing, yet predictive models that capture the non-equilibrium kinetics governing the competition between epitaxial recrystallization and amorphization remain limited. In this work, we developed a two-dimensional axisymmetric numerical model at the continuum level for picosecond laser-induced melting, resolidification, and amorphization of crystalline silicon at 532 nm laser wavelength, coupling transient heat conduction with Wilson–Frenkel interface kinetics and Lagrangian marker-based interface tracking. The model predicts a bounded amorphization window defined by lower and upper fluence thresholds, within which the central amorphous thickness exhibits a bell-shaped fluence dependence. Under a Gaussian beam, this window governs a morphological transition from a central amorphous spot to an amorphous ring. The predicted amorphization threshold of ≈0.22 J/cm² agrees with published experimental data for 20 ps, 532 nm irradiation. Parametric studies reveal that reducing the spot diameter or substrate temperature shifts or eliminates the upper threshold, transforming the bounded window into a monotonically increasing function, while increasing the pulse duration narrows the window symmetrically until collapse. These results provide quantitative guidelines for selecting irradiation parameters to control phase change in silicon photonic and laser processing applications. Full article

With the rapid expansion of wind energy infrastructure, there is an increasing accumulation of wind turbine blade waste (WTBW), which is mainly composed of glass fiber-reinforced thermosetting composites. Due to the irreversible nature of polymer crosslinking, conventional recycling methods remain limited. In this study, plasma vitrification was employed to convert WTBW into a reactive calcium-aluminum-silicate slag suitable for use in geopolymer materials. Plasma treatment at a temperature of approximately 2750 K resulted in the formation of predominantly amorphous vitrified slag (VS). Structural characterization using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) revealed the spatial heterogeneity of the VS. This heterogeneity was influenced by thermal gradients and varied between samples collected from different slag discharge zones, both vertically and horizontally from the reactor. All VS samples contained between 30 and 89% amorphous phase and 10–55% anorthite, with the proportions varying by sampling location. Chemical stability tests showed the dissolution of calcium and aluminum in acidic media, resulting in a silica-enriched residual structure in which the Ca and Al content decreased to less than 0.5 at.% after 100 days. In contrast, exposure to alkaline media caused only minimal surface reorganization—the addition of 5 wt.% VS to acid-based geopolymers made with two metakaolin precursors resulted in a 35% decrease in the mechanical strength of pure metakaolin-based systems. In contrast, when metakaolin containing illite impurities was used, strength values were similar to those of the reference geopolymer. The results quantitatively demonstrate that plasma-derived slag exhibits composition-dependent reactivity, directly linked to its amorphous content and dissolution behavior. 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

Blueberry anthocyanins (BAs) exhibit strong antioxidant and lipid-regulating activities; however, their chemical instability and low oral bioavailability limit their practical application. In this study, two plant-based bilayer nanocarriers were developed using soybean lecithin as the lipid core and gum arabic (GA) or carrageenan (CGN) as the shell polysaccharide. The optimized systems achieved encapsulation efficiencies of 79.7% and 81.9%, respectively. Structural analyses showed that anthocyanins were stably incorporated into the carriers through multiple non-covalent interactions and transformed from a crystalline to an amorphous state. The two shell polysaccharides exhibited distinct conformation-dependent protective behaviors: GA provided better thermal protection, whereas CGN showed superior resistance to light, metal ions, ascorbic acid, and simulated intestinal digestion. After INFOGEST digestion, anthocyanin retention in the intestinal phase was 47% and 51% for the GA- and CGN-coated systems, respectively, and antioxidant activity was better preserved than in the free anthocyanin group. In an oleic-acid-induced HepG2 lipid accumulation model, the CGN carrier showed good biocompatibility and significantly enhanced the lipid-lowering effect of anthocyanins, with the most pronounced reduction in intracellular triglycerides. These results indicate that the CGN carrier has considerable potential for maintaining anthocyanin stability, modulating digestive behavior, and enhancing biological efficacy, and provide a reference for the design of plant-based delivery systems for bioactive ingredients. Full article

This research investigates the formation of an amorphous phase in a non-equiatomic aluminum-based alloy, Al₈₂Fe₁₂Cu₂Nb₂Co₂, synthesized via mechanical alloying. By utilizing minor additions of Nb, Co, and Cu, structural stability and “chemical complexity” effects are achieved in a matrix dominated by a single element (82% Al). Thermodynamic analysis reveals that a moderately negative mixing enthalpy (ΔH_mix = −6.89 kJ/mol) and elevated configurational entropy (ΔS_mix = 5.420 J/mol·K) are the primary thermodynamic drivers of amorphization, supplemented by a transitional-regime atomic size mismatch (δ = 4.82%). The evolution of the structure, morphology, and magnetic properties of mechanically alloyed amorphous Al₈₂Fe₁₂Cu₂Nb₂Co₂ as a function of milling time was systematically investigated using X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and a vibrating sample magnetometer. Full article

