Search Results (1,438)

FeNiCrMo austenitic stainless steel has good corrosion resistance but a low surface hardness, which limits its wear resistance under high load. FeNiCrMo, FeNiCrMo with 10 wt.% tungsten carbide (WC) (45–106 μm) and FeNiCrMo with 10 wt.% WC-17Co (15–45 μm) were deposited by laser cladding at 1200 W and 480 mm/min, and their phase composition, microstructure, microhardness, wear behaviour and corrosion resistance were compared. Both particle additions promoted a columnar-to-equiaxed transition and the formation of W₂C. The coarse WC particles dissolved only partially and raised the hardness little, from 473 to 475 HV_0.2, while the finer WC-17Co particles dissolved more completely and raised it to 550–600 HV_0.2. On the worn surfaces, the ploughing grooves of the unreinforced coating were still present but shallower and narrower, indicating that abrasion was reduced in severity rather than replaced. The particles nevertheless impaired the corrosion resistance, most strongly for WC-17Co. FeNiCrMo/WC gave the best overall result. Its specific wear rate was the lowest of the three coatings, 0.73 × 10⁻⁶ mm³·N⁻¹·m⁻¹ at 90 N and roughly an order of magnitude below the unreinforced coating, and its mass loss was the smallest at every load, while its corrosion resistance fell far less than that of FeNiCrMo/WC-17Co, with an Ecorr of −0.393 V against −0.738 V. The coarse, only partly dissolved WC particles provide the most favourable combination of wear and corrosion resistance and are recommended for FeNiCrMo components operating under high load in only mildly aggressive conditions. Full article

Alloys often face a well-known trade-off: enhancing strength typically results in a reduction in ductility, and vice versa. This inherent limitation poses a significant challenge in materials engineering, particularly in applications requiring both high strength and adequate deformability. In this study, we investigate the effects of different heat treatments on the microstructures and mechanical properties of a CoCrFeNiAl_0.5Ti_0.1 high-entropy alloy (HEA). Our findings demonstrate that with the appropriate heat treatment, it is possible to simultaneously enhance both strength and ductility. The as-rolled CoCrFeNiAl_0.5Ti_0.1 HEA sheet exhibits mechanical properties with a tensile strength of 987 MPa, a yield strength of 769 MPa, and an elongation of 20.2%. After annealing treatments at 700 °C and 900 °C followed by water quenching, the alloy demonstrates simultaneous improvements in both strength and ductility. Specifically, the alloy annealed at 700 °C achieves a tensile strength of 1314 MPa, a yield strength of 970 MPa, and an elongation of 20.3%. Similarly, annealing at 900 °C results in a tensile strength of 1208 MPa, a yield strength of 727 MPa, and an elongation of 18.3%. The enhancements in mechanical properties are due to the reduction in internal stress and the occurrence of recrystallization. Additionally, the formation of fine and uniformly distributed precipitates during the heat treatment process further contributes to improvements. Full article

Additive manufacturing generally endows high-entropy alloys (HEAs) with distinctive microstructures and excellent properties unattainable by conventional processing. This study elucidates how annealing-induced phase decomposition and elemental partitioning govern pitting corrosion behavior in a laser-directed energy-deposited (LDED) Al_0.5CoCrFeNi HEA. Notably, the rapid LDED solidification process produces a metastable B2 phase with anomalously high Cr content in this HEA compared to its conventional manufacturing counterpart. Upon annealing at 650 °C for 1 h, (Cr, Fe, Co)-enriched σ and (Cr, Fe)-enriched body-centered cubic (BCC) phases preferentially precipitate within the B2 phase, concurrently depleting Cr and enriching Al in the residual B2 matrix. This elemental repartitioning critically degrades the protective capability of the B2 phase’s passive film, thereby compromising the alloy’s overall pitting corrosion resistance, as evidenced by decreased pitting and repassivation potentials. These findings advance the fundamental understanding of corrosion mechanisms in additively manufactured HEAs and offer a mechanistic rationale for designing corrosion-resistant HEAs via controlled phase transformation. Full article

