Search Results (9,921)

Chloride-induced deterioration is a major threat to the durability of marine concrete structures, especially in tidal and submerged zones. This study simulated these environments by immersing C45 concrete specimens in NaCl solutions (5%, 10%, 15%) under both constant immersion and wet–dry cycles. Compressive strength tests, low-field NMR for pore structure, chloride ion profiling, and SEM-EDS analyses were conducted. A modified chloride diffusion model was developed based on Fick’s second law, incorporating time- and concentration-dependent parameters. The results showed that higher NaCl concentrations and tidal zone exposure significantly accelerated concrete degradation. In the tidal zone, wet–dry cycles led to larger macropore formation, higher chloride penetration, and more severe microstructural damage compared to the submerged zone. Compressive strength initially increased and then declined in high-salinity environments, with strength losses reaching up to 25% under 15% NaCl after 120 days. NMR data confirmed the transformation of micropores and mesopores into macropores, especially in the tidal zone. SEM-EDS analysis revealed decalcification, gypsum formation, and Friedel’s salt accumulation on eroded surfaces. It was determined that chloride ion diffusion behavior in concrete is significantly influenced by the chloride content and diffusion concentration, as well as the exposure zone. The developed model indicates that depth increased over time and with concentration. The proposed diffusion model achieved high fitting accuracy (R² > 0.97), effectively capturing the effects of erosion age and salt; this makes it a reliable tool for predicting chloride ion ingress in marine concrete, and for supporting service life evaluation and durability design. Full article

Red mud, a major solid waste from the alumina industry, suffers from an extremely low utilization rate due to its high alkalinity, complex chemistry, and particularly low cementitious activity, which drives the need for novel activation strategies. This study presents a new method for red mud activation through electrochemical treatment, which simultaneously enables iron recovery as a valuable by-product. The electrochemical activation was systematically investigated by performing experiments in alkaline, neutral, and acidic electrolytes. The alkaline system showed a pronounced enhancing effect on the electrochemical process. Under alkaline conditions, the average Faradaic efficiency exceeded 80%. The electrochemical treatment modified the microstructure of red mud particles and transformed iron oxides into magnetic species, which could be effectively separated via magnetic separation. More importantly, this activation process significantly enhanced the cementitious activity of the treated red mud by removing iron oxide that encapsulates reactive aluminosilicate phases and increasing surface reactivity. When used as a supplementary cementitious material with ordinary Portland cement and gypsum, the electrochemically activated red mud demonstrated remarkably improved mechanical properties, with 28-day compressive strength reaching up to 69 MPa. Characterization analysis revealed that the electrochemical activation promoted the formation of key hydration products, including C-S-H gel (formed through both OPC hydration and pozzolanic reactions between activated red mud and portlandite), ettringite, and portlandite. This work provides a green and low-carbon pathway for the stepwise utilization of red mud through activation and resource recovery. Full article

This study takes 18CrNiMo7-6 wind power gear steel as the object. Following the first holding stage of isothermal normalizing, the 18CrNiMo7-6 wind power gear blanks were cooled to the isothermal temperature via air cooling (AC) and forced-air cooling (FA), respectively. The influence of cooling rate on the roughness of the mechanically polished surface of wind power gear blanks was comprehensively studied by means of white light interference, EBSD, TEM, DSC and other technical characterization methods. The results show that a difference in cooling rate leads to a variation in the morphology and distribution of Cr-rich carbides (mainly Cr₇C₃), which affects the roughness of the mechanically polished surface. During air cooling (slow cooling), atoms diffuse fully. Owing to the relatively low cooling rate in the inner ring of the blank, C and Cr segregate, and abundant Cr-rich carbides precipitated and accumulated at grain boundaries, forming coarse blocky structures. This resulted in uneven mechanically polished surfaces and bright spot defects. The average roughness of the inner and outer ring is 2.648 nm and 2.096 nm, respectively. Forced-air cooling (fast cooling) eliminates surface quality defects by inhibiting long-range atomic diffusion. Meanwhile, radial elemental segregation in the original cast blanks was inherited in subsequent processes, which affected the uniformity of carbide precipitation during cooling. In addition, the differences in cooling rates will also cause variations in the precipitation temperatures of carbides in steel, which in turn further affects the homogenization distribution of carbides in steel. This research provides a theoretical basis and an optimization method for the microstructural regulation and surface quality enhancement of wind power gear steel. Full article

