Search Results (1,150)

Background: Drilling slurry, a waste material generated during natural gas extraction, requires careful chemical characterization to determine its environmental hazard classification and inform appropriate management strategies. Methods: This study characterizes the drilling fluid used as raw material and the resulting drilling slurry waste, using a case study sample from the Buzău extraction area (Well 1 Florica, S.N.G.N. Romgaz S.A.), including total composition analysis, three-stage leaching tests, linear regression of leaching kinetics, and standardized geoaccumulation indices (Igeo, CF, PLI). Results: Total composition analysis confirmed low heavy metal concentrations (Cd = 0.02, Cr = 0.05, Pb = 0.64, Zn = 2.82 mg/kg dry matter). All leachate parameters remained below non-hazardous waste thresholds (Order No. 95/2005), with safety factors of 20–100× for regulated metals and 1.2–2.7× for chlorides, sulphates, and dissolved organic carbon. Standardized pollution indices confirmed Class 0 (unpolluted) status for all five metals, with a composite Pollution Load Index of 0.0124. Leaching regression analysis revealed dissolution-controlled release for chlorides, sulphates, and zinc (R² > 0.93) versus matrix-retention behavior for copper, nickel, cadmium, and chromium. Comparative analysis showed horizontal drilling generates approximately 146% more waste volume than conventional vertical drilling (170 m³ versus 69 m³ at 2100 m depth). Conclusions: The analyzed drilling slurry meets non-hazardous waste classification with substantial safety margins, corroborated by three independent analytical frameworks. Waste minimization strategies and biodegradable fluid substitution offer practical pathways to reduce the environmental footprint of natural gas drilling operations. Full article

Nickel-based alloys are promising structural materials for molten salt systems; however, secondary-phase formation during long-term high-temperature exposure may introduce local corrosion susceptibility because secondary phases have compositions and redox stabilities distinct from the matrix. Here, we combine CALculation of PHAse Diagrams (CALPHAD)-based phase prediction with redox thermodynamic analysis to assess phase-specific corrosion susceptibility in Inconel 625 (IN625) and SA508 low-alloy steel under molten chloride conditions. Equilibrium phase constitutions at 1000 K were predicted using Thermo-Calc, and redox equilibrium potentials were calculated for representative-phase dissolution reactions of major metallic elements in each phase. The dominant α and γ phases in SA508 exhibited similar Fe-ionization potentials of −1.728 and −1.768 V vs. Cl2/Cl⁻, respectively. In IN625, the γ matrix exhibited a Cr-ionization potential of −1.964 V vs. Cl2/Cl⁻, whereas the P phase showed the most negative potential of −2.132 V vs. Cl2/Cl⁻, 0.168 V more negative than the matrix, identifying the P phase as the primary local thermodynamic weak point. These results show that phase-specific metal-ionization susceptibility cannot be inferred solely from nominal alloy composition or matrix behavior. The proposed framework provides a thermodynamic screening approach for identifying susceptible secondary phases in multicomponent alloys under molten-salt conditions. Full article

Selective laser melting (SLM) can effectively suppress metallurgical defects inherent to conventional manufacturing; however, subsequent aging treatments essential for engineering applications introduce secondary precipitates that alter the electrochemical homogeneity of the matrix. The underlying mechanism by which such precipitation behavior governs corrosion resistance remains elusive. In this study, a Fe-30Mn-8Al-1.5C-2.5Ni steel was investigated to elucidate the corrosion morphology and electrochemical behavior of the as-built, 450 °C-aged, and 750 °C-aged specimens during immersion in a 3.5 wt.% NaCl solution. The results demonstrate that the inherent Mn microsegregation and high-density subgrain boundaries induced by SLM trigger preferential localized anodic dissolution on the surface of the as-built sample, culminating in the formation of a loose, porous manganese oxide product layer. Aging treatment at 450 °C induces extensive precipitation of κ-carbides within grain interiors and along grain boundaries, accompanied by localized depletion of Al and Mn at the phase interfaces. A pronounced micro-galvanic coupling established between the κ-carbides and the adjacent Al-depleted zones directly compromises the continuity of the passive film, thereby further deteriorating the corrosion resistance. In contrast, aging at 750 °C relieves the residual stress and eliminates the as-built elemental microsegregation. The resulting compositional homogenization of the matrix reduces the localized electrochemical driving force, which promotes a uniform reaction of Al at the surface to construct a continuous, compact Al-rich passive film, thereby sustaining the highest charge-transfer resistance during long-term immersion. This work elucidates the correlation among the intrinsic defects of SLM, aging-induced solute-depleted zones, κ-carbide precipitation, and localized micro-galvanic corrosion, providing a fundamental basis for tailoring the microstructure and corrosion resistance of additively manufactured lightweight steels. Full article