This study investigates the micro-cutting mechanism of a 7A09 aluminum matrix composite reinforced with CoCrFeNiAlX (referred to as AlX) high-entropy alloy particles, chosen for their superior wetting properties with aluminum. Using simulation analysis, the research explores how high-entropy alloy particles with varying aluminum content influence the micro-cutting behavior of the aluminum-based composite. The results indicate that cutting force is minimized when the cutting path is above the particle and maximized when below, with a difference of approximately 201 N. Cutting force increases with cutting speed, but the rate of change varies significantly across speeds, with a maximum increase of 67%. The highest cutting temperatures, at 301 °C and 304 °C, are observed when cutting depth and speed are maximized, respectively, with temperature more strongly influenced by cutting speed, leading to a temperature variation of up to 148 °C across different speeds. For composites with different aluminum contents, cutting temperatures follow the order Al₁ > Al_0.6 > Al₀. When the cutting path passes above the particle, thinner chips undergo multiple fractures due to tensile stress; as the path shifts downward, chip breakage frequency increases with cutting depth. At a constant cutting depth, low-speed cutting produces discontinuous chips, while higher speeds yield more continuous chips, achieving the most complete chip formation at 1500 m/min. The surface smoothness, qualitatively reflected by nodal displacement, ranks as follows: path b > path d > path c > path a > path e. This research provides valuable data to enhance machining performance for high-entropy alloy particle-reinforced aluminum matrix composites. Full article

Molecular dynamics simulations were performed to examine the temperature-dependent nanoindentation response of aluminum substrates coated with amorphous or crystalline equiatomic FeNiCrCo layers. The study extends our previous 300 K baseline analysis of the same model system by comparing deformation at 300 and 600 K and by examining the spatial redistribution of local kinetic energy and local nonequilibrium kinetic-temperature indicators during loading and unloading. A spherical virtual indenter with a radius of 30 Å was driven to maximum penetration depths of 35 and 65 Å, representing predominantly coating-controlled deformation and a regime involving the coating–substrate interface and aluminum substrate, respectively. At both temperatures, the crystalline coating exhibited higher indentation resistance and serrated force–depth responses associated with intermittent lattice-mediated plasticity, whereas the amorphous coating showed lower force levels and smoother deformation through distributed local atomic rearrangements. Increasing the temperature from 300 to 600 K enlarged the deformation-affected region and promoted a greater involvement of the interface and Al substrate. Nevertheless, the spatial character of the response remained structure-dependent: the crystalline coating retained a comparatively compact region of elevated local kinetic energy beneath the indenter, whereas the amorphous coating displayed a broader and more diffuse kinetic-energy perturbation. Adaptive common-neighbor analysis was used as a qualitative local-environment descriptor; therefore, structural labels are interpreted together with force–depth curves and atomistic configurations rather than as unique phase identifiers. The results identify temperature-dependent trends in deformation localization and energy redistribution for an idealized FeNiCrCo/Al model system. Because the simulations employ a finite periodic cell, a high indentation velocity, and an empirical potential, the findings are interpreted as qualitative atomistic trends and are not quantitatively extrapolated to experimental indentation conditions. Full article

To investigate the effects of laser energy density on the microstructure, phase constitution and distribution, wear resistance, and corrosion resistance of AlCoCrFeNi high-entropy alloy coatings, three coatings were fabricated on ATI 718Plus substrates by laser cladding at different laser energy densities. Their microstructure, phase constitution, microhardness, tribological behavior, and electrochemical corrosion properties were systematically characterized. The results showed that all coatings exhibited good metallurgical bonding with the substrate. With increasing laser energy density, the coating microstructure initially became finer and more homogeneous and subsequently coarsened. All coatings were primarily composed of BCC/B2 phases with a small fraction of the FCC phase. The coating produced at the medium laser energy density (MHI) exhibited the most homogeneous phase distribution and the highest average microhardness of 576.1 HV_0.3. It also showed the lowest coefficient of friction and specific wear rate, with values of 0.52 and 6.94 × 10⁻⁴ mm³/(N·m), respectively. The dominant wear mechanism was abrasive wear, accompanied by localized delamination and tribo-oxidation. Furthermore, the MHI coating exhibited the highest charge-transfer resistance of 18,880 Ω·cm² and the lowest corrosion current density of 96.8 μA·cm⁻², indicating superior corrosion resistance. These results demonstrate that an appropriate laser energy density promotes a finer and more homogeneous solidification microstructure and a more favorable phase distribution, thereby achieving a synergistic improvement in the hardness, wear resistance, and corrosion resistance of AlCoCrFeNi high-entropy alloy coatings. Full article