Marine concrete is often exposed to multiple aggressive ions, so mechanical deterioration cannot be reliably interpreted using single-ion durability concepts. This study investigates ocean-oriented concretes incorporating high contents of mineral admixtures under coupled sulfate/chloride/carbonate/magnesium actions and develops a pore-structure-based D–P dual-parameter framework linking microstructural descriptors to macroscopic peak stress and peak strain. Three binder systems were designed: ordinary Portland cement concrete (OPC), cement–silica fume concrete (CSC, 20% silica fume), and cement–silica fume–fly ash concrete (CSFC, 20% silica fume + 50% fly ash). Specimens were immersed for 12 and 24 months in four representative binary-salt solutions. Porosity evolution and pore-size-class distributions were quantified by low-field NMR, while pore complexity was characterized using multi-scale fractal dimensions. The results show that mineral admixtures generally refine the pore system and improve the integrity of fine pores; CSFC exhibits the most robust microstructural stability across the tested environments, whereas CSC shows a pronounced degradation of fine-pore structure under CE4. A second-order response surface model built on Z-score normalized fractal dimension (D) and porosity (P) achieves reliable predictability for peak strain (R² = 0.85) and peak stress (R² = 0.79). Global Sobol sensitivity analysis reveals distinct controlling mechanisms: peak strain is predominantly governed by porosity (S_P = 85.9%), whereas peak stress is controlled by the combined effects of porosity, pore complexity, and their interaction (S_P = 42.4%, S_D = 19.8%, S_{D × P} = 37.8%). Local sensitivity mapping further identifies high-sensitivity regimes at extreme pore states, providing mechanistic guidance for mixture optimization. Overall, the proposed D–P framework quantitatively bridges pore volume/geometry evolution and mechanical degradation, offering a practical predictive tool for durability-oriented design of marine concretes under multi-ionic attack. Full article

The Polyether ether ketone (PEEK) suffers from insufficient interlayer molecular chain diffusion and weak interfacial fusion during Fused Filament Fabrication (FFF) due to its high melt viscosity and rapid cooling characteristics, restricting the mechanical properties and engineering applications of printed parts. To improve the interlayer bonding quality of FFF-printed PEEK, an in situ preheating technology integrated into the print nozzle was proposed and implemented. Through a high-temperature controllable preheating system that moves synchronously with the nozzle, local precise heating is performed on the surface of the deposited layer to actively regulate the thermal history of the interlayer interface. Systematic studies on the effect of preheating temperature were conducted. The results show that the influence of preheating temperature on part performance follows a trend of first increasing and then decreasing. When the preheating temperature is 280 °C, the comprehensive performance of the specimens is optimal: the tensile strength reaches 69.47 MPa, which is 21.3% higher than that of the non-preheated reference group; the elongation at break is 71.07%; and the porosity decreases to 8.36%. Microstructural analysis reveals that moderate preheating facilitates molecular chain diffusion and interfacial fusion, whereas excessive heating induces thermal oxidative degradation of PEEK, resulting in deteriorated mechanical performance. These findings confirm that in situ preheating represents an effective approach for enhancing interlayer bonding, thereby offering a practical solution for the additive manufacturing of high-performance PEEK components. Full article

Hedera helix (HE) contains diverse bioactive constituents, including triterpenoid saponins, flavonoids, and phenolic acids, which exhibit various pharmacological activities. In this study, ultrasound-assisted extraction (UAE) combined with natural deep eutectic solvent (NADES) was employed to enhance the extraction efficiency and elucidate the underlying mechanisms. Among the tested formulations, a ternary system composed of malonic acid (Mal), N,N′-dimethylurea (DMU), and 1,4-butanediol (1,4-BDO) achieved the highest efficiency for extracting eight target compounds from the HE leaves. In addition, the key interactions among NADES components were confirmed by Fourier-transform infrared (FT-IR) spectroscopy, providing valuable insights into the extraction mechanism. The UAE process was systematically optimized through single-factor experiments. Subsequently, response surface methodology (RSM) identified the optimal conditions as ultrasonic time of 45 min, solid/liquid ratio of 1:54 g/mL, and ultrasonic temperature of 42 °C. Scanning electron microscopy (SEM) elucidated the microstructural alterations in plant cell walls induced by NADES-UAE, alongside the enhanced penetration and disruption mechanisms. In vitro bioactivity revealed that the NADES-extracted HE exerted strong inhibitory effect on HT-29 colon cancer cells. Overall, these findings demonstrate the high effectiveness and sustainability of NADES-UAE for extracting HE bioactive compounds and provide valuable implications for the industrial-scale production of plant-based functional products. Full article