The corrosion evolution of pipeline steel was investigated in NaCl + 0.75 M NaHCO₃ solutions with different chloride concentrations using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), Mott–Schottky analysis, X-ray photoelectron spectroscopy (XPS), and surface characterization techniques. The results demonstrated that chloride concentration was a critical factor governing the transition of corrosion behavior from a relatively stable oxide-film-controlled state to active dissolution. At low Cl⁻ concentrations, a stable current-density region was observed, indicating the formation of a protective oxide film. With increasing Cl⁻ concentration, the stable current region gradually disappeared, accompanied by a continuous decrease in polarization resistance and oxide-film resistance, revealing the progressive deterioration of corrosion resistance. Mott–Schottky analysis showed that the oxide film formed in 0.5 wt.% NaCl + 0.75 M NaHCO₃ solution (pH ≈ 8.3) exhibited n-type semiconductor characteristics, with a donor density of 8.69 × 10²¹ cm⁻³. XPS analysis revealed that the oxide film mainly consisted of Fe²⁺-related oxides. The experimental results indicate that the corrosion evolution was associated with the competitive interaction between ${\mathrm{H}\mathrm{C}\mathrm{O}}_3^{-}$ and Cl⁻, where bicarbonate favored oxide-film stabilization at low chloride concentrations, whereas chloride enrichment promoted oxide-film deterioration and accelerated active dissolution. This study establishes the relationship between chloride concentration variation, oxide-film degradation, and corrosion evolution of pipeline steel in high-bicarbonate alkaline environments, providing experimental insights for corrosion assessment and control under chloride-enriched service conditions. Full article

The growing adoption of hybrid and plug-in electric vehicles increases heat generation in power electronic modules, driving demand for effective thermal management materials and reliable Al/Cu joining methods. However, large-area Al/Cu joints are challenging as conventional brazing requires high temperatures and flux, and fusion welding performs poorly with dissimilar metals. Contact-Reaction Brazing (CRB), which relies on eutectic-phase formation during heating, presents a promising alternative. Direct CRB of AA6063 and Cu might lead to severe aluminum dissolution above 570 °C. To mitigate this, large-area CRB of AA6063/Cu using a 4104 aluminum-foil interlayer is examined. Brazing temperature, holding time, and pressure are systematically varied to evaluate their influence on joint formation. Interfacial microstructures are characterized by SEM and XRD. Shear testing is used to assess fracture behavior and mechanical performance. A satisfactory shear strength of 48.8 MPa is achieved for the AA6063/AA4104/Cu joint under a brazing temperature of 540 °C, a holding time of 10 min, and an applied pressure of 600 Pa. Full article

Circulating fluidized bed (CFB) fly ash exhibits immense potential as a supplementary cementitious material, yet its application is limited by volumetric instability related to delayed ettringite formation. This study investigates the effect of grinding and ultrafine grinding on hydration behavior, microstructure, and long-term volumetric stability of CFB fly ash–cement composites using isothermal calorimetry, XRD, SEM-EDS, TG-DSC, and MIP. Results show that increasing fineness shortens the induction period and advances the second hydration peak by ~6 h. The cumulative heat release of the UCFA system reaches 95.2% of plain cement (85 h). Ultrafine grinding improves hydration activity and reduces total pore volume by 7.32% compared with cement and 22.18% compared with RCFA, leading to denser microstructures and higher compressive strength. Mechanistically, grinding modifies the outer sulfate-bearing layer, accelerating sulfate dissolution and early ettringite formation, while promoting CaO exposure and pozzolanic reactions. Long-term tests up to 730 days confirm that UCFA significantly reduces linear expansion, indicating improved volumetric stability. These results demonstrate that ultrafine grinding simultaneously enhances hydration reactivity and long-term stability, providing a feasible route for high-value utilization of CFB fly ash in cementitious systems. Full article