Direct coal liquefaction (DCL) is a critical approach to clean and efficient coal utilization. With international energy supplies becoming increasingly unstable due to geopolitical conflicts, the conversion of coal-to-liquid technology plays critical roles in securing energy safety. Inorganic elements in coal are highly variable in content and modes of occurrence. In particular, the modes of occurrence of each element largely determine their migration and transformation behavior during liquefaction, which in turn directly affects products distribution, oil quality, process stability and environmental risks. This paper summarizes the modes of occurrence of major mineral elements (Al, Si, Fe and alkali and alkaline earth metals (AAEMs)) and hazardous trace elements (Hg, As, Pb, Cd and Cr) in low-rank coals, and then discusses their redistribution and speciation evolution during liquefaction. Inorganic elements and minerals exert distinct effects during coal liquefaction. Iron (Fe), cobalt (Co), and nickel (Ni) generally promote hydrogenation and bond cleavage, whereas AAEMs inhibit liquefaction by enhancing radical cross-linking. Pyrite facilitates hydrogen transfer and hydrocracking, while clay minerals may promote condensation and coke formation. For toxic trace elements, mercury (Hg) generally exhibits high volatility and is readily released into the gas phase. Arsenic (As) and cadmium (Cd) show more complex transformation behaviors governed by their associations with sulfides, organic matter, and mineral phases. Lead (Pb) and chromium (Cr) mostly remain in the solid residue due to their low volatility and strong associations with silicates. Overall, this review highlights the importance of the modes of occurrence of inorganic elements in process optimization and environmental risk management in DCL. Full article

In this study, the concentrations of thirteen trace elements (aluminum (Al), arsenic (As), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), mercury (Hg), nickel (Ni), selenium (Se), and zinc (Zn)) were determined in the edible muscle tissues of three commonly consumed fish species (Oncorhynchus mykiss, Dicentrarchus labrax, and Sparus aurata). Specimens were obtained from farmed stocks harvested and delivered to fish markets in Sinop, Türkiye, on the day of collection, with sampling carried out on a monthly basis throughout April, May, and June 2024. Zinc and iron exhibited the highest concentrations across all species, while toxic trace elements remained at notably low levels, with Cd (0.005–0.006 mg/kg), Hg (0.015–0.018 mg/kg), and Pb (0.010–0.011 mg/kg) remaining strictly below the European Union maximum permissible limits of 0.05, 0.5, and 0.3 mg/kg, respectively. In addition, a comprehensive human health risk assessment was performed based on a mean daily per capita fish consumption of 19.72 g. The Target Hazard Quotient (THQ) for all evaluated elements and the cumulative Hazard Index (HI), which ranged from 0.0794 to 0.0818 across species, were well below 1.0, indicating negligible non-carcinogenic risk. Carcinogenic risks, evaluated via the Risk Index (RI), were negligible for Cr (1.35–2.35 × 10⁻⁷) and well within acceptable bounds for iAs (2.77–4.13 × 10⁻⁶). The quantitative outcomes of this investigation suggest that under the evaluated conditions, trace element concentrations in these aquaculture products remain within safe baseline levels, contributing meaningful data on food safety and ecological monitoring within the southern Black Sea region. Full article