This study investigated how fabrication method (milling versus 3D printing) affects the water sorption and solubility of PMMA dental materials, and how surface characteristics affect hydrolytic stability. Fifty-six PMMA samples were divided into three groups fabricated from CAD/CAM milled discs (Group A: I–III) and four groups from 3D-printed resin (Group B: IV–VII), each subjected to distinct postprocessing protocols. Water sorption (wsp) and solubility (wsl) were measured after immersion in distilled water at 37 °C for 24, 48, and 72 h, and 7 and 14 days. Surface topography and nanoroughness were assessed using atomic force microscopy (AFM). Statistical descriptive analyses were followed by correlation analyses. Milled PMMA demonstrated significantly lower water sorption and negative solubility (mass loss), indicating material dissolution. In contrast, 3D-printed PMMA showed higher water sorption and positive solubility (mass gain), reflecting water incorporation and polymer swelling. The kinetic profiles differed: milled PMMA displayed a monophasic absorption curve, while 3D-printed PMMA exhibited a biphasic pattern with accelerated water uptake after 72 h. AFM analysis revealed that 3D-printed surfaces had significantly greater nanoroughness than milled surfaces. Strong positive correlations were observed between surface roughness parameters (Sa, Sy) and water sorption capacity. The fabrication method was found to influence the hydrolytic stability of PMMA dental materials. Milled PMMA demonstrated superior stability, with lower water uptake, smoother surfaces, and lower leaching solubility. In contrast, 3D-printed PMMA exhibited increased surface roughness and water sorption, attributed to its layered microstructure and nanoporosity. Surface topography emerged as a strong predictor of wsl, related to hydrolytic degradation. For clinical applications, milled PMMA is recommended for long-term use requiring durability, whereas 3D-printed PMMA may be appropriate for short-term applications with optimised postprocessing. Full article

While self-healing concrete shows promise for infrastructure repair, its effectiveness is significantly compromised in low-temperature environments because of slowed reaction kinetics and the embrittlement of capsule shells. To address this limitation, novel composite microcapsules featuring an ethyl cellulose shell and a dual-core comprising expansive cement and epoxy resin were developed. These microcapsules were fabricated using a physical spheronization-coating method and subsequently incorporated into cement mortar. Response surface methodology was employed to identify the optimal system, which balances self-healing performance with the retention of mechanical properties: a microcapsule content of 3% (by mass of cement) and a particle size range of 1.4 to 1.7 mm. Under conditions of −20 °C, the optimal formulation achieved a crack surface healing ratio of up to 44.1% and a compressive strength recovery of up to 6.0%. Microstructural and spectroscopic analyses (SEM-EDS, XRD) revealed a synergistic healing mechanism. This mechanism involves the formation of calcium carbonate, C–S–H gel, and anorthite, all cohesively bonded within a polymerized epoxy network. This work establishes a functional material strategy for enabling autonomous crack repair in concrete structures subjected to cold climates. In such environments, even marginal strength recovery, when coupled with effective crack sealing, can significantly enhance structural durability. Full article

This work investigates the use of two photoactive polymers, functionalized with quantum dots (QDs) (ZnS and CdTe/ZnS), to develop optical sensing hydrogel films through their interactions. It examines their responses to light stimulation for potential biological applications. The optical and morphological properties of the films were studied, revealing photoactive surfaces. The photoactive copolymers were synthesized based on poly(maleic anhydride-alt-2-methyl-2-butene), P(MAn-alt-2MB), and poly(maleic anhydride-alt-1-octadecene), P(MAn-alt-OD), by attaching the photochromic agent, 1-(2-hydroxyethyl)-3,3-dimethylindoline-6-nitrobenzo pyran (SP). Subsequently, QD nanoparticles (ZnS or CdTe/ZnS NPs) were incorporated into the polymer solutions in the presence of a crosslinker agent, and were then spin-coated onto glass substrates under suitable conditions to produce porous-patterned films. These films were created using a one-step bio-inspired process called the breath figure (BF) method. SEM images of QD-containing samples show a photoactive porous surface resulting from a synergistic interaction between the components. The reversibility of these macroscopic properties results from photoinduced transformations at the molecular level. The light-emitting properties of the films were characterized by blue and violet fluorescence under UV light. Advances in film-forming techniques enable the creation of functional structures with important applications, such as microstructured hydrogel films for biological uses. Full article