To reveal the influence of pulsed current density on the microstructural evolution and mechanical properties of Mg-Gd-Y-Zn-Zr rare-earth magnesium alloy wires, extruded Mg-10Gd-3.4Y-1.3Zn-0.4Zr alloy wire was selected as the research material. By regulating the current density in the range of 12–20 A/mm², the effects on temperature rise behavior, microstructural evolution, and mechanical properties were systematically investigated. The results show that as the current density increases from 12 A/mm² to 20 A/mm², the measured surface peak temperature rises from 207 °C to 497 °C, and the mechanical properties among the electropulsing-treated samples exhibit a trend of first increasing and then decreasing. Among these treated samples, the optimal combination of strength and ductility is achieved at a current density of 15 A/mm², at which the tensile strength and elongation reach 312.2 MPa and 13.6%, respectively. Microstructural analysis indicates that appropriate pulsed electrical parameters promote the dissolution, fragmentation, and homogenized dispersion of block-shaped long-period stacking ordered (LPSO) phases, thereby optimizing the internal strain state and facilitating the activation of non-basal <c+a> slip. However, when the current density increases to 20 A/mm², excessive thermal input leads to grain coarsening and a network-like W-phase precipitation, indicating that excessive energy input can lead to microstructural instability and mechanical degradation. Full article

Quenched and tempered (Q+T) bolt steels are widely used in key load-bearing structures such as bridges, wind power equipment, pressure vessels and engineering machinery, but they are susceptible to hydrogen-induced cracking under applied stress during service. In this study, a bolt steel was subjected to Q+T heat treatment, including quenching at 850, 900, 950, 1000 and 1050 °C, followed by tempering at 500 °C. Microstructural characterization, hydrogen permeation tests, and slow strain rate tensile tests were conducted to investigate the effects of quenching temperature on microstructural evolution, hydrogen diffusion behavior and resistance to hydrogen-assisted cracking. As the quenching temperature increased from 850 °C to 1050 °C, the prior austenite grains, packets and blocks were gradually coarsened, the fraction of high-angle grain boundaries decreased from 64.7% to 54.2%, and although partial dissolution of primary carbides may occur during austenitizing, the number/area fraction and size of carbides observed in the final tempered martensitic microstructure increased after the subsequent tempering treatment. Meanwhile, the Nb/Ti-rich precipitates changed only slightly, and the dislocation density increased. The effective hydrogen diffusion coefficient, D_eff, increased with increasing quenching temperature, mainly because grain coarsening significantly reduced the high-angle grain boundary area and weakened the hydrogen-trapping effect of grain boundaries. This dominant effect masked the diffusion-retarding effects caused by increased dislocation density and coarser carbides. With increasing quenching temperature, the strength loss ratio increased from 7.3% to 12.0%, and the plasticity loss ratio increased from 10.0% to 13.6%, indicating enhanced hydrogen-assisted cracking susceptibility. The fracture morphology gradually changed from deep dimples to flat dimples and flattened ductile–brittle mixed features, while the crack propagation path became straighter. A higher quenching temperature weakened the blocking effect of grain boundaries on crack propagation and reduced the resistance of the quenched and tempered bolt steel to hydrogen-assisted cracking. Full article

This study investigated the temperature-dependent σ phase transformation behavior of 24Cr–14Ni stainless steel subjected to aging at 700–1000 °C for 1–8 h. At 700 °C, the σ phase mainly retained the original dendritic morphology, whereas at 800 °C, the δ → σ + γ₂ eutectoid decomposition became most pronounced. The σ phase begins to decompose from the dendrite arms. XRD analysis confirmed that σ phase precipitation was most significant at 800 °C, while only weak σ peaks were detected at 900 and 1000 °C, indicating suppressed precipitation and partial σ phase dissolution at higher temperatures. EPMA/WDS analysis showed that σ phase preferentially formed in Cr-rich δ-ferrite regions, while Ni was mainly enriched in the γ-phase. At 1000 °C, the more homogeneous Ni distribution suggested that δ-ferrite dissolution and δ → γ transformation became dominant. JMAK analysis revealed two distinct kinetic regimes: diffusion-controlled σ phase precipitation at 700–800 °C, with Avrami exponents of 0.4327–0.4606, and σ phase dissolution at 900–1000 °C, with higher Avrami exponents of 0.7932–0.8671. The apparent activation energies for precipitation and dissolution were 37.18 and 122.95 kJ·mol⁻¹, respectively. These findings indicate that σ phase transformation in 24Cr–14Ni stainless steel changes from precipitation-dominated behavior at 700–800 °C to dissolution-dominated behavior at 900–1000 °C. Full article