To reveal the uranium enrichment mechanism in the Daqing Placanticline area, northern Songliao Basin, this study collected a total of 41 samples of three geological types, namely uranium ore, uranium-mineralized sandstone and host rock from the Upper Cretaceous Sifangtai Formation. Combined with 109 geochemical datasets from exploration, systematic analyses were performed on major elements, trace elements, rare earth elements (REE), total organic carbon (TOC), total sulfur and other key geochemical parameters. The results indicate that uranium ore and mineralized sandstone are generally characterized by high TOC, high total sulfur, low Th/U and low Fe₂O₃/FeO ratios, while host rocks show the opposite geochemical assemblage, suggesting uranium enrichment took place in a strongly reducing sedimentary environment. The ore-forming system is significantly enriched in trace elements including U, Pb, Mo, Ba, Zn and Y, and depleted in Cu, Co, Ni, Cr, Sr, Nb, Ta, Zr and Hf. Among these elements, Mo and Pb have an extremely close relationship with uranium mineralization and can be used as effective ore-forming indicator elements. Uranium ore, mineralized sandstone and host rock exhibit consistent REE distribution patterns, implying that the strata in the study area share uniform provenance, sedimentary environment and tectonic setting. Some high-grade uranium ores are obviously enriched in heavy rare earth elements (HREE), demonstrating fluid modification during the late mineralization stage. Combined with regional tectonic evolution and hydrocarbon migration features, this study concludes that sandstone-type uranium deposits in the Daqing Placanticline mainly underwent two stages of mineralization: supergene fluid mineralization and superimposed reworking by deep hydrocarbon-bearing reducing fluids. Full article

Severe heavy metal pollution in aquatic environments demands the engineered development of structurally optimized, highly selective adsorbents. Herein, we report the intentional fabrication of a novel ternary MnO₂/NH₂-MIL-101(Fe)/g-C₃N₄ nanocomposite via an integrated in situ interfacial growth pathway. The true architectural novelty of this multi-component assembly lies in utilizing the 3D mesoporous metal–organic framework (MOF) scaffolding to structurally isolate the 2D g-C₃N₄ layers and prevent the self-aggregation of redox-active MnO₂ nanoparticles. Comprehensive characterization via PXRD, FTIR, TEM, Raman, and high-resolution XPS confirmed that this unique interfacial hybridization maximizes the spatial exposure of unblocked chemical binding sites. Batch extraction trials demonstrated a high Pb²⁺ removal efficiency of 99.5 ± 2.7% at an optimized pH of 6.0, yielding a superior maximum monolayer adsorption capacity (q_max) of 431.8 mg.g⁻¹. Competitive selectivity matrices containing co-existing ions (Cu²⁺, Cd²⁺, Ni²⁺, and Cr³⁺) revealed noticeable selectivity toward Pb²⁺ ions, driven by soft Lewis’s acid-base affinities, while background electrolyte tests identified SO₄²⁻ as the most influential competing anion. Non-linear isotherm modeling showed a better agreement with the Langmuir model, suggesting dominant monolayer adsorption on accessible surface sites, while kinetic data followed the pseudo-second-order model. Spectroscopic profiling proved that this heightened performance is dictated by a multi-modal integrated network operating via cooperative inner-sphere Mn-OH complexation, oxygen-vacancy trapping, exocyclic framework amine (-NH₂) chelation, and g-C₃N₄ triazine dative configurations. These findings establish the ternary system as an advanced, highly recyclable benchmark for targeted heavy metal decontamination. Full article