This study investigates the effects of current density on the microstructure and properties of electrodeposited NiCo-CeO₂ composite coatings. Results demonstrate that current density significantly influences coating composition, with higher CeO₂ and lower Co content increasing surface roughness (minimum at 30 mA/cm², maximum at 100 mA/cm²). Microstructural homogeneity improves with optimized Co/CeO₂ content, where the A30 coating (30 mA/cm²) exhibits the weakest texture among all coatings due to peak Co incorporation. Texture intensifies at higher current densities (30–100 mA/cm²) as Co and CeO₂ contents diminish. Internal stress depends on electrodeposition kinetics and particle dispersion, ranging from −2.22 MPa (A20) to 651 MPa (A50). Hardness correlates with (111) plane dominance and Co/CeO₂ content, reaching 449.8 HV for A30 but dropping to 288.8 HV for A100. Optimal current density tuning refines grains, enhances (111) texture, and improves compositional uniformity, endowing the A30 coating with balanced hardness and corrosion performance (corrosion potential: −224 mV; current density: 0.225 μA/cm²). These findings provide guidelines for tailoring high-performance NiCo-CeO₂ coatings through current density regulation. Full article

This paper focuses on analyzing the corrosion mechanism of stone cutting tool surfaces. Rare earth oxide films were prepared on the tool surface using the electrophoretic deposition–sintering method, and their corrosion resistance was investigated. Microstructural and compositional analyses of the surface layer of shot-peened tools and rare earth oxide films were conducted using characterization techniques such as SEM, EBSD, and XRD. The corrosion resistance of the rare earth oxide films was evaluated via an electrochemical workstation. The results indicate that the corrosion morphology on the stone cutting tool surface is pitting corrosion, which is significantly influenced by the friction of the tool coolant. Shot-peening treatment refines the grains in the tool surface layer, promoting the growth of rare earth oxide films. The rare earth oxide film is mainly composed of cerium oxide (CeO₂), presenting a continuous and dense structure with slight peeling after sintering. The Group 3 (0.1 mol/L, 3000 V/m, 5 min) rare earth oxide film exhibits the optimal electrochemical behavior and excellent corrosion resistance, with a corrosion potential (Ecorr) of −0.49 V and a corrosion current density (icorr) of 1.445 × 10⁻⁷ A/cm². Full article

Numerical weather prediction (NWP) models are essential for precipitation forecasting but are constrained by coarse spatial resolutions (10–50 km), which fail to capture fine-scale variations required for regional disaster prevention, particularly in complex terrain. While statistical and machine learning downscaling methods have been developed to bridge this resolution gap, they predominantly operate as “black boxes” without explicit physical guidance, leading to predictions that violate meteorological principles and systematic underestimation of extreme precipitation events. To address these limitations, this study aims to develop a Physics-Informed Machine Learning framework that explicitly integrates multi-scale topographic modulation and physical consistency constraints into precipitation downscaling. Specifically, a Random Forest model enhanced with Multi-Scale Structural Similarity (MS-SSIM) loss and Physical Constraint Enhancement (MSSSIM-PCE-RF) was constructed. The model introduces elevation gradient weights at low-resolution layers and micro-topographic parameters (slope, surface roughness) at high-resolution layers, while enforcing physical consistency between precipitation intensity, radar reflectivity, and ground observations via the Z-R relationship. Based on hourly data from 2252 meteorological stations in Jiangxi Province (2021–2022), coupled with topographic factors (DEM, slope, aspect) and Normalized Difference Vegetation Index (NDVI), a technical framework of “data fusion–feature synergy–machine learning–spatial reconstruction” was established. Results demonstrate that the MSSSIM-PCE-RF model achieves a validation R² of 0.9465 and RMSE of 0.1865 mm, significantly outperforming the conventional RF model (R² = 0.9272). Notably, errors in high-altitude, steep-slope, and high-vegetation areas are reduced by 45.3%, 42.0%, and 43.1%, respectively, with peak precipitation period errors decreasing by 37.2%. Multi-scale topographic analysis reveals significant orographic lifting effects at 250–1000 m elevations, peak precipitation at 12–15° slopes, and abundant precipitation on south/southeast aspects. By explicitly embedding topographic modulation and physical consistency constraints, the model effectively alleviates systematic underestimation of extreme precipitation in complex terrain, providing high-resolution data support for transmission line disaster prevention and micro-meteorological risk assessment. Full article