Infectious wounds are plagued by persistent infection, uncontrolled inflammation, and delayed repair, while traditional therapies suffer from the poor solubility of natural drugs, low bioavailability, and bacterial drug resistance. To address these issues, this study developed a photo-responsive chitosan composite hydrogel (BBR-AS@Ce6@Matrix) cross-linked by chitosan (CS) and oxidized sodium alginate (OSA), co-loaded with Berberine–Asiaticoside cocrystal (BBR-AS) and chlorin e6-loaded chitosan nanoparticles (Ce6@CS NPs). The BBR-AS co-crystal was prepared by solvent method and verified to significantly improve the solubility and dissolution of asiaticoside. The Ce6@CS NPs were fabricated via non-solvent-assisted counterion complexation, showing high encapsulation efficiency, uniform particle size, and efficient singlet oxygen generation under irradiation. The hydrogel exhibited a three-dimensional porous network, favorable rheology, high water content, pH-dependent swelling and erosion behaviors, and significantly promoted BBR/AS release in vitro. In vitro experiments demonstrated strong antibacterial activity against Escherichia coli and Staphylococcus aureus, good cytocompatibility, and enhanced migration of L929 and Hacat cells. In a rat infectious wound model, the hydrogel combined with light irradiation markedly accelerated wound closure, promoted collagen deposition and angiogenesis, upregulated VEGF/CD31, and downregulated TNF-α/IL-6. In conclusion, BBR-AS@Ce6@Matrix integrates co-crystal solubilization, nanoparticle-facilitated release, and photodynamic synergy to achieve antibacterial, anti-inflammatory, pro-angiogenic and tissue remodeling effects, providing a promising multifunctional platform for infectious wound repair. Full article

Carbon capture and storage (CCS) represents a critical technology for achieving climate neutrality targets, particularly for regions with significant industrial CO₂ emissions. This study presents a comprehensive numerical simulation assessment of CO₂ geological storage potential in the Sarmatian formations of the Getic Platform, Romania, located near the Turceni power plant—one of Europe’s largest thermal power facilities. Using ECLIPSE 300 compositional simulator with the CO2STORE option, we developed reservoir dynamic models incorporating geological properties, fluid characteristics, and pressure–volume–temperature (PVT) data specific to the Sarmatian aquifer system. Multiple injection scenarios were evaluated, including configurations with 3, 4, and 5 injection wells at varying inter-well distances (2000–10,000 m). The simulations covered a 20-year injection period followed by 300 years of monitoring. While previous assessments have provided static capacity estimates for Sarmatian formations, this study presents the first dynamic simulation-based evaluation of multi-well injection scenarios and long-term CO₂ trapping behavior in this geological setting, directly linked to the Turceni Power Plant emissions profile. Results demonstrate that the study area (Zone V) can accommodate the target CO₂ injection rate of 2.07 × 10⁶ Sm³/day using five injection wells, with final reservoir pressure increasing only 7–9 bar above initial conditions, well below fracture pressure thresholds (~280 bar). Long-term simulations reveal favorable CO₂ trapping behavior, with significant portions immobilized through residual and dissolution trapping mechanisms. The static storage capacity was estimated at 2.44 × 10¹⁴ kg CO₂. These findings support the technical feasibility of large-scale CO₂ storage in Romanian Sarmatian formations, providing quantitative evidence for CCS implementation strategies in the region. Full article

Carbonation-induced pH reduction is a key factor triggering steel depassivation and corrosion initiation in reinforced concrete. However, the influence of pore solution chemistry on passive film (PF) stability remains unclear. In this study, ordinary Portland cement simulated pore solution (OPC-SCP) and ferrite-aluminate cement simulated pore solution (FAC-SCP) were used to investigate the evolution of PF formed at pH 12.5 and subsequently exposed to pH 11.0 and 9.5 environments. Electrochemical and microscopic techniques were employed to investigate the degradation behavior of PF under reduced alkalinity. The results show that PF in both systems degraded with decreasing pH, but exhibited markedly different stability. In the OPC-SCP system, the PF resistance decreased slightly from 4.24 × 10⁶ to 2.85 × 10⁵ Ω·cm², indicating that the steel remained in a highly passive state. In contrast, the PF resistance in the FAC-SCP system dropped significantly from 1.13 × 10⁶ to 5.57 × 10³ Ω·cm². AFM and SEM observations further revealed greater surface roughness and more severe local damage in the FAC-SCP system. The superior stability of PF in OPC-SCP may be attributed to the higher Ca²⁺ concentration, which is likely beneficial for the formation of a relatively dense and protective film. Conversely, the higher SO₄²⁻ concentration and lower Ca²⁺ content in FAC-SCP may facilitate defect growth and local dissolution, thereby contributing to depassivation. These findings highlight the critical role of pore solution chemistry in regulating PF stability under reduced alkalinity conditions. Full article