Green chemistry aims to develop more sustainable and environmentally friendly chemical processes by reducing waste, minimising the use of hazardous substances, and identifying alternative catalysts and solvents. Traditional organic synthesis often relies on catalysts that are toxic, flammable, or corrosive, such as phosphoric acid, creating a need for greener alternatives. This study investigated the potential of ash derived from food industry waste as a green catalyst. Various waste materials were utilised, including onion and garlic husks, peanut skins and shells, hop and barley residues after beer production, and cocoa shells and beans. ICP-MS analysis was used to determine the content of 25 elements (Na, Mg, P, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Cd, Pb, B, Al, S, Ga, Rb, Sr, Ba, La) in the food industry waste ash. The catalytic activity of the ash was evaluated in the synthesis of acetylsalicylic acid from salicylic acid and acetic anhydride. Reactions were carried out in the presence of 20 mg of ash by heating the reaction mixture in a water bath at 80–100 °C. Reaction yields ranged from 11% (peanut shell ash) to 78% (barley ash). In addition to barley ash, good reaction yields were also obtained with hop ash, cocoa shell ash, and cocoa bean ash. The results demonstrated that ash-derived materials successfully catalysed the reaction, suggesting that metals present in the ash may play a role in catalysis. These findings indicate that food industry waste may represent a promising and sustainable source of catalysts for organic synthesis. Full article

This study investigated the corrosion resistance of laser-cladded AlCoCrFeNi high-entropy alloy coatings with varying TiO₂ content (0 wt.%, 0.5 wt.%, 1.0 wt.%, and 1.5 wt.%) in 3.5 wt.% NaCl solution. Optimal cladding parameters (1500 W, 40 mm/s, 11.9 g/min) were determined via orthogonal experiments. TiO₂ promoted Ti-rich BCC2-phase precipitation, increased corrosion potential (from −1.4185 V to −0.6841 V), decreased corrosion current density (from 2.33 × 10⁻⁴ to 2.28 × 10⁻⁶ A/cm²), and enhanced charge-transfer resistance. XPS analysis demonstrated that TiO₂ promoted the enrichment of FeO, Cr₂O₃, and TiO₂ components in the passive film while reducing the Al₂O₃ fraction, leading to the formation of a dense and stable composite passive film that effectively inhibited chloride ion attack. In summary, an appropriate amount of TiO₂ doping significantly enhances the corrosion resistance of laser-cladded AlCoCrFeNi HEA coatings, with the 1.5 wt.% addition being the best-performing among the investigated compositions. Full article

The Berca–Arbănași region of Buzău County (Romania) is of exceptional geochemical interest due to diapiric structures, active mud volcanoes, and historical subsurface hydrocarbon deposits. This study presents the first comprehensive geochemical assessment of surface soils from the Berca–Arbănași Subcarpathian zone, based on the analysis of 27 soil samples collected along three north–south transects and the determination of 12 potentially toxic elements (As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V, Zn) using aqua regia digestion and ICP-MS. The local geochemical background was calculated using the iterative median ± 2MAD method. Twelve pollution and ecological risk indices were computed: the Pollution Index (PI), Contamination Factor (CF), Geoaccumulation Index (Igeo), Enrichment Factor (EF), Pollution Load Index (PLI), Modified Degree of Contamination (mCd), Nemerow Integrated Pollution Index (PINemerow), Ecological Risk Factor (E_rⁱ), Ecological Risk Index (RI), Mean Effect Range-Median Quotient (MERMQ), Degree of contamination (Cdeg), and the V/Ni petroleum origin indicator. Results show that 66.7% of samples are classified as polluted (PLI ≥ 1; mean = 1.102), with moderate enrichment in Cd, Cu, Hg, Pb, and Zn, attributable to diffuse anthropogenic sources. The ecological risk index (RI) remains low across all samples (mean = 35.96; all < 150), indicating that, despite moderate pollution, ecological risk is currently low. The V/Ni ratio (0.391–0.884, mean = 0.608) is below 1.0 for all samples, indicating a lithogenic (not petroleum) origin of vanadium and nickel and confirming a negligible geochemical impact of mud volcanoes and hydrocarbon extraction activities in the area at the sampled locations. The study establishes baseline geochemical reference values for the Berca–Arbănași area and provides data for sustainable land management, environmental monitoring, and evidence-based policymaking. These results directly support the objectives of the EU Soil Strategy 2030 and align with the United Nations Sustainable Development Goals on food security (SDG 2), good health and well-being (SDG 3), and life on land (SDG 15). Full article