In metal additive manufacturing, the molten pool directly influences the performance of the fabricated components. Therefore, a comprehensive understanding of the molten pool behavior is essential for improving the quality of the parts and mitigating the formation of defects. Selective arc melting (SAM) is a promising additive manufacturing method for fabricating metal matrix composites. However, the melting and solidification process of the powder layer under the arc heat source remains unrevealed. This study aims to elucidate the formation mechanisms of surface morphology during SAM processing and the influence of carbide addition on the melting and solidification behavior of Inconel 718 powder. In this study, thin-walled parts of Inconel 718 and TiC/Inconel 718 composite were fabricated and their microstructures were studied. The melting and solidification behavior of Inconel 718 and TiC/Inconel 718 composite during single-track single-layer deposition was investigated using high-speed photography. Focusing on the differences in the sidewall surface morphology of the Inconel 718 and TiC/Inconel 718 composite parts, the edge feature formation of the deposition track of both materials was studied. Furthermore, the formation mechanism of the differences in forming height at different positions of the deposition track was explored. The results indicate that the melted material in the molten pool of Inconel 718 mainly comes from the mass transport of the beads generated around the molten pool, while the liquid material in the molten pool of TiC/Inconel 718 composite mainly comes from the in situ powder melted under the arc center. During the melting process of Inconel 718 powder, beads at the edge of the heating area come into contact with the boundary of the molten pool and solidify in situ, forming protrusion features. The randomness in the bead size leads to different volumes of molten material at different positions within the same time, thereby causing variations in building height. Full article

Cr-Al composite coatings were fabricated on Ti-6Al-4V alloy substrates via mechanical alloying using a high-energy planetary ball mill. The coatings exhibited a distinctive bilayer architecture comprising an inner layer with coarse reinforcing particles and an outer layer featuring a refined, homogenized microstructure. Systematic investigations were conducted to elucidate the influence of rotational speed on coating formation, microstructural evolution, phase composition, and high-temperature oxidation performance. The findings revealed that insufficient milling speeds failed to facilitate adequate powder deposition, resulting in poor interfacial adhesion and the formation of porous or thin coatings. Conversely, excessive rotational speeds induced surface roughening and coating delamination. Optimization studies identified 250 r/min as the optimal milling speed, yielding dense, well-adherent coatings with superior oxidation resistance. Cyclic oxidation testing at 850 °C demonstrated that coated specimens exhibited significantly reduced mass gain compared to uncoated substrates. Post-oxidation characterization confirmed the formation of a protective corundum-type oxide scale (α-Al₂O₃ and Cr₂O₃) and revealed a four-layered structure in the oxidized coating: (I) a dense oxide film serving as an oxygen barrier, (II) a dense alloyed layer, (III) a porous alloyed layer, and (IV) an inner diffusion zone. These results demonstrate that the mechanically alloyed Cr-Al coatings provide effective protection against high-temperature oxidation for Ti-6Al-4V alloy substrates. Full article

Addressing the challenges of multi-parameter interactions and unclear micro-mechanisms in poplar biomass panel manufacturing, this study employed a multi-scale approach integrating statistical optimization, microstructural characterization, and mechanism validation. A central composite design was used to investigate the effects of pressing time, pressure, and baking temperature (conditioning step) on modulus of rupture (MOR), modulus of elasticity (MOE), water absorption (WA), and thickness swelling (TS), establishing predictive models for multi-objective performance. Quantitative SEM analysis correlated macroscopic properties with microstructural parameters (porosity, pore size distribution, fiber–fiber contact ratio), elucidating how process conditions govern performance via interface quality and material densification. The optimized parameters yielded panels with MOR of 30.04 MPa, MOE of 10,716 MPa, WA of 4.98%, and TS of 1.75%. Modifier incorporation enhanced MOR and MOE by 23.10% and 26.38%, respectively, while reducing WA and TS by 50.59% and 29.89%. SEM confirmed an improvement in fiber–matrix interfacial bonding under optimized conditions. Environmental emission and combustion tests validated compliance with green development principles. This work establishes a cross-scale framework linking processing, microstructure, and performance, offering theoretical foundations for green manufacturing of high-performance biomass panels. Full article