In carbon sequestration in saline aquifers, many factors affect multiphase fluid migration and reservoir pressure change. This study developed a high-resolution three-dimensional numerical model to investigate large-scale CO₂ geological storage in the Ordovician carbonate aquifer of the Tarim Basin, China. This study focuses on the quantitative prediction of CO₂ plume migration, multiphase flow interactions between supercritical CO₂ and brine, and formation pressure evolution under coupled injection operations. Injection strategies were compared by constant rate (CR) and variable rate (VR) injection, and two caprock morphology-type selection by placing wells into monocline traps (wells 1/3/5) and anticline traps (wells 2/4) with varying limb dip angles and closure depths. The results demonstrate that both injection speed and caprock morphology strongly control CO₂ trapping evolution and storage security. At the end of the 500-year simulation, the dissolved-CO₂ migration distance followed the order CR > VR, indicating that, under the studied conditions, VR injection most effectively limited the lateral spread of dissolved CO₂ and thereby enhanced dissolved-CO₂ immobilization. In addition, CR and VR injection schedules have a subtle impact on long-term pressure change; Across all cases, formation pressure remained below the caprock breakthrough pressure. CR injection promotes the fastest CO₂ dissolution and pressure dissipation but yields the weakest long-term immobilization, whereas VR injection trades early dissolution rate for more effective plume containment. This result indicates that injection-strategy selection should be matched to dominant site controlled near-term pressure management versus long-term containment and to the trapping behavior imposed by caprock morphology. This study provides a mechanistically grounded optimization framework linking injection-speed control and caprock morphology to the coupled evolution of pressure-buildup safety and long-term CO₂ immobilization, supporting CCUS decision-making in the Tarim Basin. Full article

This study systematically investigated the effects of Co/Ni ratios (0.6–2.0) on the solidification behavior, as-cast microstructure, and element segregation of Co-Al-W-based superalloys, and elucidated the mechanism of thermodynamic and kinetic synergistic regulation. The results show that increasing the Co/Ni ratio has a negligible effect on the liquidus and solidus temperatures, but it significantly lowers the dissolution temperature of the γ′ phase, thereby expanding the alloy’s heat treatment window (HTW) from 215 °C to 269 °C. As the Co/Ni ratio increased from 0.6 to 2, the SDAS at the center of the alloy ingot decreased from 112.4 μm to 43.3 μm, resulting in a significant refinement of the as-cast microstructure. The dendritic segregation coefficients for positively segregating elements such as Ta, Hf, and Al, as well as negatively segregating elements such as W, all approached 1 significantly, effectively suppressing microsegregation during solidification. This study reveals the multidimensional synergistic regulation mechanism of the Co/Ni ratio on the non-equilibrium solidification behavior of highly alloyed Co-Al-W-based superalloys and quantitatively elucidates the relationship between the Co/Ni ratio, the microstructural uniformity of as-cast specimens, and the heat treatment process window. For the first time in a highly alloyed multi-component Co-Al-W system, a correlation has been established between the Co/Ni ratio, element segregation, dendrite coarsening coefficient, and heat treatment window. Full article

Phenolic resin is widely used as a binder in high-temperature industries; however, its pyrolysis generally yields isotropic glassy carbon, which strongly influences its high-temperature oxidation behavior. In this work, cupric tartrate was introduced as a catalyst precursor to investigate its effects on the thermal decomposition behavior, microstructural evolution, and oxidation behavior of the phenolic resin pyrolytic carbon. Upon heating, cupric tartrate decomposed at 250–320 °C into nanoscale Cu/Cu₂O composites, which were then converted into metallic Cu nanoparticles through reduction by gaseous products generated during the pyrolysis of phenolic resin. The in situ formed Cu nanoparticles were associated with the growth of tapered carbon nanofibers (CNFs), reaching maximum lengths of 30–50 μm at 700 °C. Based on the observed microstructural features and established literature reports, a dissolution–precipitation pathway is proposed to rationalize the formation of these CNFs. The presence of Cu-catalyzed CNFs correlates with enhanced structural ordering of the pyrolytic carbon, as reflected by reduced I_D/I_G ratios, and with an increased apparent oxidation activation energy in the selected fitting region (from 103.73 to 137.45 kJ/mol). Overall, this work demonstrates a facile strategy in which cupric tartrate serves as an effective catalyst precursor that generates Cu nanoparticles in situ; these nanoparticles then catalyze CNF growth from phenolic resin, enabling the construction of low-dimensional carbon nanostructures. Full article