Juniperus species form critical, long-lived high-mountain forest ecosystems in Central Asia, serving essential phytocoenotic and ecological functions in environmentally challenging habitats. However, the relationships between the elemental composition of these evergreen conifers and their underlying soils remain poorly understood. This study evaluated and compared the distribution of major elements (Fe, Ca, P, Mg, Al, Na, K, S), trace elements (Cu, Pb, Zn, Ni, Co, Mn, As, Cd, Cr, Mo, U, Th, Sr, Sb, Bi, V, La, Ba, Ti, B, W, Sc, Zr, Tl, Ta, Nb, Se, Te, Ga, Cs, Ge, Hf, Rb, Sn and others), and environmental pollution indices (Igeo, EF, CF, BAF) in plant tissues (leaves and cones) and canopy soils of three key juniper species (Juniperus seravschanica, J. turkestanica, and J. semiglobosa) in the Fann Mountains, Tajikistan. Soil and plant samples were collected across natural habitats and analyzed for total chemical composition using ICP-OES. The soils showed a near-neutral reaction (pH 7.02–7.42 in H₂O and 6.41–7.15 in KCl), with considerable variability in Corg. content (5.04%–21.82%) and Nt content (0.337%–1.149%) in the humus (A) horizons. Geochemical indices (Igeo up to 2.42, EF up to 35.30) indicated noticeable soil enrichment and localized contamination by arsenic (As) and cadmium (Cd), likely driven by a combination of regional industrial and mining activities alongside natural geogenic enrichment. Across all sites, elemental concentrations followed a consistent sequence: soil > leaves ≈ cones. Heavy metals in plant tissues remained well below toxic thresholds. High organ-specific partitioning was observed: K predominated in cones (K > Ca > P), whereas Ca and Fe accumulated predominantly in leaves (Ca > K). Low bioaccumulation factor values (BAF < 1) indicate limited element accumulation relative to total soil concentrations for all three species, which may be influenced by both reduced bioavailability in neutral-to-alkaline soils and potential physiological regulation. As the first data reported from this region, these findings establish an essential baseline for long-term ecological monitoring, soil–plant chemistry, conservation, and environmental risk assessment in the Fann Mountains’ juniper ecosystems. Full article

Potentially Toxic Elements (PTEs) contamination of the soil is a global environmental problem, which can seriously affect the ecosystem, agricultural development, and human health. To evaluate the degree of potentially toxic metal contamination, 32 soil samples were collected from different sites in the Yanbu and Khulais areas of Saudi Arabia to analyze eight PTEs (Co, Cr, Cu, Fe, Ni, Pb, V, and Zn). The contamination indices used including the Geo-accumulation Index (Igeo), Enrichment Factor (EF), Contamination Factor (CF), and Pollution Load Index (PLI), as well as Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) for source identification. Because metals taken up from soil can move along the soil-to-plant pathway into crops, characterizing the degree and likely origin of potentially toxic metal enrichment in agricultural soil is a necessary first step for any subsequent land-management or food-safety assessment, particularly in a country that imports the majority of its food. The results of PCA and HCA indicate that the basement rocks of Arabian Shield-associated minerals are a plausible primary source of these potentially toxic elements. The mean EF values of the PTEs in decreasing order are as follows: Co (0.93) > Ni (0.92) > Cu (0.80) > Zn (0.74) > V (0.65) > Cr (0.59) > Pb (0.27). This implies that the soils in the study area are not enriched or only slightly enriched with PTEs. According to the geoaccumulation index values, nearly every PTE was classified as practically unpolluted (Igeo < 0), the exception being Ni, which reached the unpolluted-to-moderately-polluted class (Igeo ≥ 0) at four Khulais sites. The CF and PLI values indicate that the soil is unpolluted on average. In summary, the combined pollution-index and multivariate framework offers a practical geochemical screening tool for this arid coastal region; monitoring soil quality in this way is a useful contribution to sustainable land management in water- and land-limited environments. Full article