To achieve carbon neutrality, increasing efforts have been devoted to the clean utilization of fossil fuels. This study investigates the effect of reaction temperature on methane catalytic cracking over a biochar-supported iron catalyst. Corn stalks were heated to make biochar which was used as the carrier. To obtain biochar with a high specific surface area and well-developed porous structure, chemical activation was employed. The catalyst was made by adding iron to the biochar using the soaking method. This iron biochar catalyst is used to study its effectiveness in catalyzing methane cracking. The biochar-supported Fe catalyst was studied for its effectiveness in catalyzing methane cracking at different temperatures (800–950 °C). The results indicate that a higher temperature favors methane conversion in terms of reaction efficiency and cumulative conversion levels. At 950 °C, the catalyst exhibits the best performance, with a peak conversion rate of up to 85%, and it can still maintain a stable conversion rate of around 55% after prolonged reaction, yielding the total conversion of 57.6%. Raising the temperature can significantly promote the transformation of solid-phase products from highly blocking amorphous carbon to more ordered graphitized carbon. In addition, the reacted catalyst shows a remarkably reduced specific surface area, the disappearance of micropores, and a considerable increase in average pore size. Carbon nanotubes with various diameters and morphologies were formed on the catalyst surface. Full article

This article describes a study on the synthesis and annealing processes of thin-film coatings of vanadium oxide on flat, parallel substrates made of quartz glass, sapphire, and silicon, as well as optical fibers using an organometallic precursor, triisopropoxy vanadium (V) oxide. For the first time, optical constants of nanomaterials were estimated in real time during synthesis and subsequent annealed using the lossy-mode resonance effect. The coatings produced in an inert atmosphere after deposition were amorphous, comprising a mixture of VO₂, V₂O₅, V₆O₁₃, and V₃O₅. This method allowed for accurate determination of the threshold temperature for the transformation of oxide mixtures into a monocomponent phase. Optimal conditions for synthesis and annealing were determined for the production of vanadium dioxide (VO₂) and pentoxide (V₂O₅). Morphological changes in coated surfaces were observed as a result of heat treatment. The composition and properties of these samples were studied using optical, terahertz and Raman spectroscopy, as well as temperature-dependent analysis of electrical resistance. The morphology of the coating surface was determined using a scanning electron microscope and an atomic force microscope. The reduction of VO_x to VO₂ was studied in an atmosphere of hydrogen and argon during annealing after deposition, with its effectiveness being compared. It was shown for the first time that the reduction of higher vanadium oxides is due to the presence of elemental carbon in the volume of the material formed from a metalorganic precursor during growth of vanadium oxide. Coatings obtained by annealing in hydrogen had a smaller hysteresis loop width (~5 °C) during phase transition compared to coatings obtained by argon annealing (~9 °C). Both types of coatings demonstrated a 50–60% increase in transmission at 1 THz frequency and in the IR region, accompanied by a 10³–10⁴-fold change in electrical resistance. Full article

Lignin is an abundant aromatic biopolymer, but its conversion into high-performance fibers remains challenging due to intrinsically poor spinnability, structural heterogeneity, and inefficient stress transfer in lignin-rich systems. In this study, a processing and structure strategy is demonstrated to overcome these limitations by transforming industrial black-liquor kraft lignin into a spinnable and load-bearing fiber component. Kraft lignin recovered from black-liquor waste was extracted and subsequently purified using a hot-water treatment to remove inorganic impurities and thermally unstable fractions, increasing lignin purity to 95.9% through extensive deionized water purification using a water-to-lignin ratio of 300:1. The purified lignin was then blended with poly(vinyl alcohol) (PVA), wet-spun into continuous filaments, and subjected to post-spinning hot drawing to induce molecular orientation. This sequential extraction, purification, blending, spinning, and drawing approach enables stable wet spinning and the continuous formation of lignin-rich lignin/PVA filaments without filament breakage, directly addressing the primary processing bottleneck of lignin-based fibers. Molecular-level miscibility between lignin and PVA is confirmed by the presence of a single glass transition temperature at 88.3 °C, indicating the formation of a homogeneous amorphous phase. SEM observations reveal composition-dependent surface roughness and non-circular cross-sectional morphologies arising from differential coagulation and shrinkage, demonstrating that lignin actively participates in the load-bearing fiber network rather than acting as a passive filler. As a result of purification-enabled spinnability, true blend miscibility, and post-spinning hot drawing, fibers with a lignin-to-PVA composition of 40:60 achieve a maximum tensile strength of 2.8 GPa, approaching the performance range of commercial high-strength polymer fibers. This work establishes a clear relationship between material structure, processing strategy, and resulting properties, highlighting the potential of industrial lignin waste as a sustainable precursor for advanced fiber applications. Full article

Calcium–silicate–hydrate (C-S-H), the primary binding phase governing cement paste cohesion, undergoes progressive physicochemical transformation upon carbonation—a process that critically dictates concrete durability in atmospheric environments. When CO₂ penetrates the porous cement matrix, it triggers a cascade of degradation mechanisms: calcium leaching decalcifies the C-S-H structure, inducing polymerization of silicate chains from dimeric to longer-chain configurations, while concurrent precipitation of calcium carbonate and amorphous silica gel fundamentally reconstitutes the nanoscale architecture. These nanoscale alterations propagate to macroscopic property evolution, manifesting as initial strength and stiffness gains due to pore-filling carbonation products followed by eventual deterioration as the cohesive binding network deteriorates. This review synthesizes current understanding of carbonation-induced structural evolution, examining the coupled influences of environmental parameters—CO₂ concentration, relative humidity, and temperature—alongside C-S-H intrinsic chemistry (Ca/Si ratio, aluminum substitution, and alkali content) on reaction kinetics and material performance. However, significant knowledge gaps persist: predictive models for in-service carbonation rates remain elusive due to the disconnect between idealized laboratory conditions and the heterogeneous, cracked reality of field concrete; the causal linkage between nanoscale C-S-H alteration and macroscale cracking patterns along with physical performance is poorly resolved, and most mechanistic studies rely on synthetic C-S-H, neglecting the compositional complexity of real Portland cement systems. We further propose emerging protection strategies, including surface barrier coatings and low-carbon alternative binders (geopolymers, calcium sulfoaluminate cements, carbon-negative materials such as recycled cement), which demonstrate enhanced carbonation resistance. Future research priorities include developing effective coating barriers for carbonation protection, developing operando characterization techniques for real-time reaction monitoring, deploying machine learning algorithms to bridge atomistic simulations with structural-scale predictions, and establishing long-term field performance databases to validate laboratory-derived degradation models. Full article

TaC/amorphous-carbon (TaC/a-C) composite coatings with varied a-C contents were deposited on graphite by dual-target magnetron sputtering to mitigate the thermal-expansion mismatch that commonly triggers cracking and spallation in TaC coatings on carbon substrates during rapid thermal cycling. However, existing TaC–C (often termed “free carbon”) approaches rarely identify the carbon’s structural state and spatial distribution explicitly, and a clear correlation between carbon fraction, thermal-shock-driven microstructural evolution, and cyclic damage remains insufficiently established. Increasing the a-C fraction progressively refines the TaC grain structure and introduces an a-C phase along grain boundaries, thereby lowering the effective coefficient of thermal expansion (CTE) and improving compatibility with the graphite substrate. Under laser thermal cycling, coatings with higher a-C contents exhibit markedly enhanced resistance to cracking and spallation. After 15 cycles, the high-a-C (~28.99 at.%) coating remains free of through-thickness cracks, maintains its thickness, and retains a single-phase TaC structure without detectable Ta₂C, whereas the low-a-C coating shows severe thinning, through-cracks, and partial TaC → Ta₂C transformation. Microstructural observations indicate that the a-C phase forms a compliant, stress-relaxing boundary network and promotes a porous, mechanically interlocked TaC architecture, synergistically redistributing thermal stresses and deflecting crack propagation. Full article

This study investigates the gel characteristics of alkali-activated materials (AAMs) synthesized using wood ash (WA), and metakaolin (MK) as solid precursors. The research explores the influence of precursor type and sodium hydroxide (NaOH) concentrations in the alkali activator solution on the resulting physicochemical, microstructural, mechanical, and radiological properties of gels. The alkaline activators were prepared by mixing sodium hydroxide solutions (6 M and 12 M) with a sodium silicate (water glass) solution at a volume ratio of 1.5. The physicochemical characteristics of raw materials and AAMs were thoroughly analyzed using X-ray fluorescence (XRF), Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) with EDS elemental mapping. FTIR analysis confirmed the formation of an amorphous gels geopolymer network. XRD revealed the presence of characteristic crystalline phases (quartz, calcite) within an amorphous matrix. Mechanical properties, such as compressive strength, depended on precursor type and alkali molarity: metakaolin (12 M) reached ~14 MPa, while wood ash showed ~4 MPa (6 M) and ~0.5 MPa (12 M) due to high CaO, low Si and Al, and unfavorable SiO₂/Al₂O₃ (5.71) and Na₂O/Al₂O₃ (3.19) ratios. Furthermore, this research estimates radiological doses by quantifying radionuclide content via gamma-spectrometry. Alkali activation significantly reduced radiological hazard parameters, with radium equivalent activity (Ra_eq) decreasing to 238.0 Bq/kg and the external hazard index (H_ex) to 0.643 for A₁₂MK, while the annual effective dose rate for A₁₂WA was only 0.265 nSv/y-all values remaining well below the recommended safety limit of 370 Bq/kg (≤1 mSv/y). The decrease in activity concentration index (I_γ), Ra_eq, and H_ex with increasing NaOH concentration indicates effective radionuclide immobilization within the geopolymer matrix, confirming the suitability of these alkali-activated materials for safe use in construction from a radiation protection perspective. Full article